April 2021 - Silicon Chip Online

Outer Front Cover
Contents
Publisher's Letter: Adobe making our lives difficult
Feature: Digital Radio Modes - Part 1 by Dr David Maddison
Project: Digital FX (Effects) Pedal - Part 1 by John Clarke
Project: Refined Full-Wave Motor Speed Controller by John Clarke
Serviceman's Log: I hope the purists won't spit their dummies by Dave Thompson
Feature: The History of Videotape - Helical Scan by Ian Batty, Andre Switzer & Rod Humphris
Project: High-Current Four Battery/Cell Balancer - Part 2 by Duraid Madina
PartShop
Project: Arduino-based MIDI Soundboard - Part 1 by Tim Blythman
Product Showcase
Review: Wagner cordless soldering iron by Tim Blythman
Vintage Radio: 1948 Philips table model 114K by Associate Professor Graham Parslow
Market Centre
Advertising Index
Notes & Errata: High-Current Battery Balancer, March 2021; Arduino-based Adjustable Power Supply, February 2021; LED Party Strobe Mk2, August 2015
Outer Back Cover

This is only a preview of the April 2021 issue of Silicon Chip.

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APRIL 2021 ISSN 1030-2662 04 The VERY BEST DIY Projects! 9 771030 266001 $995* NZ $1290 INC GST INC GST 115-in-1 5-in-11 Digital 5-inEffects Unit Refined Motor Speed Controller Full-wave control ❚ 220-250V AC <at> 40-70Hz ❚ Optional soft-start switch ❚ External feedback adjustment ❚ For universal and shaded-pole motors up to 10A ❚ siliconchip.com.au 64-key MIDI Soundboard Australia’s electronics magazine April 2021 1 Want to build your own Benchtop Power Supply? Supply your own DIY power supply for your day to day project. It can be used for testing small components like LEDs through to powering your Raspberry Pi at 5.1V, using an LM317 for power, providing from 2 – 30V with up to 1.5A of regulated current. SKILL LEVEL: Intermediate TOOLS: Soldering Iron, Drill, File CLUB OFFER BUNDLE DEAL 4495 $ SAVE 35% KIT VALUED AT $73.55 What You Need: 1 × 3.5 Digit LED Panel Meter 1 × Add-On Board For Panel Meter 1 × Universal Pre-Punched Experimenters Boards 1 × Jiffy Box - 158 × 95 × 53mm 1 × Heatsink Compound - 10g tube 1 × LM317T +1.2 - 37V 1.5A Adjustable Voltage Regulator 1 × SPDT Miniature Toggle Switch 1 × 5k Ohm Linear Single Gang (B) Potentiometer 1 × 7805 +5V 1A Voltage Regulator TO-220 case 2 × TO-220 Heatsink 1 × 240 Ohm 0.5 Watt Metal Film Resistors - Pk8 1 × 10uF 25VDC Capacitor Plus your choice of sockets, knobs & switches QP5580 QP5575 HP9552 HB6011 NM2010 ZV1615 ST0335 RP7508 ZV1505 HH8516 RR0557 RE6070 $29.95 $9.95 $7.50 $5.25 $4.50 $2.95 $2.95 $3.95 $1.85 $1.75ea 85¢ 35¢ For step-by-step instructions scan the QR code. www.jaycar.com.au/benchtop-power-supply See other projects at www.jaycar.com.au/arduino 20 Piece Micro Drill Set 20 different sizes from 0.3-1.6mm. Ideal for drilling wood, composites, plastic or soft metals. Indexed case. TD2406 JUST 12 $ 95 100 $ gift card Awesome projects by On Sale 24 March to 23 April, 2021 JUST 17 $ 95 10 Piece Needle File Kit 10 different profiles (round, elliptical, half round, triangle, square, etc.) Integrated platic handle. 162mm long each. TD2128 Got a great project or kit idea? JUST 2495 $ 80W 240V Soldering Iron Up to 530°C temp range. Ideal for the hobbyist and handy person. Stainless steel barrel. Orange cool grip, impact resistant handle. Fully electrically safety approved. TS1485 If we produce or publish your electronics, Arduino or Pi project, we’ll give you a complimentary $100 gift card. Upload your idea at projects.jaycar.com Looking for your next build? Silicon Chip projects: jaycar.com.au/c/silicon-chip-kits Kit back catalogue: jaycar.com.au/kitbackcatalogue 1800 022 888 www.jaycar.com.au Shop online and enjoy 1 hour click & collect or free delivery on orders over $99* Exclusions apply - see website for full T&Cs. * Contents Vol.34, No.4 April 2021 SILICON CHIP www.siliconchip.com.au Features & Reviews 14 Digital Radio Modes – Part 1 Digital radio is an extensive field utilised by amateurs, industry, military and government alike. This article discusses the various types of digital communication throughout the ages – by Dr David Maddison 64 The History of Videotape – Helical Scan Helical scan systems were in part designed due to the lack of a pause or still frame feature. They also offered lower tape speeds, leading to longer recording and playback times. Helical scan systems would also eventually overtake quadruplex in compactness – by Ian Batty, Andrew Switzer & Rod Humphris 100 Review: Wagner cordless soldering iron This new battery-powered soldering iron from Wagner Electronics can be recharged over USB and comes with three different tips. For example, one of the tips can be used for heat-shrinking – by Tim Blythman Constructional Projects Our Digital Effects Unit has 15 different effects, with the ability to customise eight. It’s powered from 9-12V DC, and includes true bypass and no signal inversion. It works well with piezo pickups due to its high input impedance – Page 24 24 Digital FX (Effects) Pedal – Part 1 This effects unit, based on the Spin FV-1 IC, is primarily designed for use with instruments, but can also be connected to a mic preamp or mixer. It has 15 different effects built-in (reverb, vibrato, distortion etc) and you can customise eight of them; the unit even has a true bypass feature – by John Clarke 36 Refined Full-Wave Motor Speed Controller Our brand new 230V 10A universal motor speed controller is vastly superior to previous models. Changes include an external feedback controller, the softstart feature can be turned off, and improved ability to maintain motor speed under load – by John Clarke 76 High-Current Four Battery/Cell Balancer – Part 2 In the final part of this series, we handle construction and testing of the Battery Balancer along with some safety tips – by Duraid Madina 88 Arduino-based MIDI Soundboard – Part 1 This new and improved Motor Speed Controller works with universal and shaded-pole motors up to 10A. It has external feedback gain adjustment, optional soft-start and current feedback – Page 36 This simple project turns an Arduino into a 64-key MIDI matrix, which can be used similarly to a 61-key beginners’ keyboard. The MIDI shield includes a basic synthesiser and audio amplifier, making it easy to test – by Tim Blythman Your Favourite Columns 46 Serviceman’s Log I hope the purists won’t spit their dummies – by Dave Thompson 61 Circuit Notebook (1) Biofeedback for stress management (2) Latching output for Remote Monitoring Station (3) Alternative switched attenuator for Shirt Pocket Oscillator (4) Follow-up to ‘constant’ AC source 102 Vintage Radio 1948 Philips table model 114K – by Associate Professor Graham Parslow Everything Else 2 Editorial Viewpoint 4 Mailbag – Your Feedback 87 Silicon Chip Online Shop siliconchip.com.au 99 Product Showcase 107 Ask Silicon Chip 111 Market Centre 112 Noteselectronics and Errata Australia’s magazine 112 Advertising Index The 64-key MIDI matrix is a simple Arduino project which can be used to trigger sounds. It also incorporates its own synthesiser and audio amplifier – Page 88 April 2021 1 www.facebook.com/siliconchipmagazine SILICON SILIC CHIP www.siliconchip.com.au Publisher/Editor Nicholas Vinen Technical Editor John Clarke, B.E.(Elec.) Technical Staff Jim Rowe, B.A., B.Sc. Bao Smith, B.Sc. Tim Blythman, B.E., B.Sc. Nicolas Hannekum, Dip. Elec. Tech. Technical Contributor Duraid Madina, B.Sc, M.Sc, PhD Reader Services Rhonda Blythman, BSc, LLB, GDLP Advertising Enquiries Glyn Smith Phone (02) 9939 3295 Mobile 0431 792 293 glyn<at>siliconchip.com.au Regular Contributors Dave Thompson David Maddison B.App.Sc. (Hons 1), PhD, Grad.Dip.Entr.Innov. Geoff Graham Associate Professor Graham Parslow Ian Batty Cartoonist Brendan Akhurst Founding Editor (retired) Leo Simpson, B.Bus., FAICD Staff (retired) Ross Tester Ann Morris Greg Swain, B. Sc. (Hons.) Silicon Chip is published 12 times a year by Silicon Chip Publications Pty Ltd. ACN 626 922 870. ABN 20 880 526 923. All material is copyright ©. No part of this publication may be reproduced without the written consent of the publisher. Subscription rates (12 issues): $105 per year, post paid, in Australia. For overseas rates, see our website or email silicon<at>siliconchip.com.au Recommended & maximum price only. Editorial office: Unit 1 (up ramp), 234 Harbord Rd, Brookvale, NSW 2100. Postal address: PO Box 139, Collaroy Beach, NSW 2097. Phone (02) 9939 3295. E-mail: silicon<at>siliconchip.com.au ISSN 1030-2662 Editorial Viewpoint Adobe making our lives difficult Once again, Adobe has made a bizarre decision which is causing lots of problems for their customers (and probably others too). They don’t seem to care; they make these decisions, either without considering the hardships for users, or they do realise and simply don’t care. This time, they are getting rid of support for Type 1 fonts, and have given us almost no warning. The first I heard about it was just a few weeks before it started causing us profound grief. Their beef with Type 1 fonts (and it is a valid criticism) is that this older format does not support Unicode; just the basic alphabet, numeric characters etc. On the other hand, Type 1 fonts provide superior rendering because they support cubic Bezier curves instead of the quadratic curves implemented by TrueType. That is why we make (or made) heavy use of Type 1 fonts. So, you may be thinking, what’s the big deal? Either switch to using equivalent TrueType or OpenType fonts, or convert your Type 1 fonts to one of those other formats and use them. Oh, how I wish it were that easy. You see, when you convert a Type 1 font to an OpenType font, two things happen. One is that it can sometimes look nothing like the original font. I don’t understand why this is the case, but when we put the original and converted font side-by-side, they are often so different that you’d have trouble believing they came from the same file. I think it has to do with how the different font rendering engines deal with kerning and hinting, but really, that shouldn’t happen. Unfortunately, it does. The other problem is that the converted font is often considered to have a different name than the original, meaning that our software will not recognise that it is the same. So when we open up one of the many hundreds of issues we need to maintain, we’re presented with dozens of messages indicating “font not found”, even though the appropriate fonts are installed on the system. So thanks, Adobe. You’ve made our lives miserable and created a lot of work for us. And for what? Leaving Type 1 support in your software probably would have been less work than removing it. I can’t imagine it’s saving you much maintenance, either. So if you notice that some of the fonts look slightly different in this issue compared to previous issues, now you know why. Jaycar catalog delay You might be expecting this issue to come with the 2021 Jaycar catalog; it is usually bundled with our April issue. Unfortunately, it has been delayed this year, no doubt due to COVID-19. I have been told that it should be ready later this year. Staff retirements We have just said goodbye to two long-term Silicon Chip staff members, Ann Morris and Ross Tester. Both of them have been with us for more than 20 years – well before I was involved. They have contributed much to the success of the magazine and we wish them the best in their retirement. Printing and Distribution: Nicholas Vinen 24-26 Lilian Fowler Pl, Marrickville 2204 2 Silicon Chip Australia’s electronics magazine siliconchip.com.au siliconchip.com.au Australia’s electronics magazine April 2021 3 MAILBAG your feedback Letters and emails should contain complete name, address and daytime phone number. Letters to the Editor are submitted on the condition that Silicon Chip Publications Pty Ltd may edit and has the right to reproduce in electronic form and communicate these letters. This also applies to submissions to “Ask Silicon Chip”, “Circuit Notebook” and “Serviceman”. Test Master origin revealed I was just browsing the March 2021 issue and I found an item that made me very excited. On page 18, in the article on Urban Electronic Archaeology (siliconchip.com.au/Article/14773), there was an ‘apparatus’ called a “Test Master”. I made this thing! I was a third-year apprentice/trainee tech with Telecom in 1984. This was one of the big projects we all had to complete as part of our apprenticeship. We had to cut and fold the mild steel base and lid, drill all the holes and populate the PCBs. The lid and base were anodised off-site. Every hole had to be precisely located, or we would have to start over. No one dared muck it up. The wiring had to be accurately laced as lacing cables would be, for many of us, our bread and butter when we qualified. It had to be perfect. I still have mine in my garage, slightly the worse for wear though, and I still occasionally use it. I cannot say for how many years this was part of apprentices’ training, but even when I was building it, I felt pride that I built it just about from scratch. At the time, there was some discussion about whether we should have made the PCBs from scratch (they were premade). Ahh, great memories! Tony O’Halloran Former tech, Telecom/Telstra, Healesville, Vic. More details on the Test Master In the March 2021 issue, you had a great article on hoarding by Dr David Maddison. One piece of equipment he found was a “Test Master”, and he was wondering about the origin of the device. Any Telstra technician who did their apprenticeship at the Tooronga training facility will immediately recognise it. It was built as a training ex4 Silicon Chip ercise by many apprentice electronic technicians. It taught metalwork, soldering, basic electronic theory, circuit reading and much more during the construction. Including, yes, cable lacing; considered an important and useful skill back in those days. I made my “Test Master” in the early-to-mid-80s, and it sat on my hobby desk, actually being used for many years. It’s currently packed away in a box after a move a couple of years ago, but was still occasionally used up until then. I hope this information is useful, though no doubt plenty of other ex Telstra techs will write in with similar stories. Peter Tremewen, Drouin, Vic. Very high-quality AM reception with DAB+ radio I am writing again with what will probably be the last update of my alternative AM/FM/DAB+ radio code, described in the Mailbag section of the October 2020 issue (January-March 2019; siliconchip.com.au/Series/330). I received a lot of feedback and suggestions from my friend Ingo Evers and have added a fair number of new features to the earlier version, and resolved many of its problems. It was helpful working on a project like this with a friend, because we have each found and fixed small problems with the way we constructed our radios. And by seeing the same unexpected behaviours on two independent radios, we have noticed and corrected some software problems. I’m motivated to share this update because we made a surprising discovery. A few weeks back, Ingo was lamenting that AM quality on this radio was not up to the standard of his other receivers despite great DAB and FM performance. I agreed that I felt my radio’s AM was the same. Australia’s electronics magazine But then I remembered from earlier in the lock-down when I was studying the radio chip’s programming guide, there was an AM setting for changing the audio bandwidth. I went back to the data, found that setting, and saw that the radio chip defaults to an AM audio bandwidth of 3.5kHz, which is barely equivalent to an analog telephone. You can easily change this setting in multiples of 100Hz. A quick experiment showed that the Silicon Chip DAB+ radio is more than capable of astonishing AM fidelity, and I was surprised in a good way. Now we can say even more than earlier that the radio is capable of providing a superb sound quality through a decent hifi setup, and we are even happier than we were with how the project has turned out. The latest version of my revised software lets you configure the AM audio bandwidth on a station-by-station basis, from the radio’s minimum of 1.5kHz (which sounds rather muffled) up to its maximum of 10kHz (which sounds almost the same as a welltuned FM station). You can change the audio bandwidth in near real-time, so the improvement is very noticeable as you wind it up. I had always assumed that the audio bandwidth of Australian AM broadcasts was just 4.5kHz (half of the 9kHz nominal channel spacing), and that this was the reason for the muffled sound we have all become accustomed to over the years. Clearly, that is not the case, and Australian AM broadcasts are transmitted with at least 10kHz of audio bandwidth. When I searched for information about how much audio bandwidth Australian AM broadcasters are permitted to utilise, I could not find the answer. It would be interesting if you can find out. I had also assumed you’d hear a siliconchip.com.au “Setting the standard for Quality & Value” ’ CHOICE! 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Designs from Sofia and Tehran are prolific, and perhaps warrant a short biographical story on each of these clever circuit designers. To me, this indicates the worldwide appeal of Silicon Chip content. Peter Johnston, Merimbula, NSW. Average speed tracker needed Prices are subjected to change without notice. 6 9kHz squeal if the receiver’s AM audio was not severely band-limited. I guess that unlike traditional analog receivers, digital radios don’t have that problem. It would be great to explore that more. This (maybe) final version of the alternative software implements almost all of the features of the original Silicon Chip software, and several more. One of the many changes in this version is a new infrared remote control configuration file, to make it easier to use any remote control device without modifying the BASIC program. There are also now optional favourite buttons on the main screen; the in-built speaker is supported properly, there’s a mute function, it is much easier to customise the colour scheme and so on. As the code size grew, Ingo complained to me that it would no longer fit into his Micromite. I discovered that the Linux “CRUNCH” script that I’d been using actually generates smaller crunched code than the built-in MMEdit crunch function. The difference is rather significant; the MMEdit crunched code is maybe 15% larger than the Linux crunching script’s output. But MMEdit will happily load the Linux-crunched output onto the Micromite, so just load the pre-crunched version into MMEdit and download to the Micromite as you previously would have done with the uncrunched code. Cheers, and thanks again for publishing this design. I think I’ll screw down the lid of my radio now and move onto the next project! Stefan Keller-Tuberg, Fadden, ACT. Comment: we appreciate all the effort you’ve put into this. Legislation determines that an AM radio broadcast can be nominally flat to 7kHz, and while it can extend past 9kHz, it must be attenuated beyond 9kHz. Therefore, a receiver bandwidth greater than 9kHz may improve the resulting frequency response. The supplied software is freely available for download at siliconchip.com.au/Shop/6/4940 As usual, I’ll start by saying that Silicon Chip is a great magazine. I used to be a subscriber, but I like going into newsagents and browsing. Some Australian magazines have been lost lately (for example, Australian Model Australia’s electronics magazine siliconchip.com.au WHAT IF WE COULD STOP DISEASES BEFORE THEY COULDN’T BE STOPPED? The key to beating more illnesses is earlier detection, and ADI’s precision sensing technology is powering new, ultra-fast disease testing, bringing us one step closer to a healthier future for all. Analog Devices. Where what if becomes what is. See What If: analog.com/WhatIf Engineering Magazine), and I think one of the reasons was the low sales volume. Once it dropped out of the public eye, the closure was inevitable. I don’t want that to happen to Silicon Chip. You recently asked for feedback. Yes, I don’t read the whole magazine, but I read most articles. I don’t build many projects any longer, but I look forward to what is on offer as I like the idea of building things. I am in Bathurst, and recently our cash-strapped local government has changed the time/speed/distance cameras to monitor all traffic – it used to be just trucks – and at the same time has lowered the allowed error to +3%. There is one of those machines just east of Bathurst, in a 100km/h area for about 26km. The road is virtually straight with no blind spots, some overtaking lanes, and generally very safe. Not a ‘blackspot’, so seemingly, this is just a cash-raising exercise. My idea is to have an Arduino or Raspberry Pi take GPS data and convert that to an average speed. A large button could start the process, and a second press could clear the data, ready to begin again. I am not advocating speeding or unsafe driving, but it is quite easy to stray slightly over the limit, and the penalties are severe. A loss of license would be catastrophic to my ability to work – yes, at 69, I am still working and plan to for a few years yet. Ed Pinder, Bathurst, NSW. Comment: You’ll be pleased to know that we are working on an updated version of the GPS Car/Boat Computer (originally from April 2016), and have added this to our list of features. It should appear in the magazine later this year. Thanks for the idea! Compact compass for Car/Boat Computer I have used the Micromite LCD BackPack for many purposes over the years. Recently, we bought an old Cray boat with a Sumlog, which was not reliable. I have replaced it with Greg Hoyes’ version of the BackPack-based Boat Computer, which works well. This version has the best compass; it works like a gyro repeater and is easy for navigation. I have upgraded the code to give a speed readout in knots to one decimal place, and it is very reliable. 8 Silicon Chip I am currently working on upgrading it to use the BackPack V3. The bigger display looks more in scale with other instruments, and is easier to read. But I came unstuck with the compass card, as the code is customised to the 2.8in screen. I am having some difficulty modifying this code to work with the 3.5in screen, as it is not documented and uses lots of constants. Ross Munn, Paynesville, Vic. Comment: we agree that this compass card style is useful, so we have added support for it to our new GPS Car/Boat computer, which also uses the 3.5in screen and will be described within the next few months. Advantages of DIY electronics The request to comment in your Editorial Viewpoint, January 2021, is much appreciated. I am a long-time reader of your magazine, and for over 60 years I have built my own electrical equipment and continue to use many past projects from Silicon Chip and other magazines that no longer exist. I live off-grid in a remote location, and have built my own power supplies, mainly from salvaged materials at a fraction of the cost of the commercial alternatives. I have a bias towards building my own gear which I can repair myself, as I have to drive around two hours to where I can purchase replacements for anything that fails. I believe that some of my projects work much better than the commercial alternatives. For example, I get almost twice the usable power from my solar panels, so don't need anywhere near as many. When I went to tech school in the early sixties, there was a hoard of us kids who made our own crystal sets etc, and tried to repair valve radios. We just went through every copy of Radio, TV & Hobbies. L. Ralph Barraclough, Licola, Vic. Details about VNG radio shutdown Thank you for replying to my query about projects requiring the insecure and buggy Windows OS; I did not know about Bootcamp for Mac, so I might try it (but I see that Windows 10 is still required). I have tried WINE with some success on simpler programs, but things like SPICE need libraries (DLLs) that are only provided with Windows. Australia’s electronics magazine The article on time sources was most interesting, especially VNG, as hearing its "beeps" is what introduced me to shortwave listening, thence Amateur radio. Did you know that when the Western Sydney site was going to be shut down by the short-sighted government, the then NSW Division of the Wireless Institute of Australia considered running it from its Dural site VK2WI? Unfortunately (or perhaps, fortunately), the idea was discarded, as the power bill would have been prohibitive (not to mention wiping out the callbacks!). As for the "talking clock", there used to be a human one, consisting of a woman sitting in front of two clocks with a telephone by her side. I have long since lost the link to the photograph. Dave Horsfall VK2KFU, North Gosford, NSW. Information on Philips BX205 radio Charles Kosina's article on the Philips BX205 B-01 radio in the February 2021 issue (siliconchip.com.au/ Article/14756) was both interesting and excellent. It started with some head-scratching regarding the unmarked dial. I can possibly enlighten him. It was originally intended for use in the tropics, which meant Indonesia or Malaysia in the 1940s and 1950s. Apparently, new radio stations popped up, disappeared or changed frequency at random intervals. Regulation was not a strict affair. All radios destined for the tropics were fitted with a 'standard' dial layout, having a zigzagged centre line, sometimes embellished with frequency or wavelength indications. Other manufacturers, mostly Dutch, also copied this layout. Bakelite versions were known as "Radio Roti" and were mostly transformerless. Yes, exciting times! Ben Heij, Caloundra, Qld. Building a DC-DC battery charger Being a semi-retired electronics engineer, I have tried to build my own DC-DC charger to fully charge the camper batteries via the vehicle Anderson socket. As you may be aware, the commercial DC-DC chargers are prohibitively expensive for us ‘grey nomads’ on a limited income. siliconchip.com.au WHAT’s new Our dedication to provide you with Excellence in Engineering APEM offers the broadest range of quality HMI products in the industry. They have the largest profile of Switches, Joysticks, LED indicators and Keypads to cater to several markets. 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WP SERIES PUSH BUTTONS FNR SERIES ROCKER SWITCH Q25 & Q30 SERIES LED INDICATORS MECA SWITCH PANEL OTHER products SWITCHES E-STOPS LED INDICATORS LINEAR SENSORS ROTARY SENSORS TILT SENSORS Anti-vandal Switches Rocker Switches INDUSTRIAL JOYSTICKS FINGERTIP JOYSTICKS DIGITAL PANEL METERS ANALOGUE METERS PCB SWITCHES TACTILE SWITCHES Emergency Stop Switches Toggle Switches FOOT SWITCHES HAND CONTROLS ENCODERS ACCELEROMETERS INCLINOMETERS INTERFACE MODULES Push button Switches Miniature Joysticks Air Switches Switch Panels USB Desktop Joysticks Hand Controls ContaCt us today for a quote. www.controldevices.com.au TOGGLE SWITCHES ROCKER SWITCHES AIR SWITCHES PRESSURE SWITCHES VACUUM SWITCHES SWITCH PANELS CONTROL DEVICES Unit 17, 69 O’Riordan Street ALEXANDRIA NSW 2015 sales<at>controldevices.net 02 9330 1700 I built mine using a Geekcreit 400W DC-DC boost converter module I bought from Banggood for $15 (siliconchip. com.au/link/ab77). I found that if I set the output to 14.5V, it would charge the half-discharged camper battery bank (two 100Ah AGM deep cycle batteries) with the voltage at the Anderson plug on the 4WD showing 12.5V. But it runs fairly hot at 15A, so it would require a cooling fan if mounted in an enclosure. I was reasonably happy with the performance of this cheap solution. Still, I noticed that without the vehicle running, the voltage would drop below the minimum required for the module at this load, and the output voltage would drop. Even when the vehicle was restarted, the output voltage would not recover until the Anderson connection was broken and reinserted. Most commercial DC-DC chargers have an MPPT solar input as well, so if that could be incorporated, I’m sure it would be a very popular project. I know MPPT can be complicated, so perhaps just an input from a solar charge controller would suffice. An LCD status screen would also be a nice addition. The option of selecting either lead-acid or lithium-ion type storage batteries of different chemistries would also be great. Onboard Bluetooth or WiFi could be used to monitor the charger remotely using a suitable app on a smartphone. I hope your technical team will give some serious thought to a project such as this. With the explosion of caravan and camper sales due to COVID-19, and the popularity of off-road self-sufficient camping, there is a real need for a reasonably priced DC-DC charger to keep these expensive batteries in peak condition. Bruce Hinton, Cleveland, Qld. High voltage and current tracking supply wanted Here’s a challenge for you. How about taking the 45V 8A Linear PSU (October-December 2019; siliconchip. com.au/Series/339) and turning it into a bi-polar or tracking supply? One obvious use of a bench supply would be to test a power amplifier. ±45V DC at 4A or so should cover a lot of the power amplifier applications out there. I’d imagine that a bi-polar supply is well within your capabil10 Silicon Chip Australia’s electronics magazine ities. The trick would be a sensible modification to the original project. If that could be done, then serious kudos to you. Iain McGuffog, Indooroopilly Centre, Qld. Easier way to transfer files to and from Raspberry Pi I am writing about your article “A Virtual Electronics Workbench” from the February 2021 issue (siliconchip. com.au/Series/357). After installing RealVNC on a laptop and enabling VNC server on the Raspberry Pi, Tim Blythman then describes how to install and use WinSCP to transfer files between the RPi and laptop. But there’s an easier way; VNC viewer and VNC server can both perform file transfers. To transfer files from the laptop to the RPi, move your mouse to the top middle of the VNC viewer window on the laptop, and a drop-down menu will automatically appear. Click the centre icon, which has a left and right arrow. This is for file transfers. In the pop-up box, click “Send files ...”, navigate to the file you want to transfer to the RPi and double click it. It will appear on the RPi desktop. Transferring files from RPi to the laptop is similar. Move your mouse to the RPi taskbar and right-click the VNC server icon. Select “File Transfer ...” from the pop-up box. Click “Send files ...”, navigate to the file you want to transfer to the laptop and double-click it. It will appear on the laptop’s desktop. Peter Ihnat, Wollongong, NSW. Comment: thanks for this very helpful information. Various comments on the March issue It was interesting to see the article on Fetron valve substitutes by Dr Hugo Holden in the March 2021 issue. Late last year, I mentioned the Fetrons to my ex-Telecom mate. To my surprise, he told me that Telecom used them and that he had experience with them. Also, Fetrons were not the only FET-based valve substitute. Earlier this year, I found an advertisement in a magazine for another brand of FETbased valve substitutes, but I cannot remember the magazine or issue. Perhaps another reader will mention it. I was also happy to see the Battery siliconchip.com.au HIGH-PERFORMANCE SOLDERING IRONS A family of wattages: • Fast heat up time • Reliable performance • Comfortable ergonomics 25 40 80 Find your favorite. • 3 LED lights illuminate your work • The world’s No.1 brand in soldering POWER SUPPLIES PTY LTD ELECTRONICS SPECIALISTS TO DEFENCE AVIATION MINING MEDICAL RAIL INDUSTRIAL Our Core Ser vices: Electronic DLM Workshop Repair NATA ISO17025 Calibration 37 Years Repair Specialisation Power Supply Repair to 50KVA Convenient Local Support SWITCHMODE POWER SUPPLIES Pty Ltd ABN 54 003 958 030 Unit 1 /37 Leighton Place Hornsby NSW 2077 (PO Box 606 Hornsby NSW 1630) Tel: 02 9476 0300 Email: service<at>switchmode.com.au Website: www.switchmode.com.au 12 Silicon Chip Balancer project. For anyone who wants a battery system of some power, this is the solution for balancing the batteries. It is even more desirable for batteries that are charged from a limited power source. Unfortunately, I suspect that the SMD parts and their availability will probably deter some people from it. It is probably overkill for the small systems that I use. Also, the processor is not a PIC chip, and that goes against the project. It is not that I dislike the SAM processors. It is just that I prefer to use projects which are PIC-based. If things go wrong, I already have the means to reprogram it etc. I do not want to invest in tools that I might only use a few times. I read Dr Maddison’s article “Hoarding: Urban Electronic Archaeology” with some interest, since his friend and I are obviously clones. With a deep interest in most things technical, and the space to store things that might be useful, it is not hard to gather a large number of items that are personally desirable, even if others think that they are rubbish. I am faced with the same problem that Dr Maddison’s friend would have faced in his later years: what I should do with my collection? The beneficiaries of my will don’t want these items, but at the same time, I do not wish to dispose of them because they provide me with parts for my projects etc. I have asked those who have suggested getting rid of most of it to please tell me what I will need in the future. Then, I can dispose of the other things. Of course, prediction is impossible, and the replacement cost of what I have works against getting rid of anything. I have been experimenting with Li-ion cells. I have a large quantity of used but good 18650 cells. To get batteries with the desired voltage and sufficient current capability, I need to connect the cells in parallel and then connect the parallel assemblies in series. I am trying to find the limit for the number of cells in parallel, if there is one. I know that four cells can be joined, but is that the limit? I have seen websites warn about connecting cells of different capacities in parallel, but that makes no sense. I can understand that cells of different types should not be combined but not ones of varying capacity. Cells with different internal resistances will charge and discharge differently. Still, I would expect that cells with different capacities would maintain the same voltage, and hence the same level of charge. However, there might be other factors involved which are unknown to me. George Ramsay, Holland Park, Qld. Comments: now that Microchip owns Atmel, pretty much all their chips (including the SAM series used in the Battery Balancer) can be programmed using their software and the latest PICkit (as mentioned in the article last month). So the use of that microcontroller should not be a negative point for the Battery Balancer project. We agree that if it’s OK to connect two cells of the same type in parallel, there should be no practical limit to the number that can be combined as such, as long as their chemistries are identical. It would be a good idea to use cells of the same age/lifecycle point to prevent one or more from failing prematurely and taking out the whole pack. SC Australia’s electronics magazine siliconchip.com.au Digital Radio Modes You are probably familiar with digital radio and broadcast technologies like DAB+, DRM, DVB-T and LoRa (we have reported on all of these in the past). But digital radio is a lot more widespread than most people would realise. It’s used extensively by amateur radio operators, industry, governments, militaries and many others and there are dozens of different modes. Read on and learn more; much more... more... 14 Silicon Chip Australia’s electronics magazine Part One . . . by Dr David Maddison siliconchip.com.au M any analog radio communication modes are being phased out in favour of digital methods. Some relatively recent examples include the switch to digital TV (DVB-T) and the introduction of digital broadcast radio (DAB+) and digital radio modes for commercial, government and radio amateur use. Advantages of digital radio modes include: • greater voice clarity • interference immunity • proper encryption • more efficient use of the radio spectrum • greater channel capacity • faster channel changing or searching • the ability to add new functions to radios as new software and applications are developed Disadvantages of digital radio include: • more complicated software • possibly higher costs compared to analog (especially with proprietary systems) • intolerance of major RF interference (despite good tolerance to minor interference) • the ‘digital cliff’ at extreme range, where communication suddenly drops out compared to analog, which gradually fades out Analog radio still has some benefits such as relatively simple and well-understood equipment and hardware-only solutions with no software to go wrong. Remaining analog radio in common use, for the moment, includes: • AM and FM broadcast radio (although some other countries have already phased these out) • HF and UHF CB (citizens’ band) • standard amateur radio modes • commercial and government shortwave services • various short-range transmitters such as baby monitors and wireless doorbells (which can be either digital or analog) Of all the analog radio modes, it is most likely that broadcast AM and certain government-sponsored shortwave services will last the longest before being phased out, as the ownership of these types of analog receivers is vast worldwide. Digital radio history Overall, though, the advantages of digital radio greatly outweigh analog radio. On 27th July 1896, Guglielmo Marconi first publicly demonstrated ‘wireless’ signals, and in March 1897, he transmitted Morse Code signals over 6km. That was interesting because Morse Code is arguably a form of digital radio transmission, so the concept of digital radio isn’t altogether new. Early digital radio modes such as RTTY (radioteletype) were successfully tested as early as 1922, and have been in commercial use since 1932. However, the data throughput at the time was relatively low, typically 60 words per minute (wpm) for RTTY45 mode at 45.45 baud (bits per second) to 100 wpm in RTTY75 mode at 75 baud. Much higher data rates have become possible because of large increases in computing power and digital signal processing technology. Computers can also compress data, conserving radio bandwidth. There are vast numbers of digital radio modes, and we can’t cover all of them in this article. So we will describe the most interesting or unusual techniques. Digital radio basics With digital radio (or TV), information is transmitted via radio waves in discrete steps, rather than with the continuous gradation of values used for analog transmissions. The advantage is that the original data can be precisely reproduced at the receiving end with close-to-ideal reception. In contrast, an analog signal is always subject to some degradation of the original signal (eg, noise). Just like analog radio, which uses a variety of modulation schemes such as SSB (single sideband), AM (amplitude modulation), FM (frequency modulation) etc, various digital modulation schemes can be used. There’s also the option of digital compression, which is applied to the data before it is transmitted and reversed upon reception. This reduces the amount of data that needs to be transmitted. i) Early Digital Modes 1) Morse code Arguably, the first digital mode was Morse code (also known as CW), first used in 1844. Information is sent as a short “dot” (normally refrred to as a dit), or longer “dash” (known as a dah), with spaces being delineated by a lack of transmission. The “dah” is nominally three times the duration of the “dit”. There is a one-dit-length gap between each dit or dah within a group, a three-dit-length gap between ‘letters’, and a seven-dit-length gap between each word. What is not commonly realised today is that the “American” code Morse developed (originally for the US telegraph service), and the “Continental” or “International” Code we know today, bear only a passing resemblance to each other. Some letters are the same but the American code also has long daaaaahhhhs and spaces within letters. It has all but died out these days; even the Gugliemlmo Marconi (1874-1937), acclaimed as “the father of radio”. He is shown at left with his apparatus assumed to be set up on the Isle of Wight around 1897/8. At right is the illustration from his radio patent. siliconchip.com.au Australia’s electronics magazine April 2021 15 theory which was not established until 1948 (it is similar to Huffman coding). For reference, “SILICON CHIP” sounded in Morse code looks like this: dididit didit didahdidit didit dahdidahdit dahdahdah dahdit dahdidahdit didididit didit didahdahdit Samuel FB Morse (1791-1872), generally credited with the code which bears his name and, perhaps more importantly, the telegraph system which used it. More detail: en.wikipedia.org/wiki/Samuel_Morse International Code has few users (mainly amateur radio operators dedicated to keeping it alive!). Morse code was created with maximum efficiency in mind. The more common letters were coded with the shortest sequences, and less common letters with longer sequences. The most common letter “E” is simply “dit” and a “T” is “dah”. Conversely, a “Q” is “dah dah didah” It turns out that Morse code is close to the optimal efficiency for encoding data, as is predicted by information (Only when there is a space following a “dit” is the “t” at the end sounded; otherwise it is shortened to “di”– the dits and dahs flow into each other). Note too that Morse code is an aural, as distinct from a visual, language – hence the dits and dahs. You will often see it written down as dots and dashes (eg, A = .–) but this is discouraged, especially if you are trying to learn the code. You can write your own code sequences and see how they look and sound at the following website: siliconchip.com.au/link/ab65 2) Radioteletype Teleprinters are electromechanical printers that can print information transmitted either over a wire (telegraphy), leased line, telephone circuit, or radio waves, as in a radioteletype or RTTY. The Teletype Corporation Model 15 was an extremely popular machine that was in production from 1930 un- Fig.1: a Model 19 radioteletype. These machines are still used today by radio amateurs and computer enthusiasts for fun. Source: www.railroad-signaling.com 16 Silicon Chip til 1963. The Model 19 (Fig.1) was a Model 15 with a paper tape unit and a Model 14 transmitter distributor. The model 14 reads the paper tape encoded with a 5-bit Baudot-Murray US TTY version of ITA2 code and transmits it via landline, or it can key a radio transmitter for wireless transmission. The US Navy commonly used the AN/FGC-1 diversity FSK converter and its companion AN/FRR-3 diversity receiver to receive RTTY comms (see www.navy-radio.com/rcvr-div. htm). Radio amateurs appear to have started using surplus RTTY units in the 1940s around the New York area. For more information, see the following videos: • “Teletype Model 19 (and Model 15) Demonstration” – https://youtu.be/ jxkygWI-Wfs • A 19 part series “Teletype Model 19 - Part 1: A Teletype Arrives for Restoration” – https://youtu.be/ _NuvwndwYSY • “Using a 1930 Teletype as a Linux Terminal” – https://youtu.be/ 2XLZ4Z8LpEE 3) Hellschreiber The German Hellschrieber (Schrieber means printer), invented by Rudolf Hell, was a surprisingly advanced instrument, implementing a form of Fig.2: a Hellschreiber machine. Characters are encoded on a spinning drum behind the keyboard and decoded messages (or sent messages), are printed out on a strip of paper on the right. Australia’s electronics magazine siliconchip.com.au Fig.4: a printed message from a Hellschreiber with slight timing errors. The message is still intelligible because it is printed twice. Source: Wikimedia user Mysid. Fig.3: how a Hellschreiber creates the letter E, and the corresponding transmitter carrier. Note that the letters written on the wheel are column designators. Source: video by J. Mitch Hopper titled “Hellschreiber - What is that?” at https://youtu.be/Ayhf51fUpLs what we now know of as dot-matrix printing (Fig.2). This was equivalent to a teleprinter but was mechanically much simpler and cheaper. It was invented in 1925, and in 1929, Hell patented the invention and founded a company to produce it. It was first used in the 1930s for press services, and was later used during World War 2. Like a teleprinter, it could be connected to another device either by a wired connection, such as a landline, or via a radio link. However, the inventor stated that “The development of the Hellschrieber was specifically done for wireless communication” and he also said, “The objective of the development was a practical device for the reception of messages from news agencies. This could only be achieved with a very simple teleprinter.” It was still in use well into the 1980s. It has developed into a software-based radio amateur standard using a sound card on a PC and an external transceiver, because original machines are rare and hard to find. A fundamental difference between the Hellschreiber and a teleprinter is that a teleprinter or teletype transmits data via coded symbols such as the 5-bit Baudot code. Teleprinters have no data siliconchip.com.au Fig.5: a modern emulation of Hellschreiber using software from radio amateur Nino Porcino IZ8BLY (http://antoninoporcino.xoom.it/Hell/index.htm). Source: Ernie Mills, WM2U. redundancy, so in the event of interference, data can be lost or the wrong character printed, or start (synchronisation) bits missed or misinterpreted. But with the Hellschreiber, characters are not sent encoded. Characters are represented by a 7x7 matrix (larger matrices are possible) and they are sent as a raster image – see Fig.3. There might be image distortion in the event of a noisy transmission, as shown in Fig.4, but no incorrect characters, since there is no encoding to be corrupted. There are no start bits sent to synchronise with the receiving machine, so nothing to miss or misinterpret. The device requires a small signal bandwidth and can be used over conventional voice channels, even when they are too degraded for useful voice transmission. It can even be used with equipment designed for CW (Morse) telegraphy. Several different wireless transmission modes can be used, such as PSK (phase-shift keying), FM (frequency modulation) and multitone. When a particular letter is pressed, say “E” as in Fig.3, a series of pulses are generated from a rotating encoder wheel which closes an electric circuit, or not, depending on the location of raised contacts. For column A, no pulses are generatAustralia’s electronics magazine ed in this example, and all seven rows are blank. For column B, the first and last rows are empty, and five pulses in a row are generated. For column C, the pattern through the seven rows is offon-off-on-off-on-off and so on. You can see the modulation of the carrier wave at the bottom of the diagram. At the receiver end, an electromagnet brings an inked marker into contact with a paper tape each time a carrier is detected. Since the transmitter and receiver are not synchronised, there is some possibility that signal delays due to radio propagation conditions or mismatches in the printer speed will cause image distortion. Therefore, the image is printed twice, so even if distortion is present, there is a good chance it can still be read. There is a detailed discussion of using modern software and hardware to emulate Hellschreiber modes on modern equipment at siliconchip.com.au/ link/ab66 (see Fig.5) and videos showing them in operation titled “Hell Feldfernschreiber and 15W.S.E.b in use” at youtu.be/VDB7wmV7ekA and “Feld Hell, WW2 German Hell Feldfernschreiber” at youtu.be/Rs4YZv6s70g We published an article by Stan Swan on using Hellschreiber in our May 2005 issue (siliconchip.com.au/ Article/3062), which has quite a bit April 2021 17 Fig.6: a screenshot of swradio-8 decoding DRM from Voice of Nigeria (https://von. gov.ng/) on 15.120MHz. This software runs on Windows and Linux and supports HackRF, RTL-SDR using the RT820 chip and SDRplay SDR devices. more detail along with instructions on transmitting and receiving data yourself using a computer sound card. For further details, see siliconchip.com. au/link/ab67 ii) Broadcast digital radio and TV 1) DAB+ Digital radio broadcasting in Australia was tested from 1999 and introduced in 2009, using the DAB+ (Digital Audio Broadcasting) standard, as used in Europe (but not the UK & Ireland). In Australia, these are broadcast on VHF frequency blocks 8C (199.360MHz), 9A (202.928MHz), 9B (204.64MHz) and 9C (206.352MHz) in multiplexed form, with multiple radio stations per frequency block. At the time of writing, DAB+ broadcasts were predominantly in capital cities; and not all cities use all channels. Each frequency block occupies 1.536MHz and supports 1152kbps of usable data. Each radio station uses a different amount of data according to their requirements. Data rates of 24, 32, 40, 48, 56, 64, 80, 88 and 96kbps are used on Australian stations. At the moment, many of these stations are also simulcast on regular AM or FM bands. Using 3A Forward Error Correction at a “code rate” of 1/2 each frequency block, it can support 18 x 64kbps stations (1152kbps total), or more at a lower data rate. The DAB+ standard supports features such as Program Assisted Data (PAD) with text of up to 128 characters per segment, Slideshow (SLS) images, 18 Silicon Chip Electronic Programme Guide (EPG) and other data services such as traffic reports, location of fuel and price, etc. We published a series of detailed articles on DAB+ by Alan Hughes in the February, March, April, June & August 2009 issues (siliconchip.com. au/Series/36). We have also published two radios capable of receiving DAB+ broadcasts, most recently in the January-March 2019 issues (siliconchip. com.au/Series/330). For further information, see the PDF at siliconchip.com.au/link/ab68 2) Digital AM and FM broadcasts The most popular broadcast bands are AM medium wave (525-1705kHz), FM broadcast (87.5-108MHz) and to a lesser extent, shortwave bands (discontinuous between 2.3MHz and 26.1MHz). In the USA, Canada and Mexico, the proprietary HDR (HD Radio) system is used on the AM and FM broad- cast bands. HD Radio allows for either hybrid digital/analog broadcasts or digital-only. With hybrid broadcasts, regular AM and FM broadcast-band equipment can still receive the analog portion. As implemented in the USA, in AM or FM hybrid mode, analog and digital signals are broadcast on the same frequency. For FM, the bandwidth required for a hybrid signal is 400kHz, double their usual channel spacing of 200kHz. They have a wide channel spacing because stations that are close in frequency are geographically separated. Europe and Australia use a 100kHz channel spacing, making adoption of this system problematic. In the hybrid FM mode, data rates up to 150kbps can be transmitted along with the analog broadcast, while in pure digital mode, up to 300kbps is available, allowing features like surround sound. For AM, 20kHz channels are the standard (they use 10kHz channel spacing, while Australia and Europe use 9kHz). In hybrid AM mode, digital data is usually transmitted at 40kbps. In the AM pure digital mode, the full 20kHz channel width is used, giving 20-40kbps, although up to 60kbps can be achieved if 5kHz overlap into the adjacent channels is allowed. That could cause interference on adjacent channels unless there is sufficient geographical separation, and there could still be problems at night with large skip distances. In the USA, many car manufacturers offer subscriber satellite radio in their car receivers, and all majors offer HD Radio as well. Satellite radio is transmitted at 2.3GHz and offers nation-wide reception. Fig.7: a Samsung “Anycall” mobile phone from South Korea with hardware and software to receive DMB-T. This is an older model; there no longer appear to be phones available today with this feature. Source: Wikimedia user Ryuch Australia’s electronics magazine siliconchip.com.au 3) Digital Radio Mondiale (DRM) DRM digital audio broadcasting can be on longwave (as used in Europe), the AM and FM broadcast bands, and shortwave. As it is more spectrally efficient than analog modes, more stations can fit into the same bandwidth using the xHE-AAC digital codec (“codec” is an abbreviation of encoder/decoder). DRM30 is the mode used below 30MHz, while DRM+ is used between 30MHz and 300MHz. Other data can be transmitted along with the audio. Countries that use DRM include New Zealand, India, France, Brazil, China, Hungary, Russia, Romania, Kuwait, UK, USA, Singapore, Nigeria, and Abu Dhabi. ACMA is considering the possibility of its use in Australia – see siliconchip.com.au/link/ab69 We published a detailed article on DRM (not to be confused with ‘digital rights management’) in the September 2017 issue (siliconchip.com.au/ Article/10798). It is very suitable for use in sparsely populated areas, like much of Australia, because a low-power transmitter can serve a vast area. If you are interested in listening to DRM, and conditions and your antenna are right, you can try to pick it up in Australia. DRM signals abroad are not explicitly aimed at Australia, but it seems that New Zealand transmissions can sometimes be picked up. See the comments at siliconchip.com.au/link/ab6a and the schedules at www.drmrx.org/ drmschedules/ DRM can be heard by: • a radio designed to receive it, such as the Tecsun Q-3061 DRM Shortwave Radio (www.tecsunradios.com.au/ store/), certain WiNRADIOs with licensed software (www.winradio. com/home/drm.htm) plus models from Gospell, Avion and Starwaves • a radio modified to obtain a 12kHz IF signal for software processing • a radio with an existing 12kHz IF output for software processing • a software-defined radio (SDR) used in conjunction with the “Dream” software Software to receive HDR, DAB+ and DRM HDR, DAB+ and DRM can be resiliconchip.com.au Don’t pay $$$$ for a commercial receiver: this uses a <$20 USB DTV/DAB+ dongle as the basis for a very high performance SSB, FM, CW, AM etc radio that tunes from DC to daylight! Published October 2013 Features: Tuned RF front end Up-converter inbuilt Powered from PC via USB cable Single PCB construction Want to know more? Search for “sidradio” at siliconchip.com.au/project/sidradio PCBs & Micros available from On-Line Shop ceived on dedicated receivers or via a computer, sound card and appropriate receiver. • NRSC5 is multi-platform software that allows reception of HD Radio using an SDR – see www.rtl-sdr. com/tag/nrsc-5/ Note that as HD Radio is only broadcast in North America, it could only be received in Australia/NZ under extremely rare skip conditions. • To decode DAB/DAB+ signals, you can use qt-dab (siliconchip.com.au/ link/ab6b) for Linux and Raspberry Pi, or QIRX SDR (https://qirx.softsyst.com/ and www.welle.io) for Windows, Linux, macOS and Android. • swradio-8 (siliconchip.com.au/link/ ab6c) for Windows and Linux decodes DRM and many other modes – see Fig.6. • For a variety of digital radio opensource tools for DAB for Linux, see https://github.com/Opendigitalradio • Dream (https://sourceforge.net/ projects/drm/) is a software DRM decoder. Signals can be received with a modified analog receiver (SW, MW or LW) and fed to a PC sound card, but read comments at the link before trying to use it. See our detailed articles on this topic in the November 2013 and September 2017 issues at siliconchip.com.au/Article/5456 and siliconchip.com.au/Article/ 10798 More details are in the video titled “Decoding Digital Radio Mondiale DRM Using Dream Decoder” at youtu. be/lextsInwtUQ restrial Digital Multimedia Broadcasting) is a video and multimedia delivery service by radio on VHF and UHF bands. It is used in South Korea (Fig.7), Norway, Germany, France, China, Mexico, the Netherlands, Indonesia, Canada, Malaysia and Cambodia. See the video titled “Korean Mobile TV, DMB” at https://youtu.be/ 2kx92SZ4grU The ATSC-M/H (Advanced Television Systems Committee – Mobile/ Handheld) standard is used in the USA. The signals are broadcast in the digital TV spectrum, and it is an extension of the digital TV format used in that country. Fig.8: the VK3RTV transmission tower on Mount View in Melbourne. It is a shared tower, but the transmit antenna is at the very top, and there are three receive antennas covering onethird of the horizon each, just below the tower ‘outriggers’. 4) Mobile TV S-DMB or T-DMB (Satellite or TerAustralia’s electronics magazine April 2021 19 Fig.9: a screengrab of EasyPal from the video titled “EasyPal Digital SSTV 40m Band #Shortwave, 02nd January 2019, 1100-1120 UTC” at https://youtu.be/K0bcrnIB7sU About 65 TV stations transmit this format, although there don’t appear to be any phone-type devices that can receive it. 5) Digital TV Australia’s TV system is now fully digital, with the transition occurring from 1st January 2001 to 10th December 2013. We use the European DVB-T standard, although there are numerous variations within this standard including the codecs used, the number of sub-carriers, channel bandwidths and modulation schemes. The data stream is transmitted using coded orthogonal frequency-division multiplexing (COFDM). The precise details are beyond the scope of this article. You can see an overview of the standard at siliconchip.com.au/link/ab6x We published articles on digital TV in the March & April 2008 issues (siliconchip.com.au/Series/49), plus March 2010 (siliconchip.com.au/ Article/77), June 2013 (siliconchip. com.au/Article/3820) and April 2016 (siliconchip.com.au/Article/9903). Australia’s DTV system allows for high-quality video and sound, datacasting, video program information and a higher number of channels for a 20 Silicon Chip similar spectrum space than was possible with analog TV. The government is currently calling for submissions regarding reforming television in Australia including the technical standards. Submissions close very soon: 23rd May 2021. Go to siliconchip.com.au/ link/ab6d to find out more. In the USA, Canada, Mexico and South Korea, the digital TV standard used is ATSC. Japan uses its own IDSB standard, and several countries in Asia, South America and Africa have adopted it. (Does this remind anyone of the PAL/NTSC/SECAM mess?) Fig.10: a daily weather map from the BoM. This can be downloaded from www. bom.gov.au/difacs/IDX0854.gif For other maps from the weatherfax service, see the list under “Australian Weather Charts” at www.weather.gov/media/marine/ otherfax.txt (they don’t appear to be listed on the Australian website!). Australia’s electronics magazine siliconchip.com.au You can watch some live analog and digital SSTV streams at www. g0hwc.com iv) Analog slow-scan TV (SSTV) and radio fax These two types of transmission might initially seem to be digital, but both are transmitted by an HF or VHF analog modulated radio signal using the same bandwidth as voice. Like voice transmissions, it is possible to have long-distance or global reach under the right ionospheric conditions and frequencies. Of course, modern transmission and receiving equipment is likely to be digital, such as a computer, making these modes much easier and cheaper to work with. So we are including them here due to the extensive digitisation at both ends. The hardware requirements are modest, typically just needing an old PC with a sound card in addition to Fig.11: a screengrab of DroidSSTV from a suitable radio receiver (possibly an SDR) and antenna. a smartphone. The original way to view slow-scan TV was with a military-surplus long iii) Amateur digital TV persistence ex-radar CRT, where the image would stay long enough until 1) Amateur DVB-T broadcasts that part of the screen was refreshed Melbourne has a DVB-T amateur with a new image. This is unnecessary 200W TV repeater, VK3RTV (www. when the image is stored digitally in vk3rtv.com) at Mt Waverley, shown a computer. in Fig.8. You need to be a radio ham to transUnlike the SSTV modes mentioned mit SSTV, but anyone can receive both below, this operates at a full video frame rate, just like consumer digital TV. The signal can be received on some TVs or set-top boxes at 445.5MHz, or you can view live streams online from anywhere, according to the details on their website. You can view a recorded video of Amateur TV Net night titled “VK3RTV Net 05th January 2021 Off-air log [mixed quality, missing first 3 minutes]” at https://youtu.be/fNgK3B6ptr0 2) Digital slow-scan TV Strictly speaking, this mode is not slow-scan TV (see next section) because it’s digital, but the name has stuck. The late Australian Erik Sunstrup VK4AES developed a digital SSTV for radio amateurs known as EasyPal (Fig.9). Versions of his program are still available for download. For more information, see www.g0hwc.com/ sstv_drm_news.html siliconchip.com.au SSTV and weather fax. Radio fax is now primarily used to transmit weather information (weather fax) to ships at sea, but has been mostly replaced by other methods such as satellite transmissions. Nevertheless, several weather fax transmissions are active worldwide, including from North America, Europe, Asia and Australia (see Fig.10). Some useful radio fax links are: • a schedule of worldwide transmissions: siliconchip.com.au/link/ab6e • a schedule of Australian transmissions: siliconchip.com.au/link/ab6f • software to receive and decode weather fax on a PC: https://arachnoid .com/JWX/ • receive weather fax on your Android or iOS device: http://siliconchip. com.au/link/ab6g You will need an appropriate radio receiver. • interesting commentary on problems and sample images from the BoM: siliconchip.com.au/link/ab6h • video showing receipt of Australian weather fax titled “Weather Fax from Australian BOM HF radio transmission”: https://youtu.be/SxKn69JAuaE • receive SSTV on a PC: www. essexham.co.uk/sstv-the-basics • another popular SSTV receiver program for PC, MmSSTV: https:// hamsoft.ca/pages/mmsstv.php • a newer version of MmSSTV is called YONIQ: http://radiogalena. es/yoniq/ (in Spanish but you can Fig.12: HDSDR, popular free software for SDR radios although it only supports analog modes. Australia’s electronics magazine April 2021 21 v) Software-defined radios (SDRs) Fig.13: two self-contained SDRs: a Malachite SDR (left) and PortaPack H2 combined with Hack RF (right). Source: the video at https://youtu.be/ Ja6LTDf9wAk use a translator on the web page, and the program can run in English). • view SSTV images from the International Space Station on VHF 145.800MHz FM: https://amsat-uk. org/beginners/iss-sstv/ It is even possible to view SSTV on your phone by holding the phone next to a radio loudspeaker tuned into an SSTV channel with the right App. The App for iOS is “SSTV Slow Scan TV”. For Android, use “DroidSSTV - SSTV for Ham Radio”, shown in Fig.11. We haven’t tested either ourselves. These can be very cheap devices, available for as little as $20, that can receive various digital signals on your computer. Popular free software for doing this is HDSDR (Fig.12), SDR Console, SDR# (see our article in November 2017; siliconchip.com.au/ Article/10879), Linrad, SdrDx, Gqrx SDR, and SDR Touch. If you plan to buy an SDR dongle, make sure its chipset is compatible with any software you intend to use. Besides the November 2017 issue, we have published multiple articles on SDRs, including two projects to build your own. The following issues and articles are relevant: • LF-HF Up-Converter For VHF/UHF Fig.14: a screengrab of fldigi in action. 22 Silicon Chip Australia’s electronics magazine siliconchip.com.au Fig.15: an image received by US radio amateur KD8TTE from Shortwave Radiogram (https://swradiogram.net/). Digital TV Dongles, June 2013: siliconchip.com.au/Article/3810 • SiDRADIO integrated SDR, October & November 2013: siliconchip.com. au/Series/130 • More Reception Modes For SiDRADIO & SDRs, December 2013: siliconchip.com.au/Article/5629 • Tunable HF Preamp for SDRs, January 2020: siliconchip.com.au/ Article/12219 • New wideband RTL-SDR modules, May & June 2020: siliconchip.com. au/Series/306 Self-contained SDR radios with inbuilt software and a display can also be purchased or constructed – see Fig.13. You can try your hand at receiving digital radio with a communications receiver or SDR and appropriate software. There are a large number of software packages, due to space we will just look at one. “fldigi” is a free and popular software suite for digital radio modes (see Figs.14-16). It can transmit or receive digital radio when connected to a transceiver, although you need to be a ham or commercial radio operator to transmit. The software runs on many types of PCs and other computers; even the Raspberry Pi. It supports many general and ham radio digital modes such as Contestia, CW, DominoEX, FSQ, Hell (for Hellschreiber machines), IFKB, MFSK, MT63, Olivia, PSK, RSID, RTTY, Thor and Throb. It is available for download at www.w1hkj.com and https:// sourceforge.net/projects/fldigi/ There is a detailed 576-page PDF user manual at http://siliconchip.com. au/link/ab6i and a comprehensive collection of spectra and the sounds of various digital modes at www.w1hkj. com/modes/index.htm In the United States, this software is used by various emergency management services for communications during natural disasters. Shortwave broadcasters such as Radio Australia (before they became an online-only service) have experimented with digital modes using this software. Shortwave Radiogram (https:// swradiogram.net/) is a radio show by Dr Kim Andrew Elliott KD9XB that transmits digital text and images via shortwave radio. It can be decoded with fldigi, TIVAR or AndFlmsg on Android devices. We have seen various reports that it can be received in Australia. For tips on receiving Shortwave Radiogram, see siliconchip.com.au/link/ ab6j and the videos titled “Receiving Shortwave Radiogram – A Digital Text and Image Shortwave Broadcast” at https://youtu.be/0mNgGnvjzVs and “Shortwave Radiogram 170, 20th September 2020, 7780 kHz, 2330-2400 UTC” at https://youtu.be/ Stt4C8Rwu18 For an extremely comprehensive guide to what various digital mode signals sound like and look like in spectrograms check the following links: siliconchip.com.au/link/ab6j siliconchip.com.au/link/ab6k http://m0obu.net/digital-modes.html There is a comprehensive list of other software packages to receive digital modes at www.qsl.net/rv3apm/ (it is not clear if it is entirely up to date) and http://siliconchip.com.au/link/ab6l NEXT MONTH: In Part 2 of this feature, Dr David Maddison will look at more of the digital modes in use today and the promSC ise of things to come! Fig.16: some digital modes as they appear on the fldigi waterfall display. Source: Summerland Amateur Radio Club (https://sarc.org.au/fl-digi/). siliconchip.com.au Australia’s electronics magazine April 2021 23 Digital FX Unit Part 1 by John Clarke Make like a pro muso with this Digital FX (Effects) Unit. It will produce unique sounds when connected to a variety of instruments . . . like an electric guitar, bass, violin or cello, even the output of a microphone preamp or within the effects loop of an amplifier or mixer. I t’s very common for musicians to add effects to the sound of their musical instruments. These are used to add depth, ambience and tonal qualities and to personalise the sound. Effects can be subtle or extreme, and can be tailored to produce a unique sound. Purely analog audio circuitry can be used for effects units such as in the Overdrive and Distortion Pedal from March 2020 (siliconchip.com.au/Article/12576). But for complex effects, digital signal processing (DSP) is more convenient and flexible. Our Digital FX Unit utilises a digital signal processing integrated circuit (IC) that is designated the SPN1001 FV-1 (or FV-1 for short). This is preprogrammed with eight effects, and while one of these is a test function, the remaining seven provide flange, chorus and tremolo as well as pitch shift and reverb effects. A further eight extra effects are stored within an external EEPROM that connects to the FV-1. These effects have been chosen by us. However, you can change the stored effects patches. The FV-1 has been available for many years, and has been used in many commercially available effects units. 24 Silicon Chip The FV-1 has a somewhat cult following amongst digital effects enthusiasts. This has led to the production of numerous freely-available effects patches and software to enable the writing of your own unique effects. For our Digital FX Pedal, the preprogrammed EEPROM is filled with eight effects that add to the seven usable effects preset within the FV-1. These individual effects are selected using a rotary control knob, while the parameters of each effect are adjusted using up to three rotary controls. Many effects have already been created for the FV-1 IC, and these are free to use. These effects include chorus, echo, flange, phase shift, vibrato, limiter, wah, various reverberation effects, distortion, octave shifts and a ring modulator. For information on what some of these effects are and how they are achieved, see www.spinsemi.com/ knowledge_base/effects.html We will explain some of the basic effects at the end of this article. There is also an assembler and a graphical software package to help you write your own effects if you feel inclined to experiment. The software can then be assembled and programmed into the EEPROM. This requires an EEPROM programmer; we will have more details on where to get effects patches, how to store Australia’s electronics magazine siliconchip.com.au Features • 15 different effects including chorus, echo, flange, vibrato, wah, reverb & distortion • Each effect has up to three adjustable parameters • Provision to experiment by adding new effects • Rugged enclosure, suitable for stage use • Power supply reversed polarity protection • High input impedance to suit piezo pickups etc • Low power consumption • Battery or DC plugpack power • True bypass switch • No signal phase inversion them in EEPROM and how to use the assembler and graphical software later. Presentation Our Digital FX Pedal is designed for live music use, and so is housed in a rugged diecast aluminium case. On the top, it has a footswitch, eight rotary controls plus indicator LEDs. The signal inputs and outputs are two 6.35mm (1/4in) jack sockets at the rear, along with a DC barrel socket for power. The unit can also be powered via an internal 9V battery. Its power is automatically switched on when a jack plug is inserted into the output socket. Operating principle Fifteen different effects are available, with the option to change eight of the effects to your liking. You can choose them from a list of many freely available effects, or create them yourself using freely available tools. The block diagram, Fig.1, shows the signal flow of the Digital FX Pedal. The original signal is applied to CON1, and this is connected to the bypass switch (S2a). When not bypassed, this signal goes to the high input impedance buffer (IC1a) and is then filtered with a 19kHz low-pass filter. This prevents unwanted artifacts in the subsequent digital signal processing (DSP) stage, by removing RF and ultrasonic signals. l Fig.1: the input signal is fed into the SPIN FV-1 effects chip, and the resulting modified signal is mixed with the original signal in a ratio set by the user via potentiometers VR2 & VR3. VR4 adjusts the mixed signal gain and this is then fed to S2 which controls whether CON2 receives the original or modified (mixed) signal. siliconchip.com.au Australia’s electronics magazine April 2021 25 9–12V DC INPUT + D1 1N5819 CON4 A V+ K +3.3V OUT IN (ACTIVATED BY CON2) 9V BATTERY CON3 REG1 LD1117V33C S1 GND A l K IC2: OPA1662 10kW 200 W 100 m F 100 m F +3.3V 1 POWER LED1 10kW 100mF 2 S2 c 2 3 IC2a A 1 l BYPASS LED2 K 4 200 W Vcc/2 Vcc/2 V+ V+ 1MW INPUT 1 S2a FB1 100 W 2 CON1 1 0 0 pF 100nF 3 2 100nF 8 IC1a IC1: OPA1662 10k W 1 4 1.2nF 10kW 5 6 560pF BUFFER 7 IC1b EFFECTS INPUT LEVEL 22 m F VR1 10kW LOW PASS FILTER BYPASS SIGNAL 2N7000 LEDS LD1117V33C 1N5819 K K A SC Ó2021 D G S A O UT GND OUT IN DIGITAL AUDIO EFFECTS UNIT Fig.2: the complete circuit, which expands on what is shown in Fig.1. There are two options for selecting the current effect: the 16-way BCD rotary switch (S3) is the simplest, but could be somewhat hard to get. The alternative is potentiometer VR8, which has its position read by microcontroller IC6 and converted into a binary value to control IC4. IC6 includes hysteresis to avoid unwanted effects changes. V+ Specifications • Supply requirements: 9-12VDC, 100mA (can operate down to 7V on battery) • Current draw: 70mA typical • Maximum input & output signal levels: 2.3V RMS with a 9V supply; 3.3V RMS at 12V • Frequency response: -0.25dB at 20Hz and -2dB at 20kHz for ‘dry’ signal; -2dB at 20Hz, -1dB at 15kHz and -6dB at 18kHz for modified signal • Signal-to-noise ratio (SNR), 1V RMS in/out: 95dB for ‘dry’ signal; 85dB for modified signal The signal from the filter is fed to two separate level controls, VR1 and VR2. VR2 sets the level applied to the signal mixer (more on this later), while VR1 sets the signal level applied to the SPIN FV-1. VR1 is required so that the level can be set below the clipping level for the FV-1 input. The clip LED lights up to indicate signal limiting when the level is too high. The SPIN FV-1 contains a stereo analog-to-digital converter (ADC), a DSP core and stereo digital-to-analog converter (DAC) to produce the output signals. All processing is done using 24-bit digital audio samples. For more information, see www.spinsemi.com/knowledge_base/arch.html Note that while the FV-1 can process stereo signals, the Pedal is a mono device, so we are only using a single channel. There are two versions of the Pedal, where the effects se26 Silicon Chip Vcc/2 BYPASS SIGNAL lection is made using either a rotary switch (S3) or potentiometer (VR8) and associated components – more about this later. The effect parameters are adjusted using potentiometers VR5, VR6 and VR7. The FV-1 also has inputs for the crystal oscillator and EEPROM serial connections. After processing within the FV-1, the output signal goes through a 19kHz low-pass filter, to remove high-frequency noise (DAC step artefacts) and then to the effects level control, VR3. Both the effects signal and the original (or dry) signal from VR2 are combined in the inverting mixer stage, comprising IC3a and IC3b. The mixing allows adjustable portions of the dry and effects signal to be blended to provide the desired result. The mixer can also provide a signal gain of up to five times, adjusted with potentiometer VR4. The resulting sig- Australia’s electronics magazine siliconchip.com.au +3.3V +3.3V +3.3V C VR6 10kW VR5 10k W B K VR7 10k W A S3 CLIP LED3 200 W 6 5 20 LIN LIN LIN l 21 22 1m F 1kW SIG INPUT 1 2 +3.3V 1nF 3 10 m F 100nF 10 X1 40kHz 9 8 3 VCC A2 2 A1 1 7 A0 IC5 24LC32A SDA S CL WP 15 5 14 12 6 15pF VSS 4 1 2 3 4 5 23 DVDD AVDD DVDD REFP CLIP 10 m F POT 1 100nF LED4 l K 100nF A B C D 1 200 W VDD S2 LIN S1 RIN S0 IC4 FV–1 SPN1001 MIDREF T0 18 C 7 17 B 6 16 A 13 D GP1 RA0 IC6 5 RA2 PIC12F1571 2 3 Q1 2N7000 D RA1 RA3 RA5 4 G VSS X1 8 4x 10kW X2 SDA LOUT SCK ROUT T1 REFN GND GND GND GND 4 7 11 19 S 1.2MW 28 27 25 CIRCUITRY INSIDE THIS AREA IS ALTERNATIVE TO USING IC6, VR8, Q1, LED4 AND ASSOCIATED COMPONENTS GND 24 DIGITAL PROCESSOR (CON5) V+ V+ 100nF 10kW 10 m F 10kW 5 6 8 VR4 100kW LIN 20k W VR3 10kW 1 0 0 pF VR2 10k W Vcc/2 4 .7 m F 2 3 5 8 IC3a 1 10m F 4 6 LOW PASS FILTER DRY MIX 10k W 4 .7 m F MIXER 100 m F 10kW EFFECTS MIX 7 IC2b 100nF IC3: OPA1662 OUTPUT LEVEL 1.2nF 560pF SELECT LIN POT 2 6 SELECTED A V R8 10kW BCD ROTARY SWITCH 26 POT 0 EEPROM ICSP (PICKIT) 8 E 100 W SIG OUTPUT A PARAMETER ADJUST IC3b 100 W 100k W 7 20k W 1 S2 b 2 BYPASS OUTPUT CON2 INVERTER AMPLIFIER Vcc/2 BYPASS SIGNAL BYPASS SIGNAL nal is then applied to the bypass switch, S2b. This selects between the original signal from CON1 and the signal with effects, with the selected signal going to the CON2 output. signals can be mixed along with the dry signal to produce the desired effect. How the effects work The full circuit for the Digital FX Pedal is shown in Fig.2. The input signal from CON1 passes through a 100Ω stopper resistor and ferrite bead FB1. In conjunction with the 100pF capacitor, these block RF signals from entering the circuit and causing radio-frequency detection and reception. The 100pF capacitor also provides a suitable load for piezo string pickups. The signal is AC-coupled to pin 3 of IC1a, and is biased to half-supply (Vcc/2 or about 1.65V) via a 1MΩ resistor. This keeps the input impedance reasonably high at 1MΩ, suitable for a piezo pickup. IC1a is connected as a unity-gain While it is difficult to show many of the various effects available, the “octaver” effect can be easily demonstrated. This is where the dry signal is mixed with a signal shifted up or down by one octave. These are harmonically related, at half the frequency and double the frequency, respectively. In Scope1 (overleaf), the top yellow trace (channel 1) shows the dry signal and the lower white trace (Ref A) the up octave signal, produced by doubling the frequency. The middle blue trace (channel 2) is the down-octave signal, at one half the frequency. The up and down octave siliconchip.com.au Circuit description Australia’s electronics magazine April 2021 27 Scope1: the signal being fed into the device is shown at the top, in yellow. Below are the outputs of the ‘octaver’ effect, set for one octave lower (blue) or higher (white). These effects signals can be mixed into the original to create richer harmonics and different sounds. buffer that can drive the following low-pass filter stage. The Vcc/2 voltage is derived using two 10kΩ resistors connected in series across the supply and is bypassed with a 100μF capacitor to remove supply noise, then buffered by unity-gain amplifier IC2a. Note that all the op amps in the circuit have very low noise and distortion figures of 0.00006% at 1kHz at a gain of 1, with a 3V RMS signal level. Therefore, the op amps do not contribute any audible distortion to the signal. The low-pass filter is a Sallen-Key two-pole 19kHz Butterworth type that rolls off at 40dB per decade (12dB per octave). It is included along with further passive filtering to remove any high-frequency signal components above 20kHz. This prevents signal aliasing due to digital sampling at 40kHz. Without the filter, strange audible artifacts could be generated by the ADC. Following this filter, the signal is AC-coupled to the level potentiometer, VR1. This sets the signal level applied to input pin 1 of IC4, the FV-1. IC4 provides an internal half-supply DC bias for this pin, hence the AC coupling. The 1kΩ resistor and 1nF capacitor after the AC-coupling capacitor attenuate any remaining high-frequency noise. The signal fed to IC4 must be lower than about 1V RMS to avoid clipping. Clipping occurs when the signal goes beyond the 0-3.3V supply range of IC4. The clip indicator output, pin 5, goes low and drives LED3 if this happens. VR1 should be adjusted so that this LED does not light. IC4 includes a crystal oscillator amplifier. The typical circuit for the FV-1 depicts the crystal as a 32,768Hz watch type. This is recommended mainly because it is commonly available, but the high-frequency audio response suffers if one is used. Instead, we use a 40kHz crystal, extending the processor’s frequency response from around 16kHz (when using the watch crystal) to just under 20kHz. Per the Nyquist theorem, the highest frequency that an ADC can handle is at half the sampling rate. Effects IC4 requires several supply bypass capacitors. These are 100nF for the analog and digital 3.3V supply 28 Silicon Chip pins, while the half supply bypass at the MID pin (pin 3) is 10µF. As mentioned above, the mid supply is about 1.65V. IC4 also requires positive and negative reference voltages for the ADC at pins 25 and 26. Pin 25 is tied directly to GND (0V), while pin 26 connects to the +3.3V supply via a 100Ω resistor and with a 10µF filter capacitor, to keep supply noise out of the signal path. Effects parameters are varied using potentiometers VR5, VR6 and VR7. These are connected across the 3.3V supply and can provide voltages of 0-3.3V to the POT2, POT1 and POT0 inputs of IC4. The function of each pot depends on the selected effect. Effects are selected by the state of IC4’s digital inputs S0, S1 and S2 (pins 16, 17 and 18) and the voltage level at the T0 input, pin 13. When the T0 input is low, the effects selected by the S0, S1 and S2 inputs are those that are preprogrammed within IC4. If all the S0, S1 and S2 inputs are low, the first effect is selected. Further effects are chosen with different levels at S0, S1 and S2. S0 is the least significant bit, and S2 is the most significant bit of a binary value. The three inputs provide for eight possible selections (23). The effects stored on the EEPROM (IC5) are selected when the T0 input is high (3.3V). Eight further selections are then available using the S0-S2 inputs. IC4 connects to the EEPROM via an I2C serial bus using two pins, the serial clock, SCL and serial data SDA. These connections are also brought out to the ICSP header for in-circuit programming of the EEPROM memory chip (if required). The EEPROM’s supply is bypassed by a 100nF capacitor. The EEPROM is a 32kbit (32,768 bit) memory arranged as 4096 x 8bits (ie, 4k bytes). Effects patches stored within the EEPROM are placed in memory blocks of 512 x 8bit. There are eight 512 x 8bit memory blocks in the full 4k x 8bit memory. Output signal handling The effects signal from the left channel output of IC4 (pin 28) is fed to a low-pass filter comprising IC2b, two 10kΩ resistors plus 560pF and 1.2nF capacitors. This is another Sallen-Key two-pole 19kHz Butterworth low-pass filter. It is included to remove high-frequency DAC switching artifacts from the signal. The output signal from IC2b is applied to the VR3 effects level potentiometer. The signals from the wipers of VR3 and the dry signal potentiometer, VR2, are combined in the inverting mixer stage based on IC3b. The mixer gain is adjusted using VR4, with a maximum gain of negative five times when VR4 is at its maximum resistance of 100kΩ. The following inverter stage, built around IC3a, re-inverts the signal so that the output signal is in-phase with the input. The output of IC3a is fed via a DC blocking capacitor and stopper resistor to the bypass switch, S2b. When in position 1, this signal goes to the CON2 output socket. When bypass is selected (with S2 in position 2), the input signal at CON1 bypasses the effects circuitry, connecting directly to the output at CON2 via the S2b terminals. The S2a terminals tie the input for IC1a to ground. This prevents noise from being picked up and amplified by IC1a in bypass mode. The remaining switch pole, S2c, controls indicator LED2. This bypass LED is lit when the signal is bypassed; the 200Ω resistor from cathode to ground limits the LED current to around 6.5mA. Australia’s electronics magazine siliconchip.com.au Two effects selection options So effectively, a binary value of 0000-1111 (0-15 decimal) is required to select one of the 16 possible effects. This value controls the states of the S0-S2 and T0 inputs of IC4. Our circuit provides two ways to make this selection. The simple way is to use a BCD (binary-coded decimal) switch, which has 16 positions and four outputs that provide the required binary states. However, 4-bit BCD switches can be difficult to obtain, so we offer the alternative option of using a potentiometer instead. So circuit Version 1 uses a potentiometer (VR8) and a microcontroller (IC6) to convert the voltage from the potentiometer’s wiper to a BC (binary-coded) value. VR8 connects across the 3.3V supply and can provide 0-3.3V to the pin 3 analog input of microcontroller IC6. This voltage is internally converted to a digital value. The micro’s digital outputs at RA2, RA1, RA0 and RA5 then generate the required binary (0V or 3.3V) values to feed to the S0, S1, S2 & T0 inputs of IC4 respectively. The resulting binary value varies smoothly from 0-15 decimal as VR8 is rotated from fully anticlockwise to fully clockwise. Hysteresis is included to avoid the binary value flicking between two adjacent values near each voltage threshold. This requires you to rotate the selection pot a little clockwise further than the threshold to select the next higher BC value output, and a little further anticlockwise from the threshold to select the next lower BC value. A change from one effects selection to another is indicated using LED4. The LED flashes off and then on again as the pot is rotated, to indicate a change in the binary value. Typically, an 8-pin PIC microcontroller does not have sufficient pins to handle the analog sensing, 4-bit binary output and the indicator LED drive. We solve this by using the master clear (MCLR) input at pin 4, and task it as a general-purpose input to drive the LED. It might seem that an input cannot be used as an output, but this input includes the option of a selectable pull-up current. While many of the 8-pin microcontrollers include an internal pull-up when the MCLR input is set to operate as a master clear input, there are not many microcontrollers that also allow the pull-up to be switched on or off when this pin is used purely as an input. However, the PIC12F1571 does have that capability. To be used as an output, the internal pull-up current is enabled, so the input will be pulled high near to the 3.3V supply. The input will go low without the pull-up when there is an external pull-down resistor. The pull-down resistor must be sufficiently high in resistance to allow the internal pull-up current to pull the input high enough to switch on the following stage. Using a 1.2MΩ resistor as the pull-down resistance, the minimum pull-up current for that input at 25μA is sufficiently high to swamp the pull-down current from the resistor. Thus, this pin will be quite close to 3.3V with the pull-up engaged. We use a 2N7000 N-channel Mosfet (Q1) to convert the high-impedance drive from this ‘output’ to a low-impedance drive for the indicator LED. It then drives LED4 via the 3.3V supply and 200Ω current-limiting resistor when its gate is high. The second version of the circuit (Version 2) simply uses a 4-bit BCD rotary switch (S3) to select the effect. This requires 10kΩ pull-down resistors at the A, B, C & D siliconchip.com.au Common effect descriptions Reverb Several delayed versions of the original sound are mixed back with the original dry sound, to simulate sound in a room or area where there are sound reflections (a complex form of echo). The ideal reverb period or delay setting depends on the type of sound; for music, it depends on the music’s tempo. As a general rule, longer reverb times are for slow tempo music, while shorter reverb times are suited to faster tempo tunes. Different reverb programs will have their own tonal qualities due to differences in the reverb time of high or low frequencies and differences in the reverb sound’s overall frequency response. Be careful not to apply too much reverb, particularly in the high frequencies, as this will result in an unnatural sound (unless that’s what you want!). Start with reverb level all the way down, then gradually bring the reverb mix up until you can just hear the difference. Any more than this will give an unrealistic sound. Phasing, chorus, and flanging (modulation effects) All of these effects have a portion of the audio signal delayed and then mixed back with the dry signal. The amount of delay is modulated by a low-frequency oscillator (LFO). The delay is quite short compared to the reverb effect. For phasing effects, the delay is less than the period of the signal. This phase difference between the modulated and direct signals causes cancellation at some frequencies and reinforcement at others. It produces a comb filter like effect, where some frequencies are amplified, and others are attenuated across the audio band. It causes a ‘shimmering’ type of sound. Phasing is the subtlest of all these effects, producing a gentle shimmer that can add life to a wide range of sources without being too obtrusive. For chorus and flanging, the signal is delayed by a longer period, up to several milliseconds, with the delay time modulated by an LFO. This also produces a comb-filter effect and a pitch-shift effect after mixing with the dry signal, giving a harmonically rich ‘swirling’ or ‘swishing’ sound. Chorus and flanging effects mainly differ in the amount of delay time and feedback used. Flanging uses longer delay times compared to chorus, and chorus generally uses a more complex delay structure. Chorus is most often used to ‘thicken’ the sound of an instrument, while flanging is usually used to produce other ‘whirling’ sounds. Pitch and octave shifts Australia’s electronics magazine These effects involve altering the frequency of the signal. Pitch varies the frequency by a variable amount, while the octave shift changes the frequency by a factor of 0.5 for octave-down and 2.0 for octave-up. Mixing the octave-shifted signals with the dry signal produces various effects, including making a single instrument sounding fuller, or sounding as though there are multiple instruments. April 2021 29 Fig.4: two versions of the project have been designed, as described in the text. Each uses a slightly different PCB so make sure you order the appropriate board. Note that in the switched version, four resistors are mounted on the PCB underside. switch pins. The common E pin connects to 3.3V, and so pulls a combination of the A-D pins high, depending on the switch’s rotation. Power supply The circuit is powered when microswitch S1 is activated by inserting the output jack plug into CON2. The plug physically raises the socket’s ground connection, lifting the microswitch actuator and activating the switch. While many effects pedals are switched on when a jack plug is inserted, it is usually done by a switch internal to the socket. We are not using a socket that has isolated switching mainly because they are not commonly available. These also have the disadvantage of stressing the PCB connections each time a jack plug is inserted, especially if the jack is moved at an angle to the socket. This eventually causes the solder joints to harden and break. While the sockets we use also solder directly to the PCB, the body is secured to the case at the socket entry as well. That keeps the socket fixed in place against the enclosure side, minimising movement of the solder joints. Power is automatically selected between 9V battery or DC supply. When there is no DC power plug inserted, the DC socket (CON3) will supply battery power via its normally-closed switch connecting, the negative of the battery to ground. When a power plug is inserted, power is via the DC input and the battery negative is disconnected. 30 Silicon Chip Power switch S1 connects power to the rest of the circuit whether via the battery or an external source, while diode D1 provides reverse-polarity protection. REG1 is a low-dropout 3.3V regulator which supplies IC4, IC5 and IC6 (if used). The input and output pins of REG1 are bypassed with 100µF capacitors. Its output drives the power LED (LED1) via a 200Ω resistor. Construction The Digital FX Pedal is built using a double-sided, plated-through-hole PCB measuring 86 x 112mm. The version using the BCD switch is coded 01102212, while the version using potentiometer VR8 is coded 01102211. Either way, it is housed in a diecast enclosure measuring 119 x 94 x 34mm. Figs.3 & 4 are the two PCB overlay diagrams for the different versions. Refer to the appropriate diagram during construction to see which parts go where. Begin by fitting the surface-mount parts, IC1-IC5 (and possibly IC6), on the top side of the PCB. These are not difficult to solder using a fine-tipped soldering iron. Good close up vision is necessary, so you might need to use a magnifying lens or glasses. If you’re using the version with potentiometer VR8, also mount IC6 now. In each case, make sure the chip is orientated correctly before soldering it in place. Make sure that IC1-IC3 are the OPA1662 op amps, IC5 is the 24LC32A and IC6 is the PIC12F1571 (if used). For each device, solder one pad first Australia’s electronics magazine siliconchip.com.au the DC socket, CON3. Switch S1 must be mounted so that the lever is captured under the front sleeve contact of jack socket CON2. We have provided slotted holes so that the switch can be inserted and slid along until the lever slips under the contact. Check that the switch is open-circuit between the two outside pins when there is no jack plug inserted, and closed between the two outer pins when a jack plug is inserted. The lever might need to be bent a little so that the switch works reliably, switching at the centre of the travel between the open and closed position of the CON2 jack contact. Mount foot switch S2 and rotary switch S3 (if used) now. Make sure these are seated fully and not skewed before soldering. Leave the LEDs until later, when the PCB is mounted in the case. The next step is to cut the battery wires to 60mm, then crimp or solder them to the plug pins. Insert these pins into the plug shell, making sure you get the red and black wires in the correct position. When you plug it in, the red wire should go to the terminal marked + on the PCB, adjacent to D1’s anode. It’s necessary for the GND terminal on the board to be connected to the case, to prevent hum injection via the enclosure. Cut a 50mm length of green medium-duty wire, solder a solder lug to one end and the other to the GND terminal on the PCB. It’s a good idea to place some heatshrink tubing over the lug terminal and the GND PC stake. When assembled, the solder lug is secured to the case using an M3 x 6mm screw, star washer and M3 nut. Powering up and testing Same-size photo of the switched version, the version at right opposite. The cutout is for a 9V battery, as shown. and check its alignment. Readjust the component positioning by reheating the solder joint if necessary before soldering the remaining pins. Continue construction by installing the resistors (use your DMM to check their values), followed by the ferrite bead (FB1). Use a resistor lead off-cut to feed through the bead and solder to the board. Push the bead lead fully down so that it sits flush against the PCB before soldering its leads, so it doesn’t rattle later. Diode D1 can be installed next. Take care to orientate it correctly. The MKT and ceramic capacitors can now go in, followed by the electrolytic capacitors. The electrolytics are polarised, so they must be orientated with the correct polarity; the longer lead goes into the hole marked with a + symbol. Install potentiometers VR1-VR7 (and VR8 if used), noting that VR4 is 100kΩ and the remainder are 10kΩ. The 10kΩ potentiometers may be marked as 103, while the 100kΩ pot may be marked 104. Crystal X1 can now be fitted, along with CON5, the 6-way header EEPROM programming connection. Next, mount REG1 with its leads bent over so that the regulator body lies above VR4. Make sure it does not lean so far as to make contact with the metal parts of VR4. A 45° angle to the PCB face will prevent contact with the enclosure and VR4’s body. Also install the PC stake at the GND test point, and the two-way polarised header for the battery lead (CON4) now. Follow by fitting the two jack sockets (CON1 & CON2) and siliconchip.com.au If you are planning to use a battery, connect this now. Alternatively, connect a DC supply (9-12V DC). Plug a jack lead into CON2 to switch on the power. Then, using a multimeter set to read DC volts, connect the negative probe to the GND point and measure the regulator input and output voltages. The input should be about 0.3V below the battery or DC supply voltage. The regulator output should be between 3.267V and 3.333V. If that checks out, you can connect up a signal source and some sort of amplifier, fiddle with the knobs, and check that they appear to be working as intended. Housing The PCB is housed inside a 119 x 94 x 34mm diecast aluminium enclosure. We use the lid as the base, with the controls protruding through the main enclosure body. Use the drilling template, Fig.5, to make the required holes in the base. You can also download this as a PDF from the SILICON CHIP website. The only differences for the two versions are that the board with a potentiometer needs an extra 3mm hole for LED4, and the shaft hole is 6mm rather than 10mm. Cut-outs are also required in the side for the two jack sockets and DC power socket. The template shows the slots required for the jack sockets so they can be slid in place. The resulting gaps in the side of the enclosure, after the jack sockets are inserted, can be filled in. These can be covered with a small blanking piece made from a 45mm x 9mm piece of 1mm thick (or up to 1.5mm) aluminium. You can also glue shaped plastic or aluminium ‘infill’ Australia’s electronics magazine April 2021 31 Fig.5: same-size drilling diagrams for both the mechanical switching version (top left) and the potentiometer switching version (lower left). End drilling and blanking, or infill pieces are the same for both versions. These diagrams can also be downloaded from siliconchip.com.au 32 Silicon Chip Australia’s electronics magazine siliconchip.com.au There are quite a few holes to be drilled in the diecast box – see the drilling template (Fig.5, opposite) for details. Note also the “infill”, or blanking, piece – this helps seal the box after the PCB is placed in it. And speaking of placing the PCB, this photo shows how it’s done Ignore the tacked-on components in our prototype: PCBs have these additions already made. Note, though, the four resistors top left are required in the switched version. pieces to the rectangular backing piece for the neatest possible appearance, as shown in Fig.5. If doing this, cut a piece 31 x 12mm or a little larger, then drill a 12mm diameter hole in the centre. Once carefully filed, the piece will break apart so there will be two pieces that match the gaps in the enclosure. For the enclosure feet, you can stick rubber feet on the ‘lid’. Alternatively, you can replace the original lid securing screws with Nylon M4 screws. The Nylon screw head then acts as the feet. To allow this, the holes in the enclosure for the original mounting screws will need to be drilled out to 3.5mm, and tapped using an M4 thread tap. ink will be between the enclosure and film when affixed. Use projector film suitable for your printer (either inkjet or laser) and affix it using clear neutral-cure silicone. Roof and gutter silicone is suitable. Squeegee out the lumps and air bubbles before the silicone cures. Once cured, cut out the holes through the film with a hobby or craft knife. For more detail on making labels, see siliconchip.com.au/Help/FrontPanels Panel labels The front and side panel label artwork is available for download from our website. The two side panels show the effects available (1-8 & 9-16). These can be affixed to the sides of the enclosure. Note that there are two front panel labels and you need to select the one which suits your build (rotary switch or pot). A rugged front panel can be made using overhead projector film, with the label printed as a mirror-image so the Final assembly Attach the 9mm-long M3 tapped spacers to the underside of the PCB. These are located just behind CON1 and CON2, and between VR5 and VR6. Secure them using an M3 screw from the top of the PCB. The spacer keeps the PCB in place by resting on the lid when the case is assembled. For the version using VR8, there is another 9mm M3 tapped spacer required near VR8. The ground lug mounting position is adjacent to the DC socket. This is secured using an M3 screw, star washer and nut before the PCB is inserted into the case. Have the solder lug orientated so that the wire is closest to the enclosure base, so it does not foul the components on the PCB. Before mounting the PCB in the enclosure, insert the LEDs into the PCB (longer leads to anode pads, marked “A”). Place the Nylon washers for the footswitch onto its shaft before inserting the PCB into its position in the enclosure. Then feed the LEDs into the bezels to capture them. Solder the LED leads from the rear of the PCB and trim them. The battery compartment is the rectangular cut-out on the PCB. The battery can be prevented from moving with some foam packing sandwiched between the end of the battery and the PCB’s edge. If you are not using the battery option, remove or fully insulate the battery clip at CON3 to prevent the contacts shorting onto a part of the circuit. Knobs An upside-down view of the finished project: the box base becomes the front panel (with appropriate label) and the box lid, with four Nylon screws used as feet, becomes the base. Labels fixed to each side make effect selection simple. siliconchip.com.au Since the potentiometer shafts do not protrude much more than 9mm above the panel, standard knobs with a skirt to cover a potentiometer securing nut will not have sufficient internal fluting length to keep the knobs secured. So use knobs that don’t have the skirt, as listed in the parts list. Australia’s electronics magazine April 2021 33 POWER POWER (Jack plug inserted) (Jack plug inserted) Clip . . .. .. . .. .. . . . IN . OUT .+. .9-12VDC . + . . .(centre . . +)+ + + . . . . . POWER . . . . . (Jack plug inserted) Clip . . .. .. . .. .. . .. .. . .. . +. IN . 9-12VDC . .OUT . . . . (centre +) + . . . . . .. . + + + + . POWER . . . . . . . . . . . . . . . (Jack plug inserted) Min. Min. Max. Max. Min. Max. . . Clip . . . . . . . .Dry . . . . + . .Eﬀects . . . .Eﬀects . . . . . input level . . . mix mix . . . . . . . . . + . . + . . + . .. .. + . . . . . . . . . . . . .. . . Min. Max. Eﬀects input level Min. Max. Dry mix . Min. Max. . Eﬀects . + mix . . .Max. Min. .. Output .level . . . + . . . .. . . Min. Min. Max. . + . . Min. Max. . Eﬀects . input level Min. Max. Min. Max. Min. Max. Min. Dry mix . . . . .. .. SILICON CHIPA Digital FX C B Min. Max. Clip .. . . . . . . .Dry Output . . . . . + . . . . . .Eﬀects . . . . . . . input level mix. level . + .. .. + .. .. + .. .. + .. . . . .. . . . . . . . . . .. . . . Min. Max. .Min. Max. . Min. Max. . . . .C . . . . B A . . . . . . . .. . . . Eﬀects parameters + + + . . . . . . . . . . . . . .. .. Min. Max. . Min. Max. + C . Max. Max. Eﬀects mix . . .. . . . .. .. + . . .. . . Min. . . . . .. . . Max. Eﬀects mix .. . Min O le . .. .. .. .Min. Max. . . . . . .Output .. . . level+ . . + . . . . . . . Min. Max. Min. Min . . Max. . .. C B . . parameters + Eﬀects . . . SILICON CHIP Dig B A . Min. . Max. Min. Max. 8. .9 Eﬀects parameters 10 . . .11 P CHIPB Digital FX SILICONBYP CHIP Digital FX56. . SILICON Y .12 A 8. .9 P T + + 10 + 7 . . + + A . . A 13 C 4 7 8 9 10 6. 11 P . B . S 6 11 B S . H P Y 5 12 S 14 A3 . Y . . 12 S 5 4 13 A P P T 2 + + Eﬀects parameters . . 2 ++ . . . 4 3 1 + .13 .14 CH . . . . A S S 7 1A 16 15 S S 16 15 + + Fig.6 (above): front panels for the two Patch Effect Adjustment C Adjustment B versions of the project – on the right 1 Chorus-reverb Chorus mix Chorus rate is the potentiometer-selected version 2 Adjustment Flange-reverb Flange mix rate Patch Effect C Adjustment B Adjustment Flange A while the left panel is for the switch 3 Tremolo-reverb Tremolo mix Tremolo rate 1 Chorus-reverb Chorus mix Chorus rate Reverb mix selected. Once again, this artwork can be 2 Flange-reverb 4 FlangePitch mix shift Flange rate Reverb mix downloaded from siliconchip.com.au 3 Tremolo-reverb Tremolo mix Tremolo rate Reverb mix 4 5 6 7 8 Pitch shift Pitch echo Test Reverb 1 Reverb 2 5 6 7 8 Patch Fig.7 (right): the side labels arePatch identical Effect 9 for both versions and show at a9 glance Octaver 10 Pitch shift glider what the various combinations10achieve. 11 11 Oil can delay Label 1-8 should be fixed to one side and 12 12 Soft clip overdrive label 9-16 to the other side. 13 Bass distortion 13 14 15 16 Pitch echo Test Echo mix Reverb 1 Reverb 2 Low ﬁlter Low ﬁlter 14 Aliaser Wah 15 Faux phase shifter 16 Effect Silicon Chip Echo delay Adjustment C Adjustment B + 1 14 15 16 T C H Adjustment A Reverb mix Reverb mix Reverb mix Side panels +/- ~4 semitones Pitch shift Reverb time Reverb time Adjustment C Adjustment B octave Adjustment Octaver Down level A Up octave level DownPitch octaveshift levelglider Up octaveGlide level Dry mix Depth Glide Depth Oil can delay FeedbackRate Chorus width Feedback Chorus width Time rate Volume Tone Soft clip overdrive Volume Tone Gain threshold Bass Dry/wet mix Tone Dry/wet mixdistortion Tone Gain Aliaser Sample rate Filter Q Sensitivity Wah Filter Q Reverb Sensitivity Feedback level Faux phase Time shifter FeedbackSpeed levelwidthTime For the PCB version that uses the rotary switch, you will need to cut the switch shaft, leaving sufficient length for the knob to attach securely close to the panel. Also, a flat will need to be filed on the side of the shaft to form a D-shape suitable for the knob. This will need to be carefully filed so it is a tight fit. The knob pointer will also need to be prised off and orientated correctly. Knob pointer orientation is best found during the testing procedure. While 15 of the 16 positions will give an effect, position six is the test position, and the output signal closely matches the input signal. With the knob rotated to this position, adjust the pointer to line up with 6. Another way is to measure the voltage at the A, B, C and D points at pins 16, 17, 18 and 13 of IC4 when powered 34 Echo mix +/- ~4 semitones Echo delay Pitch shift Low ﬁlter High ﬁlter High ﬁlterLow ﬁlterReverb timeHigh ﬁlter High ﬁlter Reverb time 3 2 Adjustment A Dry mix Rate Time rate Gain threshold Gain Sample rate Reverb Speed width up. Position 1 is when all of these are at 0V. Finally, secure the lid in place using either the original screws or Nylon M4 screws, as mentioned previously. Stick rubber feet to the base if you are not using the Nylon screws as ‘feet’. Removing the knobs After installation, the knobs are likely to be difficult to remove. You will need to lever them off; make sure the lever (such as a flat-bladed screwdriver) is against a packing piece placed on the front panel to prevent damage to the panel. Usage Note that some patches available in the default selec- Australia’s electronics magazine siliconchip.com.au S Parts list – Digital FX Unit 1 double-sided PCB coded 01102212, 86 x 112mm* [SILICON CHIP ONLINE SHOP 01102212] 3 panel labels (one front, two sides – see opposite) 1 diecast aluminium enclosure 119 x 94 x 34mm [Jaycar HB5067] 2 6.35mm PCB-mount jack sockets (CON1,CON2) [Jaycar PS0195] 1 PC-mount barrel socket, 2.1mm or 2.5mm ID (CON3) [Jaycar PS0520, Altronics P0621A] 1 2-pin vertical polarised header, 2.54mm spacing (CON4) [Jaycar HM3412, Altronics P5492] 1 2-pin polarised plug (CON4) [Jaycar HM3402, Altronics P5472 and 2 x P5470A pins] 1 6-way pin header with 2.54mm spacings (CON5) 1 C&K ZMA03A150L30PC microswitch or equivalent (S1) [eg Jaycar SM1036] 1 3PDT footswitch (S2) [Jaycar SP0766, Altronics S1155] 1 Lorlin BCK1001 16-way 4-bit binary-coded switch* (S3) [RS Components 655-3162] 6 B10kΩ linear pots (VR1-VR3,VR5-VR7) [Altronics R1946] 1 B100kΩ linear pot (VR4) [Altronics R1948] 7 11.5mm-diameter 18 tooth spline (6mm) knobs (see text for special requirements) [Altronics H6560, RS Components 299-4783] 1 13mm-diameter D-shaft knob* [Jaycar HK7717] 1 ferrite RF suppression bead 4mm OD x 5mm (FB1) [Altronics L5250A, Jaycar LF1250] 1 40kHz crystal (X1) [Citizen CFV-20640000AZFB or similar; RS components 1849668] 1 9V battery clip lead (optional) 1 9V battery (optional) 1 PC stake (GND point) 1 solder lug (for grounding the enclosure) 4 M4 x 10mm Nylon screws or stick-on rubber feet (see text) 2 9mm-long M3 tapped Nylon standoffs (support for PCB rear) 3 M3 x 6mm panhead machine screws (for solder lug and standoffs) 1 M3 nut and star washer (for solder lug) 1 50mm length of medium-duty green hookup wire 1 6.3mm mono jack plug or jack-to-jack lead (for testing) Semiconductors 3 OPA1662AID dual op amps, SOIC-8 (IC1-IC3) [RS Components 825-8424] 1 SPN1001-FV1 digital FX processor, wide SOIC-28 (IC4) [www.profusionplc.com/parts/spn1001-fv1] tions use the A, B and C parameter adjustments while other patches only use adjustment A. Also, some effects give you control over the effect/dry mix while others do not. See the side panel labels (opposite) for details. When the effects parameters include a mix control, the main dry mix control should be set fully anticlockwise, the effects mix control set fully clockwise, and the mixing done with the parameter mix control(s). Where an effect has no mixing control, the dry mix level adjustment provided can be used instead. When connecting to an amplifier, it should have a switch siliconchip.com.au 1 24LC32A-I/SN EEPROM, SOIC-8, programmed with 0110221A.hex (IC5) 1 1N5819 1A schottky diode (D1) 1 LD1117V33C 3.3V low-dropout regulator (REG1) [RS Components 6869767] 1 3mm high-intensity green LEDs (LED1) 2 3mm high-intensity red LEDs (LED2, LED3) Capacitors 4 100µF 16V PC electrolytic 1 22µF 16V PC electrolytic 4 10µF 16V PC electrolytic 2 4.7µF 16V PC electrolytic 1 1µF 16V PC electrolytic 5 100nF MKT polyester 2 1.2nF MKT polyester 1 1nF MKT polyester 2 560pF ceramic 2 100pF NP0/C0G ceramic 1 15pF NP0/C0G ceramic Resistors (all 1/4W, 1% metal film axial) 1 1MΩ (Code brown black black yellow brown) 1 100kΩ (Code brown black black orange brown) 2 20kΩ (Code red black black red brown) 12 10kΩ* (Code brown black black red brown) 1 1kΩ (Code brown black black brown brown) 3 200Ω (Code red black black black brown) 3 100Ω (Code brown black black red brown) Parts for version using a potentiometer for effects selection (delete items marked * above) 1 double-sided, plated-through PCB coded 01102211, measuring 86 x 112mm 1 B10kΩ linear potentiometer (VR8) [Altronics R1946] 1 11.5mm-diameter 18 tooth spline (6mm) knob (see text for special requirements) [Altronics H6560, RS Components 299-4783] 1 9mm-long M3 tapped Nylon standoff (support for rear of PCB) 1 M3 x 6mm panhead machine screw (for standoff) 1 PIC12F1571-I/SN 8-bit microcontroller programmed with 0110221A.hex, SOIC-8 (IC6) 1 2N7000 N-channel small-signal Mosfet (Q1) 1 3mm high-intensity red LED (LED4) 2 100nF MKT polyester capacitors 1 1.2MΩ 1/4W 5% carbon axial resistor 8 10kΩ 1/4W 1% metal film axial resistors 1 200Ω 1/4W 1% metal film axial resistor that allows the jack’s shield connection to be either Earthed or floating. A guitar with piezo pickups should have less hum when the switch is selected to connect to Earth. Next month We’ll have a follow-up article next month that describes how to create and load your own effects into the EEPROM chip, changing the nature of effect selections 8-15. This can be done using freely available software and a Microchip PICkit 2 or PICkit 3 programmer. SC Australia’s electronics magazine April 2021 35 Full Wave Universal Motor Speed Controller Want exceptionally smooth speed control over the entire range for your power tool? You want our new Universal Motor Speed Controller. It is ideal for use with mains-powered electric drills, lawn edgers, whipper snippers, circular saws, routers or any other appliance with universal (ie, brush-type) motors, rated up to 10A. By JOHN CLARKE O ur latest Full Wave Universal Motor Speed ControlWe have also added the ability to switch the soft-start fealer is an upgrade on the one we published in March ture off, also via an external switch. Soft start is useful when 2018. That one worked very well, but we identified the speed controller is set at a certain speed and the motor several upgrades and improved features that could be made is switched on and off at the appliance. When the appliance to the design. is switched on, the motor speed is slowly and automatically One of the main drawbacks of the previous design was brought up to the set speed. Without it, power to the motor that the feedback gain control was located inside the Con- is suddenly applied, and the motor can kick back. troller’s housing. That control set the amount of compensaSoft start is essential when using the Controller with a tion for maintaining motor speed under load. high-powered router or circular saw. For smaller appliancOnce set, the Controles, and when the moler was only suitable tor is switched on and for the appliance being off often, you might This Speed Controller operates directly from the 230V AC mains used, since the feedback find that it limits how supply and contact with any live component is potentially lethal. control would require fast you can work, as Do not build it unless you know what you are doing. changing for different you wait for the motor DO NOT TOUCH ANY PART OF THE CIRCUIT WHILE IT IS motors. to come up to speed. PLUGGED INTO A MAINS OUTLET and never operate it This control is now exThat would be the outside its Earthed metal case or without the lid attached. ternally adjustable via a case when used with This circuit is not suitable for use with induction motors and must control knob, making it a whipper snipper and only be used with universal ‘brush type’ (series-wound) motors or easy to use the Control- shaded pole (fan) motors with nameplate ratings up to 10A. For more some hand drills. So ler across a range of difwe made it so you can information, see the section titled “What motors can be controlled”. Power tools with inbuilt fans must not be operated at low speeds for ferent power tools and easily switch the soft extended periods; otherwise, they could overheat. other devices. start feature off. While WARNING! 36 Silicon Chip Australia’s electronics magazine siliconchip.com.au we were making those changes, we took the opportunity to improve its ability to maintain motor speed under load, especially at low speed settings and for low-power appliances. The Full Wave Universal Motor Speed Controller can be used with mains supplies over the range of 220250V AC at 50Hz or 60Hz. This means that it can be used in many different countries, although it is not suitable for use with 100-120V AC mains supplies. The Controller is mounted in a relatively low-profile diecast aluminium case with mains plug and socket leads attached to one end, through cable glands. A panel fuse is also provided on the same end of the case. The speed control and feedback gain potentiometers, and soft start switch, are mounted on the lid. Features * For universal and shaded-pole motors rated up to 10A * Runs from 220-250V AC at 50Hz or 60Hz * Full-wave motor speed control * Full speed range (from nearly zero to close to 100%) * Current feedback for maintaining speed under load * Feedback gain adjustment * Optional soft start from zero speed and at power-up * Optimised control for inductive loads such as motors Why do you need speed control? Most power tools will do a better job if they have speed control. For example, electric drills should be slowed down when using larger drill bits as they make a cleaner cut. Similarly, it is useful to be able to slow down routers, jigsaws and even circular saws when cutting some materials, particularly plastics, as many will melt rather than be cut if the speed is too high. The same comments apply to sanding and polishing tools, and even electric lawn trimmers; they are less likely to snap their lines when slowed down. What motors can be controlled? This Controller suits the vast majority of power tools and appliances. These generally use universal motors which are series-wound motors with brushes. They’re called universal motors because they can operate on both AC and DC. You cannot control the speed of any universal motor which already has an electronic speed control built in, whether part of the trigger mechanism or with a separate speed dial. That does not include tools such as electric drills which have a two-position mechanical speed switch. In that case, you can use our speed controller with the mechanical switch set to fast or slow. The slow selection usually drives the motor with a half-wave voltage. Scope1: the output waveform (Active voltage, in cyan) at a higher speed setting with a resistive load (a light bulb). You can see that the output voltage matches the input voltage most of the time, so the attached load will receive almost full power and, if a motor, will run at high speed. siliconchip.com.au Induction motors (except shaded-pole types, which are often found in fans and such) must not be used with this speed controller. How do you make sure that your power tool or appliance is a universal motor and not an induction motor? One clue is that most universal motors are quite noisy compared to induction motors. However, this is only a guide, and it’s certainly not foolproof. In many power tools, you can see that the motor has brushes and a commutator (usually through the cooling vents) and you can see sparks from the brushes during operation. That indicates that the motor is a universal type. But if you can’t see the brushes, you can also get a clue from the nameplate or the instruction booklet. Most induction motors used in domestic appliances will be 2-pole or 4-pole types which operate at a fixed speed, typically 2850 RPM for a 2-pole unit or 1440 RPM for a 4-pole unit. The speed will be on the nameplate. Bench grinders typically use two-pole induction motors. If you do need to control the speed of this type of motor, use the 1.5kW Induction Motor Controller published in April and May 2012 (siliconchip.com.au/Series/25) with important modifications in the December 2012 issue. Phase control The AC mains voltage closely follows a sinewave. It starts at 0V, rises to a peak, falls back to 0V, then does the same Scope2: by triggering the Triac later in each mains halfcycle, the output voltage (cyan) is zero most of the time, and the load power is greatly reduced. This will cause an attached motor to spin quite slowly, as the average applied voltage will be low. Australia’s electronics magazine April 2021 37 Specifications * Power: 230V AC sinewave up to 10A * Operating frequency: any fixed frequency between 40Hz and 70Hz * Soft start rate: two seconds from start to full speed * Triac gate drive: 68mA * Triac gate pulses, phase angle <90°: 40µs gate pulses repeated at 200µs intervals thing in the opposite direction. This repeats 50 times per second for 50Hz mains, or 60 times per second for 60Hz mains. A motor connected to the mains makes full use of the energy from each cycle so that it runs at its maximum speed. So if supplied only a portion of this sinewave to the motor, with less energy available to power it, the motor would not run so fast. Varying the time during each half-cycle when voltage is applied to the motor gives speed control. This is the basis of phase control: start feeding power very early in the cycle, and the motor runs fast; delay power until much later in the cycle, and it runs more slowly. The term ‘phase control’ comes about because the timing of the trigger pulses is varied with respect to the phase of the mains sinewave. Several devices can be used to switch the mains voltage; here, we are using a Triac. That device can be used to switch both the positive and negative voltage excursions of the mains waveform. The oscilloscope traces show phase control varying the power to an incandescent light bulb, as this shows phase control in its pure form, without the extra hash caused by driving a motor. Scope1 shows the chopped waveform from the phase control circuit when the incandescent light bulb is driven at high brightness. This is equivalent to driving a motor at a fast speed. Here, the Triac is triggered 2.5ms after the zero-crossing (the point where the mains waveform passes through 0V). The voltage applied to the load is the cyan trace, and measures 200V RMS. That is less than the 219V RMS mains waveform shown by the yellow trace. Scope2 shows the waveform from the phase controller driving a light bulb at a lower setting, with the Triac triggered later in the cycle. The voltage applied to the load is now much less at 87.9V RMS. Scope3 shows the waveform when driving a motor. The lower blue trace is the voltage applied to the motor, with the input mains shown on the top (yellow) trace. Note the extra hash on the lower trace due to the motor being an inductive load. Speed control For a motor to have good low-speed performance, the Controller needs to compensate for any drop in motor speed as the load increases. Many phase-based speed controllers rely upon the fact that a motor can be used as a generator when it is spinning with no power applied. When the motor is loaded and the motor speed slows, the back-EMF (electromotive force) produced by the motor drops, and the circuit compensates by providing more of the mains voltage cycle to the motor, 38 Silicon Chip Scope3: the same speed setting as shown in Scope2, but this time with a motor attached. The inductance of the motor windings causes the Triac to switch off after the zero-crossing due to the output current phase shift from its reactance. triggering the Triac earlier in the mains cycle. But in practice, the-back EMF generated by most series motors while the Triac is not conducting is either very low or non-existent. This is partly because there is no field current, and the generation of voltage is only due to remnant magnetism in the motor core. If there is any back-EMF produced, it is too late after the end of each half-cycle to have a worthwhile effect on the circuit triggering in the next half-cycle. So we use a different method for speed regulation, by monitoring the current through the motor. When a motor is unloaded, it draws a certain amount of current to keep itself running. When the motor is loaded, the motor speed drops and the current draw increases. The motor controller senses this, and compensates for this speed drop by increasing the voltage to the motor. This might sound like positive feedback, where the detection of more current drawn will increase the voltage and so allow the motor to draw more current. It’s true that this can happen if the amount of compensation is too high, which is why we include a feedback control knob, to adjust the compensation gain. With the right setting, the speed regulation is very impressive, but too much feedback will have the motor increasing in speed with increased load instead of maintaining the set speed. Controlling a Triac with an inductive load One major problem when using a Triac for full-wave control of a motor is the way a Triac switches off and the nature of the motor load. A Triac is usually switched on by applying a current to its gate. If the current flowing between the Triac’s main terminals is greater than its holding current, the Triac will remain switched on for the remainder of the mains cycle. A Triac will only switch off when the gate is not being driven and the Triac current drops below its holding current. As a motor is not a purely resistive load, but instead has a significant inductance, the motor current lags the voltage. That means that a Triac driving a motor will not nec- Australia’s electronics magazine siliconchip.com.au Scope4: the first stage of the precision full-wave rectifier works as a half-wave rectifier with an output voltage half that of the input. Both signals (original and clipped/ attenuated) are fed into the second stage and combined to produce the output shown in Scope5. Scope5: the final output waveform of the precision full-wave rectifier is in cyan. It is identical to the yellow trace, except that the negative portions have become positive voltages, so that it can be fed to a single-ended ADC for measurement. essarily switch off at the zero-crossing; motor current can continue to flow until sometime after. Our circuit uses a microcontroller to produce the required gate pulses to correctly drive an inductive load like a motor using a Triac. It feeds a series of gate pulses to the Triac to provide for the full range of phase control. time the Triac turns off. The snubber network acts to damp transients and reduce their amplitude. The DC supply for the microcontroller is derived directly from the 230V AC mains supply via a 470nF 275VAC X2 rated capacitor in series with a 1kΩ 5W resistor. The capacitor’s impedance limits the average current drawn from the mains, while the 1kΩ resistor limits the surge current when power is first applied. When the Neutral line is positive with respect to Active, current flows via the 470nF capacitor, diode D1 and 47Ω resistor to the 1000μF capacitor to charge it up. On negative half-cycles, the current through the 470nF capacitor is reversed and flows through diode D2, discharging the capacitor back into the mains. Zener diode ZD1 limits the voltage across the 1000µF capacitor to 5.1V. This is the supply for microcontroller IC1, op amps IC2a and IC2b, and for the gate current of Triac Q1. IC1’s 5.1V supply is bypassed with a 100nF capacitor while IC2 is bypassed with 100uF. Switch S1 allows the soft-start feature to be enabled or disabled. This switch controls the input level of the GP3 input (pin 4). When S1 is open, the GP3 input is held high at 5.1V via a 47kΩ resistor, so soft start is disabled. When switch S1 is closed, GP3 is pulled low, and the program runs the soft-start routine. S1 pulls GP3 low via a 100Ω resistor, which is included to protect the input from current transients that could cause latch-up in the IC. The 100nF capacitor provides a low impedance to transients, preventing incorrect detection of the GP3 input when S1 is open due to transients or interference. VR1 is the speed potentiometer, and it is connected across the 5.1V supply. IC1 converts the voltage from VR1’s wiper into a digital value using its internal analog-to-digital converter (ADC). The 100kΩ resistor from the wiper to ground holds the AN1 input at 0V, setting the motor speed to zero should VR1’s wiper go open-circuit. Potentiometer VR2 is connected similarly. Its wiper voltage sets the feedback gain to maintain motor speed under load. It is also converted to a digital value within IC1. The capacitors at the wiper of VR1 and VR2 provide a low source impedance to IC1’s ADC, and to filter out supply ripple. Circuit description The Speed Controller circuit is shown in Fig.1. Its key components are Triac Q1 and PIC12F617 microcontroller IC1. IC1 monitors the speed potentiometer, VR1, at its analog input AN1 (pin 6) and the feedback gain potentiometer, VR2, at AN0 (pin 7). It also monitors the motor current at analog input AN3 (pin 3), with that signal originating at current transformer T1 and passing through a full-wave rectifier based around IC2. The mains voltage waveform is monitored for zero crossings at pin 5, via a 330kΩ resistor. In response to all those parameters, IC1 produces a series of pulses at its digital output GP5 (pin 2), and these drive the base of NPN transistor Q2 which, in turn, sinks current from the gate of Triac Q1. The Triac gate current flows via the 47Ω resistor connected between the 5.1V supply and the Triac’s A1 terminal, then out through the gate and to circuit ground via Q1 (ie, the gate current is negative). This method of connection places the 47Ω resistor between the 230V AC mains supply and the 5.1V supply which runs the PIC microcontroller. This avoids Triac switching noise getting into the 5.1V supply, which can cause the microcontroller to latch-up. Snubber The snubber network comprises two 220Ω 1W resistors in series and a 220nF 275V AC X2-rated capacitor connected between the A1 and A2 terminals of the Triac. This network prevents rapid changes in voltage from being applied to Triac Q1, which would otherwise cause it to turn on (due to dV/dt switching) when it is supposed to be off. These rapid changes in voltage can occur when power is first applied, or can come from voltage transients generated by the inductance of the motor being controlled each siliconchip.com.au Australia’s electronics magazine April 2021 39 Both VR1 and VR2 are connected to IC1 via screw connectors. CON2 provides the common +5V and 0V connections for VR1 and VR2, while VR1’s wiper also connects to CON2. CON3 provides the wiper connection for VR2, with switch S1 utilising the remaining two connections in CON3. Mains synchronisation The timing of the Triac’s trigger pulses is critical to its correct operation. IC1 monitors the mains voltage at its pin 5, with the 330kΩ resistor connecting to Neutral plus a 4.7nF low-pass filter capacitor. An interrupt routine is triggered in IC1 whenever the voltage at pin 5 changes from a high to a low level or vice versa. The interrupt tells IC1 that the mains voltage has just passed through 0V, so it can synchronise its gate triggering with the mains waveform. The phase lag introduced by the 4.7nF capacitor is compensated for within IC1’s software, as is the asymmetry of the triggering due to the 5V difference between low and high levels. Current feedback T1 is a current transformer comprising a ferrite toroid with a two-turn primary winding in series with the Triac. The secondary winding has 1000 turns, and it is loaded with a 510Ω resistor. With this loading, the transformer produces 800mV per amp of load current at the secondary output. This is proportional to the current through the motor being controlled. Its output signal is applied to a precision full-wave rectifier comprising IC2a and IC2b. This configuration is unusual in that it does not use any diodes. Most precision rectifiers with diodes require a negative supply for the op amps. While we could have incorporated a negative supply, it would increase the circuit complexity and cost. The full-wave rectifier operation relies on op amps that have specific characteristics. The first is that the op amp output has to swing fully to the negative supply rail (ie, all the way down to 0V). Also, this 0V output must be maintained when the input to the op amp drops below 0V. The LMC6482 op amp (IC2a and IC2b in the circuit) has these characteristics, as well as a low supply current. 40 Silicon Chip We have labelled several points in the circuit and shown the expected waveforms to help explain how this section works. The signal from the transformer secondary appears at point A. This signal swings above and below 0V as shown. The signal flows along two paths from here. One is through the 20kΩ resistor to point D, and the other through the two series-connected 100kΩ resistors to 0V. IC2b is connected as a unity gain buffer. The op amp’s internal diode will clamp any voltage at the non-inverting input (pin 5) below -0.3V. Its output (pin 7) will be at 0V whenever its input is 0V or less. The operation of this part of the circuit is best explained by describing the signal flow for the negative and positive excursions of the waveform separately. Negative portion When the voltage at point A is negative, the voltage at point B is clamped to -0.3V by the internal protection diode at the pin 5 input of IC2b. The output of IC2b at pin 7 (point C) is therefore at 0V, and so is the non-inverting input to IC2a. As a result, IC2a acts as an inverting amplifier with a gain of -1. This is set by the input 20kΩ resistor and the 20kΩ feedback resistor from the pin 1 output to the inverting input at pin 2. So IC2a will produce a positive voltage at its output pin 1, proportional to the negative voltage at point A. To understand how this works, consider that the op amp operates to keep the voltages at its inputs equal. As the non-inverting input is held at 0V, with equal value resistors in the feedback path forming a 1:1 divider, the output voltage (E) must have equal magnitude and opposite polarity compared to the input voltage (A) for the inverting input voltage (D) to be at 0V. So for example, when point A is at -1V, point E will be +1V, so point D will be at 0V, equal to C. Note that the 10kΩ resistor at point D does not have any effect in this case, since pin 2 is at 0V, and therefore there is no voltage across that resistor. It has a function only during positive signal excursions. Positive portion For positive voltages at point A, the voltage at point B will be half the voltage of point A due to the 100kΩ/100kΩ Australia’s electronics magazine resistive divider. Point C and the non-inverting input to IC2a will also be half the applied voltage at A, as IC2b is acting as a buffer. Remember that usually, the inverting input voltage will be the same as the non-inverting input. The op amp will ensure this by adjusting its output so it can maintain that voltage via the feedback resistor. The only way that can happen for IC2a in this case is when the op amp output at point E is the same as the signal input at point A. In that case, the same voltage is applied to both 20kΩ resistors and they are essentially in parallel, forming an equivalent 10kΩ resistor to point D. This forms a 1:1 divider with the 10kΩ resistor from point D to ground, halving the voltage at this point compared to points A & E. So to conclude. IC2a provides the same positive voltage at its output E as the input at A during positive excursions. During negative excursions, IC2a instead inverts the voltage. So siliconchip.com.au Fig.1: the Motor Speed Controller uses current sense transformer T1 and op amps IC2a & IC2b (operating as a full-wave precision rectifier) to sense the motor current. IC1 adjusts the gate pulses from its pin 2 output to the gate of Triac Q1 to maintain a more-or-less constant motor speed under load the output of IC2a is positive for both negative and positive inputs at point A. Thus, we have a full-wave rectifier. Its output is low-pass filtered using a 4.7kΩ resistor and 10µF capacitor for a smooth DC output that’s then applied to the AN3 analog input of IC1, ready to be digitised. Scope4 shows a sinewave signal at point A (in yellow) and the lower blue trace shows waveform C, the half-amplitude positive waveform output. When waveform A goes below 0V, waveform C stays at 0V. Scope5 shows the same sinewave signal at A in yellow, and the fullwave rectified output at E in the lower blue trace. Construction Most components for the Full Wave Universal Motor Speed Controller are mounted on a double-sided, plated-through PCB (printed circuit board) coded 10102211 and measuring 103 x 81mm. This is mounted inside a diesiliconchip.com.au cast box measuring 119 x 94 x 34mm. Follow the PCB overlay diagram, Fig.2. Begin by installing the resistors except for the 5W type. The resistor colour codes are shown in a table, but you should also double-check each resistor using a digital multimeter. Following this, fit the diodes, which must be orientated as shown. There are two different diode types: 1N4004 for D1 and D2, and zener diode ZD1 is a 5.1V 1W type (1N4733). IC1 is mounted on an 8-pin DIL socket so install this socket now, taking care to orientate it correctly, with the notch facing towards the top of the PCB. Leave IC1 out for the time being, though; we’ll fit it later on. IC2 can be installed on a socket or directly on the PCB. Additionally, Q2 can be installed now. Place the capacitors next. The MKT and polypropylene types are usually printed with a code indicating their value. These are all shown in the parts list. Australia’s electronics magazine By contrast, electrolytic capacitors are almost always marked with their value in μF, along with their polarity. Typically, the negative lead is marked with a stripe. They must be inserted with the polarity shown. The screw terminals are next. The 3-way terminal blocks for CON2 and CON3 are installed with the lead entries facing each other, while CON1 does not have a specific orientation. Then fit the 5W resistor about 1mm above the PCB for improved cooling. Finally (for now), install current transformer T1. It does not matter which way it is orientated. Triac Q1 will be fitted later. Cut the underside pigtail leads from all components short to prevent contact with the base of the case. Drilling the case Fig.4 shows a template/guide for drilling the case. The lid requires 9.5mm diameter holes for potentiometers VR1 and VR2, a 19mm x 10mm April 2021 41 SILICON CHIP Fig.2: most of the components are mounted on the top of the board, with the main exception being Triac Q1. It mounts on the inside of the case, under the PCB. Once you have finished the wiring, check it carefully against this diagram. The Earth screws and lugs must all make good contact, and use cable ties to bundle up the control wires as shown. rectangular cutout for switch S1 and a 4mm hole for the Earth screw. The PCB is mounted in the base of the case using 6.3mm-long M3 tapped spacers, which require mounting holes. Use the PCB as a template, and note that the CON1 screw terminal end sits further away from the end of the box compared to the other end. This allows space for the cable gland nuts. With the PCB in place, mark out the hole positions, remove it and drill them to 3mm. Attach the 6.3mm-long spacers to the PCB using short machine screws, then bend the Triac leads up by 90° 4mm from its body. Insert the leads into the PCB from the underside (see Fig.2). Secure the PCB to the case with screws from the underside and mark the Triac mounting hole position on the base of the case. Remove the PCB again and drill this to 4mm. Clean away any metal swarf and slightly chamfer the hole edges, then reattach the PCB and adjust the Triac lead height, so the metal tab sits flush onto the flat surface. Secure the Triac tab to the case with an M4 screw and nut. The metal tab is internally isolated from the leads, 42 Silicon Chip so it does not require any further insulation between its tab and the case. Solder the Triac leads on the top of the PCB and trim them close. Now remove the screws to gain access to the underside of the PCB and solder the Triac leads from the underside of the PCB as well. Now is a good time to attach rubber feet to the base of the case. Panel preparation As well as drilling the holes in the lid mentioned above, you need to partially drill a 4mm hole on the inside for the pot location pin that prevents Close-up, same-size photo of the Speed Controller PCB. Because it is a mainspowered and mains-controlling device, your construction must be exemplary. Don’t attempt this project if you’re not experienced with mains devices. Australia’s electronics magazine siliconchip.com.au the pot body from rotating. Drill it so that it almost reaches the outside of the lid, but doesn’t go all the way through. If you use a countersunk-head Earth screw and countersink its hole appropriately, it can be mounted under the panel label for a neater appearance. Otherwise, you’ll need to cut a hole in the panel label (with a sharp hobby knife) when the label is stuck on. The panel label file can be downloaded from our website and printed. To produce a front panel label, you have several options. For a more robust label, print as a mirror image onto clear overhead projector film (using film suitable for your type of printer). Attach the label, printed side down, to the lid with a light-coloured or clear silicone sealant. Alternatively, you can print onto a synthetic “Dataflex” sticky label that is suitable for inkjet printers, or a “Datapol” sticky label for laser printers. Then affix the label using the sticky back adhesive. There’s more information online about Dataflex labels at siliconchip. com.au/link/aabw and Datapol at siliconchip.com.au/link/aabx, plus hints on making labels at siliconchip. com.au/Help/FrontPanels Wiring Cut the 10A extension lead into two, to provide one lead with a plug and another with a socket. Where you cut the lead depends on how long you want each section to be. You might prefer a long plug cord and short socket lead, so the appliance is located near the Controller, or the lead can be cut into two equal lengths. Before cutting, make sure you have sufficient length to strip back the insulation as detailed in the next two paragraphs. Make sure the two leads are fed through the correct gland and wired, as shown in the wiring diagram, Fig.2. For the socket (output) lead, you need a 100mm length of Earth wire Fig.3: Triac Q1 mounts on the base of the case, using it as a heatsink. A hole in the PCB gives access to hold the nut while you tighten the screw. siliconchip.com.au Parts list – Full Wave Motor Speed Controller 1 double-sided PCB coded 10102211, 103 x 81mm 1 diecast box, 119 x 94 x 34mm [Jaycar HB5067] 2 linear 50k 24mm potentiometers (VR1,VR2) 2 plastic knobs to suit VR1 & VR2 1 SPST mini rocker switch (S1) [Jaycar SK0984 or Altronics S3210] 1 Talema AX-1000 10A current transformer (T1) [RS Components 775-4928] 1 M205 10A safety panel-mount fuse holder (F1) [Altronics S5992] 1 M205 10A fast-blow fuse 1 4-way PCB-mount screw terminal (CON1) [Jaycar HM-3162] 2 3-way PCB-mount screw terminals, 5.08mm pitch (CON2,CON3) 2 GP9 cable glands for 4-8mm diameter cable 1 8-pin DIL IC socket (for IC1) 1 2m-long 10A mains extension cord 3 chassis lugs with 4mm eyelets 4 6.3mm-long M3 tapped Nylon spacers 3 M4 x 10mm panhead or countersunk machine screws (for mounting Q1; Earthing) 2 4mm inner diameter star washers 3 M4 nuts 8 M3 x 5mm panhead or countersunk machine screws 4 stick-on rubber feet 1 20mm length of 12mm diameter heatshrink tubing 1 80mm length of 3mm diameter heatshrink tubing 1 600mm length of 7.5A mains-rated wire (for VR1, VR2 & S1) 4 100mm-long cable ties Semiconductors 1 PIC12F617-I/P 8-bit microcontroller programmed with 1010221A.hex, DIP-8 (IC1) 1 LMC6482AIN dual CMOS op amp, DIP-8 (IC2) 1 BTA41-600B 40A 600V insulated tab Triac, TOP3 (Q1) 1 BC337 500mA NPN transistor, TO-92 (Q2) 1 5.1V 1W (1N4733) zener diode (ZD1) 2 1N4004 400V 1A diodes (D1,D2) Capacitors 1 1000µF 16V PC electrolytic 1 100µF 16V PC electrolytic 1 10µF 16V PC electrolytic 1 2.2µF 16V (or higher) PC electrolytic 1 470nF 275VAC X2-class metallised polypropylene 1 220nF 275VAC X2-class metallised polypropylene 3 100nF 63/100V MKT polyester 1 4.7nF 63/100V MKT polyester (value printed on body) (value printed on body) (code 103 or 100n) (code 470 or 4n7) Resistors (all 0.25W, 1% unless otherwise stated) 1 330k 5% 1W carbon film (code orange orange black orange brown) 3 100k (code black brown black orange brown) 1 47k (code yellow purple black red brown) 2 20k (code red black black red brown) 1 10k (code brown black black red brown) 1 4.7k (code yellow purple black brown brown) 1 1k 10% 5W wire wound (no code - value printed on body) 1 510 (code green brown black black brown) 1 470 (code yellow purple black black brown) 2 220 5% 1W carbon film (code red red black black brown) 1 100 (code brown black black black brown) 2 47 (code yellow purple black gold brown) Miscellaneous Super Glue (cyanoacrylate), thermal paste, solder Australia’s electronics magazine April 2021 43 Fig.4: drill the three holes in the lid as shown here, plus the rectangular cut-out. It is most easily made by drilling a series of small holes inside the outline, knocking the central piece out, then carefully filing the edges flat and to shape until the switch snaps in. The three large holes in the box end are for the two cable glands and fuseholder,with a small one (4mm) in the box side for the Earth screw. (green/yellow stripe) for the connection between the chassis and lid, so strip back the outer insulating sheath by about 200mm. Cut the Active (brown) and Neutral (blue) wires to about 50mm long and keep the offcuts. The spare 150mm brown wire can be used later, to connect from the fuse to CON1 via the transformer, T1. This requires two turns of the Active wire looped through the transformer hole. The 100mm Earth wire (green/yellow stripe) which is routed around the edge of the PCB, and twists together with the Earth wire from the plug (input) lead, to be crimped into one of the Earth lugs. Strip the plug lead outer sheath insulation back to expose 100mm of wire. All three wires pass through the cable gland and connect it as shown in 44 Silicon Chip Fig.2. Cut the Neutral wire to 50mm and strip back the insulation before connecting it to the terminal block. Now mount the fuse holder in the hole you made earlier and prepare to solder the Active (brown) wire to it, as shown. But before doing that, slide 10mm diameter heatshrink tubing over the Active (brown) wire. After soldering that wire, slide the tubing up and over the fuse holder to cover the fuseholder side terminal and shrink it. Similarly, use 3mm diameter heatshrink tubing to cover the fuse holder end terminal after soldering that wire. Now twist the ends of the input Earth (green/yellow stripe) wire and the output Earth wire together and crimp both into one of the eyelet lugs. Cut VR1 and VR2’s shafts to 12mm long from the front of the pot bodies and file the edges smooth. Then atAustralia’s electronics magazine tach the three 100mm lengths of 7.5A mains-rated wire to the three terminals of VR1, plus a fourth 100mm wire to the middle terminal of VR2. Use short lengths of the same wire to connect the two ends of VR2’s track to the same terminals on VR1. Cover all six terminals with 3mm heatshrink tubing. Next, connect the free ends of these wires to CON2 and CON3, making sure to do so as shown in Fig.2. You will also need to wire up switch S1 now in a similar manner. It is simply wired to the two remaining terminals in either order. Now secure all these wires to the PCB using a cable tie that feeds through the holes provided in the PCB. Attach VR1, VR2 and S1 to the lid of the case, noting that the potentiometers must be located as shown (ie, with their leads emerging away from the edge of the siliconchip.com.au children or other curious people. Attach the lid, ensuring the wiring is routed so that it fits around the higher components on the PCB. Use the four screws supplied with the case; don’t be tempted to run the speed controller without the lid in place! Testing This “opened out” photo matches the PCB/wiring diagram on P42. Of course, we made sure that the Controller was not plugged into mains power before removing the lid! case). This is so that they will fit between the two mains-rated capacitors on the PCB. Add cable ties around the wire bundles closer to VR1, VR2 and S2 as well. Fit the knobs now; you might need to lift out the knob caps with a hobby knife and re-orientate them so that the pointers match the rotation marks on the lid panel. That 100mm length of Earth wire you cut off from the output lead can now be crimped into two eyelet lugs, which are screwed to the underside of the box lid and the Earth screw on the side of the case using M4 screws, star washers and nuts. Ensure that the nuts are fully tightened. pins on both the mains plug and socket. Check this with a multimeter set to read low ohms. You should get readings below 1Ω between all Earth points. The cable glands need to be tightened to hold the mains cords in place. Because these are easily undone, apply a drop of Super Glue to the thread of the glands before tightening. That way, the glands cannot be undone by SILICON CHIP www.siliconchip.com.au 10A Fuse GAIN Final assembly Apply a smear of thermal paste to the underside of the Triac tab before installing the PCB inside the case. As mentioned, the tab of the Triac is insulated, so it can contact the case. The last components to insert are IC1 (taking care it is orientated correctly), the 10A fuse into its holder and the cover for the barrier terminals (CON1). This is simply pressed on to cover the screw terminals. Finally, rotate VR2 fully anticlockwise to initially disable feedback. Now check your construction carefully. Verify that the Earth wires (green/yellow striped) connect together the case, to the lid and the Earth siliconchip.com.au Connect up a universal motor appliance (eg, a mains-powered electric drill) to the Controller, apply power and check that the motor can be controlled when adjusting the speed potentiometer. VR2 may need adjustment to avoid speed changes when under load. Rotate it clockwise if the speed drops off too markedly under load, and anticlockwise if the motor speeds up under load. Check that the soft-start feature works when enabled by switching the power off, letting the tool spin down, then switching it on again to verify that it ramps up smoothly with S1 in the sc correct position. For universal motors rated up to 10A, 50/60Hz 230V AC. Not suitable for induction motors. SOFT START OFF ON . . . . . . . .. . . . . . .. . . . . . . . . . . SPEED Full Wave 10A Motor Speed Controller Fig.5: full-size “front panel” artwork which can be copied or downloaded and printed (from siliconchip.com.au). This is glued to the top of the diecast box – and it can also be used as a template to drill the three panel holes and cutout for the soft start switch. Australia’s electronics magazine April 2021 45 SERVICEMAN'S LOG I hope the purists won’t spit their dummies Dave Thompson I love a good restoration; it’s great when old gear is kept working into the 21st century in original condition. But sometimes that just isn’t possible, and it’s a good enough result to get something working again while keeping it looking original. So what did I do that will get certain knickers in a twist? Read on to find out... As I mentioned last month, all these lockdowns are (generally) bad for business, but they do give us time to do those jobs that were waiting for the shipment of round tuits to arrive. One of these jobs is a 1940s Gulbransen valve radio a friend had given me a while ago to check over. It has been sitting in a corner of my workshop gathering dust for a while, simply because it looked like a huge mountain to climb. This is one of those large mantel radios with an oak-veneered timber case. It has a gently-glowing dial displaying 46 Silicon Chip the many short and long-wave bands available at the time, a nifty ‘magic-eye’ tuning indicator and a sizeable built-in speaker, all giving it a typically warm valve radio sound and aesthetic. The problem with this radio is it had been stored in an outside shed for the last 40 years, and the moisture has really gotten into it. The timber finish has cracked, faded and lifted in places, and the fawn-coloured grille-cloth and paper speaker cone now almost Australia’s electronics magazine Items Covered This Month • • • • The week old vintage The self-made (repair)man Yamaha E303 keyboard repair Peak Instruments component analyser repair *Dave Thompson runs PC Anytime in Christchurch, NZ. Website: www.pcanytime.co.nz Email: dave<at>pcanytime.co.nz siliconchip.com.au non-existent (possibly due to rodents or other critters chewing on them). Worse still, the metal chassis and internals are so corroded they are – in my opinion anyway – beyond reasonable repair. The guys from the Vintage Radio section of this magazine will likely scoff at this assessment. It seems that anything is restorable and/or worth restoring to them! I’m imagining them right in their beautiful, wood-panelled office with Venetian blinds, stippled-glass windows, walls of filing cabinets and not a computer screen in sight, scoffing away. But keep in mind that I’m new to this vintage stuff, and I don’t want to start a job that I can’t finish! For me, the problems arise when I quote to the customer the huge amount (including many labour hours) it would take for me to restore this radio to health. Someone – a specialist restorer perhaps – might be able to do it less-expensively, and I put this to him as an option. He (rightly) had a minor coronary when I told him how much I would charge, and told me in no uncertain terms it simply isn’t worth that kind of money to him. I surmised as much, as I’ve been down this road many times before. People assume it’s just a lick of paint, a few lines of code, or the push of a button that fixes their prized possession; but we know it’s much more involved. That said, he did say this radio was owned by a favourite relative whom he used to visit as a child, and so it has much sentimental value. It would also be great to get it going again. So what could I do? Unless someone really wanted to put the time and love (and money) into this radio, I wouldn’t consider it a viable restoration project. For one, Collier and Beale (made locally under license from Gulbransen and distributed by HW Clarke) likely made many hundreds, if not thousands, of this radio model back in the 1940s. So it probably isn’t all that special, aside from the obvious sentimental value to my client. By now, I imagine dedicated restorers/collectors are frothing at the mouth at what I’m saying. But I suspect the vast majority of these have ended up in refuse tips all over the country. The tuning gang is seized, the valves have simply gone, and the chassis is siliconchip.com.au so rusted it would need stripping and mechanical restoration, I’m just not up for it; at least, not without being paid handsomely. Consider that the wiring, the valve sockets and every other electronic component would likely need replacing. While I have a reasonably extensive collection of new, old stock (NOS) and salvaged parts from old valve and early transistor radios and amplifiers, I just don’t have what this radio needs. So I’d need to spend time sourcing and purchasing those parts before I could even get stuck into the restoration. The woodwork wouldn’t be a problem for me, given my proclivity for working with timber, and I suppose the metalwork restoration wouldn’t be too onerous either when it comes down to it. But if the customer doesn’t want to spend the money, what am I supposed to do? Sadly, working for the sheer love of it doesn’t pay the bills, and I just can’t do that these days. The customer then came up with the idea of replacing the guts with modern components, keeping the radio’s outward aesthetic but using the likes of modern amplifiers and tuners. He asked me if it would be possible to combine modules that he’d seen advertised on eBay and AliExpress to do this, and I agreed it should work, and would cost a lot less than a full restoration job. He was OK with this option, so I did some research and ordered some inexpensive modules and a suitable speaker from our Chinese friends. While I waited for them to arrive, I set about tidying up the cabinet. I will be keeping everything I remove (the chassis etc) in its original condition, just in case the customer wants to do a complete restoration later. I won’t be altering anything externally to maintain the radio’s authentic look, other than to re-finish the timber bits and pieces. I only say this to deflect any blowback I’ll be getting from the vintage radio mafia! Gutting it and cleaning it up The first thing I had to do was remove everything from the case. This involved just a few screws and unplugging a few interconnecting wires. Obviously, I was very careful in keeping the integrity of the original parts, but in the end, I needed to get it all out so I could work on the case. Veneer is a tricky material. It looks Australia’s electronics magazine April 2021 47 fantastic, but is just a hyper-thin layer of some more-expensive timber laminated (glued) onto a cheaper timber underneath. Better-quality radios and stereograms were made out of solid, furniture-grade timbers like oak, walnut and elm. But sadly, not this one. Veneer is usually so thin that any damage to it, such as a hole worn through it, renders the rest of it pretty useless. Patching it often looks awful, unless you are very skilled, know what you are doing and have a selection of similar veneers on-hand. I am not skilled at veneer repairs, don’t know what I’m doing and don’t have any suitable materials on-hand, so that’s three strikes and out for me. Fortunately, in/on this case, the veneer had simply lifted and cracked a little here and there, most likely due to moisture dissolving the glue that held it down in the first place. So I thought that it might not be too challenging to repair. There was the odd chip, probably where something had fallen onto the radio while it was stored in the shed, but these dings were all small. So I thought I’d be able to get away with merely soaking and re-gluing the veneer down, sanding it all lightly and then re-oiling the whole thing with Danish oil. It actually turned out quite well, given the age and damage and my lack of skills in this area, and once it was oiled and I applied a couple of clear coats of lacquer, it looked very nice and still maintained a realistic vintage vibe. The other problem that I had to solve was the dial glass. The magic-eye tuning indicator is mounted in the middle of it, and it is connected to the rest of the old electronics via a flying lead/valve socket arrangement. The glass was quite dirty, and many of the screen-printed station markings were a bit worse for wear. I was unsure how to clean it without damaging it further. I started with soap and water, then progressed to methylated spirits with a very careful application in one hidden corner to make sure it wouldn’t wipe the whole thing totally clean. The outside surface was no problem; just soap and water cleaned off all the accumulated dust and grime quite well. I managed to remove most of the dirt from the inside – the printed side – without damaging any more of the station information. We’d not be using any of it now anyway, but I wanted to retain the radio’s original look. Now for the fun bit The modules and speaker I ordered arrived not long after finishing the case. I purchased an 8W amplifier module, an FM tuner module and a Bluetooth receiver that could be connected to a smartphone, complete with a small remote control. Grand total: $29. You just couldn’t make any of this hardware for the money. The speaker I bought is a 5-inch, 20W multi-range model that would happily handle anything the amp would throw at it, for just $11. The most expensive part I had to buy was the replacement grille cloth. While there were more modern-looking cloths available, I wanted a traditional look, so I had to buy a square meter of it, expecting to use just a third of that. No matter; what I don’t use will go in my parts bins for another project. Fitting all this gubbins into the case was the next challenge. Once I removed the chassis, there was nothing left to mount anything on. And I still needed to sort out a light to shine through the old dial gauge to give the appearance of a soft-glowing bulb. First, I needed to mount the new speaker, which had a completely different footprint from the old one. I made up a thin, custom timber insert with the correctly-sized hole cut into it, and tacked it directly to the old speaker-mounting facia. I then removed the old grille cloth, squeezed the new one in around the sides, and stapled it after pulling it taut. It looked almost original, and I was quite pleased with it. Next, I’d need a power supply for everything. The modules required ei- Servicing Stories Wanted Do you have any good servicing stories that you would like to share in The Serviceman column? If so, why not send those stories in to us? We pay for all contributions published but please note that your material must be original. Send your contribution by email to: editor<at>siliconchip.com.au Please be sure to include your full name and address details. 48 Silicon Chip Australia’s electronics magazine ther 5V or 12V, so it wouldn’t be too difficult. I thought about purchasing a power supply module at the same time as the others, but fortunately, I’d already bought a suitable one a few years ago for another project and had never used it. It would do nicely here. The only extra component to add was a power transformer, and as I have about 200 of the things lying around after buying a transformer-winding machine a while back, it didn’t take me long to find one to do the job. The amplifier would require the most power, with the Bluetooth module and tuner lapping up the remainder. I mounted the transformer directly to the bottom of the timber case with a couple of wood screws. Inter-wiring was done using standard light-gauge cables, routed and tied-wrapped into place. The mains lead was simply clamped into place (to proper specifications) and run directly out from the back of the box. The FM antenna was routed around the inside of the case. Our FM reception here is generally OK, so this ad-hoc aerial should suffice. I used stand-offs and long screws to mount the other modules to the inside sides of the case close to where they needed to be. They all use terminal blocks for interconnections which made things simple, and P-clamps and cable ties kept everything looking nice and neat. Tuning was the next challenge. The various FM modules available online are tuned with either a remote control, a manual up/down push-button or rotary tuning using a potentiometer. Many of these modules come with comprehensive LED displays, none of which my customer was keen on. A vintage-looking radio with an LED display chopped into the front isn’t that appealing. We decided that, since he usually tuned into a single station, he would forgo any gaudy displays and just manually tune it, hopefully using something resembling the original knob, if possible. Volume control was similarly problematic; many of the modules used a digital volume adjustment system. But in choosing an amplifier module that used an old-fashioned pot, that made my job much easier. All I had to do was remove the pot from the module and, using suitable flying leads, connect it via an adaptor to the case where the original volume pot used to be. siliconchip.com.au Our capabilities CNC Machining UV Colour Printing Enclosure Customisation Cable Assembly *** Box Build *** System Assembly Ampec Technologies Pty Ltd Australia’s electronics electronics magazine magazine Australia’s siliconchip.com.au Tel: (02) 8741 5000 Email: sales<at>ampec.com.au Web: www.ampec.com.au April 2021 2021 49 FEBRUARY 37 The original knob obviously wouldn’t fit the new pot, so I turned up a simple brass adapter so it could fit onto the much smaller shaft of the new volume control. I did the same thing with the ‘tuning’ pot, and a new rotary on/off switch that mimicked the originals. It actually all ended up looking very stock-standard, and the customer was happy with how it presented. A bit of solder here and there had the speaker and other ancillaries connected up, and it was ready to test. It worked very well, especially as he is a ‘set-and-forget’ user. The only thing left was the dark dial. Obviously, I couldn’t tee up the new tuning with the old manual dial-cord system or magic-eye, but he wasn’t worried about that. What would make a difference is the glow from the old dial. To this end, I simply rigged up a couple of orange LEDs and, after a bit of experimentation, adjusted the series resistors to provide a convincing soft glow. I could have gone for blue or something a bit more modern, but instead tried to maintain the vintage look of the original radio. All in all, it ended up looking OK and working very well, and as a bonus, he can stream music from his phone if he desires. The sound is excellent and the volume punchy, so all in all, it was a good solution to the problem. Another happy camper! The self-made (repair)man S. G. of Mildura, Vic had a frustrating time chasing a fault which seemingly he had caused, but he still can’t figure out how... You might laugh at my story, but you wouldn’t if it happened to you! I just spent over a week trying to repair one of my stuff-ups. A couple of weeks ago, I purchased an amateur band radio for the 2m and 70cm bands. This was going to replace the 2m radio that I had in the back of my Pajero ever since I first got my license. It also involved installing a new antenna on the bullbar, where the old UHF CB antenna used to live. I moved the UHF antenna to the side of the bonnet and mounted it with a special Z bracket, so the bonnet will still close. This works fine, and so does the new VHF/UHF antenna for the new radio. The only thing that I had left to do was to drill a hole in the firewall, right next to the cable feeding 12V to the caravan. 50 Silicon Chip This cable is also used to supply a 6-way fuse block so I can run fridges from the auxiliary battery, as well as the CB radio and the new amateur band radio. I used a 25mm hole saw and a short length of 25mm flexible conduit to act as a gland through the firewall. I took care in drilling the new hole, as there are several wires in the area that go off in all directions on the inside of the firewall. Yes, I did check before drilling the hole, but still managed to take out the interior lights, the digital clock and the hazard and turn indicators! First, I decided to check the fuse. The Pajero has two fuse boxes, with one in the engine compartment that houses the fuse for the hazard lights. The second fuse block is under the dash and requires removing the trim piece around the steering column just to gain access. The clock and interior lights are both on the same fuse, and I fixed them by replacing the fuse. The hazards are fed from two power sources, one permanent power (from the fuse block in the engine compartment) and the other is the accessories circuit fuse block under the dash. This is so that the hazards will work independently of the ignition key. Pressing the hazard button changes over the power feed from accessories to permanent power. This hazard switch also links both the right and the left blinker circuits so that all the lights flash at once. After more head scratching, I checked more fuses. I pulled the Australia’s electronics magazine blinker fuse (not easy due to the poor access) but it appeared OK. Next on the list was the blinker can itself. The only way I could think of to check whether it was faulty was to try replacing it. I then had the idea to bypass the blinker can, which involved fitting a small link wire between the B and the L pins on the socket. I now had all of the hazard lights and blinker lights working. At this point, it looked like I would have to pull the whole dash apart just to gain access to the wiring loom. I took out the gauges, speedo and tacho cluster, just to see if I could find any damaged wiring, but it was impossible to see properly behind the dash. I even tried to feel for damage to the wiring back there, but if I found it, how would I repair it? It looked like the Pajero was built around the wiring loom! After some further checking of the blinker can, though, I struck gold. This was a three-pin can (some have just two pins), and on checking the can in my workshop, I determined that the third pin was a ground and was needed as it is an electronic type and has a constant flash rate, independent of the lamps. Tracing around the blinker can socket, I soon found that while power was present, there was no ground return. I ended up cutting the ground wire from the socket, soldering on a new ground wire and attaching it to the chassis. It still didn’t work, so I called it a day. On Monday morning, I popped into a local shop and bought a new can. siliconchip.com.au After fitting it, my hazards and blinders worked – I breathed a sigh of relief! I don’t know how the blinker can failed; there is not much in it in terms of electronics. It just looks like a 555 timer driving a small relay. Anyway, I don’t care, it all works now! Yamaha E303 keyboard repair J. K. of Castlecrag, NSW spent a long time tracking down a problem in his keyboard, but at least the fix cost virtually nothing once he had diagnosed the fault... I purchased a Yamaha E303 electronic keyboard about 10 years ago, siliconchip.com.au second-hand, for about $300. It is an excellent learning tool, and had been enjoyed by my grandchildren almost every time they visit. A few years ago, the highest note (high C) stopped sounding. Since I seldom used it, I didn’t do anything about it. Actually, that key plays an important role in one of the resets, but I did not need it for that purpose. In the last couple of months, several more keys stopped sounding. I jumped online and found the service manual, but it did no more than show how to disassemble the unit. Disassembly is fairly intuitive, but Australia’s electronics magazine removing the keys to expose the pressure pads was not obvious. Luckily, the manual provided some pictures which showed how to do it. There are 61 keys in total. Each is sounded by two carbon sticks contacting the pads on the keyboard, completing a circuit. The E303 is a touch-sensitive piano, so the harder the key is pressed, the louder the note. This happens because of the resistance of the carbon sticks on the pads changes with pressure. A very common problem is dirt on the pads or the carbon sticks. Spilling coffee or sticky drinks on the keyboard April 2021 51 will cause significant problems, but cleaning the carbon sticks and the pads (with isopropyl alcohol) did not help. So I had to check that the connections between the keyboard and the control unit were solid. That is a very tedious job which required tracing voltages through the connecting sockets and onto the keyboard. The control unit (DMLCD in the service manual) provides 3.3V to the two keyboard circuit boards 61L and 61H via multi-cable leads 1 and 2 (see the accompanying diagram). I traced the +3.3V DC supplied to CN831 on the DMLCD board, at pins 1, 4, 5, 8, 9, & 12. The 3.3V supply is referenced to Earth as it appears on the control boards, but there is no cable carrying the Earth connection. Instead, pin 7 of CN833 is about -0.2V referenced to Earth and that translates to +3.095V on each of the pins mentioned above. All the voltages were present and correct. I had hoped that the service manual or Yamaha themselves would give me some leads, but they stated that they do not get involved in repairs, and refer all such enquires to their “Service Agents”. Strangely, the Service Agent for the Sydney area is located beyond Windsor. Each pad serving a note consists of two contacts which are “connected” by the carbon sticks when a key is depressed. Each contact on the circuit board connects through a diode to other pads, then connects to the control unit. Its a very clever system, because just twelve or so leads convey information about which of 61 keys has been pressed and whether two or more keys are involved. The diagram shown on the previous page is part of the left-hand keyboard circuit board 61L. The squiggly lines are the contact pads, two for each note. So it became a job of tracing all of the 122 diode connections back to the control board. That’s when I found five copper tracks with no continuity. Some kind of corrosion or stress had broken the links. The tracks are very fragile, so even a small amount of corrosion could break them. I considered spraying the boards with a conformal coating, but the risk of some spray getting on to the contact pads discouraged that idea. If more connections break in future, I will know what to do. Luckily, the fix was relatively easy; I just soldered a short length of wire 52 Silicon Chip between each of the diodes with a failed connection. After doing that for the five tracks, all of the failed keys came to life! I expect that a very experienced technician would recognise the problem quickly and would simply replace the two (low and high) keyboard PCBs, 61L and 61H, with a component cost of about $100 plus the time of swapping the new boards in. Doing what I did – tracing the problem – took about 30 hours which would have cost about $2000-3000 at standard labour rates. Which is why, these days, most repairs are not made at the component level, and instead, the boards are simply swapped. I think the control board for this keyboard costs about $350 – more than I paid for the whole thing! Repairing the Peak of test instruments P. B. of Kaitaia, New Zealand had given up trying to repair a piece of test equipment, but then when he went to take another look, a solution presented itself... I am a retired service technician. Some 20 years ago, I decided that a Peak semiconductor component analyser would greatly assist my servicing work despite its relatively high price. I took extra care to ensure that I did not connect it to any live equipment, and that any capacitors were discharged before using it. At some stage in its life, the self-analysis check it does on startup came up with a fault code. Sadly, Australia’s electronics magazine the user manual gives no information on what the codes signify. Looking at Peak’s site, I rapidly concluded that returning it to the UK for service would cost more than purchasing a new one. Dave Thompson recently mentioned his Peak instrument in a Serviceman’s Log column (March 2021; siliconchip. com.au/Article/14784), which jogged my memory. I decided to have a look at it again and started by replacing the battery. However, as I went to remove the battery, I became aware of what seemed to be a dry joint where the negative battery spring terminated on the board. It looked dull grey and pitted. Ancient memory then stirred into life, of a discussion with a serviceman in the area some years back, of a similar fault of another piece of batterypowered equipment where the negative wire had dropped off. The consensus was that it was a common occurrence on aging batterypowered equipment, only affecting the negative terminal. Sure enough, a hot soldering iron and a shiny solder joint later, the analyser sprang into normal operation. I wonder if this is a form of electrolysis. Three different metals are in contact: the plating on the battery spring clip, the copper PCB track and the solder. With the passage of time and current passing through it, the solder joint deteriorated. The voltage drop was not enough to stop the self-analysis or the display working, but it was sufficient SC to trigger the fault code. siliconchip.com.au Y I D r u o s Y l a i t n e s Es 4 ale 2 On S 23 h to Marc 1 , 202 April new JST Creality Connectors Dual Filament Kit 3D Printer CR-X Includes the popular JST XHP 2.54mm and PH 2.0mm housings & headers. Used for prototyping, repairs, and hobby applications. PT4457 Create amazing high-quality prints with two colours or materials. Easy to level print bed. Dual fan cooling. SD card slot. Prints up to 300Lx300Wx400Hmm. TL4410 See website for details. 1995 $1299 $ ONLY 48W Hobbyist Soldering Station NOW 99 $ ONLY Bonus Gift SAVE $20 FREE 1kg Filament Perfect for the advanced hobby user. 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Visit your local store or our website jaycar.com.au USB 3.0 4 Port Hub FROM 24 $ 95 Perfect for connecting all your peripherals to a laptop or port-limited device. No power required, plug and play operation. XC4979 We reward our industry professionals ONLY 1995 $ Arduino® made easy NOW 5995 $ SAVE $20 NOW 89 Arduino® Compatible Learning Kit Linker Base Shield for Arduino® Arduino® Compatible UNO R3 Board ONLY ONLY 2495 CHECK OUR WEBSITE FOR FULL RANGE OF MODULES 4 95 NOW 11 $ Connects Linker sensors/modules to the Linker base shield. 4 pin, 2.54mm headers. 150mm. Pk 5. XC4559 Bright white LEDs to use as lamp or camera flash. 20mA. XC4570 www.jaycar.com.au/arduino NOW FROM NOW FROM 25% OFF 20% OFF 2 Grey Vented ABS Enclosures Protect your project from unwanted fingers or objects. 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XC9010 NOW 11 $ ONLY Hobby Motors 50 For hobbies, experimenters, robotics & as replacements. 1.5-4.5VDC. Low Torque YM2706 $3.50 Medium Torque YM2707 $4.95 ONLY 2 95 $ SPDT Miniature Toggle Switch Solder tag with threaded bush. ST0335 ONLY 24 95 $ Servicing saviours Multimeter Test Probes 930mm long. WT5316 $5.95 Test Leads 700mm long. WT5320 $6.50 NOW 54 $ NOW 119 95 $ SAVE $15 SAVE $20 True RMS Inductance/Capacitance DMM Measures capacitance to 100mF, inductance to 20H, and much more. High accuracy. Cat III 1000V / Cat IV 600V. 2000 display count. QM1552 True RMS DMM with Bluetooth® Connectivity Measures sound level, light, humidity, temperature, resistance & more. Noncontact voltage. CAT IV 600V. AC/DC voltages & current up to 250V/10A. 4000 display count. QM1594 Compact, lightweight. Adjustable flame, temp range up to 1300°C. Piezo ignition. Safety lock. TH1610 Full autoranging. Math functions. Duty cycle. Bluetooth® connectivity for datalogging. Cat III 1000V / Cat IV 600V. 6000 display count. IP67 waterproof. QM1578 ONLY 39 95 $ 800mm long. WT5325 $17.95 160pc of heatshrink in 7 different colours & sizes, and a gas blow torch. Piezo ignition. Flame or flameless output. TH1620 Adjustable flame, temp range up to 1300°C. Piezo ignition. Safety lock. TS1660 ONLY Multimeter Test Probes Shrouded Type Heatshrink Pack with Gas Blow Torch Gas Blow Torch 27 $ SAVE $20 Multifunction Environment Meter with DMM Pocket Size Gas Blow Torch NOW 169 $ ONLY 44 95 95 $ FREE* Bonus Butane Gas Can Gas Soldering Iron & Blow Torch Kit Gift NA1020 Worth $4.95 When you purchase a gas blow torch * 95 Pencil Gas Blow Torch Adjustable flame. Metal construction. TS1667 Offer applies to: TS1660, TH1610, TH1620, TS1112 & TS1667 Aerosol Service Aids Must have for all electronic, electrical & field service applications. 175g. Circuit Board Lacquer NA1002 $11.50 Contact Cleaner Lubricant NA1012 $11.50 Electronic Circuit Board Cleaner NA1008 $11.50 Electronic Cleaning Solvent NA1004 $11.50 Everything you need to solder, silver solder, braze, heatshrink, cut rope, etc. 5 different tips included. TS1112 ONLY 14 $ J-B Weld Epoxy CLUB OFFER: ANY 2 FOR 15 $ SAVE 30% Two part epoxy resin. Bonds to almost any surface. 25ml. NA1518 THE BEST EPOXY GLUE ON THE PLANET ONLY 16 $ 95 ONLY 3995 $ Liquid Electrical Tape Seals and protects electrical connections. 28g. Black NM2836 Red NM2838 ONLY 1995 $ EA ISUZU D-MAX COMPETITION TERMS AND CONDITIONS: Starts 12:01 AM AEDT 26/2/21. Ends 11:59 PM AEST 30/4/21. Open to AUST residents who fulfil the entry/eligibility requirements. Prize is a 21MY Isuzu D-MAX 4x4 LS-U Automatic valued at up to $61,998 (inc GST). Prize draw 10:00 AM AEST 13/5/21 at Level 2, 11 York St Sydney NSW 2000. Winners notified via email by 14/5/21 and published at jaycar.com.au/dmax-jaycar by 17/5/21. Promoter is Jaycar Pty Ltd. ABN 65 000 087 936. 320 Victoria Rd Rydalmere NSW 2116. Authorised under NSW Authority No. TP/00716, and ACT Permit No. TP 21/00078 and SA Permit No. T21/71. Actual prize vehicle not shown, specifications may vary. For full terms and conditions refer to jaycar.com.au/dmax-terms Workbench wonders 70W Ultrasonic Cleaner Effectively clean your jewellery and other small parts. Built-in timer. 2 power settings. 1.8L capacity. YH5416 NOW 129 $ SAVE $20 13.8V 5A Laboratory Power Supply 100MHz Dual Channel Oscilloscope with Digital Storage Power 13.8V electronics & comms equipment in your home, office, garage or lab. Fixed output voltage. Short circuit protection. MP3096 NOW 99 $ ONLY 4495 $ Bondic Liquid Plastic Welding Kit ONLY 39 $ 95 Helps remove dangerous solder fumes from the work area. Ball bearing high volume fan, carbon filter. ESD safe. Mains powered. TS1580 Spare filter 5-pack TS1581 $9.95 Vacuum Bench Vice Driver bits to repair phone, game consoles & other electronic gadgets. Hardened S2 tool steel. Magnetic storage for bits. TD2134 Crimp F, N, BNC, TNC, UHF, ST, SC & SMA connectors onto RG6 or RG58 coax. 220mm long. TH1833 Clamp mount, fully adjustable arm. High/low light setting. Includes 125mm dia. 3 dioptre 1.75x lens. Interchangeable lenses available. QM3554 5 Dioptre Lens QM3555 $12.95 8 Dioptre Lens QM3556 $19.95 NOW SAVE $15 48 Piece Screwdriver Set Hex Ratchet Crimping Tool LED Illuminated Magnifier Solder Fume Extractor 0-150mm (0-6") measurement range, metric & imperial. 5-digit LCD. Stainless steel. Case included. TD2082 39 ONLY 119 5995 CURES UNDER UV Digital Vernier Calipers 95 SAVE $100 $ $ Bond, build, fix & fill virtually anything in seconds. Solvent-free. Stays liquid until cured with the included UV LED Light. NA1530 ONLY 799 $ 7" colour LCD. Built-in waveform generator. PC connection via USB. SD card support. Lightweight, compact. Includes 2 probes & USB cable. QC1936 RRP $899 See website for details. SAVE $10 $ CLUB OFFER: ONLY 27 $ ONLY 32 $ 95 Heavy Duty Wire Stripper, Cutter & Crimper Strip all types of cable from 10-24 AWG (0.13-6.0mm). 204mm long. TH1827 95 ONLY 24 $ 95 6" Insulated Side Cutters Strong, tough, reliable. Can cut piano wire up to 1.6mm. Comfortable grip. GS approved. 160mm long. TH1985 NOW 2995 $ Hard-wearing diecast aluminium. Ball joint clamp, suction base. 75mm opening jaw. 160mm tall. TH1766 SAVE $10 ONLY 1695 $ Crimping Tool for Non-Insulated Lugs Spring-loaded, comfortable handles. Suits 14-18 & 22-26 AWG lugs. Built-in wire cutter. 185mm long. TH1834 TERMS AND CONDITIONS: REWARDS / CLUB MEMBERS FREE GIFT, % SAVING DEALS, & MEMBERS OFFERS requires ACTIVE Jaycar Rewards / membership at time of purchase. Refer to website for Rewards / membership T&Cs. IN-STORE ONLY refers to company owned stores and not available to Resellers. Page 1: FREE 1 x 1kg Flashforge Filament with purchase of Dual Filament 3D Printer (TL4410), select from TL4269-TL4276. Page 2: CLUB OFFER: FREE Gaming Pad (XM5101) with purchase of Gaming Keyboard & Mouse Set (XC5132). Page 6: FREE Butane Gas Can (NA1020) with purchase of Gas Blow Torches: TS1660, TH1610, TH1620, TS1112 or TS1667. Page 6: CLUB OFFER: Any 2 x Aerosols Service Aids applies to NA1002, NA1012, NA1008, NA1004 or any combination. SUPPLY CHAIN DISRUPTION. We apologise for factors out of control which may result in some items may not being available on the advertised on-sale date of the catalogue. s ' t a Wh w Ne JUST 239 $ Rear OBD II 4G/GPS Tracking Device 3" IPS TOUCH SCREEN Locate and track the whereabouts of your vehicle in realtime. Track via the Internet on a PC or Smartphone. 4G SIM card required (sold separately). Built-in microphone, SMS alerts and more. LA9039 USB Qualcomm® 3.0 Car Adaptor with Voltmeter Converts your car lighter socket to 2 x USB & 1 x USB Qualcomm 3.0 quick charge sockets. Voltage display on engine start up. PP2118 Main 4K Dashcam with Touchscreen 170° VIEWING ANGLE JUST FM Transmitters 249 $ Capture events on the road. Records to microSD card (sold separately). Bonds to your windscreen via 3M® double sided tape. Feature G-sensor, manual / loop recording. Parking mode. QV3868 32GB microSD Card XC4992 $36.95 Wirelessly play music (and talk) hands free from a Smartphone*, MP3 player, USB or SD card via the FM band. USB AR3139 $14.95 FROM Bluetooth® AR3144 $34.95 *Via Bluetooth® ONLY 119 $ HIGH POWER 100W USB Type-C Laptop Power Supply Power laptops including Macbook Pro via USB Type-C port. USB Type-C & Type-A outputs. 5-20VDC at up to 5A. MP3344 ONLY 20,000mAh Power Bank Charge compatible phones 75% faster! 2 x Qualcomm® Quick Charge™ 3.0 USB A ports. USB Type-C Power Delivery port. MB3797 NOW 39 $ 95 SAVE $20 5 Port USB Charging Station with Storage Compartment Charges up to 5 USB devices at the same time. 2.4A max per port. 8.2A shared. 6 dividers. Includes power supply. WC7766 14 95 $ 500Mbps Powerline Ethernet Extender Extend your network using your home's existing electrical wiring - up to 300m range. Speeds up to 500Mbps. Ideal for web streaming, online gaming and video chatting. YN8358 ALSO AVAILABLE: With Wi-Fi YN8359 $149 8995 $ ONLY 1995 $ NOW 5995 $ SAVE $20 NOW 99 NOW 199 $ $ SAVE $30 SAVE $50 1080p HDMI Cat5e/Cat6 Extender with Infrared Extend your HDMI signal using CAT5e/6 cable up to 50m*. Ideal for running HDMI signals to new locations or connecting through existing building cables. AC1783 *Depending on cable used & resolution. AC1200 Wi-Fi Mesh Network Base & Satellite Kit Provides seamless Wi-Fi in your entire home. Fast 1200Mbps data speed. Expand with additional satellite modules (YN8562 NOW $99 sold separately). YN8560 Got a great project or kit idea? If we produce or publish your electronics, arduino or pi project, we'll give you a complementary $100 gift card. projects.jaycar.com 1800 022 888 www.jaycar.com.au Over 100 stores & 130 resellers nationwide HEAD OFFICE 320 Victoria Road, Rydalmere NSW 2116 Ph: (02) 8832 3100 Fax: (02) 8832 3169 ONLINE ORDERS www.jaycar.com.au techstore<at>jaycar.com.au Arrival dates of new products in this flyer confirmed at the time of print. Call your local store to check stock. Occasionally discontinued items advertised on a special / lower price in this flyer have limited to nil stock in certain stores, including Jaycar Authorised Resellers, and cannot be ordered or transferred. Savings off Original RRP. Prices and special offers are valid from 24.03.2021 - 23.04.2021. CIRCUIT NOTEBOOK Interesting circuit ideas which we have checked but not built and tested. Contributions will be paid for at standard rates. All submissions should include full name, address & phone number. Biofeedback for stress management This circuit connects to a pair of skin electrodes on your scalp and gives you a ‘stress level’ reading. If you can see how your stress level varies immediately, it will help you to determine when you are particularly stressed and also what you need to do to relax. It measures the magnitude of the alpha waves produced by your brain, which have signal frequencies in the 4-11Hz range. A small amount of these waves (in the microvolts range) reaches the surface of your skin and can be picked up using electrodes. These signals are fed to a TL071 JFET-input op amp to be amplified to a level that can be read out on a digital voltmeter. A small bias current (less than 750µA, varying depending on skin resistance) is applied through the skin electrodes. siliconchip.com.au The AC alpha waves are coupled to the op amp input via a 1µF MKT capacitor, and they are DC-biased to around -26mV by the resistor network following that capacitor. Higher-frequency signals are filtered out using a 1kW/1nF RC low-pass filter plus a series ferrite bead. This filter also helps to eliminate any RF that is picked up by the electrode leads. The 1µF coupling capacitor and 39kW resistor form a high-pass filter with a -3dB point of 4Hz to eliminate very low frequency signals, below the range of alpha waves. The gain of this op amp stage is adjusted using trimpot VR1. It can be up to about 1000 times (1MW ÷ 1kW). The signal is then fed through a 15kW/1µF RC low-pass filter which has a -3dB point of 10.6Hz. This filters out most Australia’s electronics magazine signals above the 11Hz maximum frequency of alpha waves. The signal is then rectified by diode D3, which also reduces the reading by about 0.2V, eliminating noise from the results. A DMM set to read millivolts connected across the output terminal therefore gives a reading proportional to your alpha wave activity, with VR1 correctly adjusted. The circuit runs from a pair of 9V batteries which produce an approximately ±8.4V split supply after reverse polarity protection diodes D1 & D2. 100µH chokes reduce RF pickup from the battery leads while 47W resistors and 100µF bypass capacitors provide further supply filtering. David Strong, Penshurst, NSW. ($105) April 2021 61 Latching output for Remote Monitoring Station This simple circuit adds extra capabilities to the 4G Remote Monitoring Station (February 2020; siliconchip. com.au/Article/12335). It provides a way for the Remote Monitoring Station to drive the Opto-Isolated Mains Relay (October 2018; siliconchip.com. au/Article/11267). I wanted to be able to switch an appliance on or off by sending an SMS. As the Monitoring Station project has a battery-saving feature, the status of the Arduino output pins is lost when the Arduino goes to sleep. This circuit adds a way to preserve the state without increasing the current consumption very much. However, in my case, mains power is available so that is not a significant concern. This circuit is based on a 555 timer which is used as a flip flop to switch the relay on and off. It keeps it in the last state, even when the Arduino is in sleep mode. When the circuit is first powered up, pin 2 of IC1 is held high via the 10kW pull-up resistor, while pin 6 is kept low by a 10kW pull-down resistor. The pin 4 reset input is briefly pulled low by the 10kW/100nF RC network. This ensures that the 555 won’t switch the appliance on after blackouts or power glitches. The Remote Monitoring Station code needs to be modified (as per the instructions in Ask Silicon Chip, March 2020) to send the selected Arduino pin high when you want the appliance switched on. The code also needs to be modified to send another Arduino pin high when you want the appliance to switch off. The selected switch-on pin connects to the base of the NPN transistor Q1 via a diode and 22kW resistor. When this pin goes high, it switches Q1 on, pulling pin 2 of IC1 low and thereby bringing its output pin 3 high. This powers the appliance up via the Opto-Isolated Mains Relay. The 555 will stay in this state when the Arduino goes to sleep. When the Arduino receives a command to switch off, the other pin going high pulls pin 6 of IC1 high, bringing its output pin 3 low, which switches the appliance off. The diodes on the inputs isolate the Arduino from the circuit and ensure that the circuit will only respond to logic high output levels. Geoff Coppa, Toormina, NSW. ($60) Alternative switched attenuator for Shirt Pocket Oscillator I am building the Shirt-Pocket Sized Audio DDS Oscillator (September 2020; siliconchip.com.au/Article/14563) in a 100 x 70 x 50mm aluminium box, using AA batteries for power and RCA and binding post outputs. This circuit shows the switched attenuator I will be using, which is different from the one suggested in the article. It uses a centre-off switch that I already had, which is smaller and easier to fit securely than a rotary switch. The ranges are not sequential, which is not ideal, but at least the middle position has the lowest output level. The need for the 150kW resistor is debatable, given the tolerance of the potentiometer resistance, but it does give an 11.111kW resistance in parallel with 12kW, which is the exact value needed. Rick Arden, Gowanbrae, Vic. ($60) 62 Silicon Chip Australia's Australia’s electronics magazine siliconchip.com.au Follow-up to ‘constant’ AC source This circuit develops my ideas on the “infinite impedance” alternating current source concept, previously described in the December 2020 Circuit Notebook section (siliconchip.com.au/ Article/14681). That circuit used a direct digital synthesis (DDS) sinewave generator and standard op amp to drive the resonant network. The result is a sinewave at the output that delivers an essentially constant magnitude alternating current into a resistive load. To simplify the circuit, I have ditched the DDS sinewave generator and I am instead using an LM3900 dual Norton (current input) amplifier chip. The circuit snippet below is cribbed from my October 2019 Circuit Notebook submission (siliconchip.com. au/Article/12027) describing how to build a stable sinewave oscillator using a Norton amp, and also gives the formulas (in the blue box) for the oscillation condition and to derive the frequency. For the output resonant circuit, I had a 0.7mH inductor available. Using the inductance vs capacitance and frequency charts published in the December 2020 issue, that sets the capacitance required as 70nF (eg, 68nF, siliconchip.com.au 1.8nF & 200pF in parallel) for a frequency of 22.66kHz. The oscillator circuit achieves this frequency with the values shown. VR2 is used to fine-tune the frequency, with a nominal value of 4kW giving 11kW + 4kW = 15kW to set the frequency close to 22.66kHz. VR1 sets the amplitude of the input voltage to the resonant circuit and hence the value of the ‘constant’ current. IC1b buffers the oscillator’s signal and then drives a current booster circuit using NPN and PNP emitter-followers Q1 & Q2, with their base voltages biased around 0.7V above and below the oscillator signal by diodes D1 & D2. The output at the emitter junctions of Q1 & Q2 drives the resonant circuit that, in turn, drives the load resistance. I built this circuit and tested it, and the results are shown in scope grabs Scope 1-3. Scope 1 was with a load resistance of 100W, Scope 2 with 50W and Scope 3 with 200W. In each case, the oscillator’s output is the trace plotted in yellow while the voltage across the load resistance is shown in cyan. The current waveform leads the voltage waveform by 90° in all three test cases, and as expected, the voltage amplitude adjusts to supply the same current to the load. So in Scope 2, the voltage is halved as the load resistance is halved, while in Scope 3, it is doubled as the load resistance is doubled. This is not obvious from the sinewaves since the channel scaling changes in each plot; check the scale values at the bottom. Mauri Lampi, Glenroy, Vic. ($75) Australia’s electronics magazine April 2021 63 The History of Videotape – part 2 Helical Scan By Ian Batty, Andre Switzer & Rod Humphris Last month, we described the major innovation that was the Ampex quadruplex videotape recording and playback system. Of course, technology did not stand still, and it was only a few years before more breakthroughs were made, enabling not only better video quality but also some significant new features... Thanks to the Toshiba Science Museum for use of this image: toshiba-mirai-kagakukan.jp/en/learn/history/ichigoki/1959vtr/index.htm A mpex’s quadruplex video recording was a revolutionary technology. Casting off the existing linear tape paradigm, Alex Poniatoff’s company invented a system where four tape heads, mounted on a spinning disc, scanned the tape transversely. Coupled with the adoption of frequency modulation, ‘quad’ established videotape recording (VTR) machines as television broadcasting’s workhorse for replay, editing, distribution and archival work. Yes, the first VTRs were horrendously expensive, and the size of a few refrigerators. And yes, the tape is not entirely robust – it can break and 64 Silicon Chip distort. But its added flexibility was well worth it for news and broadcast companies. For the rest, videotape recording was out of reach. But the principles established by quad were sound: rotating head scanners and frequency modulation were clearly the way ahead. If only someone could devise a simpler, cheaper system. And it would be helpful for it to produce a picture in pause, or at slow or fast picture search; things impossible with quad. Enter Toshiba Dr Norikazu Sawazaki at Toshiba’s Matsuda Research Laboratory develAustralia’s electronics magazine oped a prototype helical scan recorder in 1953. The first experimental VTR1 was completed in 1958 and demonstrated to the public in September 1959. Commercial production of the new videotape recorder followed. At around the same time, Eduard Schuller of Telefunken had also devoted himself to the recording of television signals. Having already invented the “ring-shaped” audiotape head still in use today, he was awarded a 1953 patent for magnetic recording and playback of television pictures using helical scanning. The tape runs around the head drum, giving much longer video tracks siliconchip.com.au Fig.9: the basic concept of helical scan recording. The tape is wrapped around a drum head at an angle so that as the head spins, it scans diagonal strips. This means that the diagonal tracks overlap continuously along the length of the tape, avoiding the segmentation necessary with the quad system. Fig.10: this gives you an idea of how the tracks are laid down on the tap in a helical scan system. While they are diagonal when the tape is laid flat, when the tape is wrapped around the drum, the tracks actually form a helix shape. than was possible with quadruplex. Figs.9 & 10 show a simplified single-head system. The tape engages the head drum (the scanner) high and exits low, so the system records a number of slanted tracks at a shallow angle of perhaps 5°. Viewing the tape on the drum, the video tracks appear as a series of spirals, a bit like a coil spring, hence the term “helical scanning”. Early helical-scan VTRs used the available 2-inch tape. Despite not needing vacuum air to form the tape path, they were hardly more compact than their quad predecessors. A slower tape speed of 3.7ips allowed five hours recording or playback on 12.5inch tape reels. Video recording and playback demand continuous head-to-tape contact. Quad solved this by always having one of four heads engaged with the tape, and switching to the active head, but this resulted in the possibility of mismatches causing head banding. Helical scanning aimed to record an entire field of 312.5 lines over 20ms in a single scan over the tape. This demanded a much longer track length than quad’s 46mm, with its 16 lines per scan. Quad systems were able to record signals in the megahertz range by virtue of the high headwheel speed, and helical scan would also need high head-to-tape speeds. siliconchip.com.au Helical scan needed to use realistic tape speeds, say 7.5ips, but the headto-tape speed needed to be in the order of 20m/s. The solution was to use a head drum with a large enough diameter to give the required head-totape speed for FM recording. The Ampex 5800~7900 series VTRs (Fig.11) used a head drum diameter of 135mm, creating a track length of some 425mm. This gave a writing speed of just over 11m/s, adequate for FM recording. They matured with the 7950, a timebase-corrected VTR capable of broadcast performance. Using a single head with one field for each scan of the tape, this system’s head drum rotated at 50 revolutions per second (3000 RPM) for our CCIR/PAL standard. But with such a long track, tape tension has much more effect on the horizontal rate. Television broadcasters had been the market for the first generation of VTRs, and broadcast demands very stable images. With a track length of only 46mm laid across the tape (and thus much less affected by tape stretch), quad’s greater immunity to tape variations meant that it remained the preferred format. Helical systems would have to play catch-up for some time. Broadcast vs non-broadcast video tape recorders As described in the last article, broadcast VTRs must be locked to station sync, both in frequency (to prevent vertical rolling or horizontal drifting) and in-phase (to register VTR pictures over the station program). But if a VTR program is to be replayed on a local monitor, or sent Fig.11: an Ampex helical-scan VTR which used 2-inch tape. One big advantage over the quad system was lower tape speeds, which meant longer recording and playback times (more photos at www.ebay.com/ itm/182696338060). Source: www. labguysworld.com/Ampex_VR-660.htm Australia’s electronics magazine April 2021 65 done quickly and accurately. The long tracks of helical-scan formats made cutting-and-splicing impractical, so helical systems need to use electronic editing (re-recording) in some form. The end of segmentation Fig.12: this type of ‘flag waving’ image distortion was a result of timing errors due to the tape stretching slightly, or the tape or head speed varying slightly between recording and playback. to a non-station destination, the rigid demands of broadcast don’t apply. Non-broadcast equipment can have relaxed timebase stability, as the VTR will supply vertical and horizontal references for any destination equipment: monitors, other VTRs, etc. Non-broadcast programs may be in colour, and of high visual quality; non-broadcast does not imply poor quality. The best off-tape video may be as good as – or better than – off-air programs. Non-broadcast just means that the destination equipment is more tolerant of variations in the exact line and field rates and phasing of video signals. Domestic TV receivers were designed with high-performance timebases capable of locking to very weak signals. Such designs respond well to weak but constant signals. They do not easily tolerate signals with timing errors. It was common when early VTRs were fed to high-performing television sets for the TVs to lose sync with picture rolling or horizontal tearing (or ‘flag-waving’; see Fig.12). The solution was to speed up the monitor’s timebase response, allowing better tracking of the VTR video with its higher degree of timing errors. Tape editing Since quad recorded transversely, it was practical to cut-and-splice tape for editing. This skill, adopted from movie film editing, could be Segmentation – the splitting of a field into discrete scans – was a systemic problem with quad. The smallest mismatches in playback level, timing or equalisation caused problems. Helical scanning would solve this by recording an entire field in one scan of the tape. The simplest way of doing this was with just one rotating head. The head would need to be continuously in contact with the tape, so this dictated a full 360° wrap, as shown in Fig.9. VTR development was driven by the opportunity of bringing the technology to education, commerce and industry. A teacher could show a science video at any time, not just when it came to air. A sports coach could play back a tennis player’s serve and analyse just how to get that drop shot. A plant supervisor could not only explain, but actually show the company’s board just what the problem was. The rapid onslaught of solid-state technology and its radical miniaturisation of electronic circuitry helped, of course. No longer would VTRs be the size of several equipment racks. Before long, the physical mechanism would be the main determining factor on the size of VTRs. Just about every major electronics manufacturer would have a go. Get ready for the first VTR format war. Format wars: the first battle Helical scan systems use a rotating head, or heads, to provide the very Fig.13: the layout of the magnetic recordings on Ampex 1-inch helical-scan videotape. 66 Silicon Chip Australia’s electronics magazine siliconchip.com.au Fig.14: an Ampex VR-6000 helical scan VTR also used 1-inch tape. It went on sale in 1966 (more photos at www.ebay.com/itm/183994149450). Source: www.labguysworld.com/Ampex_VR-6000.htm high head-to-tape speeds used in all videotape systems. The head disk rotates within a drum, with the drum accurately guiding the tape to give just the right amount of head-to-tape contact and the correct head-to-tape path. The tape must be wrapped around the head drum, but how? Do we use a full 360° wrap, with just one head, or do we use a 180° wrap and two heads? (See Fig.15) A single head removes the problem of matching head amplitude/frequency differences. But since a 360° wrap implies that the entire tape width must be reserved for the video tracks, where will we put the control and audio tracks? The solution was for the video head to scan less than the full tape’s width. While this could be made to work, it left a short period of each video field unrecorded; there was an inbuilt dropout period in the video playback. But a two-head system could be designed so that the video heads scanned less than the full tape width, allowing for control and audio tracks. Since there were two heads, the design allowed each head to record a full field, with electronic switching guaranteeing an uninterrupted playback signal. Ampex & IVC 1-inch systems These two pioneers adopted the single-head, 360° wrap format using 1-inch (25mm) tape. They released incompatible 1-inch systems: Ampex (see Figs.13 & 14) used the “alpha” wrap while IVC used the “omega” wrap; both names are derived from the Greek letters. With Ampex’s alpha wrap, the tape is led around a near-90° entry guide before contacting the drum. The tape runs anti-clockwise. On exit, the tape is led around another near-90° exit guide. Tape loading is done with the two guides retracted. When ready, the operator closes the guides to give the correct tape path over the head drum. Fig.15: the three most commonly used helical scan tape paths. The alpha and omega systems have the advantage of only needing a single head. In contrast, with the omega system, there is no discontinuity in tape scanning, so any signals in the blanking periods are recorded. This was critical for broadcast use, and almost all videotape systems standardised on the two-head approach. siliconchip.com.au Australia’s electronics magazine The tape enters the scanner station from the reel table and ascends as it traverses around the drum, to exit one inch above the entry point, thus giving almost the complete 360° (see Figs.16 & 17). There is a small gap where the head loses contact with the tape, and thus creates a loss of signal. This is timed to occur during the vertical blanking interval. Although this prevents the disturbance from being seen, the loss of sync pulses during this dropout period renders the format fundamentally incompatible with broadcast standards. Each video track stores one field of signal. Audio is recorded on a conventional linear track using a bias signal. A control track is laid down during record to allow accurate scanning in playback. International Video Corporation (IVC) led the tape directly on to the head drum, also running it anti-clockwise. This meant that tape guiding was simpler than Ampex’s, but there was still a short gap in the signal. Like Ampex’s 1-inch system, the IVC format could not reproduce the entire vertical blanking period’s synch pulse block. Audio is recorded on a conventional linear track using a bias signal, and a second audio track, used for cueing, is provided. A control track is laid down during recording to allow accurate scanning in playback. German engineers working for Bosch-Fernseh broke out with BCN, a segmented helical scan system using a single 1-inch tape (Fig.18). With a high slant angle and a small two-head drum rotating at 9600 RPM, this system recorded only 52 lines per track. Like quad, it could not display a still picture, nor a picture during search. Released in 1976, BCN was widely used in Europe. A, B and C formats Ampex’s single-head, 1-inch system was developed to the point where its resolution was equal to quad’s. Capable of recovering and playing back the full video bandwidth, timebase correction (TBC) gave this system full-colour capability, but still with the loss of signal in the vertical synch block. This could be corrected by a digital TBC that re-inserted sync pulses (which they commonly do), but the format was not intrinsically broadcast-standard. It was, however, registered by the Society of Motion Picture and Television Engineers (SMPTE) as Type A in 1965. April 2021 67 Fig.16: this shows how the alphawrap system used in Ampex 1-inch helical scan VTRs was implemented. Bosch-Fernseh’s BCN was registered as Type B. Signal loss in the vertical synch block was more than a nuisance. It potentially destroyed vital engineering information: the vertical interval test signal (VITS). Not visible to the viewer, VITS was valuable to engineers and technicians. There was also the SMPTE’s vertical interval time code (VITC) that uniquely identified each frame on the tape, critical to editing and verification of events recorded on tape. So, if no 360° wrap system could record a full field, why bother trying? Why not allow a laneway in the slanted video tracks? By adjusting the phasing of the video head against that of the active vid- eo signal, it would be possible to start the video track someway in from the tape edge, but end it before the bottom edge of the tape. This means there is no loss of contact (dropout) period in the active video. However, the loss of the vertical synch block would have to be addressed. The solution was to add a second head to the drum, around 30° behind the video head. The second head simply recorded the vertical synch block, also without any loss of contact during its active period. So the system records (and plays back) the active video and the vertical synch block, both without any interruption or dropout disturbances. This was a system Sony pioneered. Fig.17: this IVC 1-inch omega-wrap VTR is mechanically a bit simpler than the Ampex VR-6000, and like the Ampex system it uses a single record-playback head. Source: https://youtu.be/EIhI85cHIfg 68 Silicon Chip Australia’s electronics magazine The whole field (active video and vertical synch bloc) could be recovered by switching and combining the outputs of the two heads. Known as the “one-and-a-half head” system, this reproduced an entire field with no gaps or losses. Ampex and Sony co-operated to mature and formalise their designs, registered by the SMPTE as “Type C” in 1976 (see Fig.19). It would supplant quad and become the open-reel standard, surviving into the 1990s. Easeof-handling, enhanced still, slow forward and reverse play and fast forward and reverse play made Type C the system of preference, especially for editing. Prior to Type C’s release in 1976, Fig.18: a Bosch-Fernseh Type B helical tape scanner head. Source: https://w.wiki/gyb siliconchip.com.au Fig.19: the layout of the Ampex/Sony “Type C” tape format of 1976. It supplanted quad to become the open-reel standard, surviving into the 1990s. single-head systems could not record an entire field without some period of signal loss. A two-head system can use each head to lay down an entire field, and reconstruct the whole frame from the combined, sequential output of the two playback heads. This eliminated the problem of signal dropout during the vertical interval. Two-head omega wrap systems Single-head systems require a complete 360° scan in 20ms (PAL/CCIR), giving a speed of 50 revolutions per second or 3000 RPM. A two-head system sees each head scanning only 180°, halving the drum speed to 25 RPS/1500 RPM (Fig.20). In practice, the wrap was slightly more than 180°, ensuring uninterrupted recovery of the entire video frame. Sony released an omega wrap twohead system, and 180° omega wrap became the preferred format for the successful and well-known ¾-inch U-matic, ½-inch Electronic Industry Association of Japan (EIAJ), Betamax, VHS, Philips VCR, Akai ¼-inch and Sony 8mm Video 8 systems. Two-head omega wrap was also used in digital audio tape (DAT), in computer implementations of DAT for data storage, and Digital Video (DV) handycams. Armistice: the EIAJ format The format wars came to an end when the Electronic Industries Association of Japan released the EIAJ-1 standard for half-inch open-reel videotape recorders (see Fig.21). Initially monochrome only, it was re-engineered for colour operation and appeared in at least two cartridge/ cassette systems. It was intended for non-professional use by businesses, schools, government agencies and hospitals but was also adopted by some consumers. Timebase errors remained For all of helical scan’s advantages, it was even less suited to broadcast than quad. With their long video tracks, helical format machines had worse timing stability than quad. Around the time that helical scan was being taken up, advances in semiconductor technology were delivering digital integrated circuits of some complexity. Digital signal processing, also in development, made it possible to digitise analog video signals. Fig.20: the mechanical layout of a basic two-head omega-wrap VTR system. siliconchip.com.au Australia’s electronics magazine April 2021 69 Frame store also freed cameras from the need for station lock. With a frame store, a remote non-synchronous camera feed could be accepted, then mixed in directly. Previously, such “outside broadcast” (OB) programs would be recorded, then played back from a station-synchronised VTR. On rare occasions, a producer would punch to the OB camera, and run the entire station in sync with the OB. Not desirable, but sometimes, “you gotta do what you gotta do!” DTBC technology advanced to the point that it could be offered in the pro versions of domestic video cassette recorders, such as Panasonic’s ProLine AG-1980. Colour made it harder Fig.21: a Sony EIAJ ½-inch VTR. Comparing this to its predecessors demonstrates the degree of miniaturisation which made Sony famous. More photos at https://historictech.com/product/sony-cv-2000-videocorder-c1965/ With digitisation came the possibility of highly-responsive timebase correction. The principle is simple: digitise the off-tape video at its own varying rate and store it in digital memory. Then read the data out of memory at the station sync rate, convert the digital data back to analog and deliver fully-corrected, station-synchronous video (see Fig.22). Early digital timebase correctors (DTBCs) had only enough memory to store a few lines, and could not correct a video signal unless it was vertically-locked to station sync. Further developments offered larger memories, and it eventually became possible to store an entire video frame. A frame store system can correct timing errors, but also to accept a video signal that is not locked to station sync. This allows any video signal with the correct format (PAL, NTSC etc) to be combined with station video sources. A version of frame store was used in the Bosch- Fernseh’s BCN system to display still frames, otherwise impossible with its 52-lines-pertrack format. Before the introduction of frame store, satellite feeds were commonly recorded and then played back on a VTR locked to station sync. Frame store allowed satellite feeds to be corrected to station sync, then mixed directly into station programs. Both PAL and NTSC encode colour (chroma) as a quadrature amplitude modulated (QAM) signal. This appears as a phase-modulated signal, and it must fit in the same bandwidth as the monochrome (luminance) signal. To reduce interference, the chroma signal has its carrier removed, leaving only the signal’s upper and lower sidebands. The problems of phase modulation are explained below. The receiver’s demodulators must have a suitable carrier to work, so a short reference “burst” is added at the start of each line of video, For PAL, it’s about 4.5µs of a 4.43361875MHz sinewave. This is vital to a receiver’s colour processing. This makes the stability problems even worse. NTSC’s chroma frequency is exactly 3.579545MHz, and PAL’s is 4.43361875MHz(!) Any colour system must deliver the colour (chroma) signal at very close to those precise frequencies. Also, both the American NTSC and European PAL systems encode colour signals using phase modulation. Even Fig.22: once digital technology had matured sufficiently, it became possible to implement timebase correction (TBC) mostly in the digital domain. This shows the basic layout of such systems. Once mature, they finally provided a simple means to interface a colour VTR to just about any broadcast system, providing stable phase, line and frame sync. 70 Silicon Chip Australia’s electronics magazine siliconchip.com.au Fig.23: hetereodyne VTRs accept the full colour signal, then use a low-pass filter to remove the chroma component. The remaining luminance is fed to the frequency modulator to create the FM signal for recording. On playback, the FM signal is demodulated to recover the luminace component of the original video signal. if the chroma signal frequency can be made accurate, any phase errors will cause colours to “slew” in one direction or another up and down the spectrum. Just a few degrees of phase error will be obvious, especially in the range of human skin tones. Given that the 4.433MHz PAL subcarrier has a period of only 225ns, an error of just 10ns translates to a phase error of 16°. That’s enough to make a healthy skin tone look either badly sunburned or dangerously jaundiced! Recalling the size and expense of quad machines, it was feasible to add colour correction and still sell the hardware. Correction used a recorded pilot tone signal. In replay, you would expect minor tape speed variation, and variations in tape tension, to affect all signal frequency/phases. Luminance phase and timing errors were corrected by the timebase corrector. Any errors in the pilot tone’s phase could be applied as a correction to cancel out errors in the chroma signal. See, for example, E. M. Leyton’s 1957 US Patent 2,979,558 (https://patents. google.com/patent/US2979558A/en). Helical scan systems had two particular barriers to proper colour operation. While quad could accommodate NTSC’s 4MHz bandwidth and PAL’s 5MHz bandwidth, only the highest-performing helical systems could meet this demand. 1-inch systems, siliconchip.com.au Fig.24: the tape bandwidth occupied by a monochrome video signal. As you can see, there is plenty of spare bandwidth to fit colour information. Fig.25: the bandwidth occupied by a composite PAL video signal. As can be seen, the chroma (colour signal) occupies a relatively narrow bandwidth centered on the chroma carrier frequency of ~4.43MHz. This allows the luminance and chroma signals to fit in the 5MHz original monochrome bandwidth, but with minimal interference with each other. Australia’s electronics magazine April 2021 71 Fig.26: this is the scheme eventually arrived upon to shift the colour (chroma) information to lower frequencies so that it can occupy tape spectrum not used by the FM luminance signal. such as Ampex’s VR-6000 (released in 1966, well after their first 1-inch outing) had a video bandwidth of only 3.5MHz, not enough even for NTSC (see Figs.24 & 25). Also, timebase errors in helical systems are far more severe than for quad. Even if a full-bandwidth colour signal could be squeezed onto a helical machine, colour correction would be vital even for CCTV use, let alone broadcast. To overcome both problems, they separated the chroma signal from the luminance signal and handled them separately. Colour television’s chroma (colour) bandwidth is quite small, despite its 3.58/4.43MHz carrier frequency; it’s -1.5/+0.5MHz for NTSC (a wider lower sideband) and -1.0/+0.6MHz for PAL. Now, there’s a lot of tape bandwidth not being used; even low-definition helical systems used signal frequencies above 2MHz for their low end. Fig.25 shows the 3.8~4.8MHz FM bandwidth of VHS. Sony’s U-matic and Betamax and JVC’s Video Home System (VHS) used the similar solution. The chroma content was filtered out, heterodyned (“down-converted”) to 626.953kHz (~627kHz), then recorded in the unused spectrum below the luminance signal. Fig.26 shows a simplified block diagram of this scheme, while Fig.27 shows the resulting on-tape spectrum for VHS. Yes, down-converting to around 627kHz reduced the colour bandwidth, and thus its fine detail, but this is domestic-grade equipment that’s not expected to give broadcast resolution. 72 Silicon Chip Just as recorded analog audio needs a bias signal to overcome tape non-linearity, so does this analog chroma recording. Happily, there is already a high-amplitude signal at maybe five to ten times the chroma frequency being recorded, ie, the luminance signal. So the luminance signal acts as a bias signal for the chroma, without creating any interference. On replay, the chroma signal is heterodyned (up-converted) back to 3.579545MHz or 4.43361875MHz, mixed with the off-tape luminance signal, and hey presto! Colour recording and playback. But let’s recall the problems of timebase errors, and the need to keep the chroma signal’s phase errors as low as a few nanoseconds. Now, converting the highly-precise 3.579545/4.43361875MHz signal down to 627kHz for recording, then (in replay) attempting to reconvert up to exactly 3.579545/4.43361875MHz with no frequency errors or phase jitter is a big ask. To keep the discussion simple, let’s consider a PAL colour signal, calling it 4.433MHz, and the down-converted signal 627kHz. Any heterodyne/colour-under system must be able to correct the chroma signal phase errors. Several different methods were developed, relying on newly-available digital circuitry to manage the down- and up-conversions with sufficient accuracy. The actual signal processing would continue to use plain old analog techniques. The mature solution arrived at by both Beta and VHS used a phaselocked loop (PLL) to generate the down-converter’s local oscillator, shown in Fig.26. This description uses VHS frequencies; Beta is similar. The PLL was locked to the incoming video’s line rate (15.625kHz), and it produced an output of 40.125 times Fig.27: the bandwidth occupied by the video signal after the processing shown in Fig.24 & 28. This assumes that the FM carrier for the luminance information is still over 4MHz; however, that can easily be changed to suit different tape speeds. Australia’s electronics magazine siliconchip.com.au Fig.28: how down-converted colour video signals are played back; it is basically the reverse of Fig.26. The colour signals must be recovered with very accurate phases and frequencies or the hues will be different from the originals. the line frequency (~627kHz). This was added to the 4.43MHz colour burst from the incoming signal to create the 5.06MHz local oscillator. The incoming video signal’s chroma component was filtered off through a 4.43MHz bandpass filter, then applied to the mixer, along with the 5.06MHz local oscillator, to produce the 627kHz chroma signal. This was combined with the frequency-modulated luminance signal and recorded onto the tape. Fig.27 shows the record signal’s spectrum Colour playback The hard part was up-converting the 627kHz chroma signal back to 4.433MHz in a stable manner. Remember that the recording LO was generated partly from the incoming signal’s line rate of 15.625kHz, and partly from the incoming signal’s chroma frequency of 4.433MHz. This means there was a fixed frequency ratio between the original and highly accurate 4.433MHz input chroma and the 627kHz down-converted signal. We can expect some phase errors and jitter in the off-tape 627kHz chroma signal. But this 627kHz signal was derived using a local oscillator phaselocked to the 15.625kHz line rate. So we can use the line rate itself as a stable reference for the replay up-converter’s local oscillator. And that’s what is done, as shown in Fig.28. A PLL recovers the 15.625kHz line frequency from the luminance playback circuitry, and creates a 627kHz reference. Another PLL recovers the 4.433MHz chroma frequency from the upconverter’s output. The local oscillator takes the 627kHz reference and the 4.433MHz chroma signal to create a local oscillator signal of 5.06MHz. The local oscillator is now applied to the up-converter’s mixer and heterodyned with the 627kHz off-tape chroma to produce 4.433MHz replay chroma. Using the replay signal’s line rate reference gives sufficiently good phase correction for a domestic colour television. The final stage in playback processing mixes the replay colour signal with the replay luminance signal, to Fig.29: once the luminance and chrominance signals have been extracted from the videotape, it is a relatively simple matter to mix them to produce a standard video signal, which a colour TV will happily accept. siliconchip.com.au Australia’s electronics magazine re-create the composite video output, as shown in Fig.29. Heterodyne colour systems are complicated, but were implemented for two reasons. First, it made colour recording possible on video tape systems that could not provide the full broadcast bandwidth of 4.2MHz (NTSC) or 5MHz (PAL). Second, heterodyne colour applies correction during replay, making the colour signal stable enough for display on monitors and television sets, and for editing and copying. The alternative to heterodyne colour’s replay processing would be a TBC in every VCR, making VCRs too expensive to market. That’s it for this article; next month, we will discuss the cassette systems that were used as a convenient means of storing and protecting videotape. Thanks to Randall Hodges, Richard Berryman and Rod Humphris for their help in preparing this article. References • A write-up on the history of video recorders etc: www.labguysworld. com/VTR_TimeLine.htm • Dana Lee’s website on TV and more: www.danalee.ca/ttt/ • An introduction to VCRs: https:// youtu.be/KfuARMCyTvg Many other videos on the above YouTube channel are also worth taking a look at. • Video Tape Recorders, 2nd Ed. Kybett, Harry, Howard W. Sams, Indianapolis, 1978 • Video Recording Record and Replay Systems. White, Gordon, Newnes-Butterworths, London, 1972 April 2021 73 Transports, Mechanisms and Servos As stated in last month’s article, this is a full description of the operation of servo motors as used in helical scans and the like. A tape transport draws tape from the supply reel, passes it over the heads and collects it on the takeup reel. The tape needs to move at a constant speed, and the usual mechanism is a spinning shaft (the capstan). The rubber-covered pinch roller presses the tape against the capstan to ensure a steady speed. Audio recorders, with their heads in fixed positions, can use mains-powered capstan motors, or speed-controlled DC motors. However it is achieved, the motor just needs to run at a constant speed. For different tape speeds, it’s common to see a stepped drive shaft, like on a multi-speed record player. Video recorders use a combination of fixed (audio, control track) and moving (video) heads. It’s vital for the video drum to spin at precisely the correct speed for the heads to scan the video tracks on the tape accurately. There is a reference for tracking: the control track, with its 25 ‘pips’ per second, indicating where the video tracks are located. So the head drum’s speed and position (phase) must be accurately forced (by a control system) to follow the control track signal. This control system is a servo. Phase servo The simplest VTR transports relied on a mains-powered motor running at a predictable speed to drive the tape capstan, and thus to transport the tape. Since the control track was part of the original recording, it would indicate the head drum’s desired position for correct playback. The main motor also drove the head drum mechanism, so it was naturally ‘in step’. The drum servo’s simple task was to adjust the position of the head drum relative to the tape, so that the heads scanned the slanted video tracks precisely. It isn’t enough to just have the correct speed; the position relative to the tracks needs to be correct, too. Fig.30 shows a simple phase servo. A pickup on the head drum feeds a trapezoidal waveform former, and the control track pulse is amplified to form a narrow sampling pulse. The sampling pulse operates an electronic sample-and-hold switch that delivers the trapezoid’s instantaneous amplitude at the time of sampling. A capacitor stores the instantaneous value as a DC voltage. The voltage across the capacitor will be low for early sampling or high for late sampling. This voltage is fed to the inverting input of a differential amplifier, with its non-inverting (reference) input voltage being adjustable via the ‘tracking’ control pot so that tapes from other VTRs can be played back successfully. Fig.30: an example of how a simple phase servo operates. 74 Silicon Chip Australia’s electronics magazine The output of this amplifier is proportional to the difference between the actual and desired phase, and this is then amplified to control the tape speed and thus bring the system into phase lock. Fig.31 shows a simplified mains-powered head drum mechanism. An eddy current brake, incorporating an aluminium disc mounted on the head drum’s driveshaft, applies a small amount of ‘drag’ against the drive belt’s force as the DC control current passes through the brake’s coil. This force is enough to create a minute amount of slippage between the belt and its drive wheel, and give an adjustable head drum position relative to the moving tape. The head drum speed was set just a little too fast, so that the drum servo would be able to adjust the drum phase to advance (less braking) or retard (more braking). Speed servos Mains-powered VTRs relied on the stable mains frequency to transport the tape at the correct speed, and the drum’s phase servo to deliver accurate tracking. Battery-powered VTRs also needed to transport the tape at the correct speed, and two methods were adopted. Akai’s VT-100 applied their clever DC brushless servomotor design first used in their X-IV and X-V portable audio recorders. It’s a three-phase motor driven by a high-power phase-shift oscillator. This design delivered excellent speed accuracy, but the drum servo could not use eddy-current braking for head positioning. Instead, the differential amplifier sent a control signal to the motor drive amplifier (MDA), and the MDA’s DC output powered the drum motor directly. So Akai’s circuit replaced the eddy current brake of Fig.30 with a DC drum motor. Sometimes the tape transport would also use a conventional DC motor. In this case, the transport motor would need a speed servo. A simple speed servo generates a voltage proportional to the difference between the motor’s actual speed and desired speed. If the actual speed is too low, this signals the Motor Drive Amplifier (MDA) to increase power to the motor. When the motor speed reaches siliconchip.com.au Build the world’s most popular D-I-Y computer! ALL-NEW COLOUR 2 Plastic Case Optional See SILICON CHIP July & August 2020 Fig.31: a simplified mains-powered head drum mechanism as used in a videotape recorder. its desired (setpoint) rate, this voltage moderates the MDA’s output to hold the motor at the setpoint speed. If the motor runs too fast, the voltage will swing in the opposite direction and signal the MDA to reduce power to the motor. As before, once the motor’s speed reaches to set point, the differential amplifier will moderate the MDA output to hold it at the set point. The basic speed servo (Fig.32) uses a simple speed pickup that delivers one pulse for each motor revolution. It could be a simple magnetic pickup, or it could use an LED with its light is transmitted to a phototransistor through a slit in a disk on the motor shaft. The tacho(meter) amplifier takes the incoming tacho pulses and converts them to a DC voltage proportional to the pulse frequency. The differential amplifier produces a voltage proportional to the difference between its two inputs. When they match, its output is such that the MDA maintains a constant speed. But if there’s a difference between the + and – inputs, the voltage will swing to signal to the MDA that it should change the motor speed and consequently, to bring the inputs back to balance. The actual setpoint speed is easily changed by adjusting the speed reference potentiometer. Combined speed/phase servos Phase servos are accurate, slow-responding systems. Speed servos respond quickly, but lack phase accuracy. High-performance designs combine a speed loop (for rapid startup) and a phase loop (for accurate positioning). Ultimately, mains-powered VCRs would take up these techniques, and would incorporate sophisticated direct-drive motors for capstan and head drum mechanisms. While more complicated, these advanced designs did not need speed-reducing belts or gears, were lighter and could be controlled more accurately, and could easily be slowed or reversed for slow-motion, reverse play and other useful ‘trick’ modes. SC 480MHz, 32-bit processor; 9MB of RAM; 2MB flash memory; 800 x 600 pixel colour display Don’t miss your opportunity to experience Australia’s own worldclass, world-famous single board computer that you build and program yourself, using the world’s easiest programming language – MMBASIC. Learn as you build! And it’s so easy to build because all the hard work is done for you: the heart of the Colour Maximite II, the Waveshare CPU Module (arrowed) is completely pre-assembled and soldered. YOU SIMPLY CAN’T GO WRONG! Short Form Kit includes: Waveshare CPU module pre-loaded with MMBasic the PCB – with solder mask and screen overlay front & rear panels to suit plastic case shown above and all other components required to build the Does not include plastic instrument case, Colour Maximite 2 CR12xx cell or USB power supply/cable 14000 $ All this for only Plus $10.00 p&p in Aust Fig.32: this basic speed servo uses a simple speed pickup to deliver one pulse for each motor revolution. siliconchip.com.au SILICON CHIP SUBSCRIBERS: $AVE 10%! Subscriber’s price just $126 plus p&p Order now (or more information) at www.siliconchip.com.au/shop/20/5508 Australia’s electronics magazine April 2021 75 Care for your rechargeable batteries High current Battery Balancer Our new High Current Battery Balancer, introduced last month, is an advanced design which provides high efficiency and fast balancing by efficiently transferring charge between the connected cells or batteries. It can handle cells or batteries up to 16V, and two units can be combined for larger installations. This second and final article describes the assembly and testing steps, and how to use it. W e put considerable effort into keeping this design as simple as possible, while still providing excellent performance and many useful features. As a result, the parts count is not especially high. However, we have had to use mostly SMD parts to keep the size reasonable, and also because many of the best part choices were not available in through-hole packages at all. While the board assembly is not overly difficult, it is not suitable for beginners. Some SMD soldering experience is desirable. You will need a decent temperature-controlled soldering station (and ideally a reflow oven or hot air rework station), a syringe of flux paste, some solder wick, fine-tipped tweezers, a magnifier and a strong light source. None of the SMD parts are especially difficult to handle, although the smaller six-pin parts in SOT-363 packages are on the tricker side, along with QSOP-16 ICs, which have pins that are fairly close together. Finally, the transformers can present a bit of a challenge in making good solder joints due to their high thermal mass. But with a little care, the PCB can be built by hand. Refer to the PCB overlay diagrams, Figs.4(a) & 4(b) overleaf, for details on which parts go where. We suggest you start construction by populating the surface-mount components on the board’s underside, followed by the SMDs on the top side, then finally, the through-hole parts. As touched on earlier, you can use various assembly methods, including reflow soldering or hand-soldering. We will describe the hand-soldering method as it requires the fewest specialised tools, listed above. The general procedure is to place each part (with the correct orientation for polarised parts, which is pretty much all ICs, diodes & Mosfets) and tack down one pin. You then check the alignment of the other pins and re-position the part by melting the tack solder and gently nudging the part if it is not perfectly aligned with its pads. Once aligned, it is a good idea to add flux paste to all the pins, as that greatly reduces the chance of solder not adhering. You then solder the remaining pins, refresh the initially tacked pin (if you have added flux paste then all you need to do is touch it with the tip of the iron), then use solder wick and flux to clean up any bridges which might have formed. The order in which components are placed is not critiConstruction cal, but we think it is best to place the most difficult parts The High-efficiency Battery Balancer is built on on each side first, so that you do not have to deal with ina four-layer PCB coded terfering adjacent compo14102211 which measures nents. The following proPart 2 – Construction – by Duraid Madina cedure uses that method. 108 x 80mm. 76 Silicon Chip Australia’s electronics magazine siliconchip.com.au Note that SMD resistors are typically marked with a tiny code on the top that indicates the value (eg, 47kΩ = 473 [47 x 103] or 4702 [470 x 102]), which you probably need a magnifier to see. SMD ceramic capacitors are usually unmarked. Finally, note that most of the semiconductor devices used are sensitive to electrostatic discharge (ESD) – particularly those in the smaller packages. Therefore, when handling these devices, try and avoid touching their pins. A grounded anti-static wrist strap will usually ensure you can’t damage any parts, but there are many other ways of ensuring ESD safety. Assembly details Start by fitting the eight 1Ω gate drive resistors, because they are the smallest passive components on the board and are generally out of the way of other parts. Next, fit the eight gate drive NMOS/PMOS FET pairs: Q27, Q28, Q22, Q23, Q16, Q17, Q11 and Q12. These are relatively large as six-pin SMDs go, so they should not give you too much trouble, but watch the orientation! You might need a magnifier to find the pin 1 dot on the top of each device, which in each case goes in the bottom right corner, as shown in Figs.4(a) & 4(b). Next, mount the eight 4.7µF capacitors which are adjacent to these Mosfet pairs. Follow with the five 330Ω resistors on this side of the board, plus the four 20Ω resistors, then the eight 10µF capacitors alongside the mounting pads for Mosfets Q1-Q4. The components labelled “Rsnub” and “Csnub” are required if you are balancing 12V batteries, but are not needed for lower voltage balancing such as Li-ion/LiPo/LiFePO4 cells. If you need them, fit them now, using the values suggested in the parts list published last month (30Ω & 470pF). Now install Mosfets Q1-Q5. These are in LFPAK56 SMD packages, which are similar to 8-pin SOIC devices, but with a tab replacing four of the pins on one side. As such, it should be obvious which way round they go, but don’t get the BUK9Y8R5-80E used for Q5 mixed up with the similar BUK9Y4R8-60Es used for Q1-Q4. In each case, spread a little flux paste on the tab pad before tacking one of the small pins, then solder the remaining three small pins before the tab. You might need to crank your iron temperature up to solder the tabs as they have a lot of thermal mass. The flux paste you added earlier should help draw the solder you feed in under the tab for a good thermal and electrical connection. With those in place, fit the eight remaining Mosfets on this side of the board using the same technique. They are all BUK9Y14-80Es (a different type again from Q1-Q4 & Q5). Now fit the four SMB TVS diodes, ZD1-ZD4, ensuring that their cathode strips are oriented as shown in Fig.4. Note that the voltage rating of these parts varies depending on what type of cells or batteries you are balancing (see the parts list last month). Solder them similarly to the passives, but being larger, they take a bit more heat. Their leads wrap around the sides, so make sure the solder adheres to both the PCB and the device leads (flux paste makes this much easier to achieve). siliconchip.com.au The next job is to solder the four 3A SMD fuses, which mount similarly to resistors (they are not polarised). That just leaves two small resistors: one 100kΩ 0.1% resistor, and another 0.1% resistor, the value of which varies depending on your application. Make sure you don’t get them mixed up. Top-side SMDs Flip the board over and continue assembly by fitting the four larger, 3.2 x 2.6mm (M3226 or 1210) sized ceramic capacitors near the transformer T1-T4 footprints. We used 4.7µF 100V capacitors (TDK CNA6P1X7R2A475K250AE) but you can more than double the capacitance by using 10µF 75V capacitors which cost only a little bit more (TDK CGA6P1X7R1N106K250AC). Follow by fitting the five small dual Mosfets, Q8, Q18, Q13, Q19 and Q24. In each case, make sure that the pin 1 dot is lined up correctly first. These are in smaller packages than the ones you mounted on the bottom of the PCB, with more closely spaced pins, so they might be a little bit trickier. But they aren’t too hard as long as you remember to carefully check for bridges between pins using a magnifier and fix any bridges you find using flux paste and solder wick. Mosfet Q7, in the bottom-right corner, is in the same package as those five but it is a slightly different device so don’t get it mixed up. Again, check its orientation carefully before soldering it in place. Now is a good time to mount the microcontroller, IC2. It should be relatively easy compared to the devices you have already soldered, but make sure that the pins on all four sides are lined up before soldering more than one pin, and as usual, be careful to get its pin 1 in the correct location. Follow with the four isolators: IC4, IC6, IC8 & IC10. In each case, pin 1 is at upper left. These have a similar pin pitch to the small dual Mosfets you already mounted, so should not be any harder to install. Next, fit the eight 470nF capacitors, followed by the five regulators. For the regulators, spread a little flux paste on the large pad before taking one of the smaller pins, then Australia’s electronics magazine April 2021 77 solder the remaining small pins before tacking the tabs. You might need to turn your iron temperature up a bit when soldering the tabs. With those in place, now you can fit the six 1µF SMD capacitors, the two ferrite beads, plus the 680Ω and 100Ω SMD resistors. Then mount the two ESD protection arrays, which are in four-pin packages with one larger than the others. Check Fig.4(a) and to verify their orientation if you are not sure. Now install the eight 10kΩ resistors and then the five 1nF, three 100nF and three 10µF capacitors. Follow by fitting the remaining TVS (the higher voltage one, ZD5). Make sure it is orientated correctly. Then mount the two fuses, with the lower-current (0.75A) fuse being F7, near 8-pin header CON15, and the higher-current (3A) fuse near CON2 at upper left In terms of passives, that just leaves the sole 20Ω resistor near CON10, plus the eight 0.1% resistors. As mentioned last month, the lower value 0.1% resistor values need to be changed depending on your battery voltages. The upper resistor in each pair is 100kΩ. Ensure that the lower resistor is either 6.8kΩ, for a total stack up to about 24V, or 2.2kΩ for higher stack voltages. Fig.4(a): top-side PCB component overlay, with matching photo below. Transformer mounting Due to the significant thermal mass of the transformers and the large power planes they connect to, we recommend avoiding the use of solder paste for mounting these parts, unless you have a very high-quality reflow oven. Instead, we suggest placing them as accurately as possible, holding them in place with Kapton tape, then soldering their four tabs with a hot iron and flux-cored wire solder. Once the transformers are fitted, it is essential to ensure that all flux residues are removed. This can be challenging as most residues will be hidden between the underside of the transformers and the PCB. If flux residues are allowed to remain, the idle current can increase by orders of magnitude (beyond 1mA). The flux can break down at higher voltages, resulting in erratic behaviour and even arcing through the residues. Here, an ounce of prevention is worth a pound of cure, so try to limit 78 Silicon Chip the build-up of flux residue by not allowing too much to accumulate in the first place. If you have the choice, try to use a “no-clean” flux. However, if the flux you are using requires cleaning, make sure to wash the transformers thoroughly with a high-quality flux remover and wipe off any visible residue. Through-hole components Fit tactile switch S1 now. It has a standard footprint, so switches with various actuator heights are available. If you will be frequently adjusting the unit, you might consider chassis-mounting a switch and wiring it back to the pads. If doing that, make Australia’s electronics magazine sure the wires connect to one of the upper pair and one of the lower pair (which is GND). Then you can fit terminal blades for battery/cell connection as required. Most 5.08mm-pitch two-terminal types will work, but check to make sure your intended spade connector will fit. An example blade is Wurth Elektronik 7471286, or use the Altronics parts suggested in the parts list last month. It may be preferable to solder wires instead of spade lugs for some installations, perhaps to reach panel-mounted connectors. However, the Balancer should not be directly soldered to batteries. A failure siliconchip.com.au Fig.4(b): and here’s the underside of the board, again with matching photo below. in either the Balancer or the batteries will be more difficult to resolve if the two are permanently connected. There is no need to use particularly heavy gauge wire as balancing currents are modest, but as a rough guide, they should be able to carry 2A with a negligible temperature rise. 0.8mm diameter copper wire (20AWG) is a reasonable option. If using spade lugs, ensure that no part of the blade, lug, or wire can contact other nearby components. Insulated spade quick connectors are available, and it’s a good idea to use them. For some installations, you might want to mount the board inverted and siliconchip.com.au have terminals or wires exiting from the rear of the board. You can also fit a 5-position 2.54mm header (either vertical or right angle) at CON13 for lower-power applications such as balancing smaller lithium-polymer (LiPo) batteries. CON13 is conveniently located at the edge of the board. If the board is mounted right at the edge of a case with a cut-out in the side, you can plug a standard balance connector straight in. Watch the polarity, though! Now is a good time to fit the 2x4-pin header for JP1. For some installations, where the batteries are of a fixed type, this could be replaced with a soldered Australia’s electronics magazine wire link if desired. Follow with trimpot VR1, ensuring its adjustment screw is located as shown. If you will be adjusting the balancing voltage frequently, you could instead use a chassis-mount 100kΩ potentiometer and run flying leads back to VR1’s pads, possibly plugging into a pin header. Neither the potentiometer’s accuracy nor power dissipation are critical, but we suggest using a sealed design for greater long-term reliability. Follow with the four LEDs, ensuring that the cathodes go towards the top as shown. If mounting the LEDs on the PCB, you will need to use 3mm types. Still, you could instead fit pin headers or flying leads and mount them in a location that will be externally visible (eg, mounted onto a panel or case side using bezels), in which case you could use 5mm LEDs or virtually any other types. For some colours, a different value of current-limiting resistor from the 680Ω specified could be desired to increase the brightness or decrease power consumption. As the drive voltage is 3.3V, blue or white LEDs are not recommended, although you might find that such types give adequate light given their high efficiency. Pin headers CON14 & CON15 are optional. CON14 is only required if you need access to the serial port, such as for debugging or connecting two Balancers to work together (via an isolator) on an 8-cell battery. CON15 is only needed if you have fitted a blank microcontroller and will need to program it on-board, or wish to reprogram it later. That just leaves the six capacitors. Don’t get the two different types mixed up, and make sure to insert the longer leads into the holes marked with + signs. We have specified organic polymer capacitors, not ordinary electros, for their much superior performance characteristics. Programming On the topic of programming IC2, as mentioned last month, it can be done with a PICkit 4 plugged into CON15 (pin 1 to pin 1). This can be done using the MPLAB X IPE software, which comes with Microchip’s free MPLAB X IDE. (Or simply use a pre-programmed chip from our Online Shop). April 2021 79 Safety notes Working with batteries presents some hazards. The most important thing to do is to be thoroughly familiar with your particular batteries’ safety requirements. In general, having fuses close to the terminals of all larger batteries is a good idea to prevent cables catching fire. You can buy fuses that connect directly to the terminals, with provision to attach thick wires at the other end. You can also use inline fuses, but you should ideally keep the section of wire between the terminal and fuse short. There are a few other things to keep in mind when using the Balancer: • Always check that the Balancer is working as intended before attaching it to batteries or other power sources. Ideally, this is done with current-limited power supplies, as described in the main text. • Don’t leave the Balancer unattended until you are satisfied that it works reliably for your particular application. Take particular care if setting a lengthy timeout period. • Keep the Balancer physically separate from the batteries. If they are too close, heat from the Balancer could degrade the batteries, or lead to a hazardous situation. • Ensure that the Balancer is kept clean and dry at all times. • Don’t permanently attach the Balancer to batteries or other power sources; if a hazardous situation arises, it is good to have the ability to quickly disconnect the Balancer. • Periodically check that your batteries are healthy: if the Balancer is constantly balancing one cell, or if you notice that your batteries are losing their ability to store charge, be sure to test and replace any failing cells. • Remember that the Balancer can’t stop a battery from being charged or discharged by external circuitry: over-charging and over-discharging cells can not only damage them, but can lead to hazardous situations. • Note that in higher voltage applications, some of the voltages present on the Balancer could be dangerous (although its maximum rating of 60V total is well within the extra-low-voltage or ELV domain) and so the Balancer should not be touched. Additionally, some components on the Balancer can get hot during operation. It’s very important not to program the device while attached to any kind of power source (cell/battery or otherwise), so enable the “power target from PICkit” option. Test the device in low power/current limited situations after programming, as described below, in case there’s an error with the newly programmed software. Testing Before connecting the Balancer to batteries, it’s essential to test it to ensure that nothing has gone wrong with the assembly that could affect safety or reliability. The easiest way to do this is with a pair of isolated, current-limited power supplies. Set their output voltages to be the same (eg, 4V each) and their current limits to around 500mA. Connect one supply between STACK- (CON7) and CELL1 (CON6), with the positive terminal to CON6. Connect the other between CELL1 (CON6) and CELL2 (CON5), with the positive terminal to CON5. Ensure that a jumper is installed so that the control block is powered from one of these two points, ie, at the positions marked 1 or 2 for JP1 (across pins 80 Silicon Chip 1 & 2 or pins 3 & 4). With an oscilloscope, check to see periodic pulses on the SENSE_EN and SAMPLE lines (pins 19 & 20 of IC2 respectively). If these are absent, there is a fault in or around the microcontroller, or it is not receiving power. If you don’t have a scope, you might be able to pick up the pulses using the frequency counter mode on a DMM, or even an analog voltmeter. If the microcontroller is functional, tie the top-most cell to the stack voltage rail (connecting CON5 [CELL2] to CON2 [STACK+]), and slowly make a small change to the voltage of one of the cells. You should see that the voltage on the power supply with the lower output voltage increases. If this is difficult to observe, you can use an oscilloscope to check the CSPWM/SSPWM lines on the corresponding cell (pins 11 & 17 for the lowest cell or pins 12 & 18 for the second-lowest). You should see narrow, square pulses on these lines. If this test is successful, check the third and fourth cell sections, but note that cells must always be populated in-order from ground; none can be left empty except at the top. Australia’s electronics magazine If you are considering higher-voltage applications, test these carefully, taking great care to use appropriate current limits, and ensuring that the control logic section is powered from only the lowest possible cell. This avoids wasted power in the control regulator (REG1) and potential damage if its maximum input voltage is exceeded. In general, if your lowest expected cell or battery voltage is above 3.6V, then you should always leave JP1 in position 1, so the control circuitry runs off the lowest cell. If your lowest expected cell voltage is lower than this, down to the minimum supported of 2.5V, then it should always be safe to run the control circuitry off the second cell (position 2 on JP1). Higher positions are only useful if you need to ensure that the small current which powers the control section comes from the whole stack, which would be unusual. Final assembly Once you’ve tested your Balancer board, it should be enclosed to protect it from dust and other contaminants. siliconchip.com.au You can use just about any box that’s large enough to fit the PCB module, and which that allows cables to be fed through. Ideally, it should offer some method of exposing the LEDs (eg, a clear lid), potentiometer and pushbutton (possibly via a screwdriver through small holes in the lid). Mount the PCB to the bottom of the case using standoffs so that the board does not flex, and take care that all of the components have adequate clearance from the case walls as it can dissipate some heat. Four mounting holes are provided to suit M3 machine screws, and plastic or metal spacers can be used. Just be careful if using metal spacers that they fit within the copper areas provided around the holes. Heatsinking is not usually required on any of the components, but allowing even a modest amount of airflow will go a long way towards keeping the Balancer cool, prolonging its life. In harsh environments, a small temperature-switched fan could be used (eg, with the thermal switch glued to transformer T1). But in most cases, passive airflow will be adequate, with a few vents or holes drilled in the bottom and the top, or the sides of the case, being sufficient for convection to remove the heat. Using it Now that you’ve built and tested your Balancer, how can you use it? Before connecting it to a battery, run through the following checklist to make sure it’s correctly configured: 1) Configure the source of control power. As described above, if balancing 12V batteries, ensure that the control power source select jumper is securely installed in the right-most position (marked 1), so that the lowest cell is providing control power. If balancing ~3.6V cell (eg, Li-ion, LiPo or LiFePO4), you will probably want the power source select jumper in the second-rightmost position, so that the lowest pair of cells are providing control power. 2) Connect the battery leads to their respective terminals. We suggest connecting them either sequentially (CELL1, CELL2…) or simultaneously (if using an external connector). Plug spade quick connects onto CON8-CON12 for higher-current applications, or a plug designed to mate with 2.54mm-pitch header pins to siliconchip.com.au Screen1: sample serial output. CON13 for balancing up to 1A. If using CON13, make sure the plug orientation is correct, with the negative-most terminal to pin 1! There might be small sparks when connecting battery leads, but these should be momentary. 3) Finally, connect the stack leads (STACK- to CON7 and STACK+ to CON2). If balancing, you can simply bridge the positive stack voltage terminal to the top-most cell terminal. For charging, connect the negative stack terminal to the negative end of your power source, and the positive stack terminal to the positive end. If available, we recommend setting a reasonably low current limit on your power source, to help prevent damage to batteries in case of malfunction. Making adjustments Operation is essentially automatic, with the Balancer simply transferring charge based on the differences it senses in voltage across the batteries or cells. However, there are some options you can set, either using trimpot VR1 and pushbutton S1, or via the serial interface. The options include the minimum difference between battery/cell voltag- es for balancing to start, the maximum balancing current and the minimum and maximum battery/cell voltages outside which balancing will cease. The defaults are for the maximum possible balancing current (about 2.5A), to begin balancing with a 50mV imbalance for 12V lead-acid batteries or a 10mV imbalance for li-ion cells, and for an operating cell voltage range of 2.5-4.3V for li-ion applications and 10-14.8V for nominally 12V batteries. You can change most of these settings using trimpot VR1 and pushbutton switch S1, although a larger range of configuration and calibration settings are available via the serial/USB interface. Table 1 shows the various commands which can be issued by pressing pushbutton S1 in various ways – either a single, long press or with several short presses in a row. Some of these control the unit while others adjust settings in combination with the current rotation of trimpot VR1. Unfortunately, making settings changes this way is a bit imprecise. You can measure the voltage at the wiper of VR1, either by probing its centre pin on the bottom of the board with a DVM or by probing pin 3 of nearby Mosfet Function Check that unit is powered up Pause/resume balancing Switch between li-ion and lead-acid presets Set allowable voltage delta (0-300mV/0-1V) Set maximum balancing current (0-2.5A) Set minimum battery/cell voltage (0-5/0-15V) Set maximum battery/cell voltage (0-5/0-15V) Number of S1 presses One short (<500ms) One medium (1-2s) One long (5s+) Two short Three short Four short Five short Table 1: functions accessible by pressing pushbutton S1 Australia’s electronics magazine April 2021 81 Example Result p r t 600 l 3000 h 4300 d 50 i2 50 o3 25 c2 100000 6790 st 100000 6812 v 3280 Pauses automatic balancing Resumes automatic balancing Set balancing timeout to 600s; if balance not reached in this time, shut down Set low battery/cell threshold to 3V (3000mV); below this, it shuts down Set high battery/cell threshold to 4.3V (4300mV); above this, it shuts down Batteries/cells can vary by up to 50mV before balancing starts Move charge into battery/cell #2 (1-4) at 50% of maximum rate (1-100) Move charge out of battery/cell #3 (1-4) at 25% of maximum rate (1-100) Calibration – set battery/cell divider #2 to have a voltage division ratio of 100kΩ:6.79kΩ Calibration – set stack divider to have a voltage division ratio of 100kΩ:6.812kΩ Calibrate – set the typical supply voltage to 3.28V (3280mV) Table 2: Serial Commands Q7 relative to GND. You then need to divide that reading by 1.65V (or better, the actual measured 1.65V ADC reference voltage) and then multiply by the range given in Table 1. If you can hook up the serial interface, you are much better off making changes that way as they will be exact, and you can also calibrate the unit properly that way. Read on for further details on the serial interface. Monitoring its operation The simplest way to do this is visually. One of the four LEDs on the board will flash to indicate when balancing is occurring, with the right-most LED (LED7) corresponding to the bottom-most cell, LED8 to the next cell up in the stack, etc. They blink slowly if a battery/cell is being charged, or rapidly if a battery/ cell is being discharged. If no balancing/charging is occurring, LED7 will occasionally flicker very lightly, just to let you know that the circuit is ‘alive’, while consuming as little power as possible. If there is an over-voltage error, all four LEDs will flash simultaneously at 1Hz, with a 50% duty cycle. If an under-voltage error is detected, the unit simply shuts down and does not flash the LEDs at all (not even a heartbeat). If you are paying attention, the lack of heartbeat will tell you something is wrong, and by leaving the LEDs off, we don’t risk discharging an already over-discharged cell or battery. If you want more details of the unit’s operation and be sure that it is doing its job, you can monitor the serial port at CON14. Ideally, this should be con82 Silicon Chip nected to your computer via an isolating interface (a good one is described below). You can then wire the output of that isolating interface to a USB/serial adaptor. Set a terminal emulator to 38,400 baud N,8,1 and you should see a stream of information, like that shown in Screen1. This shows you the measured voltage at each input, plus the whole stack, whether it is currently moving any charge into or out of a battery/cell, and how fast it is doing so (0-100%). The data is both human-readable and machine-readable, so it would be quite easy to create software to parse the information and display it differently, or take actions depending on the results. As shown in Table 2, you can also send commands to pause or resume balancing, change the settings, or even force it to transfer charge into or out of a given battery/cell. This means that you could centralise the control via a computer program if you are using several Balancer boards. Combining multiple balancers You can use two Balancer boards to balance up to eight batteries or cells, as long as the total stack voltage is still within the 60V DC maximum rating. The only extra hardware that you need to do this is an isolated serial link. Fortunately, we published just such a design in March 2021 (siliconchip. From last month’s SILICON CHIP, this isolated serial link is ideal to link together two Balancer boards together. Australia’s electronics magazine com.au/Article/14785), and PCBs are available. Build that board, but leave off the headers, and set both jumpers (JP1 & JP2) to the 5V position (they will actually be supplied with 3.3V, as that is the only low-voltage rail available on the Balancer boards). You can then solder pins 3-6 of either CON1 or CON2 directly to CON14 on one of the Battery Balancer boards, as the pinout is an exact match. Run a ribbon cable or similar from the other end of the board to CON14 on the other Balancer board. The wiring will be the same as the other end and you should have the TX pin on the Balancer connected to the TX pin on the Isolator board. Similarly, the RX pin on the Balancer connects to the RX pin on Isolator. The reversal is effected within the Isolator. Then, all you have to do is connect between one and four contiguous cells/ batteries in your stack to one balancer board, starting with the CELL1 connection, and join the remainder to the other. Connect both full stacks across the STACK- and STACK+ terminals on both boards. The two units will power up and negotiate over the serial link, automatically detecting that they are talking to each other. They will then balance as if they are one eight-input Balancer instead of two four-input balancers. Finally, there is an error in the parts list in last month’s part 1: on p27, several Mosfets (Q11,Q12…) are listed as “S6M4” types. The correct type code is QS6M4. SC siliconchip.com.au GOOD R GrEenA zy! Build It Yourself Electronics Centres® SAVE $319 F 1050 $ K 8604 ench with Build the ultimate workb ril 30th. Ap these deals - only until Everything a maker space needs in one compact unit! Not just for desoldering works great as a regular hot air gun! 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Includes desk stand - plus narrow, medium and wide nozzles for different tasks. SAVE $34 95 $ T 1461 45 .95 $ d Charges: Li-Ion, Ni-Mh & Ni-C SAVE 12% Ultimate Flexible Helping Hands A 0289A Do-It-All Battery Charger 6pc Soldering Helper Tool Kit A 6 piece set of tools for reworking solder joints, cleaning pad surfaces and removing debris. T 2351 29 $ .95 19.95 A must have for any electronics enthusiast. Includes: • Side cutters. • Flat long needle nose pliers. • Flat bent needle nose pliers. • Long nose pliers/cutters. • Bull nose pliers/cutters T 2758A Powered by USB, allowing you to stay powered up anywhere. Works with 10440 to 26650 size lithium and AAAA to C size Ni-MH/Ni-Cd. $ 5pc Plier & Cutter Set SAVE 25% M 8994 20 $ Upgrade to the ultimate in soldering helper hands. Includes magnifier to assist with those fiddly jobs. Arm length ≈30cm. NEW! USB-C laptop 90W output charges any Need an extra laptop charger? 70 $ D 2323 Desk Mount USB PD Charger A 96W USB type C power delivery charger, plus dual QC 3.0 USB charging in the one compact near flush mount unit. Requires 60mmØ hole. Includes power supply. This 90W USB-C power delivery (PD) charger offers fast recharging for MacBooks, Nintendo Switch and other type “C” devices. Plus a standard 2.4A USB charger output. 27.95 16.95 $ $ T 2802 A handy accessory for any workbench, this 130mm 6x magnifier uses premium quality glass and LED lighting for a clear view of PCBs and tiny parts. Premium Grade HSS-R Drill Bit Set 19pcs between 1mm and 10mm for plastic, wood and metals. Metal storage case. X 0433 Get a crisp close up view! Charges a laptop, a phone & tablet at the same time! Chewed out a screw head? No problem! This unique set of pliers features two serrated jaws, plus serrated circular opening on the front face for extracting screws up to 13mmØ. 26.95 $ T 2306 Order online <at> altronics.com.au | Sale pricing ends April 30th 2021. Deals! Test & Tool SAVE 22% T 2694A SAVE $50 165 $ T 2120 SAVE 18% 30W Lithium ‘Go Anywhere’ Soldering Iron 30 $ Q 1129 69 45 minute run time. 600°C max. Ideal for occasional soldering jobs or light duty repairs and field servicing. Recharge by USB power adaptor in your car or at home - or USB battery bank. Includes replaceable 18650 battery. $ INCLUDES ACCESSORY PACK: • 3 tips: conical, hot knife/3D print finishing tool, hot air • Micro USB cable • Solder container & 1m of solder • Tip sponge. All-Rounder Student DMM The perfect beginner, student or enthusiast multimeter. 12 auto ranging test modes with good accuracy and an easy to read jumbo digit 4000 count screen. Includes test leads. Cut, Polish, Grind, Sand & Carve. 14 Quality Resin Core Solder Great for finishing and smoothing your 3D prints! Perfect for odd jobs and hobbies. Powerful 130W motor with variable speed between 8000 and 33000 RPM. Included is a 172pc accessory kit of grinding wheels, drills, cutters, sanding discs, polishing pads and more. $ Premium grade for leaded soldering. 200gm reels. 60% tin, 40% lead. SAVE 15% a roll T 1100 0.8mm, T 1110 1.0mm, T 1122 1.6mm SAVE 27% SAVE 15% 1000’s sold! 29 $ 30 $ T 2186A SAVE 22% 40 $ SAVE 15% T 2480 T 4015A All heat & no flame! Features 95 security, philips, pozi and slotted bits made from tough S2 alloy. Includes two way ratchet handle with comfy rubber grip. See web for full contents list. 69.95 $ X 0102 Blast away dirt & grime on parts Makes jewellery sparkle again! Clean small parts, jewellery, shaver heads, glasses and more! Shifts grease, dust and gunk from tiny crevices in just minutes using ultrasonic waves. Tank size: 155x98x52mm. 22.95 $ T 1302A Dual Solder Reel Holder Heavy weight base with solder guide. All metal construction. Hands free, head worn magnifier. Offers four levels of magnication (1.5x, 3x, 8.5x,10x) in the one head mounted magnifier. Requires 2xAAA batteries for LED lamp. A 35x26cm heat resistant silicon work mat, plus a 25x20cm magnetic mat to keep screws and materials organised while you work. SAVE $15 *Solder not included. New low price! 29 Never lose a tiny screw again! 101 Pc Ratchet Driver Kit Iroda® Pocket thermo-gun. Great for removing adhesives & heatshrinking. 650°C max. Refillable. Add T 2451 butane gas for $9.35. T 2555 $ 50 $ T 2090 Top buy for the students & makers! AMAZING VALUE! SAVE 22% 62 $ T 2163 Get started in electronics with this handy 20pc kit. To buy these separately would normally cost $154! A jam packed starter kit including soldering iron, multimeter, solder sucker, wire stripper, cutters, pliers and more! Ideal for beginners & enthusiasts. Bargain 40W Soldering Station The perfect balance of value for money and features for beginners or cash strapped students and enthusiasts. Slim, lightweight non-slip handle with tip cleaning sponge and iron safety holder. Full range of spare tips also available. 15.95 Deburring Hand Tool $ New low price! SAVE 15% SAVE 20% 17.50 $ 19.95 $ T 2488 Iroda® Mini Jet Blowtorch Produces a powerful jet like flame - up to 1300°C! Refillable design is great for hobbyists. Rotating PCB Holder T 2356 A must have for the electronics enthusiast! Work on boards up to 200 x 140mm. Magnetic Bowl T 4018 4” stainless steel bowl with magnetic base to keep screws from straying while you work 16 $ Blow Brush T 1480 Remove fine debris from 3D prints when smoothing or reworking. Remove rough edges and neaten up 3D prints with this comfort grip external chamfer tool. NEW! T 2370 18.50 $ Make, Invent & Create. Raspberry Pi® 4 Z 6415 4GB RAM The latest Pi 4 is now capable of running two monitors at once - in 4K resolution too! It’s also equipped with USB 3.0, upgraded CPU and a choice of 4GB or 8GB RAM. Micro sized desktop computing has arrived! 125 $ The Raspberry Pi® 400 A complete computer the size of a keyboard! A neat new portable design ideal for education environments. With all the same features as the Raspberry Pi 4, it’s a powerful computing platform for work, education and play! Rear panel provides access to all ports including the GPIO header. Add on accessories: P 6631 1.5m micro HDMI cable $22.95. M 8821 Power supply $19.95. D 0313A Noobs 16GB micro SD card $23.95. 109 $ Now with dual 4K HDMI outputs! Z 6302G 4GB RAM 144 $ Create Amazing LED Light Effects! 1m length of addressable RGB 5050 LED strip - this means you can program the colour of every individual LED using an Arduino/Raspberry Pi. 60 LEDs per m. WS2812B chip on board. 10mm width, adhesive backed. 5V, 3.6A/m (max). SAVE 22% 23 $ $ X 3222A Quartz DIY Clock Kits A much requested item by our builders and makers, this handy clock kit comes with 3 different styles of hands to suit your DIY clock design. Requires 1xAA battery. Available in dual fan cooled or passive cooled versions. These cases provide protection and thermal dissipation for your Pi 4. *Pi not 469 $ K 8620 33.95 $ BBC micro:bit GO Kit FREE! 16.95 Keeps your cables neater, peel off as many as your need for prototyping. 500ml of UV resin Valued at $59.95 Creality® LD-002R Resin 3D Printer P 1021 Pin to Socket P 1022 Pin to Pin P 1023 Socket to Socket Affordable entry level resin printer for fast, strong & smooth prints. 4 $ ea SAVE 22% Resin based 3D printers are rapidly becoming the go to tool for high resolution 3D prints. They offer a faster print process with excellent accuracy and a stronger finished product thanks to UV curing on each layer. The LD-002R can print objects up to 120 x 65 x 165mm. It is capable of printing up 20-30mm per hour, making it much faster than traditional FDM 3D filament printers. LoRa Arduino Shield Allows long range communication with an Arduino without the need for a GSM 4G network - even over distances of up to several kilometres! 3.3/5V input. SAVE 25% 45 $ NEW! Z 6440A $ Ribbon Jumper Leads 39.95 $ H 8954 Passive Design your own wall clock! X 1010A: Suits 2-6mm panel. X 1014A: Suits 16-21mm panel. Z 6432 .95 included. 5050 size LEDs for superior light output! H 8959 Dual Fan 29 Red Raspberry Pi® 4 Aluminium Cases Z 6302H 8GB RAM per 1m A complete desktop computer in a keyboard size case! Latest model! Now with in-built microphone and speaker, capacitive touch button, double the storage space and 8 times more RAM! GO kit includes batteries, battery box and USB cable to get you up and running in no time. Hobby Wire Packs 6 colour hobby pack for project building. 10m of each colour. 19.95 $ W 2431 Stranded. W 2430 Solid Core. Jumbo RGB LED Matrix 64 bright RGB LEDs are contained in a 60x60mm housing. NEW! Z 0977 19.95 $ SAVE 25% 19 $ NEW! NEW! 19.95 $ CAN-BUS Arduino Shield Z 6426 Allows you to interface Arduino with CANBUS control found in automotive electronics. Use Arduino for your own sensor monitoring. Z 6459 NEW! 9 $ .95 I2C LCD Module Connects to a 16x2 LCD allowing you to drive the screen from just 2 IO pins on an Arduino. 5V input. Supports I2C. 14.95 $ Z 6522A USB to TTL Cable A simple way to connect TTL serial devices to USB inputs. 1m length. Jumper Header Kit K 9642 A huge assortment of single row header connectors for making your own custom length wiring. Includes male & female pin headers, plus 2.54mm housings. Power Up M 8193 Deals! SAVE 27% SAVE $50 50 $ Table Lamp With Wireless Charger 199 $ NEW! A great bedside or study lamp 39 .95 $ Portable Battery Bank Jump Starter An all round portable charging device - plus vehicle jump starter! Not just for car battery emergencies, this high capacity battery bank also wirelessly charges your phone, powers laptops and other devices. Jumpstarts most 4-6 cylinder vehicles. *Devices shown for illustration purposes. A stylish glossy white table lamp with adjustable dimming, colour temperature & wireless charging. Great for the desk or bedside table. Powered by any USB wall charger 2A minimum (M 8862A $13.95). & USB charging! Keeps devices charged with wireless X 4221 D 2322 Build wireless charging into your desk An low profile desk mount 10W wireless fast charger. Requires 60mmØ hole. Includes power adaptor & USB cable. Ultra Slim 10W Charging Pad D 2326 SAVE $10 19 $ 10W wireless charger. Requires USB wall charger, such as M8862A $13.95. Includes USB cable. N 2023 SAVE 20% 63 $ SAVE $46 SAVE $65 Pure AC Output Power! 150 $ M 8010A 150VA Power mains appliances on the road! Part ONLY 2 Pin P 7892 3 Pin P 7893 4 Pin P 7894 6 Pin P 7896 $8 $11.95 $17.95 $19.95 .95 NEW: Now suits LiFePo4, lead acid & calcium type batteries! NEW! Provides a max charge current up to 5A (suits solar panels up to 60W). The entire PCB assembly is housed in an epoxy filled housing. 80Wx37Dx22Hmm. IP67. Anderson Style To USB Charger Cable Great for automotive wiring - requires no special crimpers to terminate! Use a standard automotive crimper, pliers or solder terminate. 14A rated. 199 $ M 8536A 12V 10A Multi-Stage Vehicle Battery Chargers 5A Waterproof Charge Controller Pins IP67 Dust & Water Proof DC Conectors 99 $ M 8534A 6/12V 4.5A Each model utilises a microprocessor to ensure your battery is maintained in tip-top condition whenever you need it. Helps to extend battery service life. Suitable for permanent connection. Great for caravans & seldom used vehicles. Weatherproof casing. • Delivers pure AC power from your car battery • Ideal for tricky loads, such as laptops, & game consoles • USB charging output • 12V input • 300W surge rated, 170x108x60mm NEW! SAVE $70 34 .95 $ P 7869 NEW! 12.95 $ Easy Wire Anderson Style Plug Phone: 1300 797 007 Fax: 1300 789 777 Mail Orders: mailorder<at>altronics.com.au Anderson Style & Car Accessory Plate A handy connection point for 4WD & camper installation. 60Wx75Hx42Dmm. P 7811 NEW! 19.95 $ Simple screw connection - no need for crimping lugs. 8AWG max cable size. N 2005 P 7810 59.95 $ NEW! NEW! 14.95 M 8655 $ Anderson Style Connector Panel A handy connection point for 4WD & camper installation. 60Wx40Hx42Dmm. Western Australia Sale Ends April 30th 2021 This MPPT regulator employs special circuitry to gain up to 20% additional charge from your existing solar panels. Suits 12 or 24V systems. Easy to set up and connect yourself. NEW! A 2m Anderson style cable fitted with USB type C Power Delivery Charger (18W) & USB QC 3.0 port for keeping devices charged. Build It Yourself Electronics Centres Get the most from your solar panels with an MPPT regulator » Perth: 174 Roe St » Joondalup: 2/182 Winton Rd » Balcatta: 7/58 Erindale Rd » Cannington: 5/1326 Albany Hwy » Midland: 1/212 Gt Eastern Hwy » Myaree: 5A/116 N Lake Rd 12V DC+USB Power Panel 36.95 $ Can be easily surface mounted to custom panels to provide power to your devices & portable appliances. 15A DC breaker. P 0697 50x130x70mm. Victoria 08 9428 2188 08 9428 2166 08 9428 2167 08 9428 2168 08 9428 2169 08 9428 2170 » Springvale: 891 Princes Hwy » Airport West: 5 Dromana Ave 03 9549 2188 03 9549 2121 New South Wales » Auburn: 15 Short St 02 8748 5388 Queensland » Virginia: 1870 Sandgate Rd 07 3441 2810 South Australia » Prospect: 316 Main Nth Rd 08 8164 3466 Please Note: Resellers have to pay the cost of freight & insurance. Therefore the range of stocked products & prices charged by individual resellers may vary from our catalogue. © Altronics 2021. E&OE. Prices stated herein are only valid until date shown or until stocks run out. Prices include GST and exclude freight and insurance. See latest catalogue for freight rates. B 0092 Find a local reseller at: altronics.com.au/storelocations/dealers/ SILICON CHIP .com.au/shop ONLINESHOP PCBs, CASE PIECES AND PANELS IR REMOTE CONTROL ASSISTANT PCB (JAYCAR) ↳ ALTRONICS VERSION USB SUPERCODEC ↳ BALANCED ATTENUATOR SWITCHMODE 78XX REPLACEMENT WIDEBAND DIGITAL RF POWER METER ULTRASONIC CLEANER MAIN PCB ↳ FRONT PANEL NIGHT KEEPER LIGHTHOUSE SHIRT POCKET AUDIO OSCILLATOR ↳ 8-PIN ATtiny PROGRAMMING ADAPTOR D1 MINI LCD WIFI BACKPACK FLEXIBLE DIGITAL LIGHTING CONTROLLER SLAVE ↳ FRONT PANEL (BLACK) LED XMAS ORNAMENTS 30 LED STACKABLE STAR ↳ RGB VERSION (BLACK) DIGITAL LIGHTING MICROMITE MASTER JUL20 JUL20 AUG20 NOV20 AUG20 AUG20 SEP20 SEP20 SEP20 SEP20 SEP20 OCT20 OCT20 OCT20 NOV20 NOV20 NOV20 NOV20 15005201 15005202 01106201 01106202 18105201 04106201 04105201 04105202 08110201 01110201 01110202 24106121 16110202 16110203 16111191-9 16109201 16109202 16110201 Subscribers get a 10% discount on all orders for parts $5.00 $5.00 $12.50 $7.50 $2.50 $5.00 $7.50 $5.00 $5.00 $2.50 $1.50 $5.00 $20.00 $20.00 $3.00 $12.50 $12.50 $5.00 ↳ CP2102 ADAPTOR BATTERY VINTAGE RADIO POWER SUPPLY DUAL BATTERY LIFESAVER DIGITAL LIGHTING CONTROLLER LED SLAVE AM/FM/SW RADIO MINIHEART HEARTBEAT SIMULATOR I’M BUSY GO AWAY (DOOR WARNING) BATTERY MULTI LOGGER ELECTRONIC WIND CHIMES ARDUINO 0-14V POWER SUPPLY SHIELD HIGH-CURRENT BATTERY BALANCER (4-LAYERS) MINI ISOLATED SERIAL LINK NOV20 DEC20 DEC20 DEC20 JAN21 JAN21 JAN21 FEB21 FEB21 FEB21 MAR21 MAR21 16110204 11111201 11111202 16110205 CSE200902A 01109201 16112201 11106201 23011201 18106201 14102211 24102211 $2.50 $7.50 $2.50 $5.00 $10.00 $5.00 $2.50 $5.00 $10.00 $5.00 $12.50 $2.50 APR21 APR21 APR21 APR21 APR21 10102211 01102211 01102212 23101211 23101212 $7.50 $7.50 $7.50 $5.00 $10.00 NEW PCBs REFINED FULL-WAVE MOTOR SPEED CONTROLLER DIGITAL FX UNIT PCB (POTENTIOMETER-BASED) ↳ SWITCH-BASED ARDUINO MIDI SHIELD ↳ 8X8 TACTILE PUSHBUTTON SWITCH MATRIX PRE-PROGRAMMED MICROS & ICs As a service to readers, Silicon Chip Online Shop stocks microcontrollers and microprocessors used in new projects (from 2012 on) and some selected older projects – pre-programmed and ready to fly! Some micros from copyrighted and/or contributed projects may not be available. $10 MICROS 24LC32A-I/SN ATmega328P-PU ATmega328P-AUR ATtiny85V-10PU PIC10F202-E/OT PIC12F1572-I/SN PIC12F617-I/P $15 MICROS EEPROM for Digital FX Unit (Apr21) RF Signal Generator (Jun19) RGB Stackable LED Christmas Star (Nov20) Shirt Pocket Audio Oscillator (Sep20) Ultrabrite LED Driver (with free TC6502P095VCT IC, Sep19) LED Christmas Ornaments (Nov20; specify variant) Car Radio Dimmer Adaptor (Aug19), MiniHeart (Jan21) Refined Full-Wave Universal Motor Speed Controller (Apr21) Tiny LED Xmas Tree (Nov19) Digital Interface Module (Nov18), GPS Finesaver (Jun19) Digital Lighting Controller LED Slave (Dec20) Ol’ Timer II (Jul20), Battery Multi Logger (Feb21) 5-Way LCD Panel Meter (Nov19), IR Remote Control Assistant (Jul20) Ultrasonic Cleaner (Sep20), Electronic Wind Chime (Feb21) Flexible Digital Lighting Controller Slave (Oct20) UHF Repeater (May19), Six Input Audio Selector (Sept19) Universal Battery Charge Controller (Dec19) PIC12F675-I/SN PIC16F1455-I/P PIC16F1455-I/SL PIC16F1459-I/P PIC16F1705-I/P PIC16F88-I/P ATSAML10E16A-AUT High-Current Battery Balancer (Mar21) PIC16F1459-I/SO Four-Channel DC Fan & Pump Controller (Dec18) PIC32MM0256GPM028-I/SS Super Digital Sound Effects (Aug18) PIC32MX170F256D-501P/T 44-pin Micromite Mk2 (Aug14), 4DoF Simulation Seat (Sept19) PIC32MX170F256B-50I/SP Micromite LCD BackPack V1-V3 (Feb16 / May17 / Aug19) RCL Box (Jun20), Digital Lighting Controller Micromite Master (Nov20) PIC32MX170F256B-I/SO Battery Multi Logger (Feb21) PIC32MX270F256B-50I/SP ASCII Video Terminal (Jul14), USB M&K Adaptor (Feb19) $20 MICROS PIC32MX470F512H-I/PT Stereo Echo/Reverb (Feb 14), Digital Effects Unit (Oct14) PIC32MX470F512H-120/PT Micromite Explore 64 (Aug 16), Micromite Plus (Nov16) PIC32MX470F512L-120/PT Micromite Explore 100 (Sept16) $30 MICROS PIC32MX695F512L-80I/PF PIC32MZ2048EFH064-I/PT Colour MaxiMite (Sept12) DSP Crossover/Equaliser (May19), Low-Distortion DDS (Feb20) DIY Reflow Oven Controller (Apr20) KITS & SPECIALISED COMPONENTS MINIHEART HEARTBEAT SIMULATOR (CAT SC5732) MICROMITE LCD BACKPACK V3 KIT (CAT SC5082) (JAN 21) All SMD parts, including IC2 – does not include PCB $5.00 AM/FM/SW RADIO (JAN 21) $2.50 $3.00 $7.50 - PCB-mount right-angle SMA socket (SC4918) - Pulse-type rotary encoder with integral pushbutton (SC5601) - 16x2 LCD module (does not use I2C module) (SC4198) LED CHRISTMAS ORNAMENTS (CAT SC5579) (NOV 20) $14.00 Complete kit including micro but no coin cell (specify PCB shape & colour) RGB STACKABLE LED CHRISTMAS STAR (CAT SC5525) (NOV 20) $38.50 Complete kit including PCB, micro, diffused RGB LEDs and other parts D1 MINI LCD WIFI BACKPACK KIT (OCT 20) $70.00 Complete kit including 3.5-inch touchscreen, PCB and ESP8266-based module SHIRT POCKET AUDIO OSCILLATOR (SEP 20) Kit: including 3D-printed case, and everything else except the battery and wiring - 64x32 pixel white OLED (0.49-inch/12.5mm diagonal) - Pulse-type rotary encoder with integral pushbutton COLOUR MAXIMITE 2 in stock now $40.00 $10.00 $3.00 (JUL 20) Short form kit: includes everything except the case, CPU module, power supply, optional parts and cables (Cat SC5478) Short Form kit (with CPU module): includes the programmed Waveshare CPU modue and everything included in the short form kit above (Cat SC5508) $80.00 $140.00 (AUG 19) Includes PCB, programmed micros, 3.5in touchscreen LCD, UB3 lid, mounting hardware, Mosfets for PWM backlight control and all other mandatory on-board parts $75.00 Separate/Optional Components: - 3.5-inch TFT LCD touchscreen (Cat SC5062) $30.00 - DHT22 temp/humidity sensor (Cat SC4150) $7.50 - BMP180 (Cat SC4343) OR BMP280 (Cat SC4595) temp/pressure sensor $5.00 - BME280 temperature/pressure/humidity sensor (Cat SC4608) $10.00 - DS3231 real-time clock SOIC-16 IC (Cat SC5103) $3.00 - 23LC1024 1MB RAM (SOIC-8) (Cat SC5104) $5.00 - AT25SF041 512KB flash (SOIC-8) (Cat SC5105) $1.50 - 10µF 16V X7R through-hole capacitor (Cat SC5106) $2.00 VARIOUS MODULES & PARTS - Spin FV-1 IC (Digital FX Unit, Apr21) - 15mW 3W SMD resistor (Battery Multi Logger / Arduino Power Supply, Feb21) - DS3231 or DS3231M real-time clock SMD IC (Battery Multi Logger, Feb21) - MCP4251-502E/P (Arduino Power Supply, Feb21) - Pair of CSD18534 (Electronic Wind Chimes, Feb21) - IPP80P03P4L04 (Dual Battery Lifesaver / Vintage Radio Supply, Dec20) - 16x2 I2C LCD (Digital RF Power Meter, Aug20) - WS2812 8x8 RGB LED matrix module (Ol’ Timer II, Jul20) - MAX038 function generator IC (H-Field Transanalyser, May20) - MC1496P double-balanced mixer (H-Field Transanalyser, May20) - AD8495 thermocouple interface (DIY Reflow Oven Controller, Apr20) - I/O expander modules (Nov19): PCA9685 – $6.00 ¦ PCF8574 – $3.00 ¦ MCP23017 – $3.00 $40.00 $2.50 $3.00 $3.00 $6.00 $5.00 $7.50 $15.00 $25.00 $2.50 $10.00 $10 flat rate for postage within Australia. Overseas? Place an order via our website for a quote. All items subect to availability. Prices valid for month of magazine issue only. All prices in Australian dollars and included GST where applicable. To Place Your Order: INTERNET (24/7) PAYPAL (24/7) eMAIL (24/7) MAIL (24/7) PHONE – (9-5:00, Mon-Fri) siliconchip.com.au/Shop Use your PayPal account silicon<at>siliconchip.com.au silicon<at>siliconchip.com.au Your order to PO Box 139 Collaroy NSW 2097 Call (02) 9939 3295 with with order & credit card details You can also order and pay by cheque/money order (Orders by mail only). Make cheques payable to Silicon Chip Publications. 04/21 64-KEY This simple project turns an Arduino into a MIDI key matrix. These are popular with musicians for triggering samples, but commercial versions cost hundreds of dollars. Ours costs a fraction of that, and you can customise it by changing the Arduino software. It supports regular or illuminated buttons and can also be programmed to act as a MIDI pass-through, among other roles. T his project was inspired by a reader request to create something similar to the Infra-red Remote Control Assistant project from July 2020 (siliconchip.com.au/ Article/14505) but for MIDI. MIDI is a standard that allows musical instruments and computers to communicate. Just in case you didn’t know, MIDI is an acronym for Musical Instrument Digital Interface. A MIDI encoder takes inputs from a musical instrument (such as a keyboard) and converts them into MIDI format. Such a device could be connected to a computer to record playing, or to a synthesiser, to turn the MIDI data back into music. Such devices commonly utilise 8x8 switch matrices to generate up to 64 different MIDI messages; they effectively emulate a five-octave keyboard with some keys to spare. This allows you to easily interface with a synthesiser or digital audio workstation (DAW) to generate music from real-world inputs. The Arduino community has done a lot of the work for this already, creating libraries which can generate MIDI messages both in hardware (as serial 88 Silicon Chip data) and also as a virtual USB MIDI device (which many DAW PC applications can read). The basic system can be implemented with not much more than an Arduino Leonardo development board. The Leonardo is based on an ATmega32U4 microcontroller, which has a USB peripheral. Along with an Arduino library, that makes this job much easier. To do this, the Leonardo scans columns assigned to eight of its I/O pins and checks if they have been shorted against any of eight other I/O pins, assigned to the button rows, thus giving up to 64 combinations. These 16 I/O pins are then wired to an array of tactile switches or pushbuttons which form the keys. This simple system cannot detect more than one ’closure’ at a time, so any state that is identified as having more than one button pressed is reported as ‘nothing pressed’. Some, but not all, combinations of multiple keys could be identified, but we have erred on the side of keeping this simple. To be able to detect simultaneous keypresses correctly would require a Australia’s electronics magazine diode to be fitted to each switch (and would also make our simple device considerably more complicated). Each key (close or release) event results in a MIDI event being sent over USB. We are using the Leonardo’s hardware serial port to generate a hardware MIDI signal. This can then be fed through our MIDI Shield, described below, to convert it to the correct electrical format to go to a synthesiser etc. Note that if all you want to do is send MIDI events to a computer over USB, you don’t even need to build the Shield. But you probably will want to assemble our Switch Matrix PCB, also described later, as wiring up the switches manually would be a lot of work! To help make this project more useful, we’ve also added a very basic synthesiser to the Leonardo. A PWM signal is produced from pin 13, approximating a sinewave at the frequency of the note being played. The waveform shape is defined in an array, so it could be changed to produce a different sound. This sound can be heard by connecting a piezo transducer between pin 13 and GND of the Leonardo, although these devices don’t have a great resiliconchip.com.au Part 1 – by Tim Blythman MATRIX Use this photo to help guide your wiring between the MIDI Shield and the Switch Matrix PCB. In all cases, pin 1 goes to pin 1 (the green wire), but CON1 on one PCB goes to CON2 on the other and vice versa. sponse to lower frequencies. Hence, our MIDI shield also provides an audio amplifier which can drive a speaker (the larger the better – they’re usually more efficient) for better audio quality. While we were at it, we thought we’d also add a MIDI Input to the Shield. As presented here, all you can use that for is to replicate the received data directly to the MIDI Output, allowing this device to act as a basic extender. However, the hardware is set up to allow the micro on the Leonardo to receive and decode the incoming MIDI data, so with appropriate software, it could do a variety of other jobs. The MIDI Encoder Shield This small PCB is an Arduino ‘shield’ (aka daughterboard) which adds some useful hardware for interfacing with MIDI equipment. The board effectively combines four different ‘modules’ which operate independently. That means that, if you don’t need all of the functions, you can leave off some of the parts. These four parts are the interface to the switch matrix, an audio amplifier, a MIDI transmitter and a MIDI receivsiliconchip.com.au er. The circuit diagram for the whole Shield, incorporating those four sections, is shown in Fig.1. Switch matrix Since the switches are intended to be mounted off-board, we have just provided some convenient connection points on the PCB. CON1 and CON2 are standard 2.54mm (0.1in) pitch headers, and could be fitted with pin headers or sockets. For prototyping, we recommend header sockets, as these allow jumper wires to be plugged in. CON1A and CON2A have a 3.5mm pitch and are sized to fit smaller screw terminals such as Altronics’ P2028. This is a good way to rig up something more permanent. You could also solder wires directly to any of these pads. Note that the pins marked with the arrows correspond to the ‘lowest’ ends of each row and column. Thus, shorting the two pins marked with arrows will give the lowest note. Shorting the two pads at the opposite ends will give the highest note. You will probably not be able to install both of CON1 and CON1A or Australia’s electronics magazine CON2 and CON2A, as the headers will foul the cable entries for the screw terminals. Thus, you should choose which of the two you will fit before starting construction. Audio amplifier The amplifier circuit is based around IC1, an SSM2211 class-AB amplifier IC, which we previously used in the AM/FM/SW Radio published in January 2021. It provides a push-pull output at up to 1.5W into 4Ω, so it is a good choice for low supply voltages. A 100nF capacitor bypasses its supply rails at pins 6 and 7. Jumper JP2 can be used to connect Arduino pin D13 to the amplifier. If you want to use another I/O pin to feed the amplifier, it can be patched into JP2. IC1 is surrounded by components to condition the input signal (including filtering out any high-frequency PWM artefacts) and to set the gain. The 1kΩ resistor and 100nF capacitor provide low-pass filtering to remove PWM switching harmonics from the generated audio signal. This results in the 180kHz PWM frequencies being attenuated by around 40dB. April 2021 89 l SC Ó MIDI SHIELD FOR ARDUINO The 10µF capacitor provides AC-coupling into the amplifier, while the other 100nF capacitor provides bypassing of the internal mid-rail reference output on pin 2 of IC1. This reference rail is fed directly to pin 3, the non-inverting input, as we are supplying a single-ended signal. The half-rail reference also biases the inverting input via the 1MΩ resistor, while the filtered audio comes into the inverting input via a 10kΩ resistor. The amplifier’s A output (at pin 5) is also fed back in to pin 4 via VR1. This is used to set the gain, and thus the resulting sound volume. The B output at pin 8 is derived from the A output using an internal inverting stage referenced to the mid-rail voltage. Thus, the overall gain of the circuit is 90 Silicon Chip Fig.1: the circuit of our MIDI Shield. It is broken up into four modules: the MIDI input, MIDI output, audio amplifier and pushbutton matrix interface. You only need to install parts corresponding to the parts you wish to use. Note that our sample software does not make use of the MIDI input (CON4). double the value of the feedback resistor divided by the value of the input resistor. The factor of two is due to the outputs being bridged. VR1 can be used to linearly set the output level from zero (at 0Ω) to fullrail (at 10kΩ). But note that this is limited by the fact that the outputs can only get within 400mV of the power rails. The pushpull outputs mean that the total maximum swing is around 8V peak-to-peak. The complementary push-pull outputs also mean that the quiescent state has both outputs near the mid-rail level, so little (if any) direct current flows through the speaker, and thus no output coupling capacitor is needed. The complementary outputs at pins 5 and 8 are connected to screw termiAustralia’s electronics magazine nal CON5, for wiring up a 4Ω or 8Ω speaker. The SSM2211 can deliver up to 350mA, giving up to 1.5W into a 4Ω load or about 1W into an 8Ω load. MIDI transmitter While the Arduino Leonardo can generate the MIDI signal in software, we need some hardware to feed this to a standard MIDI device, like a synthesiser (which is likely to sound better than our little speaker) or even a USB-MIDI converter for feeding the data to a computer. This is quite simple, as the MIDI interface uses optoisolated connections at the receiver end. We use two 220Ω resistors to connect the 5V supply to pin 4 of 5-pin DIN socket CON3, and the MIDI signal to siliconchip.com.au pin 5. At the receiving end, we expect another 220Ω resistor and an optoisolator with a forward voltage of around 1.5V, giving a nominal 5mA current flow when our micro pin is low during data transmission. Note that the signal from the micro must jump from pin 4 of JP1 to pin 3 to reach CON3. The signal itself is just 31,250 baud serial, easily generated by the Leonardo’s UART peripheral. JP1 allows the signal to be patched in from another pin, if you wish to use the Shield for some other MIDI application. Otherwise, you’d just leave a jumper shorting pins 3 & 4. Note the use of the 5V rail for the return signal. Since the serial idle state is a high level, this means that no current will flow in the loop when data is not being transmitted; the same as in the disconnected state. CON3’s pin 2 and its DIN shield are connected to ground at the transmitter end only, to avoid ground loops. MIDI receiver As alluded to above, the MIDI receiver consists of a 220Ω resistor and an optoisolator connected between pins 4 and 5 of CON4. Diode D1 protects against a reverse voltage which another device might apply. So when pin 4 is a couple of volts higher than pin 5, the internal LED in OPTO1 is forward-biased, and thus its output transistor conducts. The specifications for the 6N138 suggest that under adverse conditions, the propagation delay of the 6N138 could violate the timing requirements of the MIDI signal. But most MIDI designs appear to use this device without any problems. The circuit is compatible with the 6N137 optoisolator, which, as we noted in our Digital Lighting Controller article (October 2020; siliconchip.com. au/Series/351), requires more current to operate, but is much faster. The nominal 5mA loop current is close to the minimum recommended for the 6N137, but should be sufficient under most conditions. In either case, the output side of OPTO1 has power supplied at pins 8 (5V) and 5 (GND), bypassed by a 100nF capacitor. The output, pin 6, is pulled up to 5V by a 1kΩ resistor and is pulled to GND whenever the opto’s LED is forward-biased. This output signal is fed via pins 1 & 2 of JP1 to the Leonardo’s UART RX siliconchip.com.au pin, D1. This can also be patched into another pin if necessary. JP1 also offers the possibility of using the Shield as a MIDI bridge, by placing the jumper across the middle two pins (pins 2 & 3). This will connect the output of OPTO1 to the transmitter at CON3, passing any signal straight through. This might not be much use on its own, but could be used in combination with a connection to the Leonardo’s RX as a MIDI signal monitor or sniffer. Switch & LED Matrix We imagine that most people using our MIDI Encoder will hook it up to a bunch of tactile switches in a matrix to trigger the various notes. You could do this manually, which is the cheapest option, but it would be a lot of repetitive work. So we’ve designed a PCB which breaks out 64 tactile switches to a pair of eight-way headers, which can be directly connected to the headers on the MIDI Shield (or even straight to the Leonardo). We have even incorporated LED wiring so that you can use illuminated switches. We’ve designed the Switch Matrix to fit the larger 12mm footprint switches, as some of these have nice big buttons that are easy on the fingers. We also added footprints to suit small illuminated tactile switches like Jaycar’s SP0620/SP0622 or Altronics’ S1101/S1103. These also suit the typical 6mm tactile switches, for which you might like to add keycaps (eg, 3D printed ones) for a larger key area. If you fit illuminated switches, you can use the separate bank of eight-way headers to interface their internal LEDs. Current-limiting resistors are included for each row. All these embellishments are optional. Since the original aim was to create a MIDI Encoder at minimal cost, nothing is stopping you from buying a bulk lot of simple switches to populate the Switch Matrix. Fig.3 shows the circuit diagram for the Switch Matrix with all parts fitted. The resistors are only needed if you are using illuminated switches. The LED polarity is not fixed by the PCB, but can be changed by rotating the buttons 180° on installation. When the Switch Matrix’s CON1 and CON2 are connected to the MIDI shield’s CON2 and CON1 respectively (all pin 1 to pin 1), pressing S1 will Australia’s electronics magazine trigger the lowest note, S2 the next note and so on. You can swap or reverse the connectors to change this order. The LEDs are similarly wired to CON3 and CON4, although there is no corresponding output on the MIDI shield or Leonardo (since we’ve already used all the Leonardo’s pins). Thus, if you want individual LED control, you’ll need a separate circuit. Later, we’ll describe some sample Arduino code to light up the LEDs using simple timer-based multiplexing. Alternatively, if you just want the LEDs to light up, you could connect all of CON3’s pins to a 5V supply and CON4’s pins to ground (assuming the LED cathodes are towards the top of the PCB). Switch options If you wish to use non-illuminated switches, then you should ensure that they suit the footprints we have used, which measure 6.5mm x 4.5mm for the smaller parts and 12.5mm x 5mm for the larger parts. We recommend using a larger switch with a large actuator surface for easeof-use. The switches are installed on a 16mm pitch, so if you are using separate keycaps, make sure they are smaller than 16x16mm. For illuminated parts, the footprints suit some smaller switches. One critical factor here is to check the LED polarity before fitting. This will depend on the design of your drive circuitry. For our examples, we have assumed that the LED anodes are towards the top (S1S8) of the PCB. Our design assumes that the pins in the corners of the switch are shorted when the button is pressed, and open the rest of the time. Since most switches have pairs of pads connected internally lengthwise, that will typically be the case. Shield construction Before assembling the Shield, decide which set of the four sections you will need. If you are unsure, it’s probably safest to build them all. Note that the MIDI receiver section is not used in our MIDI Encoder software, although we would be inclined to build it anyway, as we think the Shield will be a great way to tinker with MIDI, which you might want to do in the future. Also, you will find it is harder to fit April 2021 91 parts later, especially after the headers are fitted. We will explain the construction procedure as though all parts are to be fitted, but you can omit any you don’t need. Refer now to the Shield PCB overlay diagram, Fig.2, along with the same-size photo, which show which parts go where. Start with IC1, as it is the only surface-mounted part. We chose the SOIC (small outline IC) version as the alternative is a DFN (dual flat no-lead) package, which is a lot harder to solder. We recommend that you have some solder flux paste, tweezers, a magnifier and solder wicking braid on hand for fitting this chip. Check the orientation of the chip; pin 1 goes to the pad nearest the notch on the silkscreen. The chip itself will be marked with a bevel along one edge, which corresponds to the stripe shown on the PCB (best seen from end-on), and also with a dot near pin 1. Apply some flux to IC1’s pads on the PCB and rest the chip in place. Apply a small amount of solder to the tip of the soldering iron and touch it to one pin to tack the IC in place. Check that the IC is flat and square with all pins within their pads. If not, adjust the IC’s position with tweezers while melting the solder on the pin. Once you are happy that it is correctly placed, carefully solder the remaining pins. This can be done by applying a little more flux to the top of the pins and adding some solder to the iron’s tip. Touch the tip of the iron against where each pin meets its pad and the flux should induce a small amount of solder to run into the joint. Don’t worry about solder bridges between pins as long as the IC is correctly placed. Once all the pins are secured, check for bridges with a magnifier. Apply more flux and rest the braid on top of the affected pins. Gently rest the iron on the braid until the solder melts and carefully pull it away from the IC once it draws up excess solder. Clean up any excess flux using the recommended solvent. Isopropyl alcohol works well for most fluxes, although you should take care as it is flammable. Through-hole parts Now you can mount the resistors. Check their values with a multimeter if you are unsure of the colour codes, 92 Silicon Chip Fig.2: use this overlay diagram and the photo above as a guide when assembling the MIDI Shield PCB. Apart from IC1 (which is the amplifier for the speaker), all parts are common through-hole types. While IC1 is an SMD, it can be soldered without any special tools, although we recommend using tweezers and a magnifier. Solder it first so that you aren’t restricted by nearby parts. and match them to the values printed on the silkscreen. Next, fit the capacitors, as shown in Fig.2. There is only one diode, and it must be soldered with its cathode band aligned with the mark on the PCB silkscreen. Trimpot VR1 will only fit in one orientation, but you might need to bend its leads slightly, after which it should snap into place. After soldering its leads, check that it is set near its mid-point, which is a safe default. OPTO1, like IC1, must be orientated correctly. The notch in its body should face towards the centre of the PCB, with pin 1 on the side nearest the (currently vacant) DIN sockets. We used an IC socket so that we could test out a few different optoisolators, but we recommend that you solder it directly to the PCB. Install JP1 and JP2 next, with the jumper shunts inserted to hold the pins in place. They also provide a bit of thermal insulation if you need to manipulate the jumpers while soldering them, although this should be done with care as they can get quite hot. Solder the headers in place, ensuring that they are flat against the PCB and Australia’s electronics magazine straight, then move the jumpers to the default positions shown in Fig.2. Now fit either CON1 or CON1A, and CON2 or CON2A. If you are fitting the screw terminal headers (CON1A and CON2A), ensure that these are orientated with the wire entry holes facing out of the PCB. If you have a collection of shorter terminals, slot them together into a single block using tabs on their ends before soldering them. Mount CON5 next. Like CON1A and CON2A, make sure that the wire entries face the edge of the PCB. Follow with the DIN sockets (CON3 & CON4). They should only fit in one way. Solder one pin and check that they are sitting correctly before soldering the remaining pins. The final parts are the headers used to attach the Shield to the Leonardo board, which are mounted on the underside of the board. The easiest way to manage this is to fit the headers to the Leonardo board, then slot the Shield onto the headers. Check that the PCB is flat and if necessary, trim any long leads on the underside of the Shield that may be preventing it from sitting flat. Then solder each pin from the top side of the PCB. siliconchip.com.au SC Ó l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l l MIDI SHIELD SWITCH MATRIX siliconchip.com.au Fig.3: there isn’t much to the Switch Matrix circuit. Each pin of each connector goes to either a row or column of contacts on the switches or LEDs. Australia’s electronics magazine April 2021 93 Parts list – MIDI Shield 1 double-sided PCB coded 23101211, 69 x 54mm 1 Arduino Leonardo module 2 6-way pin headers (part of the Arduino shield headers) 1 8-way pin header (part of the Arduino shield headers) 1 10-way pin header (part of the Arduino shield headers) Switch matrix interface parts 2 8-way pin headers or sockets (CON1,CON2) OR 2 8-way 3.5mm screw terminals (CON1A,CON2A) [eg, 8 x Altronics P2028] wiring to switch matrix Audio amplifier parts 1 4-8Ω 1W loudspeaker 1 2-way 5/5.08mm-pitch screw terminal (CON5) 1 2-pin header and jumper shunt (JP2) 1 SSM2211 audio amplifier, SOIC-8 (IC1) 3 100nF 63V MKT capacitors 1 10µF through-hole ceramic capacitor (ideally 5.08mm lead pitch) 1 1MΩ 1% 1/4W metal film resistor 1 10kΩ 1% 1/4W metal film resistor 1 1kΩ 1% 1/4W metal film resistor 1 10kΩ mini horizontal trimpot (VR1) MIDI output parts 1 5-pin, 180° DIN socket, right-angle PCB mount (CON3) [eg Jaycar PS0350, Altronics P1188B] 1 4-pin header and jumper shunt (JP1) 2 220Ω 1% 1/4W metal film resistor MIDI input parts 1 5-pin, 180° DIN socket, right-angle PCB mount (CON4) [eg Jaycar PS0350, Altronics P1188B) 1 4-pin header and jumper shunt (JP1) 1 6N138 optoisolator, DIP-8 (OPTO1) 1 1N4148 small signal diode (D1) 1 100nF 63V MKT capacitor 1 1kΩ 1% 1/4W metal film resistor 2 220Ω 1% 1/4W metal film resistors Parts list – 8x8 Switch Matrix 1 double-sided PCB coded 23101212, 131 x 140mm 64 tactile pushbutton switches* (S1-S64) – see text 2 8-way pin headers (CON1,CON2) 16 female-female DuPont jumper leads (to connect CON1 & CON2 to the MIDI Shield) M3 mounting screws and spacers to suit your application (optional) * we used Diptronics DTS-21N-V (non-illuminated, from Mouser) and C&K ILSTA250 30 (illuminated, from Digi-Key). Jaycar SP0620/SP0622 and Altronics S1101/ S1103 are also suitable alternatives. Extra parts for illuminated switches 2 8-way pin headers (CON3,CON4) 16 female-female DuPont jumper leads (for CON3 & CON4) 8 1/4W axial resistors to suit LEDs That completes the construction of the Shield. Switch Matrix construction We recommend fitting the resistors first as they sit lower than the switches, although if you are not using illuminated switches, they are not required. Follow by mounting the switches. If they are illuminated types, choose the 94 Silicon Chip orientation based on your LED wiring needs, and ensure that all LEDs face the same way. If you don’t have illuminated switches, then their orientations won’t matter. Push each switch in place and ensure it is sitting flat before soldering. We’ve slightly oversized the holes to allow for some variation in parts, but the switches should still snap into place. Australia’s electronics magazine One good way of ensuring that they are all aligned is to insert all the buttons, then rest a flat board on top, hold onto this board and the PCB, then flip the assembly over. The flat board will align the tops of the switches. Solder all the terminals to the PCB and trim them if they are long. Finally, fit headers CON1, CON2, CON3 and CON4 as needed. We used socket strips on our prototypes, as we had a handful of pre-made eight-way cables that we could run directly to the headers on the MIDI PCB. We suggest that you figure out how you will be mounting the board (see below) before soldering these, and test-fit the headers/ cables, as that might affect what connectors you need. You could solder ribbon cable straight to the pads on the Switch Matrix PCB and then to the MIDI PCB; that is the cheapest way to connect the two boards. But headers make the wiring removable, which can be handy. If soldering wires to the board, you could run them to the underside of the PCB if you will be mounting it on spacers. If you need those wires to be pluggable, you could mount right-angle pin headers on the underside. Note on our photos that the wire from pin 1 of CON1 on the MIDI PCB goes to pin 1 of CON2 on the Switch Matrix PCB, and pin 1 of CON2 on the MIDI PCB goes to pin 1 of CON1 on the Switch Matrix PCB. Mounting the Switch Matrix Despite the small space available, we’ve squeezed seven M3 mounting holes into the design. Some of these might not be usable depending on the switches you have chosen, although an M3 screw should still fit in the central hole, even with 12mm switches fitted. The PCB material is strong, but repeated flexing from enthusiastic keypresses could fatigue it, so we recommend mounting it to something solid, like a piece of plywood. Use some short spacers or a stack of washers to provide clearance for the component leads under the PCB. Wiring up switches manually If you really want to do it this way, you can. Wire up the switches in rows and columns like in our circuit (see Fig.3). siliconchip.com.au Fig.4: overlay diagram for the Switch Matrix PCB. This is shown with 12mm large nonilluminated tactile switches in place; they fit to the four pads just outside the switch footprint. The next set of four pads are for smaller 6mm switches, while the innermost two pads are for the LEDs of illuminated switches. Most illuminated switches are reversible, so that the LEDs can be installed with either polarity. If you have built the MIDI Shield, connect the rows and columns to CON1 and CON2 respectively, with the ends going to the lowest-numbered switch at pin 1 in each case. If you’re using a bare Leonardo to pass MIDI messages to a computer via USB, you can instead use Fig.1 as a guide for the wiring, as it shows how rows and columns connect to the Arduino pins. You can connect a piezo buzzer between pin D13 and the adjacent GND for sound output, and raw MIDI data is available at pin D1 (TX), referenced to one of the GND pins. Software If you don’t already have the Arduino IDE (integrated development environment) installed on your computer, download it from www.arduino.cc/ en/software (it’s free and available for Windows, Mac and Linux). If you already have the IDE, check that you are using a recent version (at siliconchip.com.au least 1.8.x). We are using version 1.8.12. Launch the IDE and open the Library Manager (Sketch -> Include Libraries -> Manage Libraries) and search to “TimerOne”. This library is used to provide regular timer interrupts to produce the audio waveform. Install it now, if you don’t already have it on your system. The second library we need is called MIDIUSB and can be found by searching for “MIDIUSB” in the Library Manager. The final library is simply called “MIDI Library”. Several different libraries are found in a search for “midi”, so you should see our screenshot (Screen1) to verify that you have found the correct library. We have also included the zipped versions of all three libraries in our download package, which you can install via the Sketch -> Include Library -> Add Zip Library menu option. MIDI Library is set up to use the hardware serial port on the Leonardo’s pins D0 and D1, with the MIDI data Australia’s electronics magazine being produced at the TX pin, D1. We tested this with an Arduino synthesiser sketch, and it worked as expected. Once all the libraries are installed, open the ‘MIDI_ENCODER’ sketch. Select the serial port of the Leonardo and upload the sketch to the Leonardo. In our sketch, the SAMPLE_RATE define is set to an integer number of microseconds between interrupts (to minimise rounding errors). This is followed by the sinewave data, as 256 unsigned integer bytes (0-255). The matrix pin definitions follow this. The rows each contribute a multiple of +8 to the key number, while the columns contribute +1. The key count thus spans zero to 63, and is offset by the START_NOTE value, which we’ve set to 28. That means that the MIDI Encoder will produce notes from E1 (about 41Hz) up to G6 (1568Hz), centred near middle C (262Hz). The range is limited to 64 notes by the size of the matrix, but changing April 2021 95 At left is the non-illuminated version of the Switch Matrix, at right the rear of the illuminated version; note the extra leads, tapped standoffs and CON3 and CON4 fitted at the bottom. These are shown about 3/4 life size. The actual PCB size is 131 x 140mm. the start note changes where that range spans. The notes[] array sets the frequencies that are produced on pin D13. You might want to tweak these if they don’t sound right or you prefer a different scale. Some parameters associated with the library follow. These set the channel and velocity that are used in the data that is sent. The defaults should work with most software, although some programs might map channel 0 (in the Arduino code) to channel 1. Testing the Shield At this stage, you should have built the Shield, plugged it into the already programmed Arduino Leonardo and attached the Switch Matrix (or whatever switches you will be using). Plug the Leonardo into a USB port, launch the Arduino IDE (if it isn’t already running), make sure the correct COM port is still selected, then open the Arduino Serial Monitor. Start pressing buttons in the matrix, one at a time. You should see the Serial Monitor report that S1 causes UP/ DOWN actions on MIDI note 0. This is because we’ve started the switch numbering at 1, but the MIDI notes begin at 0. 96 Silicon Chip If you check that the four corner keys are correct (the switch number is one more than the note number), then the remaining keys are probably correct. If you find that you get incorrect notes, try flipping the connections end for end at CON1 or CON2 on the Switch Matrix PCB, or swapping CON1 for CON2. Test all the keys; if you see any single keypresses not being detected, check the PCB for bad solder joins on the corresponding switch. Usage After the sketch is uploaded, the Leonardo appears as a native USB-MIDI device to a computer. As well as the audio and USB and hardware MIDI outputs, the Leonardo also prints information to the serial monitor (accessible from the Leonardo’s native USB-serial port) about which note is being played. This can be handy for testing. We used a program called MuseScore (https://musescore.org/en) to test that the computer was correctly receiving MIDI data. It automatically detected that a MIDI device was present and played synthesised piano sounds, although it can also transcribe to played notes among other features. Australia’s electronics magazine Without a computer, you will have to connect something to the audio output (on pin 13) or the hardware MIDI data (on pin 1). As we noted, we tested another Arduino sketch which worked as a synthesiser (this sketch expects MIDI data on the Arduino’s serial port; typically pin 0). This might be a better option if you would like to get better sounds without much expense. Note that it is possible to trigger sounds from the Shield using simple jumper wires. Anything that connects one of the row wires to one of the column wires will trigger a sound. Using something like the cheap membrane matrix keypads could be a simple way of adding an input device, especially if you want to create percussion sounds. Four of the 4x4 matrixes could be connected to give the full complement of 64 inputs. Just make sure to wire up each matrix to a different combination of row and column wires. Of course, since we’ve included the Arduino source, code, you can use it as a starting point for creating your own MIDI-based project. LED test sketch We have created a test Arduino sketch to light the LEDs if you have siliconchip.com.au fitted illuminated switches. We’re assuming that you’ve fitted them with the anodes to the top, as we did on our prototype. We also assume that you’ve got the Arduino IDE installed, including the libraries for the MIDI Encoder. We only need the TimerOne library for this sketch. Open the “MATRIX_LED_DRIVER” sketch and upload it to the Leonardo. Connect CON3 of the Switch Matrix PCB to CON2 on the MIDI Encoder. Then connect CON4 of the Switch Matrix PCB to CON1 on the MIDI Encoder. You should see a diagonal row of LEDs light up. You can change the starting state with the LED[] array, and manipulate this in the loop() function to animate. We’ve also created a self animating version ‘MATRIX_LED_DRIVER_GOL’, which implements a simple “Conway’s Game of Life” simulation on the 8x8 matrix. The array is loaded with a pair of ‘gliders’, which move as long the Matrix is powered. You can find out more at https:// en.wikipedia.org/wiki/Conway%27s_ Game_of_Life Using it If you’ve built the amplifier section, now would be a good time to wire up a speaker. Generally, a short length of twin-core cable is all you need to wire it up, and most speakers have tabs that suit soldering or quick-connect spade The MIDI Encoder Shield PCB simply slots onto the Leonardo board using header pins. Our build shows all parts fitted except for the headers CON1 and CON2. This is because screw terminals CON1A and CON2A are fitted instead. There’s no point fitting stackable headers as practically all of the Leonardo’s pins are used up. lugs. The other ends of the wires can then be screwed into CON5. The polarity doesn’t matter much as the output at CON5 is AC. With the MIDI Encoder sketch uploaded to your Leonardo, you should be able to get a tone from the speaker by connecting any of CON1’s pads to any of CON2’s pads (eg, by pressing a button on the attached key matrix). However, we found that our small speaker was not able to render the lower notes too loudly. If the audio is distorted, reduce the volume by turning VR1 anti-clockwise. The mid-point should be audible for practically all speakers, so if you can’t hear anything, check your construction before increasing the volume. The MIDI output socket (CON3) can be connected to the MIDI input port of another device, such as an electronic piano or DAW (digital audio workstation). Similarly, the MIDI input connection (CON4) can be driven from another device’s MIDI output port. Note that CON4 does not do anything with our default software, as it is not programmed to have any function. Conclusion While originally intended as a simple bit of hardware to make better use of the MIDI Encoder software, we think that this Shield will be handy for anyone who wants to dabble in custom MIDI hardware. Screen1: the Arduino Library Manager will give a lot of results for a ‘midi’ search, so use the one highlighted here or use the zip version. siliconchip.com.au Australia’s electronics magazine April 2021 97 This is the deluxe version of the matrix PCB, with illuminated switches, although you’ll have to provide your own keycaps (this might be a good use for that 3D printer!). We’ve fitted it with standoffs to prevent the pointy leads from damaging the surface it’s on or, conversely, shorting out on any conductive surface. Note the Shield PCB at left fitted with only headers to allow it to be used as a USB MIDI device only. It could, for example, be used as a MIDI synthesiser by using the hardware MIDI input (CON4) or USB MIDI input (in software) to receive MIDI messages and turn them into sounds from the speaker. In a follow-up article, we will show how to control illuminated pushbuttons from our MIDI sketch. This requires some extra hardware, as the Leonardo doesn’t have enough pins free to do this by itself. We will also describe how to connect this device to a smartphone or 98 Silicon Chip tablet running Android, and install a MIDI synthesiser app which can then be controlled using the Key Matrix. We also intend for this article to contain some more detailed information on the MIDI protocol, for those who wish to expand upon our software, or are just interested to learn how it works. Note that the Switch Matrix presented here could be useful in many other contexts; it doesn’t have to be used for MIDI. It can serve as a general-purpose Australia’s electronics magazine switch array with up to eight rows and eight columns; you don’t even need to populate all the switches. For example, you could wire up the row and column headers to an Arduino Mega board (or similar) and use it as a general keyboard, to type in letters and numbers etc (with suitably labelled keycaps). And as the Mega has many more pins than the Leonardo, it could also easily drive the LED matrix to light up keys as they are typed, show which keys are SC valid inputs etc. siliconchip.com.au PRODUCT SHOWCASE Microchip’s first PIC32C microcontroller If your design has outgrown the capabilities of one of the 8- or 16-bit micros, the PIC32C family (siliconchip.com. au/link/ab78) delivers easy scalability, enhanced performance and larger memory options while still being part of the MPLAB development ecosystem. The first of the PIC32C families, the PIC32CM MC, combines the performance and energy efficiency of an Arm Cortex-M0+ based micro with an optimised architecture and powerful peripherals. These 5V micros are ideal for motor/industrial control, home appliances, and other 5V applications. Key features include: • CPU clock speed up to 48MHz. • Up to 128KB embedded flash memory and 16KB of SRAM. • Operating voltage of 2.7-5.5V, which ensures the best possible SNR and noise immunity, EMC, ESD and latch up. • Dual 12-bit simultaneous sampling ADCs. • Positional decoder for motor control. • Timer/counter for control peripheral provides dedicated timers for industrial and motor control. • Four serial communication modules that can be configured to act as a USART, UART, SPI, I2C, RS485 or LIN bus interface. • 12-channel direct memory access controller with CRC module. • Functional pin compatibility with current SAM C20 devices in 32and 48-pin packages. Microchip Technology Inc. Unit 32, 41 Rawson Street Epping 2121 NSW Tel: (02) 9868 6733 www.microchip.com New analog products from Maxim provide double the battery life The MAX41400 (https://bit.ly/ MAX41400 Product) instrumentation amplifier enhances sensor system accuracy by four times and extends battery life by 55% compared to the closest competitive offering. The MAX41400 provides low offset of 25µV, low noise and programmable gain with only 65µA current consumption. The MAX40108 (https://bit.ly/ MAX40108 Product) is the lowestvoltage precision opamp in its class, operating with supplies as low as 0.9V. The combination of low operational supply voltage, lower power consumption and 25.5µA quiescent current allows engineers to double sensor battery life. The MAX31343 (https://bit.ly/ MAX31343 Product) I2C RTC with integrated MEMS oscillator provides timekeeping accuracy of ±5ppm, substantially better than the closest competitor, plus robust protection afforded by a MEMS resonator. With its integrated resonator, the MAX31343 eliminates crystal me- chanical failures and enables the smallest WLP compared to any other competitor in the market. All these products are offered with multiple and small form factor package choices. Maxim Integrated 160 Rio Robles San Jose, CA 95134 USA www.maximintegrated.com New APEM Q25 & Q30 series LED indicators The Q25 and Q30 series LED indicators use a PCB with 6 SMT chips and built-in failsafe protection. A molded Fresnel lens scatters the LED light to give that all-round illumination making long distance and daylight viewing crystal clear. This series is suitable for material handling or off-highway vehicles where reverse and over voltage protection is required. It also comes with low heat generation suitable for mounting into heat sensitive plastics. The chamsiliconchip.com.au gered bezel is made from 316L marine grade stainless steel and is IP67 and IP69K front panel sealed. Control Devices is the official APEM distributor for Australia and New Zealand. Control Devices Unit 17, 69 O’Riordan Street Alexandria, NSW 2015 Phone: (02) 9930 1700 Web: www.controldevices.com.au Mail: sales<at>controldevices.net Australia’s electronics magazine April 2021 99 Review by Tim Blythman Cordless Soldering Iron & Heatshrink kit It’s remarkable how far battery technology has come over the years. More and more devices that previously would have used some other power source have now become practical to run from battery power. W agner Electronics loaned us their new Cordless Soldering Iron Kit, and we found it to be a handy item that could well replace a gas-powered soldering iron. The Cordless Soldering Iron comes as a Soldering Iron and Heatshrink kit, available as Cat SI50HSK from www. wagneronline.com.au, with a current RRP of $139. There are also numerous different tips available, in addition to those that come in the kit. The kit gives you a good set of mid-level tools, and would make an excellent portable standby kit. But it would also be quite adequate as a primary soldering tool. The Iron itself measures 160mm long and 28mm in diameter. Roughly cylindrical, the grip is moulded rubber and quite comfortable to hold. The kit includes three interchangeable tips. There is a 30W 4mm conical tip, a 50W 6mm conical tip and 30W radiant heatshrink tip. An assortment of smaller diameter pieces of heatshrink is included. The kit comes with a protective cap for the Iron (which fits even with a tip installed), a USB-A to micro-USB charging cable and a small punched metal stand. All the parts are supplied in a simple plastic case with internal dividers. A micro-USB socket at one end of the tool is used for charging, with a clearly marked ON-OFF switch at the other end near the grip. The switch needs to be slid and a button held in to turn the Iron on, so there’s little chance of it being left on inadvertently, even when resting on the button. The cap also forces the switch off when it is fitted – a thoughtful design touch. There is a small white LED near the tip which lights up whenever the button is pressed. It doesn’t quite illuminate the tip, so it is not very useful. You would be in a tough situation if you had to rely on this light to illuminate your work. While the Iron’s hot! With a prototype PCB to be assembled, we dove in to try it out. The PCB in question measures 123mm x 58mm and hosts nearly all throughhole parts; around 100 joints to solder. We didn’t try the Iron on the surface-mounted parts as the smallest included tip is too large. We used the smaller 30W tip, and as specified, the Iron takes about 10 seconds to come up to working temperature and holds the heat quite well. For most parts, it was sufficient to simply give the Iron a short burst of power while applying solder. Apart from the heat-up time after leaving the Iron idle, it felt no different to using a regular iron. The large tip is probably overkill for this sort of work; there is also a smaller 12W tip Inside the SI50HSK Iron is a single 2400mAh Li-ion cell which will give up to 45 minutes of continuous use. For normal (intermittent) soldering use you could expect several hours of operation. 100 Silicon Chip Australia’s electronics magazine siliconchip.com.au (Right): this kit includes a storage case, main heating tool body with two cone-shaped soldering tips, a heat radiator tip with focusing sleeve for heatshrink and a micro-USB charging cable (charger itself is optional). In addition, there are 200 pieces of 45mm long, red, blue, yellow and black heatshrink tube in diameters of 2.2mm, 3.5mm, 4.5mm and 7mm. The SI50HSK can be recharged from an USB outlet with the USB cord included, but Wagner also offer an optional mains USB charger if required. available and a finer 30W tip. If we were purchasing this kit for our own use, we would undoubtedly pick up those two as well. The shape is well-thought-out. It’s uniformly cylindrical enough that whichever way it sits, the tip won’t touch a flat work surface, while the moulded grip means that it won’t roll away. In short, we had no problem simply putting it down between uses. In use, the Iron feels well-balanced and sturdy. We tried the small stand, and though simple, it was effective. But we didn’t find it necessary. The battery life is listed at 45 minutes of continuous operation, so it could be expected to last for hours with intermittent use. We certainly didn’t have any trouble with it going flat during our testing. Each tip has a good-sized plastic collar which allows the tip to be handled, even while hot. The collar is wide enough that the tip can balance on it, so there’s no need to worry about where to rest it. We also tried the heatshrink tip. Those readers of a certain age might be reminded of an item that was once a feature of most cars; the electric cigarette lighter. The heatshrink tip is much like one of these, glowing red when turned on. The heatshrink tip worked well on small pieces of heatshrink, but it was not as quick as something like a hotair gun would be. This tip’s radiant nature means it’s not quite as easy to aim and use as a hot-air gun. We did get that sense of something smelling a bit burnt, so the heat appears to be quite concentrated too. A small shroud that fits on the heatshrink tip is included. Working with heatshrink is probably where a gas iron would win out, although the battery Iron is certainly adequate. Accessories A range of fourteen spare tips is available; they are each around $20. There are six different soldering tips (including the two included in the Iron kit) and tips for cutting plastic, pyrography (wood-burning) and styrofoam forming. The heatshrink tip is also available as a spare part. Wagner Electronics also offers a suitable AC-USB adapter for charging purposes. Verdict As the kit comes, it is well-suited to replacing a gas soldering iron. There’s certainly enough heat and runtime to handle most of those jobs you would use a gas iron for. And USB power is convenient and ubiquitous enough to allow the Iron to be topped up as needed. It would make a good emergency standby tool. It’s handy enough that it could become a replacement for a mains-powered iron if space is at a premium, unless you’re the type who is running the iron for hours on end. It does end up being a bit more expensive than similar gas irons, but has the advantage of being usable where flames or flammable substances are prohibited. And you avoid the fiddly refilling process that gas irons require. For more information, or to purchase the kit and possibly some extra tips, go to http://siliconchip.com.au/ link/ab71 (Wagner’s online shop page for this product). SC In addition to the seven soldering iron tips, Wagner also offer a range of tips for other hobby applications (as shown here). siliconchip.com.au Australia’s electronics magazine April 2021 101 Vintage Radio Philips Philips 1948 1948 table table model model 114K 114K By Associate Professor Graham Parslow The 114K radio is one set in a series of similar radios made by Philips, and was among the last alloctal radio designs, due to decreasing stock in the post WW2 era. The radio is otherwise a fairly standard six valve superhet, but weighs in at a hefty 12kg. For 12 years, this radio sat in my storage shed because I considered it an ugly duckling, but events conspired to change my opinion recently. So I got it out of storage to see if I could clean it up. I purchased this radio in a lot with other radios which I was more interested in. Recently, a friend who worked for Philips some time ago told me that one of his managers used this model of radio at his house, and took great pride in having it. That started me wondering if I had judged it unreasonably. The COVID-19 lockdown inspired me to look at my back shelf for a project. Hence, a large grubby radio entered my restoration queue, emerging resplendent, and much elevated in my estimation. 1948 was three years after the end of the Second World War, and radio manufacturers were slowly exhausting stocks of large 8-pin octal valves before 102 Silicon Chip moving to 7-pin and 9-pin miniature valves. At that time, many radios used a mixed lineup of octal and miniature valves to best utilise their inventory. The model 114K is among the last of the all-octal radios. It is also among the last of the multiple timber veneer cabinets. Through the 1950s, almost all timber cabinets were simplified to single veneers (usually stained), and cabinets were changed to easily fabricated shapes; mostly rectangular. The model 114K is a heavyweight table radio at 12.2kg, measuring 560mm wide, 245mm deep and 360mm high. It has an eight-inch Rola permanent magnet speaker (type 8K) that produces excellent sound from the baffle provided by the substantial cabinet. That sound is also optimised by circuitry that is consistent with a premium radio. The 114K sold for £46/17s/00d, more than double the price of conAustralia’s electronics magazine temporary Bakelite kitchen radios, which were usually in the range of 15-20 pounds (£). Unusual design This radio conforms in style to a series of late-1940s Philips radios with the dial mounted at the top. As the premier model, this dial articulates so it can be laid flat for moving the radio. On lesser models, the glass dial was fixed, although it could be removed and slotted back in. The advertising angle to promote this set was that while others fill the front with a dial and a small speaker, Philips builds in a large unobstructed speaker and puts the dial on top. If you are unconvinced, then you have good grounds, because this was not a good idea. One indicator is that other manufacturers did not follow. The yellow screen-printed station information is difficult to read without siliconchip.com.au Shown here is the underside of the chassis before restoration. The components with green-sleeved leads had already been replaced by a previous owner. a black background, and the printing is easily damaged or eroded while cleaning. Exposed at the top of the cabinet, a large number of those dials were broken by misadventure. Philips realised the downsides to this design, and moved their dials to the main face in the 1950s. A brief history of Philips Philips began their rise to become electronic industry leaders after founding a light globe business in Holland in 1891. A light globe can be frivolously referred to as a “monode”, but it did not take Philips long to add electrodes to the envelope and create a range of thermionic valves. The edge that Philips initially enjoyed with their Miniwatt range was the high emission efficiency they achieved at lower filament current than their competitors; a crucial advantage for battery operation. By 1933, Philips had manufactured 100 million valves and led the world in quantity and quality. Valves with an E prefix (eg, ECH and EL) follow European designations. Philips made these valves in Europe and at Hendon in Adelaide for the Australian market. The mixer valve in this radio is an ECH35, released in Europe in 1939. The red-painted opaque envelope on an ECH35 covers a metallic coating that acts as an RF shield while the primary grid is connected via a top-cap. The photo of the top of the chassis shows the uncramped layout of this large radio; all the components follow a linear arrangement by function. The speaker and output transformer connects to the octal socket adjacent to the power transformer. Circuit details The radio tunes two bands, 5301620kHz (medium wave [MW], AM broadcast band) and 5.9-18.4MHz (shortwave [SW]). The RF input is from a conventional external aerial with L1-2 tuning MW and L3-4 tuning shortwave. The aerial coil is in the indented can that is seen at the far left in the rear view of the chassis (page 106). These indented cans are an immediate give away of manufacture by Philips. C47 (5pF) is included to improve the aerial transformer’s primary-secondary coupling towards the top end of the MW The top view of the chassis shows an empty octal socket next to the power transformer. The output transformer plugs into this, as does the speaker (for feedback and Earthing). siliconchip.com.au Australia’s electronics magazine April 2021 103 The Philips ECH35 is painted red to cover its metallic coating which acts as an RF shield. Mullard also made these valves. Source: frank.pocnet. net/sheetsE1.html This table (from the service manual) shows what each valve in the set does. band, so there is a balanced sensitivity across the MW spectrum. Band change switch A1 has a third position to select pick-up from a twohole socket at the rear of the set, while also disconnecting the radio signal from the output. Overall, the circuitry around the ECH35 mixer valve has no surprises beyond featuring only a two-gang tuning capacitor in a six-valve radio. The tuning capacitor is full-sized in this radio, slightly ahead of the introduction of much smaller brass-plate capacitors used by Philips through the 1950s. The local oscillator (inductors L6–9) has two sections configured as Armstrong oscillators to provide the 104 Silicon Chip heterodyne signal that generates the 455kHz intermediate frequency (IF) difference signal. The local oscillator coils are housed in an indented can, identical to the aerial coils, and mounted adjacent to the tuning capacitor and aerial coils above the chassis. Instead of featuring an RF preamplifier stage, this radio has two IF amplifier stages that also increase its gain and selectivity. The IF amplifier stages cascade two 6K7GT valves; or at least, these were the types installed at manufacture. GT types have glass envelopes in a tubular shape (hence “GT”) that can be fitted with a cheap cylindrical metal shield. However, the second IF amplifier in this radio was a replacement type Australia's Australia’s electronics magazine 6K7G (not GT) that has the classic larger shouldered valve profile. The original GT type shield had been deformed to shroud the larger valve. It looks odd, but it works. The first IF transformer is not a standard IF transformer, because L11 is connected to the grid of V3 when switch B1 is set to select “expanded IF high fidelity”. The effect of L11 is to broaden the bandwidth passed by the IF transformer, so higher audio frequencies are less attenuated. Valve V4 (6SQ7) has two diodes providing negative AGC voltages which are fed to V1 via R15 (2MW) and to V2 via R16 (100kW). Splitting the AGC line in this way is unusual, but achieves optimum gain control. siliconchip.com.au The underside of the chassis after restoration. The rubber insulation on the valve top-cap connectors had to be replaced, along with several damaged wires. A few resistors and capacitors were also changed, as they were out of tolerance. The audio signal passes from the 6SQ7 triode through resistor R21 to switch A1, which then routes it back to volume control potentiometer R20 (500kW) unless the switch is set to select the external pick-up. R20 features a fixed tap with additional components to strengthen bass frequencies. In addition to “high fidelity”, the three-position tone control switch B1 offers two top-cut positions using C39 (6nF) or C40 (50nF). For a top-shelf radio, it is unusual to see such a simple set of choices for tone, but the circuitry ensures that the three options focus on optimising listening for the broadcast content. This optimisation includes frequencyfiltered negative feedback from the speaker (L20, connection #4). The well-established 6V6 beamtetrode (V5) completes the circuit for audio amplification. The 6V6 cathode is connected to the chassis so the grid bias, specified as -13V, is generated by R24 (35W) and R26 (150W). HT power rectifier V6 is a 6X5 with an indirectly-heated cathode. This radio generates over 300V between the 6X5 cathode and filament. In radios manufactured earlier than 1948, the most common valve in this application was a 5Y3 that had a 5V filament which also served as the cathode. It took some time to find an efficient way to isolate a cathode from arcing to a nearby heating filament. Radio construction An odd feature of all the tuned circuits in the IF section is the absence of tuning slugs in the inductors to align the set to 455kHz. Fine-tuning is instead achieved by cheap wire-wrapped stick capacitors that are inconvenient to work on after leaving the factory. Not to mention that some are at lethal high tension. Thankfully, the radio worked well as received, so I didn’t need to alter the alignment. Some Philips models of this era are notorious for being unstable due to stray capacitance. The IF stages in this radio have additional shielding under the chassis, and I have taken two under-chassis photos, one with the shield cover plate removed and one with it installed. Restoration – the cabinet The circuit diagram for the Philips 114K radio. The circuit doesn’t have any component value labels, so the parts list scanned from the AORSM is reproduced here. siliconchip.com.au Australia’s electronics magazine Restoring a timber cabinet will always take several days for completion, so it is logical to start on the case and perform electrical troubleshooting in parallel. Developed through the 1920s, the original finish was nitrocellulose. This starts with glossy clarity, but slowly decomposes to produce brown oxides of nitrogen trapped within the nitrocellulose matrix. The result is mellow golden hues that are April 2021 105 This rear chassis shot shows the size of the Rola speaker. The dial lamps were initially installed with incorrect orientation, this was fixed in the image below. often valued in vintage musical instruments. Spraying contemporary polyurethane finishes over nitrocellulose commonly produces an undesirable reaction resembling heat blistering. This is because nitrocellulose and its degradation products are chemically related to the polyols that react with isocyanates to create polyurethane. The only way to avoid this is to completely remove the nitrocellulose and start with bare timber before applying polyurethane. This radio was re-finished with satin spray-Cabothane purchased at Bunnings. Paint stripper, metal scrapers, heat guns and abrasives are all possible approaches to removing nitrocellulose. In this case, I used P40 coarse garnet paper. I have found the coarse grit resists fouling with the abraded material, so it is reasonably economical with the consumables. However, the use of P40 abrasive does require care to stop penetrating the veneer and exposing the base ply below. The top side of the chassis with the valves seated and dial lamps placed in their correct locations. There are a few radios in the 114 series from Philips; most of the differences are minor circuit and cabinet alterations. 106 Silicon Chip Australia’s electronics magazine Another requisite is to work only with the timber grain and not cut across it. Although the timber surface is left somewhat rough after P40 abrasives, there is no need to sand with finer grades because that is best done after stabilising the surface with two coats of polyurethane. I use P400 silica abrasive to sand back between finishing coats (three finishing coats in this restoration). Another part of this restoration was restringing the broken tuning system. It turned out to be less intuitive than it looked, and the photo of the front of the chassis shows the result. That photo also shows two dial globes that were installed to replace the blown original globes. At first I believed that the original globes were captive in the Bakelite mouldings at the side of the dial, however they are behind clip-on covers that can be prised off by a small blade inserted into the joint. A reproduction dial was purchased to complete the cabinet. The original dial with partly erased printing is shown in the photograph to the left. Restoration – electrical The rubber insulation on the valve top-cap connectors was badly perished, as were several links below the chassis. After replacing this wiring, it was time to check the transformer without valves installed. At switch-on, the transformer dissipated 20W, rising rapidly to 200W. Fortunately, a replacement transformer was at hand. Some components sleeved with green tubing had been previously replaced. After replacing some additional out-of-tolerance resistors and some dubious capacitors, switch-on was disappointing – it did nothing. The radio was only consuming 20W, and the HT from the 6X5 rectifier was a mere 145V. A replacement 6X5 was the answer to bring the HT rail up to the expected value. A signal injected to the 6V6 output grid produced audio, but nothing when a signal was applied to the grid of the 6SQ7. The 6SQ7 had an open-circuit filament; replacing it led to a functioning radio, drawing 41W. This proved to be a satisfying project in all aspects of the restoration. A bonus, by analogy to George Orwell’s novel 1984, was that I came to love Big Brother. SC siliconchip.com.au ASK SILICON CHIP Got a technical problem? Can’t understand a piece of jargon or some technical principle? Drop us a line and we’ll answer your question. Send your email to silicon<at>siliconchip.com.au Battery Balancer Mosfet inverter/driver query I would like to raise a potential problem with the use of the N- & P-channel Mosfets in the QS6M4 device as a complementary pair in the design of the High-Current Four Battery/Cell Balancer (March & April 2021; siliconchip.com.au/ Series/358). They are connected back-to-back across the 3.3V supply, so the only resistance in the circuit is the devices themselves. The N-channel gate threshold is 0.5-1.5V, while the P-channel is -0.7 to -2V. So potentially, from 0.5V to 2.6V (3.3V − 0.7V), both transistors are on. At -1.5V, the P-channel RDS(on) is 0.155W, and at 1.5V, the N-channel RDS(on) is 0.17W. So, if you simplistically apply V = IR, you get I = 10.15A = 3.3V ÷ (0.155W + 0.17W). The maximum pulsed drain current for both devices is 6A. You limited the surge current through Q11a/b into Q10 with a 1W resistor. I’m wondering if the complimentary pair should have similar protection, even though the ‘both on’ time is short. Could it shorten the life of the QS6M4 otherwise? (D. H., St. Ives, NSW) • Duraid responds: I spent considerable time validating the use of these Mosfet pairs during the design phase. Shoot-through currents in a CMOS inverter are a concern, especially at higher temperatures where the gatesource on-thresholds start creeping down. The 0.155W/0.17W resistance values quoted are for devices that are well and truly on. Resistances around the 1.65 (Vdd ÷ 2) point are nearly an order of magnitude higher, especially for the PMOS section. Keep in mind that the gate threshold voltages quoted are typically for channel current flows of around 1mA, not the many amps that the devices are capable of with higher gate-source voltages. At these low gate voltages, it’s thersiliconchip.com.au mal degradation that you need to be careful to avoid. These parts claim to be able to tolerate 1W, so long as thermal limits are observed. During the design phase, I ran some simulations which showed an order-of-magnitude headroom to this limit, and significant thermal headroom, even allowing for the fact that these parts are quite near the inductors/power FETs. So to summarise, you do have to be careful using Mosfet pairs as inverters like this, but we have verified that these particular parts are suitable in this configuration. Sourcing LM5163 for Battery Multi Logger The LM5163DDAR buck converter (regulator) IC used in the Battery Multi-Logger seems to be in short supply. Digi-Key and Mouser are both quoting a seven month lead time. Do you know of an alternate supplier or device? (R. M., Paynesville, Vic) • You can use the automotive version, which is identical to the part we specified, just a bit more expensive: LM5163QDDARQ1 or LM5163HQDDARQ1. It is in stock at both Digi-Key and Mouser. Reed relays are underrated for 1A PSU I am reading my way through the February 2021 issue of Silicon Chip. I have a couple of comments about the article on the Arduino-based Adjustable Power Supply, starting on page 38 (siliconchip.com.au/Series/357). There is no back-EMF diode across the coil of the reed relay. Surely one is required to prevent damage to the Arduino pin. Also, both the Altronics and the Jaycar reed relays have a contact rating of 0.5A. So rating the power supply at 1A and expecting the relay to make and break that current is not a good idea. My experience is that reed relays will tend to stick closed if overloaded. I note Jaycar do sell a reed relay with Australia’s electronics magazine 1A rated contacts, Cat SY4036. Altronics don’t seem to have any 1A-rated reed relays. Finally, I am looking forward to reading the article on the computer upgrade. It is good to have this as I am interested in learning of the potential ‘snags’ when doing so. (D. W., Hornsby, NSW) • Regarding the relay coil, since the Arduino pin is pulled to ground and effectively shorts the coil terminals when switching it off, there is no opportunity for a high-voltage spike as would occur if the circuit were simply opened. The circulating current decays via the driving pin, so it never goes above the coil operating current. We have never seen this sort of arrangement fail. It’s when you have an open-collector or open-drain relay coil driving arrangement that the back-EMF quenching diode is needed. You are probably right about the Jaycar/Altronics relays being slightly underrated for this project. We have used similar relays in the past rated to break 1A, but as you point out, the ones we specified are only rated to carry 1A. Fortunately, these relays have a quite high (100V) voltage limit, and the current limit can be set in the PSU to provide an extra degree of protection. Oddly, the Altronics Cat S4100 & Cat S4101A relays have a rated switching current of 1A but are described as “0.5A 5VDC SPST DIP PCB Mount Reed Relay”. We aren’t sure if that is a mistake, or if they can actually break a higher current than they are rated to carry continuously. Panel meters fail when used with inverters After reading Jim Rowe’s review of mains panel meters (December 2020; siliconchip.com.au/Article/14678), I bought a PZEM-051 panel meter to fit to a portable power supply. This consists of two deep-cycle AGM batteries wired in series with provision to connect up to three 24V DC to 230V AC inverters. Two of the inverters are April 2021 107 modified square wave types, while one is a pure sinewave type. The panel meter immediately failed. After checking the wiring carefully, I removed the back and checked for signs of faulty components. Q1 (a 600V Mosfet) looked stressed. Tiny globules of solder were stuck to the Mosfet and the adjacent PCB. When power was again applied, the Mosfet became too hot to touch within seconds. I contacted the supplier, who eventually advised that the meter was not designed for use with inverters, although there was no information about this in the supplied instructions. Is it possible to fit a transient voltage suppressor across the 24V power supply to a new meter to prevent another failure? The Jaycar Cat ZR1152 TVS looks good. I might have to fit two in series to prevent premature tripping, though. Any suggestions you can provide will be much appreciated. (I. M. P., Fullarton, SA) • The waveform from an inverter, especially a modified square wave type, has much greater harmonic content than a normal mains waveform, so we are not surprised that this could damage a low-cost panel meter. Adding a TVS across the DC side of the inverter probably won’t help, as it is likely the spikes and steps in the ‘230V AC’ waveform that are causing the damage. You would need to filter that waveform before feeding it to the panel meter(s). However, finding a filter that will remove enough harmonic content to keep the panel meters safe, without damaging the filter itself, might not be easy. We suggest that you try using this Jaycar EMI filter (Cat MS4001) between each inverter’s output and the panel meters/outputs. How much to build the USB SuperCodec Can you give me an approximate costing for parts to build the USB SuperCodec (August-October 2020; siliconchip.com.au/Series/349)? (R. P., Tea Gardens, NSW) • Phil Prosser added up what he paid for all the parts to build the prototype, and came up with a figure of $439.28, including the power supply and case, but not including the PCB, for which we charge $12.50 plus delivery costs. Not bad, we think, considering the resulting performance. 108 Silicon Chip High Power Ultrasonic Cleaner not working I have built the High Power Ultrasonic Cleaner (September & October 2020; siliconchip.com.au/Series/350), but I am having trouble getting it to work correctly. After setting it up, I switched on the unit and checked the 5V volt supply at IC1 and IC2. I got a reading of 5.04V. I then filled the bath with 3.5L of water, switched it on and tried to calibrate it. The 25% and 50% LEDs gave a brief flash, then the run LED lit up, but the unit would only run at 10% power. I checked the connections to the transducer; they all appear OK. I initiated the diagnostic mode and could only get a maximum reading of 2V at TP1. I rewound the transformer, adding an extra layer of 28 turns. This time, when calibrating, the 25% LED stays on, and the 50% LED pulses every two seconds. After approximately two minutes, the run LED lights up, but it will only operate at 25% power. In diagnostic mode, I now get a maximum reading of 4.8V, at which time the unit goes into current overload. I tried altering the quantity of water in the bath, to no effect. I removed ten turns/windings from the transformer. This dropped the maximum voltage reading on TP1 to 3.7V, but made no change to the calibration or running of the unit. Do you have any ideas? (P. H., Mosgiel, New Zealand) • It sounds like the transducer resonance point is not being found. Try running the diagnostics and sweeping the frequencies manually to find the maximum current by measuring the voltage at TP1. If this voltage goes over the 4.8V maximum, reduce the number of secondary turns on the transformer. The number of turns needs to be such that the current limit isn’t reached at resonance. This is the only way to find the transducer resonance frequency correctly. Then the cleaner should then run correctly, and you can achieve the ultimate power by altering the transformer secondary windings, which should be within a few turns of the ideal number once you are reaching resonance without overloading it. Tapped transformers with 45V Bench Supply I have just ordered the parts and PCB Australia’s electronics magazine to build your 45V 8A Linear Bench Supply (October-December 2019; siliconchip.com.au/Series/339). The circuit design looks good to me, but I’d like to make a few modifications to reduce heat dissipation for my use. I built a number of the older ETI-163 supplies many years ago. That design used multiple winding on the transformer, switching them in series as the rotary potentiometer was rotated on the front panel. Is there a reason why you didn’t use a similar approach for your supply? I designed my own version using three separate 14V 10A transformers switched to series or parallel combinations. I chose 14V as those combinations are a few volts above the most commonly used voltages for my industry, 13.8V and 28.8V. I used a simple op-amp voltage divider to switch the windings based on the ‘selected’ voltage on the front-mounted voltage pot. My voltage/current regulation was based on the old ETI-163 power supply. At 13.8V DC output, the transistors were only dropping 5.9V, so at higher currents, the heat dissipated was minimal (60W at 10A or 120W at 20A). This also has the advantage of lowering the output impedance of the ‘source’ as there are two windings in parallel (great for high current loads). At 28.8V DC output, two of the transformers are connected in series, with one unused. Past 32V, all three windings are in series, giving up to 60V <at> 10A before the series pass transistors. Using eight MJE15003 transistors on two large heatsinks with 2 x 80mm fans, the heat was spread out quite well, and I have never encountered any overheating problems. However, at 16V DC, the heat output is quite significant at 235W with a load drawing 10A. I also had a 0.5A/10A range select switch, which switches a different shunt in the negative line to allow fine current limit control at lower currents. Metering was analog like the ETI-163 as they are fast and easy to read at-aglance, especially the current meter. I’ll probably add this feature to the new supply, maybe with three current ranges: 0-500mA, 0-1A and 0-10A. (B. N., Marine Terrace, WA) • We did consider using a multi-tap/ series/parallel transformer configuration while designing the 45V PSU, but we couldn’t find any suitable offsiliconchip.com.au the-shelf transformers at reasonable prices. We didn’t want to use multiple transformers as that would result in a much bigger, heavier unit. The switchable shunt idea is interesting, although you’d have to have your wits about you to know what range you were using at any given time. Also, the switch resistance could introduce some inaccuracies, and possibly unreliability long-term. have not tested it with Python 3. The error “ImportError: No module named ‘urllib2’” confirms this, as per the following StackOverflow question: siliconchip.com.au/link/ab76 If you want to push ahead and try to make it work with Python 3, the advice on that web page is a good start. Tide Chart Python version mismatch A colleague (who does not read your magazine; shame on him!) has an appliance where the backlight has failed on the LCD panel. Am I correct in assuming that the light is integral to the panel, and hence cannot be replaced? I suppose that by squinting at the panel, or perhaps by shining a bright light upon it, the segments could be discerned. (D. H., North Gosford, NSW) • It depends on the LCD panel. You I am trying to get the code for your Raspberry Pi Tide Chart (July 2018; siliconchip.com.au/Article/11142) running, but I am getting an error “ImportError: No module named ‘urllib2’”. (P. C., Balgal Beach, Qld) • We suspect that you are trying to make the Tide Chart work with Python 3. It was written for Python 2, and we How to fix failed LCD backlight can experiment by applying light to the panel using a small torch. There might be a way to provide backlighting by feeding light in from the panel’s side or back. Front-lit LCD panels are harder to control for lighting, but you may get sufficient display brightness with front lighting. The display contrast is usually poor with front lighting. We occasionally publish entries in Serviceman’s Log where contributors have successfully replaced the backlighting on various LCD screens. You really have to open it up to see whether it is possible for that particular display (unless you can find information about that aspect of it online). Ferrite bead selection for amplifier The Ultra-LD Mk.4 200W RMS Power Amplifier (August-October How is negative feedback affected by phase shift? When feedback is being discussed, the effect of phase shift on a feedback loop is usually considered, but always in the most extreme situation where the phase shift is large enough to set up positive feedback and drive the circuit into oscillation. But surely, any phase shift should have a detrimental effect on feedback since phase shift is caused by a time delay in the feedback circuit. That in turn means that the circuit is feeding back an error to a different part of the signal; in effect, trying to correct an error that has already happened and the source signal has moved on. And yet, the vanishingly low distortions being measured in some high-end amplifier circuits, like those published in Silicon Chip, suggest that this is not happening. Can someone explain why feeding back a delayed signal is not a problem for a feedback circuit? (P. T., Casula, NSW) • Yes, phase shift has a detrimental effect on negative feedback used for distortion reduction or accurate gain setting. It’s worse at higher frequencies as the circuit will typically have a fixed feedback delay, representing a larger phase shift relative to higher frequency signals. This is largely siliconchip.com.au why audio amplifiers usually have rising distortion with frequency, typically evident above 1kHz. Therefore, audio amplifiers usually are designed to operate just on the edge of stability, with the minimum possible delay, pushing this point of rising distortion above 20kHz where it is not audible (and the amplifier will generally be designed not to reproduce signals above this frequency). Consider that the open-loop bandwidth of an audio amplifier will typically be in the megahertz, yet it is only tasked at reproducing frequencies (in closed-loop mode) up to 20kHz. So if the phase shift is, say, 90° at 2MHz, that equates to a feedback delay of 125ns (90° ÷ 2MHz ÷ 360°). For a 20kHz signal, that’s a phase shift of 0.9° (360° × 125ns × 20kHz). Therefore, the negative feedback is still more than 99% effective, reducing the open-loop distortion by more than 40dB. As long as the design is fairly linear (ie, open-loop distortion is not gross), this is usually enough to give a very low distortion figure even at 20kHz. If you look at the evolution of our amplifiers, 20 years ago, we were achieving figures of <0.001% <at> Australia’s electronics magazine 1kHz, but significantly higher (say, between 0.01% and 0.1%) at 20kHz. These days, the open-loop bandwidth has been raised, making feedback more effective; open-loop linearity is better, and other factors have been improved to the point that we are achieving close to 0.0001% <at> 1kHz and still well under 0.001% <at> 20kHz, leaving little room for further improvement. So you are right, the phase shift in a negative feedback circuit is undesirable, but luckily, it can be kept to a low level where it is not bothersome. In circuits like low-pass and highpass filters that inherently have a phase shift within the audio frequency band, the linearity of the change in phase with frequency is usually excellent. We make sure that it is by using all linear components in the RC networks, and so it does not introduce harmonic distortion. It does introduce a frequencydependent phase shift, but in theory, for normal ‘listening’ conditions, this is inaudible. It can cause problems in certain scenarios like interactions between drivers in multi-drive loudspeaker systems, in which case, the crossover circuit design can be critical in achieving good results. April 2021 109 2015; siliconchip.com.au/Series/289) uses an SMD ferrite bead. What value of inductance/resistance should it have? There are many to choose from at Digi-Key. (I. G., Oak Flats, NSW) • The ferrite bead type is not critical. Ferrite beads don’t have any significant inductance or resistance. They are usually specified with an impedance in ohms at 100MHz. The cheapest from Digi-Key in the M3216/1206 package are rated at either 600W or 1kW at 100MHz, and either would be fine. For example, the Bourns MH3261-601Y or Eaton MFBM1V3216-102-R. Component damage in CLASSiC DAC? I have finished building your CLASSiC DAC from the February-May 2013 issues (siliconchip.com.au/Series/63). I went through the testing procedure, and everything was fine in regards to the power supply until I bridged LK1 and LK2. The DAC chip heated up rapidly, so I inspected the board and found I had accidentally fitted TOSLINK transmitters and not receivers. I have since replaced them with the correct receivers and carried out the setup procedure again. But I still have the same problem with the CS4398 DAC chip rapidly heating. Upon further investigation, I found that when the JP1 link is set for 3.3V, the unit will continuously scan the four sampling rate LEDs and not detect any channels, and there is no audio output. The DAC chip does not get hot. When JP1 is connected to 5V, the unit does select channels and detects the sampling rate, but that is when the DAC chip gets very hot in a matter of seconds. There is audio output, but it is very noisy. I have also tried with JP1 out and the unit powers on fine, selects all channels and audio from USB and SD card can be played back, but there is a lot of noise through both the headphone and line outputs. However, the noise is not as bad as when 5V is selected. Could it be that having the wrong TOSLINK transmitters/receiver fitted has damaged the CS8416 receiver chip and introducing the noise to rest of the circuit? I would love to hear your thoughts before I purchase a new chip. (J. R., Warrane, Tas) • We can’t see an obvious way that fit110 Silicon Chip ting TOSLINK transmitters instead of receivers would damage anything. We wonder if you have another problem and the TOSLINK transmitter error is just a coincidence. Do make sure that the TOSLINK receivers you have fitted are the right type, though. The only thing that jumper JP1 controls is the voltage fed to Q13b, which then goes to the TOSLINK receivers and nowhere else. Their outputs are AC-coupled to the CS8416, so it should not be possible for the wrong voltage to be fed back. We suspect you have a short circuit from some point on this rail to something that feeds to the DAC, such as the +3.3V rail. This short could be between the pins of JP1, or perhaps between some pins of Q13. It could be elsewhere, but we can’t see any other obvious locations. We suggest removing the jumper from JP1 and check for continuity between the middle pin and both of the outer pins. If you find continuity then something is wrong. Do the same for the pins of Q13, keeping in mind that pins 5 & 6 and pins 7 & 8 are intentionally connected together. If that still doesn’t help, check the board carefully for short circuits, especially between IC pins. Modifying the IMSC to run from 115V AC I purchased a couple of kits for your Induction Motor Speed Controller (April & May 2012; siliconchip.com. au/Series/25) way back when, and am now getting around to building them. With only a couple of minor mistakes, it has gone well. I was reading through your articles describing the design and function, and I have a couple of questions/requests. Most of this has to do with the fact that I live in the USA, and our mains power is 120V AC (240V AC for large appliances). I don’t want to have to use 240V AC for all my motor applications. What is the low-voltage cutoff? Is this a software feature that could be modified? I’d like to have the speed settings ratio be based on what we have for power here. That means a 60Hz default ramp up and a 90Hz top speed. I think that could also be changed in the software quite easily. Would you be willing to share the source code? I imagine I’m not the only one that would like to make a couple Australia’s electronics magazine of tweaks. GitHub and a public license to protect you and/or keep people from profiting from your work. (A. D., Columbia Heights, Minnesota USA) • You would need to change transformers T1 and T2 to run the IMSC from 110-120V AC as they would not produce a high enough output voltage otherwise. A possible alternative to changing these transformers would be to use the specified transformers, but change how they are wired to the diode bridges. T1’s configuration would need to change from a bridge rectifier to a full-wave voltage doubler, and T2 would need to be rewired to have its secondaries in series rather than in parallel. The under-voltage lock-out can’t be changed in software. If you modify T1/ T2 to produce the correct +15V HOT and 7V rail voltages with a ~115V AC input as described above, the circuit should operate normally. You couldn’t connect it to a 220-240V AC source after those modifications, though. The 0.5-75Hz range was chosen to include 60Hz as an option. The latest software gives a way to increase the maximum speed to 100Hz, which should be more than enough. We haven’t made the source code to this project freely available upon the designer’s request, because modifying it could be very dangerous. The IMSC is not something that inexperienced people should fiddle with, and we believe that giving away the source code would encourage that. Dual Power Supply wanted Has Silicon Chip ever designed a simple variable dual power supply? (R. M., Melville, WA) • Yes, we have published a few; the latest was the Dual Tracking Supply (June & July 2010; siliconchip.com.au/ Series/8). We have PCBs available for that project, and there is an Altronics kit (Cat K3218). If building that, please check our Notes & Errata page as there were some errata published for it. Other similar supplies published include: • Easy-to-Build Bench Power Supply (April 2002; siliconchip.com.au/ Article/4083) • Beginner’s Dual Rail Variable Power Supply (October 1994; siliconchip. com.au/Article/5220) continued on page 112 siliconchip.com.au MARKET CENTRE Cash in your surplus gear. Advertise it here in SILICON CHIP PCB PRODUCTION KIT ASSEMBLY & REPAIR PCB MANUFACTURE: single to multi layer. Bare board tested. One-offs to any quantity. 48 hour service. Artwork design. Excellent prices. Check out our specials: www.ldelectronics.com.au VINTAGE RADIO REPAIRS: electrical mechanical fitter with 36 years ex perience and extensive knowledge of valve and transistor radios. Professional and reliable repairs. All workmanship guaranteed. $17 inspection fee plus charges for parts and labour as required. Labour fees $38 p/h. Pensioner discounts available on application. Contact Alan, VK2FALW on 0425 122 415 or email bigalradioshack<at>gmail. com FOR SALE GREAT VALUE PARTS and more are found in the Tronixlabs eBay store via tronixlabs.com.au – for enquiries or support please email support<at> tronixlabs.com LEDs, BRAND NAME and generic LEDs. Heatsinks, fans, LED drivers, power supplies, LED ribbon, kits, components, hardware, EL wire. www.ledsales.com.au ASSORTED BOOKS FOR $5 EACH Selling assorted books on electronics and other related subjects – condition varies. All books can be viewed at: siliconchip.com.au/link/aawx Email for a postage quote, quote photo numbers when referring to a book: silicon<at>siliconchip.com.au DAVE THOMPSON (the Serviceman from S ILICON C HIP) is available to help you with kit assembly, project troubleshooting, general electronics and custom design work. No job too small. Based in Christchurch, NZ but service available Australia/NZ wide. Email dave<at>davethompson.co.nz KEITH RIPPON KIT ASSEMBLY & REPAIR: * Australia & New Zealand; * Small production runs. Phone Keith: 0409 662 794 keith.rippon<at>gmail.com Silicon Chip Binders REAL VALUE A T $19.50* PLUS P&P Keep your copies safe, secure and always available with these handy binders These binders will protect your copies of SILICON CHIP. They feature heavy-board covers, hold 12 issues & will look great on your bookshelf. Silicon Chip Publications Order online from www.siliconchip.com.au/Shop/4 ADVERTISING IN MARKET CENTRE Classified Ad Rates: $32.00 for up to 20 words (punctuation not charged) plus $1.20 for each additional word. Display ads in Market Centre (minimum 2cm deep, maximum 10cm deep): $82.50 per column centimetre per insertion. All prices include GST. Closing date: 5 weeks prior to month of sale. To book, email the text to silicon<at>siliconchip.com.au and include your name, address & credit card details, or phone Glyn (02) 9939 3295 or 0431 792 293. WARNING! SILICON CHIP magazine regularly describes projects which employ a mains power supply or produce high voltage. All such projects should be considered dangerous or even lethal if not used safely. Readers are warned that high voltage wiring should be carried out according to the instructions in the articles. When working on these projects use extreme care to ensure that you do not accidentally come into contact with mains AC voltages or high voltage DC. If you are not confident about working with projects employing mains voltages or other high voltages, you are advised not to attempt work on them. Silicon Chip Publications Pty Ltd disclaims any liability for damages should anyone be killed or injured while working on a project or circuit described in any issue of SILICON CHIP magazine. Devices or circuits described in SILICON CHIP may be covered by patents. SILICON CHIP disclaims any liability for the infringement of such patents by the manufacturing or selling of any such equipment. SILICON CHIP also disclaims any liability for projects which are used in such a way as to infringe relevant government regulations and by-laws. Advertisers are warned that they are responsible for the content of all advertisements and that they must conform to the Competition & Consumer Act 2010 or as subsequently amended and to any governmental regulations which are applicable. siliconchip.com.au Australia’s electronics magazine April 2021 111 • Dual Tracking ±50V Power Supply (April 1990; siliconchip.com.au/ Article/7258) • Dual Tracking ±18.5V Power Supply (January 1988; siliconchip.com.au/ Article/7828) the Jaycar Cat SY4080 (3A rated) and SY4084 (40A rated). These would need to be wired up and housed in an Earthed metal enclosure and wired according to the Australian wiring standards for mains equipment. Reducing switch wear from arcing Direct Injection Box query I have a computer (Apple Mac), a printer (Brother) and several other small items plugged into a powerboard fitted with a switch. After I have finished using the computer, I shut it down, wait until all the screen displays have switched off, then turn all the power off via the switch on the powerboard. Occasionally, there is a ‘blat’ sound that comes from the switch. I assume that this is a spark. I have had to replace the switch several times over the years, as the contact points in the switch have become stuck or welded together. Is there any way to reduce or eliminate this sparking? (G. H., via email) • One method to reduce switch contact wear due to arcing is to place an X2-rated 10nF 250V AC capacitor across the switch contacts (eg, Jaycar Cat RG5230). This will reduce the transient voltage across the switch contacts as they open. Adding the capacitor leaves a residual current flow that bypasses the open switch (around 8mA). Higher value capacitors can be used, and might suppress the sparking more effectively, but with a higher residual current. Another method is to switch the mains supply using an electronic switch such as a Triac. There are electronic relays that do this, such as Some years back, you presented an active direct injection box for guitars to plug into a PA system. The design included a low-cost transformer from Altronics or Jaycar and a JFET front end powered via the audio mixer phantom power supply. We built several of these for our local church and need to make more. While you can buy a commercial unit for around $100, I recall that these DI boxes were very cost-effective; certainly a lot less than $100. I can’t remember whether it was EA or Silicon Chip magazine. The DI boxes we constructed have proven to be very robust and deliver excellent sound quality. Can you advise when that project was published? (N. A., Canberra, ACT) • The DI Box design you are after is probably the one from Electronics Australia, February 1998 (97di12: “Direct Injection [active] Preamp using a JFET” ). You can order a scan of that article via www.siliconchip.com. au/Shop/15 Alternatively, Silicon Chip has published passive and active DI Boxes. Our passive version (October 2014; siliconchip.com.au/Article/8034) uses a high-quality transformer from Altronics, while the Active DI Box (August 2001; siliconchip.com.au/ Article/4158) does not use a transformer. SC Advertising Index Altronics...............................83-86 Ampec Technologies................. 49 Analog Devices........................... 7 Control Devices Australia............ 9 Dave Thompson...................... 111 Digi-Key Electronics.................... 3 Emona Instruments................. IBC Hare & Forbes............................. 5 Jaycar............................ IFC,53-60 Keith Rippon Kit Assembly...... 111 LD Electronics......................... 111 LEDsales................................. 111 Microchip Technology...... 13, OBC Ocean Controls........................... 6 SC Colour Maximite 2............... 75 Silicon Chip Binders............... 111 Silicon Chip Shop.............. 87, 98 Silicon Chip SiDRADIO............ 19 Switchmode Power Supplies..... 12 The Loudspeaker Kit.com......... 10 Tronixlabs................................ 111 Vintage Radio Repairs............ 111 Wagner Electronics................... 47 Weller Soldering Iron................. 11 Notes & Errata High-Current Battery Balancer, March 2021: in the parts list on p27, several Mosfets (Q11,Q12…) are listed as “S6M4” types. The correct type code is QS6M4. Arduino-based Adjustable Power Supply, February 2021: while the specified SY4030 relay from Jaycar is rated to carry 1A, it only has a 500mA switch rating. The similar S4100 relay from Altronics specifies a 1A switching current. Power supplies built using the Jaycar part should set the current limit no higher than 500mA to avoid damage to the relay. Other similar relays are available with a 1A contact rating; it appears that this refers to the carry current only, and not the switching current, so check the data sheet if substituting a different part. LED Party Strobe Mk2, August 2015: the link at lower-left should be positioned as shown in the photo on p87, not the overlay diagram (Fig.2) on p86, which incorrectly has it shown in the “MAX” position. The May 2021 issue is due on sale in newsagents by Thursday, April 29th. 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