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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 had the right to edit, reproduce in electronic form, and communicate these letters. This also applies to submissions to “Ask Silicon Chip”, “Circuit Notebook” and “Serviceman’s Log”. What to do with historic electronic gear I have come across an old PMG test instrument in the family storeroom – the old Gracemere Station office. It is an AWA Type R667 Capacity Unbalance Measuring Set. A calibration note attached to the lid is dated 15/2/68, but the instrument might be older than that (see the images below). I have little idea what it was for; I presume for improving crosstalk in either open-wire lines or cables. I have not opened it, so I don’t know what is in it. It has a vernier dial reading Capacity in uuF/nF (I think – not very clear). It has a battery compartment – again, I have not opened it, but I suspect it has some active components – valves, I presume. It also has two mic earpiece headsets. I don’t have any idea how it came into the family. It is in Rockhampton but I live in Brisbane. It is secure where it is, but there may be a more appropriate place for it to live, such as a museum. Do you have any suggestions? Patrick Durack, Ashgrove, Qld. Comments: we aren’t sure what to do with this device but perhaps one of our readers has a suggestion. 4 Silicon Chip USB Cable Tester & SMD Test Tweezers What a challenge, especially with soldering the USB-C ports. I completed the USB Cable Tester (November & December 2021; siliconchip.com.au/ Series/374) without any soldering remediation or fault finding, and it will be useful on my hobby bench. My soldering skills and techniques were definitely tested and improved. This experience highlighted that traditional magnifiers now need to be supplemented with a digital scope for quality control, although my phone camera set to super macro assisted this time. The recent SMD Test Tweezers project (October 2021; siliconchip.com.au/ Article/15057) is also a great and useful project and was a fun build. Barry Hinz, Charleville, Qld. Farewell Geoff Nichols Those who followed ETI Magazine would have been familiar with Geoff as a staff member/Project designer. My good friend Geoff passed away on the 19th of October, aged 64, of pancreatic cancer. Craig Laybutt, North Ryde, NSW. Australia's electronics magazine Test Tweezers survived reverse polarity I am delighted to report that you can insert the battery the wrong way and it will still work after correcting that error! Horst Leykam, Dee Why, NSW. Comment: We believe that it’s possible for a new CR2032 cell to supply more current (100mA) than the maximum specified for the microcontroller’s clamp diodes (20mA). However, it may be that components in the OLED module are also shunting current. PICs are pretty robust and will generally withstand much higher currents than the maximum ratings if they are of limited duration. Beware of fake solar panel ratings I bought a solar panel from a toprated seller on eBay. The panel was rated at 200W, but after receiving it, I became suspicious that its rating was incorrect. I later realised that the panel was unusually cheap for 200W, a warning sign I should have paid more attention to. The panel measures 0.58m2 (820 x 710mm). This is smaller than is physically possible for a 200W panel. 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 magazine siliconchip.com.au Tel: (02) 8741 5000 Email: sales<at>ampec.com.au Web: www.ampec.com.au FEBRUARY 2021 37 Helping to put you in Control ESP32 Controller Arduino-compatible ESP32 controller with 2 relay outputs, 2 transistor outputs, 2 opto-isolated inputs, 2 0/4-20 mA analog I/ Os, 2 0-10 VDC analog I/Os and 4 GPIOs. Interfaces using USB, RS-485 serial, I2C, Wi-Fi or Bluetooth. DIN rail mountable. SKU: KTA-332 Price: $251.90 ea CS Series Closed-Loop Stepper Driver Closed-loop stepper motor driver with encoder feedback input and encoder A/B/Z outputs. Operating at 20-50VDC, max 7A output current. Suits 2 phase CS Series Closed Loop Stepper Motors. SKU: SMC-162 Price: $215.60 ea Low transformer output mystery solved Ethernet Closed Loop Stepper Driver CS3E-D507 is a new Ethercat closed-loop stepper motor driver with encoder feedback input, operating at 20-50 VDC. Suits 2 phase stepper motors up to 7.0 A. Has digital inputs and outputs for control such as limit switch and brake. SKU: SMC-171 Price: $439.95 ea CS Series Closed-Loop Stepper Motor 3.0 N·m, 2 Phase NEMA 24 closed loop stepper motor with 1,000 line encoder for feedback. Rated at 5.0 A phase current, Nema 17 to 34 sized motors available and 8.0 mm shaft diameter. SKU: MOT-162 Price: $202.29 ea Liquid Level Sensor Detector A budget priced level sensor for detecting high and low levels of water in plastic and glass vessels or tanks. SKU: HEI-140 Price: $19.20 ea LogBox Connect WiFi LogBox Wi-Fi is an IoT device with integrated data logger and Wi-Fi connectivity. It has three universal analog inputs one digital input and an alarm output. SKU: NOD-012 Price: $604.95 ea N322-RHT Temperature and RH Controller 230 VAC Panel mount temperature & relative humidity controller with sensor probe on 3 metres of cable. 2 independent relay outputs. 100 to 230 VAC powered. SKU: CET-109 Price: $290.35 ea For Wholesale prices Contact Ocean Controls Ph: (03) 9708 2390 oceancontrols.com.au Prices are subjected to change without notice. 6 Silicon Chip A general figure for solar irradiance at the surface in Australia is 1100W/m2. The quoted panel efficiency was 17%, which seems reasonable. We can therefore calculate 0.58m2 × 1100W/m2 × 17% = 108W. Allowing for empty space, this is probably a 100W panel being incorrectly sold as a 200W panel. I also made some electrical measurements. The short-circuit current is 5.84A in peak sunlight. According to the label on the panel, peak power is at 18V. This means that the panel can generate no more than 105W. The open-circuit voltage measured 21.7V. The sticker on the panel does not show the power rating or short-circuit current, which is most unusual. The situation was somewhat resolved by the seller refunding half the purchase cost after I presented these facts. The panel was worth keeping as it seemed to be of good quality for a no-name panel. But many purchasers of solar panels would not be aware they are getting much less than they paid for. I wonder how common such fraud is. Dr David Maddison, Toorak, Vic. I read the Vintage Radio article in the November 2021 issue of Silicon Chip by Graham Parslow with great interest (siliconchip.com.au/Article/15107). Graham writes in a relaxed yet informative style, easy to read and with plenty of detailed photos. I always enjoy his articles. Graham describes the restoration of a Stromberg-­ Carlson model 496 autodyne superhet receiver from 1936. The cabinet looks stunning and the knobs look the part too. It’s a real shame the electrodynamic speaker was unable to be repaired; a reality faced by restorers from time to time. Graham mentioned the problem experienced with the 6.3V heater voltage winding running at 4.9V. This could be explained by the 6V6 heater being connected to the 6.3V winding. For example, the 6C6 and 6F7 each draw 0.3A heater current and the two dial lamps draw 0.3A each, for a total specified loading of 1.2A for the 6.3V winding. Adding the 0.45A heater current required by the 6V6 modification takes the total load on the 6.3V winding to 1.65A, an increase of 37% above the power transformer’s 1.2A load specification. This could explain why the 6.3V winding voltage has dropped to 4.9V. Graham mentioned that this particular radio was manufactured before the 6V6 became available, so I presume it was manufactured with an AL3 output valve, per the circuit. Graham stated he received the radio with the 6V6 fitted. To improve the originality of the radio, the retrofitted 6V6 and socket could be removed and replaced with an AL3 and suitable socket. This would require the AL3 heater to be wired to the 4V winding, which would also remove the additional loading on the 6.3V winding. That should allow the 6.3V winding voltage to return closer to the specified 6.3V figure, overcoming the low heater voltage problem Graham reported, as well as increasing the originality of this very nicely restored radio. Graeme Dennes, Bunyip, Vic. Graham Parslow responds: I took some measurements of the 6.3V winding with Australia's electronics magazine siliconchip.com.au 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 8 Silicon Chip various loads after receiving the suggestion from Graeme Dennes. Graeme was correct in his analysis; the winding cannot cope with the load imposed on it with the 6V6 added. I did not consider this initially because most comparable 6.3V windings can handle multiple amps. In hindsight, looking at the gauge of the winding, it is thinner wire than usual (this was not immediately evident due to being sheathed in spaghetti tubing). I measured a 5.7V output when loaded with just the two 0.3A dial lamps; the low voltage is no longer a puzzle. What is padder feedback, really? In researching radio designs, I have often come across the term “padder feedback”. There are plenty of references that explain its purpose (to improve local oscillator activity and reliability), but I have not found any good explanations of its principle of operation. It looks like the classic Armstrong oscillator, which puts a feedback transformer between anode and grid. The classic circuit sees one end of each winding (anode and grid) return to RF ground: the anode winding to decoupled HT, the oscillator winding to circuit ground. The only common variant returns the secondary to ground via the padder. Since this puts the padder in series with the inductor, its effect is identical to grounding the secondary and connecting the padder between the secondary’s ‘hot’ end and the oscillator tuning gang section. This has the advantage of returning one end of the padder to ground, minimising ‘hand effect’ during alignment. But the padder feedback circuit sees the two cold ends joined (either directly or via a capacitor; C14 in the Astor Mickey Oz circuit, see page 80 of this issue for example) and returned to ground via padder capacitor C12. Whatever this forms, it is not a true Armstrong oscillator. Is it some kind of Hartley oscillator (two inductors, L5 & L6, with mutual coupling), a modified Colpitts (padder C12 and tuning capacitor C10 with a single inductor L5), or a pi-filter resonant circuit (padder C12, inductor L5 and capacitor C10), as used in permeability-tuned radios (essentially a Colpitts oscillator)? If it is a Colpitts oscillator, why bother with the transformer primary? I trust that someone is less confused than I am! Rather than clog the Editor’s inbox, readers who can explain its principle/s of operation might reply to me at the email below. Ian Batty, Rosebud, Vic. – ianbatty311<at>gmail.com Hydrogen as a storage medium for renewals As usual, the July, August, and now the September issues have been worth reading. I was intrigued to see that you published one of my earlier letters in the September edition. Unfortunately, I have not progressed very far with the Li-ion battery charging project or any other projects. It seems that there is almost a limit on how much a person can do. It has been almost 40 years since I began experimenting and creating electronic and mechanical devices plus PC and embedded programs. I have devised many hundreds of circuits, plenty of mechanical devices, and many hundreds of programs during that time. It seems that the effort has caught up with me. Australia's electronics magazine siliconchip.com.au Design Contest Win $500+ Dick Smith challenges you Win $500 by designing a noughts-and-crosses machine that can beat 14-year old me! Dick Smith has described in his new autobiography how one of the turning points in his life, at age 14, was successfully building a ‘noughts-and-crosses machine’ (also known as tic-tac-toe) that could play the game as well as anyone. Keep in mind that this was in 1958, when nobody had computers; it was a purely electromechanical device. Email Design to Enter Design your own noughts-andcrosses circuit and send your submission to compo<at>siliconchip. com.au including: a) Your name and address b) Phone number or email address (ideally both) c) A circuit or wiring diagram which clearly shows how the device works d) The display can be anything as long as it’s understandable e) Evidence that your device can always play a perfect game (it never loses) f) A video and/or supply images and text describing it g) Entries requiring software must include source code The deadline for submissions is the 31st of January 2022. ➠ ➠ Win $500 + Signed Copy of Dick Smith's Autobiography ➠ Four winners to be decided, one each for the following categories: ➊ The simplest noughts-andcrosses playing machine most ingenious noughts➋ The and-crosses playing machine youngest constructor to ➌ The build a working noughts-and- DICK SMITH crosses playing machine most clever noughts-and➍ The crosses playing machine not using any kind of integrated processor The entry we judge overall to be the best will also be featured in our Circuit Notebook column and receive an additional $200. ‘Part Bear Grylls, part Bill Gates, but Dick is a great innovator, philanth 100% Aussie larrikin. ropist and adventurer, who in my eyes can do no wrong.’ PAUL HOGAN Conditions of entry Dick Smith writes 1) You must be a resident of Australia or New Zealand 2) One entry per family (Silicon Chip staff and their families are not eligible) 3) Submissions will be confirmed within 7 days. If you do not receive a confirmation of your submission, contact us to verify that we have received it 4) Chance plays no part in determining the winner 5) The judges’ decision is final 6) The winners will be decided by the 3rd of February 2022 and will be notified immediately By 1958 I’d advanced from building crystal radio sets to designing and building what I called a noughts and crosses machine. It really was an early computer. I used second-hand parts from a telephone exchange to build it. It would play noughts and crosses against anyone and no one could beat it. This was a great boost to me, because while I was no good at rote learning and theory, I was fine at practical things. The fact that my mind was capable of working out how to build this complex machine gave me confidence as I left school. Now I just had to find a job. Because this was such a turning point in his life and he’s so enthusiastic about youngsters learning electronics, he’s putting up $2000 of his own money to award to people who can come up with a modern version of his noughts-and-crosses machine. Silicon Chip will judge the entries. Winners will be announced in the March 2022 issue of Silicon Chip magazine and will also be contacted directly for payment information. siliconchip.com.au Australia's electronics magazine January 2022  9 I used to wonder why authors of novels would need to take substantial rest after writing a novel. Now I know. Currently, I am finding it hard to do anything involving electronics and/or robotics. Instead, I have been catching up on home maintenance and seriously overdue home projects. Hopefully, in the near future, my electronics drive will return. On another topic, there is a problem with the storage of solar energy using batteries of any type, and that problem occurs when the batteries are fully charged. There is almost certainly more energy available but it cannot be stored. However, immediate conversion of solar energy into hydrogen avoids this problem. Storage tanks are far cheaper than electrochemical cells. They do not suffer significantly from cycling, nor do they suffer from over-discharge. More storage is simply changing to a bigger tank or adding more tanks. Currently, both electricity-to-hydrogen and hydrogen-­ to-electricity converters are available off the shelf. Storage tanks almost certainly would be available as well; if the high leakage of steel can be tolerated, steel tanks are readily available. The main reason for bringing this subject to your attention is that solar energy storage via hydrogen is at the stage where it is feasible for hobbyists to make their own systems. Of course, there are safety concerns, and I have no doubt that our governments’ health and safety departments will react in their usual “it’s dangerous” manner. But hydrogen is far safer than LPG with the ability of hydrogen to rapidly disperse upwards and not lay around the lower levels of a house. It is unnecessary to store hydrogen at very high pressures, and a physically large tank is not a problem like it is for vehicles. An external installation in a well-ventilated enclosure should be far safer than any current fuel storage schemes, except perhaps fuel oil, coal, coke and wood. George Ramsay, Holland Park, Qld. Comments: Most city dwellers, even those with a house, might disagree about your statement that the size of a hydrogen storage tank is not a concern. Also, safety concerns aside, the round-trip energy efficiency is not likely to be that great. Regarding motivation, try working for an electronics magazine where you have to come up with and complete four or so project articles per month. Somehow we’re not only still coming up with new ideas (admittedly, in many cases, improved versions of previous ideas), but we’re turning them into working prototypes and documenting them after all these years. Article on electric vehicle charging I recently sent you an email relating to the logistics of charging multiple electric vehicles (EVs) in a suburban front yard. I don’t know whether this topic piqued your interest, but here is a link to an ABC article that relates to EV charging and the future of service stations: www. abc.net.au/news/100627312 The broader issue becomes providing the appropriate domestic and public infrastructure to support an EV based transport sector. David George, Montmorency, Vic. SC 10 Silicon Chip Australia's electronics magazine siliconchip.com.au