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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 Purpose of indentations in some mains plug pins I was very interested in the article on the development of the Australian three-pin plug and its history by John Hunter (September 2020; siliconchip. com.au/Article/14573). But something I have always wanted to know is why the pins on some plugs (especially the older ones) are indented and not just flat? By the way, I really enjoy your great mag. which turned up here in Germany right on time. It seems the post is now back to normal. (C. R., Tuebingen, Germany) • John Hunter replies: I used to think the indentations in some sockets were for pin retention. However, in the hundreds of ancient sockets I have examined, I haven’t found any evidence of that. All of them have the plain folded flat contacts; the same type still used today. Also, if such an arrangement did exist, it would be problematic with pins having straight sides, since the contact area would be reduced. As a general observation, that indented side pin shape began to be discontinued in the 1950s, first by HPM, then later by Clipsal. I haven’t found any similar arrangement in US-made sockets, which would mate with the holes in the ends of their plug pins. I did once see a vague reference that the holes were to keep the pins in position whilst the plug was moulded around it during manufacture. A few Australian (notably CMA) plugs also had these holes, so if there is some truth to it, perhaps the indented sides were for the same purpose. Odd electrical sockets on GPOs I just read the article on the History of Australian GPOs (September 2020; siliconchip.com.au/Article/14573) – what a fascinating article! He did not show a four-pin socket, but I have a photo of one that I took at siliconchip.com.au Lanacks Castle, Dunedin, NZ when I took a tour through it. It was in a small room behind a rope and was not in use. The Castle guides did not know anything about it, nor what the house voltage was at that time. The castle was built in about 1910, and most of it was imported, including the electrics. It is a GEC 230V 10A USA socket, but it might have come from England as most of the castle came from there. I have asked electrical inspectors from both England and New Zealand about it. I was an Inspector before I retired a few years ago. Can you help to identify it? (P. J., Auckland, NZ) • John Hunter responds: I am familiar with that socket and have one in my collection. It’s designed to take the normal US blade plug with two parallel pins, as well as the ‘tandem’ type plug. The tandem plug went out of fashion early on, to be replaced entirely by the common parallel blade type. It did reappear later, but with an Earth pin, and these days is used for 240V appliances in the USA. You can see the pin pattern at https://w.wiki/jsm want to build the Balanced Attenuator later). (O. A., Singapore) • Phil Prosser responds: you certainly should not be able to hear any hum. Check the voltage levels at the ADC inputs, at pins 17, 18, 29 and 20. These should all be close to 2.5V. Then follow the signals back through the buffer; check pins 1 of IC2a and IC4a. These should have a DC offset of 0V. Similarly, IC2b and IC4b pins 7 ought to have 0V DC offset. Are the 10µF capacitors on pins 3 and 5 of IC3 and IC5 in the right way around? Check all your solder joints carefully, since a bad (high-resistance) joint could explain your symptoms. That ADC is excellent. When you find the bug, you should have a super hifi ADC and the makings of an awesome piece of test kit. Editor’s note: O. A. traced the fault back to a bad solder joint on pin 3 of the ADC chip. Pressing on the chip affected the hum level, and reflowing that pin completely eliminated it. USB SuperCodec hum problem The Colour Maximite 2 is another great project (July-August 2020; siliconchip.com.au/Series/348). I managed to get it up and running after a brief problem with the VGA connector (no video output). I believe the connector holes are a little too large, so solder can wick in and wet the pin and via without forming a bridge, unless you use a lot more solder than usual. After fixing that, I found a couple more strange things. Firstly, when I plug in my Microsoft wireless keyboard, everything works OK except that the “<at>” and “:” characters were once transposed (don’t ask me how long it took to find this…), but on other sessions, remained good. Secondly, I have the latest version of Tera Term, but the connection is very “flaky”. It only connects about 1 in 10 attempts, sometimes displays graphics characters at start-up, and is prone to hang mid-sentence on occasions when After I finished building the USB SuperCodec (August-September 2020; siliconchip.com.au/Series/349), I tested the DAC section on my amplifier, and it works very very well. It’s crystal clear! I also tested the ADC. It works, but I have some hum in the background. I can adjust the input level to make it inaudible, but then when I feed it with the DAC output, I cannot hear the music (even if I set the volume to its maximum on the PC). The only way is to increase the input level, but then the hum and music are superimposed. I noticed that the +9V rail is +8.25V and the -9V rail is -8.2V. But since the DAC part works, I don’t think that’s the problem. I soldered the USB Streamer, but only the six pins that are needed (I Australia’s electronics magazine Colour Maximite 2 queries December 2020  107 entering commands (yet, the direct keyboard connection remains good). Another surprising thing – when I “Restore Setup…” in Tera Term, it never gets the saved serial port correct – I have to go back in and set the correct serial port. (I. T., Duncraig, WA) • The swapped characters (“<at>” and “:”) are probably caused by the keyboard being set to the wrong language in MMBasic. Try entering OPTION USBKEYBOARD US at the command prompt (this option is saved so it will be remembered on reboot). As for your connection problems, assuming you have checked all the solder joints, the other likely cause is that the PC or laptop does not have the grunt to supply the approximately 200mA required by the CMM2. This can be tested by using a high-capacity USB charger to power the CMM2; if everything works OK, that points to a power supply issue. Another possibility is that the USB cable is faulty. We have found that about ¾ of problems with the CMM2 can be traced to either a bad power supply or a faulty USB cable. ADF5355 DDS module output is noisy I have been testing the ADF5355 13.6GHz Touchscreen Frequency Generator (May 2020; siliconchip.com. au/Article/14437), and noted that the output signals are not as clean as those from other units (based on the ADF4351 and MAX2870). Some people online have attributed this behaviour to noisy and cheap voltage regulators used in the cheap ADF5355 boards. I have ordered a few daughter boards from Brian Flynn GM8BJF that use voltage regulators with significantly lower noise (ADM71503.3 and ADM7150-5.0). These are not cheap in small quantities (<1000 units). Did you also note that the ADF5355 board was also ‘noisy’, which the engineering chaps call “phase noise”? This was not mentioned in the May 2020 article. I looked at the output signals over the range of my spectrum analyser (3.2GHz) and noted that the ADF4351 (two versions available from BangGood – TFT/OLED) and the MAX2870 produced very clean signals. (S. G. E., Hackham West, Vic) • We did not measure the phase noise 108 Silicon Chip of that unit because, for hobbyists who need a sweep generator to test performance such as the frequency response of filters, cables etc, phase noise is not so important. We used a 5V lab supply to power our device, and did notice that the signal was somewhat noisy, but we were not too critical because we did not expect the world for $280! For your application where you need a pure signal at a fixed frequency, the changes you highlighted seem like a good way to improve the power supply and vastly reduced phase noise. We did check the unit’s harmonic distortion up to 20GHz, because this is one of the most essential factors to produce signals that do not cause interference in higher bands. We found the unit to be well within the specifications of the AD5355 with –33dBm distortion at 19.9538GHz. It seems like a lot of work to improve the module, but as long as a good 5V supply is used, it still gives a creditable performance. 2003; siliconchip.com.au/Series/293) says that its power supply can deliver a peak current of around 40mA at 265V DC. The 2016 valve supply has no details of its current delivery capabilities, can you tell me what it can deliver? I’m studying the design of boost converters and flyback converters so any help would be most appreciated concerning this topic. (J. H., Scotland, UK) • The January 2016 Stereo Valve Preamp states (p33, right-hand column) that the power supply is purposefully designed to operate at its current limit while supplying the anode current for the two 12AX7 twin triodes. If you calculate their current draw using Ohm’s Law and the values given on the circuit diagram, that is a total of around 4mA. It’s probably possible to modify the supply circuitry to deliver more than that, but as it was adequate for that particular design, we didn’t test it to see how much current it could deliver at 265V. Finding LCD for Reflow Oven Controller Identifying SMD TVS cathode I am getting together all of the parts to build the DIY Reflow Oven Controller (April-May 2020; siliconchip.com. au/Series/343). I am struggling to find an LCD screen based on the KS0108 controller (looking in the source code shows that the driver is for this chip). As far as I can see, Altronics do not have anything suitable, and Jaycar only has an ST7920-based board (XC4617). (S. G., Thurgoona, NSW) • Phil Prosser responds: I bought mine from eBay where they are prevalent and usually very cheap. A search for “KS0108 LCD” gives many results, mostly at 128x64 resolution. The choice of white on blue or black on green is up to you, but we find the blue ones have better contrast. I have not had any problems with them from that source – either they are not worth faking, or the fakes work well. In 2018, I bought two kits for your Mini 12V USB Regulator (“Install USB Charging Points In Your Car”, July 2015; siliconchip.com.au/Article/8676). I built one at the time but without success (I hadn’t mastered soldering very small SMDs). With COVID-19 shutting down New Zealand, I decided to give the second kit ago with some success, having gotten much better at soldering the very small SMDs (using solder paste and a hot air rework station). You’ve explained how to orientate the SMAJ15A and SK33A parts by identifying a stripe on one end of each these. I have had no trouble finding the stripe on the SK33A, however, even with a very strong light and magnification I can’t find one on the SMA15J. With the body of the part orientated so that it is taller than it is wide, I can read some text which says “BM” and then below it, “4LZEO”. Above the “BM” is what looks like a company logo. Is this enough information to figure out which way around it goes? (R. K., Auckland, NZ) • Unfortunately, there are multiple manufacturers of the SMAJ15A, and they use different marking schemes. So it helps to know who made the part to Switchmode power supplies for valves I built the power supply for the Stereo Valve Preamplifier (JanuaryFebruary 2016; siliconchip.com.au/ Series/295) on a small PCB to experiment with valve circuits. The Valve Preamp article (November Australia’s electronics magazine siliconchip.com.au figure this out. I checked our records to see which exact part we purchased for these kits, and it turns out it was Littelfuse. Here is their data sheet for that part: siliconchip.com.au/link/ab5p That shows that BM is the correct marking. 4LZEO is the date and batch code. With the writing orientated so that you can read it, the cathode is at the top. So, in other words, the Littelfuse logo marks the cathode. You can also check this with a DMM set on diode test mode. You should get a reading of 0.6-1.0V with the red probe to the anode (bottom) and the black probe to the cathode (top). Questions about Motor Speed Controller I see in the Notes & Errata published in the September 2020 issue that you have recommended a replacement for the obsolete IGBT used in the 230V 10A Universal Motor Speed Controller (February-March 2014; siliconchip. com.au/Series/195). However, unlike the original device, the replacement does not have an inbuilt reverse-polarity protection diode. Would that be a problem? Secondly, I am puzzled as to the reason for having the motor on the IGBT side of the bridge rectifier. No explanation for this is given in the article. If the motor were placed inline with the Active connection on the mains side of the bridge, the motor would see a more-or-less normal mains waveform, albeit PWM chopped. As you have it, the motor is effectively subject to rectified DC but with 100Hz ripple. I wonder if there may be some instances where that could cause problems. (D. S., East Melbourne, Vic) • The lack of a reverse diode within the IGBT between collector and emitter is not important in that motor controller since current does not flow in that direction in our circuit. There does need to be a diode between the positive supply and the IGBT’s collector to protect against over-voltage when the motor is switched off; hence, our inclusion of diode D1. The motor could be placed inline on the Active side of the bridge rectifier, with the collector of the IGBT connected to the positive rectifier output. But it would be very difficult and expensive to include over-voltage clamping to protect both the rectifier bridge and IGBT when the IGBT is switched off. siliconchip.com.au This protection would require two inverse-series-connected high-current zener diodes across the motor, or a similar clamping circuit that would be reliable. Since the motor controller is for universal motors that run on DC or AC, there is no problem running the motor with pulse-width modulated pulsating DC, as we have done. Running 250W Class-D amp from a car battery The local boys have had me build numerous Silicon Chip 250W ClassD amps (November-December 2013; siliconchip.com.au/Series/17) from Altronics K5181 kits for their cars. I have made it clear that they have to find power supplies to drive these amps to their full potential. After constant hounding by the natives, I have been looking at the constant voltage DC-DC converters available from Wish, AliExpress etc and am finding this very much out of my league. Can you find a converter which would suitable to power the 250W Class-D amp to its maximum or close to it, in a car? (J. C., Pialba, Qld) • We published a DC-DC Converter for the Class-D amplifier (May 2013; siliconchip.com.au/Article/3774), but it is not sufficient to get the full 250W from the amplifier. It will produce up to 125W into 4W on program material. You would need two converters for a stereo amplifier. For more power, our 600W DC-DC converter (October-November 1996; siliconchip.com.au/Series/152) could be used. Adjust its output voltage to ±55V by winding fewer turns on the transformer. This could power a stereo amplifier for 500W (250W per channel). We looked for suitable commercially-made DC-DC converters but couldn’t find any. Electronic control of induction motor speed I have built a device to give closedloop torque control of a 3-phase induction motor using your 1.5kW VSD (April & May 2012; siliconchip.com. au/Series/25) which I built from an Altronics kit (Cat K6032). It works well with manual torque control and PID control; however, I noticed that the motor speed would sometimes have some annoying chatter. Australia’s electronics magazine When driving the inverter and motor in open-loop mode with a steady voltage that I vary up or down, I discovered the motor speed steps neatly in 60RPM increments and chatters when the control voltage approaches inverter speed step thresholds. So basically, the inverter produces frequencies in 1Hz steps. The inverter internal speed set pot (VR1) also varies the inverter output in 1Hz steps. But when set to ramp up to a set speed via the inverter internal control, the motor spins up to the selected speed very smoothly! The specifications for the inverter state that its “speed control range” is 0.5-50 or 75Hz in 0.05Hz steps. It looks like the inverter is stepping in 0.05Hz steps when ramping between the discrete 1Hz settings, which isn’t what I was expecting. Can the inverter microcontroller be set up so its speed setting increments in 0.05Hz steps just like it does while ramping? (N. R., Glenroy, Vic) • Andrew Levido responds: the 1.5kW inverter was not designed to be controlled in this manner. While the frequency resolution is 0.05Hz, the ramp up or down between frequency setpoints will not commence unless the setpoint has moved 0.5Hz from the operating frequency. This is to avoid the ‘hunting’ that would otherwise occur if there was the slightest bit of noise on the analog input. I can see why this might look like 1Hz steps when trying to move in small frequency increments. The threshold is set in the software. This could be reduced to a threshold of 0.05Hz if the code was recompiled. This should work, but I have not tried it. Note that we have not released the source code because you need to know what you are doing to make any changes. SL32 NTC thermistor failure I’ve had the Induction Motor Speed Controller (April-May 2012; siliconchip.com.au/Series/25) operational for about a year now, but the SL32 10015 inrush current limiting thermistor has now failed. I noticed about six months ago that it had a crack in it, but I left it in place because the controller was working OK otherwise. It has obviously become very hot to December 2020  109 the point where it became an opencircuit crumbling mess. Have you had others report this problem? I’ve modified my charred PCB and mounted a new SL32 10015 offboard, in the airflow at the top of the box. Another modification I installed right from the start of the initial build is a full 12V supply to the muffin fan for maximum airflow. The new SL32 is running very hot like the original, even in its new, improved location. I expect it also will eventually fail. How would it be if I installed two MS32 5R020’s in series? That would still give 10W but spread the load (heat) between them. • We have heard of numerous failures of the SL32 devices in soft starters, but not in the IMSC. We’ve also heard reports of (expensive) commercial and industrial devices which use NTC thermistors for inrush current limiting failing during normal use, sometimes explosively. It seems that these parts can’t really handle the rapid thermal cycling, even though they are designed for this very job. We aren’t sure if it is a quality control problem at the factory, or perhaps that in some cases they are being pushed harder than intended (despite the device data sheet not giving any guidance on this matter). The SL32 10015 is rated at 15A continuous, so you would expect it to survive being part of a 10A motor controller. Your solution of the two MS32 5R020s in series should be a lot more robust. We suggest anyone building one of our SoftStarter projects for use with a large, bench-mounted power tool should do what you have done and use a larger number of lower-resistance NTC thermistors in series. Especially if it is going to experience frequent cycling. Using Soft Starter with large aircon Can I use your July 2012 Soft Starter for Power Tools (siliconchip.com.au/ Article/601) with a Panasonic 5kW split system air conditioner? It is no longer under warranty and therefore the sky’s the limit, so I am doing my research to convert it to run off-grid permanently from a dedicated inverter and bank of batteries/solar panels. 110 Silicon Chip I need to limit the inrush current the compressor draws, as to prevent the inverter going into trip mode under start-up conditions. It is rated to draw up to 5.5A continuously in cooling mode and 6.8A in heating mode, with peak currents of 14A and 17.5A respectively. During normal operation, the current I have measured is less than 5A. (B. A., Dee Why, NSW) • It might work, but we wouldn’t recommend it, at least not without a lot of testing first. It’s going to be hard on the thermistors since a compressor starts up under quite a lot of load, especially if it’s already hot. So they might fail pretty quickly (as described above, albeit in a different application). We suggest that if you do try it, use a larger bank of thermistors in series/ parallel or higher-rated thermistor(s). That would necessitate a larger box at the very least. We’re also concerned about possible compressor burnout if it doesn’t start properly, although the Soft Starter does bypass the thermistors with a relay after a short time, so the compressor should start eventually, even if it hard-starts. Still, we would want to monitor its operation very carefully for a while after installation. It’s also possible that the relay could have a short life if the compressor isn’t starting until the relay kicks in, or if the compressor is still drawing significant current by that time even if it has started. Varying Tempmaster Mk2 range I have just purchased a kit for your Tempmaster Electronic Thermostat Mk2 (February 2009; siliconchip.com. au/Article/1337) from Jaycar Electronics (Cat KC5476). I am hoping to use it to operate a cooling fan. When I opened the instructions, I found it has a range of 2-19°C, to suit fridges. I would like to change the operating range to about 15-35°C, although it would be good enough if I could just increase the upper limit to anything above 30°C. Is it possible to change any components to achieve this? Any help would be appreciated. (T. J., Adelaide, SA) • You can change the Tempmaster Mk.2 temperature range to 14-35°C by changing the 2.7kW and 3.3kW resistors in series with VR1 to 2.0kW and Australia’s electronics magazine 2.7kW respectively. Or you can get an even wider range of -5 to +40°C by using 1.2kW and 1.5kW value resistors. Coil for the High Energy Ignition System I have been searching the internet for weeks trying to find an appropriate high-energy ignition coil to use with your High-energy Ignition design (May 1988; siliconchip.com. au/Article/7739; built from a Jaycar KC5030 kit). I would appreciate it if you could recommend a high output ignition coil or coils to suit. I have been using the Prestolite points distributor in my 1962 Studebaker Hawk GT to run the ignition system for many years without a problem. I have owned the Stude since I was 21 years of age – 50 years ago! (R. B., via email) • We recommend you use a quality standard coil such as the NGK coil listed at siliconchip.com.au/link/ab5q The High-energy Ignition system is designed to work with a standard coil. So-called high-energy coils can cause arcing and misfiring if the distributor and ignition leads are not suited to the higher voltage and faster voltage rise time. Solar charger for 32V battery Several months ago, I purchased an MPPT solar controller via eBay. I am using three 20V solar panels to charge a 16-cell (32V) lead-acid storage battery. The unit has a range of desirable features including reverse current protection and continuous read-out of the panel and battery voltage, current, amp-hours delivered and battery state of charge. However, it does not seem to be a ‘smart’ battery charger, despite having an elaborate programming procedure. As a result, I conclude that the controller should not be left connected permanently between the panels and the battery, as the voltage can readily exceed 2.5V/cell (40V) in sunny weather. At that voltage, the charging current is around 3A. My method of manual regulation is to switch off the solar panels using a DC circuit breaker when the battery voltage reaches 40V. The battery remains connected to the MPPT controller. I recently noticed that there is a continued on page 112 siliconchip.com.au 4mA current flowing back from the battery to the controller. Is that normal? Have you ever published an MPPT solar charger that would suit a 32V 200Ah battery being charged from three standard 20V solar panels? (R. W., Loxton, SA) • The amount of current drawn by a charger from the battery depends upon the circuit design. It is normal for there to be some current drawn by the controller (whether it is an MPPT charger or not). After all, the charge controller circuit needs power to operate, and that can only come from the battery when there is no solar power available. The 4mA drain is not huge compared to the overall battery capacity – it would take nearly 290 days to fully discharge your battery at that rate. However, the less the charger draws from the battery, the better. Unfortunately, we have not published an MPPT solar charger to suit a 32V lead-acid battery. That is a somewhat unusual voltage; 12V, 24V, 36V and 48V are more common. It’s close enough to 36V that a charger designed for a 36V lead-acid battery might work; as long as it’s adjusted. Modifying the 40A DC Motor Speed Controller I have a customer who is using a number of your March-April 2008 40A DC Motor Speed Controllers (siliconchip.com.au/Series/48) to vary the speed of trolling motors on their boat. They want to speed up the soft-start ramp or remove it. Currently, the soft start runs for about 10 seconds, but they need it to be under three seconds. I’ve had a brief look at the assembly code for it, but my knowledge of assembly is so rusty it would take months to dissect it. I did have a go at assembling the source code which is available for download from your website, but I got several errors regarding missing functions named float_ascii2 and float_ascii4. They don’t appear to be part of the standard library. I also found that I had to add these two lines at the top of the main .asm file, which got rid of several other errors: #define P16_MAP1 0 #define P16_MAP2 1 I know that you have since released a more modern speed controller which has the soft-start control they’re after, but they’ve already built these kits and have been using them for a little while. We didn’t make a kit of the updated one so it would still be a fair amount of running around for them to switch. (Tom Skevington, Kits Manager, Altronic Distributors) • The float_ascii2 and float_ascii4 functions were in another file which was not included in the ZIP download for that project. That has now been corrected. Thanks for the tip about the two added defines which are needed. The software has two variables in which values are stored to increase or decrease the PWM duty cycle, named pdeltah and pdeltal. These are loaded with +1 on lines 819-821 of the main ASM file to decrease the speed, or -1 on lines 824-827 to increase the speed. Since this gives a soft start time of around 10 seconds, changing the increments to +4 and -4 should give a ramp time of around 2.5 seconds. To achieve this, change line 819 to: movlw 0x04 movlw 0xFC and change line 824 to: This will also make the motor speed ramp more quickly in response to the rotation of the speed control pot, or changes in load (ie, feedback). SC Advertising Index Altronics...............................81-84 Ampec Technologies............. OBC Dave Thompson...................... 111 Digi-Key Electronics.................... 3 Emona Instruments................. IBC Jaycar............................ IFC,53-60 Keith Rippon Kit Assembly...... 111 LD Electronics......................... 111 LEDsales................................. 111 Microchip Technology.................. 5 Ocean Controls......................... 11 Premier Batteries........................ 8 RayMing PCB & Assembly........ 10 Rohde & Schwarz........................ 7 SC Vintage Radio DVD.............. 34 Silicon Chip Christmas Kits...... 52 Silicon Chip Online Shop....98-99 Silicon Chip PDFs on USB....... 25 Silicon Chip Subscriptions....... 35 The Loudspeaker Kit.com........... 9 Tronixlabs................................ 111 Vintage Radio Repairs............ 111 Wagner Electronics................... 63 Notes & Errata Digital Lighting Controller pt2, November 2020: on p101, the parts list correctly includes a 27W 1W resistor for the Micromite master unit but incorrectly lists it as 25W 1W for the CP2102 Adaptor module (it should also be 27W 1W). Tiny LED Christmas Ornaments, November 2020: the parts list incorrectly lists the Bauble PCB dimensions as 91 x 98mm when they should instead be 52.5 x 45.5mm. Also, the Cane PCB is incorrectly listed as 84 x 44mm when it should be 84 x 60mm. Two new 7-band Audio Equalisers, April 2020: in the first batch of stereo equaliser PCBs sold (code 01104202), the connection between the 220pF capacitor and 51kW resistor in the lower right-hand corner of the board went to the top of the resistor instead of the bottom (which was floating). This can be fixed by cutting the track between the two components and running a short wire from the bottom of the resistor to the nearest pad of the capacitor. PCBs sold from November onwards do not have this problem. The January 2021 issue is due on sale in newsagents by Thursday, December 31st. Expect postal delivery of subscription copies in Australia between December 27th and January 15th. 112 Silicon Chip Australia’s electronics magazine siliconchip.com.au