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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 Advanced GPS Computer cable length I am thinking of building the Advanced GPS Computer (June & July 2021; siliconchip.com.au/Series/366). Could you advise whether a 2m length of cable between the GPS module and the Micromite would be possible? I note that your photos only show a cable approximately 50cm long. I also wonder what sort of accuracy one can expect if the unit was in a car doing, say, 100km/h. Keep up the good work. (D. B. S., Artarmon, NSW) • 2m is a bit long for a cable carrying TTL serial signals. It might or might not work; it could be flaky. As the GPS serial is usually only 9600 baud, you might get away with it. Still, you would be better off using a GPS module with an external antenna socket, mounting it near the Advanced GPS Computer and then running a 2m shielded antenna cable to an appropriate antenna mount. If you did want to extend the data cable, we suggest you use a shielded cable. The speed accuracy is down to the GPS module. The data for the VK2828 module we used suggests a speed error of less than 0.1m/s (around 0.3km/h). In our experience, the readings are usually within 1km/h, with the update lag introducing more noticeable errors than the speed accuracy itself. That is because many GPS modules only produce data once per second, plus there is a processing delay. GPS Computer battery charging I built the Advanced GPS Computer, and everything seems to be working OK, but the battery takes forever to charge. Could I lower the value of the 10kW resistor between pin 5 of IC4 and ground to say 4.7kW? It will draw an extra 100mA or so from the power source, but I don’t see why that would matter. (P. C., Balgal Beach, Qld) • The battery we used in our prototype siliconchip.com.au did not have a specified maximum charge current, hence the 100mA setting, which is quite conservative. Lower charging currents will be better for long-term cell longevity too. If you are confident that your battery can handle a higher charging current, then the 10kW PROG resistor can be reduced as far as 2kW. That will give a 500mA nominal charge current, which is the limit of the MCP73831 charge controller IC. A 4.7kW resistor should give around 212mA, as you suggest. USB socket part code query What type of mini USB socket have you used in the Battery Multi Logger (February & March 2021; siliconchip. com.au/Series/355)? The parts list only describes it as an “SMD mini-USB socket”. (B. C., Bray Park, Qld) • We aren’t sure who originated this design but it seems that virtually everyone has copied it. While there are surely incompatible SMD Mini Type-B sockets available, many of the parts you can find will fit this same footprint. One part we know is suitable is the EDAC Inc. 690-005-299043, available from Digi-Key (Cat 1511206-1-ND) and Mouser (Cat 587-690005-299-043). Substitute Mosfet for Ultrasonic Cleaner I’m thinking of building your High Power Ultrasonic Cleaner (September & October 2020; siliconchip.com. au/Series/350), but I’m finding most suppliers of the SUP53P06-20 Mosfet are out of stock. Jaycar seems to still have a few (Cat ZT2464), but if I can’t get those, can I use the IPP80P03P4L-04 that you sell in your Online Shop (siliconchip. com.au/Shop/7/4318)? (E. Z., Turramurra, NSW) • Yes, the IPP80P03P4L-04 should be a suitable substitute for the SUP53P06-20 in this circuit. It has high enough current and voltage Australia’s electronics magazine ratings at 80A and 30V, and its gatesource voltage on-threshold is low enough. Short circuit on Mini BackPack PCB I built your D1 Mini BackPack with WiFi (October 2020; siliconchip.com. au/Article/14599) and was able to load the demo software into it. When I power it up, the screen for entering a location appears on the LCD but the touch function is not working. Can you suggest a solution? (J. L., Tauranga, NZ) • You most likely have a short circuit somewhere on the SD card socket. The SPI pins used to communicate with the touch controller are also used for SD card socket communications. As the screen display is working, most likely, the MISO line is shorted since that line is necessary for the touch controller to work but not the screen displays. Have a close look at the pins on the SD card socket and possibly remove the SD socket if it looks as though something could be shorting out underneath. The reader followed up to confirm that this was the problem. Reflow Oven wiring diagram error I’m building Phil Prosser’s DIY Solder Reflow Oven (April & May 2020; siliconchip.com.au/Series/343). The wiring diagram, Fig.11 on page 90 of the May 2020 issue, shows the ribbon cable arrangement from CON8 to the LCD module, but pin 1 of CON8 appears to go to pin 20 of the LCD. The photo on page 89 appears correct, although I think the ribbon cable cannot be folded neatly. Also, care needs to be taken to prevent the LCD Adaptor board from shorting out on the display cover mounting clips. I’d suggest some stand-offs or insulation here. Could I have some clarification? (I. T., Duncraig, WA) • Phil Prosser responds: You are correct; Fig.11 shows the cable from the August 2021  107 controller to the LCD with pins 1 & 20 swapped. The drawing probably should have had pin 1 indicated on the ribbon cable. I should have picked that up. Yes, the photo is correct. It is possible to fold ribbon cable to ‘neatly’ swap over the pins. It is a little like origami, and it takes a little more cable, but it does work. You need to ‘squish’ it pretty hard, but a clean bend is possible. You bend the cable 90° in the opposite direction you want the corner to go in, then fold it back 180° on top of itself. This error was corrected in the online version, with errata published in the June 2021 issue of Silicon Chip. We have not had trouble with the LCD adaptor board, although thinking of the problem you describe, we wonder if you are trying to mount the adaptor close to flush with the LCD. We generally use standard 2.54mm header pins to connect the LCD adaptor board to the screen, which gives 5mm+ of separation between them. Idea to help the hardof-hearing watch TV Is there an unused audio channel on the Australian TV broadcast standards? I have searched the internet for an answer without success. Recently, TV channels have been broadcasting a secondary audio channel for the vision-impaired. I wonder if another similar facility is vacant and could be made available for the hearing impaired. Such an audio channel could exclude the background or effects sounds that make it so difficult for many hearing-impaired people to understand TV dialog. This would enable Australian programs such as current affairs to be heard with ‘clean’ dialog. It seems that once background and effects audio are mixed in, there is no way of unscrambling the combination. As an afterthought, is the primary TV broadcast audio a multichannel system so that viewers with 5.1 or 7.1 home theatre receivers can produce this effect? If so, maybe a cooperative TV broadcaster could have one audio channel (perhaps the centre channel) free of background/effects so that hardof-hearing viewers could connect to that audio and hear ‘clean’ monaural dialog. Some years ago, one of your readers suggested changing the connections to 108  Silicon Chip one ear of a pair of earphones (causing the ears to hear anti-phase) could produce clean dialog, but I have had no success with this. Any other suggestions would be most welcome. (B. H., Cornubia, Qld) • That is a great idea. While we don’t have the technical details of the Australian TV broadcast standards, channels use either MPEG2/4 digital compression and encapsulation. MPEG2 supports up to 16 audio programs, while MPEG4 supports an essentially unlimited number. So we think there is no technical reason why your suggestion couldn’t be implemented, as long as the TVs decoding the streams can handle more than one or two audio programs (and surely they should). You would have to convince the broadcasters to add those channels, however. Even people with reasonably good hearing can have trouble understanding dialog in TV programs with loud background music or sound effects. Some programs seem to have especially muted-sounding dialog. You are right that 5.1/7.1 encoded transmission usually have the centre channel carrying speech and little else. This is a good reason to have a surround sound system with a centre channel (even if you don’t need the rear channels), as it can make dialog significantly more intelligible. Not all broadcasts have surround sound encoding, though. Ultrasonic Anti-Fouling fault LED flashing I have built your Ultrasonic Anti-Fouling MkII (May & June 2017; siliconchip.com.au/Series/312) from a Jaycar kit. During the testing step, without the transformers installed, I adjusted and measured the following voltages: Input: 14.3V Between pins 5 & 14 of IC1 socket: 4.95V TP1: 1.155V TP2: 0.5V 2200μF capacitor: 0V When power is applied, the green LED comes on for about three seconds, then goes off, and the fault LED flashes. I tested all the resistors with a multimeter before fitting and have now removed and replaced them with new resistors, a new 20MHz crystal and even a couple of the capacitors. No Australia’s electronics magazine change, still the fault light is flashing. I’ve covered each high-voltage part and under the crystal with conformal coating to make sure it does not short on the board. I tried adding a 470W 1W resistor between the drain and source of the Q5 Mosfet, as you’ve suggested in the past to fix similar faults, but that didn’t help either. I also replaced the 2200μF 25V capacitors that came with the kit with Rubycon 25ZLH2200MEFC16X20 capacitors but still get the same fault light. Does it matter that it does not say “low ESR” on the packet? (T. S., United Kingdom) • Those Rubycon caps are suitable; they are listed as low-impedance. As it seems the capacitors are not leaky, we think that Mosfet Q5 isn’t charging the capacitors. Check this Mosfet and whether it is being driven at its gate when power is switched on. There should be a square wave at pin 6 of IC1, and the gate voltage of Q5 should start to increase above the source. Over a few seconds, this voltage should go above 3V, and the 2200μF capacitor should begin to charge. Read the section entitled “Soft start facility” in the instructions, and check if this is happening with your Anti-Fouling unit. Running SC200 from a 35-0-35V transformer I have a quick question concerning the SC200 Power Amplifier modules (January-March 2017; siliconchip. com.au/Series/308). I’ve read in your articles that for the lower power version, using a 160VA transformer with 30-0-30V secondaries, you suggest changing the 22kW resistor between the collector of Q7 and ground to 15kW, and the two 6.8kW resistors at the collector of Q6 to 4.7kW. As I’m using the Ferguson transformers from my old ETI500 with 35-0-35V secondaries, should I change those resistors to 18kW and 5.6kW, respectively? (T. B., Bumberrah, Vic) • The values you have suggested are about right. MMBasic and PRINT USING I have looked in all the MMBasic Manuals (versions 4.5 to 5.05.03) and on Geoff Graham’s Maximite website, but I cannot find any reference to the siliconchip.com.au PRINT USING command. Is there a workaround? I have several BASIC programs I want to convert to MMBasic from the Amiga, Amstrad, Commodore 128 and TRS-80. Also, could you let me know how many articles are in the series “Getting Started with the Maximite”, which I believe started in February 2017? (R. M., Melville, WA) • Geoff Graham responds: As you have discovered, PRINT USING is not implemented in MMBasic. Use the Str$() function instead, which provides a lot of the same functionality (although the syntax is different). The “Getting Started with the Micromite” articles were published in the February, March, May & June 2017 issues. See siliconchip.com.au/ Series/311 Sourcing parts for Ultra-LD Mk.4 Amp I would very much like to build the Ultra-LD Mk.4 200W amplifier, power supply and Mk.3 speaker protector (July-October 2015; siliconchip.com. au/Series/289). I’m starting to investigate the availability of parts before deciding whether to proceed. Are there any parts in those designs that will likely be hard to find? Also, this would be my first Silicon Chip build, and I don’t have any preferred suppliers. I see your references to suppliers such as element14, Rockby, Altronics, Mouser, Digi-Key and Jaycar. I also see that Altronics have a kit for the power supply, and I can obtain the circuit boards plus the SMD parts for the Speaker Protector Mk.3 from Silicon Chip. Does anyone supply more complete kits for the amplifier at all? As you can understand, shipping costs will be significant if I need to source lots of partial shipments (to New Zealand) from different suppliers. Sourcing the correct transformer is a problem. I haven’t found any suppliers that list a version with 2x40V plus 2x15V secondaries. The power supply kit available from Altronics doesn’t appear to include the transformer. I have had discussions with a transformer manufacturer here in Christchurch, but I’d need more detail on its specifications before proceeding. If I need to have a transformer built, can I assume the following? The siliconchip.com.au 40-0-40 secondary will need to handle up to 300VA continuously. It should preferably have a silicone steel core, and the lowest practical winding resistance using copper, not aluminium. (J. G., Christchurch, NZ) • As far as we know, all the parts to build those modules are still available. There are a few parts that you will probably have to order from us. That includes the PCBs plus the frontend transistors for the Ultra-LD Mk.4 amplifier modules, we sell these at: siliconchip.com.au/Shop/7/3400 The PCBs and other parts can be found at: siliconchip.com.au/ Shop/?article=8959 As for the less commonly available parts, it depends on which supplier(s) suit you best. We suggest you try Mouser or Digi-Key first, as they are likely to have the largest proportion of the components you need, and you will be ordering enough to get free delivery. They send out orders pretty fast; usually, we receive parts from those two suppliers within a week of ordering. For the remainder of the components, especially for ‘generic’ things like capacitors and through-hole resistors, try your local Jaycar store. Altronics have a good selection too, and if you will be ordering the power supply kit from them, you can get many of the other parts delivered at the same time. As for the transformer, you are correct that the Altronics part we used has been discontinued and it’s difficult to find a replacement. You could have a transformer made, but also consider using two separate toroidal transformers, one around 300VA with two 40V secondaries and one smaller 2x15V (say 30VA). Both are available off-the-shelf. The only real disadvantage of this configuration is the extra space and a bit more wiring. There are some advantages - you might get a bit more power for the main amplifier modules since you won’t have the preamp draw on that transformer. Your suggestions for the transformer specifications seem sound, although you didn’t mention it being toroidal, which we strongly recommend as they have lower external magnetic fields. If you do have to get one made, see if you can get it with an outer electrostatic shield layer. That helps to reduce the hum field. Australia’s electronics magazine Faulty batch of transistors I purchased several Ultra-LD Mk.4 Amplifier PCBs from your Online Shop, along with the required HN3A51F and HN3C51F transistors. This project was published in the July-October 2015 issues (siliconchip. com.au/Series/289). Following the 12-step setup procedure in the third article, steps 1 to 11 were successful, but I could not achieve the desired offset voltage (step 12) on any of the six amplifiers I assembled. The voltage across the amplifier outputs is far too high. My understanding is that it should be almost 0V. VR2 has practically no effect on the DC level. The voltages across the 68W emitter resistors of Q2a & Q2b measure 60mV rather than the 135mV specified; the voltage across the 12kW resistor in series with LED1 is 20V, not 24V; and the voltage across the 330W resistor at the emitter of Q3a is 580mV rather than 600mV. When I feed a signal generator into the amplifier, the amplifier goes into distortion for all frequencies above 1kHz. Interestingly, all six modules are performing (faulting) precisely the same. I think the fault is with the HN3C51F transistors (Q2). I am confident that the output stage is stable and is operating correctly. (I. P. V., Karrinyup, WA) • We tested several of the HN3C51F transistors that we have in stock, and it seems that we have received a batch of duds. It isn’t that they are out-of-spec transistors; they do not behave like transistors at all, and different samples we tested all behave differently. So it must be a manufacturing failure. Luckily, we were able to find and source a reasonable number of the only compatible substitute part, also now discontinued, the IMX8-7-F. We have tested several of the devices that we received, and they seem to be fine. So from now on, we will supply IMX8-7-F transistors instead of HN3C51F (siliconchip.com.au/ Shop/7/3400) and we will send you replacements for the faulty transistors you received. Luckily, Q2 acts as the current mirror for the input pair, so the performance of these transistors is nowhere near as critical as the HN3A51Fs. We August 2021  109 still have a reasonable number of those in stock. By the way, it looks like the original circuit diagram (Fig.1 on p34-35 of the August 2015 issue) had an error. The 135mV specified for the 68W emitter resistors of Q2a & Q2b should be closer to 68mV as the 2mA from Q3a is split between these two resistors in the quiescent condition. Hence, your voltage measurements were all close enough to be considered correct. Operating hydronic heating during blackout Last Wednesday, a storm broke hundreds of trees near our home, and this is the sixth day without power. We have hydronic heating and plenty of gas, but we can’t run it because the installer says that Bosch boilers are not compatible with generators. They gave no technical explanation for why this is the case, nor any solution. A local electrician said to connect Neutral to the generator ground, which sounds dangerous to me. I have also heard about difficulties powering stationary computers, washing machines and some fridges from generators. Is it possible to run the hydronic heating controller from a generator? (V. K., Mt Dandenong, Vic) • It’s difficult to answer your question without knowing what sort of generator you have. Generator outputs vary considerably depending on whether they are electronically synthesised (inverter generator) or not, and whether they have a pure sinewave output, modified sinewave, square wave etc. If you have an inverter generator with a pure sinewave output, virtually any equipment should be able to run from it the same as it does from the mains. Just make sure that the generator has sufficient peak and continuous current/power capability for the load(s) attached. The pure sinewave output would be cleaner than the typical mains waveforms! The primary power consumption in a hydronic heating system will be the water pump. If the pump is modestly sized, it will probably not draw more than a few amps, so even a modest pure sinewave inverter running from a reasonably-sized lead-acid battery should be able to run it. We do not suggest running sensitive 110  Silicon Chip loads like computers or computercontrolled equipment from a generator without a pure sinewave output. Their waveform can be very distorted, and the amplitude and frequency can vary considerably. That is probably what you are referring to when you mention stationary computers, washing machines and fridges. Easy way to calibrate multimeters I have seven multimeters. Many of them are not used regularly, so I have stored them without batteries in the original boxes, and they remain in good condition. It would be expensive to get them professionally recalibrated, so I am building the Precision 10V DC Reference for Checking DMMs (March 2014; siliconchip.com.au/Article/6729) and have ordered 10W, 100W, 1kW, 10kW & 100kW ±0.1% resistors. I plan to put all these in an enclosure. I know this will not be the same as getting them professional calibrated; it is only to check that they are still within their manufacturer’s specs so that I can use them with confidence. I have ordered the AD587JNZ and the resistors from element14. Do you have any comments on this? (R. M., Melville, WA) • That sounds like a reasonable approach. You will probably find that many of your multimeters are still spot on. They can drift over time, but don’t always do so. You could also use such a setup to calibrate the lower current ranges, in combination with a variable bench supply, ideally with an adjustable current limit. You would need to calibrate one meter’s voltage ranges first. Connect the meter in series with one of the lower-value precision resistors, with the calibrated meter across the resistor. Adjust the supply voltage until you get very close to 10mV across the 10W resistor. You then know that the current is very close to 100mA. The resistor dissipation will be 100mW in this case, so keep in mind the resistor’s power rating. Induction Motor Speed Controller radiates EMI I have built your Induction Motor Speed Controller (April & May 2012; Australia’s electronics magazine siliconchip.com.au/Series/25) from an Altronics kit (Cat K6032) for use on my pool pump, as per the instructions included with the kit. The pump starts and runs as described, but the controller is emitting RFI that interferes with our AM radio reception. The interference is quite evident and disturbing. Our AM radio uses a loop antenna mounted in the ceiling and gives excellent interference-free reception, unless the controller is running. The controller is located in the pool shed, which is about 10 metres from the house in the corner of our yard, so I cannot increase the physical separation. I am also concerned that I will be causing a nuisance to my neighbours. The pump being controlled is an 860W Davey Silensor which, according to my power meter, is drawing around 990W without the controller and about 330W with it. So it should be well within the controller’s capacity. The controller and pump leads are both around 1.8m long and cannot be shortened significantly. The Altronics kit came with a plastic case, as per your article. The pool shed is metal and is not Earthed in any way (I’m not sure if that is required). The radio and pool shed are on the same mains circuit. Please give me suggestions on how I can reduce this interference. (J. M., via email) • We tested whether the IMSC interfered with AM radio reception during the development phase. We did this while it was connected to a pool pump and operating. Bringing a portable AM radio close to the IMSC only resulted in a small amount of hash pickup at a range of about 1m. With the radio more than 2m away from the controller, very little to no interference was apparent. So your controller appears to be creating a great deal more EMI/RFI than our prototype. We therefore suspect that your problem is related to noise coupled onto the mains wiring, rather than direct radiation from the unit or its wiring. First, check your mains Earthing. The effectiveness of the line filtering is only as good as the Earthing. This could be a problem if the controller is at the end of a long cable run, and the Earth impedance is on the high side, or if your domestic Earth connection is not good. You might need to have an electrician install an Earth stake in the pool shed. continued on page 112 siliconchip.com.au If the Earth is solid, then it would be worthwhile trying a bigger mains filter. This could be as simple as winding the mains wires through a toroidal ferrite core. Speaker Protector not sensing AC I have built the October 2011 Loudspeaker Protector module (siliconchip. com.au/Article/1178) from an Altronics kit (Cat K5167). I configured it for my supply rail voltage and tested it with the prescribed method, and it seemed fine. However, as soon as I connect the AC sense lines from my transformer, it refuses to work. Connecting AC sense to the positive rail as detailed in the instructions and performing all other tests shows the module to be working. Can you enlighten me as to the likely cause of this problem? (D. J., Mandurah, WA) • The first thing to do is check that you have wired up the transformer to the AC sense terminals correctly. Typically, you would have a centre-tapped winding with the centre tap Earthed and the other connections going to both your bridge rectifier AC terminals, and the terminals of CON2 on the Speaker Protector. Assuming the connections are correct, verify that the base voltage of Q2 is low (below 0.2V) when the AC voltage is present at the AC sense input. If that is incorrect, then check diodes D2 and D3 and the transistor Q1 to ensure they are orientated correctly, have good solder joints and are not faulty. That it worked with a DC test suggests transistor Q1 is working OK and that at least one of diodes D2 & D3 is functioning correctly. It could be a problem with the resistor or capacitor values around Q1. If the 470nF capacitor is not soldered correctly or has the wrong value, the circuit will work with DC voltage applied but not AC. Similarly, if the resistor values are wrong, the circuit might not hold up through dips in the AC voltage. Flexitimer with higher supply voltage Many years ago, I built the PICBased Flexitimer Mk.4 (June 2008; siliconchip.com.au/Article/1847) from 112  Silicon Chip a Jaycar kit (Cat KC5464). Can it be modified to run from a 24V supply? (J. S., via email) • You need to change the relay to a compatible type with a 24V DC coil, the 470μF capacitor to a 35V rated type, and the 1kW LED current-limiting resistor to 2.2kW. AEE ElectroneX.......................... 7 Incorrect component in low ohms meter Control Devices..................... OBC Advertising Index Altronics...............................83-86 Ampec Technologies................. 25 I have built the Low Ohms Tester by John Clarke from the June 1996 issue (siliconchip.com.au/Article/4987), but I can’t get it working. The text says that the voltage at pin 2 of IC1 should be the same as pin 3. Adjusting VR1, I can get 2.4V on pin 3, so it appears REF1 is working OK. But the voltage at pin 2 is 1.64V. I have replaced IC1 and Q1 to no avail. (N. L., Christchurch, NZ) • Since you have replaced IC1 and Q1, that seems to rule out either component being faulty (which would explain what you are seeing). However, if Q1 is the wrong type or orientated incorrectly, that would cause this sort of fault. The only other possibilities are a lack of continuity or incorrect value with the 2.4kW resistor, trimpot VR2 or the 200W resistor. Try changing range switch S2 to see if that has any effect; if it does, it is likely one of the latter three components at fault. Note that if this part of the circuit is operating normally, pin 6 of IC1 should be around one diode drop (approximately 0.6V) below the voltage at pins 2 & 3. Dave Thompson...................... 111 Pulse generator circuit wanted Vintage Radio Repairs............ 111 I’m interested in building a pulse generator. I found a pulse generator design in Practical Electronics, February 1979. Can you suggest a circuit as simple as that one, but up to date with similar specifications and features? (R. M., Melville, WA) • We published a pulse generator circuit in the Circuit Notebook section of the November 1997 issue, which has similar features to the one you refer to (siliconchip.com.au/Article/5833). However, there was no PCB design to accompany that circuit. You could also build up the Practical Electronics design as there is nothing wrong with it. All the parts used in that circuit are still available. SC Australia’s electronics magazine Digi-Key Electronics.................... 3 Emona Instruments................. IBC Hare & Forbes............................. 9 Jaycar............................ IFC,53-60 Keith Rippon Kit Assembly...... 111 Lazer Security......................... 111 LD Electronics......................... 111 LEDsales................................. 111 Microchip Technology.................. 5 Ocean Controls......................... 11 PMD Way................................ 111 Silicon Chip Shop...............96-97 Switchmode Power Supplies....... 6 The Loudspeaker Kit.com......... 10 Tronixlabs................................ 111 Wagner Electronics................... 63 Notes & Errata Ultra-LD Mk.4 Amplifier, July-August 2015: the circuit diagram (Fig.1) incorrectly specifies 135mV across the 68W emitter resistors of Q2a & Q2b, the correct value should be around 68mV. The September 2021 issue is due on sale in newsagents by Thursday, August 26th. Expect postal delivery of subscription copies in Australia between August 25th and September 10th. siliconchip.com.au