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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 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”. The origin of Presspahn If anyone ever wondered where Presspahn insulation comes from, it’s here in Yorkshire – God’s own county, of course! You can see the location of the factory at the following link. siliconchip.com.au/link/ab8e Alan Winstanley, PE Magazine Online Editor, Brighton, UK. Transistor Test Set identified The “TRANSISTOR TEST SET” shown in the photo on page 4 of the May 2021 issue is an Electronics Australia project from August 1968, presented by your own Jim Rowe. I built one of these at the time and still use it. It’s a very useful piece of equipment. As to the “ACE” on the meter face, I think this refers to a company called ACE Radio, a regular advertiser in EA at the time. They appear to have sold mostly surplus items, but also kits for some EA projects, the Transistor Test Set being one of them. It was available as either a fully built item, or as a DIY kit. Peter Caprin, Valley Heights, NSW. it did nothing for a few turns; then it started to rise, very slowly at first, then exponentially faster. After a good half an hour of adjustment, I could get it to hover around 6V and would hold there for about thirty seconds or so, then very slowly, it started rising again, getting faster and faster. To keep the voltage below 8V, I had to wind the trimpot anticlockwise two or three turns, which started the voltage decreasing, and it continued doing so until it was under 1V. I couldn’t get it to hold at 6V. That stumped me, so I decided to finish building the second module, and was surprised to find that it had the same unstable quiescent current. I figured the problem wasn’t the SC200 modules but something in the power supply, although it was testing fine. As I was clutching at straws, I started wondering if the leads from the power supply to the amp modules were picking up EMI as I had extended them with some leftover hook-up wire (about one metre long) to make adjustments easier. So I cut the extensions off and fitted the power supply wires properly, and that cured the problem. I adjusted the quiescent current and offset as per instructions. The amp is now working perfectly, and (to our ears) my wife, daughter and I all agree that music sounds clearer, more precise and the bass is much more potent than the old ETI modules, with no hum. I wouldn’t have believed the difference in sound quality could be so evident between the two. Tony Brazzle, Bumberrah, Vic. Comment: based on the symptoms you described, we would not have guessed that it would be the power supply wiring at fault. It sounded more like a case of mismatched transistors. We’re glad you managed to sort it out, and your listening tests confirm what our test equipment shows – that the SC200 modules are high-performance modules, only falling short of the very best amplifiers, like our Ultra-LD series. Expanding the Remote Monitoring Station A huge belated thank you for the article on the Arduino-based 4G Remote Monitoring Station from the SC200 audio amplifier problem solved While trying to set the quiescent current of the SC200 amplifier module I had just completed (January-March 2017; siliconchip.com.au/Series/308), I ran into a strange problem. Everything tested fine up to the point of fitting the 68W resistors in place of the fuses. Feeding a signal into the module produced a clean waveform on the scope at the output. The problem I had was some sort of funny runaway effect happening while adjusting the voltage across the 68W resistors to the 6V specified. With the trimpot turned fully anti-clockwise, the voltage was just under 1V, which was correct. As I wound it clockwise, 4 Silicon Chip Australia’s electronics magazine siliconchip.com.au February 2020 issue (siliconchip.com.au/Article/12335). I decided to take your design and expand on it. Attempting to learn a new language and learn the inner details of the SIM7000 module at the same time may not have been the easiest choice. Learning a new language meant I spent a lot of time undoing the good work of Silicon Chip, only to put it back later. I have a water pressure sensor to monitor for stock water for cattle. The electric pump is 10km away from home. A no-pressure situation will eventually lead to no water for thirsty cows, especially in the summer months. On power-up, it sends me a text message indicating the firmware revision and the pressure level. An SMS is generated should the pressure go outside a preset range at any time. I can also make a query by sending a “q” or “Q” to the remote Arduino. The water pump will stop if AC power is lost for more than a few seconds. Manual intervention is required to reset the pump. The Arduino/SIM7000 restarts when power is restored and sends a text message. This is my cue to go to the pump. Before installing the Arduino/SIM7000, this required a visit to the pump or checking if water came out of one of the float valves. The latter is never fun in the winter, as it requires one’s arm to be immersed in the water. I obtained the gravity water pressure sensor by DFRobot (SEN0257) from Core Electronics. It has a BSP thread. I cut off the supplied connector and fitted a three-way Deutsch DT connector to provide a degree of weatherproofing. I doubled up the supplied wires for the crimp contacts. The SIM7000E is no longer sold by Core Electronics but can be obtained directly from DFRobot (www.dfrobot. com/product-1732.html). As I do not require the GPS or air pressure sensor functions of the SIM7000 card, I removed the associated code. I also modified it as I did not require the power-saving shield. I then housed the system in a waterproof enclosure from Jaycar. I used the following links to confirm that the SIM7000E was compatible with my local tower: https://whirlpool. net.au/wiki/mobile_phone_frequencies www.stelladoradus.com/finding-my-frequency-onmy-iphone/ The CAT-M frequency bands supported by the SIM7000E are B3/B5/B8/B20/B28. The band number of my local tower was 3. I determined this using the notes at www.stelladoradus.com I then added several hard-coded commands to the code to ensure that the SIM7000E is configured as I intended, rather than taking a chance. I send the SIM7000E the following commands on power-up: To set the preferred mode to LTE only (2 = Automatic, 13 = GSM only, 38 = LTE only and 51 = GSM and LTE only): MODEM.println(“AT+CNMP=38”) To set the band to CAT-M (the other choice is NB-IOT): MODEM.println( “AT+CBANDCFG=CAT-M”) To select CAT-M only (1 = CAT-M, 2 = NB-Iot, 3 = CAT-M and NB-IoT): MODEM.println(“AT+CMNB=1”) Enables full phone functionality (there are six options; 1 is the default): MODEM.println(“AT+CFUN=1”) 6 Silicon Chip Information on these commands can be found in the SIM7X00 Series_SMS_Application Note_V1.00 and SIM7000 Series_AT Command Manual_V1.04 documents. To test the SIM7000 thoroughly, I began sending it photos to see if it would be robust enough to cope. This did not go well; I would be interested from other readers how they dealt with this sort of abuse dished out to the SIM7000E. I had to keep the SIM7000E powered up for over 24 hours and wait for the network to put things right before it functioned normally again. I am building my second monitor now. I will upgrade the firmware in the future to monitor pressure trends and the duty cycle of the mains-powered pump. Ed O’Brien, Heyfield, Vic. Comments on DIY Reflow Oven project I’m building the DIY Reflow Oven controller (April-May 2020; siliconchip.com.au/Series/343) and have looked back over the previous uses of the same control board (eg, the DDS from February 2020; siliconchip.com.au/ Article/12341). I am having a little trouble understanding the logic behind the two regulator designs. Why is a low-dropout regulator specified for REG2 that is quite expensive to buy with delivery charges, rather than the readily available LM317? After all, the LD1117V is rated at only 0.8A (instead of 1A) and has far more voltage “headroom” than the 5V regulator used for REG3. Could I use an LM317T instead? Also, the data sheet for the LD1117V shows a recommended 120W value for the top resistor with the 10μF capacitor, whereas 330W has been used instead – whilst this may improve ripple performance, would it not also degrade response times? I know this project utilised a design from another application. Still, I wonder if a Micromite BackPack might have been a better option – the touchscreen has higher resolution, and it would do away with the need for a separate board, rotary encoder, cabling etc. Also, using PWM on a leading-edge dimmer-type circuit would put less thermal shock and stress on the oven elements and might be a lot less expensive than the solid-state relay. As another observation, many people have difficulties with soldering smaller SMDs. Yet, this board uses 2012 (imperial 0805) rather than 3216 (imperial 1206) parts with 3226 (imperial 1210) pads, for example – that would be much easier to deal with. The board is obviously very heavily packed, with very little clearance between parts – this caused me some problems; for example, the 100nF X7R 2012 capacitors are less readily available (unless in large quantities), and I had to fit 3216 parts onto the rather small pads. Also, many of the connectors are too close together (although, with heavy trimming, I was able to fit a few boxed headers that I prefer to avoid later connection mistakes). The specified flag heatsink does not fit due to connector and capacitor clearance issues. I did manage to get the board together – without heatsink – but with the aid of Geoff Graham’s recommendation of a stereo microscope, and a spring-loaded stylus I made to hold the parts in place for soldering. I am waiting for another part before commencing the testing phase. Ian Thompson, Duncraig, WA. Australia’s electronics magazine siliconchip.com.au Comments: In some projects, that controller board is powered from 5V DC, so the LD1117V is needed for a regulated 3.3V rail. You are correct that in the DIY Reflow Oven, this board is powered from 9V DC, so you could use an LM317 instead. The advantage of the 120W resistor compared to the 330W resistor we’ve used is that it guarantees that the regulator’s minimum load requirement is met even if nothing is drawing current from the regulator’s output. However, other devices on the board constantly draw current from the regulator’s output, so the lower value is not needed. It won’t affect the response time. Yes, the Reflow Oven could have been controlled using a BackPack controller, but a third party contributor designed this project, and he decided to re-use his existing controller design. We didn’t think it was worth the effort to redevelop the project to use the Micromite BackPack (even though we would prefer that), given that it was presented to us as a fully working, completed design. We don’t consider 2012-size parts to be all that difficult to hand solder; they are not that much smaller than 3216 metric (being 1.2mm wide rather than 1.6mm wide), and the pads tend to be a bit more generously sized in relation to the parts. We usually avoid going any smaller than that, although the next size down (1608) is not much harder to manage. We agree that the controller board for this project is packed, although we were able to successfully build and test it without having to trim anything. That includes the heatsink, which we somehow managed to fit – perhaps ours is a fraction smaller than yours. Of course, different constructors will have different skill levels and visual acuity, and we realised these projects will be challenging for some. We publish a mix of projects that use a wide variety of differently-sized components. You should not have trouble getting 100nF X7R 2012/0805 capacitors. They are a very standard item used in the millions (if not billions). Element14 sells a variety of suitable capacitors starting at around 3¢ in quantities of 10+ (cat 1759166), while RS sells them for 9.7¢ each in quantities of 100+ (cat 135-9033). One hundred might seem like a large quantity to purchase, but considering how many 100nF bypass capacitors are in the average design, and the fact that 2012 capacitors will usually comfortably fit on 3216 pads, we think it’s worthwhile to stock up on them. Dodgy switches becoming common The Serviceman’s Log entry in March 2021 about G. C.’s problem with a membrane switch on a coin counter prompted me to write in. I recently came across several faulty switches, and am beginning to think that they are getting poorer and poorer. The first one was a switch on an electric chainsaw that used to weld up and not switch off. I stopped using the chainsaw for that reason. Later, I came across an old switch that has the quick on/off function - no matter how slowly you operate the switch, it changes over really fast, and it has big contacts. I managed to fit this to the chainsaw, and that was the end of that problem. 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 Australia’s electronics magazine June 2021  7 Helping to put you in Control Mini Temperature & Humidity Sensor 0-10V output The Pronem mini from Emko Elektronik are microprocessor based instruments that incorporate high accurate and stable sensors that convert ambient temperature and humidity to linear 0 to 10VDC. Dimensions are only 40x 79 x 16mm. SKU: EES-001V Price: $149.95 ea Modbus TCP Analog Output Module The analog output module MU110-501 has 8 analog outputs (0/4-20 mA, 0-1/10V). Support for Modbus TCP, MQTT, SNMP, SNTP. SKU: AKC-263 Price: $545.95 ea Proop 7 Control 7” HMI with 2 Ethernet Ports This is a budget priced Touchscreen with a resolution 800 x 480 pixels and 260K colors; Ethernet, WiFi, RS-232 and RS-485 communication and 8 digital inputs/outputs for control. SKU: EEI-012 Price: $619.95 ea Digital ON/OFF Temperature Controller DIN rail mount thermostat with included PTC sensor on 1.5m m lead. Configurable for a huge range of heating and cooling applications. 230 VAC powered. SKU: EEC-010 Price: $89.95 ea Isolated Load Cell 2mv/V 0-10V Transmitter with Display Converts a signal for a 2 mV/V load cell to a 0 to 10 V signal. Able to power 2 load cells in parallel. DIN-rail mount. SKU: ALT-415 Price: $249.95 ea LabJack T7 Data Acquisition Module LABJACK T7 Multifunction DAQ with Ethernet, wifi and USB. Features 14 analogue inputs, 2 analogue outputs and 23 digital I/O SKU: LAJ-045 Price: $739.30 ea Ultrasonic Wind Speed & Direction Sensor RK120-07-AAC Economical Ultrasonic Wind Speed & Direction Sensor with Modbus RTU RS485 output and 4 metre cable. 12~24VDC powered. SKU: RKS-028M Price: $499.95 ea For Wholesale prices Contact Ocean Controls Ph: (03) 9708 2390 oceancontrols.com.au Low-cost buck/boost module warning Prices are subjected to change without notice. 8 Silicon Chip The second one was the remote control for my garage door. Since new, the button always required a few presses before the door opened. Then it stopped working altogether. I took it down to the workshop and split the case open to check the battery (two 3V button cells). They tested OK, so I removed the PCB. The first thing I tested was the continuity of the pushbutton switch. When pressed, it remained open circuit. I had some good quality push button switches, but they had a much higher profile, so I installed one of these and cut a hole in the case to accommodate it. The remote not only worked fine after that, but now only needs one press of the button to open the door. The final switch problem was with an auto-darkening welding helmet. I had been using it for some months when it became unreliable. I put a new 3V button cell in it, but that made no difference, and after getting a few more flashes while using it, I tossed it aside and went back to my old faithful. A medical problem put me on light duties for a while, and while wondering what to do with myself, I thought I would have a look at the faulty helmet. These helmets have a shade adjustment on the side with a grind position, which I wished was not there, because if you put the helmet down a certain way, it turns the knob onto grind, giving you a flash. When adjusting the shade on the auto-darkening filter (ADF), the screen used to flicker, which I put down to a noisy potentiometer. So I thought that was a good place to start. The ADF cartridge is made to be removed easily to facilitate the replacement of the front cover lens. The switch is removed by pulling off the knob and undoing the nut behind the knob. With it on the workbench, I prised up some plastic tabs and removed the cover to reveal an ordinary pot with a switch on the back. I was going to substitute another pot, but as it was easier to test the switch, I did that first. With the control in grind position, the switch was open, and I measured some volts across it. When I turned the pot to the darkening position, I got a reading of 1.2V. I had expected a lot lower than that, but the ADF worked fine. However, when I turned the control further, the voltage ranged all over the place, going as high as 1.6V, and the ADF did not work. As I needed little excuse to do away with the grind position, I simply soldered a piece of wire across the switch terminals. It was easy to put back together, reversing what I did to take it apart. I have used the helmet for some months now, and I have not had a single flash. Not only that, but the shade control gives a smooth change over the whole range with no flickering. Also, I have been able to adjust the other settings more precisely to suit me. I am very pleased with the result. It worries me just how many of these devices are scrapped just because of poor-quality switches. Ron Groves, Cooloola Cove, Qld. I am writing about the “Reliable solar lighting system” circuit published in the Circuit Notebook column of the January 2021 issue (siliconchip.com.au/Article/14711). Australia’s electronics magazine 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 The circuit shows a solar panel with a nominal 12V output feeding what is described as an “XL6009 based buck/ boost converter module” producing a 5V output. Converter modules using the XL6009 IC are readily available from numerous vendors online. On paper, these modules are very attractive, with wide input and output voltage ranges. While some XL6009 modules are single-mode only (buck or boost), some offer automatic changeover depending on the input supply, guaranteeing a fixed output voltage regardless of whether the input is above or below the preset output voltage. Such modules can be identified by the presence of two inductors, rather than the one used in the fixed-mode modules. There are pitfalls with the XL6009, however. Despite websites having descriptions to the contrary, according to the manufacturer’s data sheet, the minimum input voltage of the XL6009 is 5V. So it is not guaranteed to produce a regulated output voltage when the input drops below 5V. Usually this would be of little consequence, but there is a flaw with the XL6009 which, depending on how it’s used, could end up destroying the device it is powering. Within a certain range of input voltages under 5V, the output rises many times higher than the set output voltage. For example, on the multi-mode module I tested with its output set to 5V, the fault occurred with input voltages between approximately 3.0V and 3.2V. Output voltages ranging from 14V up to 51V were produced, and adding a load resistor showed that non-trivial currents could be supplied when the high output voltages were present. Obviously the XL6009 does not contain a low voltage cut-off circuit, which it needs given this behaviour. The fault could be triggered by a slowly rising input voltage (eg, when light is applied in the early morning to the solar panel mentioned above), or if something such as a flat battery prevents the input voltage from rising high enough to guarantee correct operation. It could be that the TP4056-based LiPo charger used in the “Reliable solar lighting system” is not adversely affected by short bursts of very high voltages on its input. Alternatively, perhaps the solar cell cannot supply sufficient current at voltages in the critical range to do damage. If this is the case, then the immunity of the described circuit to the XL6009 problem is due mainly to good luck. However, if anyone is tempted to use the XL6009 to power something more sensitive (such as a Raspberry Pi or Arduino board), this fault with the XL6009 could end up destroying the board. I was planning on using a dual-mode XL6009 module to power a Raspberry Pi board, but decided to thoroughly test the module first. It was while smoothly varying the input voltage that I noticed a sudden jump to over 50V on the output, which prompted a more careful investigation. As a result of this observation, I will never use anything based on the XL6009 – the IC is simply not reliable. While an external low voltage cut-off circuit could mitigate the problem, the XL6009 still has its potentially devastating problem, and I am not willing to chance it with anything of value. More recently, I discovered that others have encountered similar issues with XL6009 modules; see https:// owenduffy.net/blog/?p=12435 10 Silicon Chip Australia’s electronics magazine siliconchip.com.au I think it is worth warning your readers of this serious problem with the XL6009 and modules which use it. While such modules appear to be very useful in theory for various situations, in my opinion, they are best avoided. Jonathan Woithe, Valley View, SA. Strange capacitor value readings For the second time, I have had the curious situation where several capacitors do not measure as their stated value, but all return almost the same capacitance. Over a year ago, I measured the 200V 330μF main capacitors in two PC power supplies. All four returned a value close to 220μF. The supplies were the same brand, and the capacitors the same manufacturer. More recently, I checked three identical 440VAC 10μF power factor correction capacitors from mercury arc control units. They were made in 1981, and all three tested at about 6.5μF. If there is anything wrong with these, it is not showing. I charged them to 40V, and after an hour, they still measured over 20V, with most of the discharge due to the DVM. This makes me suspect that the manufacturers incorrectly marked the capacitors. I just cannot think of a reason why they would similarly decrease in value. I did verify that the capacitance meter was reading correctly. George Ramsay, Holland Park, Qld. Comment: we suspect that these are from ‘bad batches’ of capacitors that had some sort of variation in their manufacturing process or inputs, causing them to all have similar capacitance deficits. Or they could have been fraudulent; lower value capacitors altered with higher values to be sold at a premium (perhaps with a few ‘good ones’ on top to avoid suspicion). Digital Insulation Meter displays incorrect values I have just finished building Jim Rowe’s Digital Insulation Meter (June 2010; siliconchip.com.au/Article/186) as a “rainy day” project. I now have it up and running. I have pretty much followed the published circuit diagram; however, I built my own PCBs using a slightly different layout to accommodate a different LCD screen (the 1602A type) than the one used in the article. My meter appears to be working correctly, producing close to the correct test voltages and, pleasingly, displaying on the LCD close to the right leakage current and resistance measurements for known test resistor values of 10MW and 1MW. On the 500V setting, when the test button S2 is pressed, I obtain the following results on the LCD: Ix = 49μA, R = 10MW and Ix = 0.4mA, R = 1MW respectively. However, when test button S2 is released, the LCD then displays Ix = 16μA, R = 30MW and Ix = 1μA, R = 260MW for the 10MW and 1MW test resistor values, respectively. These values don’t appear to have much meaning, and I’m wondering if they’re correct as they create some confusion. Upon releasing S2, I expected the LCD to return to displaying something like the screen “Set Volts, Press button to Test:” that initially comes up on powering up the meter. I changed the code to behave this way by adding a couple of extra instructions in the program’s main loop to ensure that the current and resistance readings on the LCD are blank between measurements, ie, when switch S2 is released. siliconchip.com.au I’m not sure if this was what Jim originally intended, but it makes more sense to me, and it was a simple fix. An extract of the code follows, with the added instructions highlighted in red: CALL InitDig CALL SetVolts BTFSS PORTA,4 CALL Display3 BTFSS PORTA,4 GOTO $-1 I’m now very happy with the performance of my Digital Insulation Meter, so thanks to Silicon Chip for the great project (from some years ago, but it’s still very useful and was fun and educational to build and modify!). Stephen Denholm, Howrah, Tas. Comment: Jim did not experience the same problem as you with his prototype, and we think it might have to do with the characteristics of the button you have used or some other detail of your build. Regardless, your solution is a good one. The only disadvantage is that you need to make a note of the readings before releasing S2. The easiest way to cut your power bill How can Bruce Pierson of Dundathu, Qld doubt the claims of Voltex (Mailbag, May 2021, p10)? I also have a device that I guarantee will cut your power bill in half! It’s shown in the accompanying photo. This versatile device can also be used to cut you phone bill, water bill, gas bill etc in half. But seriously, it is a shame that nobody is held to account for perpetuating these obviously fraudulent claims/ sales. I imagine the people who fall for these products are the ones least able to afford them. Ron Walker, King Creek, NSW. Worshipping a greater power The accompanying photo (shown below) is of a local church that caught my eye. I guess you could call this “Heavenly Power”! SC John Chappell, Caloundra, Qld. Australia’s electronics magazine June 2021  11