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OCTOBER 2022 ISSN 1030-2662 10 9 771030 266001 $ 50* NZ $1290 11 INC GST INC GST 0-30V 0-2A bench supply P16: The History and Technology of VIDEO DISPLAYS, PART 2 p44: New PIC & AVR Chips p60: multi-stage Buck-Boost Battery Charger O R D ER YO U R S TO D A Y ! 3-in-1 Advanced 3D Printer This new generation Snapmaker 2.0 includes modules for 3D Printing, Laser Engraving and Cutting, and CNC Carving. Now with faster and quieter operation. MODULAR DESIGN FAST AND EASY TOOLHEAD SWITCHING J US T IN! LARGER WORK AREA TWICE THE SIZE COMPARED TO PREVIOUS MODEL LASER TOOLHEAD 3D PRINTING TOOLHEAD • FASTER & QUIETER OPERATION • FILAMENT RUNOUT AND POWER LOSS RECOVERY CNC TOOLHEAD IMPROVED LINEAR MODULES FOR A STABLE AND FAST WORKING SPEED FROM 2499 $ INTERCHANGEABLE BEDS FOR 3D PRINT, LASER OR CNC CARVING PRINTS UP TO 330MM HIGH! A GREAT PRICE FOR A PRINTER / ENGRAVER / LASER ETCHER PRINT LASER • 5" SMART TOUCHSCREEN • USB & WI-FI CONNECTIVITY ADDITIONAL TOOLS ALSO AVAILABLE. SHOP NOW! CNC Model Comparison 3D Printing Area (W x D x H) Laser Work Area CNC Carving Area (W x D x H) (W x D x H) Heat Bed Temp. A250T TL4620 230x250x235mm 230x250mm 230x250x180mm 100°C max. A350T TL4630 320x350x330mm 320x350mm 320x350x275mm 80°C max. 3D Printing Nozzle Laser Module 0.4mm Dia., 1600mW, 275°C Temp. 450nm, 50-300 microns Class 4 CNC Carving Machine Size (W x D x H) 0.5-6.25mm 405x424x490mm shank, 6,00012,000RPM 495x506x580mm Price $2499 $2899 See it in action at our Castle Hill and Broadway stores, and speak to our Snapmaker experts Shop Jaycar for your 3D Printing needs: • 8 Models of Filament Printers, with over 50 types of filament • 2 Models of Resin Printers, with over 45 types of resin • Massive range of 3D Printer spare parts & accessories • In-stock at over 110 stores or 130 resellers nationwide Order yours today: jaycar.com.au/snapmaker2 1800 022 888 Contents Vol.35, No.10 October 2022 16 Display Technologies, Part 2 We finish covering the latest developments in video display technology by detailing liquid-crystal displays (LCDs) and more recent advances such as quantum-dot displays, OLEDs, electroluminescents and more. By Dr David Maddison Tech feature 44 New PICs & AVRs from Microchip Microchip have released many new microcontrollers this year, including PICs as well as AVRs (previously from Atmel). We look at the features of five promising new parts and the broader families that they come from. By Tim Blythman Product review 54 Buck/Boost Battery Charging The Buck/Boost LED Driver is a versatile module. In this article we show you how to use it for charging (12 or 24V DC) and convert between different DC voltages (12 ↔ 24V) using its standard features. By Tim Blythman Battery charging 28 30V 2A Bench Supply, Part 1 Our new Bench Supply is fully adjustable with ranges of 0-30V DC and 0-2A. It features voltage and current metering, load switching, over-temperature and short circuit protection. All in an easy-to-build package. By John Clarke Bench supply project 50 PIC & AVR Breakout Boards These three Breakout Boards can be plugged directly into a breadboard and then connect to a Snap or PICkit 4 programmer. Two are designed for PIC16F18xxx-series of micros while the other is for the AVR64DD32. By Tim Blythman Microcontroller project 60 Multi-Stage Buck/Boost Charger This simple add-on turns our Buck/Boost LED Driver into a multi-stage battery charger. It works with different battery chemistries, and includes absorption, float and storage charging, temperature compensation & more! By Tim Blythman Battery charger project 70 Automatic Train Controller This project brings together multiple designs to provide level crossing and semaphore control, all to automate a model railway layout. You can even add chuff and whistle sounds to make it more realistic! By Les Kerr Model railway project 86 WiFi Programmable DC Load, Pt2 To finish our new WiFi DC Load, we cover all the assembly details and how you go about testing (with a detailed manual available separately) and then using the finished project. By Richard Palmer Test equipment project Page 28 0-30V 0-2A bench supply Page 50 PIC & AVR Breakout Boards Auto Train Page 70 Controller 2 Editorial Viewpoint 4 Mailbag 41 Circuit Notebook 52 Subscriptions 78 Serviceman’s Log 85 Mouser Q&A 98 Online Shop 1. ST7920 LCD driver for PIC32MZs 2. EEPROM programmer for FX Pedal 3. Galvanic skin response unit 100 Vintage Radio 106 Ask Silicon Chip 111 Market Centre 112 Advertising Index 112 Notes & Errata STC model 510 portable by Associate Professor Graham Parslow SILICON SILIC CHIP www.siliconchip.com.au Publisher/Editor Nicholas Vinen Technical Editor John Clarke – B.E.(Elec.) Technical Staff Jim Rowe – B.A., B.Sc. Bao Smith – B.Sc. Tim Blythman – B.E., B.Sc. Advertising Enquiries (02) 9939 3295 adverts<at>siliconchip.com.au Regular Contributors Allan Linton-Smith Dave Thompson David Maddison – B.App.Sc. (Hons 1), PhD, Grad.Dip.Entr.Innov. Geoff Graham Associate Professor Graham Parslow Dr Hugo Holden – B.H.B, MB.ChB., FRANZCO Ian Batty – M.Ed. Phil Prosser – B.Sc., B.E.(Elec.) Cartoonist Louis Decrevel loueee.com Founding Editor (retired) Leo Simpson – B.Bus., FAICD Silicon Chip is published 12 times a year by Silicon Chip Publications Pty Ltd. ACN 626 922 870. ABN 20 880 526 923. All material is copyright ©. No part of this publication may be reproduced without the written consent of the publisher. Subscription rates (Australia only) 6 issues (6 months): $65 12 issues (1 year): $120 24 issues (2 years): $230 Online subscription (Worldwide) 6 issues (6 months): $50 12 issues (1 year): $95 24 issues (2 years): $185 For overseas rates, see our website or email silicon<at>siliconchip.com.au I3C: coming soon to an IC near you If you’ve worked with digital chips, especially microcontrollers, you will be familiar with the major serial buses, including I2C and SPI. They are very common ways of controlling external chips and transferring data between them. Many of our projects that use micros include one or both. I2C has the advantage of requiring fewer wires (two plus a ground versus 3-4 for SPI), multiple chips can be on the same I2C bus as they have unique addresses, and chips running off different voltages (eg, 3.3V & 5V) can be on the same bus. However, I2C is quite a bit slower than SPI (typically around 400kbps or 1Mbps compared to, say, 20Mbps), so it’s mainly used for sending commands and small amounts of data. It turns out that a consortium including Intel, ARM, ST Micro, TI, Samsung and Nokia released the specifications for a new bus called I3C in 2017. It has some of the best features of both systems. Oddly, it hasn’t gained widespread adoption yet, and I have only just heard about it. One possible reason is that it is a somewhat ‘closed’ standard, as you have to be a ‘member’ to get the full specification; unlike I2C where it is a free download. I think that is a poor move. If they want people to actually use this and for it to become standard, they should make it fully public. DDR5 computer memory, which is coming into widespread use now, apparently makes use of I3C. I haven’t looked into it in detail; I assume it is the bus used for communications between the onboard memory controller and the computer CPU. I3C is somewhat backwards compatible with I2C and retains pretty much all of its advantages, while increasing the bus speed to the point that it’s almost as fast as SPI. SPI retains an advantage: each pair of devices has a dedicated communications channel, and other devices cannot reduce the bandwidth or interfere with timing of data transfers or commands. But there are many applications where I3C will be good enough, and I think SPI will only be used in specific situations once I3C is more widely used. Some microcontrollers are now available with support for I3C, such as the PIC18-Q20 series, and sensors supporting I3C are ‘coming soon’ from major manufacturers. For more information, see siliconchip.au/link/abgm and https://w.wiki/5fgX Please keep your e-mail address up to date Editorial office: Unit 1 (up ramp), 234 Harbord Rd, Brookvale, NSW 2100. Postal address: PO Box 139, Collaroy Beach, NSW 2097. Phone: (02) 9939 3295. ISSN: 1030-2662 Printing and Distribution: With the cost of postage constantly increasing, it has been very helpful for us to be able to e-mail subscribers when their subscription is about to expire. It’s especially important for people with online-only subscriptions as we might not even have their address for sending a renewal reminder letter. It’s frustrating when those reminders bounce because the subscriber has not told us about a change in their e-mail address. If you change your e-mail address, please update your account to reflect that. If you don’t know how to do that, let us know via phone or e-mail, and we’ll do it for you. You can recover your account if you forget your password to our website, but only if we have your current e-mail address. I advise avoiding using e-mail addresses provided by your internet service provider (ISP) or a work address. Instead, use a service like Gmail, Outlook, Yahoo!, iCloud etc. That way, if you change ISPs or jobs, your e-mail address will remain the same, and you won’t have to update it everywhere. 24-26 Lilian Fowler Pl, Marrickville 2204 by Nicholas Vinen Recommended & maximum price only. 2 Editorial Viewpoint Silicon Chip Australia's electronics magazine siliconchip.com.au 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 has 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”. Ongoing development of the Spectral Sound MIDI Synth I have been doing quite a lot of work with Dan Amos, a Silicon Chip reader who built the Spectral Sound kit (June 2022; siliconchip.au/Article/15338). The work is primarily to add a new feature that automatically creates a patch for the module by analysing samples from a real instrument. I have decided to set up a Facebook group for the module in case other builders might want to swap experiences and ideas. It’s only bare-bones at the moment. You can visit it at: www.facebook.com/groups/817026763041461 I’ve linked to my article on your site but I was wondering if you would like to link to my group too. I think that’s the only way I could get interested people to join my group! It would be nice to see how any makers of the kit get on, to help fix any problems and to see if there are other development ideas. Jeremy Leach, Shrewsbury, UK. Schrödinger’s resistor I thought you’d find this resistor amusing. It was in a batch of 10, nine of which are correctly labelled and of the correct resistance, so I’m not terribly upset. It measures several million ohms, not either of the values on its sides. Keith Anderson, Kingston, Tas. Evacuated tube solar hot water systems are ideal I note your discussion in the August 2022 edition regarding solar panels and water heating (p101) and the suggestion that a standard solar hot water system is likely to be just as effective. I wish to draw your readers’ attention to evacuated tubing systems. They are particularly effective for the Australian climate and function using the heat from the rays of the sun to heat water without the need for any external energy supply. Perhaps I am preaching to the converted here. Mounted to the roof of residential dwellings without additional reinforcement, they can be retrofitted to older houses and incorporated into new builds alike. They are far more efficient and fit for purpose than solar panels in this instance. During winter months in the southern states, gas or electric boost may be required to produce sufficient hot water during frosty mornings. Manufactured by stalwart brands within the plumbing industry, they really are the next generation in water 4 Silicon Chip heating technology – by not using much at all! I appreciate that your publication focuses on electronics rather than renewables, but evacuated tubing systems will reduce energy bills considerably and free space in your reader’s grid for other gadgets. They are an obvious choice for any passive solar building project, but I digress. The cumulative economic and security savings are undeniable if installed and used early in the life cycle. Please use these systems for the next generation. Some states are currently offering rebates to encourage the take up of these systems. Plaine Jayne, Central Victoria. History of SC articles appreciated I enjoyed the nostalgic articles on “The History of SilChip” by Leo Simpson (August & September 2022; siliconchip.au/Series/385). I was in the USA from 1986 to 1996 and never really understood what happened in Australia during those years. Leo and the team were brave indeed and had the foresight to stick with it. It’s also clear that DSE, Jaycar and Altronics helped a lot. I have collected a few sets of electronics magazines and the article has spurred me to save this kind of material. In Australia, resources were always scarce and few people appreciated that the stuff they were throwing out might have some historical value (me included). Barry Marshall, Nedlands, WA. icon On the demise of Electronics Australia I found Leo Simpson’s article on “EA” and “ETI” an interesting read. I subscribed to Electronics Australia until it turned into a product catalog. That happened in a single issue; it went from a magazine with interesting articles to a product catalog for which I was paying. I was disgusted and rang EA immediately and requested a refund of the remainder of my subscription. The lady I spoke to was very understanding and organised the refund. She did not seem surprised by my request, and I guessed that she had many such requests. I searched my magazine storage for that copy to find the date, but I think I must have binned it immediately. Keep up the good work! Doug MacLennan, Millicent, SA. Electronics Australia staff member’s recollections It was really interesting reading Leo Simpson’s article about Silicon Chip in the August 2022 issue (siliconchip. au/Series/385). I worked at Electronics Australia with Leo from 1979 to 1982 but lost touch after that, so the article has filled in a big gap. I thought some readers might be Australia's electronics magazine siliconchip.com.au interested in my reminiscences from 40 years ago at EA and just a little bit before and after. EA, as we called it, was my first job out of university. I did a double degree in Electrical Engineering and Computer Science at UNSW. For four of those five years at UNSW, I was a resident at Baxter College – great times! I once told my wife those were the best years of my life – she was not impressed. Back then, the government made university free and even gave eligible students an away-from-home allowance. The college fees were just $36 a week for a room and three meals a day. What a contrast to the current HECS fees! Anyway, I had just graduated and was looking for a job when I received a fateful call from a friend that EA was advertising a staff position. I had been a life-long electronics hobbyist and, as a kid, I used to collect old radios and TVs from the local tip and enjoyed restoring them. I was also a regular EA reader, so this seemed like a dream job – designing projects, writing articles about them and working with ‘legends’ like Jim Rowe and Neville Williams! As a bonus, I also got to work with some amazing people like Leo Simpson, Greg Swain and John Clarke. The offices were at 57 Regent St, Chippendale. We were on the ground floor in an open-plan format with Greg Swain’s and Jim Rowe’s offices next to us. Neville William’s office was down a corridor, as was the lab. Back then, we wrote all our articles on a typewriter, typing on small pieces of paper about 6 × 4 inches (15 × 10cm), called “pars” - short for paragraphs. That is basically what you put on each one. We would then make changes by writing on the pars or just re-ordering them. The re-ordering trick was great because I learned a useful technique to handle writer’s block: just blurt all your 6 Silicon Chip thoughts out in any order, then go back over it and re-­ order the pars to suit. Bob Flynn, our graphics designer, had his drafting table just behind me, and he did all the circuit diagrams from rough drawings we all provided him. He had sheets of bromide with repeated symbols like transistors and resistors that he would cut out with an art knife, stick them down on a paper grid, then draw the lines in between. We designed our own PCB artwork using black crepe tape cut with an art knife and stuck down on a transparency. One of the office staff, Danny, would then make the PCB in one of the back rooms. I got to work on some fantastic projects, like the Musicolour 4 and the On-Screen Graphics Analyser. After I completed the On-Screen Graphics Analyser, Leo suggested I should get photographed with it for the front cover. The photographer said I should get some makeup, but I thought: no, guys don’t wear makeup. So there I was, on the front cover (shown at lower left) of a nationally circulated magazine with pimples! Regarding the Musicolour 4, I received a phone call from a very irate reader claiming I had stolen his design. He wanted to know how I did it because it was locked in a safe! Another interesting project I developed was a metal locator. There were many designs out there, but I devised a novel way of digitally sampling the oscillator waveform. Hence, it only produced frequency changes, resulting in a distinct clicking sound like a Geiger counter. Many years later, I was watching an archaeology program on TV about a team from Sydney Uni when I heard that distinctive clicking, so I guess it was useful. Interesting side-note: I suggested that an attractive secretary from upstairs in the Dolly magazine offices should model holding it. Her name was Lisa Wilkinson, and I think to this day, she is still confused about how she wound up holding that thing! One of the smaller projects I did was a variable power supply. I remember Leo coming into the lab and asking me how it was going. He asked me if the output was short-­ circuit protected and then proceeded to short it without waiting for my reply! The power supply blew up. I fixed the design but never forgot the lesson I learned that day and applied it to everything I’ve done since – thanks, Leo! A couple of other non-project stories. We were putting together the April issue, and I suggested an April’s Fool article. Leo asked me to write it up and he would then look at it. It was short, but it basically said the USA was moving to decimalising dates and times to make 10 hours in a day, 10 days in a week with a three-day weekend (the French actually did something like that after one of their revolutions!). Anyway, Leo rejected it, but one idea he thankfully didn’t reject was my proposal to do a monthly column titled “25 and 50 years ago”. I was fascinated by the history of radio and electronics in this country, and we had all the back issues of “Radio, TV and Hobbies” etc. So I spent a day every month scanning them for interesting items, and honestly, they never disappointed me. There are many more stories to tell, but I need to close with why I left EA. One of the other staff, Gerald Cohn and myself, were very interested in computers, but they didn’t seem to be on EA’s radar at that time. In 1981, we Australia's electronics magazine siliconchip.com.au SOON, EXCITING THINGS WILL BE REVEALED First of a new generation, a combination of eXtremely advanced hardware and eXpanded, superior software, our new engineering achievement is on its way. www.rohde-schwarz.com/next-generation went to the first PC show at Sydney Tower (or Centrepoint, as it was then known). I remember the IBM stand in particular. It had a small white stand with a red rose on it and some chap walking around dressed as Charlie Chaplin. The XP ran at 4.7MHz and had a floppy drive. There was also the AT with a 5MB hard drive. That was sheer luxury, as we only had a TRS80 with an external cassette deck for storage! Around that time, Gerald was contacted by a friend who wanted to develop electronic scoreboards, and of course, they would be using computers – so I was interested. I was sad to leave EA and their amazing staff, but computers and software beckoned. That’s where the EA story ends. Gerald and I set up our own company called Kookaburra Computers. We worked with another company, Harwal, who did all the mechanicals from a building in Winbourne Rd, Brookvale [just around the corner from the current Silicon Chip office – Editor]. The scoreboard computer was Z80-based, and we would burn the program into an EPROM and plug it into the rack-mounted controller board, which then drove one or more driver boards. The problem was that we had to do a lot of coding on-site and walking from the scoreboard and back to the control room, where the computer was. That took 15 minutes, so we got a lot of exercise. I had already written a Z80 assembler that ran on our UNIX-based PDP, so I developed a Z80 disassembler and debugger so we could do it all from the comfort of the control room. For many years I never looked at any electronics magazines, but you’ll be glad to know I started buying Silicon Chip magazines about a year ago and look forward to each issue. Ron de Jong, Epping, NSW. Note on hybrid valve/transistor radios In the September 2022 issue, on page 74, Leo Simpson mentioned moving to EMI and said that when the car radios moved to hybrid designs, they had transistors in the RF stages and valves in the output stages. It was the other way around. I had some information on that in the article on the Astor Diamond Dot car radio I restored (July 2022; siliconchip.au/Article/15396). Dr Hugo Holden, Minyama, Qld. Feedback on current drive for loudspeakers John Cornwall’s idea of using current drive for loudspeakers (Mailbag, May 2022, p10) is not new. I wondered about it back in the 1970s. The engineer I worked with at the time said, “No no, don’t try that” (or words to that effect). John has confused the overall desire to convert electrical power into sound power with a small part of the process. As with all engineering designs, compromise is an essential part. Firstly, loudspeakers are designed with the intended drive being a voltage source (ie, a device with a low output impedance). Using current drive (with high output impedance) would have serious consequences on the frequency response and damping at the very least. For loudspeaker systems using passive crossover networks, it would cause a shift in the crossover frequencies, 8 Silicon Chip Australia's electronics magazine siliconchip.com.au ADD MOTION DETECTION TO YOUR PROJECT PIR MOTION DETECTION MODULE ADD OBSTACLE DETECTION OR AVOIDANCE DUAL ULTRASONIC SENSOR MODULE • Adjustable delay times XC4444 $5.95 • 2 - 45cm 15° range XC4442 $7.95 Expand your projects with our extensive range of Arduino® compatible Modules, Shields & Accessories. OVER 100 TYPES TO CHOOSE FROM AT GREAT PRICES. ADDRESSABLE RGB LEDS DETECT WHEN PLANTS NEED WATERING SOIL MOISTURE SENSOR MODULE • Analogue output XC4604 $4.95 VIEW OVER 70 ARDUINO® PROJECTS YOU CAN BUILD AT: jaycar.com.au/projects Shop at Jaycar for: • Arduino® Compatible Development Boards • Display Modules • Servos, Solenoids & Motors • Wheels & Chassis 1.3" MONOCHROME OLED DISPLAY • 128x64 Pixel XC3728 $19.95 ADD AMAZING COLOUR TO YOUR NEXT PROJECT 5V LED STRIP WITH 120 ADDRESSABLE RGB LEDS HALL EFFECT SENSOR MODULE • 2m long, flexible, waterproof XC4390 $29.95 • Sense magnetic presence XC4434 $4.95 • Prototyping Hardware and Accessories • Project Enclosures • Servos & Motors • Switches & relays Explore our wide range of Arduino® compatible modules, shields and accessories, in stock on our website, or at over 110 stores or 130 resellers nationwide. jaycar.com.au/shieldsmodules 1800 022 888 which could result in the death of some of the drivers in extreme circumstances. Regardless, the frequency response would no longer match the manufacturer’s specifications. A significant feature of moving-coil loudspeakers is their resonant frequency. This is usually designed to be outside their working bandwidth for mid and high-range drivers. For bass drivers, that is generally unachievable, and the resonance is usually somewhere between 100Hz and the low-frequency cut-off of the driver. This is not primarily (if at all) an electrical resonance, it is a mechanical resonance, and the loudspeaker enclosure often pushes this resonant frequency further up into the audible band. Voltage drive suppresses the worst effects of this, whereas current drive would result in a massive spike in the frequency response at the resonant frequency. Manufacturers seek to maintain an approximately flat response over most of the working frequency range by keeping the driver impedance constant with frequency. However, this is to some extent at the mercy of the speaker enclosure, the crossover network and even room acoustics. Another factor that is likely to impact the frequency response is that the output impedance of a current drive amplifier that utilises feedback will be capacitive, which will interact with the speaker impedance to reduce the bandwidth. To put it another way, the amplifier’s ability to keep the current constant (for a constant input) decreases as frequency rises. I cannot tell whether this will have a significant impact on the frequency response without exact figures for the speaker impedance and amplifier output impedance. It might not matter much for some speaker systems whether voltage or current drive is used. I once saw the impedance curve for a Magnaplanar speaker, which was ruler flat at six point something ohms across the entire audio band, but then they were about 2m tall. But rest assured that almost all loudspeakers are designed with voltage drive in mind. Phil Denniss, Darlington, NSW. Storage space grows while it shrinks Your article on the history of Silicon Chip and a recent purchase of mine made me think of the way computers have progressed in my working life. My first computer was a CP/M machine I put together with an amazing 10MB hard disk and two floppy drives. My recent purchases were a 32GB SD card and an 8TB hard disk, the latter of which is 22,000,000 times the capacity of those early floppies! The cost of the MiniScribe hard disk was around $2000 in early 1980s money, while the 8TB hard disk was just $203 in July 2022. The 32GB SD card was $15. Geoff Champion, Mount Dandenong, Vic. Nostalgic for Australian electronic manufacturing I just finished reading the article in Vintage Radio by Dr Hugo Holden on his restoration of the Astor CJ-12 Car Radio (July 2022; siliconchip.au/Article/15396). It was very enjoyable, thank you. It struck a cord of lament with the loss of electronic component manufacturing here in Australia, with the loss of the industry starting in around 1973. I started work in 1970, employed as a four-year Radio Technician Apprentice with Traeger Transceivers in Adelaide. I was directly involved with manufacturing HF transceivers that were in production at the time and later, as my skill level rose, as a production line test and alignment technician. Eventually, I became a full Service Technician, still servicing the older valve AM transceivers (including a Pedal radio) until they were phased out with the introduction of SSB transceivers. I was fortunate at that time as I was trained on valve technology moving into solid state, including ICs etc. Regarding Australian-produced transistors, I have a Hills Industries VHF two-way radio that I picked up somewhere. One notable feature is that most of the transistors are marked AWV (Australian Wireless Valve). I also remember the Fairchild transistors; I have many that I have salvaged from older radios (ex-Traeger boards). Many transceivers manufactured in the late 1960s through to the ‘70s were transistorised receivers and hybrid solid-­ state transmitters with the PA still being a valve. I remember the factory purchasing many components manufactured in Australia, from Philips, Ferguson, Ducon, IRH, Aegis and others. Traeger also manufactured some of its own components, including temperature coefficient capacitors (using bi-metal strips), coils, transformers etc. I left Traeger in 1978 for another job within the Government as an HF radio technician, but in the later years of my time at Traeger, there was a slow shift to imported electronic components. I often discuss and lament Australia’s losses in significant manufacturing enterprises with mates from the radio manufacturing and service industry whom I still communicate with frequently. We blame Government policy and lack of foresight. Ben Broadbent VK5BB, Redwood Park, SA. First cable into USB Cable Tester was faulty From left-to-right: 5.25” floppy (360KB), 3.5” floppy (1.44MB), flash card (256MB), 5.25” hard drive (10MB), micro SD card (32GB), 3.5” hard drive (8TB) 10 Silicon Chip I felt so good about this, so I decided to share the story with you. I finished building the USB Cable Tester (November & December 2021; siliconchip.au/Series/374) from the Silicon Chip kit and put the battery in for the first time this morning. The display came up with UFP: GND, RXP2 and sure enough, the first two pins of the USB C socket had solder across them. Using my newly purchased 40 times jeweller’s loupe, I could see the offending bridge and a few applications of solder wick removed it. The very first USB cable I plugged in after that came Australia's electronics magazine siliconchip.com.au standup. the world’s first desktop waterjet. desktop. 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For a list of example materials please visit our website SYDNEY BRISBANE MELBOURNE (03) 9212 4422 (08) 9373 9999 1/2 Windsor Rd, Northmead 625 Boundary Rd, Coopers Plains 4 Abbotts Rd, Dandenong 11 Valentine St, Kewdale (02) 9890 9111 (07) 3715 2200 Specifications are subject to change without notification. PERTH 08_SC_290922 Now cut anything with digital precision using high-pressure water. A compact waterjet for every workshop. up faulty: shorted. Of course, I thought there was another fault in my construction, but luckily I have enough experience by now to try another cable of the same type. The second test cable was OK. I was trying to use the faulty cable on a USB Inspector Radiation Counter I purchased a while ago and kept getting “device unsupported” when I plugged it into the computer. Now I know why. The inspector dutifully displays a nice real-time graph of the current CPM (between 28 and 58) with a functional cable. Gordon Wilson, Masterton, New Zealand. 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. Confusion over nested regulator feedback 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 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 Software subscriptions versus open-source software 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. 12 Silicon Chip Thank you for the excellent articles on the Dual Hybrid Power Supply (February & March 2022; siliconchip.au/ Series/377), which I am currently building. It is well presented with lots of juicy detail, but I was a bit confused with the text: The 12-bit devices have 4096 voltage steps. The linear output regulator compares the DAC voltage (MCP4922) to the output voltage divided by 16 (15kW ÷ 1kW + 1). This means that the output voltage is controlled in 19.5mV steps (5.0V × 16 ÷ 4095). The linear output regulator does not compare the DAC voltage with the output voltage – the LM358 op amp does this. Grant Muir, Sockburn, NZ. Phil Prosser responds: I see your point on the difference between the linear power regulators and the LM358. The LM358 implements overall feedback with a secondary local feedback loop handled by the linear regulators. The output of the LM358 sets an operating point for the reference inputs (adjust pins) of the linear regulators to keep the output voltage as defined by the DAC. The LM358 feedback is a relatively slow feedback loop; the linear regulator maintains the output on short timescales relative to this. In my mind, I see both as being the linear part of the regulator. I admit that I have been loose in distinguishing the overall regulator from its constituent parts. It was interesting reading your editorial in the May issue. The idea of subscription software is yet another way for software companies to extract more money from consumers and is really a rip-off. Older versions of the software were a one-off licence fee for the life of the program, saving the consumer money to the detriment of the software company, so they decided to change things so that they could make more money from upgrades and annual fees. Two of my sons have older versions of software that suit their needs, but my other son, who runs a videography business, uses subscription versions to keep up with new features. As for my wife and me for home use, I have never bought any software as we use freeware programs. We use Open­Office for letter writing etc, which suits our needs, and I have just found Shotcut that I have dabbled with for video editing. Still, there is a bit of a learning curve as I have not previously done video editing, other than using Handbrake to boost audio levels. Australia's electronics magazine siliconchip.com.au Design, service or repair with our 100MHz Dual Channel Digital Oscilloscope Need more info than your DMM can display? 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Watch waveforms, look at delays in actions compared to triggers, store measurements, and compare over a range of timeframes. • 7" COLOUR SCREEN • 800 X 480 RESOLUTION • DUAL WINDOW MODE • AUTO SCALE FUNCTION • 8MB MEMORY DEPTH UPDATED INTERFACE & IMPROVED PERFORMANCE USB - SAVE DATA TO A USB DEVICE OR CONNECT TO A COMPUTER Shop Jaycar for your test equipment needs: • Analogue, Digital and Specialty Meters • Test Leads & Accessories • Magnifiers and Inspection Aids • In-stock at over 110 stores or 130 resellers nationwide J US T IN! • 14 TRIGGER MODES • 25MHZ WAVEFORM GENERATOR • 2 DIGITAL VOLTMETERS • 32 AUTO MEASUREMENTS • 5 SERIAL PROTOCOL TRIGGERS • UP TO 1GSA/S SAMPLING RATE DUAL CHANNEL ONLY 549 $ QC1938 GREAT VALUE AND STOCKED IN EVERY STORE & ONLINE Order yours today: jaycar.com.au/p/QC1938 1800 022 888 As far as old hardware not working on newer versions of Windows, this is an ongoing problem, but there are often workarounds, like using a different driver for an unsupported printer, which I have done in the past. One way out of this problem is to use Linux, which may not suit everyone. I’ve dabbled a bit with Lite versions of Linux on really old laptops, and I’ve found that there is good support for older hardware. Still, I haven’t tried old printers, as I don’t print with Linux and I don’t have any old printers that still work, other than the old Epson dot-matrix LX400 series. One particular issue with Windows 10 is the lack of support for laptop touchpads, even on fairly recent laptops, and it’s often very difficult to find drivers for them. However, I have found that Lenovo touchpad drivers often work on different brands of laptops. Linux seems to always support touchpads on older laptops. Bruce Pierson, Dundathu, Qld. Comment: we use Linux extensively and find it works well for many tasks. It seems to handle common printers just fine; generally, the drivers are built-in. The only real problem for desktop use is when you have to run specific Windows-only software. While that software can usually run in a Windows VM inside Linux, there are drawbacks to that approach. How to dispose of collections of electronic gear? I’ve reached the age where some estate planning is wise: a will, a power of attorney and so on. I was trying to think of something sensible to do with the electronics I have accumulated over the last ten or so years. The kit occupies half a small room and is probably typical for many hobbyists, including: • Power supplies • Oscilloscopes • Signal generators • Microchip development boards including 8-bit, 16-bit & 32-bit PICs • Many small boxes of active and passive components • Some excellent hand tools • And an excellent library of PIC/MCU and other electronic books I’d guess it would all cost about $5,000 when new, but it is worth almost nothing second-hand. However, I remember the delight when I was in my teens and someone gave me some old bits or a radio to tinker with. Do you, or any of your readers, have a good idea so that anyone of a like mind can simply slip the words into their ‘last will and testament’? The aim is to collect useful and newish electronic items and give them to some worthy organisation: charity, school, club, whatever and not see them chucked into the local dump. Perhaps a specific charity should be established? I bet there is a lot of really good kit scattered all over the place, but no one knows what to do with it. Bill Legge, Denmark, WA. Comment: we can’t give you any definitive answers, but we think it’s better to give stuff away while you’re still around, if you find someone who can use it. For radio gear, the HRSA (Historical Radio Society of Australia) can be a good place to sell or donate items to. See their website at: https://hrsa.org.au/ SC 14 Silicon Chip Australia's electronics magazine siliconchip.com.au Create highly detailed models Resin 3D Printers The latest in 3D printing technology that produces more detailed and smooth prints with less visible print layers compared to filament printers. GREAT RANGE AT GREAT PRICES. 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TL4423 $499 Shop at Jaycar for: • Huge Range of Filament & Resin Printers • Over 50 types of Filament and counting! • Over 45 types of Resin and counting! • Massive range of spare parts, tools & accessories Explore our full range of 3D printers and accessories, in stock at over 110 stores or 130 resellers nationwide or on our website. jaycar.com.au/resin-printers 1800 022 888 Part Two The History and Technology of VIDEO DISPLAYS By Dr David Maddison Our introductory article last month mainly described the development of video display technology from its early inception to around the year 2000, when plasma and cathode ray tube (CRT) displays dominated the consumer space. This month, we describe the development of liquidcrystal display (LCD) screens and more recent advances. L CDs are currently the dominant display tech for static images, computers and video displays. The reason is a combination of factors: low cost, thinness, lightness, tiny bezels, colour accuracy, wide viewing angles, fast response times, high contrast ratios, reasonably low power consumption etc. But LCDs weren’t always that way. Early LCDs were small, very primitive, slow to update and only useful for devices like calculators. It took decades to develop and refine them until they were suitable for TVs. The advances haven’t stopped there; backlighting has improved, quantum dots are now on the market, and OLEDs and MicroLEDs are coming onto the 16 Silicon Chip scene, along with other more esoteric technologies like laser TVs. Before we get to those, we’ll start with the development of liquid-crystal display technology and its operating principles. Liquid-crystal displays (LCDs) Some have called liquid crystals “the fourth state of matter” [I thought that was plasma; perhaps they mean fifth – Editor]. What we now know to be liquid crystals were first observed by Rudolf Virchow in 1854, who saw unusual behaviour in myelin (the insulating layer around nerve bundles). Then in 1857, German Carl von Mettenheimer, also studying myelin, noticed it flowed like a liquid, but Australia's electronics magazine when viewed under crossed polarisers, the light showed highly coloured birefringence like a crystal. However, the material was not identified as a liquid crystal at the time. Austrian botanist Friedrich Reinitzer discovered liquid crystals in 1888 when he examined a material, cholesteryl benzoate, extracted from carrots. It exhibited specific properties when between two temperatures (“two different melting points”, as he described them) that were characteristic of both the liquid (amorphous) state and the solid (crystalline) state. In this ‘mesophase’ state, the material could reflect polarised light and rotate the polarisation of light. He siliconchip.com.au coined the term “fliessende Krystalle” for liquid crystal. See the following links for more details: • siliconchip.au/link/abfb • siliconchip.au/link/abfc In 1922, Vsevolod Fréedericksz and A. Repiewa discovered an effect now called the Fréedericksz transition that is the basis of LCD screen technology. When a liquid crystal is placed between two transparent glass electrodes, the light transmittance can be controlled electrically, like an optical switch – see Fig.27. Liquid crystals are essential to life. Cell membranes, the myelin sheath that insulates nerves, and the digestion of fats all involve liquid crystals. There was very little interest in liquid crystals until 1962, when Richard Williams at RCA Laboratories in the USA discovered the electro-­ optic properties of these materials. He found that liquid crystals formed striped patterns when an electric field was applied. In 1968, a liquid-crystal display was demonstrated by George Heilmeier, although it had to be run at 80°C. LCD materials were then developed that could run at room temperature. In 1970, a calculator was demonstrated at the international ACHEMA exhibition using an LCD screen based on Merck products. The first consumer calculator with an LCD was the Sharp EL-805, released in 1973. In 1976 and 1978, Merck developed LCD materials with fast switching times, reducing the transition time from hundreds of milliseconds to 20ms or less, and improving the optical properties. In 1980, a “viewer independent panel” display was developed by Merck that became the basis of all active-matrix LCD screens. In 1982, the first LCD TV was released by Seiko Epson in the form of a wristwatch. In 1984, Citizen released a 2.7in (6.8cm) colour pocket LCD screen, the first to use an active matrix or TFT (thin film transistor) display. LCDs were one of the first replacement technologies for CRT TVs and plasma displays. Early plasma displays could produce a larger image than LCDs but with poor brightness and high power consumption. Sharp produced a high-end 14in (36cm) LCD monitor in 1988, while Epson released a colour LCD projector, the VPJ-700, in January 1989. siliconchip.com.au Sizing and aspect ratio of TV and monitors The industry-standard way of measuring TV and computer monitor size is with a diagonal linear measurement. This is often given in inches, although European and Asian brands usually mention centimetres as well (remember when many Japanese CRT TVs were advertised in centimetres?). This has the advantage that it gives a reasonable idea of screen size for a range of aspect ratios. Using the diagonal to measure screen size has its historical origins in the days when CRTs were round but had to display rectangular images, and much of the tube was hidden by the bezel of the TV. The diagonal indicated the size of the rectangle that would be displayed, bearing in mind that the original TV aspect ratio was 4:3 (1.33:1). With flat panel displays, the diagonal measurement refers to the actual visible area. Videos come in many aspect ratios, but the most common TV, computer monitor and smartphone aspect ratio is 16:9 (1.78:1). However, some smartphones have exceeded this ratio by becoming taller. The 16:9 ratio has been a standard of the International Telecommunication Union since 1990. Standard HDTV resolutions like 1280 x 720, 1920 x 1080 and UltraHD 3840 x 2160 are all 16:9 when the pixels are square. To accommodate other aspect ratios of source material on a 16:9 screen, an image is cropped or ‘letterboxed’ (black bars at top and bottom), ‘pillarboxed’ (black bars at the sides) or, in some cases, ‘windowboxed’ with black space all around the image. The Academy standard film aspect ratio is 11:8 (1.375:1), but movies have been and continue to be produced in a wide range of aspect ratios, with 2.35:1 ultra-wide being quite popular for many years in feature films. For computer monitors, 16:10 is also a pretty common ratio (it’s very close to the golden ratio, 1.618:1), and 5:4 was also used in the past (and occasionally still is). For more information on TV and movie aspect ratios, see https://widescreen. org/aspect_ratios.shtml and for computer monitor aspect ratios, see https://w. wiki/5HtF 16 : 9 1:1 16 : 10 5:4 2.4 : 1 11 : 8 4:3 Some common aspect ratios Fig.27: the Fréedericksz transition is the basis of LCD screen technology. The shapes show the alignment of the liquid crystals in response to an electric field: a) no electric field applied, light transmitted; b) intermediate electric field applied, light partially transmitted; c) full electric field applied, all light blocked. Australia's electronics magazine October 2022  17 Research on LCD screens continued, and eventually, LCD screens could be produced at sizes competitive with plasma displays. Thus, they could be used at both the small size end of the market (where plasma displays were not suitable) and at the large size end, where plasma displays dominated. In 1994, a 21in (53cm) LCD screen was demonstrated at a trade fair in Japan. By the end of the 1990s, prototype displays of 40in/1m diagonal were being demonstrated. In 1995, Hitachi Ltd developed ‘in-plane switching’ (IPS), providing a much wider viewing angle than the existing TN (twisted nematic) technology without excessive colour or brightness shifts. Then, in 1997, Fujitsu Ltd produced an LCD with ‘vertical alignment’ (VA) technology that gave greatly improved contrast and a black screen when no voltage was applied. Most LCD screens today still use TN, IPS or VA technology. TN is mainly used where very fast response times are required as it has inferior colour reproduction and viewing angles. IPS provides the best viewing angles and colour reproduction, but its contrast Fig.28 & 29: the two polarisers in an LCD are at 90° to each other. When no voltage is applied via the thin-film transistor (TFT), the liquid crystals change the polarisation of the light passing through, allowing light to be transmitted. When a voltage is applied via the TFT, the liquid crystals align so the light polarisation is not altered and the light is blocked. Intermediate voltages cause partial transmission. 18 Silicon Chip Australia's electronics magazine is not as high as VA, so blacks can look grey. In the 2000s, new liquid crystal materials were developed with significantly reduced response times, down to 8ms, and even wider viewing angles for VA displays with better colours, brightness and contrast. In 2006, Sharp developed polymer-stabilised VA technology that gave better light transmission and thus lower energy requirements for the backlighting. In 2006, the price of LCD screens started to decrease dramatically and began to displace the market held by plasma displays, and LCD screens started outselling plasma TVs. By 2008, LCD TVs were also outselling CRT TVs. The principles of operation of an LCD matrix display are pretty simple, as shown in Figs.28 & 29. Linear polarising filters, as used on some cameras and sunglasses, ensure the light polarisation is uniform in one direction. Light is transmitted normally if two linear polarising filters are aligned. But if they are rotated 90° to each other, the light is blocked. Therefore, by controlling the polarisation of one of the two layers, the amount of light that passes through can be controlled smoothly, from near 100% to near 0%. In an LCD, a layer of liquid crystals is sandwiched between two crossed polarisers. In between the polarisers are also transparent electrodes made of indium tin oxide, with an alignment layer and colour filters (for colour LCDs) representing the colours of the sub-pixels. The whole ensemble is called ‘the sandwich’. The alignment layers consist of two polyimide plates, one on each side of the liquid crystals, which have been treated to cause liquid crystals to align with them. Each plate is aligned at right angles to the other. Surprisingly, one method of creating the alignment pattern is to rub the plate with a velvet cloth in the desired direction. When no current is applied to the liquid crystal, the alignment through the thickness of the crystal changes from the direction of one plate to the direction of the other. This causes the light polarisation to be twisted from one alignment to another, and thus, light is transmitted. If a voltage is applied through the liquid crystals, via either ordinary electrodes or thin-film transistors siliconchip.com.au (TFTs) in the base of each pixel element of the display, the liquid crystals align and block the light. The amount of blocking depends upon the voltage applied. Earlier LCD screens were ‘passive matrix’ types with electrodes on either side of the LCD layer. More recent displays are ‘active matrix’ types where the electrodes for each sub-pixel element are replaced with thin-film (translucent) transistors, resulting in a faster response time and a sharper and brighter image. The light source for LCD panels was cold cathode fluorescent light strips (CCFLs) for a long time, but it is now primarily LEDs. See the panel at the end of the article for additional comments about this distinction. Incidentally, you can tell if sunglasses are polarising or not by looking at an operating LCD screen with them and rotating them. If it goes dark or fades out at some angle, the glasses have polarising lenses. Quantum-dot displays Quantum-dot displays are comprised of two types, photo-emissive or electro-emissive. They are a form of nanotechnology. Photo-emissive quantum dots are used in any display technology that uses colour filters, primarily LCDs with LED backlighting. In an LCD, they are inserted as a film in ‘the sandwich’ made of other films, polarisers, glass, TFTs and electrodes. When light passes through a quantum dot film, it is re-emitted as a pure red, green or blue colour. The purpose is to give truer-tolife colours than is possible with LED illumination alone. LCD screens using quantum dots are said to be comparable to or superior to OLED (organic light-emitting diode) displays. However, quantum-dot displays are cheaper and can deliver superior colour at full brightness than OLEDs. Electro-emissive quantum dot displays emit light by themselves, but are experimental at this stage. They are thin, flexible displays that promise better life than OLEDs. LED and microLED displays LED displays are flat panel displays comprised of individual LEDs for the sub-pixels that are the actual light-emitting elements. They should not be confused with LCD screens siliconchip.com.au Fig.30: a Sony Crystal LED (CLEDIS) display makes up the walls in this image. The displays are modular, so they can be made essentially any size. Source: https://pro.sony/en_PT/products/led-video-walls/crystal-led-walls that use LED backlighting (see panel). LED displays are used for large outdoor screens such as at sporting or entertainment events or variable road signage. MicroLEDs are produced at a smaller size than standard LEDs and are thus suitable for smaller display devices (or higher resolution devices) than regular LEDs. These displays are inorganic and theoretically have a longer life than OLEDs, which are organic in nature (as explained below). Compared to LCDs, they potentially have a faster response time, lower power consumption, greater brightness, better contrast ratio and better colour saturation. They have not yet been mass-­ produced for smaller-scale devices such as consumer TVs, but Sony has developed CLEDIS or Crystal LED Integrated Structure that uses MicroLEDs. It is a modular system that can be assembled to make a display of almost any size for uses like public exhibitions or cinema screens (see Fig.30). In January this year, Samsung announced plans to sell microLED TVs in the sizes of 89in (2.25m), 101in (2.5m) and 110in (2.75m), but at the time of writing, they are not yet on the market. OLEDs OLED stands for organic light-­ emitting diode. Unlike traditional LEDs, which are made of inorganic semiconductors like gallium nitride, OLEDs are made of organic semiconductors. These are complex organic materials either based on small molecules or molecules joined together as polymers (plastics). These materials all have the characteristic of loosely-bonded electrons that enables them to conduct electricity to various degrees. They are known as organic conductors. The active layer (recombination region) of an OLED is electroluminescent, meaning it emits light in response to an applied voltage. Electroluminescence in organic Non-working or defective pixels in displays In matrix-based displays such as plasma, LCD and OLED screens, there is the possibility of receiving a screen with non-working pixels (also called a “dead pixel”). Possible defects include pixels or sub-pixels that are stuck on or off. An international standard has been developed to categorise the types and quantity of pixel defects that are considered acceptable, ISO 13406-2. The number of acceptable defects varies according to the manufacturer. It depends on the types of defects, the location of the defective pixels on the screen and the proximity of defective pixels to each other. Image source: https://w.wiki/5JET Australia's electronics magazine October 2022  19 Figs.31: how an OLED screen pixel works. It’s somewhat similar to a regular LED but uses organic polymer semiconductors. Among other benefits, that means OLED screens can be flexible. materials was observed in the 1950s, and the fundamental research was done in the 1960s, but Eastman Kodak developed the first practical OLEDs in 1987. White OLEDs were first produced and commercialised in Japan in 1995 for display backlighting and other lighting purposes. In 1999, Kodak and Sanyo entered into a partnership and produced a 2.4in (61mm) OLED display, followed by a 15in (38cm) HDTV screen in 2002. Sony released the XLE-1 television commercially in 2007, and in 2017, JOLED started producing OLED panels printed by an ink-jet process. A simple OLED structure consists of a protective layer, cathode (−), electron transport layer, recombination region, hole transport layer, transparent anode (+) and glass substrate – see Fig.31. More advanced OLEDs have extra layers with different regions to produce different colours. An OLED requires a simple potential difference (voltage) to start operating. The cathode has electrons (-) from the power source and the anode loses holes (the absence of an electron, +). Fig.32: Samsung smartphones with foldable OLED displays. We’ve seen reports of these screens cracking after many months or years of folding and unfolding, so do your research before buying one, especially as they are expensive. Source: Wikimedia user Ka Kit Pang, Apache 2.0 license 20 Silicon Chip Australia's electronics magazine Opposite charges are attracted to each other, and they meet at the recombination region, the boundary region between the electron transport layer and the hole transport layer. These electrons and holes come into contact forming an ‘exciton’ and emits a photon of light. This happens a large number of times, causing a continuous emission of light. A disadvantage of OLEDs is that they have a shorter lifetime than other display technologies. An advantage is that they can be made foldable, as in certain phones (see Fig.32). Fig.33: examples of Lumineq in-glass electroluminescent displays with optional touchscreen capability. The price of a taxi or Uber is displayed in the top photo, while the bottom photo shows an access code panel for a car. siliconchip.com.au Fig.34: the front of a Texas Instruments DMD chip for cinematic use. Source: Wikimedia user Binant, CC BY-SA 4.0 Fig.36: non-wobulated and wobulated images generated by the DMD. Wobulation improves the visible resolution without needing more mirrors. AMOLED is a particular OLED technology that uses an active matrix driven by thin-film transistors (TFTs). electroluminescent displays, and they are branded as Lumineq (www. lumineq.com) – see Fig.33. Electroluminescent displays Digital Light Processing (DLP) Electroluminescence (EL) is the phenomenon whereby a material such as gallium arsenide emits light when an electric field is applied to it. The colour of the light varies with the active material, but currently, the only practical displays are single-­ colour, such as yellow or orange. Displays can have fixed segments, or there can be a matrix to display any desired image. The display structure is similar to LCDs or OLEDs with striped opaque (or transparent) electrodes at the back running in one direction and transparent striped electrodes at the front at right angles to the ones at the back. One back electrode and one front electrode are energised to activate the desired segment or pixel – see Fig.35. There are two main types of EL display, either transparent or non-­ transparent, which are similar, but transparent displays have transparent back electrodes. With transparent displays, regions which are not activated are 70% transparent for matrix displays and 80% transparent for segment displays. They can be laminated within glass, such as automotive glass, and can also have touch-sensing capability. Electroluminescent displays are rugged, can operate at high or low temperatures, are resistant to high or low pressures and sunlight, and last at least 20 years. Thus, they are superior to LCDs and OLEDs in certain applications, such as outdoors. Beneq of Finland is the only manufacturer of segment and matrix DLP is a light projection technology developed by Texas Instruments (TI) in 1987 and commercialised in a projector by Digital Projection Ltd. It uses a chip with an array of micromirrors. These can be flipped into either an ‘on’ position to reflect light towards the image plane or an ‘off’ position to reflect light elsewhere, such as onto a heatsink. Although the mirrors can only be in one of two positions, intermediate brightnesses can be produced by rapidly flipping the mirrors on or off to alter the average amount of light sent to the image plane. The chip is known as a digital micromirror device or DMD (see Fig.34). The mirrors are microscopically small, siliconchip.com.au with a pitch of 5.4µm (microns, millionths of a metre) or less. The number of mirrors corresponds to the image’s resolution, except when a process known as wobulation is used to increase the effective resolution. With wobulation (see Fig.36), the DMD is moved a small amount (in both X and Y directions), such as half a pixel, to project a new subframe. This is generated by the projector firmware and half-overlaps the previous frame to give an increase in resolution without the extra expense of a higher resolution DMD. Colours are generated either by a colour wheel rotating in front of the chip, creating a series of different coloured images that the eye merges, or by three separate chips, each projecting one primary colour. The DMD is an optical MEMS (micro-electromechanical system) – see our detailed article on those Fig.35: the structure of an electroluminescent matrix (pixel) display. Original source: Electronics Weekly – siliconchip.au/link/abfd Australia's electronics magazine October 2022  21 Fig.37: the details of a digital micromirror device (DMD). Source: Texas Instruments (www.ti.com/lit/an/ dlpa059e/dlpa059e.pdf) devices (November 2020; siliconchip. au/Article/14635). In a DMD, thousands of microscopic aluminium mirrors are each supported on a yoke, itself supported on a torsion hinge between two posts and rotated about 10° between the on and off positions by electrostatic forces, as shown in Fig.37. The base layer of the DMD contains SRAM (static random access memory) cells that move one mirror by electrostatic charge according to its current state. A bias voltage is used to drive the SRAM so that when power is removed, all the mirrors reset to the same starting position, so all the mirrors move together for the next frame – see Fig.38. Due to an extensive patent portfolio, high production costs and the high level of technical know-how required, only Texas Instruments makes these devices. The DMD is manufactured according to the standard processes for MEMS and lithography, the latter described in our three-part series on IC fabrication in the June to August 2022 issues (siliconchip.au/Series/382). However, we are sure the exact processes are a closely-guarded secret. Still, we would love to know! DLP is used in some domestic projectors and about 90% of commercial movie projectors. TI offer DMD resolutions of up to 4K UHD (3840 × 2160) and frame rates from 60Hz to 240Hz with support for LED, incandescent or laser light sources. For a video teardown of an early DLP projector, see the video titled “Extreme teardown – NEC XT5000 Projector” at https://youtu.be/RzikiKqbA1U Laser TV Laser TV is a new technology, currently in the process of adoption. To generate an image, laser beams are scanned across the image plane, usually electromechanically, such as with a DLP chip. Conceptually, the image is created much like it is in a CRT, but using a laser beam instead of an electron beam – see Fig.39. The idea of laser TV was first proposed in 1966 and patented in 1977, but the laser technology was too expensive until the development of solid-state lasers. A system was demonstrated at the 2006 Las Vegas Consumer Electronics Show (CES) by Novalux Inc. In 2008, Mitsubishi Electric released a commercial 65in (165cm) 1080p HDTV model and in 2013, LG released a 100in (2.5m) 1080p consumer model. Electronic paper/ink Electronic paper is a type of display that mimics paper. Like paper, it does not produce its own light but is read by reflected ambient light. It is thus said to cause less eye strain and stress. Electronic paper can be updated reasonably rapidly, but not fast enough for full-motion video with present technology. Still, it can show slow-motion ► Fig.38: details of the individual mirror assemblies in a DMD. Original source: Texas Instruments Fig.39: a commercially-available Hisense laser TV. The image is projected from the box beneath the screen in the centre. 22 Silicon Chip Australia's electronics magazine siliconchip.com.au LCD screens: IPS, VA or TN? Fig.40: a real-time electronic paper timetable display used for Sydney buses. Source: Wikimedia user MDRX, CC BY-SA 4.0 video or frequently changing numbers, such as a clock display. Like paper, electronic paper maintains the last image written to it when the power is turned off; no power is required to maintain the display in its current state. Other names for electronic paper are electronic ink and electrophoretic displays. The name “E Ink” is a trademark of E Ink Corporation (www.eink.com). As mentioned in the text, these are the three dominant LCD technologies, although others exist. When choosing an LCD screen, this is one of the most critical decisions. While modern VA (vertical alignment) panels are said to have decent viewing angles, in our experience, IPS panels are still noticeably superior. This is especially important for computer monitors, where you usually sit close to the screen. A poor viewing angle not only means you can’t move your head much, but even with your head in a static position, the corners of the screen might appear to be fading or colour shifting compared to the centre. For this reason, we almost exclusively use IPS (in-plane switching) panels. They also tend to have the best colour reproduction, although VA screens have come a long way in that respect too. Some prefer VA panels for roles like video playback/TV or playing games because of the higher contrast ratios, ‘blacker’ blacks and faster refresh rates. However, 144Hz refresh IPS screens are now available, making the refresh rate distinction less critical. VA panels have noticeably better contrast than IPS types, but we don’t feel the trade-off is worthwhile unless they have stellar viewing angles for their class. This is a situation where it really helps to physically try out the product before you buy it, to ensure that its colour reproduction, brightness, contrast and viewing angles are to your liking. The only reason to still buy a TN (twisted nematic) screen is if you want an ultra-high refresh rate like 240Hz or higher. Again, we don’t feel the compromise is worth it as the picture looks so much worse, but some people really like these high refresh rates for gaming, in which case TN is basically your only choice. The Kindle electronic book reader is a popular application of electronic paper technology. Usage examples include electronic book readers, updateable price displays in shops, electronic signage, public transport timetables, conference badges, certain smartphones and tablet devices – see Fig.40. Electronic paper was invented at the Xerox Palo Alto Research Center Fig.41: Xerox Gyricon, the first electronic paper. Source: Xerox web page archived from 2005 siliconchip.com.au Australia's electronics magazine (PARC) in the 1970s and was called Gyricon (see Fig.41). As originally envisaged, electronic paper did not have electrodes; an image could be created by applying an external electric field in the pattern of what was to be written, like drawing with a pen. It could then be erased and a new pattern written. There are several implementation methods, but the basic principle consists of ‘Janus particles’, coated in oil or a similar fluid to enable easy rotation. These are embedded in a matrix of some sort, such as silicone – see Fig.42. Fig.42: E Ink technology. 1) Upper layer 2) Transparent electrode layer 3) Transparent micro-capsules 4) Positively charged white pigments 5) Negatively charged black pigments 6) Transparent oil 7) Electrode pixel layer 8) Bottom supporting layer 9) Light 10) White pigment 11) Black pigment. The display is about 0.51mm thick. Source: Wikimedia user FREEscanRIP, CCA 3.0 October 2022  23 When is an LED TV not an LED TV? Fig.43: a water wall projection by Australian company Laservision at an Australian event. Source: www.laservision.com.au/galleries/photos/ A Janus particle is a spherical nanoor micro-particle with different electrical or other properties on each side, such as a positive or negative charge. In the case of electronic paper, one side of the sphere might be white and the other black. The particles align with the field when an electric field is applied through or across the matrix (depending upon electrode orientation). This causes them to rotate and display either white, black, or other colours the particles have been coloured with. When the electric field is reversed, the particles rotate and present their other side. Janus particles are typically 10µm to 50µm in size. To produce colours, additive colour filters can be used. Alternatively, an electric field can control a coating of coloured oil in the so-called electrowetting process. In this latter case, a subtractive colour system is used, like with a typical colour printer that uses CMYK (cyan/magenta/yellow/ black) inks. Nearly all TVs sold as “LED TVs” are, in fact, LCD TVs with white LED backlighting. Older LCDs used cold cathode fluorescent lights (CCFL) as their backlights. TVs described as QLED are quantum-dot LCDs with LED backlighting. OLED TVs generate their own light and do not need backlighting. To avoid confusion, we would like to see the industry adopt the term “LED-backlit LCD TV” instead of “LED TV” unless it is a genuine LED TV. But manufacturers benefit from this confusion by making it seem that LED backlighting is a more significant technological advantage than it is, so they are likely encouraging it. These displays are available and suitable for experimenters and can be bought as Arduino and Raspberry Pi kits and with SPI interfaces. For example, read our article on using e-Paper displays with a Micromite in the June 2019 issue (siliconchip.au/ Article/11668). Also see the following videos below on electronic ink displays: • “Have You Ever Seen an E Ink Display Update This Quickly?” – https:// youtu.be/KdrMjnYAap4 Figs.44 & 45: a water screen nozzle sold at https://fountains-decor.ie/product/water-screen-nozzle/ The nozzle measures 930 × 528 × 802 mm and provides a semi-circular screen from a water supply of 4000L/min at 12 bar. The water film thickness is 6mm. The manufacturer did not specify the screen size that it can produce, but an example is shown. We think the semi-circle has a radius of about 10m. 24 Silicon Chip Australia's electronics magazine siliconchip.com.au • “Badger 2040 – A Raspberry Pi Pico with a Built-in e-Ink Display” – https://youtu.be/kI-_ksiYw40 • “Top 5 reasons to buy an e-ink tablet” – https://youtu.be/YKjXvjhe-Ss • “Bigme Max+ Color EINK 10.3” Note Taking Review” – https://youtu. be/RAhFzefT5DI Water screen displays A water screen is a large scale outdoor nighttime display technology where an image is projected onto a screen made of water droplets by a laser or a video projector. Water is sprayed into the air to make a waterfall or is pumped at high pressure to create a screen or a cloud of mist – see Fig.43. The Australian company Laservision (www.laservision.com.au) is a leader in this field. Unfortunately, they did not return our phone call before publication, so we can’t give any further details beyond what’s on their website. We published an article on Laservision a long time ago, in August 1990 (siliconchip.au/Article/7208). They also have the following videos available: • “Laservision Corporate Showreel” – https://youtu.be/cv04MrAJnLM • https://vimeo.com/271808280 For related products from other companies, see Figs.44 & 45. The following videos on the topic cover both home-made and commercial water projections screens: • “Homemade Water Projection Screen” – https://youtu.be/ Z7XHaKAUquA • “10’ Water Screen Projection Test” – https://youtu.be/3TPMwv2SmS8 • “Water curtains | Water Screen Projection” by Water Screen – https:// youtu.be/27YYmowUFno • “Preview 1 | Water Screen Projection” – https://youtu.be/tkCNHMvlQBk High Dynamic Range (HDR) displays High Dynamic Range (HDR) is not a type of display, but it is a set of standards designed to reflect the capabilities of new display technologies. Until HDR, video signals were designed for CRTs and could not convey video information that fully utilises the capabilities of modern displays. HDR-capable displays can show a greater range of colours, contrast, brightness, whiteness and blackness, more vivid colours, a higher frame rate of up to 120 frames per second etc. One of the critical aspects of HDR, though, is the contrast ratio of the content, ie, the ratio of the lightest areas of the picture to the darkest. Standard content has a maximum contrast ratio up to about 1000:1, while HDR content can exceed 5000:1. This better matches the human eye’s capabilities in resolving light and dark areas in the same picture. One of the key advances for HDR displays was replacing the older edge backlighting technology with LED matrix backlighting. Instead of having LEDs arrayed around the edges of the screen, there is a matrix of white LEDs behind it, and their brightnesses can be individually adjusted. This allows some parts of the screen to be very bright while others are dim, without the ‘bleed through’ associated with high brightness backlighting. The fact that the backlighting is not even is compensated for by the way the display controller drives the LCD panel itself. Typically, the more LEDs are used in the backlight matrix, the better the display’s HDR capabilities. Displays with many LEDs in the backlight are sometimes known as “mini LEDs”. Displaying HDR content HDTV and standard Blu-ray discs use 24-bit colour, which gives 16.7 million colours, but HDR content uses 30 bits for over a billion colours. This requires more data, which can be contained on an Ultra HD Blu-ray disc, although such discs will not play on standard players. HDR content can also be streamed, but you need a fast enough internet connection. If it can handle 4K video, it should be fast enough for HDR. HDR has several competing formats: Dolby Vision (Dolby), HDR10 (UHD Alliance), HDR10+ (Samsung), Hybrid Log-Gamma/HLG (BBC and Japan’s NHK), Technicolor Advanced HDR and IMAX Enhanced. Your HDR TV will need to support the particular flavour of HDR to watch HDR content. A media streaming device might be able to convert one HDR flavour into another your HDR TV can utilise. HDR10 and Dolby Vision are the most popular schemes. Note that not all 4K TVs are HDR-capable. There are also different HDR standards, with HDR10 being the most basic, but other standards may be more demanding. Still photographers can also use their cameras and software to create HDR photographs; see siliconchip.au/link/abfe among many other articles. Conclusion While LCD screens are a significant advance over plasma and CRT displays, improvements are still coming over the next few years. It seems likely that eventually, OLEDs and MicroLEDs will replace LCDs, but at the moment, they are all competitive in their own ways. That competition will drive the advancement of all these technologies over the next couple of decades unless something entirely new comes along. SC siliconchip.com.au Samsung have a 14m-wide LED cinema screen in Sydney capable of HDR content. Source: https://news.samsung.com/global/samsung-unveils-the-firstonyx-cinema-led-screen-in-australia Australia's electronics magazine October 2022  25 IDEAL FOR STUDENT OR HOBBYIST ON A BUDGET • DATA HOLD • SQUARE WAVE OUTPUT • BACKLIGHT • AUDIBLE CONTINUITY Don't pay 2-3 times as much for similar brand name models when you don't have to. 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Explore our wide range of multimeters, in stock on our website, or at over 110 stores or 130 resellers nationwide. www.jaycar.com.au/multimeters 1800 022 888 LARGE BACKLIT DISPLAY AND IP67 WATERPROOF RATED • TRUE RMS • CAPACITANCE • FREQUENCY • RELATIVE MEASUREMENT TAKE EASY ENVIRONMENTAL MEASUREMENTS • MULTIMETER FUNCTIONS • SOUND LEVEL • LIGHT LEVEL • INDOOR TEMP • HUMIDITY ONLY 99 $ 95 QM1549 WIRELESS BLUETOOTH® FEATURE FOR DATA LOGGING • AUTORANGING • TRUE RMS • 6000 COUNT • IP67 WATERPROOF ONLY 139 $ QM1594 ONLY 149 $ QM1578 Use this colour coded selection guide to pick the meter that best suits your needs. GREEN labelled product suit hobbyists and those on a budget. BLUE suit makers familiar with multimeters and want more features. For all the bells and whistles and the highest ratings, choose from the ORANGE professional range. ENTRY LEVEL * QM1500 QM1517 QM1527 MID LEVEL QM1529 QM1321 QM1020 QM1446 Display (Count) 2000 2000 2000 2000 4000 Analogue Security Category Cat II 500V Cat III 600V Cat III 500V Cat III 600V Cat III 1000V Cat II 1000V • • Autorange True RMS PROFESSIONAL QM1323 QM1552 2000 4000 2000 4000 4000 2000 4000 6000 4000 Cat III 600V Cat III 600V Cat IV 600V Cat III 600V Cat IV 600V Cat III 600V Cat IV 600V Cat IV 600V Cat III 1000V • • • • • • QM1551 QM1549 • • • • • XC5078 QM1594 QM1578 • Voltage 1000VDC/ 750VAC 500V AC/DC 500V AC/DC 600V AC/DC 1000VDC/ 750VAC 1000V AC/DC 1000VDC/ 700VAC 600V AC/DC 1000VDC/ 750VAC 600V AC/DC 1000V AC/DC 600V AC/DC 600V AC/DC 1000V AC/DC Current 10A DC 10A DC 10A DC 10A AC/DC 10A AC/DC 10A DC 10A AC/DC 10A AC/DC 10A AC/DC 10A AC/DC 10A AC/DC 200mA AC/DC 10A AC/DC 10A AC/DC Resistance 2MΩ 2MΩ 2MΩ 20MΩ 40MΩ 20MΩ 20MΩ Capacitance 100mF Frequency 10MHz Temperature Duty Cycle 20MΩ 40MΩ 200MΩ 40MΩ 40MΩ 40MΩ 60MΩ 100μF 100µF 100mF 100µF 100µF 100µF 6000µF 10MHz 10MHz 10MHz 10MHz 10MHz 10MHz 10kHz 1000°C 760°C 1000°C 760°C 750°C 760°C • Continuinty • • • • • • Relative Min/Max/Hold • Non Contact Voltage • • • $24.95 $29.95 $49.95 • • • • • • • • • • Max Hold • • • $59.95 $69.95 $69.95 IP Rated Price • • • • $19.95 *Lifetime warranty excluded on models: QM1500/QM1517/QM1527 $29.95 $49.95 4000MΩ • • IP67 $9.95 1000VDC/ 750VAC • • Max Hold • QM1493 $99.95 IP67 $89.95 $139 $149 $249 0-30V 0-2A Part 1 by John Clarke bench supply Every workshop or laboratory needs an adjustable voltage, current-limited DC power source. This 0-30V Supply includes adjustable current limiting up to 2A with voltage and current metering, plus load switching. Most of the parts are commonly available; the two harder-to-get parts and the PCB are available from Silicon Chip. B ench power supplies are necessary for any workshop, powering electronic circuits and other loads such as small motors, LEDs and testing circuits. They are even pretty handy for charging batteries and the like. Looking back through our power supply projects, we haven’t published a basic workhorse supply like the one presented here that suits most workbench applications. We have published several dual tracking supplies and higher-current single output supplies, but 0-30V at up to 2A is sufficient for many applications. This being a simpler, cheaper design also makes it suitable for relative beginners to build. Our Supply includes metering that shows the voltage and the current being drawn from it. A load switch is used to connect or isolate the load when required, with an indicator LED to show when the output is on. The current limit can be adjusted from 28 Silicon Chip near zero to 2A to protect circuitry from excess current should there be a fault. A current limit indicator LED is also included. Load switching is over-ridden if the heatsink gets too hot, in which case the output is disconnected. In this case, the load indicator LED will remain off regardless of the load switch position. Our power supply includes power- up and power-down circuitry that protects the load as the Supply is switched on and off. This ensures the voltage from the regulator is fully settled before being applied to the load. Similarly, the load is disconnected quickly at power-off, well before the output drops significantly, preventing unexpected voltages from being applied to your load. Features & Specifications ∎ ∎ ∎ ∎ ∎ ∎ ∎ ∎ ∎ ∎ ∎ ∎ ∎ Easy to build using mostly standard components Low noise output Excellent regulation Output voltage: 0-30V Current limit: 0-2A (non-foldback) with indicator Regulation method: linear Load regulation: better than 0.5%, 0-2A Output noise & ripple: <8mV RMS, <50mV peak-to-peak <at> 2A Meters: voltage (100mV resolution), current (10mA resolution) Voltage adjustment: single-turn or multi-turn knob Load disconnect: load switch, load indicator Over-temperature protection: disconnects load when heatsink reaches 60°C Other features: short circuit protection, clean switch on and off Australia's electronics magazine siliconchip.com.au Scope 1: the Supply’s output voltage only dropped by 58mV with a 2A load step and recovered in about 300ms. Another valuable feature of our power supply is that you can adjust the output right down to 0V. Some very basic supplies will only go down to about 1.2V and there are times when that isn’t low enough. For example, if you are testing a circuit that runs from a single 1.2-1.5V cell and want to see how the circuit behaves when powered from a discharged cell at or below 1V. For the voltage adjustment, you can use a standard potentiometer. However, we recommend getting a multiturn potentiometer, especially if you want fine adjustment at low voltage settings. More on that later. The Supply is housed in a folded metal enclosure with an aluminium base and ventilated steel top cover. The front panel has the mains power switch, knobs to adjust the output voltage and current limit, the load switch, the two indicator LEDs and the voltage and current meters. There is just the mains power input socket and a heatsink on the rear panel. Scope 2: output noise and ripple with no load (top), 2A load (middle) and 1.92A current limited (bottom). Performance As this Supply uses linear regulation, it has excellent load regulation, clean current limiting and low output noise and ripple. Load regulation is tested by setting the voltage to a fixed level and changing the load resistance so that the output current rapidly swings between two extremes. With the output set to 16V, it dropped by less than 100mV when the load changed from 0A to 2A at the output terminals. When measured directly on the PCB, the voltage drop was 60% less. So most of the voltage drop is due to the wires from the PCB to the terminals on the front panel. We set the oscilloscope to monitor the AC voltage so that only the sudden changes in voltage are shown. Scope 1 shows what happens with a sudden load change. This revealed that the output momentarily dropped by 58mV when the load jumped from 0A to 2A. Similarly, when the 2A load was released, there was a positive shift Fig.1: the basic regulator arrangement is essentially the standard LM317 application from its data sheet but with current booster transistor Q1 added to increase the maximum output current and improve heat dissipation. As REG1 draws more current, the voltage across the 33W resistor at its input rises until Q1’s base-emitter junction becomes forwardbiased, and Q1 takes over delivering the load current. siliconchip.com.au Australia's electronics magazine of 34mV before recovery. Note the waveform does not show the DC voltage change, just the momentary shift in voltage from 16V. There is no visible change in voltage when the oscilloscope is set to show DC voltage at 2V/div so that the full DC voltage can be seen. That’s because 58mV and 34mV are only 0.4% and 0.2% of the output voltage, respectively. Output noise We measured the output noise and ripple under three different conditions: with the Supply unloaded, at 2A load and with the current limit active just below 2A. All three results showed low levels of noise and ripple. Scope 2 shows the output noise and ripple at 16V with no load for the top waveform, a 2A load for the middle waveform and current limited at 1.92A for the lower blue waveform. There is no discernible difference between the loaded and unloaded waveforms. However, there is a little more ripple for the current-limited waveform as current limiting is taking over from voltage regulation. Operating principles The basic circuit for our power supply (Fig.1) is based on an adjustable three-terminal regulator (REG1) and current boost transistor (Q1). REG1 is an LM317 that, in its standard arrangement, can deliver a voltage ranging from about 1.2V up to 37V at 1.5A. The regulator has internal protection such as current limiting, thermal shutdown and safe operating area (SOA) protection. The output voltage is set using October 2022  29 resistors connected between the output and adjust pins (R2; 100W) and between adjust and ground (VR1). The resistor between the adjust and output pins sets the quiescent current of the regulator, which needs to be at least 12mA if it is to maintain regulation when the output is otherwise unloaded. When the adjust terminal is connected to ground, the output voltage equals the reference voltage, which appears between the output and adjust pins. This is between 1.2V and 1.3V, depending on tolerances in the regulator manufacturing. For our circuit, the resistance is set at 100W to provide the 12mA minimum load current for the worst-case specification when the regulator reference is 1.2V. There is a minimal current of typically 50μA flowing out of the adjust terminal, which is small enough that it can usually be ignored. The output voltage calculation then simplifies to the following equation: Vout = Vref × (1 + VR1 ÷ R2). If you need to include the adjust terminal current, that current, multiplied by the VR1 resistance, adds to the output voltage. What the simplified circuit of Fig.1 does not show is that, in the full circuit, the lower end of VR1 is connected to a negative supply that is greater in magnitude than Vref. That way, the output can be adjusted down to 0V. With the reference voltage cancelled out, the output voltage calculation simplifies to Vout = Vref × VR1 ÷ R2. Current boosting As shown in Fig.1, REG1 is used in conjunction with PNP power transistor Q1. This transistor supplies the bulk of the load current but with the output voltage controlled by REG1. The input voltage is applied to the base of Q1 and the regulator input via a 33W resistor. As current is drawn from the output, it also flows through the 33W resistor, so the voltage across it rises. When 18mA flow is reached, the voltage between the base and emitter is 0.6V. At this point, transistor Q1 starts to conduct and bypasses extra current around REG1. The result is that the circuit can supply more current than the 1.5A limit of the LM317, while the LM317 remains in control of the output voltage. However, we do lose the over-­ current shutdown feature provided by 30 Silicon Chip Parts List – 30V 2A Bench Supply 1 double-sided PCB coded 04105221, 76 × 140mm (main board) 1 double-sided PCB coded 04105222, 56 × 61mm (front panel control board) 1 vented metal instrument case, 160 × 180 × 70mm [Jaycar HB5446] 1 30V 2A transformer (T1) [Jaycar MM2005] 1 current and voltage meter [Core Electronics 018-05-VAM-100V10A-BL] 1 fan type heatsink, 72mm high [Altronics H0522, Jaycar HH8572] 1 SPDT 10A, 24V DC coil relay (RLY1) [Altronics S4162C, Jaycar SY4067] 1 IEC male chassis connector with integral fuse holder [Altronics P8324, Jaycar PP4004] 1 1A M205 fast-blow fuse (F1) 1 rubber boot for IEC chassis connector [Altronics H1474, Jaycar PM4016] 1 DPST neon illuminated mains-rated switch (S1) [Altronics S3217, Jaycar SK0995] 1 SPDT toggle switch (S2) [Altronics S1310, Jaycar ST0335] 1 normally-closed 60°C thermal cutout (TH1) [Jaycar ST3821] 1 red binding post [Altronics P9252, Jaycar PT0453] 1 black binding post [Altronics P9254, Jaycar PT0454] 1 green binding post [Altronics P9250, Jaycar PT0455] 1 silicone insulating washer for TO-3P package devices 1 silicone insulating washer and bush for TO-220 package devices 2 4-way pluggable terminal sockets, 5.08mm spacing (CON1, CON2) [Altronics P2574, Jaycar HM3114] 2 4-way screw terminal plugs (for CON1 & CON2) [Altronics P2514, Jaycar HM3124] 2 14-pin IDC boxed headers (CON3, CON4) [Altronics P5014] 2 14-pin IDC line sockets (for CON3 & CON4) [Altronics P5314] 1 3-way screw terminal with 5.08mm spacing (CON5) 2 2-pin vertical polarised headers, 2.54mm spacing (CON6, CON7) [Altronics P5492, Jaycar HM3412] 1 2-pin polarised header plug (for CON7) [Altronics P5472 and 2 x P5470A, Jaycar HM3422] 1 8-pin DIL IC socket (optional; for IC1) 2 5mm LED bezels 1 knob to suit VR1 1 knob to suit VR3 10 1mm PC pins (add 12 if using them for all test points) Wire & cable 1 150mm length of 14-way ribbon cable 1 150mm length of brown Active wire stripped from three-core 7.5A mains cable 1 150mm length of blue Neutral wire stripped from three-core 7.5A mains cable 1 150mm length of green/yellow Earth wire stripped from three-core 7.5A mains cable 4 100mm lengths of 7.5A hookup wire (assorted colours) 2 150mm lengths of 7.5A hookup wire (one red, one black) Hardware etc 4 M4 × 10mm panhead machine screws 4 M4 hex nuts 4 M4 star washers 4 6.35mm-long M3-tapped Nylon spacers 8 M3 × 5mm panhead machine screws 2 M3 × 20mm panhead machine screws (for Q1 and REG1) 4 M3 × 15mm panhead machine screws 1 M3 flat steel washer 6 M3 Nylon washers 6 M3 hex nuts 2 small M3.5-threaded right-angle brackets [Jaycar HP0872, pack of 8] 2 crimp eyelets (Earth connections to chassis) Australia's electronics magazine siliconchip.com.au 4 blue female spade crimp connectors (connections to mains on/off switch) 5 150mm cable ties 3 100mm cable ties 1 50mm length of 25mm diameter heatshrink tubing 1 50mm length of 6mm diameter heatshrink tubing 1 50mm length of 3mm diameter heatshrink tubing 1 small tube of thermal paste Semiconductors 1 TL072P dual op amp, DIP-8 (IC1) [Altronics Z2872, Jaycar ZL3072] 1 INA282AIDR or INA282AQDRQ1 shunt monitor, SOIC-8 (IC2) [SC6578] 1 LM317T three-terminal adjustable regulator, TO-220 (REG1) [Altronics Z0545, Jaycar ZV1615] 1 LM336-2.5 voltage reference, TO-92 (REG2) [Altronics Z0557, Jaycar ZV1624] 1 TIP36C PNP 100V 25A power transistor, TO-3P (Q1) [Altronics Z1137, Jaycar ZT2294] 1 2N7000 N-channel Mosfet, TO-92 (Q2) [Altronics Z1555, Jaycar ZT2400] 3 BC547 45V 100mA NPN transistors, TO-92 (Q3-Q5) 1 BC327 45V 500mA PNP transistor, TO-92 (Q6) 2 5mm high-brightness red LEDs (LED1, LED2) 1 33V 1W zener diode (ZD1) [1N4752] 2 12V 1W zener diodes (ZD2, ZD3) [1N4742] 1 BR106, PB1004 or KBPC1006 bridge rectifier (BR1) [Altronics Z0085/Z0085A, Jaycar ZR1320] 6 1N4004 400V 1A diodes (D1, D3, D4, D7, D8, D10) 1 1N5404 400V 3A diode (D2) 3 1N4148 75V 200mA signal diodes (D5, D6, D9) Capacitors 3 4700μF 50V radial electrolytic 1 2200μF 35V radial electrolytic 1 1000μF 16V radial electrolytic 1 47μF 16V radial electrolytic 1 10μF 50V non-polarised/bipolar radial electrolytic 1 10μF 35V/50V/63V radial electrolytic 2 10μF 16V radial electrolytic 1 1μF 16V radial electrolytic 1 1μF multi-layer ceramic 4 100nF 63V/100V MKT polyester Potentiometers 1 16mm 5kW linear single-gang potentiometers (VR1●) [Altronics R2224, Jaycar RP7508] 1 16mm 10kW linear single-gang potentiometers (VR3) [Altronics R2225, Jaycar RP7510] 2 5kW multi-turn top-adjust trimpots (VR2●, VR4) [Altronics R2380A, Jaycar RT4648] 1 500W multi-turn top-adjust trimpot (VR5) [Altronics R2374A, Jaycar RT4642] 2 10kW multi-turn top-adjust trimpots (VR6, VR7) [Altronics R2382A, Jaycar RT4650] ● alternatively and ideally, replace VR1 with a 2.5kW multi-turn pot [Bourns 3590S-2-252L – element14 2519607; Digi-Key 3590S-2-252L-ND; Mouser 652-3590S-2-252L] and delete VR2 Resistors (all 1/2W, 1% unless otherwise stated) 2 100kW 1 33kW 4 10kW 2 4.7kW 1 3.3kW 1 2.2kW 1W 5% 1 2.2kW 2 1kW 1 330W 4 100W 1 33W 1 20mW 1W M3216/1206-size SMD resistor [Vishay WSLP1206R0200FEA or similar – element14 1853240; Digi-Key WSLP-.02CT-ND; Mouser 71-WSLP1206R0200FEA; part of SC6578] siliconchip.com.au Australia's electronics magazine the LM317, limiting the output to 1.5A. But that’s what we need to get a higher output current. We use extra circuitry to add back current limiting, with the advantage of being able to adjust the limit over the 0-2A range. This boost circuit includes a hidden bonus in that it prevents the regulator from shutting down due to high power dissipation (assuming Q1 has sufficient heatsinking). This way, the circuit can supply the full 2A across the entire voltage range. Without the boost transistor, the regulator would shut down when there is high dissipation, ie, high current at low output voltages. For example, if the regulator output voltage is 12V, the input is 32V and there is a 1A current flow, the regulator (without Q1) will be dissipating (32V − 12V) × 1A = 20W. The specifications for the device package show a 5°C/W temperature rise between the case and junction. Thus, at 20W, the junction temperature will rise 100°C above the case (20W × 5°C/W). For a case temperature of 25°C, the junction will be at 125°C and the device will shut down. So the Supply wouldn’t be able to provide 1A at 12V without shutting down. By adding the boost transistor, REG1 is only handling 18mA and dissipating about 360mW in this case (18mA × [32V − 12V]) and the junction will only be 1.8°C above the case temperature. The dissipation is instead handled by Q1. Its junction temperature will not be anywhere near as high as the regulator, as it has a much lower junction-to-case thermal resistance of 1°C/W. So at 20W, its junction will only be 20°C above the case temperature. Using a large enough heatsink, we can maintain the case temperature at a reasonably low value. We do lose the thermal shutdown feature of the LM317 as a consequence of directing the primary current through Q1. The junction temperature for REG1 will essentially follow the temperature of the heatsink. To solve this, we attach a separate thermal switch to the heatsink to provide an over-temperature shutdown. It opens at 60°C, disconnecting the power supply load and allowing the transistor to cool. We haven’t mentioned the capacitors in Fig.1. The bank of three 4700μF capacitors at the input smooths out the ripple from the pulsating DC derived October 2022  31 Fig.2: the complete Supply circuit. Note how many signals are routed to CON3, then via a ribbon cable to CON4 on the front panel control board, and in some cases, back through the cable to another pin on CON3. from rectified AC. This is required to keep the regulator’s input voltage at least 2.5V above the output to maintain voltage regulation. The capacitor between REG1’s ADJ pin and ground reduces ripple and noise at the regulator output, while the capacitor between Vout and GND prevents oscillation and improves transient response. Diode D1 protects REG1 from the capacitor discharging through REG1 if the output is short-­ circuited. 32 Silicon Chip Full circuit details The whole circuit is shown in Fig.2. Power for the Supply is derived from the mains via transformer T1. T1’s primary winding is supplied with 230V AC via fuse F1 and power switch S1. The secondary winding between the 0V and 24V taps of T1 is fullwave rectified by bridge rectifier BR1 and filtered using three 4700μF 50V capacitors to produce a nominal 32V DC. Typically, the DC voltage is higher than this as the mains is usually above Australia's electronics magazine 230V AC, and the transformer is not usually heavily loaded. This filtered voltage is applied to the emitter of transistor Q1. The output of the regulator and the collector of Q1 are applied to the load via the normally-open contact of relay RLY1. The relay control circuitry will be described later. Bringing the output to 0V The circuitry around REG1 differs from that shown in Fig.1 in that, siliconchip.com.au instead of connecting to GND, VR1 is connected to the output of op amp IC1a. IC1a produces a negative voltage below ground, to cancel out the reference voltage of REG1. Setting IC1a’s output negative by the same siliconchip.com.au magnitude as REG1’s reference voltage will allow the output to go to zero. A negative voltage is derived via the 30V tapping on the secondary of the mains transformer to produce a -8V supply. This is achieved by diode D3 Australia's electronics magazine that half-wave rectifies the AC voltage, and a 1000μF capacitor filters it. Diode D4 prevents this supply from going above 0V by more than 0.6V and prevents significant reverse polarity from being applied to the capacitor October 2022  33 Everything fits neatly into the fairly compact and attractive instrument case. You can see transistor Q1 at left, attached to the case opposite the heatsink, with the thermal switch above it. The blue multi-turn voltage adjustment pot is also clearly visible. when the power is switched off. By all appearances, the -8V supply should work. But there is a hidden problem: unless the main 32V supply derived from the bridge rectifier has sufficient load, the -8V supply will not be available. This is because, under light load situations, there is no current path for the -8V supply current through D3 to flow back through the bridge rectifier. The only way is blocked by the diode in the bridge between the 24V tap and the ground supply rail. With the -8V supply, current only flows during the parts of the mains cycle when the 24V and 30V taps produce a negative voltage with respect to the 0V end of the windings. So current has to flow through the diode in BR1 that connects from the 0V transformer tapping and positive supply, then through the load on the main supply and -8V supply and back to the 30V tap via D3, as shown in Fig.3. If the load on the main supply is insufficient to maintain the -8V supply, its magnitude will drop while the voltage applied to the main supply from the 30V tapping will increase. This is resolved by adding a 2.2kW 1W resistor from BR1’s positive terminal to ground, setting a minimum load so the -8V rail is always available. The -8V supply provides a bias current for REG2, an LM336-2.5V shunt regulator. It produces a regulated negative supply with its positive terminal connected to ground, and its negative terminal connects to the -8V supply 34 Silicon Chip via a smaller 2.2kW current biasing resistor. As a result, the voltage at its negative terminal is a stable -2.49V even with temperature variations due to diodes D5 and D6 providing temperature compensation. Trimpot VR7 is adjusted until there is very close to -2.49V across REG2. This reference voltage is bypassed with a 10μF capacitor. Trimpot VR6 connects across the -2.49V reference to provide an adjustable negative voltage to offset the reference voltage produced by REG1. This negative reference is obtained from the wiper of VR6, which is adjusted to provide a fixed voltage between -1.2 to -1.3V to counter REG1’s reference voltage between its output and adjust pins. The wiper of VR6 connects to the non-inverting input of IC1a. IC1a acts as a unity-gain buffer, where the output voltage follows the input. IC1a’s output then sinks 12-13mA from REG1 at the lower end of VR1. With VR6 correctly set, REG1’s output is zero when VR1 is fully anticlockwise. Current monitoring Fig.3: the negative supply generator used to adjust REG1’s minimum output voltage (among other purposes) seems straightforward, but there’s a trick to it. The load resistance on the main rectifier (the ‘resistor’ at upper right) must be low enough for the current to flow through the path shown in red. Otherwise, the negative supply drifts positive. We ensure this is the case by adding a 1W ‘dummy’ load resistor across the positive supply. Australia's electronics magazine IC2 measures the current drawn by the load. This measurement, in conjunction with op amp IC1b and Mosfet Q2, is used to provide current limiting. IC2 is a current monitor that measures the voltage drop across the 20mW shunt in the GND supply line. The voltages at either end of the shunt are applied to pins 1 and 8 of IC2, which amplifies the difference by a factor of 50. We selected the shunt so that the pin 5 output of IC2 provides 1V per 1A of output current. There is a 20mV voltage drop across the 20mW shunt at 1A, which, when multiplied by 50, gives 1V. But note that IC2’s output voltage is with respect to the -2.49V reference rather than the 0V rail. The calibration is linear, so IC2 will deliver 2V above the -2.49V reference for a 2A current flow or proportionally lower values at intermediate currents. siliconchip.com.au There isn’t much on the rear panel – just the heatsink and IEC mains power input. Note how the heatsink hangs down below the bottom of the case as it is slightly taller. We get around this by making the case’s feet taller. For current limiting, we compare the current measured by IC2 with the maximum set current level. The current setting for limiting is provided by a voltage divider across the -2.49V supply. The main adjustment is potentiometer VR3, with VR4 and VR5 setting the maximum and minimum current range limits. Ignoring VR5 for the moment, VR4 is set so that when VR3 is set fully clockwise, the voltage at its wiper will be 2V above the -2.49V reference, corresponding to a 2A current limit. VR5 provides a small voltage offset above the -2.49V reference. It is used to set the minimum setting of VR3 to match the output of IC2 when there is no load current. Typically, IC2’s output will always be above the -2.49V reference due to the small standby current drawn by the reference, IC1, IC2 and the meters. Also, there will be an offset voltage inherent to IC2 even with no current flow. VR5 allows us to dial out this voltage so that the voltage between test point TP10 (at the top of VR5) and TP3 (at the wiper of VR3) ranges between 0V and 2V, matching the 0-2A current limit range. If the VR5 adjustment is made carefully, that will also allow VR3 to be rotated fully anticlockwise without entering current limiting when there is no load. The current limit setting voltage from VR3’s wiper is applied to the inverting input of IC1b via a 1kW siliconchip.com.au resistor. This voltage is compared with the output from IC2, which goes to the pin 5 inverting input of IC1b via a 10kW resistor. When IC2’s output is lower than the setting for VR3, IC1b’s output (pin 7) is pulled low, towards its pin 4 supply (-8V). In this case, current limiting indicator LED1 is reverse-biased, so the gate of Mosfet Q2 is held at its source voltage, with no current flowing through the Mosfet. When the output from IC2 goes above the threshold set by VR3, the output of IC1b begins to go high, lighting LED1 via the 1kW resistor between Q2’s gate and source pins. This also starts to switch on Q2 as its gate voltage rises. The channel of Mosfet Q2 then begins to conduct, pulling the adjust terminal of REG1 down to reduce its output voltage. Note that the adjust terminal is isolated from the voltage setting resistance of VR1 via a 330W resistor. This allows Q2 to drive the adjust terminal without being loaded by the voltage setting resistance. The 100nF capacitor between pin 5 of IC1b and the drain of Q2 acts as a compensation capacitor for the current limiting feedback, preventing it from coming on too rapidly, possibly leading to oscillation. Compensation for the op amp is also provided using a 1μF capacitor between the pin 6 inverting input and the pin 7 output. While this capacitor Australia's electronics magazine could be as low as 47pF to prevent oscillation, the 1μF value gives better output ripple reduction when the supply is in current limiting. Load switching As mentioned previously, we use a relay to switch the Supply’s output to the load. This relay (RLY1) allows the circuitry to disconnect the load during power-up, power-down or if the heatsink gets too hot. Disconnecting the load when power is first applied, and when it is switched off, prevents unexpected voltages from being applied to the load. This circuit section comprises diodes D7 and D8, transistors Q3 to Q6 and associated components, plus RLY1. We use the 18V transformer tap to derive a 25V supply. Diode D7 halfwave rectifies the AC, and a 2200μF capacitor filters the resulting voltage to a relatively smooth 25V DC or so. The positive power supply for op amp IC1 is taken from this rail via a 100W resistor. As the negative supply for IC1 is from the -8V rail, ZD1 is included to ensure that the overall supply to IC1 does not exceed 33V. Diode D8 also provides half-wave rectification of the 18V tapping, but this is not filtered so that we have a pulsating voltage. This way, the voltage from diode D8 will immediately cease when power is disconnected, allowing us to quickly detect when the power is switched off. October 2022  35 When power is applied, the positive voltage at D8’s cathode switches on transistor Q3 for half of every mains cycle. With our 50Hz mains, the positive excursion is over a 10ms period. Q3 discharges the 1μF capacitor via a 100W resistor each time it is switched on; this capacitor begins to charge via a 100kW resistor from the 25V supply during the negative half of the waveform. This capacitor will stay mostly discharged, provided that Q3 repeatedly discharges it every 10ms. Potentiometer options We have provided the option of using a standard single turn (300° rotation) potentiometer for VR1, which adjusts the Supply output voltage. In this case, it’s a 5kW linear potentiometer connected in parallel with a 5kW trimpot. This is the cheapest option, but not the best. The alternative is to use a 2.5kW multi-turn potentiometer, making it easier to adjust the output voltage, especially for low values. While we are using a potentiometer for the voltage adjustment, it is used as a variable resistance (or rheostat) rather than as a potentiometer. With a potentiometer, the wiper can produce a range of voltages between the voltages applied at the two ends of the potentiometer’s track. The wiper and just one end of the potentiometer are used to produce a variable resistance. The unconnected end of the potentiometer is often connected to the wiper, but this does not alter the resistance-versus-rotation law. When using a standard 300° potentiometer to adjust the voltage over a 0-30V range, a slight adjustment causes the output voltage to change quickly. So, for example, a 0.3V change is made with each 1% (3°) of rotation. So to change the voltage by 1V, just over 3% of rotation (10°) is required. Another problem is that while the physical end stops are 300° apart, the actual resistance element generally only changes over a 270° range, further ‘squashing up’ the adjustment range. Also, we don’t use a 2.5kW single-turn pot since they are difficult to obtain and rather expensive. Instead, we use a 5kW linear pot in parallel with a 5kW resistance to provide an overall 2.5kW range. This means that the plot of resistance vs rotation is not linear, further exacerbating the adjustment sensitivity for low voltage values, as shown in the plot below. The cyan line is for a 2.5kW linear pot, while the red line plots the resistance law for the 5kW pot in parallel with a 5kW resistance. The parallel resistances do not provide a linear change in resistance versus rotation, with the largest difference being near the ends of the pot rotation, making accurate low-­voltage adjustment even more difficult. For the first 10% of rotation, the linear 2.5kW pot changes resistance by 250W, while the 5kW pot and 5kW parallel resistance changes by nearly 500W. At half rotation, the 2.5kW pot measures 1.25kW (half the total resistance value), while the 5kW pot gives 1.67kW (2/3 of the resistance value). At 90% rotation, the 2.5kW pot is at 2.25kW (90% of the total resistance), while the 5kW pot gives 2.37kW (95% of the resistance). This non-linearity causes the adjustment at the low end to be much coarser than in the middle of the range. This plot shows the difference in resistance vs rotation for a regular 2.5kW pot and a 5kW pot shunted with a fixed resistance. They start and end at the same points, but the shunted pot’s resistance law is not linear. If you can get the multi-turn 2.5kW potentiometer to use for the output voltage adjustment, you’ll be able to set the output voltage much more easily and accurately. 36 Silicon Chip Somewhat similarly, transistor Q4 controls the charge on the 47μF capacitor. When Q4 is off, it allows the 47μF capacitor connected to TP8 to charge via the 100kW and 100W resistors. Q4 remains off, provided that the 1μF capacitor connecting to Q4’s base is discharged. So when there is an output from the transformer, the 47μF capacitor charges up. The base of Q5 needs to be above 13.2V to switch on due to the voltages across diode D9 and zener diode ZD2, the latter being biased via a 3.3kW resistor from the 25V supply. As a result, when power is first applied, there is a five-second delay before the 47μF capacitor charges enough to switch Q5 on. But when the power switch is flicked off, within a few tens of milliseconds, the 1μF capacitor at Q4’s base charges enough to switch it on, discharging the 47μF capacitor and switching Q5 off. When Q5 is on, it pulls current from the base of PNP transistor Q6 via a 4.7kW current-limiting resistor. The current from Q6 flows through the load switch (S2), then through thermal switch TH1 and to the relay coil. So the load is only connected by RLY1 when Q6 is on, S2 is on and thermal switch TH1 is not open. To put it another way, the load is disconnected during power-up, power-­ down, when S2 is off or when the temperature of TH1 is too high. Diode D10 clamps the negative voltage when the relay coil is switched off. By the way, we sneakily reuse the 12V supply from zener diode ZD2 to power IC2, the INA282 shunt monitor. Metering The voltmeter and ammeter connect to the regulated output of the Supply. The voltmeter measures the voltage before the relay contact. The shunt for current measurements is in the negative supply line; it has a very low resistance, so there is a minimal voltage drop across it. The meter is supplied from the 25V positive rail and uses the MI- terminal as its ground. Next month We have now described what our new Supply can do and how it works. Next month’s follow-up article will have the assembly details for the two PCBs, chassis assembly instructions and wiring details. SC Australia's electronics magazine siliconchip.com.au Gear UP 4r e Build It Yourself Electronics Centres® INTRO SPEC Hurry, only 20 av IAL! ailable at this price. 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Easy power connection via binding posts. SAVE 28% 35 $ P 1012A 1660 Hole SAVE 26% 42 $ P 1015A 2309 Hole Your one-stop electronics shop since 1976. | Order online at altronics.com.au Must have for the electronics maker! Save on workbench upgrades. Amazing value under $100 SAVE $21 NEW! 99 $ 375 Clean & Revive Small Parts Save space on your bench with this top performing 60W soldering iron and 90W vacuum desoldering station. Removes a 16 pin through hole IC in 30 seconds! Sucks molten solder away from components & pads in no time and is easily cleaned. 160° to 480°C adjustable. Includes 0.2mm soldering tip and three desoldering tips. s in Nibbles hole tic metal & plas e Toolbox spac saver! NEW! T 1534B Also great for cleaning jewellery and glasses. Soldering & Vacuum Desoldering Station Our first multimeter with wireless USB charging in-built! No more changing batteries. 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Western Australia Build It Yourself Electronics Centres 99 159 $ Q 2115 SAVE $30 SAVE $40 » Perth: 174 Roe St » Joondalup: 2/182 Winton Rd » Balcatta: 7/58 Erindale Rd » Cannington: 5/1326 Albany Hwy » Midland: 1/212 Gt Eastern Hwy » Myaree: 5A/116 N Lake Rd Q 2100 Peak® DCA55 Component Analyser This easy to use, component analyser is like having a library of electronic info at your fingertips! Saves hours of looking up specs. 2 year warranty. Made in the UK. Victoria 08 9428 2188 08 9428 2166 08 9428 2167 08 9428 2168 08 9428 2169 08 9428 2170 » Springvale: 891 Princes Hwy » Airport West: 5 Dromana Ave 03 9549 2188 03 9549 2121 New South Wales » Auburn: 15 Short St 02 8748 5388 Queensland » Virginia: 1870 Sandgate Rd 07 3441 2810 South Australia » Prospect: 316 Main Nth Rd 08 8164 3466 Please Note: Resellers have to pay the cost of freight & insurance. Therefore the range of stocked products & prices charged by individual resellers may vary from our catalogue. © Altronics 2022. E&OE. Prices stated herein are only valid until date shown or until stocks run out. Prices include GST and exclude freight and insurance. See latest catalogue for freight rates. *All smartphone devices pictured in this catalogue are for illustration purposes only. Not included with product. B 0010 Find a local reseller at: altronics.com.au/storelocations/dealers/ CIRCUIT NOTEBOOK Interesting circuit ideas which we have checked but not built and tested. Contributions will be paid for at standard rates. All submissions should include full name, address & phone number. ST7920 LCD driver for PIC32MZ projects Phil Prosser has published several designs that share a common CPU control board based on a PIC32MZ microcontroller. In many of those designs, that micro drives a 128×64 graphical LCD based on the KS0108 controller. However, many 128×64 graphical LCDs are also available that use the ST7920 (or compatible) controller. I have updated the software for two of his designs to support that. Those projects include the DIY Reflow Oven Controller (April & May 2020; siliconchip.au/Series/343) and the Low-Distortion DDS Audio Signal Generator (February 2020; siliconchip. au/Article/12341). For the Two-Channel DDS Audio Signal Generator, if an ST7920 screen is used, in addition to installing the updated firmware, RB2 must be held low by installing a jumper from pin 3 to pin 9 of CON9. For the Reflow Oven, if an ST7920 screen is used, RB3 must be held low by installing a jumper from pin 1 to pin 9 of CON9. siliconchip.com.au While revising the Reflow Oven code to add ST7920 LCD controller support, I made another enhancement, adding an ‘oven timer’ mode. After selecting “timer mode”, the user can set the temperature & time in “Settings” before starting the cycle. An on-screen timer will count down to the end of the cycle and then the temperature will revert to the previous setpoint. To make space for “timer mode” in the top-level menu, the functions to adjust thermocouple coefficient & offset and the PID parameters have been moved under the “Settings” menu. Constructors should also note that the ST7920 displays are typically a different size from those with a KS0108 controller, so the cutout in the front panel will need to be adjusted. In both cases, the revised software still supports KS0108-based LCD screens; without the jumpers mentioned above being fitted, the code reverts to that original mode. One of the challenges of adding ST7920 support is that the two Australia's electronics magazine controllers utilise different memory layouts, as shown in the accompanying figure. To support both screens, the code does the following: • Graphics are drawn to a screen buffer in memory with the KS0108 memory layout. • Depending on the screen attached, a different function is called to write the screen buffer to the display. The KS0108 function sends the buffer directly to the controller. The ST7920 function copies the buffer to a second buffer, changing the memory layout as it does so, before sending that secondary buffer to the controller. This approach would be inappropriate for high-resolution displays but is fine for a 128×64 monochrome screen. The function that copies one buffer to another only takes about 350 microseconds, and the second buffer consumes only 1KiB. A library supporting both displays is online at https://github.com/gordoste/ pic32glcd Stephen Gordon, Thurgoona, NSW. ($100) October 2022  41 Simple EEPROM programmer/Wireless Digital FX Pedal control I’ve ‘spun’ up an easier method to program the 24LC32 EEPROM chip in the Digital FX Pedal (April-May 2021; siliconchip.com.au/Series/361) than hacking into a poor PICkit 3! I have an incompatible PICkit 4, so directly programming via my PC was out. But I have dozens of ESP8266 development boards (“ESP-12E dev 42 Silicon Chip board, NodeMCU 1.0” in the Arduino IDE) with 3.3V logic pins that can connect directly to the FX Pedal PCB using I2C. I wrote some code to access a remote SPIFFS file system containing an appropriately named file (“effect. hex”). It reads this file byte-by-byte and writes the data to the EEPROM. Australia's electronics magazine Depending on which ESP8266 module is used, the I2C pins (SDA and SCL) will be numbered differently on the board. Using the Arduino core, there’s no need to set those pins numbers directly; calling the “Wire” library handles that. But you need to be careful to connect the correct pins to the board, as shown in the circuit. siliconchip.com.au The other pins control the current patch without needing a rotary encoder, or the VR8 select switch and IC6 alternative; the present effect can also be selected remotely, over WiFi. They could be left disconnected if you only want to upload patches wirelessly. The web interface allows effect selection and provides an upload page to process the new hex file. A success message is shown once the EEPROM is flashed. The web server is mainly built on the excellent examples found at siliconchip.com.au/link/abcs After programming the Arduino sketch into the ESP8266, you will need to upload the webserver HTML files (part of the same download package on the Silicon Chip website) to the file system on the ESP8266 using the plugin from https://github.com/ esp8266/arduino-esp8266fs-plugin The sketch also includes code to handle a heavy-duty foot toggle switch to replace the rotary switch to select between effects. It’s debounced and works alongside the web control. I’ve found a few people asking for a similar solution on SPIN forums. Tamsin Bromley, Melbourne, Vic. ($100) Galvanic Skin Response unit for stress management This circuit connects to the user’s skin via a pair of electrodes and produces an output voltage related to their stress level. It does this by measuring the resistance of the user’s skin between the electrodes. It’s powered by a small 12V battery for safety. The 12V battery feeds in via a pair of LC filters and is converted to a semi-regulated ±5V supply using zener diodes ZD1 & ZD2 and 10W current-­ limiting resistors. This supply powers µa741 op amp IC1. The +5V supply also provides a DC bias current to the upper electrode via an RC low-pass filter and a 470kW current-limiting resistor, giving around 10µA of bias current. Circuit Ideas Wanted siliconchip.com.au The other electrode connects to the 0V rail via a 10W resistor. The voltage across the electrodes, related to skin resistance (as the bias current is fixed), is amplified by op amp IC1. First, the signal is fed through an 18kW/1µF low-pass filter, with a time constant of 18ms, then it is AC-coupled to the non-inverting input and applied to the inverting input via a 100kW resistor. The result is a DC gain of -22 times (27dB), set by the ratio of the 2.2MW and 100kW resistors. The AC-coupled signal going to the non-inverting input via a high-pass filter has the effect of reducing this gain with increasing frequency, from 25dB at 1Hz down to 15dB at 10Hz, 0dB at around 85Hz and negative gain (attenuation) of around -3dB above 300Hz. So low-frequency signals dominate the output. The output of IC1 is AC-coupled to level control pot VR1 via an RC highpass filter with a -3dB point of 16Hz. The resulting voltage is applied to a two-terminal connector so it can be read out on a DMM set to measure millivolts. As the signal is AC-coupled, the reading indicates the change in stress level at any given time, rather than the current stress level. That could be changed by shorting out the 1µF capacitor at the output of IC1. David Strong, Kogarah, NSW. ($65) Got an interesting original circuit that you have cleverly devised? We will pay good money to feature it in Circuit Notebook. We can pay you by electronic funds transfer, cheque or direct to your PayPal account. Or you can use the funds to purchase anything from the SILICON CHIP Online Store, including PCBs and components, back issues, subscriptions or whatever. Email your circuit and descriptive text to editor<at>siliconchip.com.au Australia's electronics magazine October 2022  43 NEW PIC & AVR Chips from Microchip The parts shortages over the last few years have given By Tim Blythman us the incentive to look more widely for alternatives to the parts we’ve been using. Microchip Technology offered to send us samples of new microcontrollers and, as newer chips tend to have more features at a lower cost, we were keen to find out what the new parts bring. S earches for alternative parts are now something we do far too often. Microcontrollers have been some of the worst affected parts (along with Mosfets), but other ICs and even some passives are becoming harder to find. Many of our favourite microcontrollers from years past are falling out of favour as newer, cheaper parts appear. The older PIC and AVR parts haven’t been discontinued, but as manufacturers cannot keep up with demand, they are allocating more resources to making the latest parts. As a result, many of the older chips have become scarce. As they say, every cloud has a silver lining, and many of the newer parts are much more capable than their predecessors. Many are also ‘drop-in replacements’, at least in terms of having the same pin allocations. In the April issue, we wrote about the new range of 8-pin parts we were using (siliconchip.au/Article/15277). They are the PIC16F15213 and PIC16F15214, about the cheapest 8-pin, 8-bit PICs available. Despite that, they have more features than the earlier 8-pin parts we used, like the PIC12F675 and PIC12F1572. That article also mentioned the then-upcoming PIC16F171xx series of parts, which includes (amongst many other features) a 12-bit analogto-­digital converter (ADC) peripheral. The PIC16F17146 is (or was, at the time of writing) available from DigiKey, so we got a handful to try out. 20-pin chips Microchip gave us further suggestions and sent sample parts for us to try. We bought some PIC16F18146 chips ourselves and received free samples of the PIC16F18045. These are all new 20-pin parts in DIL packages (ie, DIP). Other pin counts are available, but we figured that a 20-pin chip is a sweet spot for many applications. Another reason for choosing to try out parts with 20 pins is that this is a bit of a gap in our repertoire; we tend to use either very small 8-pin chips or larger 28-pin chips. One 20-pin part we often use is the PIC16F1459. It’s handy because it includes a USB peripheral but is relatively inexpensive. Unfortunately, though, three pins are occupied by the USB function, and one cannot be used for any other purpose. The other two can be used as inputs only, even if the USB peripheral is not used. With the next lower pin count being 14 pins, there is often little call for the PIC16F1459 unless the USB function is needed. So we figured it was time to see if there were other options for parts around this size. The next step above a 20-pin micro is usually 28 pins but they are pretty bulky, especially in DIP. There are other advantages for the 20-pin parts; for example, the PPS (peripheral pin select) feature can be used to remap all digital pins on 20-pin and smaller parts, but not on larger parts. Smaller parts The five subjects of this review include a new 8-pin PIC, three new 20-pin PICs from different families and a 32-pin AVR microcontroller. They all have a slew of interesting features. From left to right, they are: PIC16F18015, PIC16F18045, PIC16F18146, PIC16F17146 & AVR64DD32. 44 Silicon Chip Australia's electronics magazine To continue our theme of 8-pin parts from previous articles, we took up Microchip’s offer of a sample of the PIC16F18015. It is from the same family as the PIC16F18045 and has much the same complement of peripherals, although they are exposed on fewer pins, so it’s likely they can’t all be used simultaneously. So we have a good range which should provide some interesting comparisons both between families and between members of the same family. We can also draw some comparisons to the other 8-pin PICs. siliconchip.com.au Fig.1: parts from the PIC16F180xx family, like many of the newer enhanced core 8-bit PICs, have matching pinouts that give an easy path to upgrade to parts with more pins. In this case, the topmost pins have the same designations across the 8-pin PIC16F18015, the 14-pin PIC16F18025 and the 20-pin PIC16F18045. Currently, the PIC16F18015 also appears to be the cheapest 8-pin 8-bit PIC microcontroller with the most RAM and flash memory, at 1kiB of RAM and 14kiB of flash. The upcoming (at the time of writing) PIC16F17115 and PIC16F18115 will have similar quantities of RAM and flash memory. They belong to the same families as the 20-pin parts we are looking at here. The Improved SMD Test Tweezers project (April 2022; siliconchip. au/Article/15276) was only possible because the PIC16F15214 offers an increase in available flash memory over the PIC12F1572 used in the original Tweezers. That allowed us to add extra features to the firmware. AVR64DD32 chips, part of their latest AVR DD series. One of the more interesting features we read about is MVIO (multi-voltage I/O), which allows some I/O pins to operate at a different voltage than the rest of the chip. We’ll get to the AVR64DD32 a bit later. Cracking the code Microchip’s acquisition of Atmel in 2016 has meant that the popular AVR microcontrollers, used extensively in Arduino boards, are now also part of the Microchip stable. We reviewed the ATtiny816 in the January 2019 issue (siliconchip.au/ Article/11372). That article included details on using a PICkit 4 and MPLAB X to program an AVR chip with the tinyAVR core. In January 2021, we looked at Microchip’s AVR128DA48 microcontroller and the Curiosity Nano evaluation board (siliconchip.au/Article/14715). It was one of the first members of the new AVR Dx series. We also received samples of some One thing we like about Microchip’s recent 8-bit PIC offerings is that there is a clear path to upgrade to different members of the same family, as well as between different families, due to a high degree of pin compatibility. The most recent parts, such as those discussed in this article, have five-digit part codes after the PIC16F architecture prefix. Of this code, the first three digits indicate the family. Parts in the same family will have much the same peripheral set. The fourth digit dictates the number of pins, while the fifth digit reflects the amount of RAM and flash memory. This is summarised in Tables 1 & 2 for the PIC16F181xx family. Note that “kiB” is a unit of 1024 bytes, compared to “kB”, which might refer to 1000 bytes. While we drew up those tables from the PIC16F181xx data sheet, they seem to fit all recent 8-bit PIC parts with a five-digit suffix. For example, the PIC16F15213 has 256 bytes of RAM and 3.5kiB of flash memory. We expect the gap between 2 and 4 for the fourth digit is to accommodate 18-pin parts Table 1 – PIC16F181xx pin counts Table 2 – PIC16F181xx memory sizes AVR chips 4th digit Pin count # I/O pins 5th digit RAM Flash 1 8 6 (3) 256B 3.5kiB 2 14 12 4 512B 7kiB 4 20 18 5 1kiB 14kiB 5 28 25 6 2kiB 28kiB 7 40 36 siliconchip.com.au Australia's electronics magazine that could substitute for older devices like the PIC16F88. Compatibility From the very limited examples we have tested, some parts that share a data sheet will run the same HEX file without problems, as long as it has been compiled for the part with the least RAM and flash memory. That’s because all the critical peripheral registers are in the same locations, and all the peripherals are mapped to the same pins. There is even a degree of drop-in compatibility between parts in the same family with different pin counts. Fig.1 shows this for members of the PIC16F180xx family. These parts share the same data sheet and have a similar set of peripherals. You can see how pins 1-8 of the 8-pin part correspond exactly to pins 1-4 and 11-14 of the 14-pin part, with six extra pins corresponding to PORTC being appended as pins 5-10 in between, but physically below the existing PORTA pins. Similarly, the 20-pin parts add more PORTC and PORTB pins without interfering with the relative locations of the existing pins. What is great about the 20-pin parts is that they offer the PPS (peripheral pin select) feature for all digital pins and peripherals. That means the digital peripherals can be shuffled around very easily at the software design stage, simplifying hardware design. Some peripherals appear to change locations between parts, but that would only be a problem for analog peripherals that cannot be remapped with PPS. We noted this with some of the earlier enhanced 8-bit parts and our PIC Programming Helper from June 2021 (siliconchip.au/Article/14889). October 2022  45 Screen 1: MPLAB X can now install DFPs (device family packs) to provide device support. If a project is loaded that requires a specific DFP, you can install it by clicking on the blue link. The AVR64DD32 requires the AVR-Dx DFP, which also supports AVR DA and AVR DB series parts. It uses a 20-pin socket which can work with 8-pin and 14-pin parts due to their similar pinouts, at least in relation to the pins used for programming. This is straightforward enough for small DIP parts, which all have rows of pins spaced 0.3in (7.62mm) apart. The 20-pin SOIC parts are usually wider than the 8-pin or 14-pin parts, but a drop-in replacement could be made to work with a carefully crafted PCB pad pattern (‘footprint’) that caters for multiple widths. You might think that this is pure speculation, but the parts shortage has had us contemplate whether we could supply, for example, a 14-pin SOIC microcontroller in place of an 8-pin SOIC part from the same family. Editor: can we convert a 14-pin chip to an 8-pin chip with a Dremel? It is not that bad yet, but our new designs try to keep a few spare millimetres of space to allow that to happen if it’s needed in the future! It’s worth noting that all the recent PIC families we’ve seen have followed this trend, meaning that parts from different families come close to being drop-in substitutes too, as the power and programming pins are in the same locations. With the smaller parts having PPS on all pins, purely digital applications should have no trouble being ported between different families with nothing more than minor code changes. We must admit that the vast range of PICs available can be overwhelming, and we are pretty well spoilt for choice. However, the range narrows somewhat when you limit yourself from choosing parts currently in stock. Unlike the older MPLAB, MPLAB X can be run on Linux and Mac as well as under Windows. MPLAB X is Microchip’s IDE (integrated development environment) for programming their microcontrollers and other devices. An IDE allows programs to be written, compiled and uploaded using the same application. Version v5.40 was the first version to only support 64-bit operating systems, so if you are working on an older 32-bit computer, you can only use earlier versions of the IDE, which may not support some of the newer parts that are available. MPLAB X v5.40 also introduced the concept of DFPs (device family packs). To use the PIC16F1xxxx parts requires a DFP to be installed. That is easily and automatically done through the IDE – see Screen 1. The 8-bit parts (which includes those parts with a PIC16 prefix) also require a separately installed compiler, known as XC8, which can be downloaded from the Microchip website. We tried using a previously installed older (v2.20) compiler which gave some warnings about unknown identifiers. An upgrade to XC8 v2.40 removed those warnings. MPLAB X v6.00 and new chip support Earlier this year saw the release of MPLAB X v6.00, a major version jump from the various v5.xx versions that we’ve been using for the past few years. 46 Silicon Chip The MPLAB X IDE is the primary programming software to use with Microchip microcontrollers. Australia's electronics magazine From our experience, this combination of IDE (MPLAB X v6.00) and compiler (XC8 v2.40) will work best for the newer parts. It’s a reasonably large install, with MPLAB X taking almost 9GB and the compiler nearly 2GB of storage space on Windows. It’s possible to install different MPLAB X and compiler versions simultaneously, so you can continue to use older configurations for your other projects. XC8 v2.40 and other recent versions of the XC8 compiler will also work with supported AVR microcontrollers. These are the 8-bit parts that Microchip took over from Atmel and that Microchip continues to develop. All our tests on the AVR64DD32 were performed using MPLAB X v6.00 and XC8 v2.40. If you have not used XC8 before, user guides are available for download. There are separate user guides for PIC and AVR parts, so ensure you are referring to the correct document. New 20-pin PICs Table 3 summarises the differences between the new 20-pin parts. It isn’t a complete list of the features of these parts, but many of their other peripherals are much the same. That table is not intended to be a comprehensive list of the features of these parts, but to highlight their differences. All the PIC16F devices use a 14-bit flash program memory word. The only difference we could see between the PIC16F17146 and the PIC16F18146 is that the former has an op amp. Apart from that, they both have a very strong analog peripheral set. The Microchip product page for the PIC16F1846 notes that “It is the first product family to offer the 12-bit differential ADC with computation in low pin count packages.” The parts are recommended for raw sensor applications that require gain siliconchip.com.au In addition to the DIP-20 package, these 20-pin PICs also come in VQFN-20 and SSOP-20 packages. or filtering, assisted by the new ADC with computation. The page for the PIC16F18045 indicates that it is “for cost-sensitive sensor and real-time control applications.” All three parts have the following features: zero-cross detect (ZCD), numerically controlled oscillator (NCO), peripheral pin select (PPS) and numerous communication and PWM channels. As mentioned earlier, PPS allows digital peripheral functions to be mapped to different physical pins. Parts with more than 20 pins only offer a subset of pins with the PPS feature. Other features we have seen on many of the newer parts include the Microchip Unique Identifier (MUI). John Clarke used the MUI feature of the PIC16FLF15323 to generate a unique rolling code sequence for each transmitter in the Secure Remote Mains Switch (July-August 2022; siliconchip. com.au/Series/383). The PIC16F18045 The FVRs offer 1.024V, 2.048V or 4.096V, subject to an adequate supply voltage. One can be used by the comparator and DAC, the other as a reference or input to the ADC. While the FVR voltages may vary up to 4% from nominal, their measured values are written to the DIA (Device Information Area) at the time of manufacture. That means a running program can calibrate itself by reading from the DIA. They can even be read from within the MPLAB X IDE or IPE, so a one-off design could use an accurate hard-coded value. The DIA sits alongside the MUI and is read-only data imprinted on individual chip dies with a laser during manufacturing. Since the comparator output is digital, it can be routed to any I/O pin or used internally to trigger interrupts. Separate rising and falling edge interrupts are available. The comparator can even be used to trigger an ADC conversion. provide the option to implement either sequential or combinatorial logic. Each CLC module has four inputs and one output and can provide various fixed logic functions. The CLC outputs can be directed to digital I/O pins or used to trigger interrupts internally. The internally-­ generated CLC output can be used as one of the inputs to other (or the same) CLCs to allow more complex logic to be created. The intent is to avoid needing an extra external logic chip to achieve a specific function. ADC advances This ADC on the PIC16F18015 and PIC16F18045 is referred to as an ‘ADCC’ or analog to digital converter with computation. The computation feature means that the hardware can do things like averaging or low-pass filtering and perform comparisons to trigger interrupts. The ADCC also has hardware support for capacitive divider applications. A typical application for that is capacitive touch sensing. We experimented with this in the ATtiny816 Breakout Board using a standard ADC peripheral. While the PIC16F18045 clearly has fewer features than the PIC16F17146 CLC modules and PIC16F18146, it is still better-­ The four CLC (Configurable Logic endowed than members of the Cell) modules in the PIC16F18045 PIC16F152xx family, the 8-pin members of which were the subject of our Table 3 – a comparison of the 20-pin PICs we tested last microcontroller review. PIC16F18045 PIC16F18146 Since the PIC16F18015 and Flash memory 14kiB 28kiB PIC16F18045 share the same data sheet, much of the following applies CPU Speed 8 MIPS 8 MIPS to the PIC16F18015 as well. The data EEPROM 128 bytes 256 bytes sheet notes that their complement of peripherals is much the same, CCP channels 2 1 although fewer pins are available on PWM channels 3 × 10-bit 2 × 16-bit the PIC16F18015 to use them simul8-bit timers 3 2 taneously. The PIC16F18045 (or PIC16F18015) ADCs 1 × 17 channel 1 × 17 channel includes a complementary waveform ADC resolution 10 bits 12 bits (differential) generator and four configurable logic Comparators 1 2 cells (CLCs). There are two fixed-­ voltage references (FVRs), a comparaOp amps 0 0 tor and a zero crossing detector (ZCD), DAC 1 × 8-bit 2 × 8-bit adding to the ADC amongst the analog peripherals. Processor DOZE No Yes siliconchip.com.au Australia's electronics magazine PIC16F17146 28kiB 8 MIPS 256 bytes 1 2 × 16-bit 2 1 × 17 channel 12 bits (differential) 2 1 2 × 8-bit Yes October 2022  47 The hardware support makes it simpler to implement touch sensing, while other features like the pre-charge control, guard ring and adjustable sampling capacitance make the sensing more robust. 12-bit differential ADC On the PIC16F18146 and PIC­ 16F17146, there is also the benefit of a 12-bit (vs 10-bit) ADC and the option to perform differential readings between two channels. Whilst doing differential readings, both channels must sit inside the range set by the negative and positive ADC references. A legacy mode makes it behave much the same as older parts, so just because there are new features doesn’t mean that setting up the ADC is more difficult. Interestingly, the two PWM peripherals on the PIC16F18146 (with two ‘slices’ each, giving a total of four channels) do not require a separate timer to be configured, simplifying configuration in straightforward cases. The CCP peripheral can also be used to provide more PWM channels. The PIC16F18146 and PIC16F17146 have the option of running the processor more slowly than the main clock. This is called ‘DOZE mode’, and the clock ratio can be set dynamically at runtime. It’s even possible to return the processor to full speed while interrupts are executing. That is handy for an application that needs to save power but also respond quickly to external events. All these parts provide other peripherals for serial communication protocols such as SPI, UART and I2C. We recommend taking a look at the data sheets (even just the contents) to get an idea of what else they provide. Practical applications We were curious about peripherals like the CLC and comparator, as we hadn’t had much experience using these types of peripherals on a microcontroller. We thought we’d put them to the test and see what we could achieve with a minimum of external components. We have designed a boost DC/DC converter using several of the chip’s peripherals along with an inductor and low-side switch in the form of an N-channel Mosfet. This configuration also requires a diode and capacitor to 48 Silicon Chip capture the energy from the inductor. We did some initial breadboard testing and succeeded in getting a circuit working with all four PICs we’re looking at, including the tiny PIC16F18015. It went so well that we have put together a demonstration board that does just that. We’ve secured some stock of the PIC16F18146, so we will base our PIC16F18146 Boost Regulator on this part. This project will be published in a later issue. AVR64DD32 As we noted earlier, we have covered several AVR parts since the Microchip takeover of Atmel, and the AVR DD family is the latest. Like the earlier ATtiny816, AVR128DA28 and AVR128DA48 parts, the AVR64DD32 uses the single-wire UPDI programming interface. UPDI stands for ‘unified program and debug interface’ and performs much the same role as ICSP (in-circuit serial programming) in PIC devices, although it is a pretty different protocol. It replaces the traditional SPI programming for AVRs that required more pins to be used. The DD family appears to focus more on low pin count applications than the DA family. For example, the DD family data sheet shows parts from 14 to 32 pins, while the DA family has 28 to 64 pins. Fig.2 is an excerpt from the AVR64DD32 data sheet and shows other members of the AVR DD family. The DB family introduced MVIO (multi-voltage I/O), allowing some of the I/O pins to operate on a separate digital voltage domain, powered from a dedicated pin. The DD family also has the MVIO feature. For the AVR64DD32, the four PORTC pins can use the MVIO feature, with a VDDIO2 pin controlling the second IO voltage. Whether MVIO is operational is set by a configuration fuse, so it cannot be changed at runtime. There are status bits that report if the VDDIO2 rail is present and can trigger interrupts when it fails. If the VDDIO2 rail is too low, the MVIO pins are set to high impedance. The VDDIO2 rail can be between 1.8V and 5.5V, the same range as the main supply rail. Like the AVR128DA, the AVR64DD32 has ample flash memory and RAM. There are also 256 bytes of EEPROM. So it appears that the DD family has many of the features of the DA and DB families, but with smaller pin counts and package sizes. CCL CCL (Configurable Custom Logic) is a similar peripheral to the PIC CLC. It is also intended to provide simple logic that can be attached to the digital peripherals and eliminate the need for an external logic chip. Rather than several fixed logic functions that can be selected (as for the PIC CLC), the CCL uses an eight-bit lookup table that takes three inputs and provides one output. It is an elegant idea and works well if you can reduce your logic to a truth table. You can also add sequential elements such as flip-flops and latches to the logic. Like the PIC CLC, signals can be passed between CCL units to create more complex logic. The AVR64DD32 also has peripherals that can provide serial communication features, as well as timers, a comparator, zero crossing detector and DAC. The ADC is a 12-bit differential type. The AVR64DD32 does not have PPS, but most digital peripherals can be switched to one alternative pin. The pin allocation is quite good, with several peripherals able to be allocated to PORTC to make use of the MVIO feature, including groups such as, for example, the four lines needed to implement an SPI interface. Software support As we saw with the AVR128DA parts, the integration of AVR parts into MPLAB X is quite good. We had no trouble creating a simple project from The AVR64DD32 is a Microchip / Atmel microcontroller with an AVR CPU core running at up to 24MHz. It is shown here in a VQFN-32 package but is also available in TQFP. Australia's electronics magazine siliconchip.com.au scratch in MPLAB X v6.00 to flash one LED on a breadboard. We encountered two minor problems with the AVR64DD32 and MPLAB X v6.00 but found solutions in online discussions. Those revealed that many people are interested in these new parts! Since the PICkit 4 cannot provide power in UPDI mode, we resorted to using the Snap programmer modified to supply 5V power from its own USB supply. We explained how to do that in the PIC Programming Helper article from June 2022 (siliconchip.au/ Article/14889). The Snap has a pull-down on the pin used for UPDI, which interferes with programming. While we could have removed a resistor from the Snap, we found that a 1kW pull-up to the supply voltage (ie, between pins 2 and 4 on the Snap) was sufficient for UPDI programming to work. Also, it appears that the button for reading from the device in the Configuration Bits window of MPLAB X does not work. The workaround is simply to use the Read Device Memory button from the main toolbar instead. The debugging feature works well. We could set breakpoints, pause program operation, view variables and view special function registers. The default configuration fuse settings mean that the processor uses an internal 4MHz oscillator when it starts up; it can be changed at runtime to 24MHz with a line of code. There are also options for using an external crystal or an internal or external 32.768kHz clock source. There is even the option of using a 48MHz clock (derived from a PLL) to feed peripherals that can use a higher clock speed than the processor (great for high-­ precision PWM). With a lot of oscillator configuration able to be done in software, there is no longer the need or risk of setting the fuses to use an external oscillator, which could prevent reprogramming – an AVR bugbear. As with our ATtiny816 project, it wasn’t necessary to change from the default configuration fuse settings, avoiding such problems. Arduino compatibility Since the Arduino ecosystem started with 8-bit AVR parts like the ATmega328, it is no surprise that a cohort continues to add support for newer Atmel parts to the Arduino IDE. The core at https://github.com/­ SpenceKonde/DxCore supports many AVR Dx parts, including the promise of adding support for the AVR DD parts such as the AVR64DD32. We haven’t had a chance to try out DxCore since support for the AVR DD is so new, but it might be another way to start working with the AVR DD and other AVR Dx parts. You can find detailed installation instructions on the Installation page of the GitHub repository (linked above). For those familiar with the process, it’s as simple as adding http://drazzy. com/package_drazzy.com_index.json to the Additional Board Manager URLs and then installing the board package via the Boards Manager. Breakout boards We made a few small breakout boards to help test these parts, mainly to simplify connections to a programmer while the parts were on a breadboard. They’re not much more than a small PCB with some headers and a handful of passive components, but they proved so handy that we’ve decided to make them available in the Silicon Chip Shop. See overleaf for information about the breakout boards and the parts you’ll need to assemble them. Summary We plan to keep the PIC16F18146 as our new 20-pin 8-bit PIC part of choice. Its core is similar to the recent PICs we have used, although the new DOZE feature could be pretty handy for low-power applications. While many recent parts support runtime flash memory writing, a separate EEPROM space (as found on all three of the 20-pin PICs described here) helps simplify development through its simpler interface and the ability to write a byte at a time. Choosing a set of peripherals to match a project design and potentially unknown future applications can be tricky, but the PIC16F18146 has a good set for just a little more cost than the less capable PIC16F18045. That said, all three chips have a rich set of features, sufficient to fully implement the digital boost regulator we used to demonstrate their capabilities. It’s handy to see this ability to drop in parts across families, especially when some parts remain in short supply. Working with AVR parts in MPLAB X is now quite simple. If you’re accustomed to working with PICs under MPLAB X and want to try AVR parts, try putting an AVR64DD32 onto one of our smaller breakout boards. We look forward to the smaller 14-pin and 20-pin members of the AVR64DD32 family becoming available. The AVR64DD32 data sheet indicates that some of these will have up to 64kiB of flash memory and 8kiB of RAM. With the AVR parts having a hardware multiplier that the PICs do not, and often much more flash memory and RAM, we can see these parts becoming useful in more complex applications or those requiring substantial calculation and computation. At the time of writing, Digi-Key (www.digikey.com.au/), Mouser (https://mouser.com/) and Microchip Direct (www.microchipdirect.com/) all have stock of at least some of the PIC16F17146 and PIC16F18xxx chips. Stock of the AVR64DD32 is due in October at Digi-Key and Mouser. SC Fig.2: this excerpt from the AVR64DD32 data sheet shows the other members of the AVR DD family, with the AVR64DD32 being the most powerful. The other members have fewer pins but still a similar number of peripherals. siliconchip.com.au Australia's electronics magazine October 2022  49 PIC and AVR Breakout Boards By Tim Blythman T he three Breakout Boards we designed are intended to plug into a breadboard while also connecting to a Snap or PICkit 4 programmer for power and programming. Two can be used with the four PIC parts we discussed in the feature article: one for SOIC parts and the other for DIP. The circuit for these two boards is identical – see Fig.3. The other is designed for the AVR64DD32 and its circuit is shown in Fig.6. The PICkit 4 cannot provide power in UPDI mode (as for newer AVR chips), so we recommend using a Snap modified to provide 5V with the AVR64DD32. PIC Breakout These PIC Breakout Boards accept SOIC (Fig.4) or DIP (Fig.5) devices up to 20 pins and are designed to provide basic programmer connections and the two passive components needed for a minimal working setup. They break out each pin of the microcontroller to an adjacent header pin. This could be a standard header below to plug into a breadboard, or a header socket above, into which you can plug jumper wires. We’ll describe the parts needed to plug into a breadboard. Many recent 8-bit PIC parts have standard pinouts on their topmost pins, shown as pins 1-4 and 17-20 in Fig.1 (page 45). So this Breakout should work for most recent 8-pin, 14-pin and 20-pin 8-bit PICs, as long as they are placed at the top of the Breakout. You could fit the DIP breakout with a 20-pin narrow IC socket to allow parts to be changed in and out. Alternatively, a narrow ZIF (zero insertion force) socket could be used, turning the Breakout Board into a handy programming jig. Assembly of the PIC Breakout During construction, refer to the appropriate overlay diagram, Fig.4 or Fig.5. Both are double-sided boards, with the SOIC version being 15.5 × 32.5mm and the DIP version being 15 × 35.5mm. If you have the SMD version, start by soldering the microcontroller in place. If it is a 20-pin part, it will be a tight fit, so keep it clear of the pads for the header pins. Apply flux and rest the chip in place, ensuring that pin 1 goes to the end near CON1. 8-pin and 14-pin parts won’t be as fussy as they are narrower but should have their pin 1 in the same location. Tack one lead and check that all the remaining pins are aligned before soldering the others. Check there are no bridges between pins or to the header pin pads; if there are, clean them up with flux, solder braid and a clean iron. Then use an appropriate solvent to remove any remaining flux. If you have the DIP version, solder the socket or IC in place. Like the SMD part, you can tack one lead and then check that the socket or IC is flat and flush before soldering the other leads. Next, solder the capacitor and resistor and trim their leads close to the PCB. To fit and align the header pins, it’s a good idea to plug them into a breadboard first. This will guarantee that the pins will align with the breadboard in the future. Place the PCB over the pins Fig.3: the 20-pin Breakout Board circuit connects the programmer header (CON1) to the chip with all pins also going to a pair of SIL headers. Figs.4 & 5: the breakout boards have been designed for breadboarding or general use (eg, plugging into a pair of SIL sockets). They accept 8, 14 and 20-pin devices with pin 1 in the same position. 50 Silicon Chip Australia's electronics magazine siliconchip.com.au and push it down flat. Tack the corner pins and adjust if necessary before soldering the remaining pins. Finally, fit the right-angled header, CON1. Connect your programmer, being sure to align the arrows that mark pin 1 on both the programmer and the Breakout’s programming header. AVR Breakout The PCB overlay for the 16 × 53.5mm AVR Breakout Board, coded 24110223, is shown in Fig.7. We’ve made it as narrow as possible to conserve breadboard space, resulting in a gap in the middle of the rows of pins. It therefore has 16 pins down each side, but they take up 20 rows on a breadboard. Since there are two main power rails and the VDDIO2 pin for the MVIO feature, there are three bypass capacitors. The jumper shunt connects the two rails, which is necessary for applications that don’t use MVIO. The 1kW resistor on this board is connected between VDD and UPDI. This is discussed in the accompanying article and is necessary if you are using a Snap programmer. Assembling the AVR Breakout The pitch of the TQFP AVR64DD32 chips is finer than SOIC parts, but still Parts List – PIC Breakout Board 1 double-sided PCB coded 24110225, 15.5 × 32.5mm (for SOIC parts) OR 1 double-sided PCB coded 24110222 15 × 35.5mm (for DIP parts) 1 8/14/20 pin PIC16F18xxx microcontroller in SOIC/DIP package 1 20-pin DIL IC socket (optional; for DIP micros) 2 10-way pin headers, 2.54mm pitch 1 5-way right-angle pin header, 2.54mm pitch (CON1) 1 100nF MKT or ceramic capacitor 1 10kW axial 1/4W resistor Parts List – AVR64DD32 Breakout board 1 double-sided PCB coded 24110223, 16 × 53.5mm 4 8-pin headers, 2.54mm pitch 1 4-way right-angle male header, 2.54mm pitch (CON1) 1 2-way header and jumper shunt, 2.54mm pitch (JP1) 3 100nF MKT or ceramic capacitors 1 1kW axial 1/4W resistor 1 AVR64DD32-I/PT 8-bit microcontroller, TQFP-32 (7×7mm) (IC1) not too difficult to solder. Apply flux and rest the part roughly in place, ensuring pin 1 is in the correct location, then tack one lead. Take care to check that all four sides are aligned before tacking another pin on an opposite corner, then soldering all the remaining leads. Remember that you can use flux, solder wicking braid and a clean iron to remove any bridges. Fit the three capacitors next and follow with the 1kW resistor if that is needed. JP1 can be installed next. You should leave the jumper shunt in place unless you plan to connect an alternative VDDIO2 supply and activate MVIO. Like the DIP PIC Breakout, you can align the header pins by pushing them into a breadboard first. Leave a gap of four rows in the middle, then push the PCB down firmly before soldering the pins. Finally, fit the four-way header (CON1) for the programmer and attach the programmer. The arrow marks pin 1 and the programmer should have a corresponding mark. MPLAB X If you haven’t used the MPLAB X IDE before, see our feature in the January 2021 issue (siliconchip.au/ Article/14707). If you need to manually install the DFP (device family pack) for the AVR64DD32 or any of the PIC parts, use the Tools → Packs SC menu item. Fig.6: The AVR64DD32 Breakout Board is similar but brings the pins out to four headers as the chip has pins on four sides. Fig.7: the four headers are arranged in two rows so they can be plugged into a breadboard. The gaps mean the board is narrow enough for a standard breadboard. siliconchip.com.au Australia's electronics magazine October 2022  51 Subscribe to SEPTEMBER 2022 ISSN 1030-2662 09 The History and Technology of 9 771030 266001 nc hro n i s e d A n a lo gC GPS f e it h lo n g b at t e ry li WiFi-Controlled P rogrammable dC load magazine Silicon Chip is one of the best DIY electronics magazines in the world. Each month is filled with a variety of projects that you can build yourself, along with features on a wide range of topics from in-depth electronics articles to general tech overviews. Published in Silicon Chip * does not include the cost of postage Display Technology; September 2022 New Zealand Australia If you have an active subscription you receive 10% OFF orders from our Online Shop (siliconchip.com.au/Shop/)* Rest of World INC GST ck w Australia’s top electronics INC GST lo -Sy VIDEO DISPLAYS $1150* NZ $1290 Length Print Combined Online 6 months $65 $75 $50 1 year $120 $140 $95 2 years $230 $265 $185 6 months $80 $90 1 year $145 $165 2 years $275 $310 6 months $100 $110 1 year $195 $215 2 years $380 $415 All prices are in Australian dollars (AUD). Combined subscriptions include both the printed magazine and online access. Try our Online Subscription – now with PDF downloads! Long battery life GPSSynchronised Analog Clock; September 2022 isoundBar with built-in woofer; August 2022 VGA PicoMite; July 2022 An online issue is perfect for those who don’t want too much clutter around the house and is the same price worldwide. Issues can be viewed online, or downloaded as a PDF. To start your subscription go to siliconchip.com.au/Shop/Subscribe Prototyping Accessories GREAT RANGE. GREAT VALUE. In-stock at your conveniently located stores nationwide. PB8815 QUICK AND EASY PROTOTYPING HP9572 MAKE YOUR BREADBOARD PROTOTYPE PERMANENT Solderless Breadboards PB8820 FROM 4 $ 6 models available. 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JUST 3995 $ HG9980 Shop at Jaycar for: • Soldering & Accessories • Components, Cables and Connectors • Magnifiers and Inspection Aids • Tools, Service Aids and Chemicals Explore our full range of prototyping accessories, in stock at over 110 stores, or 130 resellers or on our website. jaycar.com.au/prototyping 1800 022 888 Using the Buck-Boost LED Driver By Tim Blythman as a Charger or Voltage Converter The High-Power Buck/Boost LED Driver design (June 2022; siliconchip.au/ Article/15340) is a versatile module for driving large LED panels, but it can do much more. This article examines some of its other uses and applications, including charging batteries and converting between different DC voltages. T he High-Power Buck-Boost LED Driver was designed to provide a current-limited output from a voltage that might be above or below the available input voltage. That makes it ideal for driving constant-­ c urrent devices such as bright white LEDs. But it isn’t just a one-trick pony; far from it. It’s a switchmode design that can operate in both boost (increasing voltage) and buck (decreasing voltage) modes with a smooth transition blending between the two. Dedicated circuitry reduces the output voltage when the load current rises above a set threshold. The target design specification was for it to deliver at least 6.5A at the nominal 12V of the LED panels that we had procured. But the LM5118 chip that controls the Driver can operate over a much wider voltage range, as can the other main components, such as the Mosfets that perform the switching. The PCB and other components limit it to handling an input current of 10A and about 8A at the output. Since it can regulate both voltage and current over a wide range, the Driver can be used for many other purposes rather than just driving LEDs. In the same vein that a laboratory PSU is often pressed into service as a battery charger, you can also use the Driver as such. Adding a beefy mains-powered DC Applications for the Buck/Boost LED Driver ∎ Driving high-brightness LEDs/LED arrays ∎ Charging/maintaining a ‘house battery’ in a caravan or boat ∎ Making a portable charger with an internal SLA or Li-ion battery ∎ Powering 12V accessories from a 24V battery or a laptop charger ∎ Powering 24V accessories from a 12V battery ∎ Powering/charging a laptop from a 12V battery (eg, in a car) ∎ Providing a regulated 12V DC supply from a 12V battery ∎ Recharging a backup power battery from a car during a blackout ∎ As a high-current USB power source (eg, to run multiple devices at once) from a 12V battery ∎ Providing a high-current, low-voltage rail within a device that has a higher voltage rail ∎ Powering 12/24V DC equipment directly from a solar panel 54 Silicon Chip Australia's electronics magazine supply to the Driver’s input will allow that, with a few provisos, which we’ll discuss shortly. The beauty of the Driver is its wide input voltage range, meaning that many types of supply can be used. Common laptop power supplies produce around 19V and would be ideal for feeding the Driver, especially as this means a lower current demand on the supply for a ~12V output. This article will also look at options such as solar panels and other battery voltages. We will present some charts based on measurements we made to guide you in setting up the Driver for these sorts of applications. In particular, we’ll look at typical settings and what they mean across the Driver’s operating range, including efficiency. We’ve reproduced the entire Driver circuit in Fig.1 to assist you in following our reasoning and explanation. We’ll also mention a few of the subtler points that may need to be addressed along the way, such as extra parts that may need to be added. Fig.2 shows the most basic way of connecting a battery to the board for charging, with a supply at CON1 and a battery directly connected to CON2. However, we strongly suggest some of the improved alternatives discussed later. We’ve also included digital oscilloscope grabs Scope 1 to 3 to demonstrate siliconchip.com.au Fig.1: the circuit of the Buck/Boost LED Driver, reproduced to aid in how to use it. It’s based around an LM5118 buck/ boost controller chip and uses a bridge of Mosfets, schottky diodes and inductors to perform voltage conversion. the operation of the Driver in its three main modes (buck, buck/boost and boost). Soft current limiting One important point to consider when using the Driver is that it does not have a ‘brick wall’ current-limiting response. Our very early prototypes considered this option, but suffered from instability and oscillation when the current limiting was active. The final design has a softer response, leading to the sort of curves seen in Fig.3. We plotted that with the Driver’s current limit trimpot (VR2) set to three arbitrary positions across its scale, including its minimum. As mentioned in the original article, 1.8A is the minimum current limit threshold. The output voltage has been set to 14V, in the typical charging range for a 12V lead-acid battery. This setup is a good starting point for charging such batteries. This graph was produced by connecting our Arduino Load (also from the June issue; siliconchip.au/ Article/15341) to the Driver and stepping through its 16 load levels. siliconchip.com.au As described in the panel at the end of this article, we achieved higher load currents by connecting a second Load to the first. The result is a variation across what would be the operating range of the battery, with more current flowing initially upon charging a flat battery. We ran the tests used to plot Fig.3 with both 12V and 15V at the input but the results were indistinguishable. It is reassuring that the behaviour will be consistent when powered from the typical range of a 12V battery. This means that you can use a range of different power sources for charging, including another 12V battery! As shown in Fig.3, the current delivery increases as the voltage drops further below 10V. But any healthy 12V battery should have a terminal voltage of at least 10.5V at rest, and probably higher; if your battery is measuring 10V or less, you will want to do something about that before you go about charging it. For charging batteries, we suggest that the output fuse of the Driver (F2) be sized not much larger than the set current limit, to prevent damage to Fig.2: these are the most basic connections for using the Buck/Boost LED Driver to charge a battery. But they are only really suitable for when you are actively monitoring the battery. A few additions need to be made to turn it into a proper battery charger. Australia's electronics magazine October 2022  55 both the battery and Driver in case of a battery fault. Battery charge leakage Scope 1: this scope grab shows buck-only operation, delivering an 8V DC output from a 17V DC input. The blue trace is the output voltage, red the gate of Q1, green the gate of Q2 and yellow/brown Q2’s drain. In this case, only Q1 is being driven as no boost action is required. Note how Q1’s gate ‘floats’ during the off-time, but it never gets high enough (>17V) for Q1 to conduct. Q2’s drain also floats after the inductors’ magnetic fields have fully discharged. Scope 2: this is similar to Scope 1 but with a 13V DC output, close enough to the 17V input that it is now in buck/boost mode. Both gates (Q1, red and Q2, green) are now switching on, with Q2 switching on for a fraction of the time that Q1 is on. The inductor magnetic fields don’t discharge as quickly as in Scope 1, but it is still operating in ‘discontinuous mode’ as the load is relatively light. Scope 3: with the output voltage set to 20V, the unit is now operating in pure boost mode, where both Q1 and Q2 are switched on simultaneously and for the same period. As soon as they switch off, energy stored in the inductors pegs Q2’s drain voltage one schottky diode drop above the output voltage as the inductors feed energy into the output. The output filter capacitors sustain the load current between these pulses. Fig.3: these three curves demonstrate the ‘soft’ current limiting characteristics of the Buck/Boost LED Driver. They show its behaviour at three different current limit settings. The voltage drops off quickly once the current limit is exceeded, but it’s hardly a ‘brick wall’. 56 Silicon Chip Australia's electronics magazine Depending on how you configure the Driver, it may be that the charged battery (at CON2) remains connected while no power is available at the Driver input (CON1). Our tests show that such a state will not damage the Driver or the battery. Most of the circuit is isolated from the downstream battery by diodes D1 and D2. However, in this condition, there is a constant load on the battery at CON2 of around 5.6mA due to the voltage sense divider formed from the 1kW resistor, 5kW trimpot and 220W resistor. 5.6mA is consistent with 1.23V being present across the 220W resistor, which is expected when the Driver is operating normally. IC2, the current shunt monitor, has high impedance inputs when its supply is absent, so it does not present any further load. The only other possible load is via the 1kW resistor back into IC1’s FB pin (pin 8), and we did not detect any current from this in our tests. While the 5.6mA load would take a long time to discharge a large battery, it is not ideal. We have two suggested approaches to eliminate it. The simplest is to fit a suitably rated schottky diode between CON2 and the charged battery; this will naturally drop some voltage between the Driver output and battery, but you can compensate by increasing the output voltage a little. This arrangement is shown in Fig.4. Even at the minimum current setting, such a diode will typically dissipate 1W or more. So you will need to use a chunky diode. You might be tempted to use several in parallel, but it’s hard to guarantee current sharing with such an arrangement. A TO-220 schottky diode with a small heatsink would be a better solution (eg, Altronics Z0065 or Jaycar ZR1029). A better solution, if slightly more complicated, is to add a 10A automotive relay to only connect the charged battery if a suitable supply voltage is present. This is shown in Fig.5. The relay coil is connected in parallel with the Driver’s supply at CON1. Be sure to check the polarity in case the relay is the type that has an integral diode. The normally-open contact is connected between CON2’s ‘+’ terminal and the charged battery’s positive. siliconchip.com.au For the terminal numbers shown on typical automotive relays, the 85 pin should connect to the Driver’s ground and the 86 pin to the CON1’s + terminal. The common 30 pin should connect to CON2’s + terminal, with the 87 pin going to the charged battery positive. The disadvantage of the relay approach is that the power consumed by its coil will reduce overall efficiency, but possibly not as much as the schottky diode approach, depending on the coil power. Automotive relays typically have a coil power on the order of 2W, so the relay is a more attractive option at higher current levels. The diode approach is probably more efficient for lower currents, but remember that its forward voltage will make setting the correct charge voltage harder. Fig.4: a high-current schottky diode should be added to prevent the battery from being drained by the parasitic load of the Driver when the input supply is cut off. This is not necessary if you will always disconnect the battery after charging, though. Charging stages The bare Driver module is essentially stateless; what it does is based only on the prevailing conditions. Because it has voltage and current limits, it can provide float or bulk/absorption charging, but it will charge continuously as long as it has power. So unless you only want float charging, some thought is required to ensure it will not damage the battery. You can bulk charge a battery using the Driver by setting its output to the appropriate bulk charge voltage (eg, around 14-14.4V for a 12V lead-acid battery). But you need to limit the charging time somehow, as batteries can be damaged by charging at this voltage for extended periods. Check your battery’s manufacturer data for its limits. Because we think the Driver will be handy for charging batteries, we have developed a low-cost add-on board described starting on page 60 of this issue. This board’s primary job is to reduce the Driver’s output voltage after the bulk and absorption charging phases have finished so that it switches to float charging for the remainder of the time it is powered. It does this by monitoring the output current and voltages. It determines that the bulk charging stage has ended once the voltage has stopped rising and the charge current starts to drop off. The absorption phase ends (and float charging begins) once the charge current has reduced to about 10% of the siliconchip.com.au Fig.5: a relay can disconnect the battery when the input power is off instead of a schottky diode. This is more efficient at higher charging currents, although it is more costly and involves extra wiring. It also limits the input voltage range. current at the end of the bulk stage. It also includes a timer to terminate absorption if it takes too long. As it can draw a little power from the battery, this timer is not reset if the input power is briefly lost (eg, if the vehicle engine/alternator is switched off, then restarted). This add-on board only has a couple dozen components, fits right on top of the Driver and provides a convenient charge display, plus some extra adjustments. We strongly recommend using it if you want to use the Driver for unattended fast battery charging. See that article for more details on how it works, how to build it and the adjustments and indications it provides. Charging setup If you’re using the add-on board mentioned above, see that article for instructions on setting it up as a charger. Otherwise, the rest of this section applies. To set up the Driver for battery charging, set the voltage to the required charge voltage of the battery; around 13-13.8V is typical for float charging a standard lead-acid type battery, or 14-14.6V for bulk charging. The current limit you choose may depend on your battery (especially for a smaller type), power source and Australia's electronics magazine wiring. In any case, remember that the actual current delivered may vary slightly, especially if the battery is flat and the Driver is providing a much lower than nominal voltage. Allow 10% to 20% extra current when charging a flat battery. One way to handle this is to set the current while the battery is close to flat. Also remember to change fuse F2 to have a trip current just above this setpoint. The next nominal value just above the maximum charging rate (when flat) is a good starting point. This will help avoid runaway conditions if the battery is excessively discharged. Remember to add a diode or relay as described earlier if you don’t want the battery to self-discharge back through the Driver. Efficiency The Driver itself is a source of some inefficiency. The data sheet for the LM5118 (IC1 in Fig.1) has a graph that shows efficiencies between 80% and 95%, varying with input current and voltage. With a 12V supply and 14V output setpoint, we measured a no-load supply current of about 35mA. At 1.8A, this amounts to about 2% of the supply power being dissipated, limiting maximum efficiency to 98%. October 2022  57 Aside from this quiescent current, the main offenders regarding losses are the diodes and inductors; in practice, these are the components that heat up the most during operation. We ran some simple load tests to determine the overall efficiency for some likely configurations. The first test used a 12V input and 12V output, followed by a 24V input and 12V output and a 12V input feeding a 24V output. The results are shown in Fig.6. These cover the most common operating regimes of the Driver: with the input and output voltages similar (hybrid mode), with the input much higher than output (buck mode) and the input lower than output (boost mode). What isn’t obvious from the graphs is that the quiescent current is lower for higher input voltages and higher for higher output voltages. The highest we saw was 47mA at 12V for a 24V output (564mW), compared to 34mA at 12V for 12V output (408mW) and 12mA with a 24V input for a 12V output (288mW). As is typical, the Driver is more efficient when reducing the voltage. Unsurprisingly, the hybrid mode that occurs when the input and output voltages are similar has an efficiency between that of the buck and boost modes. Our measurements show that the efficiency ranges quoted in the data sheet are correct, at least for meaningful current outputs. The buck mode doesn’t suffer from the drop in efficiency at higher currents of the other modes, so having a higher input voltage is beneficial. Solar power You might think that the Driver’s wide input range would be well We used a laptop power supply like this Jaycar MP3346 for our tests. The Driver adds a fully adjustable voltage output with current limiting. The Driver can also run from power sources like batteries and car accessory sockets, to name a few. suited to taking power from a solar panel. For example, a nominally 12V solar panel can vary up to 22V under no-load conditions and will typically have its maximum power point (MPP) at around 17V. It might even deliver less than 12V under low-light or heavy load conditions. We did a few brief tests to test this theory using a 40W solar panel charging a 12V battery with a 1.8A current limit. The basic outcome is that it will work, but it is probably not the best way to do it. It certainly won’t work as well as a good MPPT solar charge regulator. All solar panels vary their output voltage depending on load, and the first thing we found was that the Driver would rapidly oscillate as it would switch on and draw current, causing the solar panel voltage to drop. This triggered the UVLO (under-­ voltage lockout), decreasing the load and causing the solar panel voltage to rise, repeating the cycle. Overcoming this was straightforward; we simply connected a 1000μF electrolytic capacitor across the input at the Driver’s CON1. If doing this, Fig.6: efficiency plots for three different common voltage conversion scenarios. The Driver is most efficient when the output voltage is below the input voltage and least efficient when the output voltage is higher. However, it’s above 80% efficient in virtually all cases. ensure that such a capacitor is rated to handle the open-circuit solar panel voltage, which might be near double nominal voltage. We also tried a 4700μF capacitor. It worked well too, and larger values should also. But this is not the main limitation. Since the Driver primarily strives to deliver the target voltage, it does not fare well under lower light conditions. Any time the outgoing power demand exceeds the available incoming power (minus losses), the input voltage sags, the UVLO activates and no power is delivered to the battery. This is in contrast to a purposely-­ designed solar charge regulator, which modulates its output to provide at least some current based on the power available. In practice, using the Driver this way worked well in full sunlight, but as soon as some cloud cover appeared, the output current dropped to nothing, with brief bursts of activity as the capacitor charged up. Low-light conditions (such as first thing in the morning) will typically be when the demand for charging current is the highest, so there is a definite mismatch in needs against capabilities. On the other hand, if you want to use the Driver to directly power equipment from a solar panel, this behaviour is probably preferred. The device will operate at its rated voltage and current, or not at all. Charging a battery from a solar panel Fig.7: the pinout for a Type-A USB socket. 58 Silicon Chip Australia's electronics magazine siliconchip.com.au via the Driver will definitely need a diode between CON2 and the battery (as described earlier), as a solar panel will spend most of its time (overnight, at least) not providing any charge at all. A relay will not work in this situation as there will be long periods when the solar voltage will be high enough to trigger (or at least hold in) the relay while not having enough power to allow charging. So, in brief, the Driver can work as a solar charge regulator in a pinch, but it won’t be very good at it. That is not surprising, as it wasn’t designed with that in mind. As a USB 5V power source While not envisaged in the original design, the Driver could deliver a regulated 5V for powering USB devices with a minor change. The default divider chain gives a nominal output voltage range of 7V to 34V. To achieve lower output voltages, the 1kW resistor at the top of the divider chain (in green at lower right in the schematic, Fig.1, and in Figs.2, 4 & 5) can be replaced with a 0W jumper. We have not tested this configuration, but expect it will be a stable modification as it does not unduly change the impedance seen by the FB pin. Also note that this will reduce the maximum output voltage to around 29V. You would then need to wire up the Driver’s output to one or more USB sockets (probably several if you intend to pull multiple amps). The pinout of a Type-A socket is shown in Fig.7; the D+ and D- pins can be left disconnected. Test it with something you don’t care about first (such as an old USB drive), as reversed polarity could easily damage a device. Final notes In the original Driver article, we mentioned that it makes sense to change the UVLO divider if you are using a 24V battery to the values mentioned. This is to shut off the Driver if the battery gets too flat. If you want another threshold, keep the lower resistor around 10kW and modify the upper resistor to put 1.23V at the divider at the threshold voltage. Also remember that JP1 is available to control the Driver too. So far, we haven’t had any of our prototypes fail, so we’re happy that it’s a robust design. But the oscillating behaviour we have seen when the siliconchip.com.au Modifying the Arduino Programmable Load to monitor external loads The Arduino Programmable Load project from June was invaluable in developing and testing the Driver. We also used it extensively to collect the data presented in this article. But you might note that we were testing with currents and voltages much higher than a single Arduino Load can handle. The higher-voltage tests (up to 24V) were made possible by connecting a 70W LED panel in series between the Driver’s output and the Load’s input, to drop around 12V at up to 6A safely. We found that this worked well, with both the LED panels and Arduino Load operating within their respective limits. But handling higher currents was a bit trickier. We made a very simple modification to the Arduino Load that allowed us to connect further loads downstream of the 47W resistors built into the Arduino Load. This change allows the current sunk by the external load to be measured and reported by the Arduino Load. Some of our tests used the LED panels, but we also used a second Load downstream of the first. This allowed us to test the Driver at much higher currents than the Arduino Load could otherwise handle. Of course, we made sure the wiring used could handle the necessary currents. A downstream load can simply connect between the VPS and GND rails, meaning that current from a power source connected to CON1 flows through the 15mW shunt and through the secondary load via the VPS rail to GND. Since it passes through the shunt, any current it sinks is also measured by the Load. To do this, we simply soldered a set of screw terminals to the PCB using component lead off-cuts. Refer to our photos and diagram to see the change. Note the terminal polarity; the negative terminals are the two that are closest together. Keep in mind that the Arduino Load still has a 6.67A measuring limit, and the screw terminals themselves should not carry more than 10A. This modification also means that the Arduino Load can be used as a load monitor if none of the 47W loads are active. The output of the serial terminal will sim- By adding another two-way terminal to the Arduino Load, as ply be the prevailing current due to any shown here, you can connect two downstream loads and the voltage level in parallel to handle double the as measured at CON1. current. It’s also possible to connect We have also revised the Arduino Load a high-power LED array in series PCB with provision for this extra terminal, with the load to increase its voltagehandling capability. available in our Online Shop. supply voltage is near the UVLO voltage might not be good for connected devices. So if your setup does have the possibility of operating near the UVLO voltage, make sure that the supply wiring has low resistance and check that connected devices will be unaffected by UVLO dropouts. Conclusion The Driver’s wide input range allows it to be a versatile battery charger, especially if you build the Charge Controller add-on board described on the next page of this issue. It is not the best choice as a solar charge controller, but it might come in handy if a regulator is needed to Australia's electronics magazine power some equipment directly from a solar panel. It’s particularly suited to working and converting between different voltages and is most efficient when stepping the voltage down. However, it can seamlessly work with widely varying input voltages. As the Driver is more efficient when the input voltage is higher than the output, common laptop power supplies that deliver 19V are a good choice for powering a 12V system via the Driver. If you want to power the Driver from a vehicle supply, see the DC Filter article in the November 2022 issue, which will protect the Driver from the damaging voltage spikes that are common in automotive supplies. SC October 2022  59 Multi-Stage By Tim Blythman Buck-Boost Battery Charger This simple, low-cost add-on turns our Buck-Boost Driver into a fully-featured multi-stage battery charger. It can be used with multiple battery chemistries but is especially useful for lead-acid types. Its features include adjustable absorption and float charge voltages, temperature compensation, a long-term ‘storage’ mode, charge status display and low quiescent current. W hen we presented the BuckBoost LED Driver project (June 2022; siliconchip.au/ Article/15340), we explained that you could also use it to charge batteries from a wide range of DC input voltages. However, in its original form, it only acted as a single-stage battery charger. For proper charging, especially with lead-acid batteries, you want a multi-stage charger and that’s what this simple add-on provides. One beneficial side-effect of its wide input voltage range is that you can use low-cost, high-power laptop chargers (typically delivering around 19V) as the power source. In the article starting on page 54 of this issue, we have quite a bit more information on how This Charger module (shown at actual size) is built from our Buck-Boost LED Driver and a new addon board. This combination turns it into a multistage charger, suitable for lead-acid batteries. 60 Silicon Chip Australia's electronics magazine to use the original Buck/Boost board by itself to charge batteries. But we expect anyone serious about using it in that way to build the add-on described here since it makes it so much more versatile and useful. The Charger Adaptor We call this add-on board the Charger Adaptor (Adaptor for short). Combined with the Buck/Boost Driver, we have a complete battery charging system. With the Adaptor, it can now perform bulk, absorption, float and storage charging. It does this while retaining the original Driver’s wide input voltage range, high efficiency and high current delivery. The Adaptor has a compact OLED screen to report the Charger’s current activity and monitor the battery and power supply status. Along with this screen, three buttons allow the Charger to be configured. The Charger has been conceived mainly for use with 12V and 24V lead-acid type batteries and their various equivalents and substitutes, such as AGM and even lithium types. But, with so many of the Driver and Adaptor parameters being adjustable, it could also be used with other battery types. That’s especially true of the LiFePO4 batteries that are designed to mimic lead-acid types. You can use the original Driver design if all you need is a float charger. siliconchip.com.au You would simply set its output voltage to the float voltage for the battery. For many 12V batteries, such as leadacid types, this is typically around 13.5-13.8V. The current limit can then be set at an appropriate level for the particular arrangement of battery, supply and wiring used. The Driver’s current limiting means that even if a deeply discharged battery is connected, it can be safely charged up to its float level without damaging the battery, overloading the supply or damaging the wiring. But float charging alone will not make the best use of a battery’s capacity, nor is it the quickest way to charge. Bulk charging applies a higher current (and higher voltage) to the battery to quickly raise the battery’s charge to near 80% of its capacity. Absorption charging follows. This involves applying a voltage above the float voltage to bring the battery up to around 95% of its capacity. After these stages, it will revert to float charging to maintain the charge level near its maximum. To enable bulk and absorption charging, we need to be able to increase the Driver’s output voltage. We should also monitor the battery current and voltage to know the battery condition. Ideally, a battery charger can monitor the battery temperature and adjust its output voltage to provide the optimum voltage levels for a given temperature. Cell voltages vary with temperature, so if you use a fixed charging voltage under varying ambient conditions, you can end up under-charging or over-charging the battery. The Charger solves this by monitoring the battery temperature with an NTC thermistor and calculating the appropriate charge voltage based on a user-specified temperature coefficient. The Charger is highly configurable. The default settings are functional, if not optimal, for 12V lead-acid type batteries, providing the current limit setting is appropriate. Note, though, that it is possible to program settings that may cause damage if you aren’t familiar with how multi-stage battery chargers work. And because the current limit on the Driver cannot be set any lower than around 1.8A, it is not practical to use with small batteries that cannot handle this rate of charge. Sealed lead-acid types of around 7Ah (such as the type commonly sold siliconchip.com.au The complete Charger assembly is a compact stack of modules. It’s intended to be fitted inside a cabinet, but the front acrylic cover panel could also be used as a mounting bezel to allow the display to be seen from outside, or it can be used as a standalone assembly. Features & Specifications ∎ Input: 11.3V to 35V DC at up to 10A ∎ Output: from 7V to 34V DC ∎ Charge current: up to 8A (extra heatsinking may be needed over 5A) ∎ Suitable for most 12V and 24V batteries ∎ Can perform bulk, absorption, float and storage charging ∎ Charging currents, voltages and times can be adjusted ∎ Compact OLED display for configuration and complete battery status ∎ Onboard pushbuttons for configuration and setting ∎ Battery voltage temperature compensation ∎ 10mA typical quiescent current, down to 1mA with power supply off as NBN backup batteries) are about the smallest we suggest charging with this device. These typically specify a maximum charge current of around 2A. The default bulk charge values (such as time and start voltage) also assume a battery no smaller than that. Charger Adaptor details The Charger Adaptor connects to the Buck/Boost LED Driver at four of its existing test points. While we didn’t originally envision this use, they’re the perfect place to interface another circuit. Fig.1 shows the circuit of the Adaptor and how it connects to the Driver. The Adaptor is based around IC3, a PIC16F1459 microcontroller. Australia's electronics magazine We’ve numbered the various components across the two boards as though they are one circuit, so there should be no confusion about which part is being discussed. Output terminal CON2 on the Driver board connects (by high-current wiring) to CON3 on the Adaptor, with the battery connected to the Adaptor’s CON4. This is so we can insert high-current schottky diode D6 in the charging path to prevent the battery from discharging into the Driver when the power supply is off. It also allows us to monitor the charger output voltage and battery voltage independently. The Driver’s CON1 input terminals October 2022  61 Fig.1: there isn’t much to the Adaptor circuit as it is mostly just components to connect the added microcontroller, IC3, to various points on the Driver board for monitoring and control. The microcontroller modifies the Driver’s output voltage by biasing its feedback pin via TP7. You can find the matching Driver circuit diagram on page 55. are used as the incoming supply connection, just as in any other Driver application. The four test points we connect to on the Buck/Boost board TP2, TP3, TP5 and TP7; they are numbered identically on both boards and connect directly through low-current pin headers. The input supply of the Buck/ Boost board is available at TP2, and this feeds into a 100kW/10kW divider to ground, allowing the analog-to-­ digital (ADC) peripheral of IC3 (via analog input AN6, pin 14) to monitor the input voltage. A similar divider monitors the output voltage at CON3 connected to the Driver output, while a 1MW/100kW divider is used to sense the battery voltage at CON4. 62 Silicon Chip The relatively high value of those two resistors reduces the current drawn from the battery while charging power is unavailable. A 10kW NTC (negative temperature coefficient) thermistor is connected across CON5, forming the top half of a voltage divider with a 10kW fixed resistor. The thermistor is placed in contact with the battery under charge to allow its temperature to be monitored. TP5 is connected to a similar 33kW/10kW divider so the micro can monitor the charging current. All five dividers include 100nF capacitors across their lower resistors to reduce noise and provide a low input impedance to the ADC. They connect to pins 7, 9, 12, 13 & 14 of IC3. With a 3.3V rail and reference, and Australia's electronics magazine 10:1 dividers, IC3 can measure voltages up to 36.3V with a resolution of around 0.03V. Current measurement is limited by the voltage output by the Driver and can thus be measured up to the full capacity of the Driver. The remaining connection from the Adaptor to the Driver is at TP7, which is connected to the feedback comparator inside IC1 on the Driver PCB and usually sits at 1.23V. If this rises, the Driver will decrease the output voltage. Conversely, a voltage reduction will cause the output voltage to rise. So we can modify the set output voltage by sourcing or sinking current via TP7. The pair of RCR networks attached to TP7 do just that. PWM (pulse width modulated) waveforms from pins 5 siliconchip.com.au and 8 of IC3 are smoothed by the first resistor of each pair and its associated 1μF capacitor. The second resistor in each network turns that smoothed voltage into a small control current which can raise or lower the Driver’s output voltage. The smoothing is necessary as any ripple will be translated into a corresponding ripple at the Driver’s output. The two RCR networks are used for different purposes. The network with the two 10kW resistors is used to apply the minor temperature compensation adjustments. The network with the two 4.7kW resistors can sink or source more current and thus make a larger adjustment. This is used to set the bulk and absorption voltages. With a 3.3V supply, a 37% duty cycle will result in around 1.23V and not cause any change in the Driver output. A fixed low signal or 0% duty cycle (which gives 0V at the input to the RCR network) will cause the Driver output voltage to rise about 15%. Note that the change is proportional to the output voltage because the fixed 1.23V comes from the variable divider on the Driver board (including VR1 etc). While we could have used one RCR network and PWM peripheral, the firmware is slightly simplified by keeping them separate. So microcontroller IC3 on the Adaptor board can monitor the various voltages on the Driver and adjust its output voltage to provide several different charge modes. One of the interesting quirks of the Driver design is that the actual current and voltage setpoints (as set by the trimpots on the Driver) are not known to the Adaptor board. This means that some parameters are set as proportions of other values. Monochrome I2C OLED module MOD1 is connected to pins 6 and 11 of IC3 as well as the 3.3V supply rail and ground. IC3 uses a bit-banged I2C interface to control MOD1. Tactile pushbuttons S1, S2 and S3 connect between ground and pins 2, 3 and 10 of IC3. The OLED, MOD1 and these three buttons provide the user interface for the Adaptor. supply current flows through common-­ cathode dual diode D7 and a 220W resistor to REG1, a 3.3V regulator which provides power to PIC16F1459 microcontroller IC3, which provides all the multi-stage charging functions. REG1 has been chosen for its wide input range and low quiescent current. The 220W resistor gives the regulator more headroom to operate at high input voltages by sharing some dissipation with REG1. A pair of 1μF ceramic capacitors provide input and output bypassing for REG1. D7 is fed at its second anode from the battery positive at CON4, so the Adaptor is still powered even if its primary power supply is absent. Thus, IC3 can remember the charging state even when the incoming supply is off. Microcontroller IC3 has a 100nF bypass capacitor between its 3.3V supply (pin 1) and ground (pin 20), while pin 4 (MCLR) is pulled up by a 10kW resistor to the 3.3V rail to prevent spurious resets. The usual in-circuit programming pins (1, 4, 15, 16 & 20) are brought out to optional ICSP programming header CON6, so IC3 can be programmed in-circuit if necessary. Powering the Charger For a couple of reasons, we recommend that the input voltage to the Charger via CON1 is higher than the typical battery voltage if possible. The first reason is that the Driver is more efficient when reducing the voltage in its ‘buck’ or step-down mode. The second is that the Adaptor PCB will draw power from whichever anode of D7 is at a higher voltage. If the output fuse F2 on the Driver blows and the supply is lower than the battery, the battery will slowly drain. Neither of these are critical, but we thought they would be worth mentioning so you can get the most out of the Charger. Firmware control The operation of the Adaptor and thus the Charger is controlled by microcontroller IC3. The default mode is equivalent to the float mode that is available with an unmodified Driver, as no adjustment is made to the output voltage. The three voltages (input, outage & battery), the output current and thermistor temperature are displayed on the screen. It’s assumed that the Driver output current is flowing out of CON2, into CON3 and then to the battery at CON4. Up to 10mA is actually used to power the Adaptor, but that is a small enough amount to be ignored. If you have anything else that can draw current from CON2 (or further downstream), you will have to take that into account, especially when setting the bulk charge current cutoff. Excess current drain may prevent the bulk stage from ending correctly. Single pin headers on the Driver PCB connect to the header sockets on the Adaptor PCB. The simplest way to do this is to slide the sockets onto the headers and then locate the Adaptor PCB using the mounting hardware. Adaptor power supply Power for the Adaptor is primarily taken from TP2 and TP3, which are connected to CON1 input via fuse F1 on the Driver. The Adaptor’s siliconchip.com.au Australia's electronics magazine 63 When the Adaptor detects that the supply is absent, it goes into a lower-­ power mode and blanks the OLED, reducing the current draw to around 1mA. This is necessary because the Adaptor will be running from the battery at these times. The supply could be absent for many reasons, depending on how the Charger is powered, and it is expected to be a relatively regular occurrence. The Adaptor may also display “PWR FAULT”, meaning that the supply has been detected, but there is no output from the Driver. This would typically indicate a problem with the Driver, such as a blown fuse. This situation requires attention, as the Charger will not be able to charge a battery until the Driver can provide an output. The temperature at the NTC thermistor is monitored by measuring the voltage at its divider junction and mapping that to temperature via a table. If the thermistor has an open-circuit or short-circuit fault, that is detected and displayed. If there is no fault, then the temperature compensation is applied in proportion to a coefficient set by the user. This is one of the parameters that is set as a proportion, and we’ll discuss the particulars of this during setup and testing. Multi-stage charging A typical multi-stage charger will have bulk, absorption and float modes. In bulk mode, current is supplied to the battery up to a set current limit and up to a set voltage (higher than the float voltage). When this voltage is reached and the current begins to fall off, such a charger will switch to a voltage-­limited absorption mode. The current tapers off until the Charger considers that the absorption mode is complete, after which the lower fixed float voltage is applied. The Charger works much like this, although the distinction between bulk and absorption is not that important. We call this the combined bulk/ absorption stage or just bulk for Parts List – Buck/Boost Charger Adaptor 1 assembled Buck-Boost LED Driver Module [June 2022; kit Cat SC6292] 1 double-sided PCB coded 14108221 measuring 75mm x 80mm 2 2-way barrier terminals, 8.25mm pitch (CON3, CON4) 1 lug-mount 10kW NTC thermistor on cable with two-pin 2.54mm XH plug 1 2-way JST XH 2.54mm header (CON5) 1 5-way right-angle male header (CON6; optional, for ICSP) 1 1.3-inch OLED with 4-pin I2C interface (MOD1) 1 4-way header socket (for MOD1) 4 single pin header sockets (TP2, TP3, TP5, TP7) 4 single header pins (TP2, TP3, TP5, TP7) 2 2-pin 6×3mm SMD tactile switches with black actuators (S1, S2) 1 2-pin 6×3mm SMD tactile switch with red actuator (S3) 4 5-6mm panhead M3 machine screws 4 15-16mm panhead M3 machine screws 4 10mm-long M3-tapped Nylon spacers 4 15mm-long M3-tapped Nylon spacers 1 75 × 80mm laser-cut clear acrylic cover plate [Cat SC6567] 1 8mm-long panhead M3 machine screw (for D6) 1 M3 shakeproof washer (for D6) SC6512 Kit ($40) 1 M3 hex nut (for D6) Includes everything except 2 5cm lengths of 10A wire (for CON2-CON3) the Driver Module Semiconductors 1 PIC16F1459-I/SO micro programmed with 1410822A.HEX, SOIC-20 (IC3) 1 AP7381-33V-A 3.3V linear regulator, TO-92 (REG1) 1 MBR20100CT 20A 100V dual schottky diode, TO220 (D6) 1 BAT54C dual common-cathode SMD schottky diode, SOT-23 (D7) Capacitors (all SMD M3216/1206-size multi-layer ceramic) 4 1μF 50V X7R 6 100nF 50V X7R Resistors (all SMD M3216/1206-size 1/8W 1%) 1 1MW 3 100kW 1 33kW 7 10kW 2 4.7kW 1 220W 64 Silicon Chip Australia's electronics magazine brevity. The Driver is set to supply the float voltage by default, but during the bulk/absorption stage, the Adaptor increases the output voltage by sinking a small current from TP7. The bulk/absorption stage is started when the battery voltage falls below a given setpoint. This setpoint is chosen with the assumption that, at this voltage, the battery is pretty flat and can take a substantial charge. You can also trigger the bulk/absorption stage manually. When the Driver’s current limiting dominates, this is the bulk phase. After a while, as the battery voltage rises, the current will begin to taper off, equivalent to the absorption stage. The Adaptor has a current setpoint, below which it assumes that the bulk and absorption stages have completed. Then, the float settings are reinstated and the output voltage drops. A timer also limits the maximum time in bulk/absorption stages (recommended by many battery manufacturers). There is also a ‘storage’ stage, intended for batteries that are left continuously on float charge. In storage mode, the Adaptor reduces the Driver’s output voltage below the float voltage. Periodically (once a week), it will start a bulk charge to ‘equalise’ the battery. That’s assuming there isn’t a load on the battery, which will trigger the Charger before then. This is the best strategy for getting a long life from a ‘standby’ lead-acid battery. Keeping a battery under float charge for extended periods can damage it. This state’s commencement and ending are simply controlled by timers and can also be disabled by setting the starting timer to zero. Although not as critical as bulk/absorption charging, the amount by which the voltage is decreased in storage mode is adjustable. The OLED and buttons allow various parameters to be set and configured. As you can see from the photos, holes in the Adaptor PCB give access to the current and voltage trimpots on the Driver PCB so that all settings can be changed in the assembled state. We’ll delve deeper into the configuration options after the assembly steps. The default software settings are pretty conservative and should be functional (if not optimal) for most common lead-acid battery types. They siliconchip.com.au Fig.2: the Adaptor has a mix of surface-mounting and through-hole parts and should be straightforward to assemble. If you take care to orientate IC3 correctly and don’t mix up the (unmarked) capacitors, you should have no trouble. The four test points are fitted with sockets on the underside to connect to pin headers on the Driver; see the photos for details. depend on appropriate Driver settings to work correctly. Construction The Adaptor is fairly self-contained, but won’t do anything useful without the Driver, so we’ll start by assuming that you have a Driver PCB assembled as described in the June 2022 issue (siliconchip.au/Article/15340). We can supply a complete kit for the Driver (Cat SC6292) and the Adaptor (SC6512), including the preprogrammed micro. If you haven’t assembled the Driver yet, we don’t have any changes to the original build instructions. However, you could substitute soldered wires for the barrier terminals between CON2 on the Driver and CON3 on the Adaptor. The Adaptor is built on a 75mm × 80mm double-sided PCB coded 14108221. The component locations are shown in Fig.2. Like the Driver, the Adaptor uses many surface-mounting components, so you will need flux paste, tweezers, solder-wicking braid, a fine-tipped iron, a magnifier and preferably a solder fume extractor. Fortunately, the parts are not as tightly packed as on the Driver, so the PCB assembly is straightforward. Start by soldering IC3, the PIC16F1459 microcontroller. Apply flux to the pads and rest the part on siliconchip.com.au the pads, being sure to align the pin 1 markings. Tack one pin in place and check that the pins remain aligned before soldering the rest of the pins. Use solder wick to remove any bridges and apply extra flux if needed. The SOT-23 diode, D7, is the other part with small pins, although once the pins are aligned, it’s easy to solder. Be sure to align the part with the PCB silkscreen and, like the IC, tack one lead and confirm the part is flat and square before soldering the remaining pins. Fit the M3216/1206-size ceramic capacitors next, working through each value in turn. There are two different values that you must not mix up. Follow with the various resistors. There are a few different values; they are marked with codes that indicate their values. Tactile switches S1-S3 are soldered similarly to the other surface-mounting parts. Clean the PCB of any excess flux now using an appropriate solvent. Allow the PCB to dry thoroughly before proceeding. The remaining parts are through-hole types and won’t require extra flux. REG1 is the TO-92 package regulator. Ensure its body lines up with the PCB silkscreen before soldering it. D6 is a TO-220 power diode that is mounted flat against the PCB. Bend the leads around 7mm from the body and slot them into the holes in the PCB. Secure the tab using the 8mm screw, nut and shakeproof washer, being sure The underside of the Adaptor board showing the sockets that connect to the test points. The added wire is because it is a prototype; this has been replaced by a PCB trace in the RevC version. Australia's electronics magazine October 2022  65 not to twist the leads. When you are happy with the location of the diode, solder its leads and trim them. This arrangement is suitable for a few watts of dissipation. If you plan to run the Charger above 5A, you might need to enhance the heatsinking. This could be as simple as clamping a steel or aluminium strip with a 3mm hole drilled in it between the diode and PCB. Take care that it can’t short against any other components. The four-way header for MOD1 is a female type to match the male header on the OLED. When soldering this, check that it is perpendicular to the PCB to allow the OLED to mount neatly. CON3 and CON4 can be fitted next. As noted, you could omit CON3 on the Adaptor PCB and CON2 on the Driver PCB and run heavy-duty wires directly. But we recommend keeping the barrier terminals to retain modularity. These two parts may require extra heat from the iron since they are physically larger and also sit on substantial copper areas of the PCB, so turn up the iron if possible while soldering them. CON5 is a two-way header for the thermistor. We’ve used a simple polarised header on our prototype, but we will supply JST-type headers to match the pre-wired thermistor leads in our kits. They are 2.54mm pitch headers, so they will fit the same pads. The thermistor is not polarised, so the orientation is not important. Finally, if you need to program your microcontroller (which won’t be necessary if you have bought our kit), fit a right-angled ICSP header at CON6. Programming If your microcontroller is already programmed, skip to the next section. You can use a PICkit 3, PICkit 4 or Snap programmer to program the PIC16F1459. You should set the PICkit to provide a 3.3V supply as this is what the circuit has been designed to use. Otherwise, apply 10-35V between TP2 (positive) and TP3 (negative) to power the micro via the regulator. Connect your programmer as indicated by the arrow marks and upload the 1410822A.HEX file using the MPLAB X IPE. Note that the grounds at CON3 and CON4 are not connected to the circuit ground at TP3 and the ICSP header, so you can’t use them for a programming ground connection. This arrangement prevents unexpected currents from flowing through the Adaptor’s digital ground circuit. Disconnect power before the next step. Testing Connect the thermistor and plug the OLED module into the header, then apply 10-35V DC via TP2 (positive) and TP3 (negative). The OLED screen should start after a second or so, showing a roughly correct supply voltage. The temperature reading should be sensible. If T_ERR is displayed, there may be a circuit problem, or an incorrect thermistor has been used. If the displayed supply voltage is way off (say, by more than 10%), you may have mixed component values in the dividers. Now is the time to fix any problems, before the Adaptor is let loose and connected to the Driver. Mechanical assembly This more clearly shows the connection arrangement between the Adaptor PCB and the Driver PCB. 66 Silicon Chip It’s best to temporarily detach the OLED while assembling the boards. They can be quite fragile as they are made of thin glass. To help align all the parts, start by fitting four 10mm spacers to the underside of the Driver in the extreme corners and attach them using short M3 screws. These will act as feet. Remove any other spacers under the Driver to allow the Adaptor to be fitted above. Use four 15mm machine screws to secure four 10mm tapped spacers facing up from the Driver PCB that correspond to the ‘corner’ mounting holes Australia's electronics magazine on the Adaptor. This will allow the Adaptor PCB to rest above the Driver. Now solder the four single header pins to TP2, TP3, TP5 and TP7 so they face out of the top of the Driver PCB. We’ll do these male headers first as they are much easier to install squarely. Slot the single pin sockets onto those newly soldered pins. It’s expected that they don’t push all the way down. Rest the Adaptor PCB over the screws and pins and ensure that the pins come out through the test points on the Adaptor PCB, then solder the sockets to the Adaptor PCB. If you need to separate the two PCBs, do so with care and also be sure to align the headers when reconnecting to avoid bending them. Now run two short lengths of 10A-rated wire between CON2 on the Driver PCB and CON3 on the Adaptor PCB, being sure to connect with the correct polarity according to the PCB silkscreen. You can see the colour coding in our photos. Reconnect the OLED module and thermistor and secure the Adaptor PCB with the four 15mm tapped spacers into the exposed upwards-facing threads. The acrylic cover piece is fitted after commissioning and setup. Commissioning & calibration Start by connecting your power supply to CON1, paying attention to the polarity. The OLED should spring to life and display FLOAT mode after a few seconds. To conserve power, it’s only updated about once per second unless one of the buttons is pressed. This is the main status page; you can access the remaining configuration pages by pressing S3 to cycle through. It’s a good idea to leave the main status page active as the other pages will not allow the display to blank when the supply is disconnected. Even though no battery is connected, the diode will cause a voltage to be present at CON4, where the battery voltage is measured. With no battery connected, the current should be close to zero, probably showing 0.01A due to the internal draw of the Adaptor PCB. Press and hold S1 for two seconds until the BULK/ABS mode starts. You should see the voltage increase above its FLOAT value. The BULK/ ABS mode should run for ten seconds until it detects that no current is siliconchip.com.au Table 1: Charger settings pages Title Function Notes BATTERY V Battery voltage (CON4) calibration constant SUPPLY V Supply voltage (CON1) calibration constant These pages also display the calculated voltage/current based on the calibration constant. These are best adjusted by using S1/S2 to adjust the constant while comparing the calculated value to a multimeter reading until the two match. OUTPUT V Output voltage (CON3) calibration constant OUTPUT I Driver current (from CON2 to CON3) calibration constant LOW V BAT Low battery voltage error threshold LOW V SUP Low supply voltage error threshold LOW V OUT Low output voltage error threshold 11.0V BULK START Voltage below which bulk charging is triggered These parameters determine the operation of the bulk and absorption modes. A timer also determines the maximum time that bulk charging will operate (see The current below which bulk below). charging stops 12.0V BULK BOOST The amount by which the output voltage is increased (above float voltage) in bulk mode 4% STORE DROP The amount by which the output voltage is decreased in storage mode The 4.5% value is based on a per-cell reduction from 2.3V to 2.2V. Higher values up to 10% may completely stop charging. 4.5% BULK TIME The maximum time that bulk charging runs for Assuming the bulk current limit has not been reached, bulk charging will run for this period (in hours and minutes). If bulk charging is interrupted by a low supply voltage, the remaining bulk time will slowly ramp back up to this limit until bulk charging recommences. 2:00 hours (HH:MM) STORE TIME The time for which storage charging occurs Apart from pressing S2 on the main page or a low voltage error, this timer expiring is the only condition that will end storage charging. 144:00 hours (<1 week) STORE DELAY The time between consecutive storage charges This timer is reset when float charging begins and counts down as long as no error or other state change occurs. If this is set to zero, no storage charging occurs. 0:00 hours (off) TEMP COEFF Battery voltage temperature coefficient It’s recommended that the battery float charge be modified at different temperatures. This parameter sets the change from nominal at 25°C. 0%/°C Use Edits Either load or discard the edited settings values Changes made to parameters do not affect charging until you press S1 on this screen. Pressing S2 instead discards the changes and reverts to the previous settings. Save Flash Save current setting to flash memory Pressing S1 will save the current values in use to flash memory so that they will be loaded at power-up. BULK END siliconchip.com.au Defaults Note that you will need a reasonable load (eg, a flat battery) to calibrate the current, and you should adjust for the Adaptor using around 10mA internally. If any voltage is measured below its LOW threshold, the Charger enters an alarm state and stops all bulk, absorption and storage charging. An error is displayed on the main page. Australia's electronics magazine 11.0V 11.0V 0.5A October 2022  67 Screen 1: when everything is operating normally, you should see this screen. The Adaptor is not modifying the output voltage and based on the current displayed, the battery is floating in a fully charged state. The dashes at lower right indicate that Storage mode is disabled. Screen 2: during Bulk charging, the Adaptor increases the output voltage. In this case, the Driver has current limiting active, which results in a lower output voltage than in Screen 1. The timer at lower right indicates the maximum remaining Bulk charging time. Screen 3: the output voltage is reduced below the Float voltage in Storage mode, and minimal current will flow into the battery, just enough to stop it from discharging. Either Bulk or Storage modes can be cancelled by pressing S2. flowing due to no battery being present. You can stop BULK/ABS charging anytime by pressing the S2 button on the main page; this will also end storage charging. The default temperature coefficient is zero, so you will need to change the value to test this feature. A negative value means that an increase in temperature will cause a decrease in voltage, and the change will be quite small. There are four calibration parameters that can be adjusted if necessary, although the defaults should be functional. Press S3 to cycle through the configuration pages. The first four are to set calibration constants, while the next 12 set various operating parameters. Two further pages are used to activate and save the various settings. Table 1 summarises the configuration pages. The four calibration constants are displayed alongside their calculated values. This means they can be calibrated using a multimeter to measure the actual value. The calibration constant is then adjusted until the multimeter value matches the displayed value. These constants are simple multipliers, so increasing the constant will increase the calculated value. If calibrating the current in this way, you will need to ensure there is a load on the Driver so that the proportions are meaningful. Adjust these as needed, then cycle through to the “Use Edits” page and press S1; the “Loaded” message should appear. Then press S3 once more and press S1 again to save the settings to flash memory; you should see the message “Saved”. is probably not a suitable setting for the Charger. Remember also that the current will creep higher at lower output voltages. Refer to the Driver article for details or run some tests with a deeply discharged battery to check this. You can also adjust this later. A good time will be when a flat battery is first connected to the Charger, as this is a typical maximum load condition. The other Adaptor settings will be fine for a typical lead-acid 12V battery but will need to be changed for a 24V battery. For example, change the low-voltage alarms if using a 24V battery. In general, the Low Battery, Low Output and Bulk Start voltages should be altered to suit a 24V battery by doubling them. The Wikipedia article on IUoU charging (which is the DIN designated name for this type of charging) has several suggested settings. See https://w. wiki/5SR9 Leave it to the Deutsches Institut für Normung to come up with such a catchy name for this charging scheme – Editor Table 2 also has some suggested Voltage and current settings Dial in your desired Float voltage using the voltage trimpot on the Driver. Diode D6 will drop some voltage, even at low currents, so you’ll want to tweak this later. Setting the voltage 0.3V higher is a safe starting point and can be adjusted later when a battery is connected. Adjust the current to your desired maximum using the trimpot on the Driver. Remember that the minimum is around 2A, and the maximum is around 8A, at the ¾ position of the trimpot. Anything above the ¾ position will disable current limiting and Table 2: suggested settings (check manufacturer’s recommendations) Battery Type SLA 12V AGM / Flooded lead-acid 12V LiFePO4 12V SLA 24V AGM / Flooded lead-acid 24V LiFePO4 24V Float voltage (Driver trimpot) 13.5V 13.8V 12.6V 27.0V 27.6V 25.2V LOW V BAT/ OUT 11.0V 11.0V 11.0V 22.0V 22.0V 22.0V BULK START 12.0V 12.0V 12.0V 24.0V 24.0V 24.0V BULK BOOST 4% 4% 10% 4% 4% 10% TEMP COEFF -0.17%/°C -0.14%/°C 0%/°C -0.17%/°C -0.14%/°C 0%/°C 68 Silicon Chip Australia's electronics magazine siliconchip.com.au Screen 4: you will see this screen if the power supply is off or disconnected. The output voltage is low and the displayed current is 0.00A. The counter at lower right counts down until the screen blanks; you can reactivate it by pressing any button. Screen 5: the calibration constants for the three voltages and the current value displayed on the main screen can be adjusted on these pages by simply using the S1 and S2 buttons. The newly calculated value is displayed and can be easily compared to a reading from a multimeter. Screen 6: several voltage thresholds can be set. There are three alarm thresholds and a Bulk charging start threshold. Each press of S1 or S2 changes the value by 0.1V, or you can hold the buttons to speed through the values. values for specific parameters related to the Charger. As we mentioned, we’ve picked some pretty conservative values to start with. You may need to switch to more aggressive values if your batteries will see heavy use. The storage mode is disabled by default but should be enabled for batteries that see infrequent use. The bulk/absorption time will depend on the current and battery capacity. Keep in mind that these phases can contribute up to 80-90% of the total charge delivered. This depends on the bulk/absorption start voltage; the 80% figure for bulk charging only applies to a very flat battery. The temperature coefficient does not need changing when switching between 12V and 24V batteries as it is a proportion of the charge voltage. The default value is zero, which means no correction occurs. That’s ideal for LiFePO4 batteries, but you should set it to the manufacturer’s suggested value for lead-acid batteries to ensure proper charge termination. Typical values around 0.15%/°C correspond to 3.6mV/°C per 2.4V cell, and you can also see suggested values in Table 2. In float, bulk/absorption and storage modes, a timer is shown in the bottom right-hand corner of the display. This will count down to the following timed state change, to the float state for bulk/ absorption and storage modes. In float mode, the timer counts down to storage mode if it is enabled. If storage mode is disabled, no timer will be seen on the float page. If there is a power-off error, the timer is the number of seconds until the screen blanks to save power. You can press any button to enable the screen again and reset this timer. manually trigger bulk/absorption cycles if necessary. This will allow you to tweak the Driver’s voltage setting trimpot to account for the drop across the diode. If possible, let the battery run down to permit bulk/absorption charging from a flat state. This will allow you to adjust the bulk/absorption boost percentage. Screen 7: the single current threshold is the trigger for ending Bulk charging and is adjusted on this page. This is changed with S1 and S2 in increments of 0.05A (50mA). Screen 8: none of the changes made on the preceding pages are used immediately but can be activated by pressing S1 on this screen. S2 reverts the edited values. The text on this screen will change to indicate when a button has been pressed. siliconchip.com.au Battery charging You can connect the battery now that the float charge settings have been configured. Depending on the settings, bulk charging may start. This is a good time to check that D6’s heatsinking is adequate, as bulk charging is typically the time of highest current draw. Ideally, you should let the battery charge fully. Recall that you can Australia's electronics magazine Conclusion Once the Charger has been set up, the acrylic cover piece can be placed over the spacers and secured with the last four screws. Note that there are holes in the cover piece to allow occasional access to the buttons. If you need to mount the Charger, you can either use the four tapped spacers at the rear, or the four at the front if you have a clear panel or bezel. The Driver is a versatile board that is handy for producing a wide range of voltages at handy current levels. The addition of the Adaptor PCB turns it into a versatile Battery Charger. The Charger is highly configurable and can be used to work with many different SC types of batteries. Screen 9: changes are not automatically saved to flash memory. Pressing S1 on the Save Flash screen stores the active settings to flash memory so that they will be loaded as the defaults on the next power-up. October 2022  69 Automatic Level Crossing & Semaphore Control with chuff and whistle sounds This project combines the Model Railway Level Crossing and Semaphore Signal projects with a Li’l Pulser Mk.2 train controller to automate a model railway layout. It also adds chuffing and whistle sounds to make it as realistic as possible. T he Automatic Train Controller makes your train pull up to the Semaphore Signal, triggering the Level Crossing, then proceed through the crossing when safe, all automatically and with accompanying sound effects. It made sense to integrate this with my Li’l Pulser Mk.2 Model Train Controller. All of the projects required to build the Automatic Train Controller are listed in the adjacent panel; except the Carriage Lights which are optional. To make it more realistic, I added two sound modules, one to produce steam whistle sounds and another to add engine chuff noises. You can see a video of all these devices operating in concert at siliconchip.au/Videos/ Automatic+Train+Controller 70 Silicon Chip In that video, the Signal goes up to alert the train to stop, then the train slows down and stops at the Signal. The barriers on the Level Crossing close, the bells sound and lights flash, then the Signal goes down and after a delay, the train moves off slowly. As the train approaches the Level Crossing, the whistle sounds. Once the train has passed through the crossing, it resets. A beautiful feature of the Li’l Pulser train controller is its built-in inertia, which means that the train slows down like its full-size version and moves off slowly. It does this simply by charging and discharging a capacitor. BY LES KERR Australia's electronics magazine In case you only want to make the chuff sound module and not the train controller, I have split the design up into two separate circuits and PCBs. Automatic train control The overall arrangement of the Train Controller is shown in the block diagram, Fig.1. It still allows you to operate the Level Crossing and Semaphore Signals manually by associated toggle switches. Double-pole, double-throw (DPDT) toggle switch S1 switches between automatic and manual control. In manual mode, the Li’l Pulser controller operates as usual. So that the Crossing and Signal can be utilised in each mode, we use diode OR gates on their control inputs. This means that siliconchip.com.au Fig.1: the overall arrangement of the modules in this system. Most of them are linked to the Automatic Control Module (the Chuff module is not shown here as it operates independently). The Control Module can start or stop the train by using RLY1 to change how the Li’l Pulser operates. When required, it also triggers the Steam Whistle, Semaphore Signal and Level Crossing modules. Fig.2: this timing diagram shows the sequence of events. If this is unclear, see siliconchip.au/Videos/ Automatic+Train+Controller Three of the delays are adjustable using trimpots VR1-VR3 on the Control Module. the automatic control board drives the control inputs of these modules when it is selected, while the manual switches drive them when the Automatic Controller is disabled. A reed switch under the track is used to start the automatic process. In automatic mode, a magnet on the engine closes this reed switch as the engine passes, starting the timing sequence shown in Fig.2. Timer 1 (adjustable from half a second to 10 seconds) starts, the Signal goes up and the relay on the PCB operates, closing contacts RLY1b. The closure of those contacts connects the 250kW brake potentiometer to the 47μF capacitor on the positive input of IC3b in the Li’l Pulser controller, stopping the train. At the end siliconchip.com.au of Timer 1’s period, the Signal goes down. Timer 1 is adjusted so that the Signal goes down one second after the train has stopped. Timer 3 (0.5 to 10 seconds) is adjusted for the driver’s reaction time to start the train. I set that to one second for my layout. When Timer 3 expires, the Level Crossing closes and the relay is de-energised, opening contacts RLY1b. The 47μF capacitor is now connected to the 1MW inertia pot, causing the train to move off slowly as the capacitor charges. Then there is a fixed four-second delay before a signal is sent to operate the whistle in the sound module. The train runs on through the Level Crossing and then, when the train has passed and Timer 2 expires, the Level Crossing opens. Control circuit details The circuit of the “Auto Control Module” black box from Fig.1 is shown in Fig.3. It is pretty straightforward as most of the functions are provided by the PIC16F1455 microcontroller, IC1. Projects needed to build the Automatic Train Controller Li’l Pulser Mk.2 Model Train Controller, July 2013; siliconchip.au/Series/178 Model Railway Level Crossing, July 2021; siliconchip.au/Article/14921 Model Railway Semaphore Signal, April 2022; siliconchip.au/Article/15273 Model Railway Carriage Lights, November 2021; siliconchip.au/Article/15106 Australia's electronics magazine October 2022  71 Fig.3: the Control Module is based around microcontroller IC1, which uses internal timers to generate the control signals at RA5, RC4 and RC5 when appropriate. Those timer durations are adjusted using trimpots VR1-VR3 that apply varying DC voltages to the AN4, AN6 and AN3 analog inputs. The close of the reed switch at pin 9 of IC1 (the RC1 input) starts the whole sequence. When the reed switch closes, the RC1 input (pin 9) of IC1 that is usually held low by the 10kW resistor is pulled high. This triggers the software into action. It uses three identical 0.5-to-10-second timers, adjusted using trimpots VR1-VR3. The 680W padder resistors set the minimum voltage achievable for each pot’s wiper to about 0.5V, which corresponds to half a second. Taking Timer 1 as an example, VR1 adjusts the voltage at analog input pin RC0 (AN4) of IC1. The 100nF capacitor filters out any ripple or interference, so there is a steady voltage at that pin. The microcontroller’s internal analog-­ to-digital converter (ADC) is used to turn this voltage into a number to calculate the time delay. The other two timers are similar, using VR2/RC2/ AN6 and VR3/RA4/AN3. IC1’s RC3 digital output (pin 7) is used to switch NPN transistor Q1 which controls the coil of relay RLY1. IN4004 diode D1 protects the transistor from the back-EMF generated by the coil’s inductance when the relay switches off. Contact RLY1a switches yellow LED4 while contacts RLY1b are used to change the Li’l Pulser between the brake and run modes. 72 Silicon Chip IC1’s digital outputs RA5, RC4 and RC5 are used to produce the three control signals to trigger the Semaphore Signal, Level Crossing and Whistle Sound modules, respectively. These signals are also applied to LEDs LED1LED3 via 1kW current-limiting resistors so you can see when different modules are being triggered. Output RC4 (pin 6), when high, closes the Level Crossing and switches on blue LED2. Similarly, when output RC5 goes high (pin 5), the Signal goes up and red LED1 lights. Then, when output RA5 goes high (pin 2), the whistle module is triggered and white LED3 flashes for 200ms. The only other components are the 10kW pull-up resistor at the MCLR input of IC1 (pin 4), to prevent spurious resets, and the 100nF and 100μF supply bypass capacitors, mainly for the benefit of IC1. Chuff Sound circuit details Greg Hunter’s March 2006 Circuit Notebook contribution (siliconchip. au/Article/2601) was for producing the ‘chuff’ sound of a steam locomotive. I based my design on his. The voltage supplied to the locomotive is sensed to vary the chuff rate. The higher the Australia's electronics magazine voltage, the faster the ‘chuffs’. When the locomotive is stationary (no track voltage), it produces a ‘panting’ sound that is like an engine compressor running. The resulting circuit is shown in Fig.4. It is separate from the other modules; while they are great in combination, it can also be used as a standalone device. The voltage from the rails is applied to a bridge rectifier, and the resulting DC is reduced by an adjustable resistive divider, clamped to a safe level by an LM4040 IC acting like a 5V zener diode and filtered by a 10μF electrolytic capacitor. The result is a 0-5V signal applied to the GP2 analog input (pin 5) of PIC12F675 microcontroller IC1 that, when VR4 is adjusted correctly, lets it measure what speed the train is currently moving at. VR4 is adjusted for 3.3V at its wiper when the train is running at a realistic maximum speed. Depending on the make of your controller, you might have to change the 15kW resistor value to achieve that. Note that this won’t work with a DCC system since those systems do not vary the voltage across the tracks but instead send digital signals to the locomotives. siliconchip.com.au Fig.4: the Chuff Sound Module is pleasingly simple. The voltage across the rails is rectified, filtered, reduced and then applied to the GP2 analog input of IC2 so it can sense the train speed. It produces the panting or chuff sounds at its pin 6 digital output (GP1), and these signals are fed to audio amplifier IC3 and ultimately, the speaker. Microcontroller IC2 and LM386 audio amplifier IC3 are powered from a separate 5V DC regulated supply. This 5V supply must be floating with respect to the track supply; one can be Earthed, or the other, but not both. Otherwise, the supplies will be shorted out via the bridge rectifier. A separate 5V DC regulated plugpack is a good option here. The voltage applied to the GP2 input of IC1 is converted to an 8-bit digital number (0-255) by IC1’s internal ADC. This number is proportional to the locomotive speed. A nice feature of this PIC is its internal square-wave oscillator that can be programmed to produce 127 tones and 128 notes of white noise. To simulate the hissing noise of the engine, we use a couple of the white noise outputs. The output is switched on and off depending on the ADC voltage, so we get more chuff pulses as the train accelerates. The reverse happens when the train slows down. When the train is stopped, the panting sound is generated by another white noise channel with the pulses separated by a few milliseconds. These waveforms are applied to the GP1 digital output (pin 6), which is AC-coupled to the input of IC3 via a variable attenuator. In this configuration, IC3 has a gain of 20 and can deliver up to 300mW into the 8W speaker. The 1kW potentiometer VR5 determines the output volume. I used a 57mm diameter speaker with a 100mm square white card mounted on its back to stop the siliconchip.com.au reflected sound, which resulted in just the right amount of bass to match my Peckett tank engine. Depending on what you are running, you may have to experiment to get the optimal sound for your engine. Putting the speaker in a box will increase the bass. Construction The first step is to assemble the PCB module(s). For the Li’l Pulser, Semaphore and Level Crossing modules, see the instructions in the July 2013, July 2021 and April 2022 issues respectively (links above). There was an update to the Li’l Pulser in January 2014 to stop the train lurching at switch-off. The Train Control module is built on a single-sided PCB coded 09109221 that measures 50 x 51mm. The necessary parts are in the parts list, and the component layout (overlay) is shown in Fig.5. While the PCB is a single-sided design, if you buy it from our Online Shop, we will supply a double-sided board that will save you having to fit the two wire links. Start by fitting the PCB pins, followed by the IC and relay sockets. Take care to orientate the sockets correctly. There is no onboard programming This shot shows off the semaphore signalling section of the project. Australia's electronics magazine October 2022  73 Fig.5: assemble the Control Module as shown here. It can be etched as a singlesided design, but then two wire links are needed (shown in red). They are already part of the commercially-made double-sided PCBs we supply. When building it, watch the orientations of the IC, relay, diodes, transistor and electrolytic capacitors. header, so you will need to remove the chip from the socket later if you wish to re-program it. Next, fit the resistors (mounted vertically), followed by the capacitors and trimmer potentiometers. The electrolytic capacitors are polarised (longer lead to + pad), but the ceramic capacitors are not. If you have a single-sided PCB, fit the two wire links now using resistor lead off-cuts. Next, install the diode, LEDs and transistor. They all need to go in the right way round; check Fig.5 if you are unsure. Then plug in the relay, orientated as shown. Don’t plug in the PIC microprocessor yet. If you have purchased this from the Silicon Chip Online Shop, it will already have the firmware loaded. If you have a blank micro and need to program it yourself, you can download the HEX file from the Silicon Chip website. You will need a PICkit 4, Snap programmer or similar to load the file along with a socket adaptor for the PIC16F1455. mid positions. Switch the power on and momentarily connect a wire link between the reed switch terminals, SW and SW+. Upon doing that, the red and yellow LEDs should light. About five seconds later, the red LED should go out. After a further five or so seconds, the yellow LED should extinguish and the blue LED should light. Four seconds later, the white LED should switch on for 200ms and in a further five or so seconds, the blue LED should go out. If that all went well, power it off and give the bottom of the PCB a coat of clear varnish to protect it from corrosion. Whistle Sound module My initial plan was to add the Whistle Sound to the Chuff generator, but it is difficult to produce a whistle sound electronically that covers the full range of possible locomotives. PCB testing First, inspect the board for dry solder joints and check that the diode, capacitors and sockets are inserted correctly. Connect the PCB to a 5V DC power supply, switch it on and connect the negative lead of a voltmeter to pin 14 of IC1’s socket. Probe pin 1 of that socket with the positive lead and the meter should read close to +5V. If it doesn’t, check the power supply and socket polarity. Switch off power and plug in IC1, checking that it is correctly orientated, then adjust the three trimpots to their 74 Silicon Chip The ISD1820-based module we supply is slightly different in appearance from the version Jaycar sells. However, the required connections are the same. Australia's electronics magazine Instead, I decided to use the simple ISD1820-based sound recording and playback module. This means that you can record a suitable locomotive whistle sound from the internet. Another advantage of this approach is that the chuff sound and the whistle sound are present simultaneously. The first step in setting this up is to record the whistle sound onto the module. Connect the 76mm 8W loudspeaker (SPK1) to the green terminal block marked “speaker”, then wire a 5V DC supply between the terminals marked VCC and GND on the module. Looking at the component side of the module with the green terminal block on the left, ensure that the two slide switches marked FT and repeat are to the left-hand side (both open). For the jumper-based version pictured below, the jumper positions shown highlighted in red should be suitable. Next, find the whistle sound file you need via an internet search. Hold the module so that the electret microphone is about 100mm from the computer’s loudspeaker and set the sound to maximum volume. Hold down the REC button on the module, then hit play on the computer. Continue holding down the record button until LED1 goes out (the maximum recording time is around 10 seconds). Now momentarily press the PLAYE button. You now should hear the recording of the whistle. If it sounds distorted, try turning the computer playback volume down and re-record it. Chuff sound PCB assembly The Chuff circuit is built on a 59 × 30mm single-sided PCB coded 09109222. Refer to its overlay diagram, Fig.6, during assembly. As mentioned earlier, it could be used independently, not just as part of the automatic system. Start assembly by fitting the PCB pins and the IC sockets, ensuring the latter are orientated correctly. Like the Control board, there is no provision for onboard programming of the microcontroller. Now add the resistors, mounted vertically, followed by the capacitors; the electrolytics are polarised (the longer lead goes to the + pad), but the others aren’t. Follow with the two trimmer potentiometers but don’t get the two different values mixed up. If using a single-sided board, you can fit the wire link now (which can be siliconchip.com.au Fig.6: assembly of the Chuff Sound Module is similar to the Control Module, just simpler as there are fewer parts. The parts where polarity is critical are the diodes, ICs and electrolytic capacitors. The LM4040 is ideal, but a 4.7V zener diode can be used instead, with the cathode (striped) end to the middle pad and the other lead to the bottom-most pad. made from a component lead off-cut); it isn’t needed for the double-sided version. Solder in the diodes next; they need to be the right way around. If using a 4.7V zener diode rather than the LM4040, solder its cathode (striped) end lead to the centre pad of the TO-92 footprint, and the other (anode) lead to the LM4040 pad closest to the edge of the board. Otherwise, if using the LM4040, mount it as shown in Fig.6. Temporarily connect the positive of the 5V power pack to the +5V PCB pin, and the negative to 0V. Also wire in the loudspeaker as shown. At this stage, don’t plug in the audio amplifier (IC3) or the PIC microprocessor (IC2). If you have purchased the microprocessor from the Silicon Chip Online Shop, it will already have the firmware loaded. If you have a blank chip and need to do this yourself, you can download the HEX file from the Silicon Chip website. Use a PICkit 3, PICkit 4, Snap programmer or similar to load the HEX file into the chip via a socket adaptor. You can use the free Microchip MPLAB IPE software. Testing the Chuff module First, inspect the board for dry solder joints and check that the diodes, capacitors and sockets are inserted correctly. Switch on the power supply and connect the negative lead of a voltmeter to pin 8 of IC2’s socket, with the positive lead to pin 1. The meter should read close to +5V. If it doesn’t, you have likely wired the power supply the wrong way round or the socket is reversed. Assuming it’s OK, switch off the power and insert the two ICs, checking that they are correctly orientated and not swapped. Adjust both potentiometers to the mid position. Switch the power on and you should Silicon Chip as PDFs on USB ¯ A treasure trove of Silicon Chip magazines on a 32GB custom-made USB. ¯ Each USB is filled with a set of issues as PDFs – fully searchable and with a separate index – you just need a PDF viewer. ¯ 10% off your order (not including postage cost) if you are currently subscribed to the magazine. ¯ Receive an extra discount If you already own digital copies of the magazine (in the block you are ordering). The USB also comes with its own case EACH BLOCK OF ISSUES COSTS $100 OR PAY $500 FOR ALL SIX (+POSTAGE) NOVEMBER 1987 – DECEMBER 1994 JANUARY 1995 – DECEMBER 1999 JANUARY 2000 – DECEMBER 2004 JANUARY 2005 – DECEMBER 2009 JANUARY 2010 – DECEMBER 2014 JANUARY 2015 – DECEMBER 2019 WWW.SILICONCHIP.COM.AU/SHOP/DIGITAL_PDFS Ordering the USB also provides you with download access for the relevant PDFs, once your order has been processed siliconchip.com.au Australia's electronics magazine October 2022  75 Fig.7: once you’ve built all the modules, wire them up as shown here. The manual switches can still be used to control the Semaphore and Level Crossing if S1 is in the manual position. The Chuff Module wiring is shown separately, in Fig.6. Note that you will need to cut a track on the Li’l Pulser Mk2 PCB before adding the four wires that go to S1 and the Control Module. hear a ‘panting’ sound coming from the speaker. Adjust VR5 so that the sound is at a comfortable level. Connect a 12V variable supply to the track inputs and slowly wind up the supply. The speaker should now emit a chuffing sound with the frequency increasing as the voltage rises. Finally, give the bottom of the PCB a coat of clear varnish to protect it from corrosion. Wiring it up We need to determine where to place the reed switch in relation to the Signal. To do this, we first have the train running at a realistic speed in the normal mode and apply the brake. Measure its stopping distance and place the reed switch under and perpendicular to the rails at that distance before the Signal. I set the reed switch in a groove so that its cylindrical top was level with the bottom of the rail. You may have to experiment with this, depending on the type of engine you have and where you place the magnet within it. Be careful not to place the magnet in direct contact with the reed switch, as this can demagnetise it, causing it to fail. I built the Li’l Pulser Mk2 Train Controller in a larger enclosure than specified, Jaycar HB6128 ABS, measuring 171 × 121 × 56mm. This was so that I would have more room to mount the Automatic Control PCB, its corresponding on/off switch, the manual whistle push button, the manual signal toggle switch and the manual crossing toggle switch. If you have already built the Li’l Pulser into the smaller specified case, you will need another box to house these components. Either way, once you’ve mounted all those components in the box, it’s just a matter of wiring it up as per the wiring diagram, Fig.7. The only tricky part is interfacing with the Li’l Pulser Train Controller. To do this, you must cut the connection between the middle contact of switch S1 and the 47μF capacitor and attach flying leads to the brake side of S1, the run side of S1, the central contact of S1 and the positive terminal of the 47μF capacitor. Getting it all going The Chuff Sound module is simple enough to breadboard, otherwise you can purchase a double-sided PCB from our Online Shop. Before applying power to the finished system, check the wiring to the modules. Attach the small magnet to the front of the locomotive, ideally on the underside near the front. Also Australia's electronics magazine siliconchip.com.au 76 Silicon Chip Parts List – Automatic Train Controller with Whistle Sounds 1 assembled Li’l Pulser Model Train Controller, Mk2 (July13, Jan14) 1 assembled Steam Train Whistle module (Sept18) 1 assembled Level Crossing (July21) 1 assembled Semaphore Signal (Apr22) 1 assembled Chuff Sound module (see below) 1 ISD1820-based sound recording & playback module (MOD1) [Jaycar XC4605, SC5081] 1 single-sided or double-sided PCB coded 09109221, 50 × 51mm 1 5V DC 500mA supply 3 5kW mini single-turn top-adjust trimpots (VR1-VR3) 1 16-pin DIL IC socket (for RLY1) 1 14-pin DIL IC socket (for IC1) 1 DPDT toggle switch (S1) [Jaycar ST0355] 1 SPST momentary pushbutton (S2) [Jaycar SP0711] 1 76mm 8W loudspeaker (SPK1) [Jaycar AS3006] 1 TE Connectivity V23105A5001A201 5V DC coil DPDT 3A relay or equivalent (RLY1) [element14 1652604, Digi-Key PB383-ND] 1 Comus RI80SMDM-0510-G1 miniature SPST reed switch [Digi-Key 1835-1161-1-ND] 1 small rare earth magnet [Jaycar LM1622] 11 1mm PCB pins various lengths of light-duty hookup wire Semiconductors 1 PIC16F1455-I/P microcontroller programmed with 0910922A.HEX, DIP-14 (IC1) 1 BC547 45V 100mA NPN transistor, TO-92 (Q1) 1 5mm red LED (LED1) 1 5mm blue LED (LED2) 1 5mm white LED (LED3) 1 5mm yellow LED (LED4) 1 1N4004 400V 1A diode (D1) 6 1N4148 75V 200mA signal diodes (D2-D7) Capacitors 1 100μF 16V radial electrolytic 8 100nF 50V radial multi-layer ceramic or MKT check that the train rails and wheels are clean before proceeding. Switch the Auto on/off switch to off (ie, manual control). Increase the train’s speed to that previously used to determine where to place the reed switch. Now change the switch back to on (ie, automatic control) and adjust potentiometer VR1 on the Automatic Controller PCB so that the Signal goes green close to one second after the train has stopped. Next, adjust VR3 to what you think the driver’s reaction time should be to start the train once the Signal goes green. I set this to one second. Once the Semaphore goes off, the train should start to move away and the Level Crossing should close, flashing its LEDs siliconchip.com.au Resistors (all 1/4W 1% axial) 2 10kW 1 4.7kW 1 1.5kW 4 1kW 3 680W Chuff Sound module 1 single-sided or double-sided PCB coded 09109222, 59 × 30mm 1 5V DC regulated plugpack or other 5V floating supply (cannot be shared with the Train Controller module) 2 8-pin DIL IC sockets (optional; for IC2 & IC3) 1 10kW mini single-turn top-adjust trimpot (VR4) 1 1kW mini single-turn top-adjust trimpot (VR5) 1 SPDT toggle switch (S3) [Jaycar ST0335] 1 57mm 8W 250mW loudspeaker (SPK2) [Jaycar AS3000] 6 1mm PCB pins various lengths of light-duty hookup wire Semiconductors 1 PIC12F675-I/P 8-bit microcontroller programmed with 0910922C.HEX, DIP-8 (IC2) 1 LM386N-1 audio amplifier, DIP-8 (IC3) [Jaycar ZL3386] 1 LM4040 5V shunt regulator or 1N4732 4.7V zener diode (ZD1) 4 1N4148 75V 200mA signal diodes (D8-D11) Capacitors 2 100μF 16V radial electrolytic 1 10μF 16V radial electrolytic 1 100nF 50V radial multi-layer ceramic 1 47nF 63V MKT 1 22nF 63V MKT Resistors (all 1/4W 1% axial) 1 15kW 1 10kW 1 8.2kW 1 10W and playing bell sounds. The whistle should sound four seconds after the train starts moving again. Finally, adjust VR2 so that the crossing opens once the train has passed through. Note that if this time is set too long, the train could pass the reed switch again before the crossing closes. The result is that the train won’t stop when it passes over the reed switch. Chuff Module wiring Connect the track input wires on the Chuff module to the railway tracks and wire in the on/off switch and power supply, as shown in Fig.6. Switch it on and adjust the speed controller so that the train is travelling at a maximum realistic speed (not necessarily Australia's electronics magazine the speed it runs with the controller supplying full voltage). Using a digital voltmeter, measure the voltage between the GP2 input (pin 5) of IC1 and ground, and adjust VR4 until the voltage reads 3.3V. Wind back the speed and the chuff rate should decrease until the train is stopped, at which point the sound will revert to panting. The sound level can be adjusted using potentiometer VR5. As mentioned earlier, if you can’t achieve 3.3V at pin 5 of IC1 by adjusting VR4, you’ll have to replace the 15kW resistor with a higher or lower value. You shouldn’t have to increase the value, but you might have to reduce it if you don't get 3.3V at pin 5 of IC1 even with VR4 at its maximum. SC October 2022  77 SERVICEMAN’S LOG Fixing feline follies Dave Thompson Some people spend a lot of money on their pets. The pet industry is massive, with people in the USA alone dropping approximately $110 billion on their fur babies in the last 12 months. My wife and I probably spent about that on our cats here in New Zealand. One way to save a little cash is to fix the pet-related gear rather than replace it... Those in the pet trade know owners will spend whatever it takes to keep pets safe, entertained and healthy; it seems nothing is off-limits as far as marketing goes. Now there is pet insurance, pet funerals, special diets and much more, all designed to emotionally engage owners. We are not immune because we want our cats to be ‘happy’ in their lives with us. We think they are (especially when they want food), but that doesn’t stop us from buying them treats, toys and other seemingly useless accessories. The old gag is that cats will typically ignore whatever came in the box and spend hours playing in that carton instead. It is, of course, totally accurate. Cats love boxes and will happily sit in one for hours. They also love sitting on any papers you might spread out in front of you, such as a newspaper or a circuit diagram. I can put a paper kitchen towel on the floor and, within a minute, a cat will be sitting on it. If only pet-owning life were always that simple. Over the years, we’ve purchased many funky ‘toys’ for our cats. Some are passive devices, like a plastic stick with a short string and feather arrangement attached to the end, which we wave about to get their attention (if they are interested). Lately, though, an increasing number of ‘electronic’ toys for pets are showing up at stores around the globe. The first we bought for our cats was a simple enclosed plastic track with gaps in it, with a clear plastic ball with a motion-activated flashing red high-intensity LED inside that can be ‘batted’ around by an intrigued feline. The ball sits idle until tapped, then it flashes (apparently enticingly), 78 Silicon Chip so the cat will maintain interest and swat it until it gets bored, usually in about two minutes tops. The good news is that this ‘toy’ was relatively cheap; the bad news is that once the battery in the ball goes flat, you have to buy new ones – available as an ‘extra’, of course. This is a great marketing ploy from the manufacturer, and as long as the cats remained interested, they could milk money out of us for years to come (much like the printer ink business model). The case of the trapped battery Now, as a serviceman and electronics guy, having something with an onboard battery that goes flat pretty quickly and cannot be replaced rails against my code of ethics. Simply chucking that ‘expired’ ball into the rubbish is neither green nor kosher (even though the ball is actually tinted green), so I did what anyone else would do in my position – I tried to change the battery. I already knew what type of battery the ball took because the ball is made of a green-tinged transparent plastic, which allows the LEDs flashing inside the ball to be seen outside. The balls are the size of a ping-pong ball and two halves are joined together – obviously, once the circuit board and battery-holder assembly are installed – using glue. I can tell because there is a noticeable seam around the ball; theoretically, all I’d have to do is open that up, change the battery and rejoin the two halves together. I say theoretically because they don’t come apart that easily. It appears that plastic-welding glue is used to close it up (the kind that dissolves plastic to join it, rather than just tacking the two bits together), so simply cracking the glue bead won’t help. They’d obviously thought about this a lot and intentionally made these things to be consumable items – another of my pet peeves (pun intended!). Getting them apart was going to be the challenge. Anyone who has tried to cut a ping-pong ball in half will know how incredibly difficult it is to hold something like that while attempting to separate it. I once used a Dremel jigsaw to bifurcate a ping-pong ball and feared for my fingers at every step of the process. I’d likely need to use something like that to crack these flashing balls open. Still, where there’s a will, there’s a way. By this time, many of you are likely eye-rolling and asking your good selves why I don’t just suck it up and buy replacements – which, in all honesty, aren’t that Australia's electronics magazine siliconchip.com.au Items Covered This Month • The irreplaceable cats and their non-replaceable batteries • • • Simpson’s odyssey Outdoor motion sensor repair More playthings for pussy-cats Troubleshooting a cordless lawnmower Dave Thompson runs PC Anytime in Christchurch, NZ. Website: www.pcanytime.co.nz Email: dave<at>pcanytime.co.nz Cartoonist – Louis Decrevel Website: loueee.com expensive. Well, the answer in three words is: The Serviceman’s Curse. I can see the battery inside; therefore, I must be able to replace it! The balls ship with one of those really thin transparent plastic pull-tabs on them, so the battery doesn’t go flat on store shelves. When you get one, you pull the tag out, which connects the battery, and off you go. That means there’s a slot in the seam, and that’s where I started. I tried the usual spudgers and prying tools, hoping that the seam would give way and the ball would just pop open. No such luck. These things were tighter than an All-Black scrum. The only way in was to score the seam deeply with a craft knife – a horrifying task to finger health – followed by carefully using a modified junior hacksaw blade to cut around the edge and through to the inside of the ball. Clearly, I couldn’t just chew through it with a jigsaw like an empty ping-pong ball, as that would also slice the innards in half, defeating the purpose of the exercise. Well, I got it open eventually, but at the expense of about a millimetre of material cut away by the blade kerf. Replacing the battery was easy enough – it had a typical plastic-moulded holder with a spring at one end and a contact at the other. The battery itself comprised just three garden-­variety SR44 cells in series. Once the cells were installed, I had to reconnect the two halves. After smoothing the ragged hacksaw cuts and matching the two halves as best I could, I used a tiny spot of superglue at three points around the circumference to tack it back together. The result was still quite strong, but time would tell if it stood up to the punishment of being batted about by cats, when they could be bothered. Still, I consider it a good result. siliconchip.com.au Theoretically, I can now crack it open easily any time the battery dies, which is how it worked out. I’ve replaced the battery in the two balls that came with the toy several times now, and while we’ll have to replace the balls eventually, at least we’ve gotten some decent use out of these ones before having to discard them. Of course, it depends on the cats still being interested! My wife was buying some items from an online store recently and came across a ‘chirping’ cat toy that was ‘on special’. She ordered it, even though all our cats are getting older now and play with toys less. But, on occasion, especially with a new toy, they will still find that inner kitten and go mental over something. This particular toy is like a large plush housefly, with exaggerated bug eyes and wings. Once again, it came with one of those plastic pull-tabs to activate the battery, and when that was removed, just tapping the toy lightly would result in a chirping sound for a few seconds. Unusually, our cats loved it straight away. It didn’t say so on the packaging, but it was probably soaked in catnip, such was the interest they all showed in it. At all hours of the day, we’d hear the thing going off, indicating one of the cats was having fun with it. Sadly, after a few days, it stopped working altogether. While the cats occasionally swatted it when walking past, they soon lost interest. Being a plush toy, there wasn’t any real way of getting to the module inside. I could feel it in there, but no sound came out. The wife played around with it, and suddenly it started chirping again. So we threw it back to the cats and it worked as expected for the next few days. But it stopped working again and this time, no matter what we did, we couldn’t get it going again. My wife suggested we just buy another one since the cats liked it so much, but the Serviceman’s Curse reared its ugly head again, and I resolved to discover why it had failed. After looking it over carefully to see how they managed to embed the module inside and sew it up without any visible seams, I found a section in the toy’s body with several tiny clear threads holding it together. I guessed this was where they’d inserted the capsule and then sewn it back up. Like the flashing balls above, the only way in was to be a bit destructive. This shouldn’t be as bad, though; snipping a few threads is much easier than cutting a ball in two! And so it proved to be. Once I had removed those clear stitches, I could spread the outer material and push the Dacron packing aside to reveal the electronic module. The circular insert is a well-made plastic unit about the size of a small stack of 10¢ pieces, 25 × 18mm or so. Australia's electronics magazine October 2022  79 A cover on one end was clipped to the rest at each 120° point by a small plastic tab, and a small flat screwdriver bit soon had them loosened. The PCB inside is tiny and has a small chip-on-board (COB) IC plus a few ancillary components. Unlike the balls, which use a very simple arrangement for sensing movement, this device appears to use some kind of accelerometer within the COB to detect when the toy is moved. With the PCB out, I could faintly hear chirping when I tapped the side of the board, indicating that perhaps the battery had once again gone flat, although, after only a few days of play, that seemed unlikely. This device uses even smaller cells than the balls with two SR421 types mounted in a moulded plastic holder. As soon as I touched one to extract it, the thing chirped away merrily, so clearly, the cells were still good. There were no apparent signs of dry joints or anything suspicious on the bottom of the PCB, so perhaps it was just a dodgy connection between the battery and the holder. After giving the module a good going over and quickly buffing the spring and terminal ends of the battery holder with my diamond contact file, it seemed to be working reliably. I reassembled the whole thing and my wife put one broad stitch in the plush body to seal it up. It still seems to be going well. Another toy for the tabbies Finally, our latest (and possibly our last) online purchase of a cat toy resulted in the frustration of intermittent operation. This device is about the size of a tennis ball and clamps via a plastic holder and screw assembly to any windowsill or similar surface. When a button on the case is pressed, a fluffy ball on a length of twine-sized string drops out of the bottom of the unit and randomly rises and lowers using a spindle inside the device. Think of a bucket rising and sinking in a water well, and you have the idea. There is a timer built in that quickly raises and lowers 80 Silicon Chip the ball at short intervals, hopefully enticing the animal. If the cat grabs onto the ball, it plays out the length of the string while the base unit pulls on it with varying strengths after different delays to keep the pet engaged. It’s a clever idea, and quite well-implemented. However, the noise of it working put all our cats off initially – the motor running backwards and forwards is quite loud. After a while, though, they got used to it and were hooking into the fluff ball with gusto. After a few minutes of inactivity, the ball retreats back up into the bottom of the base unit, and the device shuts down. It requires another push of the power button to get it going again. If we want to stop it, another push of that button also resets the ball back ‘home’ and shuts the toy down. This device is powered by two AAA cells, accessible by undoing two screws holding one half of the round case together. I don’t know why they didn’t put a battery cover/door in there, but this is still a lot easier than cutting something open, and they do provide one of those small, mass-produced, plastic-handled Phillips screwdrivers you get with many phone-repair kits in the box. Once again, I couldn’t turn the thing on after a few days. I knew the cells were good, so something else must have happened. The switch itself felt odd and didn’t seem to toggle as well as I thought it should, so there was only one thing for it: break out the tools. Getting in was a breeze because it was all just screwed together. Separating the two halves was as simple as removing the PK screws and cracking it open. Inside was the spindle, with the string wound on it, a PCB mounted in the bottom half – again using a COB chip and a couple of other surface-mounted components – with some flying leads to a DC motor and the battery holder in the top half. The PCB itself was screwed to the bottom half, and the power switch was mounted directly to that, while the switch actuator protruded into a plastic button moulding, allowing it to be toggled from outside the case. I immediately saw a problem: the case moulding the switch toggle mounted into was being impeded by a small piece of plastic ‘flashing’, a product of the injection-­ moulding process. Usually, when plastic items are moulded, any excess material is removed either by machine or hand before the device is assembled. Unsurprisingly, that process is known as ‘deflashing’. It is not unusual for stray bits to be either left in the case or missed in the removal process, only to break away once the unit is built. Whatever happened here, the switch was fouled by this thin shard of plastic, so it could not operate properly. A pair of tweezers soon had it out, and its operation returned to normal. Repairing such things appears folly, but it goes against the grain to buy something that doesn’t work correctly, and for items as cheap as these, especially if they are mail-­ ordered, returns are hardly practical. I think it’s always worth having a look to see what can be done when one of them goes wrong. Simpson’s odyssey B. P., of Dundathu, Qld had such a long saga repairing a Simpson washing machine that it makes Homer’s Odyssey seem like a brief jaunt and Joyce’s Ulysses look like a short story... Australia's electronics magazine siliconchip.com.au We have a boneyard at our place where we store old washing machines. Some are units that we had used previously that had developed unrepairable faults, some are donor machines for parts, and one or two are machines that we had been given but hadn’t used yet. So when our current washing machine stopped working, I took a look to see whether there were any good replacements. I found a Simpson Contessa 425 machine under a cover that looked OK. I noticed that the power cable had been cut off, but there was a spare cable on top of the machine that I could use. I would start by fitting the replacement cable so that I could test it. The cable enters the machine at the back of the control panel at the top and is held in by a cable clamp. I removed the three screws from the back of the panel and lifted the panel clear to access the inside. I could then pull the cut cable through from the inside, remove the cable clamp and fit the replacement cable. The Masonite back panel was missing, but I would worry about that after discovering whether the machine worked. The spin solenoid was burnt out, so I went back to the boneyard and removed the solenoid from a Simpson 728 machine that I’d repaired years ago, that we’d used until it developed an unrepairable fault. With the solenoid fitted, I spun the timer to the spin cycle and pulled the knob up. The solenoid clunked, but the motor did not turn. It looked like the motor was faulty, so I got the one from the 728, as I knew it was good. With the motor fitted, the machine sprang into life, so I gave it a good clean. I looked around to see what I could make a replacement back panel from and found a sheet of painted ribbed metal. I cut that to size, drilled mounting holes and fitted the panel. Then I replaced the two broken feet from another machine in the boneyard and set the machine up for testing. My wife ran a load of washing, and she said it was working well. However, the next day, she said that it was not spinning very well and it would only spin dry half a load. I suspected that the belt was slipping, which proved to be the case. I tried to tighten the belt without success, so I checked my parts box and found two belts of the same size. One belt looked beefier than the other, so I fitted it, but it still slipped. Then I noticed that the pulley was badly worn; it was so thin that it broke off. These pulleys are nearly impossible to remove to replace, so I would have to replace the motor (again). I got one from the shed, fitted it and put the machine back. The next morning, my wife went to use the machine and she reported that it would wash but not spin. I knew the previous motor was good, so I would try to replace the broken pulley with the one from this motor. I tried to remove the broken pulley, but it kept breaking more, and in the end, all that was left was the section attached to the motor shaft. I ended up chopping it off with a chisel. The motor shaft had some rust where the pulley had been, so I cleaned it up, ready to fit the replacement pulley. Now to remove the good pulley from the other motor without breaking it. After removing the Allen head grub screw, I found that the pulley would not budge. I heated the pulley and, prying the pulley up with two screwdrivers and my siliconchip.com.au wife hitting a rod on the motor shaft, we finally got the pulley off. I fitted it to the other motor while it was still hot. I had lunch while the pulley cooled down, then I replaced the grub screw and fitted the motor to the machine. Now the machine would not spin. I wondered if the motor might have been damaged when I’d chopped the broken pulley off it, so I looked for another motor. There was a Simpson Delta in the boneyard that we’d been using until the bowl drive had failed. I plugged it in and confirmed that motor was good, then I removed the motor and fitted it to the 425. Well, it still would not spin. Maybe the capacitor was bad. I used the capacitor from the Delta, but it still would not spin. I was starting to suspect the timer, as I thought that maybe the contacts in it were not making good contact from the machine being stored for so long outside under a cover. However, I found that if I rotated the motor pulley by hand on the spin cycle, the motor would turn slightly. That indicated that the motor was getting power from the timer. So what could be causing the machine to wash correctly but not spin dry? I’d ruled out the motor, the timer and the capacitor, so what was left? The one component left that could cause this was the electronic forward-reverse module. But I could not understand how it could wash correctly and initially spin, then not spin at all. It’s a sealed module, so it is not serviceable. The module in the Delta was definitely sound, so I removed it and compared it with the module in the 425. They looked identical but had slightly different part numbers. One had longer coloured wires, while the other had shorter white wires. Considering that these washing machines were very similar, I wondered if the modules were interchangeable. I checked the codes on the wires, and they were identical, so I decided to take the chance that the Delta module would work in the 425. I took careful note of the wiring and removed the old module. However, one of the plastic retaining clips broke in the process. This is not surprising with plastic that must be well over 20 years old. I fitted the Delta module, plugged the machine in, turned the dial to the spin cycle and pulled up the knob. The machine sprang to life, indicating that the original module was faulty. I was then pretty confident that the ‘suspect’ motors were all actually good. If I needed to replace a motor in the future, I would check then, but I was not going to swap any motors just to test them. Australia's electronics magazine October 2022  81 To repair the broken clip, I glued a piece of bread tag onto its side with superglue. I had to attend to something else, and when I came back, the glue had dried and the clip was solid. I added a blob of hot-melt glue to reinforce it, and I added a blob to the other clip too. I then fully reassembled the machine and set it up, ready to use again. After a few days, my wife said it was not spin-drying or pumping out the water. She’d already bailed out most of the water, so I pulled the machine out, removed the back and checked the pump. It was jammed, so I turned the fan by hand and the pump freed up. These small squirrel cage induction motors have bushes, not bearings, and after years of use, the lubricant can harden, causing the pump to stop. With the pump now free, I pumped out the remaining water and added a few drops of oil to both ends of the shaft where the bushes are. I also unscrewed the cap on the end of the pump to check for debris, but it was clear. After several weeks of use, the machine was still working well, but one morning, my wife told me that the machine would now spin but not wash. I wondered what went wrong with it this time. I looked in the shed and found another electronic forward-reverse module, so I decided to fit that and see what happened. The next day, I got the same report, but this time the machine still had water in it, so I could check it. I spun the timer to the wash cycle and pulled up the knob. I could hear the water solenoid buzzing, so I suspected that the pressure switch wasn’t working for some reason. I removed the front panel and disconnected the pressure switch’s hose from the machine while leaving it connected to the switch. To test the switch, I blew into the hose and heard it make a loud click, indicating that it had been jammed. Now I could repeatedly blow into the switch hose, and it seemed to be working, so I expected the machine to work correctly now. The following day, the machine performed correctly, but the day after that, it would not spin. I checked the motor, and it was blazing hot, so I changed it. I fitted one of the previous motors that I’d swapped out as suspected of being faulty, but I later thought it was likely to be good. Sure enough, it was good, and the machine spun again. The saga continued, with the machine working for a couple of days, but now washing but not spinning. Could the replacement forward-reverse module have failed? I swapped it back to the Delta one with the short white wires, and once again, the machine worked correctly. However, the following day, we were back to the situation of it not washing, but it was spinning. It would seem that the pressure switch was playing up again. I knew the pressure switch in the Delta was good, so I attempted to retrieve it. However, when I tried to remove the knob, it would not budge, and it took some levering with two screwdrivers before I got it off. I unscrewed the pressure switch and took it over to the 425. I noticed that the switch was not turning freely, but some grease on the cam and a couple of drops of oil on the shaft fixed that. I had no problem removing the pressure switch knob on the 425, so I could then remove the switch. I screwed the replacement switch in, then swapped the wires from the old switch to the new switch one by one to ensure that I plugged all the wires into the correct terminals. That done, I refitted the front panel, and the machine was ready for testing again. The next morning, my wife reported that the washing machine was working correctly. After several months, it’s still working well. This has again saved us from having to buy another machine. With new machines costing over $600 and second-hand machines being hit and miss, I was happy that I’d been able to get this old Simpson machine working well again. This is why we keep ‘junk’, to be able to repair other ‘junk’! The photo below shows the inside of the front panel, with the pressure switch on the right and the forward-reverse module on the left. The timer is adjacent to the forward-­ reverse module, and the capacitor is located between the two switches for the water temperature and cycle. When the panel is refitted, the loose hose in the lower right plugs onto the pressure switch. Outdoor motion sensor repair M. L., of Frenchs Forest, NSW says he likes a challenge. But sometimes, a job can be so challenging that it leads to nothing but frustration... I thought I’d share one of my (bitter) experiences that took considerable time for me to solve. I had a Clipsal C-Bus system I installed in my house many years ago. It is still going strong, but there was a problem with one particular motion sensor not working for some time. This Clipsal 5750WPL automation system infrared (IR) motion sensor would not work at night. It wouldn’t sense movement, and the respective lights would not switch on. All the programming was correct, and it was recognised on the C-Bus network, but it just wouldn’t detect movement when the light level sensitivity pot was set to full darkness. Two forward-reverse modules, one from the Simpson washing machine (left) and a Delta machine (right). This photo shows the inside of the washing machine’s front ► panel. On the left is the forward-reverse module and on the right is the pressure switch. 82 Silicon Chip Australia's electronics magazine siliconchip.com.au Refresh your workbench with our GREAT RANGE of essentials at the BEST VALUE. Here's just a small selection of our best selling workbench essentials to suit hobbyists and professionals alike. 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ONLY jaycar.com.au/workbench 1800 022 888 The original 5750 installed 20 years ago worked without a hitch, never missed a beat until the seals failed and it filled with water, so I had to replace it. I programmed the new unit, walk tested it, then set the pot to full darkness like the previous unit. I walked away and didn’t think another thing of it until one night, I went out to the area where the 5750 should be sensing my movement, and no lights came on. I checked the programming, and it was all good. The PIR Enable function was set to Enable via the touchscreen. So why wasn’t it working? I re-checked the programming and the terminations. I spent a considerable time messing around with no success. It worked fine in daylight mode. I eventually gave up and decided that I should replace the sensor because the sensing level pot was faulty. Eventually I did, and since my house was going through renovations that required scaffolding, I waited for the scaffold to come down to replace the ‘faulty’ unit. I replaced it, programmed it, did the walk test, and life was good, so I set the unit to full darkness. The following night I went out to check if the unit would pick me up. Nope. Lots of expletives were heard by the neighbours. The next day, I checked it again in daylight, and it was working... There is a camera monitoring the area where the sensor is located. The camera is five metres above the sensor, under an eave. This camera has been replaced four times over the years due to failures. The original cameras were day/night types, and I used a Jaycar long-range bullet-type IR illuminator to illuminate the area monitored by the camera at night. The camera didn’t have built-in IR emitters because it was a varifocal type. I removed the Jaycar illuminator when I installed the third new camera because it had a built-in illuminator, as do most recent cameras. The illuminators in the latter two cameras provided more output than the Jaycar unit. The next day, late in the afternoon, as the light levels were dropping, I decided to undertake a little experiment where I adjusted the 5750 light level pot from the daylight setting a small amount towards total darkness. When the light level dropped below the sensor hysteresis point, the light would come on when it sensed my movement. That is until I got to the full darkness setting, and the lights would not come on. More expletives. I knocked the pot back to daylight and bingo! The unit was sensing. I set the pot to full darkness and no more sensing. At that point, the light bulb above my head exploded! It was the !<at>#$^&* camera! The IR emitted by the camera was providing enough reflected (IR) illumination to stop the sensor from activating. I tweaked the pot about 5° back towards daylight, and the 5750 started working again. So, I figure that the problem must have commenced around about the time I installed the third camera. The camera illuminators produced more IR output, but because I don’t spend much time at night in this area, I didn’t notice the problem until I had to replace the 5750 sensor. Also, the electronics in the 5750s were updated to full surface-mount technology in the early 2000s, so Clipsal most likely tweaked the sensitivity of the IR detector when they updated the design, exacerbating the problem. 84 Silicon Chip I have spoken to several electricians who have had similar problems with other systems sporadically switching lights and other equipment on. Having described my findings to them, they are looking at the devices installed in the areas where the problems occur. I bet it’s the IR devices that are the cause. Troubleshooting a cordless mower B. C., is a frequent contributor to Serviceman’s Log; this time, he has had to repair a Gardenline cordless mower... This mower had been working reliably for over three years. However, on this particular day, it went for only about three metres on a light cut, then the motor stopped running. Upon pressing the Charge Check pushbutton, the LED bargraph indicated a fully charged battery. Despite this, I changed the two 20V lithium-ion battery packs over to the spare set. But the mower motor still would not run. So I brought the mower into my workshop and put it on the bench. I removed the plastic top to reveal a brushless motor, a controller module and a wiring harness. Googling the part number on the module nameplate (30070030) came up with an ALM (China) brand mower. There was an exploded view and a complete parts list for this mower. However, this module number was not available through any eBay or AliExpress sellers. It was now time to determine whether the motor or the controller module was faulty. Some further research on the internet came up with this information on how to test a brushless motor: 1. Short the three motor leads together and check for resistance when the shaft is rotated by hand. 2. Connect a voltmeter across each winding in turn and spin up the motor with a cordless drill. It should generate a similar voltage across each phase. 3. Check for a short circuit between the windings and the stator (body of the motor) using an ohmmeter. 4. Check for an equal inductance for each winding using an LC meter. I checked the brushless motor using those steps, and it passed with flying colours on all four! So I decided to take a closer look at the controller module circuitry, as it now seemed likely that there was no output drive to the motor. After removing the module end caps and the sheet metal sleeve, the PCB and heatsink were revealed. I then plugged the PCB/heatsink assembly back into the mower harness. After pressing the handle operate switch, a surface-­ mounted LED near the microprocessor flashed five times, which I assume was a fault code. This was a welcome sign. I unplugged the module and removed it for further testing. Along the back edge of the PCB, I found six HY1707 power Mosfets. Of these, three (V1A, V1B and V1C) tested faulty! I ordered ten HY1707 Mosfets via eBay. Upon their arrival, I replaced them all (including the apparently still functional V0A, V0B and V0C) for long-term reliability. I then refitted the module into its case and plugged it back into the mower harness. After pressing the operate switch, the motor ran again! The mower has now been going properly for over three months since the module repair. Perhaps the failure was due to overloading in the past when trying to cut heavier grass, resulting in incipient damage, which made it finally give up the ghost later. SC Australia's electronics magazine siliconchip.com.au questions and answers with Mouser Electronics We were offered the chance to publish a Q & A with answers provided by Mouser Electronics’ Senior Vice President of Global Service & EMEA and APAC Business, Mark Burr-Lonnon. Q Ongoing parts shortages have resulted in many items being on backorder. We have noticed that Mouser provides regular updates on the ETA for back-ordered parts. How do you keep track of the delivery dates for so many products at once? As a leading distributor of electronic components worldwide, Mouser Electronics provides the fastest and easiest access to the widest selection of the newest semiconductors and electronic components — available to order or in stock and ready to ship. The electronics industry and supply chain have faced significant challenges in recent times due to manufacturing contractions, chip shortages, and transportation disruptions. Supply-chain delays coupled with rising demand have complicated the task of sourcing and buying components, putting many items into backorder. As a global authorised distributor with a strong customer focus, we are committed to fulfilling the needs of our customers and helping to solve purchasing pain points. We collaborate with our manufacturer partners and provide regular updates for customers on expected delivery timetables, along with real-time inventory updates and lead times on our website. A Based on current lead times, it is pretty clear that many parts will be in short supply into 2023. Do you think the situation will ease by the end of 2023, or can we expect serious shortages to continue into 2024? Q With the current uncertainties, it would be inappropriate to speculate on the global semiconductor supply chain two years into the future. Various factors have disrupted manufacturing across many industries, and supply chains across the globe remain in a state of flux, resulting in extended lead times and restricted allocation on some product lines. As distributors, our teams work to project supply and demand, helping customers tide over supply chain instabilities. Customers rely on us because of our wide breadth of inventory and ability to offer alternate products. Along with stocking the widest selection in the industry, we continue to focus on expanding product choices for customers and having inventory on hand. In 2021, we added over 113 new manufacturers to our product line card and have added over 35 year-to-date in 2022. A siliconchip.com.au Q Any recommendations for those putting together a BOM (bill of materials) for a design to minimise the risk that critical items will be out of stock when it comes time to manufacture the product? Mouser is committed to providing a bestin-class customer experience and, as such, we offer a full suite of customer-focused online tools to simplify and optimise component selection and purchasing. Our resources and guides help customers map their data to create a new BOM, and our service professionals can suggest strategies to mitigate delays when lead times can impact projects. Customers are naturally frustrated by the product shortages and are placing orders many months ahead. The recent disruptions have also compelled designers to plan ahead even further for their projects. Distributors are not immune to global factors and there have been extended lead times and restricted allocation on some of the more popular product lines. Our teams are closely monitoring shortages and are working closely with manufacturers to replenish products as quickly as possible. Customers can register for stock notifications through email, so that they can stay abreast of a part’s availability in real time. If a particular part is not available, we suggest looking for a similar or alternative part that might be in stock. In semiconductors, customers might evaluate if memory can be increased, and if it does not overextend the budget, ordering the same part with a larger memory capacity might be a solution to reduce the lead time. Similarly, customers may evaluate if tolerance can be increased for capacitors and order suitable alternatives to avoid delays. We offer several suggestions on best practices, along with efficient, time-saving solutions, along with an Intelligent BOM tool, and order automation resources through our Services & Tools page. A Q How do you decide what new products to stock? Do you take any steps to ensure that new products are in stock in sufficient quantities upon release so they are viable choices for new designs? Mouser is the industry’s leading New Product Introduction (NPI) distributor, offering the widest selection of semiconductors A Australia's electronics magazine and electronic components. More than 1,200 manufacturer partners rely on us to help them successfully introduce their products into the global marketplace. We work closely with manufacturers to stay up to date, which helps us to better support customers’ needs, and helps engineers and designers innovate with new products. Despite the current supply chain challenges, innovation continues to be strong, and this is driving demand. Our teams collaborate closely with the manufacturers to promote their newest products, and we are seeing exciting new sensor technologies, as well as the latest in power management and, of course, advancements in microprocessors, automotive, factory and home automation components. Certainly, IoT, 5G, artificial intelligence, robotics, industrial automation and transportation are major growth drivers in the industry and are driving design. We have received counterfeit parts from other suppliers in the past which have caused many problems. How do you prevent counterfeit parts getting into Mouser’s supply chain? Q In recent years, the rise in counterfeit components entering the supply chain has been a serious problem. With Mouser, customers are assured of 100% certified, genuine products that are fully traceable from each of our manufacturer partners. Mouser takes every precaution to ensure that the products are obtained directly from the original manufacturers or through their authorised channels. We have the most stringent product traceability and anti-counterfeit controls in place, which have earned us coveted certifications such as the AS9100D, securing the supply chain for the aviation, space and defence industries. Mouser is also the first distributor to be accredited with the SAE AS6496 standard for anti-counterfeit measures in authorised electronic component distribution, providing full traceability to the original manufacturers on every product we stock and sell. We also make sure that the products are handled and stored in accordance with industry quality standards. As an Electronic Components Industry Association (ECIA) authorised distributor, we are committed to providing factory-warranted, first-quality, genuine components. Mouser provides access to our manufacturers’ full range of up-to-date technical and product information, as well as comprehensive technical support. SC A October 2022  85 WiFi-Controlled Programmable DC Load Part 2: by Richard Palmer ѓ Handles up to 150V DC, 30A & 300W ѓ Uses a computer CPU cooler to handle high power dissipation with modest noise ѓ Constant voltage (CV), constant current (CC), constant power (CP) and constant resistance (CR) modes ѓ Step test modes (square, ramp and triangle) with variable rise/fall times ѓ Data logging ѓ Touchscreen, USB or WiFi (web browser) control, including via smartphone/tablet ѓ SCPI programmable over WiFi and isolated USB ѓ Retains settings with power off ѓ Over-voltage, over-current and reverse voltage protection ѓ Useful for power supply, battery and solar cell testing This Programmable Load can handle supplies delivering up to 150V, 30A or 300W. That makes it ideal for testing power supplies, solar panels or other DC sources. We explained how it works last month. This article includes the PCB assembly details, overall construction, testing and some usage tips. 86 Silicon Chip Australia's electronics magazine siliconchip.com.au It is vital that a dummy load can dissipate a lot of power, and this one can handle up to 300W, thanks to the use of two CPU tower coolers and four large TO-247 package Mosfets. It can be controlled using its onboard touchscreen, via a web interface over WiFi or using SCPI. SCPI support is ideal for integrating it into a suite of test instruments, and it allows for semi or fully automated testing. There are three PCBs to build: one control panel, which has the ESP32 with WiFi, the touchscreen and the other user controls; the main Load board with two Mosfets; plus a daughterboard with two more. Once those boards have been built, they can be wired up, tested and then housed in a ventilated metal case that is just the right size for fitting everything inside. Importantly, it also provides decent ventilation for safely dissipating up to 300W. There are quite a few construction steps, so let’s start by building the control board. Control board assembly The first steps are to build and test the touchscreen control module, followed by the main load PCB. Once both are working correctly, the load daughterboard (which adds the two extra load Mosfets) can be built and tested. To build the controller board with a 3.5in touchscreen, you can follow the instructions in the original articles (May & June 2021; siliconchip.com. au/Series/364). Note that the overlay diagram presented in June 2021 was incorrect (it’s now fixed in the online version). So you’re better off using Fig.9 in this article instead. As some slight circuit changes are required on the control board (described last month), I have created a new PCB coded 18104212 (167.5 x 56mm). This can still be used to build the original Programmable Hybrid Lab Power Supply with WiFi, or it can easily be adapted to this project, depending on which link options are used (made by soldering across pairs of closely-spaced pads). Assembly of the control module is Fig.9: this updated control PCB has extra link options on the back (JMP_ENCB, JMP_PIN13 & JMP_LED), so it can be used for the Hybrid WiFi Lab Supply and the WiFi DC Electronic Load. Some extra component pads are needed in this application to filter analog voltages that the Lab Supply did not require. This overlay diagram fixes significant errors in the originally published version. There are two locations for the rotary encoder, to allow for different-sized knobs. siliconchip.com.au October 2022  87 The Control board can be cut into three separate pieces and then joined with ribbon cable. If you use a large enough case the boards do not need to be cut. straightforward as there aren’t many components on it – see Fig.9. If you are using the recommended case, start by cutting the board into three pieces along the dashed lines and through the rectangular cut-outs, to separate the switches and encoders from the display section. Clean up the edges and make sure you haven’t created any short circuits between the cut tracks. Next, fit all the SMD passives where indicated. We’ve ‘cut some holes’ in the ESP32 module in Fig.9 so you can see where the components go underneath it, including the two 100nF we’ve added as per the Fig.8 circuit diagram in the previous issue. The 10μF and 47μF capacitors are shown as polarised tantalum types, but you can use (and we recommend) ceramics, which are not polarised, so their orientation doesn’t matter. The next step is to bridge the appropriate pairs of solder pads. Leave all four links, labelled LK1 to LK4, open (do not solder them). The other three sets of solder pads labelled JMP_LED, JMP_ENCB and JMP_PIN13 have three pads each, and you need to bridge from the middle pad to one of the outer pads, but not both. These have little arrows which show the pad to bridge the centre pad for the original design. For this design, 88 Silicon Chip bridge the pair of pads furthest from the arrows at JMP_ENCB and JMP_ PIN13. The existing bridges closest to the arrows will need to be cut. JMP_LED is bridged to force the LED backlighting for the LCD panel on at full brightness. The other position is for software control, but there aren’t enough spare pins on the ESP32 for that function in this project, so just set it at full brightness by shorting the arrowed pair of pads. Now fit the through-hole parts, including CON2 (but not CON1 and REG1) and the headers for the ESP32 modules on one side. Before soldering the headers for the ESP32 module, plug them into that module and then slot them into the PCB to get them at the proper spacing (there are two possible rows of solder pads on one side). Next, install the switches, rotary encoders and LED on the other side of the board. Solder the LED so that the top of its lens is about level with the top of the tactile switch actuators without caps. Attach the 14-pin and 4-pin headers on either side of the touchscreen module (if they didn’t come pre-soldered; usually, the 14-pin header is, but the 4-pin header isn’t). Insert these headers into the holes on the control PCB so that the pins just project through to the rear, then solder them in place, ensuring the face of the screen is parallel with the PCB. The DC socket and micro SD card socket are not needed for this project. Power is supplied to the board through the pads for CON1, labelled + and −. With the three sections of the control board now essentially complete, join them with two 10cm lengths of ribbon cable as in Fig.9. The encoder’s integral switch is not used in this project, and GPIO pin 26 is employed for another purpose, so you should only bridge the bottom six pins between the main control board and the encoder panel, as shown. While you could modify the earlier PCB (coded 18104211) for use in this project, there isn’t much point as the new one is the same price and makes it much easier. But if you must, cut and re-route the two tracks as per Fig.8 last month and tack on two 100nF throughhole ceramic capacitors. Commissioning the Control board The bare ESP32 module and a USB Australia's electronics magazine cable are all that are required for the first stage. Mounting the module on the Control board will come later. We assume that you’re already somewhat familiar with the Arduino development environment. If you don’t already have the Arduino IDE (integrated development environment) installed, you can download it from www.arduino.cc/en/software If you haven’t already, you will need to add ESP32 board support. Go to File → Preferences and add “https:// dl.espressif.com/dl/package_esp32_ index.json” to the Additional Boards Manager URLs. Next, open the Boards Manager (Tools → Board → Board Manager), search for ESP32 and click “Install”. This will set up the development environment and add an extensive list of example programs to the list. Set the Board to “ESP32 Dev Module” via the menu (see Screen 1). The rest of the settings may be left as the defaults. Plug in the ESP32 module and select the new communication port that appears in the menu. To check that it is working correctly, open the Communication → ASCII Table example and upload it (CTRL+U in Windows). Open the Serial Monitor, set the baud rate to 9600, and the screen should fill with the ASCII output out of the test sketch. Loading software over-the-air To demonstrate other possible applications for the Control board, we’ve created a version of the WiFi weather app as a demonstrator program for the D1 Mini LCD BackPack (October 2020; siliconchip.com.au/Article/14599). This is also a good way to test the Control board independently. The GitHub repository for this project is at https://github.com/palmerr23/ ESP32-DCLOAD We have made a ZIP file available for download from siliconchip.com. au/Shop/6/6518, which includes two display options: a 2.8in or 3.5in touchscreen. The 2.8in version ends with -28.BIN while the other version ends with -35.BIN. Load it using the OTA update process described below. The Weather app has a built-in OTA function to simplify loading the power-supply controller code. Over-the-air programming of the ESP32 is a two-stage process. First, we load a simple sketch with the over-theair (OTA) updater via USB. Load up the siliconchip.com.au #include #include #include #include #include <WiFi.h> <WiFiClient.h> <WebServer.h> <ESPmDNS.h> <Update.h> const char* host = “esp32”; const char* ssid = “YourSSID”; const char* password = “YourPassword”; WebServer server(80); Screen 2: to upload code to the ESP-32 via WiFi (OTA update), you need to add your network credentials towards the top of the program, as shown here. The hostname can be left as-is or changed to suit your requirements. Screen 1: once you have selected the correct Board in the Arduino IDE Tools menu, the settings should be set to the same values as shown. ArduinoOTA example (File → Examples → ArduinoOTA → OTAWebUpdater). Fill in your WiFi credentials (SSID and password) at the top of the program (see Screen 2). Open the Serial Monitor and change the baud rate to 115,200. Save the Arduino sketch, as we’ll be using it again. Compile and upload the sketch, and note the IP address displayed in the Serial Monitor. Move the Data folder and its contents from the download pack into the same folder as your saved OTAWeb­ Updater.ino file. Edit your WiFi credentials into the profile.json file. Close the Serial Monitor. In the Tools menu click ESP32 Sketch Data Upload to copy the files in the Data folder to the ESP32’s local file system (SPIFFS). This file system remains intact when new programs are uploaded. Now you can disconnect the ESP32 module and plug it into the Control board, ensuring that its 5V pin is closest to CON2 and its 3.3V pin is towards CON1 & REG1 (see Fig.9). Plugging it in the wrong way around Screen 3: when presented with the ESP-32 login page, use the default credentials of “admin” & “admin”. There’s no need to change these as they are only used once. could be catastrophic! Make sure that the TFT touchscreen is mounted on the Control board. Power this combination up using a USB cable or (if you fitted CON1) a DC supply of about 9-12V. The USB cable doesn’t have to be plugged into your computer, although it could be. Open a web browser on your computer and type in the ESP32’s IP address. You should be presented with a login screen (Screen 3). The username and password are both “admin”. There’s no point changing these to something more secure, as we’ll only be using this sketch once. After logging in, select the software file you’ve downloaded with the “Choose file” button (Screen 4), then “Update”. The web page will track the upload progress; then, after a short delay, the ESP32 will reboot, running the weather app (see Screen 5). Once you have verified that the Control board is working correctly, you can load the DC Electronic Load program. It is part of the same ZIP package that contained the weather app, and like that one, the suffix of -28.BIN or -35. BIN indicates which screen size it is for (this project is designed around the 3.5in option). The controller should display an error message at startup, as the I2C ADC and DAC chips are not yet connected to the Control board. Screen rotation & calibration Some TFT screens come with the origin of the touchscreen rotated 180° from that of the display. If your touchscreen appears not to be working, that Screen 5: if your module has been assembled and programmed correctly, once it has connected to your WiFi network, it should give local weather data, as shown here. Screen 4: once logged into the OTA page, you can select a file and then upload it into the ESP-32’s flash memory remotely using the “Choose file” and “Update” buttons, respectively. siliconchip.com.au Australia's electronics magazine October 2022  89 Screen 6: from the launch screen, pressing the SET button at upper right brings you to the calibration screen. Pressing the ROT button in the centre of this screen will adjust the orientation of the display if the touch controls are reversed. could be why. Try tapping the screen near the SET legend at upper right. If this lights the ST or NOR button, simply tap the ROT button in the centre of the screen (see Screen 6). The number below it should change from 3 to 1. Wait for the yellow [E] indicator to go out (after around 30 seconds), and the new value will be stored permanently in the ESP32’s EEPROM. Use this TCH button at the calibration screen’s bottom-left corner to align the touchscreen accurately with the display. Follow the prompts, touching each of the two + symbols six times. As above, it will permanently store the values after 30 seconds. Building the main Load PCB The main Load PCB is coded 04108221 and measures 107 x 81.5mm – see Fig.10. Install all components on this PCB other than Mosfets Q1 & Q2 and 5V regulator REG1. Start with the five SMD ICs, taking particular care to orientate them as shown in Fig.10, then follow with all the SOT23 devices and surface-mounted resistors and capacitors. With all the SMDs in place, give the board a good clean to eliminate any flux residue and then inspect all the solder joints, especially those on the fine-pitch ICs. If you find any dodgy looking joints, add some flux paste and briefly touch them with the tip of your soldering iron to reflow them. If you find bridges between pins on an IC, use flux paste and solder wick to remove the excess solder. Now fit the two larger through-hole resistors and the two smaller ones, which are mounted vertically. Follow with axial inductor L1, also vertical, plus the sole through-hole capacitor, a 1μF plastic film type. 90 Silicon Chip Now is a good time to solder the wire shown in blue in Fig.10. Use a short length of medium or heavy-duty hookup wire as this carries the current for one of the two Mosfets. Similarly, add the wire shown in red between the middle pin of the two Mosfets. You don’t have to loop it the way shown in our diagram; make it as direct and short as possible, without covering the Mosfet mounting pads. Next, fit the connectors. There are a few options here. CON1 and CON2 are required, and their notches must be orientated as shown. If you will be using 4-pin PWM fans as recommended, install CON9 and CON10 with the locking tabs facing as shown. Otherwise, fit CON11 and CON12, which suit 2-pin or 3-pin fans. You can solder the lug-mount NTC thermistor directly to the CON15 pads, or use a polarised header as shown. Either way, don’t attach the thermistor to anything yet. We recommend using headers for convenience for CON13, CON14 & CON16, but soldering wires to the PCB pads instead (eg, lengths of ribbon cable) is certainly possible. Early testing You will need to make the two ribbon cables for testing, as shown in Fig.11. They aren’t just for testing; they will be used in the final assembly. Connect the main Load PCB to the control board via the 20-wire ribbon cable and the ESP32 to a computer or 5V 1A power supply via USB. Do not connect the 12V supply at this stage. You should have already loaded the software, but this time, no hardware-­ related warning messages should appear on the control screen. The voltage and current readings on the screen should be close to zero initially and should reset to zero after a few seconds. The temperature reading on the control screen should indicate the approximate room temperature. Grip the thermistor between your fingers, and the temperature should change. Fig.10: assemble the main Load board as shown here. Most of the components are SMDs; start with the ICs and then fit the passives, transistors and other parts. The main decisions to make during assembly are whether to leave some of the headers off and solder wires directly to the board instead. That will initially save you time, but it makes testing and disassembly more arduous. Australia's electronics magazine siliconchip.com.au If you have a serial monitor (terminal) program, like the Arduino IDE Serial Monitor, set the baud rate to 115,200 and connect the ESP32 controller to your computer (or restart it if it was already connected). The serial monitor output should indicate that two I2C devices are registered, the ADC at address 0x48 and the DAC at address 0x60-67. MCP4725 devices are programmed at manufacture with one of four different I2C base addresses. Any variant may be used as the controller searches for I2C devices in the appropriate address range. If either I2C device has not registered, check for open or short circuits on the SDA and SCL lines. Check that the two I2C pull-up resistors are mounted on the control board. If only one device is showing, check for soldering problems on the other device – particularly the SDA, SCL, ground and supply pins. Setting up the WiFi network Now that the Control board has been programmed, when you power it up, the control menu should appear with a green box overlaid (see Screen 7). The program will try to connect to a local WiFi LAN and time out after 10 seconds, if you have not yet provided it with credentials by editing the profile.json file. Fig.11: the two ribbon cables needed are simple to make as they just have one IDC connector at each end. Make sure to crimp them hard enough for all the blades to penetrate the ribbon cable’s insulating and make good contact with the copper inside, but not so hard that you crack the plastic! Note that some IDC connectors lack the top locking pieces. If no network is found, another 10-second delay should occur while it seeks an existing ESPINST network. Finally, it should become the Access Point for the ESPINST network. At this point, the green box should disappear, leaving the main menu displayed. A small green “W” near the top right corner indicates that WiFi is operating. cases, you can resolve this by powering the ESP32 module from an independent 5V supply. If the problem persists, try adding a 47μF electrolytic between the module’s 3.3V supply rail and its ground pin, as shown in Fig.12. I highly recommend using a USB isolator for any USB connection to your computer while testing or operating the Load. Otherwise, the appliESP32 module stability cation of a reverse polarity voltage or Some ESP32 modules have over-­ other fault conditions could destroy sensitive brownout detectors causing both the ESP32 and your computer by multiple restarts, particularly when creating a high-current ground loop if connected via a USB hub. In most a USB isolator is not used. Screen 7: once the Control board has been programmed, when you first power it up the screen shown above should be displayed. This is the program trying to connect to a local WiFi LAN address. This photo shows one of the mounting arrangement options for the Mosfets. The mounting holes can be drilled between the heat pipes if there is room, or just outside them; either way works. Note that this is a prototype PCB. siliconchip.com.au Australia's electronics magazine The 9mm thick CPU cooler to PCB mounting block made from MDF. October 2022  91 Fig.12: a 47μF electrolytic between the 3.3V and ground pins on an ESP32 module can help if repeated ‘brownout detector triggered’ restarts are encountered. The bare leads should be insulated. USB isolators are available offthe-shelf at a relatively low cost on websites like Amazon, eBay and Ali­ Express. For example, www.ebay.com. au/itm/313938468819 Finishing board assembly Now install the 5V regulator (REG1) on the main Load board, being careful with its orientation, and plug the cooler fan(s) into their headers. Apply 12V to CON16 with the indicated polarity, and the fan(s) should briefly operate at full speed, then reduce to idle. The fan speed should start to rise as the thermistor temperature exceeds 28°C. Gently use a hairdryer to raise the thermistor temperature. Above 35°C, the fans should be running at full speed. At a reading of 65°C, an over-temperature warning message should appear on the screen. This is a convenient point to calibrate the thermistor, before it is attached to the Mosfet’s case. Follow the instructions in the user manual PDF, part of the software download package for this project at siliconchip. com.au/Shop/6/6518 The voltage on the Mosfet gate terminals (labelled “G” in Fig.10) should be close to 0V when any of the following is true: the output is switched off, the current setpoint is 0.0A and the load is on (connected), or the thermistor temperature is over 65°C. Set the voltage and current setpoints to any value greater than 1.0, and the load set ‘on’. Both gate terminals should rise to 8-9V. Now connect the relay control wiring to CON13, using the appropriate pin (+5V or +12V) for your relay coil voltage. The relay should operate when the load is on and release when the Off button is pressed. Temporarily connect KELVIN+ on CON14 to VIN and KELVIN− to GND. Temporarily bridge the 12V supply to VIN. The voltage reading on the control panel should be close to 12V when the output is on. Basic operations have been validated at this stage, and we can add the power components. Mosfets and power testing Mark out the Mosfet mounting holes on the CPU cooler, as shown in Fig.13. Drill and tap the mounting holes to 3mm or 1/8in (3.175mm). Drill either the holes between or outside the heat pipes, depending on the cooler used. Either is possible for the Hyper 103, but using the outside positions gives greater clearance. Depending on the CPU cooler chosen, the holes may be between the heat Fig.13: the drilling pattern for the heatsink cooler. Drill the holes either between or outside the heat pipes, depending on the cooler used. For the Hyper 103, the outside position gives greater clearance. 92 Silicon Chip Australia's electronics magazine pipes or outside the heat pipe group. With the dimensions of the PCBs, the maximum spacing between holes is 30mm, leaving just enough lead length to solder in the Mosfets in the outer positions. Compare the photos on the previous and next spreads, which show the difference between the two different mounting options. The minimum difference in the Y-axis position of the two holes on either side is 9mm, when the Mosfet leads are bent as close as possible to the package. Mount the Mosfets on the cooler with thermal paste but no insulating washers. Cut the 9mm-thick mounting blocks from MDF or similar and insert them between the CPU cooler and PCB, as shown on the previous spread. Blocks, rather than standoffs, are used for better lateral stability. Bend the Mosfet leads up and solder them to the PCB. Mount the thermistor onto either of the Mosfet cases. You can now complete the wiring as per the wiring diagram, Fig.14. Remember to use heavyduty wiring for the current-carrying cables between the two Load PCBs, the relay module and the output terminals. More testing Connect a low-voltage supply across VIN and COM (you can patch the 12V supply powering the PCB to VIN for this test). Set the target voltage to a few volts above the supply voltage, set the target current to 50mA and press the On button. The control panel current should read 50mA. Increase the current value to 500mA and measure the voltage across each of the two shunt resistors. Each reading should be close to 10mV, and they should be within 10% of each other if the load is balanced correctly. If you are using a supply that can deliver higher currents, increase the set current to a few amps and check that the voltages across the two shunt resistors remain balanced. Now build and connect the daughterboard using the PCB coded 04108222, which measures 81.5 x 66.5mm (Fig.15). It is basically a cut-down version of the main board, so use the same procedure, and like before, leave out the Mosfets initially. Similarly to that main board, it also requires two heavyduty wire links, as shown. Connect the daughterboard to the relay and negative terminal using siliconchip.com.au mSDCARD SKT REAR OF CONTROLLER PCB (LCD MODULE AT FRONT) 19 20 CONTROL CON2 – CON4 CON3 CON1 1 2 12V DC INPUT SOCKET (ON REAR PANEL) WIFI ENABLED INSTRUMENT PANEL REVB + 10kW NOTE: VERIFY SOCKET PINOUT, INCLUDING WITH RESPECT TO PLUGPACK POLARITY 100nF LK3 ENC_SW 1kW C 2022 100nF REAR OF ROTARY ENCODER AND DIRECTION SWITCHES PCB 100nF 10kW REM ON/OFF 100nF 100nF 100nF REAR OF ON/OFF SWITCH PCB DAUGHTER BOARD Q4 FQA32N20 IC2 VIN 20mW 3W Q3 FQA32N20 20mW 3W CON3 TO MAIN PCB GND + SENSE 10 IC4 INA180B MAIN BOARD CON1 TO CONTROL BOARD 20 Q2 FQA32N20 L1 Q1 FQA32N20 IC1 TO RELAY CON13 1 CON16 12V + – GND VCC IN1 + NC ON_H 100W OPTO-ISOLATED RELAY MODULE VIN – CON10 4-PIN (PWM) FANS CON9 20mW 3W THERMISTOR CON15 THERM 1 +5V COM HIGH/LOW LEVEL TRIGGER TP-I SLA05VDC-SL-C TP-V KELVIN 20mW 3W CON2 30A 250VAC 30VDC GND CON14 LOW HIGH CON2 NO 1 100W CON11 CON12 2x PWM COOLING FANS – SENSE Fig.14: running separate wires between each board and the front terminals helps distribute the current load. Run the GND bridge between the boards with a short stout cable to minimise ground potential differences and double the cable from the relay to the Load’s positive terminal to increase current capacity. siliconchip.com.au Australia's electronics magazine October 2022  93 Fig.15: the daughterboard has two power modules and a current monitor IC, identical to those on the main board. Control and sensing are transmitted to the main board via a ribbon cable. Note that the daughterboard layout has changed substantially since the photo was taken. separate wires to balance the currents between the boards, as shown in the wiring diagram (Fig.14). Note the short but thick ground wire (green) connecting the main and daughter boards at the GND points on each. You can now install the daughterboard Mosfets and re-test the Load. Mounting it in the case The CPU coolers, which support the load PCBs, are mounted on a plate attached to the side rails of the enclosure, as seen in the photographs, using a custom side panel with dimensions shown in Fig.16. Mount the coolers as far to the rear of the case as practical. This ensures there is enough space for the control panel components and relay at the front of the case. Take care that the CPU cooler fins are well clear of the metal case and wiring, as they will be at the full input potential. It may be necessary to reverse the fans on the coolers, so that they suck air through the fins and blow it out the side of the case. All mounting screws on the support panel should be countersunk to avoid interference with the enclosure sleeve. The prototype used 3mm Perspex, with top and bottom folds to increase rigidity. You can cut this yourself, or we can supply it laser-cut from 3mm clear acrylic (but without the bends). Alternatively, you could use metal or thin plywood. The support plate mounts on the inside of the case’s side rails, with the fan mounting holes 30mm above the base of the case. This provides airflow below the cooler and headroom for the components on the PCBs. Additional ventilation is provided by cutting a hole in the rear panel to mount a 120mm fan guard, and making a substantially larger opening in the panel on the CPU cooler side, covered by two 120mm plastic fan guards. A 100 x 100mm grid of 61 x 7mm holes in the bottom panel toward the front of the case boosts airflow to the front CPU cooler (see Fig.17). To ensure good airflow, it’s best to remove any filtering material from the fan guards. Once the cooler support panel is in place, mark the two fan guard cutouts and mounting holes on the side panel. They should be placed side-byside, covering the existing slots in the sleeve. Once the cut-outs and holes in the sleeve have been made, slide the sleeve in place and mark the screw holes onto the CPU cooler panel. Fig.16: this CPU cooler mounting plate attaches to the enclosure’s side rails. The coolers are mounted towards the rear (right) of the enclosure to allow space for the control panel at the front (left). All holes should be countersunk to prevent the screw heads from binding on the case’s metal sleeve. You can mark additional clearance holes for the fan guard screws with the cover sleeve in place. Fan mounting holes are 4.5mm in diameter, while the case mounting holes are 3mm. 94 Silicon Chip Australia's electronics magazine siliconchip.com.au Fig.17: the airflow hole pattern for the base of the case. Position it towards the front of the case. Holes will be needed in the CPU support panel so that the fan guard mounting screws don’t bind on it. Drill relief holes for the screws and nuts, or self-tappers, a few millimetres larger than their diameter. Mount the third fan guard toward the top of the rear panel and the coaxial power socket toward the bottom corner furthest from the CPU cooler panel. The relay module mounts on the case floor, at the front and on the opposite side to the CPU cooler support plate. Ensure adequate clearance is provided for the CPU cooler fins. On my relay module, one of the mounting screws was uncomfortably close to the tracks going to the contacts, so I used a Nylon standoff and screw on that corner. Front panel The front panel components mount on the metal faceplate provided with the case. A 2mm black acrylic cover panel or decal finishes off the face. See siliconchip.com.au The photo shows how the PCBs mount on the CPU coolers, the coolers mount to the custom side panel via the fans, and the side panel mounts to the case rails. Australia's electronics magazine October 2022  95 Screen 8: the web browser control interface’s main tab. Screen 9: the Load’s TestController device popup. the cutting diagram, Fig.18, and note that you can also purchase a laser-cut and etched acrylic panel to save a fair bit of effort. You might still want to add labels to that panel, though, or fill the etched areas with white paint. Drill and cut holes in the metal panel shown with red or black outlines in Fig.18. The mounting holes for the TFT panel and switch modules should line up with the parts on the control board, and they should be drilled to 2.5mm, then countersunk so that the screw heads are clear of the cover panel or decal. The countersink will expand the holes; then, they can be drilled out to 3.5mm. The hole marked C is for the LED, and those marked B are for component mounting screws. The touchscreen is mounted directly to the back of the metal panel. Spacers are needed for the switch and encoder panels, to ensure the keycaps protrude a few millimetres. The spacers are 6mm if a 2mm Perspex cover plate is used, or 8mm for a decal. The ‘wings’ on the touch panel cutout provide clearance for the TFT connector pins, which should be filed down or snipped on the TFT module so that they don’t touch the cover panel or decal. If a Perspex cover panel is used, a printed paper label sits behind the clear piece of Perspex to protect against screw-head damage. Once you’ve finished mounting everything to the front panel, your Load should be ready for calibration. Calibration A power supply capable of providing more than 12V at 1A is required for calibration. Higher voltage and current capacity will result in more accurate calibration. Set the Load’s voltage setting at least 5V higher than your supply’s voltage to avoid the Load going into voltage limiting. Connect an accurate ammeter in series with the Load, set the current to the desired test current and switch on the Load. Follow the current calibration instructions in the Load user manual. Repeat with a voltmeter across the load for voltage calibration. Also calibrate the thermistor now, if you didn’t do it earlier. Using the Load Screen 10: the main screen displayed on the Load. 96 Silicon Chip Australia's electronics magazine The manual included in the project download package describes the opersiliconchip.com.au Fig.18: the touchscreen mounts directly behind the mounting panel. 6-8mm spacers are needed for the switch panels, so that the keycaps protrude a few millimetres from the finished front panel. The location of the encoder cutout shown is for the encoder mounted at the lower location on the control board. ation of the WiFi DC Load in detail. Most functions can be accessed from the instrument’s front panel, via the browser interface or using TestController or another SCPI control application. Logged data is downloaded via the browser interface in CSV format. The web browser interface is comprehensive, as shown in Screen 8, mirroring all settings and readings of the siliconchip.com.au touch screen other than calibration and communication. You can find the Load’s IP address in the touch screen’s Settings → Comms menu; communication is not encrypted. A TestController instrument definition file for the load is included in the project downloads. It has a device popup (Screen 9) with the most common settings and controls available. Australia's electronics magazine TestController has its own logging and analysis functions. To limit the interaction between the automatic update cycle of values on the control panel and web interface, and the ability to set parameters in TestController, the update cycle is set to 20 seconds. Values changed elsewhere and readings will update on this cycle. SC October 2022  97 SILICON CHIP .com.au/shop ONLINESHOP HOW TO ORDER INTERNET (24/7) PAYPAL (24/7) eMAIL (24/7) MAIL (24/7) PHONE – (9-5:00 AET, Mon-Fri) siliconchip.com.au/Shop silicon<at>siliconchip.com.au silicon<at>siliconchip.com.au PO Box 139, COLLAROY, NSW 2097 (02) 9939 3295, +612 for international You can also pay by cheque/money order (Orders by mail only) or bank transfer. Make cheques payable to Silicon Chip. 10/22 YES! You can also order or renew your Silicon Chip subscription via any of these methods as well! The best benefit, apart from the magazine? Subscribers get a 10% discount on all orders for parts. PRE-PROGRAMMED MICROS For a complete list, go to siliconchip.com.au/Shop/9 $10 MICROS $15 MICROS 24LC32A-I/SN ATmega328P ATmega328P-AUR ATtiny85V-10PU ATtiny816 PIC10F202-E/OT PIC10LF322-I/OT PIC12F1572-I/SN PIC12F617-I/P Digital FX Unit (Apr21) Si473x FM/AM/SW Digital Radio (Jul21), 110dB RF Attenuator (Jul22) RGB Stackable LED Christmas Star (Nov20) Shirt Pocket Audio Oscillator (Sep20) ATtiny816 Development/Breakout Board (Jan19) Ultrabrite LED Driver (with free TC6502P095VCT IC, Sep19) Range Extender IR-to-UHF (Jan22) LED Christmas Ornaments (Nov20; versions), Nano TV Pong (Aug21) Model Railway Level Crossing (two required – $15/pair) (Jul21) Range Extender UHF-to-IR (Jan22) PIC12F617-I/SN Model Railway Carriage Lights (Nov21) PIC12F675-I/P Heater Controller (Apr18), Useless Box IC3 (Dec18) Train Chuff Sound Generator (Oct22) PIC12F675-I/SN Tiny LED Xmas Tree (Nov19) PIC16F1455-I/P Digital Interface Module (Nov18), GPS Finesaver (Jun19) Digital Lighting Controller Slave (Dec20), Auto Train Controller (Oct22) PIC16F1455-I/SL Ol’ Timer II (Jul20), Battery Multi Logger (Feb21) PIC16LF1455-I/P New GPS-Synchronised Analog Clock (Sep22) PIC16F1459-I/P 20A DC Motor Speed Controller (Jul21) Fan Controller & Loudspeaker Protector (Feb22) Secure Remote Mains Switch Receiver (Jul22) PIC16F1459-I/SO Multimeter Calibrator (Jul22), Buck/Boost Charger Adaptor (Oct22) PIC16F15214-I/SN Improved SMD Test Tweezers (Apr22) PIC16F1705-I/P Flexible Digital Lighting Controller (Oct20) Digital Lighting Controller Translator (Dec21) PIC16LF15323-I/SL Secure Remote Mains Switch Transmitter (Jul22) ATSAML10E16A-AUT PIC16F18877-I/P PIC16F88-I/P High-Current Battery Balancer (Mar21) USB Cable Tester (Nov21) UHF Repeater (May19), Six Input Audio Selector (Sep19) Battery Charge Controller (Dec19 / Jun22) Railway Semaphore (Apr22) PIC24FJ256GA702-I/SS Wide-Range Ohmmeter (Aug22) PIC32MM0256GPM028-I/SS Super Digital Sound Effects (Aug18) PIC32MX170F256D-501P/T 44-pin Micromite Mk2 (Aug14), 4DoF Simulation Seat (Sep19) PIC32MX170F256B-50I/SP Micromite LCD BackPack V1-V3 (Feb16 / May17 / Aug19) RCL Box (Jun20), Digital Lighting Controller Micromite Master (Nov20) Advanced GPS Computer (Jun21), Touchscreen Digital Preamp (Sep21) PIC32MX170F256B-I/SO Battery Multi Logger (Feb21), Battery Manager BackPack (Aug21) PIC32MX270F256B-50I/SP ASCII Video Terminal (Jul14), USB M&K Adaptor (Feb19) $20 MICROS ATmega644PA-AU PIC32MX470F512H-I/PT PIC32MX470F512H-120/PT PIC32MX470F512L-120/PT PIC32MX795F512H-80I/PT AM-FM DDS Signal Generator (May22) Stereo Echo/Reverb (Feb 14), Digital Effects Unit (Oct14) Micromite Explore 64 (Aug 16), Micromite Plus (Nov16) Micromite Explore 100 (Sep16) Touchscreen Audio Recorder (Jun14) dsPIC33FJ64MC802-E/SP dsPIC33FJ128GP306-I/PT 1.5kW Induction Motor Speed Controller (Aug13) CLASSiC DAC (Feb13) $25 MICROS $30 MICROS PIC32MZ2048EFH064-I/PT DSP Crossover/Equaliser (May19), Low-Distortion DDS (Feb20) DIY Reflow Oven Controller (Apr20), Dual Hybrid Supply (Feb22) KITS, SPECIALISED COMPONENTS ETC BUCK/BOOST CHARGER ADAPTOR KIT (CAT SC6512) (OCT 22) Includes everything in the parts list (see page 64) except the Buck/Boost LED Driver (see below; Cat SC6292). $40.00 - laser-cut acrylic cover panel (SC6567) $2.50 - cyan/blue 1.3-inch OLED (SC5026) $15.00 - white 1.3-inch OLED (SC6511) $15.00 WiFi PROGRAMMABLE DC LOAD (SEP 22) Short Form Kit: includes all SMDs, the power Mosfets, four 0.02W 3W resistors and the VXO7805 regulator module (Cat SC6399; see page 39) - laser-cut 3mm clear acrylic side panel (SC6514) - 3.5-inch TFT LCD touchscreen (Cat SC5062) MINI LED DRIVER (SEP 22) NEW GPS-SYNCHRONISED ANALOG CLOCK (SEP 22) Complete Kit: includes everything in the parts list (Cat SC6405; see page 81) - XL6009 4A DC-DC boost module (Cat SC6546; red PCB) Complete Kit: includes everything in the parts list (Cat SC6472; see page 63) - VK2828U7G5LF GPS module with antenna and cable (Cat SC3362) WIDE-RANGE OHMMETER (CAT SC4663) $85.00 $7.50 $35.00 $25.00 $6.00 $55.00 $25.00 (AUG 22) Partial Kit: includes the PCB, programmed micro, all SMDs, most semiconductors, PPS capacitors and calibration resistors $75.00 - 16x2 alphanumeric LCD with blue backlighting (Cat 5759) $10.00 VGA PICOMITE KIT (CAT SC6417) (JUL 22) Complete kit with everything needed to assemble the board, you just require a few external parts such as a power supply, keyboard and monitor $35.00 MULTIMETER CALIBRATOR KIT (CAT SC6406) (JUL 22) 110dB RF ATTENUATOR SHORT-FORM KIT (CAT SC6420) (JUL 22) BUCK-BOOST LED DRIVER KIT (CAT SC6292) (JUN 22) SPECTRAL SOUND MIDI SYNTH KIT (CAT SC6261) (JUN 22) Complete kit with everything needed to assemble the board Includes the PCB, programmed micro, OLED and all other on-board parts Complete kit with everything needed to assemble the board Complete kit including all programmed PICs (no case or power supply) $45.00 $75.00 $80.00 $200.00 siliconchip.com.au/Shop/ IMPROVED SMD TEST TWEEZERS KIT (CAT SC5934) (APR 22) RASPBERRY PI PICO BACKPACK KIT (CAT SC6075) (MAR 22) 500W AMPLIFIER HARD-TO-GET PARTS (CAT SC6019) (APR 22) CAPACITOR DISCHARGE WELDER (MAR 22) SMD TRAINER COMPLETE KIT (CAT SC5260) (DEC 21) HUMMINGBIRD AMPLIFIER (CAT SC6021) (DEC 21) USB CABLE TESTER KIT (CAT SC5966) (NOV 21) Complete kit with PCBs, all onboard parts, new microcontroller and gold-plated header pins to use for the tips. Does not include a lithium coin cell $35.00 Complete kit, includes all parts except the optional DS3231 IC $80.00 All the parts marked with a red dot in the parts list, including the 12 output transistors, driver transistors, VAS transistors, input pair (2SA1312), BAV21 & UF4003 diodes, TL431 ICs, 75pF capacitor, E96 series resistors and 10kW 1W resistor $200.00 Parts for the Power Supply – includes the power supply PCB, IC1-3, D1, the 1W shunt and sole SMD capacitor (Cat SC6224) $25.00 Parts for the ESM – includes one ESM PCB, IC8, Q3 & Q4 (IRFB7434G), D9 plus the SMD capacitors and resistors (Cat SC6225) → 8-14 sets typically needed $20.00ea Includes PCB & all on-board components, except for a TQFP-64 footprint device Hard-to-get parts includes: two 0.22W 5W resistors; plus one each of an MJE15034G, MJE15035G, KSC3503DS & 220pF 250V C0G ceramic capacitor Short form kit with everything except case and AA cells VARIOUS MODULES & PARTS - INA282AIDR + 20mW shunt (30V 2A Bench Supply, Oct22, SC6578) - ISD1820-based recording module (Auto Train Controller, Oct22, SC5081) - 70W LED panel (cool white, SC6307 | warm white, SC6308) - 0.96in SSD1306-based yellow/blue OLED (AM-FM DDS, May22, SC6421) - Pulse-type rotary encoder (AM-FM DDS, May22, SC5601) - DS3231 real-time clock SOIC-16 IC (Pico BackPack, Mar22) - DS3231MZ real-time clock SOIC-8 IC (Pico BackPack, Mar22) - 4-pin PWM fan header (Fan Controller, Feb22) - 64x32 pixel white 0.49in OLED (SMD Test Tweezers, Oct21) - VK2828U7G5LF GPS module (Advanced GPS Computer, Jun21) $20.00 $15.00 $110.00 $10.00 $7.50 $19.50 $10.00 $3.00 $7.50 $10.00 $1.00 $10.00 $25.00 *Prices valid for month of magazine issue only. All prices in Australian dollars and include GST where applicable. # P&P prices are within Australia. Overseas? Place an order on our website for a quote. PRINTED CIRCUIT BOARDS & CASE PIECES PRINTED CIRCUIT BOARD TO SUIT PROJECT ULTRABRITE LED DRIVER HIGH RESOLUTION AUDIO MILLIVOLTMETER PRECISION AUDIO SIGNAL AMPLIFIER SUPER-9 FM RADIO PCB SET ↳ CASE PIECES & DIAL TINY LED XMAS TREE (GREEN/RED/WHITE) HIGH POWER LINEAR BENCH SUPPLY ↳ HEATSINK SPACER (BLACK) DIGITAL PANEL METER / USB DISPLAY ↳ ACRYLIC BEZEL (BLACK) UNIVERSAL BATTERY CHARGE CONTROLLER BOOKSHELF SPEAKER PASSIVE CROSSOVER ↳ SUBWOOFER ACTIVE CROSSOVER ARDUINO DCC BASE STATION NUTUBE VALVE PREAMPLIFIER TUNEABLE HF PREAMPLIFIER 4G REMOTE MONITORING STATION LOW-DISTORTION DDS (SET OF 5 BOARDS) NUTUBE GUITAR DISTORTION / OVERDRIVE PEDAL THERMAL REGULATOR INTERFACE SHIELD ↳ PELTIER DRIVER SHIELD DIY REFLOW OVEN CONTROLLER (SET OF 3 PCBS) 7-BAND MONO EQUALISER ↳ STEREO EQUALISER REFERENCE SIGNAL DISTRIBUTOR H-FIELD TRANSANALYSER CAR ALTIMETER RCL BOX RESISTOR BOARD ↳ CAPACITOR / INDUCTOR BOARD ROADIES’ TEST GENERATOR SMD VERSION ↳ THROUGH-HOLE VERSION COLOUR MAXIMITE 2 PCB (BLUE) ↳ FRONT & REAR PANELS (BLACK) OL’ TIMER II PCB (RED, BLUE OR BLACK) ↳ ACRYLIC CASE PIECES / SPACER (BLACK) IR REMOTE CONTROL ASSISTANT PCB (JAYCAR) ↳ ALTRONICS VERSION USB SUPERCODEC ↳ BALANCED ATTENUATOR SWITCHMODE 78XX REPLACEMENT WIDEBAND DIGITAL RF POWER METER ULTRASONIC CLEANER MAIN PCB ↳ FRONT PANEL NIGHT KEEPER LIGHTHOUSE SHIRT POCKET AUDIO OSCILLATOR ↳ 8-PIN ATtiny PROGRAMMING ADAPTOR D1 MINI LCD WIFI BACKPACK FLEXIBLE DIGITAL LIGHTING CONTROLLER SLAVE ↳ FRONT PANEL (BLACK) LED XMAS ORNAMENTS 30 LED STACKABLE STAR ↳ RGB VERSION (BLACK) DIGITAL LIGHTING MICROMITE MASTER ↳ CP2102 ADAPTOR BATTERY VINTAGE RADIO POWER SUPPLY DUAL BATTERY LIFESAVER DIGITAL LIGHTING CONTROLLER LED SLAVE BK1198 AM/FM/SW RADIO MINIHEART HEARTBEAT SIMULATOR I’M BUSY GO AWAY (DOOR WARNING) BATTERY MULTI LOGGER ELECTRONIC WIND CHIMES ARDUINO 0-14V POWER SUPPLY SHIELD HIGH-CURRENT BATTERY BALANCER (4-LAYERS) MINI ISOLATED SERIAL LINK REFINED FULL-WAVE MOTOR SPEED CONTROLLER DIGITAL FX UNIT PCB (POTENTIOMETER-BASED) ↳ SWITCH-BASED ARDUINO MIDI SHIELD ↳ 8X8 TACTILE PUSHBUTTON SWITCH MATRIX HYBRID LAB POWER SUPPLY CONTROL PCB ↳ REGULATOR PCB VARIAC MAINS VOLTAGE REGULATION DATE SEP19 OCT19 OCT19 NOV19 NOV19 NOV19 NOV19 NOV19 NOV19 NOV19 DEC19 JAN20 JAN20 JAN20 JAN20 JAN20 FEB20 FEB20 MAR20 MAR20 MAR20 APR20 APR20 APR20 APR20 MAY20 MAY20 JUN20 JUN20 JUN20 JUN20 JUL20 JUL20 JUL20 JUL20 JUL20 JUL20 AUG20 NOV20 AUG20 AUG20 SEP20 SEP20 SEP20 SEP20 SEP20 OCT20 OCT20 OCT20 NOV20 NOV20 NOV20 NOV20 NOV20 DEC20 DEC20 DEC20 JAN21 JAN21 JAN21 FEB21 FEB21 FEB21 MAR21 MAR21 APR21 APR21 APR21 APR21 APR21 MAY21 MAY21 MAY21 PCB CODE Price 16109191 $2.50 04108191 $10.00 04107191 $5.00 06109181-5 $25.00 SC5166 $25.00 16111191 $2.50 18111181 $10.00 SC5168 $5.00 18111182 $2.50 SC5167 $2.50 14107191 $10.00 01101201 $10.00 01101202 $7.50 09207181 $5.00 01112191 $10.00 06110191 $2.50 27111191 $5.00 01106192-6 $20.00 01102201 $7.50 21109181 $5.00 21109182 $5.00 01106193/5/6 $12.50 01104201 $7.50 01104202 $7.50 CSE200103 $7.50 06102201 $10.00 05105201 $5.00 04104201 $7.50 04104202 $7.50 01005201 $2.50 01005202 $5.00 07107201 $10.00 SC5500 $10.00 19104201 $5.00 SC5448 $7.50 15005201 $5.00 15005202 $5.00 01106201 $12.50 01106202 $7.50 18105201 $2.50 04106201 $5.00 04105201 $7.50 04105202 $5.00 08110201 $5.00 01110201 $2.50 01110202 $1.50 24106121 $5.00 16110202 $20.00 16110203 $20.00 16111191-9 $3.00 16109201 $12.50 16109202 $12.50 16110201 $5.00 16110204 $2.50 11111201 $7.50 11111202 $2.50 16110205 $5.00 CSE200902A $10.00 01109201 $5.00 16112201 $2.50 11106201 $5.00 23011201 $10.00 18106201 $5.00 14102211 $12.50 24102211 $2.50 10102211 $7.50 01102211 $7.50 01102212 $7.50 23101211 $5.00 23101212 $10.00 18104211 $10.00 18104212 $7.50 10103211 $7.50 For a complete list, go to siliconchip.com.au/Shop/8 PRINTED CIRCUIT BOARD TO SUIT PROJECT ADVANCED GPS COMPUTER PIC PROGRAMMING HELPER 8-PIN PCB ↳ 8/14/20-PIN PCB ARCADE MINI PONG Si473x FM/AM/SW DIGITAL RADIO 20A DC MOTOR SPEED CONTROLLER MODEL RAILWAY LEVEL CROSSING COLOUR MAXIMITE 2 GEN2 (4 LAYERS) BATTERY MANAGER SWITCH MODULE ↳ I/O EXPANDER NANO TV PONG LINEAR MIDI KEYBOARD (8 KEYS) + 2 JOINERS ↳ JOINER ONLY (1pc) TOUCHSCREEN DIGITAL PREAMP ↳ RIBBON CABLE / IR ADAPTOR 2-/3-WAY ACTIVE CROSSOVER TELE-COM INTERCOM SMD TEST TWEEZERS (3 PCB SET) USB CABLE TESTER MAIN PCB ↳ FRONT PANEL (GREEN) MODEL RAILWAY CARRIAGE LIGHTS HUMMINGBIRD AMPLIFIER DIGITAL LIGHTING CONTROLLER TRANSLATOR SMD TRAINER 8-LED METRONOME 10-LED METRONOME REMOTE CONTROL RANGE EXTENDER UHF-TO-IR ↳ IR-TO-UHF 6-CHANNEL LOUDSPEAKER PROTECTOR ↳ 4-CHANNEL FAN CONTROLLER & LOUDSPEAKER PROTECTOR SOLID STATE TESLA COIL (SET OF 2 PCBs) REMOTE GATE CONTROLLER DUAL HYBRID POWER SUPPLY SET (2 REGULATORS) ↳ REGULATOR ↳ FRONT PANEL ↳ CPU ↳ LCD ADAPTOR ↳ ACRYLIC LCD BEZEL RASPBERRY PI PICO BACKPACK AMPLIFIER CLIPPING DETECTOR CAPACITOR DISCHARGE WELDER POWER SUPPLY ↳ CONTROL PCB ↳ ENERGY STORAGE MODULE (ESM) PCB 500W AMPLIFIER MODEL RAILWAY SEMAPHORE CONTROL PCB ↳ SIGNAL FLAG (RED) AM-FM DDS SIGNAL GENERATOR SLOT MACHINE HIGH-POWER BUCK-BOOST LED DRIVER ARDUINO PROGRAMMABLE LOAD SPECTRAL SOUND MIDI SYNTHESISER REV. UNIVERSAL BATTERY CHARGE CONTROLLER VGA PICOMITE SECURE REMOTE MAINS SWITCH RECEIVER ↳ TRANSMITTER (1.0MM THICKNESS) MULTIMETER CALIBRATOR 110dB RF ATTENUATOR WIDE-RANGE OHMMETER WiFi PROGRAMMABLE DC LOAD MAIN PCB ↳ DAUGHTER BOARD ↳ CONTROL BOARD MINI LED DRIVER NEW GPS-SYNCHRONISED ANALOG CLOCK DATE JUN21 JUN21 JUN21 JUN21 JUL21 JUL21 JUL21 AUG21 AUG21 AUG21 AUG21 AUG21 AUG21 SEP21 SEP21 OCT21 OCT21 OCT21 NOV21 NOV21 NOV21 DEC21 DEC21 DEC21 JAN22 JAN22 JAN22 JAN22 JAN22 JAN22 FEB22 FEB22 FEB22 FEB22 FEB22 FEB22 FEB22 FEB22 FEB22 MAR22 MAR22 MAR22 MAR22 MAR22 APR22 APR22 APR22 MAY22 MAY22 JUN22 JUN22 JUN22 JUN22 JUL22 JUL22 JUL22 JUL22 JUL22 AUG22 SEP22 SEP22 SEP22 SEP22 SEP22 PCB CODE 05102211 24106211 24106212 08105211 CSE210301C 11006211 09108211 07108211 11104211 11104212 08105212 23101213 23101214 01103191 01103192 01109211 12110121 04106211/2 04108211 04108212 09109211 01111211 16110206 29106211 23111211 23111212 15109211 15109212 01101221 01101222 01102221 26112211/2 11009121 SC6204 18107211 18107212 01106193 01106196 SC6309 07101221 01112211 29103221 29103222 29103223 01107021 09103221 09103222 CSE211002 08105221 16103221 04105221 01106221 04107192 07107221 10109211 10109212 04107221 CSE211003 04109221 04108221 04108222 18104212 16106221 19109221 Price $7.50 $5.00 $7.50 $35.00 $7.50 $7.50 $5.00 $15.00 $5.00 $2.50 $2.50 $5.00 $1.00 $12.50 $2.50 $15.00 $30.00 $10.00 $7.50 $5.00 $2.50 $5.00 $5.00 $5.00 $5.00 $7.50 $2.50 $2.50 $7.50 $5.00 $5.00 $7.50 $20.00 $25.00 $7.50 $2.50 $5.00 $2.50 $5.00 $5.00 $2.50 $5.00 $5.00 $5.00 $25.00 $2.50 $2.50 $7.50 $5.00 $5.00 $5.00 $7.50 $7.50 $5.00 $7.50 $2.50 $5.00 $5.00 $7.50 $7.50 $5.00 $10.00 $2.50 $5.00 BUCK/BOOST CHARGER ADAPTOR 30V 2A BENCH SUPPLY MAIN PCB ↳ FRONT PANEL CONTROL PCB AUTO TRAIN CONTROLLER ↳ TRAIN CHUFF SOUND GENERATOR PIC16F18xxx BREAKOUT BOARD (DIP-VERSION) ↳ SOIC-VERSION AVR64DD32 BREAKOUT BOARD OCT22 OCT22 OCT22 OCT22 OCT22 OCT22 OCT22 OCT22 14108221 04105221 04105222 09109221 09109222 24110222 24110225 24110223 $5.00 $7.50 $2.50 $2.50 $2.50 $2.50 $2.50 $2.50 NEW PCBs We also sell an A2 Reactance Wallchart, RTV&H DVD, Vintage Radio DVD plus various books at siliconchip.com.au/Shop/3 Vintage Radio STC model 510 portable superhet from 1939 By Assoc. Prof. Graham Parslow This radio is not an outstanding design icon, nor is it among the most collectable Australian radios. However, it is rugged and an excellent performer. Although described as portable, it is really more like “luggable” at 10.2kg. The circuitry and chassis work are first-class, and the vinyl fabric covering was innovative and modern at the time. W orking on this radio took me back to my youth in country South Australia, but more on that later. First, let’s look at the electronic side of it. Electronic design The radio is a conventional superhet with the bonus of RF amplification. One significant problem for all portables in the 1930s was the antenna. Some radios like the Astor Porta had a telescopic antenna, similar to contemporary FM radios. For the model 510, a loop antenna is built into the back panel, with the ends terminating on the two hinges. This arrangement can be seen in the picture of the bare case from the rear with stubs of the connecting wires soldered to the hinge mounts. The upper yellow wire leads to the aerial coil, while the lower black wire goes to ground (the chassis). In many valve portables, the loop antenna is part of a tuned circuit, but not in this case. This means that the radio still functions with the back panel removed. The loop antenna is directional in receiving radio waves, and it can be rotated on the hinges to optimise the reception of a particular station. However, this is not a user-friendly solution because the rear panel is wide (~370mm) and bumps into any close items as it swings. It also looks untidy with the rear open. To overcome this, and get better reception, I connected an additional aerial wire during restoration. The designers of this radio took care to produce an aesthetically pleasing chassis by lining up the three tuned-circuit coils in identical canisters placed next to the capacitor gang that tuned each coil. Few portable radio chassis are as neat as this one. Circuit details The original circuit diagram is reproduced in Fig.1. The aerial coil has a tuned secondary connected to one gang of the three-gang tuning The STC model 510 has a hinged front and back cover with a small pocket, in the front cover, that is used to house aerial equipment. The set measures 375 x 295 x 300mm and comes in a “hogskin” finish cabinet. siliconchip.com.au An advert for the STC model 510 from Australasian Radio World, November 1939, page 42. siliconchip.com.au Australia's electronics magazine October 2022  101 Fig.1: the circuit diagram for the STC model 510 portable superhet radio. The set has a standard intermediate frequency of 455kHz. capacitor. Three gangs are the first clue that the radio has an RF amplification stage to optimise the reception of weak stations. RF amplification is essential for farm use (ie, in distant rural areas) while also compensating for a minimal aerial. However, I have encountered non-RF amplified radios with a threegang capacitor when the manufacturer decided not to modify the mountings or change inventory to use a two-gang capacitor. Three gangs can also be found when both sides of the aerial coil are tuned. Confirmation of an RF stage comes from counting the valves, in this case, five in total. That is equivalent to a sixvalve mains radio as they require an additional rectifier valve in the power supply. As for the coils, the third coil is for the local oscillator, while the two larger canisters are the IF transformers. All valves except the output pentode are shielded in two-section metal cylinders. In keeping with a high-end radio, all of the metalwork is plated with a copper-hued finish that is characteristic of STC chassis of the time. The RF preamplifier is a 1P5 tube. Specifically, for this radio, the valve is a 1P5GT where G indicates glass (not metal) construction and T indicates that the shape is tubular rather than bulb-like. The prefix 1 indicates that the filament voltage is notionally 1V (in practice, it is 1.4V). Following the mixer-oscillator stage, using a 1A7G The top side of the restored STC 510 chassis. 102 Silicon Chip Australia's electronics magazine siliconchip.com.au The chassis was supplied in a fairly battered condition, with cobwebs abound and the cabinet frayed. The loop antenna is wound into the back panel. valve, a second 1P5 valve is used as an IF amplifier. The valves are all of short stature and have octal bases. In this case, the reduced size is of little advantage because the valves are shielded by conventionally-sized aluminium cans. A 1H5 valve provides audio signal rectification and preamplification. In this application, there is only one diode; there is no second diode to generate an AGC signal. Instead, a 1MW resistor from the detected audio provides AGC to the grids of both 1P5 valves. The volume control potentiometer (500kW) feeds the signal to the grid of the 1H5 audio preamplifier. A simple top-cut tone control is connected to the anode of the 1C5 amplifier valve. The 1C5 data sheet claims its maximum output as 500mW with 150V on the anode. In this radio, the anode is at 90V, so it can only produce 200mW before clipping. It is surprising how The underside of the restored STC 510 chassis. siliconchip.com.au Australia's electronics magazine 200mW can even be excessively noisy in a quiet environment. The speaker in this radio is a 6-inch STC unit with high efficiency to make the most of the limited audio power available. A sculpted space at the front of the chassis allows the speaker to recess into the chassis. Two sides of the metal frame are cut back to allow the speaker to clear the large dial assembly. The large dial size is due to reusing the escutcheon and tuning The STC model 510 is described as having an “extralarge” dial, and station names are radially grouped per state. arrangement of the STC table-top model 528. Restoration It was a welcome surprise that the speaker cone was in pristine condition. In general, battery-powered portable radios survive in better condition than their mains-powered cousins. This is because there are no voltages over 90V, and little heat is generated to stress components. The only electrolytic capacitor in this radio is a low-voltage cathode bypass. Hooking up bench supplies of 90V and 1.5V instantly produced a working radio. Dropping the HT to 80V produced little degradation in the performance, but dropping the filament voltage to 1.3V noticeably cut its output. Through the 1920s, filament voltage control by a rheostat was often used as the volume control, with the advantage of conserving battery capacity at lower output levels. The STC valve filaments took 260mA <at> 1.5V (0.39W) and the HT required 14mA <at> 90V (1.26W) for a total power consumption of 1.65W. Even with batteries lasting months, it was expensive to buy two new 45V batteries plus a heavy-duty 1.5V battery. When this radio was new, the 45V batteries used were likely to be the Eveready type 762 that packaged thirty The set uses a 6-inch permanent magnet speaker branded by the same company. The chassis has a cut-out to make room for the speaker to mount next to the dial. Compared to the state of the rest of the set, the speaker was in pristine condition initially. individual 1.5V cells. The filament battery was likely to be an Eveready type 741. The STC model 510 has four battery wires ending with one centimetre of bare wire. The wires are clearly labelled and would be joined to brass Fahnstock clips on the top of the batteries. Dedicated plugs and sockets made battery connection more foolproof at a later time. To operate the STC 510, there are three current options for power: 1) 60 AA cells to produce 90V (or 10 x 9V batteries) plus D cells for 1.5V. 2) A DC-to-DC converter to generate the HT from a lower-voltage battery, using an oscillator and transformer. 3) A mains-powered battery eliminator. I chose option 3. Looking through my bits boxes, I found a salvaged transformer from which I made a voltage doubler based HT supply (see Fig.2) plus a separate 1.5V source from a different transformer. The 1.5V supply came from a full-wave rectified source of 9.5V DC reduced to 1.5V by a prebuilt step-down regulator module. With this, the radio performed flawlessly. I built the eliminator onto a piece of Masonite and placed it in the radio’s battery compartment, leaving space to pack the mains cord and aerial wire. Condition as received The pictures hardly convey the Australia's electronics magazine siliconchip.com.au ► The battery eliminator (partial circuit shown in Fig.2) was designed from a salvaged transformer and other components to power the set. The set came with a little bonus in the ► form of a Broadcast Listener’s licence. degraded appearance of the radio when I saw it in a large emporium of pre-loved objects at Minlaton, South Australia. The proprietor had a great knowledge of his stock and showed me several other radios that I was able to resist for various reasons. But this orphan radio struck a chord with me, and we decided that an exchange of $50 would make us both happy. A bonus attraction was a moth-eaten bundle of papers in the radio’s front panel pocket. The papers were the seven paid-up Broadcast Listener’s licences from 1949 to 1956. The most intact licence covered 1949-1950 and cost one pound (written as 20/- if you can read the handwriting). The fee rose to two pounds in 1952. That fee was subsequently increased when a combined radio and TV licence was sold from 1956 onward. Every individual radio needed a licence. The licence fees were substantial enough for evaders to ingenuously hide radios, TVs and aerials from inspectors. The saga of licences ended in 1975 when Gough Whitlam said “enough”. Johann Launer of Anderson St, Yorketown, SA was the licensee. The S preceding the license number indicates SA and other states had their own identifier. I was born in 1948, and for the period covered by the listener’s licences, I lived in Edithburgh, ten miles (16km) from where this radio was being used. Anderson Street is on the fringe of Yorketown, next to an open wheat field with a salt lake in the middle. So the location is ultra-quiet, and 200mW of audio would suffice for comfortable listening. I passed Anderson Street each school day from 1961-1964 when I rode a bus to Yorketown Area School. Discovering the contents of those licences brought back happy memories of the period. Restoring the vinyl The vinyl covering at the base was almost completely destroyed (dissolved) by the radio lying in a pool of oil. I scrubbed all of the intact vinyl surfaces with detergent, and they cleaned up well, while the oil-affected vinyl washed away. I used PVA glue to reattach the loose vinyl, but this left several bare timber patches. I used Montmartre-brand artist’s oil paint to paint over these spots in a colour that matched the original vinyl. I then coated the whole radio with clear polyurethane to get an even surface lustre. And so it was that this neglected radio came to have a semblance of its SC former glory. Fig.2: the circuit for a mains-powered battery eliminator that can be used to produce the HT supply for this set. The valves used in the set from left-to-right: 1C5, 1H5, 1P5, 1A7 and another 1P5. All these valves have 1.4V filaments. siliconchip.com.au Australia's electronics magazine October 2022  105 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 Noisy starter causing cam sensor fault codes I’ve been a reader of your magazine for many years, and I’m wondering if you or another reader can help me with a tricky car problem. I have a 2008 Mazda BT50 2.5L Diesel model. When the car is started, the engine fault light sometimes comes on with fault P0340 (cam angle sensor). I’ve replaced the sensor to no avail. I have tested the resistance of the wiring and wiggle tested the looms without finding any problems. Out of desperation, I sent the engine management computer to a reputable place in Melbourne and despite them saying they had found and fixed a fault, the same problem occurred. I then came across a document from JAS explaining that ripple or harmonics from the starter motor causes the computer to see a fault. I have since changed the starter motor, but the same problem occurs if the car cranks more than five or so times. If it starts straight away, the fault light doesn’t come on. The cam angle sensor is a 5V Hall Effect sensor producing a square wave. How would I filter any hash or harmonics from the line to the car computer? (L. E., Darwin, NT) ● Filtering the Hall Effect sensor output could cause a phase shift that will then give inaccurate timing for the cam angle sensor. However, you could experiment with some capacitor values. A 10nF MKT polyester capacitor between the Hall Effect sensor output and chassis shouldn’t have much of an effect on the cam angle reading. It depends on the sensor pull-up resistor value. Assuming a 1kΩ resistance, the 10nF capacitor should be suitable as it will only cause a 10µs delay. Additionally, you could filter the 5V supply at the Hall Effect sensor, as that could be the most likely path for noise to get into the Hall Effect output. A 100nF capacitor may help. Also make sure that the ground for the Hall Effect 106 Silicon Chip sensor has a low resistance reading to the vehicle chassis. Collection of early articles wanted I just finished reading your articles on the History of Silicon Chip (August & September 2022; siliconchip.au/ Series/385). An editor of one of the other magazines described Silicon Chip as a boutique magazine and said it wouldn’t last. You proved them wrong. Initially, you started a series of articles on “The Evolution of the Electric Railways”. Was this ever produced as a booklet? I became interested in electric trains when I joined Connex and was able to locate back issues in the library. I gave my original issues away when I lost interest in electronics in the 1990s. (I. F., Wantirna South, Vic) ● The Evolution of Electric Railways is part of the first block of Silicon Chip PDFs on USB (November 1987 to December 1994); this is the easiest way to read all those articles: www. siliconchip.au/shop/digital_pdfs 2V RMS test oscillator wanted at 1kHz I’d like to know if your Shirt Pocket DDS Oscillator (September 2020 issue; siliconchip.au/Article/14563) is capable of 2V RMS at 1kHz for audio testing. (B. T., Thomastown, Vic) ● The specifications panel on the second page of the article states that the maximum output level is 530mV RMS with the specified 3V battery. If you ran it from a regulated 5.25V supply, that would increase to nearly 1V RMS, but that is not as high as you want. Our Roadies’ Test Oscillator (June 2020; siliconchip.au/Article/14466) delivers 1.2V RMS from a 3V supply, so it might provide the 2V RMS you want if run from a 5V regulated supply (eg, a 9V battery feeding a 5V LDO linear regulator). However, it is a fixed frequency design at 440Hz by default. You would need to adjust some component values to set it to 1kHz. Australia's electronics magazine Our calculations show that changing the three 6.8kΩ resistors to 3kΩ each should give you close to 1kHz, although some experimentation may be needed. For example, if you try 3kΩ and get a frequency close to 900Hz, swap them for 2.7kΩ resistors (ie, 10% lower in value). 5kW dual-gang log motorised pot substitute I’m having trouble sourcing the 5kΩ motorised pot for the Ultra LowNoise Stereo Preamp (March & April 2019; siliconchip.au/Series/333). (D. F., Aberdeen, NSW) ● While linear pots are not ideal for volume control, we can’t find any suitable logarithmic taper substitutes. So, you could use the PRM162-K415K503A2 50kΩ linear dual-gang motorised pot instead, which is currently in stock at Mouser. If using that pot, install resistors R1 & R2 on the preamp board with values around 7.5kΩ. 8.2kΩ or 10kΩ probably being OK. That will give you an overall resistance below 10kΩ for low noise, with a relatively loglike response. It won’t be as good as a proper log pot, but better than just using a linear pot. Super-9 FM Radio alignment questions In constructing the Super-9 FM Radio (November & December 2019; siliconchip.au/Series/340), I have arrived at the alignment procedure for the IF circuitry. Measuring with my multimeter on the Signal and GND test points, I initially got a reading of 3.74V; by adjusting the slug in T1, I could increase that voltage figure a little, but it never got to 4V. Next, connecting the multimeter between TP REF and TP TUNE, I initially found about 0.5V, but I could only reduce it to 0.4V or so by turning the slug of L6, whereas the instructions state that I should adjust L6 to bring this reading to 0V. Why can’t I get the siliconchip.com.au Meet the new & improved Creality CR-X Pro Dual Filament 3D Printer Print detailed two colour prints without the need to swap colours mid-print. New features include automatic bed levelling, high quality power supply, upgraded motherboard and quieter operation. 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Order yours today: jaycar.com.au/p/TL4411 1800 022 888 Confusion over the operation of a bridged amplifier I am inquiring regarding the Compact High-Performance 12V Stereo Amplifier from May 2010 (siliconchip.au/Article/152). I have built two of these units, and they both worked perfectly on completion. But I have a problem bench-­testing them; the uncommon circuit with the inverting/noninverting bipolar arrangement has somewhat confused me. Just to have a look at the waveforms, for my interest, I set up a bench test. I have an oscilloscope and a GW Instek function generator, both of which have their BNC connectors referenced to mains Earth. I determined that first, so the set-up used my commercial isolation transformer. I terminated the amplifier outputs to individual 4Ω wirewound resistors on separate heatsinks and connected the output marked negative to the scope return clip lead. The amplifier was powered by the intended 12V SLA battery. This configuration resulted in the instant incineration of the 10Ω resistors at the amplifier inputs connected from the input cable screen to circuit chassis return. I have done this twice now, and in reflection, while typing this up, I can see that the TDA7377V has a differential output, not referenced to the circuit low-side. Also, is the input fuse marked 6.5A such that it fails with reversed polarity and conduction of Q1? (R. S., Emerald, Vic) ● We would not call it an unusual configuration – many amplifiers operate in bridge mode, especially car amplifiers and Class-D amplifiers. Due to the DC offset, you cannot connect a load between a single output terminal and ground. Loads should only be connected between the pairs of output terminals, as you would connect a loudspeaker, so the DC offsets cancel out. We would do the initial testing without a load anyway. Still, that should not affect the 10Ω resistors. They could only burn out if you applied a significant voltage between the input cable screen and power supply ground. We think what happened is the following. You connected the scope Earth clip to the negative output, which sits at around half supply (eg, about 6V with a 12V battery). Then, when you plugged in the signal generator, which is also Earthed, that applied 6V across the 10Ω input resistors. That’s a dissipation of 3.6W (6V2 ÷ 10Ω), so it’s unsurprising they burned out. Adding an isolation transformer won’t help if you plug both the scope and the function generator into the same transformer since they will still share the same ‘Earth’, even if it is floating relative to mains Earth. Connecting one and not the other to the isolation transformer would probably prevent the resistors from burning out. Still, you’re better off connecting the scope Earth to the circuit ground and then individually probing the two bridged outputs. If it’s a digital scope, you can then use the Ch1 - Ch2 (or Ch2 - Ch1) function to show the difference waveform that would appear across the speaker or test load. The 6.5A fuse is just a regular fuse to protect from overload or a short circuit on the board. Q1 prevents a reverse polarity supply from powering the circuit at all. 0V reading between TP REF and TP TUNE? (C. B., Bonville, NSW) ● T1 is adjusted to get a maximum voltage. This can be within the region of 3-4V. So if 3.74V or a little more is the maximum, that is OK. The main thing is to keep the voltage within the 3-4V range and find the peak. As for the adjustment of L6, ensure the correct number of windings are on the core. Also check that L5 and the 100pF capacitor have correct values and that the 3.9kΩ resistor is as specified. Additionally, for L6, make sure there is a connection to the circuit 108 Silicon Chip for the winding. The enamelled wire can sometimes seem to solder but not be stripped of the insulation to make proper electrical contact. 45V 8A Bench Supply transistor mounting I have built the 45V Linear Supply (October-December 2019; siliconchip. au/Series/339), and during the current set-up/calibration procedure, I burnt out the 0.1Ω resistors and my meter leads. After some troubleshooting, I found that transistor Q3 (BD140) was the wrong way around. Australia's electronics magazine After changing all the damaged parts, fixing the fault and recalibrating everything, I repeated the current calibration and found that two of the FJA4313 transistors had failed. They were causing a short to the heatsink. I thought maybe it was just poor alignment with the isolated pad for the heatsink connection. I then went back, took them off, re-tested and checked the solder joint on the board. Everything was OK. I then bought better thermal paste, making sure it wasn’t electrically conductive. I lined everything up (I even made a 3D-printed jig). I tested all the FJAs and found no shorts. I went through all the tests, and again, all passed. But when I got to the current calibration, at about 2A, it failed again. And short to the heatsink again. I plan on starting from scratch again, but I am wondering if that could be my problem, or is it a poor connection between the heatsink and the FJA transistors? (M. M., Glasgow, UK) ● Note that the collectors of Q4-Q7 (FJA4313) are connected to the heatsink (for optimum thermal performance, see p25 in the October 2019 issue). Thus, the transistor collectors should read as a short-circuit to the heatsink, but the heatsink should be floating with respect to ground (and just about everything else). We aren’t sure what’s causing your failure since it is normal for the transistor collectors to measure as short circuits to the heatsink. If you are blowing fuses, there may be a short elsewhere, eg, from the heatsink to the case. Note that our design incorporates a plastic spacer to prevent such contact and also specifies that Nylon screws be used to attach the heatsink to the case. Check that the heatsink is not shorting to anything except the collectors of Q4-Q7. Sourcing transformers for the Magnetometer I just bought the December 2018 online issue with the article on the Incredibly Sensitive Magnetometer (siliconchip.au/Article/11331). I ordered the PCB then, having a good look at the components, I nearly had a heart attack when I realised I would need two transformers worth $180 each. Is there a more affordable solution? siliconchip.com.au Alternatively, is there another project you can think of in another edition for a metal/relic detector? I am more interested in relics, on the beach, in historic locations etc, than gold. (R. B., Ballarat, Vic) ● The Author, Thomas Scarborough, responds: I was delighted to receive this message through Silicon Chip. Any two transformers will do for the sensors. Say, half-amp transformers. I obtained my very big transformers from a home lighting outlet. The lighting was obsolete, and the transformers were going cheap. So the parts list in the magazine specified similar transformers to the ones I had used. There are two things to bear in mind. Firstly, this device detects metal only when it is in motion. Although one moves them over the ground, metal detectors can detect metal when stationary. Secondly, this magnetometer is sensitive way beyond what most people imagine. Search a river bed with small pebbles in it, and it will detect the magnetism in the pebbles. Search a beach with it, and it will detect the magnetism in the ocean’s waves. One needs to consider: where will this device not be too sensitive? A sandy lagoon, for instance. For this reason, smaller sensors might, in fact, work better because they will not pick up extremely small magnetic fields. While Silicon Chip housed their prototype in a timber enclosure, I used a fibre-reinforced cement pipe. In my first tests, I found that the magnetometer was disturbed by vibrations even when I placed the sensors on top of two pylons driven into the ground. Theoretically, it would be disturbed by solar storms. So, this is an unusual device with unusual applications. It is quite different to handle compared to, say, PI or IB metal detectors. Controlling a 12V DC motor with an H-bridge I want to control a 12V DC motor with an H-bridge to run it forward and reverse. I also need to control the speed of the motor, which I should be able to do with PWM. I have a Jaycar YM2770 12V DC motor and want to use a Jaycar ZK8880 L239D motor driver. In theory, I should be able to connect 12V to the input pins of the L239D and create a PWM signal with an Arduino on the Enable pin. The output pins should then provide the appropriate voltages to the motor. This is my first attempt at this, so I am wondering if I am thinking it through properly. What is the best way to do this? (A. P., Wodonga, Vic) ● You will need to use a much smaller, low-current motor with the L239D as the YM2770 draws 23A and the L239D is only rated at 600mA. Either that or use a much bigger motor controller. For heavy-duty use, see our January & February 2017 project article on the High Power DC Motor Speed Controller (siliconchip.au/Series/309). For the L293D, there are numerous websites that explain how to use that chip, eg: • siliconchip.au/link/abgl • siliconchip.au/link/abgj • siliconchip.au/link/abgk Currawong valve amp HT rail is too low I have built the Currawong Valve Amplifier (November 2014 – January VGA PicoMite Build this amazingly capable ‘boot to BASIC’ computer, based on a Raspberry Pi Pico. It has a 16-colour VGA output, a PS/2 keyboard input, runs programs from an SD card and can be quickly built Blocks is a BASIC game that runs on the VGA PicoMite $35 + Postage ∎ Complete Kit (SC6417) ∎ siliconchip.com.au/Shop/20/6417 The circuit and assembly instructions were published in the July 2022 issue: siliconchip.au/Article/15367 This kit comes with everything shown (assembly required). You will need a USB power supply, PS/2-capable keyboard, VGA monitor and optional SD card. siliconchip.com.au Australia's electronics magazine October 2022  109 2015; siliconchip.au/Series/277) from an Altronics kit (Cat K5528). Going through the final testing stages, something seems wrong. On switch-on, LEDs3-6 light up, LED2 is off and LED1 is on red. After about ten seconds, LED1 goes off but LEDs3-6 stay on. I measure 12.15V DC across pins 4 & 5 of the 9-pin valve sockets and 4mV between pins 1 & 6. Pin 3 of the 8-pin valve sockets measures 12.15V DC. I get a reading at the cathode of D1 of 170V DC, dropping to 165V DC when LED1 goes out. Can you please point me in the right direction? (J. D., Auckland, NZ) ● The first thing to investigate is your HT rail. As shown on the circuit diagram, the cathode of D1 is supposed to be around +310V. Check the AC voltage between pins 1 & 3 of CON7. It should be around 116V AC. The original Currawong design used five windings in series to achieve that voltage, and incorrect phasing could result in a low HT, but the Altronics kit uses two windings in parallel (as shown in the October 2016 issue; siliconchip.au/Series/277), so it seems unlikely that is the problem. Instead, suspicion must fall on the half-wave voltage doubler comprising diodes D1 & D2 and two 470µF capacitors. Check that those diodes and capacitors are soldered correctly and verify there is a low resistance across fuse F1 (with the power off). Verify that the capacitors are orientated correctly. If you can’t find any obvious faults, try replacing diodes D1 & D2. Hopefully, that will restore the correct HT. If the amplifier is still not working correctly after that, carefully check all the solder joints surrounding IC1, transistors Q5-Q8 and the associated passive components. In the case of the woofer, you don’t necessarily need an inductor. Still, for the Majestics, it is recommended mainly because the 15-inch (40cm) driver has an annoying peak at around 1-2kHz and will sound bad if there is no attenuation at those frequencies. The inductor can be wired in directly but do not use the same PCB as the tweeter unless you modify it to isolate the inductor. You can do this by turning the inductor upside-down and then soldering the output from the woofer amplifier directly to its positive pigtail. Each amplifier ideally should have its own volume control so that you can adjust the tweeter/woofer ratio. SiDRADIO parts availability and cost I am looking for a new shortwave radio, and most of what I have seen are now marketed as software radios. I saw an ad for your SiDRADIO (October & November 2013; siliconchip.com.au/ Series/130) in the April 2021 issue and thought I could build one myself. Is the “dongle” that you used still available, or is there something similar? Secondly, how many and how small are the SMD components, and how much would it cost for all the components needed to finish the project? (D. H., Lower Pappinbarra, NSW) ● Since it has been more than eight years since the project was published, the availability of the parts is not assured, especially with the severe current part shortages. A compatible DVB-T dongle is probably still available, but we have not tested the dongles currently on the market. It looks like the specific one we used in our prototype is no longer being sold. Some parts, like the 125MHz crystal oscillator, are now difficult to find. The good news is that we can supply How to bi-amp the pretty much all the hard-to-find parts Majestic Loudspeaker (besides the dongle) in our SC2137 Your series of articles on the Majes- parts set, currently selling for $25. We tic Speakers (June & September 2014; also sell the PCB for $20 – siliconchip. siliconchip.au/Series/275) suggest com.au/Shop/?article=5459 inserting a 4.7µF capacitor in series As far as we can tell, all the other with the tweeter if you bi-amp them. parts are available, but it would be a What about shorting out the 2.7mH good idea to check that you can get inductor (L1) for the woofer? (P. S., them all before proceeding. Hamilton, NZ) There are only eight SMDs total in ● Allan Linton-Smith replies: the the design: five passives, the oscillatweeter must be protected by a series tor, the mixer and the dual-gate Moscapacitor to prevent DC or low-­ fet. None are especially tough to solder frequency signals from damaging it. (the smallest is the BF998 in a 4-pin, 110 Silicon Chip Australia's electronics magazine 3 x 2.5mm SOT-143 package), but if your eyesight is a problem, it would be a good idea to have a desk magnifier and a strong light. We can’t tell you how much it will cost to build because the cost can vary significantly depending on the supplier(s) you choose, and prices change frequently. The PCB and parts in our SC2137 set total $45. You can then check with your preferred suppliers and add up the cost of the remaining parts (you can estimate the cheaper items like resistors to save time). That should give you a pretty good idea of the overall cost before deciding whether to build it. Modifying Gear Indicator project I have a question regarding the January 2003 Tiptronic-Style Gear Indicator project by John Clarke (siliconchip. au/Article/3991). Can it be modified so that both inputs are speed sensor based? I have a 3D-printed gearbox and want to use either Hall Effect speed sensors or magnet-based sensors. (S. N., Clayton, Vic) ● Yes, the ignition input can be used with a Hall Effect or magnet-based sensor by using the “LOW INPUT” section of the ignition coil input. Connect the sensor to this input via a 1kW resistor. You will need to add a pull-up resistor to the Hall Effect sensor so the open-collector output will be pulled high when its internal transistor is off. Ultra-LD Mk.1 Amp fault troubleshooting I built the Ultra-LD Mk.1 amplifier a long time ago (March & May 2000; siliconchip.au/Series/113), and it has been a fantastic performer! It’s still the main amplifier in my hifi setup. I built it from the complete Altronics Cat K5155 kit at the time, but I did not use the preamp board or multi-input functions and built them as “monoblock” amps, with each amplifier module in its own enclosure and with a separate power supply. For over ten years, they’ve sounded great. I hadn’t had any problems until the other day when I noticed a really loud hum from one speaker (without music playing) when I unplugged the input RCA connection to the amplifier. I was doing A/B testing between continued on page 112 siliconchip.com.au MARKET CENTRE Advertise your product or services here in Silicon Chip KIT ASSEMBLY & REPAIR FOR SALE DAV E T H O M P S O N (the Serviceman from Silicon Chip) is available to help you with kit assembly, project troubleshooting, general electronics and custom design work. No job too small. Based in Christchurch, NZ but service available Australia/NZ wide. Email dave<at>davethompson.co.nz LEDsales KEITH RIPPON KIT ASSEMBLY & REPAIR: * Australia & New Zealand; * Small production runs. Phone Keith: 0409 662 794 keith.rippon<at>gmail.com PCB PRODUCTION PCB MANUFACTURE: single to multilayer. Bare board tested. One-offs to any quantity. 48 hour service. Artwork design. Excellent prices. Check out our specials: www.ldelectronics.com.au LEDs and accessories for the DIY enthusiast LEDs, BRAND NAME AND GENERIC LEDs. Heatsinks, LED drivers, power supplies, LED ribbon, kits, components, hardware – www.ledsales.com.au VISIT THE NEW TRONIXLABS parts clearance store for real savings on new parts at clearance prices, with flat rate express delivery Australia-wide – go to https://tronixlabs.com FOR SALE SILICON CHIP ASSORTED BOOKS FOR $5 EACH Selling assorted books on electronics and other related subjects – condition varies. Some of the books may have already been sold, but most are still available. Bulk discount available; post or pickup. All books can be viewed at: siliconchip. com.au/link/aawx Email for a postage quote, quote the number directly below the photo when referring to a book: silicon<at>siliconchip.com.au Issues Getting Dog-Eared? Keep your copies safe with these handy binders Order online from www.siliconchip.com.au/Shop/4 see website for overseas prices or call (02) 9939 3295. REAL VALUE A T $21.50 PLUS P &P ADVERTISING IN MARKET CENTRE Classified Ad Rates: $32.00 for up to 20 words (punctuation not charged) plus $1.20 for each additional word. Display ads in Market Centre (minimum 2cm deep, maximum 10cm deep): $82.50 per column centimetre per insertion. All prices include GST. Closing date: 5 weeks prior to month of sale. To book, email the text to silicon<at>siliconchip.com.au and include your name, address & credit card details, or phone Glyn (02) 9939 3295 or 0431 792 293. WARNING! Silicon Chip magazine regularly describes projects which employ a mains power supply or produce high voltage. All such projects should be considered dangerous or even lethal if not used safely. Readers are warned that high voltage wiring should be carried out according to the instructions in the articles. When working on these projects use extreme care to ensure that you do not accidentally come into contact with mains AC voltages or high voltage DC. If you are not confident about working with projects employing mains voltages or other high voltages, you are advised not to attempt work on them. Silicon Chip Publications Pty Ltd disclaims any liability for damages should anyone be killed or injured while working on a project or circuit described in any issue of Silicon Chip magazine. Devices or circuits described in Silicon Chip may be covered by patents. Silicon Chip disclaims any liability for the infringement of such patents by the manufacturing or selling of any such equipment. Silicon Chip also disclaims any liability for projects which are used in such a way as to infringe relevant government regulations and by-laws. Advertisers are warned that they are responsible for the content of all advertisements and that they must conform to the Competition & Consumer Act 2010 or as subsequently amended and to any governmental regulations which are applicable. siliconchip.com.au Australia's electronics magazine October 2022  111 different preamps. Interestingly, with the RCA input plugged in, there is no hum and the amp is dead quiet. I measured 4.7V DC and 14mV AC across the speaker output (without the speaker connected). I’m assuming that is not good! The good amplifier measures only 3mV DC and 0V AC across the output. Since I have two of these amps operating independently (left channel and right channel), it’s easy to compare good and bad. I checked the DC voltage across many of the resistors, comparing them with my good working side. The voltages match on both apart from one resistor, the 10W resistor from the negative of the input connector to ground. On the good amp, this has 0V DC across it, but on the bad side, it has 4.7V DC across it. Hopefully, that can narrow down the root cause. (Murphy, via email) ● That 10W resistor has gone high-­ resistance or open-circuit. Replace it, Advertising Index Altronics.................................37-40 Dave Thompson........................ 111 Digi-Key Electronics...................... 3 Emona Instruments.................. IBC Hare & Forbes............................. 11 Jaycar........................ IFC, 9, 13, 15, ............................26-27, 53, 83, 107 Keith Rippon Kit Assembly....... 111 LD Electronics........................... 111 LEDsales................................... 111 Microchip Technology.................. 5 and we suspect the amplifier will be working again. As for the cause, we think when you were plugging and unplugging the preamps, somehow they must have applied a significant potential above or below Earth to the shield that delivered quite a bit of current through that resistor, burning it out. Perhaps due to an Earth loop. Modifying Capacitor Discharge Ignition I have some questions about the CDI system (September 1997; siliconchip. com.au/Article/4837): 1. Could I replace Q6 and Q7 with IGBTs to handle larger currents/additional leeway? 2. Could I use a 1MW bleeder resistor instead of the varistor and 680kW resistors? 3. How did cars run with this system? 4. My car (1979 MGB) has points. Would the points trigger circuit and the +12V signal from the points make the tachometer signal unnecessary? I think I could just connect the tachometer wire to the points terminal on the PCB. 5. The transformer can produce 400V. Do you see any problems with stepping up the voltage? I added an extra 33kW resistor, thinking that would keep the current flow similar to the original version. (J. M., New Haven, CT, USA) ● 1. There is no need to replace the Mosfets with IGBTs, but you could do so if you prefer. 2. The varistor is required. The two 680kW resistors are connected in series to obtain a sufficient voltage rating. Mouser Electronics..................OBC Ocean Controls........................... 12 Silicon Chip Binders................ 111 Silicon Chip PDFs on USB......... 75 Silicon Chip Shop.................98-99 Silicon Chip Subscriptions........ 52 Silicon Chip VGA PicoMite...... 109 The Loudspeaker Kit.com............ 8 Tronixlabs.................................. 111 Wagner Electronics..................... 14 112 Silicon Chip Errata and Next Issue Rohde & Schwarz.......................... 7 You could replace both with a single 1MW VR37 type high-voltage resistor. 3. Cars ran very well with this ignition system, especially during cold starts. 4. Your tachometer might not work with the CDI since it is more likely an impulse tachometer that relies on the high voltage produced as the points open on a standard Kettering ignition. You probably need to use the tachometer circuit shown in Fig.13 of that article that uses a transformer to step up the voltage for the tachometer. 5. Increasing the voltage from 300V to 400V could cause the CDI capacitor to fail as well as many of the other components. The transformer may also arc over internally. We did not design the circuit for 400V. The biggest challenge in making it work reliably at 400V DC would be obtaining a suitable CDI capacitor. Note that we have published several CDI systems since 1997, including the popular High-Energy Multi-Spark CDI for Performance Cars (December 2014 & January 2015; siliconchip.com.au/ Series/279). Finding past articles Some time ago, you published a feature on replacing the sacrificial anode in hot water systems. Could you tell me what issue this feature was in? (J. H., Nathan, Qld) ● You can search our article database here on our website at siliconchip.au/ Articles/ContentsSearch Entering “anode” in the Name field and pressing the Search button gives the following result: November 2012: Feature: Sacrifice Your Sacrificial Anode by Leo Simpson (siliconchip.au/Article/417). SC History of Op Amps, August 2021: in Figs.13 & 14 on p43, the 2π factors should be in front of the square root symbols, not within them. AVO Valve Testers, August 2022: on page 92 the text refers to potentiometer VR2 as applying the specified grid voltage, this should instead read VR5 to match Fig.4. Similarly, in the paragraph above, RLY1 should be RLYA. iSoundbar with Built-in Woofer, August 2022: the 1.2m lengths of DAR pine in the parts list should be 1.24m long to match the width of the sound bar. Also, the woofers are shown wired incorrectly in Fig.7; the two woofers should be wired negative-to-negative with the negative amp output and external subwoofer terminal going to the positive terminal of the left-hand woofer so they are phased correctly. Next Issue: the November 2022 issue is due on sale in newsagents by Thursday, October 27th. Expect postal delivery of subscription copies in Australia between October 25th and November 14th. Australia's electronics magazine siliconchip.com.au “Rigol Offer Australia’s Best Value Test Instruments” Oscilloscopes NEW 200MHz $649! New Product! 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