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SEPTEMBER 2022 ISSN 1030-2662 09 The History and Technology of 9 771030 266001 $ 50* NZ $1290 11 INC GST INC GST n ch is n o r e d A n a lo gC l oc w fe GPS k -Sy VIDEO DISPLAYS it h lon g b r e t t a y li WiFi-Controlled Programmable DC Load Fast and reliable temperature measurement. Digital Thermometers We stock a GREAT RANGE of thermometers, at GREAT VALUE, for domestic or commercial applications. MEASURE TEMPERATURES IN HOT, HAZARDOUS OR HARD TO REACH PLACES HELPS YOU AVOID FOOD FROM SPOILING FRIDGE/FREEZER THERMOMETER • -50°C to 70°C range • Min and max alarm function QM7209 JUST 29 $ 95 Non-Contact Thermometer • -50°C to 500°C range • 12:1 distance to spot ratio • Built-in laser pointer • Max, min, & auto data hold QM7410 JUST 4995 $ WATCH OVER THE TEMPS IN DIFFERENT ROOMS SUITABLE FOR THE LAB, WORKSHOP OR IN THE FIELD WIRELESS IN/OUT THERMOMETER/HYGROMETER • -45°C to 65°C (Outdoor), 0°C to 60°C (Indoor) range • 1% to 99% relative humidity range • Connect up to 3 sensors XC0322 JUST 3995 $ • -50°C to 750°C range • Built-in temperature sensor • K-type thermocouple input QM1602 RECORD AND STUDY TEMPS OVER TIME TEMPERATURE & HUMIDITY DATA LOGGER • -40°C to 70°C temp / 0-100% relative humidity range • 32,000 sample memory • Records at prescribed intervals • Easy USB interface QP6013 Shop at Jaycar for: • Thermometers & Thermocouples • Non-contact Thermometers • Probe/Stem Thermometers Thermometer with K-Type Thermocouple ONLY 119 $ JUST 4495 $ Includes Thermocouple • Digital Multimeters with Temperature • Desktop Temperature/Hygrometers • Weather Stations Explore our wide range of temperature measurement products, in stock at over 110 stores and 130 resellers or on our website. jaycar.com.au/thermometers 1800 022 888 Contents Vol.35, No.9 September 2022 14 Display Technologies, Part 1 This two-part series ventures through the history and technology used in video displays, from the Nipkow disc and the earliest CRT screens to the latest in quantum dot and laser displays. The first part of this series covers the earliest technologies up to the advent of LCD screens. By Dr David Maddison Tech feature 44 Creality CR-X Pro 3D Printer We review the Creality CR-X Pro, a dual-filament 3D printer available from Jaycar (Cat TL4411). It takes standard 1.75mm filament and has a print area of 300 x 300 x 400mm. By Tim Blythman 3D printer review 66 History of Silicon Chip, Part 2 Leo Simpson picks up the history of Silicon Chip magazine from 1993, including a failed attempt to enter the US market, the start of an offshoot magazine (Zoom), and a series of exceptional audio amplifiers. By Leo Simpson 30 WiFi Programmable DC Load, Pt1 This Electronic Load can handle up to 150V and sink 30A at up to 300W, providing it with enough power to test a variety of devices! Along with multiple different safety features, it is controllable from the front panel or via WiFi, and offers automated testing and data-logging capabilities. By Richard Palmer Test equipment project 56 New GPS-Synchronised Analog Clock Convert an ordinary wall clock into a highly-accurate timekeeper using our New Analog Clock Driver. It automatically adjusts for daylight saving, and will run for up to eight years with a pair of C cells, or two years with AAs. By Geoff Graham Timekeeping project 76 Mini LED Driver This small, low-cost module can drive relatively large 12V LEDs or panels from a USB or 5V DC power source. It can handle inputs up to 20V <at> 4A and has adjustable output current and voltage up to 20V <at> 1A. By Tim Blythman LED/lighting project 82 Wide-Range Ohmmeter, Part 2 To finish off our new Ohmmeter, we cover the construction details, go over the testing procedures and list a bunch of troubleshooting tips. After finishing it we show you how to put it to use. By Phil Prosser Test equipment project Cover background: a TV test pattern, typically used to calibrate screens Page 14 The History and Technology of VIDEO DISPLAYS Page 56 GPS-Synchronised Analog Clock mini Page 76 LE river 2 Editorial Viewpoint 4 Mailbag 29 Product Showcase 90 Serviceman’s Log 98 Circuit Notebook 1. Using a PICAXE as an Arduino co-processor 2. Simple USB power delay timer 100 Vintage Radio 106 Online Shop 108 Ask Silicon Chip 111 Market Centre 112 Advertising Index 112 Notes & Errata AVO valve testers, part 2 by Ian Batty 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 Glyn Smith (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 For overseas rates, see our website or email silicon<at>siliconchip.com.au Recommended & maximum price only. 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: Editorial Viewpoint Our binders are made in Australia I realise that only a subset of our subscribers use binders to keep their magazines (obviously they are not very applicable to online subscribers), but we do still sell quite a few. Recently, I was faced with having to decide on whether to continue selling them despite significantly increased manufacturing costs and the resulting relatively small profit for us. I decided that we should still sell binders so that people who have amassed a collection of Silicon Chip magazines in binders can continue to do so, and the good news is that the new binders should look the same as our existing stock. During the ordering process, I discovered that not only are the binders themselves made in Australia, but all the parts for them are too. The metal brackets holding the wires at either end are critical parts of the binders. As very few companies still offer this type of binder, they were no longer available, so we had to have a very large quantity of them made especially for us. That was a costly exercise but it was the only way that we could continue to offer the same product. And the company that is making those brackets is based in Queensland. All the other parts of the binders, such as the inner card, vinyl wrapping and spring wires are locally sourced, and they are all put together and printed in Smithfield, NSW. That’s good news – by buying our binders, you are supporting local industry (and Silicon Chip magazine too). Unfortunately, manufacturing in Australia isn’t cheap; we’ve had to pay almost precisely 10% more per binder for this batch than the last batch. So regrettably, we will have to raise the prices of the binders by 10% at the end of September. Another small compromise we’ve had to make to keep the price reasonable is to reduce the number of wires supplied in each binder from 14 to 12. I don’t think that is a big problem since it’s impossible to fit more than 12 issues of recent years of Silicon Chip in a binder due to the number of pages we’re printing. We will sell extra wires separately for anyone who needs them, at a low cost. They might be useful for those using our binders to house other, thinner magazines. Another consequence of having to get so many brackets made is that we have almost certainly assured a continued supply of binders for the next ten years or more, so those who are using them will be able to continue using them for the foreseeable future. New Zealand delivery problems It’s very frustrating that we mail magazines reliably and consistently but sometimes, they are not delivered to subscribers or arrive very late. Unfortunately, we have found ourselves in that situation with New Zealand subscribers over the last few months. Despite repeated enquiries and complaints, nobody has been able to explain why it has happened. I apologise to subscribers who have been affected by this. We are currently trying to find out if there are any other options for sending magazines overseas we can use that will be more reliable. The challenge is finding a reliable method that is not so expensive that we will have to increase overseas subscription rates again – that is something we definitely want to avoid if we can. We have heard from some overseas readers not based in New Zealand that they have also received their magazines late, but with the magazines travelling much further, it’s hard to say whether the cause is the same. Any solution we come up with for New Zealand readers will hopefully also improve the situation for our other overseas subscribers. by Nicholas Vinen 24-26 Lilian Fowler Pl, Marrickville 2204 2 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”. Inductors for Battery Zapper to give away In your July issue, one of your readers asked about inductors for the Battery Zapper Mk3 project (July 2009; siliconchip.au/Article/1500). I have the three items headed for the bin. I will post them in Australia at no cost if anyone wants them. Alan Middleton, Vermont, Vic. Note: interested readers email silicon<at>siliconchip.com. au and we will forward your message. Electric discharge machining with the CD Welder I have been following the Capacitor Discharge Welder articles (March & April 2022; siliconchip.au/Series/379). I think that would make a basic ‘engine’ for an electric-­ discharge machining (EDM) facility – a very handy piece of kit to have in a home workshop! Any thoughts in this direction for a future Silicon Chip project? Andre Rousseau, New Zealand. Phil Prosser responds: EDM is a little more controlled than the CD Welder from my understanding, which I admit as being limited. I think Andre is right that with the right set-up, the fundamental parts are present in the CD Welder for the discharge element of an EDM. Our maximum charge current is only 5A, which would severely limit the discharge rate in an EDM device. Yet the design of the Energy Storage Modules makes them capable of delivering pulses of energy with extremely fast rise and fall times, at extraordinarily high currents. The FETs and their drivers are designed for high-speed switching. The capacitors also have a very low ESR into the 100kHz domain, so this element of the design, coupled with an appropriate power supply and controller, could make for an EDM. Still, integrating this into an X, Y & Z CNC machine with wire feed control would be a significant undertaking. Mains wiring, built-in obsolescence and nostalgia I have followed the correspondence about aerial bundled mains cable (ABC) with interest. This method of feeding AC mains to homes has been followed for many years in NSW, at least. Here in Port Stephens, the mains reticulation system is often via open wires on intermix poles, where so-called ‘low’ voltage 240/415V four-wire supplies are carried under and on the same poles as 11kV feeds (a hazard if pole collisions occur). ABC is used to feed from the ‘LV’ lines to house poles or direct to houses. As well as its other advantages, ABC is much safer for tradesmen working on the exteriors of houses. Also, I have a comment about the letter from Cliff King that includes a statement made by a dishwasher company rep that their product had a deliberately designed cut-out that would render the dishwasher inoperative after a certain number of uses. ENCLOSURES AND TUNING KNOBS FOR TODAY‘S ELECTRONICS EQUIPMENT! www.okw.com.au ROLEC OKW Australia New Zealand Pty Ltd Unit 6/29 Coombes Drive, Penrith NSW 2750 4 Silicon Chip Phone: +61 2 4722 3388 E-Mail: sales<at>rolec-okw.com.au Australia's electronics magazine siliconchip.com.au This is similar to the possibly apocryphal story circulating in the UK years ago that black and white CRT TVs were set to ‘fail’ after a certain time to generate lucrative repair jobs. Surely that would be a criminal offence if it could be proven. Finally, I see that Jim Rowe is letting go of some quite juicy test gear! I am also of that age where I can’t justify acquiring any of it. Still, I licked my lips at some of the offers, like the legendary Bird RF wattmeter (which I used to adjust VSWR on radiotelephones in a previous life) and the AVOmeter. I saved and saved for my first AVO Model 8 in the ‘60s when I repaired valve radios in an even earlier life. I wish Jim all the best. I used to come across him in the original Dick Smith days and when he wrote for Electronics Australia, where I also wrote about BASIC. The Tandy TRS-80 (‘Microcomputer’) CPU (Z80) ran at a blistering 1.77MHz, and the hard disk was a whopping 8MB, costing a shade under $10,000. Yes, 8MB. We all knew for certain that this would be more storage than we would ever need. Those were the days! Alan Ford, Salamander Bay, NSW. Using Processing with an older CPU A year ago, I built the Arduino-based Adjustable Power Supply (February 2021; siliconchip.au/Article/14741). Some component compromises were required due to parts shortages at the time, but it ended up looking pretty good, so I ‘primed’ the Arduino and then installed Processing on my Windows 10 laptop, ready to run. However, the Processing program kept bringing up errors regarding OpenGL and frame buffers. Before I could find out what was happening, more important things (another grandson) came along, so finding a possible fix got postponed. After almost a year in a box (and while recovering from a week in isolation), I searched the internet about this problem. Updating GPU drivers was suggested as a common solution, but I already had Intel’s final Windows 10 driver for my Intel i5 Series two CPU (Intel HD Graphics 3000). From what I read, Intel i5 Series 2 CPUs are technically capable of OpenGL V3 support, but Intel’s final driver didn’t provide ‘full’ OpenGL V3 compatibility. Eventually, I found an article titled “Fix for OpenGL on Intel HD Graphics 3000 – Windows 10” at siliconchip.au/ link/abey which also referenced the required ‘patch’ or ‘shim’ file located at www.dll-files.com/ig4icd64.dll.html Following the instructions in the article was straightforward, only requiring substitution of the location of Processing’s JRE executable to apply the ‘patch’ to Java (“C:\ Program Files\Processing\java\bin\java.exe” for me). Then, to my relief, everything worked properly. I had to go back to the SC article to remind me how to calibrate and use the PSU program again. I suspect I may not be the only older hobbyist with an older CPU, so I thought I should share what I found. Gavin Krautz, Morningside, Qld. Reprint of Electronics Australia article was appreciated I appreciated the article reproduced from Electronics Australia about Fairchild transistor production in Australia in the 1970s (July 2022, pp102-104). Silvertone Electronics sells a range of Signal Hound spectrum analysers from 4.4GHz up to 43GHz. « This 4.4GHz spectrum analyser is yours from just $1677.50 This product and even more can be purchased from Silvertone's Online Store https://silvertoneelectronics.com/shop/ ► UAV & Communications Specialists 1/21 Nagle Street Wagga Wagga NSW 2650 Phone: (02) 6931 8252 https://silvertoneelectronics.com/ contact<at>silvertone.com.au Spike RF analysis software included for FREE with every Signal Hound analyser Silvertone is a reseller of these brands BitScope 6 Silicon Chip Australia's electronics magazine siliconchip.com.au Helping to put you in Control N20K48 Modular Controller 230VAC NOVUS, proudly releases our N20K48 controller family. Base unit has universal input and relay and pulse output controller. Program via USB or smartphone bluetooth. A selection of micro modules can plug into the rear for additional I/O and comms. SKU: NOC-340 Price: $186.95 ea I know you have to juggle limited space, but there must be a lot of other old articles from EA or its successors that would be of great interest to contemporary readers. I was a subscriber to EA as a teenager. Paul Howson, Warwick, Qld. Comment: we will probably reproduce a few pages from EA now and then if they are relevant. The challenge is being aware of the original article as most of the staff members who remember those articles have now retired. We recently went through dozens of EA magazines from the 1970s looking for the context of a photo for Leo Simpson’s article on the history of Silicon Chip. We saw many interesting articles while doing so but were too busy to stop and read them! (We eventually found the photo, published seven years after Leo thought – see p74). A hidden danger of hydrogen gas Fema I4L isolated signal converter for Load Cells Thhis converter can connect to 2 or 3 mV/V load cells. Features a display to show load. Configuration done by Keypad. 4-20mA/010V output. We have a service to configure the I4L for you if you require it. SKU: FMB-003 Price: $219.95 ea I3D Signal duplicator for process signals Accepts process signals in 4/20 mA and 0/10 Vdc, provides excitation voltage if needed. Dual output, with output 1 fixed to 4/20 mA, and output 2 configurable to 4/20 mA or 0/10 Vdc. Isolated 4 ways between power, input signal, output 1 and output 2. SKU: FMB-012 Price: $197.95 ea Signal Process Generator Pocket Precision The BRT LB02 Process Calibrator Resistance RTD TC mA mV signal generator is widely used as a precision multifunction process calibrator and multimeter, temperature calibrator, RTD PT100 simulator, loop calibrator, etc. SKU: HET-110 Price: $307.95 ea Praise for and advice on VGA PicoMite Adjustable 200mm Dual Float Switch Stainless steel vertically mount liquid level sensor, 200 mm in length. Floats can be adjusted to the desired length within the sensor’s overall length. SKU: HES-130 Price: $140.91 ea Mini Temperature and Humidity Sensor 0 to 10V output Panel mount Temperature (-20 to 80degc) and Humidity (0 to 100% non condensing) sensor, linear 0 to 10V output. Cable length 3 meters. SKU: EES-001V Price: $164.95 ea For Wholesale prices Contact Ocean Controls Ph: (03) 9708 2390 oceancontrols.com.au Prices are subjected to change without notice. 8 Silicon Chip I was just reading the Mailbag section in the July 2022 issue, and I noticed on page 6 a submission from George Ramsay where he mentioned using hydrogen gas for producing power in a domestic environment. Unlike any other gas, hydrogen gets hotter as it expands rather than colder. This is known as the Reverse Joule-Thomson Effect, and it increases the risk of spontaneous ignition of the gas if there is a leak anywhere in the valves or pipes. I did a quick internet search and found a paper that discusses this phenomenon called “Spontaneous Ignition of Hydrogen: Literature Review RR615” that you can view at siliconchip.au/link/abgd The paper is worth reading as it discusses several incidents and recent research on spontaneous ignition (see Section 3.2 on pages 8-10). Personally, I would not want to come near compressed hydrogen gas cylinders in homes or cars until the mechanisms for spontaneous ignition are fully understood and proven fail-proof designs come onto the market. It is too much of a serious safety risk before then. David Neville, Sydney, NSW. Many thanks for the VGA PicoMite project (July 2022; siliconchip.au/Article/15382). It has been 30-odd years since I used a soldering iron in earnest, and this looked like an easy enough project to ease back into things. I ordered the kit from you, and it arrived faster than I expected. While I definitely bodged the side pins on the SD card socket (my first surface-mount soldering), I was much better on the data pins. I checked the circuit and, thank heavens, those pins aren’t used. The whole thing, including the SD card, worked perfectly on the first run. Your instructions on surface-mount soldering were very useful, err, except I only followed those notes after I’d bodged the side pins. I have now cleaned it using solder braid. Other readers might be interested in knowing you don’t need a PS/2 keyboard to use the PicoMite (although I have ordered one). I left the USB cable connected to my PC and was able to use PuTTY to connect to it (any speed is fine, it looks like the PicoMite auto-detects). I had my monitor connected to the VGA port. All text commands appear in the PuTTY terminal and the VGA monitor. Anything colour or graphic only appears on the VGA monitor, but I was able to play Blocks using PuTTY. 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 $499 Shop at Jaycar for: • Huge Range of Filament & Resin Printers • Over 50 types of Filament and counting! • Over 45 types of Resin and counting! • Massive range of spare parts, tools & accessories Explore our full range of 3D printers and accessories, in stock at over 110 stores or 130 resellers nationwide or on our website. jaycar.com.au/resin-printers 1800 022 888 I love it; I had lots of fun and am feeling way more confident about soldering now. I am also looking forward to learning MMBasic. Michael Thompson, Roleystone, WA. Hint for VGA PicoMite I have added two extra lines at the end of the Colours. bas program so that the screen returns to Mode 1 after ending the program. Mode 2 used for the program has a much larger font than Mode 1, making editing more difficult: Input “Press Enter to end the program ”; k$ Mode 1 John Badger, Blackwood, SA. Ideas for IoT (Internet of Things)-related projects You published my letter asking for more IoT projects in the August issue (on page 6) and asked for specifics about what IoT projects readers wanted to see. Here are the IoT projects I have built myself, which should give you some ideas. My weather station has evolved over the years from a very basic system connected to a server to a full WiFi job I bought online. But I kept the small format view I liked for my phone. I did this by getting the weather station to send data to my server (as well as WeatherUnderground etc). I provided my design to a mate with a shed in the country who has an iPhone. I had used the Google Graphs library, which doesn’t work on it (surprise, surprise), so I wrote some graphing software from scratch for him. It’s SVG-based, currently limited to one day of data. This is not really IoT, but it could be. You can see the result at https://waggies.net/ws/ I published my software. One or two people have used it, and I’ve provided some support to them. One is at http:// meteocaldas.com/ws/ The same mate has a solar 12V battery setup at his shed, with permanent internet to monitor cameras. So I made a voltage and temperature monitoring setup for him, which you can view online at https://waggies.net/ volts/svggraphs.php?who=pete It is based on a NodeMCU, a few DS18B20s and an I2C ADC module. I have made several battery-powered temperature sensors for myself and my friends, which send data to my server for storage and display. They are intermittently online and offline. Here is my next-door neighbour’s: https://waggies.net/iot/T7/ I started this to monitor the temperature of a second-­ hand freezer my wife bought. The graphing software, based on SVG files, is pretty crude, like the weather and voltage graphs. I have a NodeMCU in my caravan which monitors its battery voltage and current plus the fridge, inside and outside temperatures. It acts as a WiFi hotspot. An ESP32 with an LCD (TTGO) is stuck to the ceiling, which receives the data and displays it. I can also use a spare phone in the car to see the values. This setup is pretty basic, but works. As a quick-and-dirty experiment, I put a moisture sensor in my back lawn. It is an ESP8266 just measuring the resistance across copper wires in the soil (a repurposed solar light). It works surprisingly well. I’ve since bought 10 Silicon Chip some capacitive moisture sensors to compare, but haven’t tried them yet. This one sends to my home server rather than my hosted server. See http://waggies.duckdns.org/iot/M1/ (the vertical axis is 0-1024, where lower is wetter). My sprinkler controller hasn’t come that far yet. I have some cheap 4- and 8-relay boards with an ESP8266 on them. The plan is to piggyback relays onto my existing sprinkler controller to give remote access. The software is quite involved, as you can imagine. I have some WiFi power plugs and globe controllers, but I’m not prepared to use them until I’ve hacked them, to avoid being spied on. All of these things get fiddled as I find the need or get the urge. My home server and laptop are running Ubuntu and the server code is primarily written in PHP. I save data in MySQL databases. The battery-powered devices I’m using are minimal ESP8266 units that I pay around $2 for. To program them, I’ve bought some carriers which give power, USB etc access. I haven’t figured out how to get any modules with USB built in, to go really low power while asleep. It is truly amazing how many low-cost sensors are available with matching Arduino libraries. I have tried a few of them. Ken Wagnitz, Craigburn Farm, SA. Cheap laptop batteries are just that I recently had an ancient Acer laptop upgraded and asked for a new battery at that time. The ‘serviceman’ told me when I picked the laptop up that a new battery was unavailable but he had managed to get a “refurbished one” for only $50. I then discovered two things: the battery lasted about 10 minutes, and after that, it would not charge. I was told, in no uncertain terms, that the refurbished batteries were not guaranteed. My arguments about “fit for purpose” fell on deaf ears and confirmed my impression that I would not be returning to that store. The store advertised that they would clean all machines, but the fan was still clogged with dust; it is a decade old, so that is no surprise, but a quick suck with the vacuum would have helped. Being of a particular mindset (I insist that I am not stubborn and definitely not bl**dy minded), I carefully opened the battery case. I noted that it did not wear the Acer brand anywhere; they are off the hook. The 18650 cells are clearly marked 3.7V and 2200mAh, despite the case boasting 5200mAh. Forget about cells that cannot live up to their promised rating, these cells would not recharge, and even if they did, 2200mAh x 2 (cells in parallel) could not deliver 5200mAh. Caveat emptor. Brian Wilson, Gowrie, NSW. Finding technical information online Ian Batty’s article on the History of Transistors is very good (March-May 2022; siliconchip.com.au/Series/378). I certainly learned a few things about their development, and I hope other readers do as well. What really intrigued me was the interplay of the personalities in the development of the transistor. I have read quite a few early Australia's electronics magazine siliconchip.com.au “Setting the standard for Quality & Value” Established 1930 ’ CHOICE! 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FREIGHT RATES! TO YOUR DOOR *Remote areas may require depot collection in your town DISCOUNT VOUCHERS VIEW AND PURCHASE THESE ITEMS ONLINE AT www.machineryhouse.com.au/SIC2208 NSW (02) 9890 9111 QLD (07) 3715 2200 1/2 Windsor Rd, Northmead 625 Boundary Rd, Coopers Plains VIC (03) 9212 4422 4 Abbotts Rd, Dandenong WA (08) 9373 9999 11 Valentine Street Kewdale Specifications & Prices are subject to change without notification. All prices include GST and valid until 28-09-22 07_SC_290822 CNC Machinery magazine articles, but Ian Batty’s article is the most comprehensive that I have read so far. I don’t know how easy it is for others to find technical information on the internet, but it has become increasingly hard for me to find data for specialised electronics etc. If I search for a data sheet using a part number, I usually have no problems, but if I search using only a description, I get all sorts of marketing rubbish and maybe something of interest. If I want to see what is new, forget it. Without some unique keywords, I have no hope. Before the internet, electronics magazines were the only way to get a lot of information. I am quickly coming to the conclusion that electronics magazines like Silicon Chip will once again be the best way to get information. It may not be printed data sheets or example circuits etc, but if web links to the sources of information are published, that would be fine. I quite often look at the ABC news online, and I found this recent article on solar storms to be interesting: www. abc.net.au/news/100812978 I have been aware of these events for quite some time and I believe I have protected my equipment reasonably well. But there is always that question of whether I could do better. This could be a good subject for an article, primarily referring to protection measures rather than a general description. Wikipedia has several pages around the subject, and they provide good general information, but none of them provide protection information. George Ramsay, Holland Park, Qld. Comment: we have also noticed that the ‘signal to noise ratio’ of Google searches for electronics has dropped quite a bit in the last few years. As you note, there is a lot of marketing rubbish in search results, such as companies claiming to sell every product under the sun (when they clearly don’t) rather than helpful information. We aren’t sure what can be done about it. More on ‘software as a service’ Your May 2022 editorial discussing software as a service (SaaS) certainly struck a chord with me. I also use Corel Graphics 2022, and this is the last time I will buy that program from Corel. My reasons are your reasons. In our case, the matter also extends to the Corel WordPerfect word processor. Most people guffaw when they hear that we still use WordPerfect, presumably remembering WP5.1 from the 1980s. In fact, we have found that WordPerfect (our latest is WP19) is better in many ways than other popular word processors. Its PDF conversion is smooth, and its formatting is precise. Still, the stand-out difference is the ‘reveal codes’ feature, which allows you to construct your document with the granular control of creating an HTML document. The transition from DOS to Windows versions of WordPerfect was easy in 1995, and they remain fully compatible today. Recently, our spare computer died, and transferring that (old) copy of WP18 onto the replacement computer ran foul of the activation processes. It seems pointless to pay for a subscription for WP22 just for the spare computer. So, as with Corel Graphics, the subscription model becomes a barrier, and a better solution is required. Max Williams, Ringwood North, Vic. SC 12 Silicon Chip Australia's electronics magazine siliconchip.com.au Power your projects with our extensive range of Arduino® compatible power supply modules, batteries and accessories. A GREAT RANGE AT GREAT PRICES. LED VOLTAGE DISPLAY USB OUTPUT POWER YOUR PROJECT FROM A LOWER VOLTAGE POWER YOUR 5V PROJECT FROM BATTERIES BOOST MODULE Converts 2.5-5VDC from a single Li-Po or two Alkaline cells up to 5VDC. 500mA max. XC4512 ONLY 4 $ 95 DC-DC Boost Module with Display Converts 3-35VDC up to 4-35VDC. 2A max. 1995 $ XC4609 USB OR SOLDER TAB INPUTS EASILY ADJUSTABLE BY MULTI-TURN POTENTIOMETER MAKE YOUR PROJECT BATTERY POWERED RUN ARDUINO BOARDS OFF HIGHER VOLTAGE POWER LITHIUM BATTERY CHARGER MODULE Charges a single Lithium cell from 5VDC. XC4502 ONLY ONLY 4 $ 95 DC VOLTAGE REGULATOR Accepts any voltage from 4.5-35VDC, and outputs any lower voltage from 3-34V. XC4514 ONLY 7 $ 95 Batteries not included SINGLE 18650 BATTERY HOLDER PH9205 $3.25 SWITCHED 4XAA BATTERY ENCLOSURE WITH USB PORT MP3083 $5.95 SWITCHED 4XAA BATTERY ENCLOSURE WITH DC PLUG PH9283 $5.95 3.7V 18650 2600MAH LI-ION BATTERY SB2308 $16.95 Shop at Jaycar for: • Step Up and Step Down DC-DC Converters • Huge range of Batteries and Battery Holders • Great selection of USB and DC Connectors & Leads • Regulated DC Plugpacks & Lab Power Supplies Explore our full range of products to power your projects, in stock on our website, or at over 110 stores or 130 resellers nationwide. jaycar.com.au/powerprojects 1800 022 888 Part One The History and Technology of VIDEO DISPLAYS By Dr David Maddison This two-part series investigates the history and technology of video displays, from the Nipkow disc and the earliest CRT (cathode ray tube) screens to the latest quantum dot displays. We will focus on two-dimensional displays capable of displaying video, not simple alphanumeric displays or 3D imaging technology. T his first article will cover the history of display technology until the introduction of LCDs (liquid-crystal displays) in the 1980s, which today are dominant in the market (although there are other newcomers like OLEDs making inroads). Like in other areas of technology, there has been a great deal of innovation and progress over the last 150 or so years. Next month, the second and final part of the series will cover all the latest technology from LCDs to OLEDs, quantum dot displays, microLED displays, EL displays, DLP, E Ink and more. The Nipkow disc Scottish inventor Alexander Bain 14 Silicon Chip invented the first device that allowed pictures to be transmitted remotely, sending images telegraphically using his “electric printing telegraph” in 1843. However, that device and another “image telegraph” machine by Frederick Bakewell dating to 1848 were not viable due to very poor image quality. The first viable commercial facsimile machine was the Pantelegraph, invented by Italian physicist Giovanni Caselli in 1861. It could transmit still images but not moving pictures. Arguably, the first video display device capable, at least theoretically, of showing moving images was the Nipkow disc (Fig.1) which was invented in 1883 and patented in 1884. Australia's electronics magazine It consisted of a rotating disc with a pattern of spiral holes that could be used both to generate an image for transmission via radio or wire and for reproducing the image via another synchronised disc at the receiving end. Advantages of this device include the fact that both imaging and receiving devices were similar; it used a simple imaging system requiring only a light sensor and the modulation of a light source; and it had a high resolution for each scan line. Disadvantages included the need to keep the discs synchronised and a practical limit to the number of holes the disc could have, limiting the number of lines of resolution, typically in the range of 30-100. However, up to siliconchip.com.au 200 lines were used experimentally. Also, the scan lines of the images were curved due to practical limits of the size of the disc, and the images produced were small. For example, a 30-50cm disc would yield an image the size of a postage stamp. In 1885, Henry Sutton of Ballarat Victoria designed a mechanical television apparatus for watching the Melbourne Cup live in Ballarat. Unfortunately, he never built the device because the telegraph lines he proposed to use did not have the capacity to transmit the signal. Radio, which had the needed capacity, had not yet been made practical. He called the device the Telephane and published the plans in 1890 (see Fig.2). It used the Nipkow disc, a selenium photocell and the Kerr effect (the change in the refractive index of a material in response to an applied electric field). The Nipkow Disc was a vital step toward the invention of the practical mechanical television, one of the first of which was demonstrated by John Logie Baird in October 1925. Interestingly, the Nipkow disc concept is still used today in one variation of a powerful type of optical imaging device called a confocal microscope. Instantaneous transmission of a moving image In 1909, German Ernst Ruhmer invented an early television system (Fig.3). A selenium cell array was used to detect an image and, through a method not fully disclosed, modulated the light intensity of corresponding parts of an array of a display device. The demonstration device had a 5 × 5 array capable only of displaying simple shapes and was incredibly expensive due to the high cost of the selenium cells. Any practical device with, say, 4000 cells would have been unreasonably expensive. This was followed by Frenchmen Georges Rignoux and A. Fournier, who developed a system capable of displaying an 8 × 8 matrix, enough to display letters of the alphabet. It could transmit several full images per second. These were remarkably modern concepts, comparable to today’s imaging devices, albeit at much lower resolutions. The cathode ray tube (CRT) By far the most familiar display siliconchip.com.au Fig.1: how Nipkow discs are used to reproduce images. Fig.2: Australian Henry Sutton’s never-constructed “Telephane” apparatus from 1885; we have only reproduced the transmitter section. From Telegraphic Journal and Electrical Review, November 7th 1890, p550 (https://hdl.handle. net/2027/mdp.39015012327071) Fig.3: Ernst Ruhmer’s early television system from 1909 with a 5 × 5 selenium cell imaging array and 5 × 5 modulated light-receiving array. Source: Literary Digest, September 11th 1909, p385 (https://hdl.handle.net/2027/ mdp.39015031441952) Australia's electronics magazine September 2022  15 Fig.4: making the first commercial colour CRT in 1954. Source: Early Television Museum and Foundation (www.earlytelevision.org) Fig.5: a typical monochrome CRT display with electrostatic deflection plates, as standard in an oscilloscope. Most TVs used magnetic deflection coils on the outside of the neck of the tube instead of interior deflection plates. EHT stands for extremely high tension. There are three electron guns and a shadow mask in a colour display. 16 Silicon Chip Australia's electronics magazine device of the 20th century was the cathode ray tube, widely used to display television images. Cathode rays and some of their properties had been discovered earlier, but German physicist Karl Ferdinand Braun invented the CRT in 1897 (see Fig.7), and he was the first to think that it could be used as a display. Unlike the heated cathode of more modern devices, it used a cold cathode. Here is a brief timeline of the main developments in CRT technology: • 1876: Eugen Goldstein coined the term ‘cathode rays’. • 1897: the Braun tube, the first CRT, was developed as a modified Crookes tube with a phosphor-coated screen. • 1908, 1911: Alan Archibald Campbell-Swinton writes about “distant electric vision” using the Braun CRT. • 1922: John Bertrand Johnson and Harry Weiner Weinhart develop a commercial hot-cathode CRT. • 1926: Kenjiro Takayanagi demonstrates a CRT TV with 40 lines. • 1927: Takayanagi increases the resolution to 100 lines. • 1929: Vladimir K. Zworykin coins the term ‘cathode ray tube’. • 1932: the Radio Corporation of America (RCA) trademarks the term Cathode Ray Tube. • 1930s: Allen B. DuMont made the first CRTs that could last thousands of hours. • 1934: the first CRT TVs are made by Telefunken of Germany. • 1950: RCA releases the term ‘cathode ray tube’ to the public domain. • 1954: the first colour CRTs are made by RCA. • 1957: US Patent 2,795,731 is granted to William Ross Aiken for flatpanel CRTs. • 1958: Aiken is granted another US patent (2,837,691) on a flat-panel CRT. • 1968: the Sony Trinitron flat-faced CRT is introduced. • 1987: CRTs with flat screens are developed for computer monitors. • 1990s: high-definition CRTs are released by Sony. A diagram of a typical CRT is shown in Fig.5. It is a vacuum tube containing an electron gun (cathode or negative electrode) that generates a beam of electrons that can be steered in both the X (horizontal) and Y (vertical) directions. An electron gun contains a filament siliconchip.com.au Fig.6: the geometric arrangement of electron guns and masks to ensure each colour beam strikes the correct phosphor. There were three ways to do this, each an improvement over the last. that heats an electron-emitting cathode. A grid controls the flow of electrons between the cathode and the accelerating anode and thus brightness/intensity. Up to 20kV is applied to the accelerating anode relative to the cathode, causing the electrons to form a narrow beam travelling toward the screen. A second focusing anode maintains the beam focus. After the beam leaves the electron gun assembly (heater, cathode, control grid, accelerating anode and focusing anode), it is deflected or steered to create an image. This is achieved either by coils that create a magnetic field or by electrostatic deflection plates that generate an electric field. Either way, there are two pairs of coils or plates for horizontal and vertical deflection. The electron beam impinges upon the screen coated with a phosphor, emitting light. In the case of a colour screen, there are three electron beams and three different phosphor colours (arranged as dots or stripes), and the electron beam for each colour only strikes its relevant colour of phosphor. To ensure that each beam strikes the correct phosphor, a shadow mask is employed and each colour electron siliconchip.com.au beam is slightly displaced from the others – see Fig.6. Many approaches were tried in colour CRTs to ensure that the electron beam struck the correct colour of phosphor. Still, the shadow mask concept from RCA, introduced in 1950 led them to drop all other lines of colour CRT research as it proved superior. RCA introduced the first colour tube (the 15GP22) commercially in 1954 – see Fig.4. Shadow masks are made by a lithographic process called photochemical machining. The RCA shadow mask concept was the main one used until Sony introduced the aperture grill in 1968, which serves the same purpose as the shadow mask but uses long slots instead of holes or small slots. From the late 1960s, non-Trinitron sets used rectangular phosphors and rectangular holes in the shadow mask, rather than a triad of phosphor dots and round holes in the shadow mask. You might be wondering where all the electrons go after they have struck the phosphors. The inside of the ‘bell’ of the CRT (the part between the neck and the screen) is coated with a graphite-­based electrically conductive layer called Aquadag. This collects the electrons and forms part of the anode. It also helps maintain a uniform electric field inside the tube. The electrical connection to this part of the tube is the large, prominent wire attached to the side of the bell in a cathode ray tube. Electric vs magnetic deflection The arrangement shown in Fig.5 has electrostatic deflection plates as would be used in an oscilloscope. Most TVs (except for a few early types with small tubes) instead use coils that provide a magnetic field. Magnetic deflection coils enable a higher angle of deflection and therefore a shallower tube, as used in TVs Table.1 – the largest commercial CRTs with time Fig.7: the original Braun cold cathode CRT of 1897. From Eugen Nesper, 1921, Handbuch der Drahtlosen Telegraphie und Telephonie, Julius Springer, Berlin, p78 Australia's electronics magazine 1938 51cm/20in diagonal 1955 53cm/21in diagonal 1985 89cm/35in diagonal 1989 110cm/43in diagonal September 2022  17 Fig.8: the magnetic deflection assembly (yoke) from CRT TV. Source: JHCOILS Fig.9: a type of CRT video camera tube called an image orthicon, commonly used in US television broadcasting from 1946 to 1968. and computer monitors – see Fig.8. They also allow a higher beam current for a brighter image. In traditional CRT oscilloscopes (CROs), a shallow tube was not considered necessary because the image was small, so the tube was also small. More importantly, though, the circuitry was simpler because the vertical deflection plates could be driven directly by amplified signal waveforms. Also, the deflection systems could respond faster to high-frequency signals of many megahertz because electrostatic deflection plates only present a small capacitive load, compared to the highly inductive load of magnetic deflection coils. In a TV or computer monitor, an image is built up by scanning line by line, top to bottom, in a so-called raster pattern. This happens so fast that it is not visible. There’s an excellent video that uses high-speed photography to demonstrate how the raster is scanned at https://youtu.be/3BJU2drrtCM By contrast, in an oscilloscope, the beam is instead swept left-to-right repetitively while it is moved up and down according to the applied signal voltage. As well as displaying video and for oscilloscopes, CRT screens were used for radars, heart monitors, and in some cases, a form of computer memory. From their inception to the mid1990s, they were the only practical and common form of video display device in use. LCD screens were commercially available from the early 1990s in laptops, but they performed very poorly compared to CRTs, only catching up in the late 90s/early 2000s. Flat-panel LCD TVs outsold CRT TVs for the first time in 2007, and in the same year, Sony ceased production of its famous Trinitron brand of CRTs. There were many variations of CRTs produced over the years: • Some could retain an image until it was erased, such as in certain oscilloscopes. • There were vector displays that made images using lines drawn pointto-point rather than in a raster pattern. These were used in early computer monitors for computer-aided design (CAD), in some arcade games and in the Vectrex home gaming system. • Projection CRTs formed an image on a distant passive screen. • A data storage tube from the late 1940s known as a Williams tube stored binary data, typically 256-2560 bits. • The much-beloved Magic Eye tuning device was used on certain valve radios from 1935 until the 1960s. Toward the end of the CRT TV era, CRT TVs managed to compete against LCD and plasma TVs for a while. Flatscreen CRTs were made because they were initially so much cheaper to produce. Eventually, the price of the alternative displays dropped, and the bulky and heavy CRTs went out of fashion. Today, Thomas Electronics (www. thomaselectronics.com) still makes and repairs CRTs as replacements for specialised military and aerospace equipment. In these markets, it is often more cost-effective to maintain the old technology than retrofit platforms with new LCDs screens etc. In these cases, the production cost is not a concern as the R&D cost for replacements would be huge. ► Fig.11: a proposed colour flat-panel CRT radar screen by William Aiken in 1957 (https:// patents.google. com/patent/ US2795731A/en). Fig.12: a diagram ► of the Eidophor from the original US Patent (https:// patents.google. com/patent/ US2391451A/en). 18 Silicon Chip Australia's electronics magazine siliconchip.com.au Figs.10(a) & (b): the Pye Mk III image orthicon CRT camera, first sold in 1952 and used for television test transmissions in Australia and to cover the 1956 Melbourne Olympic Games. It was motorised and could be remote-controlled, including focusing, changing lenses, plus tilting and panning with the right attachments. Source: Australian Centre for the Moving Image, siliconchip.au/link/abf9 Some gamers still use CRTs because they can have faster response times than many LCDs, and some people prefer the look of scan lines. Some vintage video games (such as classic arcade games) were designed specifically for viewing on CRTs, and good luck finding a recent LCD television with an S-Video or SCART connector if you want higher resolutions natively. CRTs also correctly display unusual, obsolete resolutions such as 256 × 224 as used by vintage Nintendo systems. The Aiken CRT William Ross Aiken made an early attempt to design a flat-panel CRT with the electron gun to the side rather than at the rear (see Fig.11). He was awarded US Patents for these designs in 1957 and 1958. Unfortunately, there were patent disputes, and development stopped. After the patents expired, the idea was further developed by Sinclair Electronics and RCA. that emits electrons when struck by photons from a light source due to the photoelectric effect. The Eidophor Very few people have heard of the Eidophor video projector. It was invented by Swiss scientist Fritz Fischer in 1939, and a US Patent for it was awarded in 1945 (see Fig.12 and siliconchip.au/link/abf7). Eidophors were used for large-scale public events, movie and video projectors and most famously by NASA in their Mission Operations Control Room during the Apollo missions. NASA used 34 Eidophor projectors from 1965 to 1969 – see Figs.13 & 14. They had a readiness rate of 99.9% despite their complexity. They cost about $85-90 million of today’s money in total. The Eidophor was a large, complex, expensive device to purchase and run but was reliable and gave the best projected video images at the time. They work as follows. A mirrored disc in a vacuum chamber is coated in an oil film about 14µm thick. An electron beam scans the surface of the oil in much the same way as an electron beam in a CRT screen scans the phosphor. The charge imparted into the oil layer causes it to deform due to electrostatic forces. A light beam from a powerful arc lamp shines onto the oilcoated mirror, and the reflected light is projected through an optical system to an image plane via a striped mirror Another type of CRT did not display an image but was used in early television cameras from the 1930s to 1980s. After that, CRT-based video camera tubes were replaced by charge-­ coupled device (CCD) image sensors, introduced to broadcast technology in 1984, followed by CMOS sensors (a development of CCDs). The principle of a CRT video camera tube is that a cathode ray is scanned across an image created by a photocathode. The returning cathode ray is modulated according to the intensity of the image created by the photocathode – see Figs.9 & 10. A photocathode is a light-sensitive compound siliconchip.com.au ► The CRT as a camera Fig.13: an Eidophor model EP 6 without its covers, of the type used by NASA in the Mission Operations Control Room during the Apollo era and beyond. Source: Swiss National Museum Fig.14: an Eidophor image (centre) at Mission Operations Control Room, Houston, during the mission of Apollo 11 on July 22nd 1969. Source: NASA, Image id=S69-39815 Australia's electronics magazine September 2022  19 Fig.15: the optical path of Eidophor. Original source: www.ngzh.ch/media/njb/ Neujahrsblatt_NGZH_1961.pdf (or similar arrangement) – see Fig.15. The deflection of the light beam to create the image is generated by optical diffraction or refraction of light as it passes through the thin oil film of varying thickness. The light projected onto the oilcoated mirror came via a slotted mirror with alternating transparent and mirrored stripes. The result is that light reflecting off the primary mirror in areas not impinged by the electron beam reflects back onto the slots and is blocked, while regions where the oil is perturbed cause the reflected light to miss the slots and pass through onto the projection screen. So the projection screen remains dark in areas where the electron beam is cut off and is brighter the higher the intensity of the electron beam in that area. For parts of the screen that are not fully light or dark, some light is reflected and is blocked, while some light makes it to the projection screen. This enables a gradation of intensity levels to generate the image, as shown in Fig.16. To remove an already-projected image from the oil in preparation for the next one, the mirrored disc is rotated to an electrode that neutralises the charge of the oil molecules, smooths the surface and resets it in preparation for the next image. Early Eidophors were monochrome, while later versions could project colour images using a colour wheel Fig.16: the function of the Eidophor’s striped mirror. (A) The light is reflected back with no image, and no light goes to the image plane. (B) With a strong image, all light goes through the transparent stripes and is projected to the image plane. (C) With a weak image, some light is blocked, but not all. Original source: www.ngzh.ch/media/njb/Neujahrsblatt_NGZH_1961.pdf 20 Silicon Chip Australia's electronics magazine or three projectors with colour filters. There is a fascinating video on Eidophors from 1944 with English subtitles named “Eidophor: Die bildspendende Flüssigkeit (1944)” at https://youtu. be/w_9NhiGeklI NASA Apollo display screens Many people have wondered how NASA set up the giant screen displays at the Mission Operations Control Room (“Mission Control”) at Johnson Space Center in Houston, Texas, during the Apollo moon landings, shown in Figs.17 & 18. Little has been documented about the technology used. These were possibly the first large video displays many people would have seen at the time and one of the first, if not the first, large-scale video displays. So how did they work? NASA used both graphic slide projectors and Eidophor video projectors. We already described how Eidophors worked, so that leaves the very special graphic slide projectors. YouTuber Fran Blanche has heavily researched these projectors. We highly recommend watching her excellent video titled “How Mission Control’s Big Displays Worked” at https:// youtu.be/N2v4kH_PsN8 According to that video, this system was in use until 1989. Graphic slide projectors displayed Earth and Moon maps, pages from manuals and any other material that could be stored siliconchip.com.au ► Fig.17: an Apollo-era image of NASA’s Mission Operations Control Room (“Mission Control”), showing the large screen displays. There were two 10 × 10ft (3 × 3m) screens on the left and right, plus a 20 × 10ft (6 × 3m) screen in the middle. An Eidophor video image can be seen on the far right, with graphic images in the middle and right. We are not sure about the two left-most images. Fig.18: the large display screens at the front of Apollo-era NASA Mission Control in the late 1960s and early 1970s. This view is from the Visitors Viewing Area to the rear of the Mission Operations Control Room. Source: NASA (www. nasa.gov/sites/default/files/atoms/files/apollo_mcc_press_release.pdf) on projector slides. The appropriate slides could be selected, under computer control, from those stored in a carousel – see Fig.19. The projectors needed to project images clearly under the bright lighting of Mission Control. This meant extremely powerful illumination was required; the heat would destroy traditional slides made of polyester. Glass slides with the images in metal coatings were therefore used. The metal was either absent, letting all the light through, or present and opaque with no gradation, much like copper on a PCB. Colours were generated using colour filters, and multiple slides could be superimposed on each other from multiple projectors. The ability to superimpose slides was important. Illustrated display shows geographical location of a spacecraft. World map is used as background reference with actual and predicted orbital paths plotted against latitude and longitude Optical fold mirror Rear projection viewing screen Projectio n plotting contro electronicsl Control el ec inputs an tronics associated d projectors convert them to p with each project or decod rop to respon e digital Plott d (chang ortionate analog e slides, Slide-acc ing data start plott voltages that cau ess com se mands ing) as re quested lay ce isp rfa r d l inte m e t u ro te mp nt sys Co / co sub Consoles operator closes selector switches to request background display and type of information to be plotted on display Plotting information from remote tracking stations PDSDD Requests go to computer display/ control interface subsystem, which changes requests to digital codes and routes them to RTCC RTCC RTCC accepts coded requests and releases data and slide-access commands to plotting display subchannel data distributor(PDSDD) for distribution to projection plotting control electronics Fig.19: how the Apollo era graphic projection system worked at NASA Mission Control. The equipment was located behind the Mission Control room (called The Pit) and in the Summary Display Projection Room or “Bat Cave”. The Eidophor video projectors are not shown in this diagram. siliconchip.com.au Australia's electronics magazine September 2022  21 Fig.20: an image showing a background map of the moon, a trajectory line, icons for orbital (command module) and landing (LEM) vehicles, plus other icons labelled 1 through 5, presumably corresponding to various landing events. It was made from multiple slides on multiple projectors and the colours were generated by colour filters. That was fine for static images, but how were real-time plots or orbital and trajectory data added? The orbital and trajectory data was generated by IBM 360 System 75 mainframe computers (see https://w. wiki/59xB). They received telemetry data and translated it into plots that could be displayed in real-time. Special charting projectors took the data from the computer. They plotted it using a diamond or similar stylus on an X/Y plotter, inscribing it into a ‘blank’ (fully metallised) slide, scratching a line in the metal. Previously plotted data stayed until a new blank slide was inserted – see Fig.20. Icons like spacecraft were also moved under computer control to show the actual position of the spacecraft. NASA has restored the original Apollo Mission Operations Control Room, which was in use until 1992, back to its original condition; see siliconchip.au/link/abf8 Sinclair TV80 / FTV1 Pocket TV Sinclair released the TV80 (also known as the FTV1) Pocket TV in 1983. It employed an electrostatically deflected CRT with a side-mounted electron gun along the lines of the Aiken CRT above – see Figs.21 & 22. It was a commercial failure, partly due to similar products being released by Sony (the “Watchman”) with other manufacturers using CRTs and later LCDs. The Seiko LCD T001 TV Watch was released in 1982, and the Casio LCD Pocket Television TV-10 (Fig.23) in 1983. For more on the TV80, see the videos titled “Doom on 1983 Sinclair FTV1 TV80 Mini Flat CRT & Teardown” at https://youtu.be/fEcs52lAI3E and Australian David L. Jones’ “EEVblog #554 – Sinclair FTV1 TV80 Flat Screen Pocket TV Teardown” at https://youtu. be/qCJPF6Ei3Vw Plasma displays Plasma displays were the first-flat panel displays over 80cm/32in diagonal and were the first to take over from CRT displays, at least for larger sizes. By 2013, they were surpassed by LCD screens. Plasma displays are now considered obsolete and have mostly been replaced in the market by OLED displays. Hungarian engineer Kálmán Tihanyi first proposed a plasma display in 1936. The first prototype plasma display was invented at the University of Illinois in 1964 by Donald Bitzer, Gene Relevant links ● The Cathode Ray Tube site: www.crtsite.com ● Picture tubes used to be rebuilt. This video is a look at the last picture tube rebuilder in the USA, titled “The Craft of Picture Tube Rebuilding” at https://youtu.be/W3G7b-DcOO4 ● The 8-bit Guy talks about modifying a consumer CRT TV to have RGB inputs for vintage games and using vintage computers in a video titled “Modding a consumer TV to use RGB input” at https://youtu.be/DLz6pgvsZ_I ● THE LAST SCAN – Inside the desperate fight to keep old TVs alive: www.theverge.com/2018/2/6/16973914/tvscrt-restoration-led-gaming-vintage ● A fascinating experiment you can do with a monochrome plasma panel: https://youtu.be/Oj4tRnLKN6U ● “vintageTek Demo of a 1930’s 905 CRT” – https://youtu.be/NBeOMsdPuT8 ● “The Cathode Ray Tube how it works 1943 16mm U.S. military training film” – https://youtu.be/GnZSopHjmYQ ● “Mullard Made for Life Vintage Documentary” – https://youtu.be/32yYfTVIzBE ● “Building A Tektronix Ceramic CRT 1967” – https://youtu.be/G0Dci5RPe94 22 Silicon Chip Australia's electronics magazine siliconchip.com.au Fig.21: a Sinclair flat-screen TV80 CRT TV. Source: Wikimedia user Binarysequence, CC BY-SA 3.0 Fig.22: the Sinclair TV80 PCB, with the CRT viewing area at left & electron gun assembly to its right. Source: Wikimedia user Binarysequence, CC BY-SA 3.0 Slottow and Robert Willson. Still, it consisted of only one pixel, so it was of no practical use. It was many more years before the first useful plasma display was developed. By 1972, Owens-Illinois Inc was selling a line of monochrome plasma computer monitors or display assemblies with resolutions up to 512 × 512 pixels – see Fig.24. The advantages of these units were that they were flat, flicker and drift-free, were all-digital and had minimal memory requirements as the display didn’t require constant refreshing like CRTs. Low memory utilisation was significant when memory was extremely expensive, and every byte saved counted. These displays were costly, up to US$2500 for the 512 × 512 unit. They lost popularity by the late 1970s as Fig.24: an advertisement for the first commercial plasma displays from 1972. Source: siliconchip.au/link/abfa Fig.23: the Casio TV-10 LCD pocket TV, released the same year as the CRT-based Sinclair TV80. siliconchip.com.au Australia's electronics magazine September 2022  23 memory became cheaper, making CRT monitors more attractive, even if they weren’t flat. In 1983, IBM produced a 19in (48cm) monochrome plasma panel, the model 3290 “information panel” that could simultaneously display four IBM 3270 terminal sessions. IBM planned to shut down their plant in 1987, but it was bought by Larry Weber, Stephen Globus and James Kehoe, who started a new company, Plasmaco. Plasmaco was subsequently acquired by Matsushita (Panasonic) in 1996 and no longer researches or manufactures plasma displays. In 1992, Fujitsu introduced the first 21in (53cm) full-colour plasma display. Fujitsu sold the first commercial Fig.25: one cell of a plasma display. Each pixel has three cells, each with one primary colour of phosphor, filled with noble gases and a small amount of mercury. The plasma discharge causes the UV light emission from the mercury, converted to visible light by the phosphor. The front electrodes are transparent conductors such as indium tin oxide. Dielectric layer Display electrodes (inside the dielectric layer) Magnesium oxide coating Rear plate gkass Dielectric layer Address electrode Pixel Front plate glass Phosphor coating in plasma cells A schematic matrix electrode configuration in an AC PDP Fig.26: a plasma display panel showing a pixel (picture element) comprised of three cells and the vertical and horizontal electrodes to address each cell. Source: Jari Laamanen, Free Art License 1.3 24 Silicon Chip Australia's electronics magazine colour plasma TV in the USA in 1997. It was 42in (107cm) diagonally with a resolution of 852 × 480 pixels and cost US$14,999. By the 2000s, prices of similar displays had dropped to around US$10,000. Panasonic demonstrated the largest plasma display at 150in/3.8m diagonal in 2008; it was 1.8m tall and 3.3m wide. By 2006, LCDs TVs were outselling plasmas. In 2013, Panasonic stopped producing plasma displays, followed by LG and Samsung in 2014. Plasma displays work much like a fluorescent light bulb. There is an electrical discharge into an inert low-­pressure gas containing a small amount of mercury. The mercury releases ultraviolet light, which then strikes a phosphor that emits visible light corresponding to the colour of the phosphor. Each pixel of a plasma display is made of three cells, one for each primary colour. One plasma display cell is shown in Fig.25, while a display assembly is shown in Fig.26. The gas pressure inside each cell is about 0.66bar (2/3 atmospheric pressure) with a minuscule amount of mercury inside. A typical driving voltage is around 300V. The voltage does not vary to change the cell intensity; instead, it is switched on and off many times per second using pulse-width modulation (PWM). ALiS ALiS (alternate lighting of surfaces) was a plasma display technology developed by Fujitsu and Hitachi in 1999 to enable lower-resolution displays to provide a higher apparent resolution. Instead of a progressive scan as per a regular plasma display, in which all pixels are illuminated every frame, it illuminated alternating lines for interlaced scanning. Thus, a 720-line panel could display an apparent resolution of 1080i. The picture of such a screen was also said to be brighter with lower power consumption. Next month Part two next month will pick up where this one left off, with LCDs taking over the display market in the mid-2000s. We will also cover the latest and upcoming display technology, such as OLEDs and high dynamic range (HDR) screens. SC siliconchip.com.au The BIG Workbench Build It Yourself Electronics Centres® The Ender 3 is the worlds best selling 3D printer! Over 1,000,000 sold worldwide. SALE SAVE $160 899 $ Spruce up the workbench this Spring with these handy deals on test, tools and more... K 8610 L! INTRO SPEavCaiIA lable Hurry, only 20 e. at this pric Top quality! NEW! 49.95 $ Jakemy 60pc All Purpose Tool Kit ® SAVE 12% T 2192 40 $ T 1461 A combined driver bit and socket set with 47 bits and 9 metric sockets. Great for odd-jobs and repairs around the house. Includes a handy magnetic latching case. Ultimate Flexible Helping Hands Upgrade to the ultimate in soldering helper hands. Includes magnifier to assist with those fiddly jobs. Arm length ≈30cm. Say to goodbyein! eye stra Creality® Ender 3 S1 Pro 3D Printer Get the Pro Ender 3 Upgrades: • Auto leveling with CR-Touch inbuilt • Up to 300°C nozzle temps for The latest generation in the popular Ender 3 wide filament compatibility. 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Easy to light, one-click piezo ignition. Blow torch & soldering iron in one. 2 year Powered by refillable warranty. Includes 1.6mm tip and cartridges! refillable butane cartridge. Extra cartridges $24.25 pk2 (T2632). Got Gas? NEW! SAVE 20% 68 $ Blow torch & iron in one! Iroda® Solder Pro 70W Soldering Tool Kit T 2596 Perfect for the occasional soldering job or hobbyist on the go! Provides 70W of soldering power with accessories kit in a handy carry case. Includes hot knife, hot air blower, blow torch tips, plus solder and sponge. Stock up on top notch scrubbed and triple filtered butane for reliable use in gas tools. 19.95 $ Iroda 3 Nozzle Blow Torch Kit ® T 2488A The new pocket rocket! Ideal for trades requiring both precision brazing and high output wide spread flame jobs. Supplied in handy carry case with stable safety stand. 120 mins run time at mid setting. Includes carry case. Trade quality! 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Charge your phone on the go with this MagSafe compatible wireless charging battery bank. 10,000mAh. 20W USB C PD in/out. *Shown with compatible Iphone 12 for illustration purposes. Top Value True Wireless Earbuds Plenty of bass! Bluetooth 5.0 offers superior range (up to 10m) & better audio quality. Sweat resistant design - great for exercise. 3-4hrs of listening time with battery bank case. SAVE 20% Take high quality audio notes with ease! 40 $ C 9037B SAVE $20 X 0705A 79 $ Record CD quality audio with excellent audio pick up for taking audio notes during lectures & recording interviews. 32GB on board memory with Micro SD slot. USB rechargeable. Great for uni students! C 9034A FREE! D 2816 + A 0981 SAVE $43.95 125 SAVE $10 Magnetic ‘edge to edge’ grilles. 39.95 $ $ C 0876A SAVE $70 349/pr $ One box for all your entertainment. Make your TV even Smarter! Stream direct to your TV from streaming services, plus play games and connect to local media on your home network. Capable of streaming stunning 4K videos <at> 60fps! 4GB ram with 32GB on board storage. Requires 2A USB power supply. Includes FREE A 0981 trackpad/keyboard valued at $29.95. Opus One® 2x30W Bluetooth® Wireless Ceiling Speakers Built to stream the best content from your favourite music streaming service, app or podcast player. Bluetooth 5.0 technology offers superb audio performance and range. In-built high performance 2x30W RMS amplifier. The ideal way to add permanent wireless sound to any room in the house. A modern, low profile finish is provided by frameless magnetic fit grilles. Includes power supply. Sold in pairs. FIRE THE WEATHER MAN! Get live, local weather at home. 279 X 7063 With outdoor sensors & smartphone app! Western Australia Sale Ends September 30th 2022 Phone: 1300 797 007 Fax: 1300 789 777 Mail Orders: mailorder<at>altronics.com.au The perfect every day commuter earphones with top notch wireless sound, compact folding design and up to 15 hours of listening between recharges ideal for longer flights. Bluetooth 5.0. $ This fantastic home weather station displays all your local weather data - great for boaties & gardeners. Bright & clear base station provides readings for indoor/outdoor temperature, humidity, air pressure, rainfall, wind speed and direction. Plus handy weather trends. You can even connect it to your home wi-fi to monitor readings & data with your smartphone. 100m sensor range. Build It Yourself Electronics Centres Great Bluetooth Sound For Less! » 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 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 0009 Find a local reseller at: altronics.com.au/storelocations/dealers/ PRODUCT SHOWCASE Automotive-focused dsPIC33C family of microcontrollers For automotive developers looking to design scalable applications for future technology, Microchip has announced a comprehensive ecosystem around AUTOSAR-ready dsPIC33C digital signal controllers (DSCs) to enable accelerated development and a high level of system optimisation while reducing total system cost. Microchip is expanding its broad portfolio of dsPIC33C DSCs to cover the large memory segment with the new ISO 26262-compliant dsPIC33CK1024MP7xx family. This new family of dsPIC33C DSCs with 1MB of flash memory enables applications running automotive software like AUTOSAR, OS, MCAL drivers, ISO 26262 functional safety diagnostics and security libraries. The family of dsPIC33 DSCs also includes a high-performance CPU with deterministic response and specialised peripherals for general automotive, advanced sensing & control, digital power and motor control applications. AUTOSAR-ready devices like this one help customers improve their risk & complexity management while decreasing development time through reusability. Customers can take advantage of Microchip’s value-added solutions, customer support and product advantages. The AUTOSAR ecosystem for the dsPIC33C DSCs includes MICROSAR Classic from Vector, KSAR OS from KPIT Technologies Ltd. and ASPICE- and ASIL B-compliant MCAL drivers from Microchip. Microchip has expanded its safety packages that include FMEDA reports, safety manuals and diagnostic libraries to cover the dsPIC33C-series of DSCs. These dsPIC33C DSCs, when used together with Microchip’s TA100 CryptoAutomotive security ICs, enable the implementation of robust security in automotive designs. Microchip Technology 2355 West Chandler Blvd, Chandler Arizona 85224-6199 USA Phone: (480) 792 7200 www.microchip.com Valve amplifiers and loudspeakers from Bertrand Audio Started in 2021, Bertrand Audio has been able to bring very exciting products for the music lovers in Australia and New Zealand and is fast becoming a reputable supplier of products that provide visceral music. We introduce the following brands into the ANZ market: From KR Audio, the KR Kronzilla VA-680 is a 2-channel amplifier with 60W of output power. It uses a reverse hybrid circuit; solid state components on the first stage and two KR T-1610 valves (double triodes in parallel) on the outage stage. It comes in two versions: either as a stereo power amplifier or an integrated model. The T-1610 valves are some of the largest valves available worldwide! The VA-680 is our bestselling single-ended amplifier due to the increased dynamics, even finer resolution of detail from the recording be it vinyl, CD or audio streaming, and an Above: the VA-680 amplifier from KR Audio. Right: a close-up of a single speaker from the Custom loudspeaker system by the AER Company. siliconchip.com.au almost tangible imaging in the sound reproduction. The AER Company has over 30 years of experience in research, development and production of speaker systems. They are the designers of the “Custom” speaker system. It is an open baffle loudspeaker made with moulded Acryglass. Its high efficiency design provides 96dB/W and is suitable for use with single-ended amplifiers. Tonally accurate and without exertion, the Custom perfectly recreates the performance on stage or in the orchestra pit. All that’s required is some space at the sides and rear of the system for optimal sound. The Custom matches well with AER’s “Subway”, a compact active subwoofer with a 38cm bass driver, delivering an adjustable 210W of class-D amplification. This is just a taste of what is offered from the KR Audio and AER line of goods. Bertrand Audio are the exclusive distributors for AER Loudspeakers and KR Audio equipment in Australia & New Zealand. Contact Bertrand Audio for more details. Bertrand Audio Phone: 0426 981 319 sales<at>bertrandaudio.com.au Australia's electronics magazine September 2022  29 WiFi-Controlled Programmable DC Load Part 1: by Richard Palmer ѓ Handles up to 150V DC, 30A & 300W ѓ Uses computer CPU coolers 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 Electronic Load can handle enough power to test almost any project, plus many kinds of batteries and solar cells. It can operate up to 150V and sink 30A within a 300W power envelope. It has overvoltage, over-current, over-temperature and reverse polarity protection. Notably, it’s programmable, from the front panel or over WiFi, and offers automated testing and data-logging capabilities. 30 Silicon Chip Australia's electronics magazine siliconchip.com.au DC electronic loads are useful for testing power supplies, batteries, solar cells and other power-sourcing devices. The design and construction of an electronic load also demonstrates many useful power electronics principles. So even if you don’t need or plan to build a DC load, you might find this article interesting. The most basic load component, the resistor, can be used to test power sources and batteries, but it lacks flexibility. Even with a high-power rheostat, plotting performance against changes in load parameters is tedious. It is difficult to change a resistor’s value quickly and cleanly to test transient response. Electronic loads overcome these and other limitations of the basic load resistor. As well as being able to mimic a resistance, electronic loads typically have several other operating modes: Constant Voltage (CV), Constant Current (CC) and Constant Power (CP). Modern electronic loads usually can generate ramps or alternate between settings in a timed sequence to test different load points and transient behaviour. Features to assist battery and solar cell testing are also common. Advanced loads are programmable, provide automation for common functions and have data logging. This Electronic Load offers all those features (see Scopes 1-3). Importantly, you can program and monitor the Load from its front panel controls, a web browser, terminal software or via SCPI. SCPI is a standard protocol used by many applications specifically designed to control test instruments, such as National Instruments’ LabView Community Edition or the open source software Test­Controller (siliconchip.com.au/ link/abev). Scope 1: the current sunk by the Load in constant-current mode with a fixed voltage applied and a Step function for the desired current. It’s alternating between 0.5A and 3A roughly once per second. This can be easily configured through the front panel or web interface. Scope 2: this is similar to Scope 1, except the Load is programmed to rapidly increase from 0.5A to 3A, then back down to 0.5A in four steps, again using the Step function. Scope 3: another example of the Step function. This time, it’s set for a period of 10 seconds with 1.5-second rise/fall times, resulting in a trapezoidal current waveform. Design goals The project’s design parameters were driven by several factors, including its intended applications and some practical limitations. One important application is the need to test various types of rechargeable batteries, from the tiny lithium polymer cells found in toys such as micro helicopters through to moderate-­duty sealed lead-acid (SLA) batteries. Another useful job for an electronic load is to automate testing of power siliconchip.com.au supplies, for example, our most recent bench supplies which include: • 45V, 8A Linear Bench Power Supply (October-December 2019; siliconchip.com.au/Series/339) • Programmable Hybrid Lab Supply with WiFi (May & June 2021; Australia's electronics magazine siliconchip.com.au/Series/364) • Dual Hybrid Tracking Bench Supply (February & March 2022; siliconchip.com.au/Series/377) 300W solar cells are now common, and solar cell testing is another situation where an electronic load is September 2022  31 Fig.1: the maximum power dissipation of the Load determines the safe operating area (SOA). At very low voltages, the maximum current that can be sunk is determined by the Rds(on) of the Mosfet and shunt resistors of the four power modules in parallel, giving a minimum resistance of 25mW. helpful, so it is designed to handle the voltages and currents such panels produce. In terms of component limitations, the maximum ratings of readily available relays and binding posts suggested 30A as a workable current limit, and 150V is a reasonable maximum voltage to handle – see Fig.1. Isolation from Earth is beneficial when ‘high-side’ testing is required or for negative voltage sources. As the Load is to be used on the test bench, comprehensive protection against overloading and reversed connection are also needed. For extended tests when you might need remote monitoring and control, it must provide comprehensive remote control facilities. To this end, the browser interface mirrors all touch screen functions other than the calibration and communications menus. It also provides logging functions and a plot of current, voltage and one other parameter over time. When testing power supplies, the ability to step quickly between settings or create ramps is helpful to plot their characteristics. Finally, the ability to collect test data from multiple runs for further analysis saves time and possible transcription errors. It is even better if the readings from several instruments can be brought together into a single log file. While we could have designed these features into this project, TestController allows instruments to be remotely controlled, test sequences to be automated and multiple devices synchronised. The measurements obtained can be analysed using the comprehensive math and graphing functions included in the program. 32 Silicon Chip As TestController supports SCPI (as do several other useful test instrument packages), that is the logical interface method. Therefore, the Load responds to SCPI protocol commands either over a WiFi connection or via an isolated USB serial connection. We have included a TestController instrument definition file for this Load to download at siliconchip.au/link/abf6 You can find detailed descriptions of the remote control options and the general operation of the Load in the PDF manual (see siliconchip.com.au/ Shop/6/4529). Also, for more information on the SCPI protocol, see page 78 of the June 2021 issue (siliconchip. com.au/Article/14891). Design overview The primary function of an electronic load is to turn electrical power into heat and then dissipate it into the surrounding air. After exploring various traditional heatsink and fan combinations, we determined that the best value was using a fan-forced computer CPU ‘tower’ cooler. Most CPU coolers have a 35 x 40mm contact pad to fit the standard Intel and AMD CPU heat spreader footprints. Two TO-247 packages mount nicely side-by-side on this sized block. While any cooler rated at 150W or more could do, the CoolerMaster Hyper 103 has mounting flanges adjacent to a generous heat transfer pad, providing a ready means of attaching it to the PCB. It also has pretty blue LEDs, which will light up the inside of the case! As in other high-power designs, good thermal transfer from the Mosfet package to the heatsink is critical. We have chosen not to use any insulating material between the Mosfets and the cooler to keep thermal resistance to a minimum. Two of these CPU coolers are used in the Load, each removing the heat from a pair of TO-247 package Mosfets. As the Mosfet drains connect to the tabs, both heatsinks are at the full input voltage of up to 150V. We have used the CPU cooler’s plastic fan shroud as a chassis mounting point to provide the required isolation. The CoolerMaster Hyper 103 CPU cooler, shown in Fig.2, is preferred for this project. They cost around $35 each and come with a 92mm 4-pin PWM fan. They use three heat pipes to transfer the heat from the Mosfets to the fins – we covered heat pipe technology in our article in the May 2022 issue (siliconchip.au/Article/15304). Mosfet control Fig.3 is the block diagram. There are four power blocks at the core of the design, each with a Mosfet, a shunt resistor and some control circuitry, shown in more detail in Fig.4. Fig.2: two Coolermaster Hyper 103 tower coolers are used to remove heat from the four Mosfets and dissipate it into the surrounding air. Other CPU coolers could be used, but they might not fit in the specified enclosure, and these are pretty good value at around $35 each (retail pricing). Australia's electronics magazine siliconchip.com.au Fig.3: a simplified block diagram showing the major features of the Load. Four identical op amp/Mosfet power blocks are controlled by a DAC, while an ADC measures the input voltage and current. A relay connects or disconnects the DUT with the ESP32 handling communications and control. A control voltage, SET_POINT, is provided to the power blocks by a digital-­ to-analog converter (DAC) common to all power blocks. An analog-to-digital converter (ADC) measures the voltages at the Load’s input and across the shunt resistors. The microcontroller controls the DAC output voltage and iterates it until the desired operating conditions are reached (see the panel on “Controlling an Electronic Load”). The case temperature of one Mosfet is read by a thermistor and fed to an ADC channel. This temperature reading is used to control the fan speed via a PWM signal from the microcontroller module, and also to implement the over-temperature shutdown safety feature. The Load’s power comes from a 12V DC plugpack which directly powers the fans and op amps. It is regulated to 5V to power the ESP32 microcontroller and several other components. A further 3.3V rail is used to power the DAC and ADC chips. The general arrangement of the controller is the same as for the Hybrid Lab Supply project (May-June 2021; siliconchip.com.au/ Series/364). To simplify the mounting of the Mosfets on the CPU coolers, one pair of Mosfets and their cooler mount on a separate daughterboard. A short ribbon cable connects the power supply Fig.4: the basic constant-current load circuit. The Mosfet drain current is reasonably proportional to its gate voltage once the gate threshold voltage has been reached, so the op amp mainly has to make minor adjustments to account for changes in temperature, non-linearities etc. We use a vented metal enclosure 270 x 210mm large to house the DC Load, as shown in the photo. A 3mm-thick piece of clear acrylic is used to mount the fans to the interior of the case. The bends at the top and bottom of the plastic coolermounting panel are to increase its rigidity. Also shown are the extra ventilation holes in the base. siliconchip.com.au Australia's electronics magazine September 2022  33 and control signals to the main load PCB. Circuit details The main Load circuit is shown in Figs.5 & 6. One power block is highlighted by the blue box; the other is virtually identical. Each Mosfet has its drain current 34 Silicon Chip controlled by an op amp, balancing the setting against the voltage generated across the corresponding 0.02W shunt resistor. Using the Q1 block as an example, the SET_POINT signal from the controller is divided by the 18kW/1kW resistor pair to match the desired voltage across the shunt resistor, which Australia's electronics magazine will reach 0.15V at 7.5A. As the op amp has a high open-loop gain, it controls the gate voltage so that the voltages at the non-inverting input pin and the Mosfet source are equal. The divider resistors are specified as having ±1% tolerances to ensure closely-­matched setpoint voltages for each power block. siliconchip.com.au Fig.5: the Electronic Load circuit, not including the control circuitry which is in Fig.8 (based on a previously published controller design). It has two power blocks similar to Fig.4 (one highlighted in blue), a current sensing circuit, a DAC for current control, an ADC for measurement, thermistor-based temperature sensing, PWM fan speed control using Q5, an on/off latch for the disconnect relay and a simple 5V power supply. In contrast, the shunt resistors are ±5% devices, balancing load sharing accuracy against cost (you could use ±1% if you wanted). Mosfets conduct very little current until the gate-source threshold voltage is reached. For the FQA32N20, this is around 2.5V, but it can vary over the range of 2-4V from batch to batch. siliconchip.com.au Above this voltage, the Mosfet’s ID vs Vgs characteristic is quite sharp (ie, their transconductance is high), rising from a typical 5A at 5V to 18A at 5.5V (see the panel on “Operating Mosfets in linear mode”). The op amp’s gain is a compromise between stability and reaching the Mosfet conduction voltage at the Australia's electronics magazine lowest possible DAC step. A gain of 1000 balances these factors, while the 1nF capacitor across the feedback resistor reduces the gain at high frequencies to enhance stability. The ESP32 controller fine-tunes the current by reading the voltage across the current sense resistor and adjusting the DAC’s setpoint. The minimum September 2022  35 controllable current, and current step, is around 7mA, equal to the maximum current (30A) divided by the number of DAC steps (4095). Each pair of Mosfets shares an INA180 current sense amplifier, which amplifies the average of the voltages across the two shunt resistors and feeds it to the ADC. The Load is unconditionally stable when connected to capacitive sources. A snubber network (capacitor and resistor in series) is connected across the load terminals to maintain stability with inductive sources. Controlling the Load The MCP4725 DAC (IC5) provides a 0-3.3V signal to control the Mosfet’s drain current. The DAC takes its reference voltage from the 3.3V supply rail, which is quite noisy, so L1 and the 100nF capacitor form an LC filter to reduce noise from the DAC output. On/off control of the power block is provided by diodes D1-D4. When their anodes are driven high, the inverting inputs of the op amps are pulled up, forcing the outputs low and so switching off the Mosfets. This is independent of the SET_POINT voltage from the DAC. The microcontroller measures the input terminal voltage and load current to calculate the appropriate setpoint for the constant current, voltage, resistance or power mode selected (see the panel on Controlling an Electronic Load). When the desired setpoint or the source impedance of the device under test (DUT) changes, the controller estimates the required current and sets the DAC accordingly. This estimate assumes that the DUT has a linear voltage-to-current characteristic, which is not always true. So to minimise overshoot while quickly reaching the target value, every 1ms, the setpoint is adjusted by 80% of the remaining gap. There’s a Catch-22 for CR, CV and CP modes: until the Mosfets are on, there is no current reading available to calculate the setpoint. To overcome this, when the On switch is pressed, the DAC is set to deliver a small output current (around 10mA), and successive approximations are made until the desired setpoint is reached, usually within a few iterations. Response time The ADS1115 (IC6) takes around 2.5ms to take voltage and current readings. While in steady-state operation, this loop time is more than adequate for fine control. However, for handling transient conditions, this is not optimal. The ESP32 has several fast 12-bit ADC channels that can make fresh current and voltage readings available each time the control loop iterates (1ms). They are not particularly linear in the top 20% of their ranges, though, and have a minimum input voltage of 150mV. While they are unsuitable for fine control, they are more than adequate for coarse control. To overcome the ESP32 ADC linearity problems, the input voltage presented to the ESP32 is boosted by Fig.6: the ‘daughterboard’ circuit basically duplicates the two load power blocks from Fig.5 and they are connected in parallel to increase its power-handling capabilities. The current sense circuitry is also duplicated and the two boards connect via a ribbon cable between CON2 & CON3 plus a few thick wire links for the high-current paths. 36 Silicon Chip Australia's electronics magazine siliconchip.com.au Controlling an Electronic Load This Electronic Load has four main control modes: constant current (CC), constant voltage (CV), constant resistance (CR) and constant power (CP). As shown in Fig.a, a Mosfet in its linear (or saturated) region translates its gate-source voltage (Vgs) into a relatively constant current. This region is between the gate-source voltage threshold, Vgs(th), and the point where the minimum drain-source resistance, Rds(on), dominates. Therefore, CC mode requires the simplest control arrangement, as in Fig.4. A reference voltage is provided to one input of an op amp, and this is compared with the voltage generated across a current shunt resistor. If the drain current is too low, the gate voltage increases, and vice versa. Because of the nature of the Mosfet described above, the changes in gate voltage in this mode are small. CV mode (Fig.b) has a similar control arrangement with a voltage divider replacing the current shunt, but note that the connections to the op amp are reversed. This is because we want the Mosfet current to increase as the DUT voltage rises. For CR (Fig.c) and CP (Fig.d) modes, both voltage and current feedback are employed in two different combinations. We need the current to change proportionally to the voltage in constant resistance mode, so positive voltage feedback and negative current feedback are applied. For constant power mode, voltage changes should be inversely proportional to current changes, so negative feedback is used for both voltage and current. Analog switches could be used to control the various input combinations, while an analog multiplier circuit could process the current and voltage inputs. But this approach would add significant cost and complexity to the circuit. It is more convenient, though slightly slower, to calculate the required control voltage in software, using ADCs and a DAC to close the control loop. For testing batteries, the CC or CR modes are most often used. The fully charged battery is discharged to a pre-set minimum voltage and the battery’s capacity; with a fixed discharge current, the battery’s capacity in amp-hours or milliamp-hours can be determined solely from the discharge time. The battery’s equivalent series resistance (ESR) can also be calculated, as the test proceeds, by momentarily suspending the discharge process, measuring the difference between the open-­ circuit voltage and the voltage under load and applying Ohm’s Law. Solar cells have a clear knee point in their V-I curve. If the load current increases beyond this point, the cell voltage drops rapidly, as does the delivered power (see Fig.e). The maximum power point for a given illumination level can be easily determined with an electronic load, by monitoring the power delivered as the current is increased. Fig.b: a constant-voltage control loop. The op amp varies the Mosfet’s gate voltage to maintain a fixed drain voltage (if it can). siliconchip.com.au Fig.a: the FQA32N20 Mosfet on-region characteristics, taken from its data sheet. The maximum drain current is substantially proportional to gate voltage after an initial slope determined by Rds(on) and the gate-source threshold voltage, Vgs(th). Fig.e: a typical solar cell V-I curve, which you could plot using this Electronic Load connected to a solar panel in strong sunlight. References 1. Martin, How Electronic Loads Work (http://blog.powerandtest. com/blog/how-electronic-loads-work) 2. Keysight, Electronic Load Fundamentals (www.keysight.com/ au/en/assets/7018-06481/white-papers/5992-3625.pdf) 3. www.pveducation.org/pvcdrom/solar-cell-operation/iv-curve Figs.c & d: CR and CP modes employ both current and voltage feedback in different combinations. Note the need for analog multiplication, rather than summing, at the negative op amp input in both cases. That requires a specialised IC or a reasonably complex discrete circuit. Australia's electronics magazine September 2022  37 current-carrying wires does not affect the reading, as depicted in Fig.7. Without this arrangement, the error could be significant when the Load is sinking several amps. A simple 100kW/1.2kW voltage divider reduces the sense voltage to a level that the ADS1115 ADC can handle, and emitter-follower Q5 buffers this voltage before feeding it to the ESP32 ADC for the reason described above. Any error in the reading due to the divider resistor tolerance and emitter-follower characteristics is cancelled out during the calibration process. Rather than making a ground-­ referenced reading, because both supply wires will have a voltage across them when handling high currents, another ADC channel is used to measure the Vsense− voltage. This is subtracted from the Vsense+ voltage to get the true reading. The main PCBs for the WiFiAdditional isolated banana plug Controlled DC Load are mounted at sockets for voltage sensing test leads the very top of the enclosure. are mounted on the front panel and the base-emitter voltage of voltage-­ connected to the main + and – terfollower PNP transistor Q5. A transis- minals via 100W resistors. While this tor is used, rather than a simple diode, introduces a small error (about 0.2%), to reduce the impact of an additional it ensures that the voltage will be corcurrent load through its emitter resis- rectly sensed when the extra sensing tor on the 100kW/1.2kW input voltage terminals aren’t used. Ideally, they divider. are connected separately to the DUT, So we take advantage of the most forming Kelvin connections. linear portion of its conversion range A 1nF capacitor between Vsense− by shifting the voltage up and using and the common rail provides an AC only the lower part of the ESP32’s 3.3V path for voltage spikes and noise. maximum input voltage. Using this arrangement, tracking Current sensing between the ADS1115 and ESP32 is The design uses two INA180 curwithin 5% for both current and volt- rent sense amplifiers (IC3 & IC4), one age measurements. on each board, to amplify the small voltage across the shunt resistors into Voltage sensing a range more suitable for the ADC. The voltage at the output termi- Each INA180 is shared between two nals is sensed using a separate set Mosfets, with two 1kW resistors proof wires back to CON14 on the PCB, ducing an average of the two shunt so that the voltage drop across the resistor voltages. The resulting average voltage is measured using the ADS1115 standalone ADC’s other input channels. A 10nF capacitor from the junction of the 1kW mixer resistors to ground reduces the noise presented to the ADC without introducing any significant measurement lag. To increase the reading accuracy, we are using the ADS1115 in differential mode with the negative current sensing pin connected to ground near the INA180 current amplifier on each board. Any significant voltage difference between the ground planes of the main and daughter boards will introduce a noticeable error at low currents. For this reason, the two PCB ground planes are wired separately to the negative front panel input terminal and a stout jumper bridges the two ground planes. The ESP32 current-sensing arrangements are the same as those for voltage sensing, using PNP transistors to shift the voltage levels. Calibration To ensure accurate measurements across the entire range of voltage and current, both full-scale and zero calibration points are provided in the software for voltage and current readings. Current readings are automatically re-zeroed every time the Load is disconnected for more than a few seconds. The remaining calibrations are performed via the front panel menu. Calibration settings are saved between sessions. Heat sensing and fan control The thermistor (NTC1) is mounted on one of the Mosfet cases and connected in series with a 10kW resistor across the 3.3V rail. The ESP32 measures the voltage at the junction and calculates the temperature. Fig.7: the voltage sensing scheme uses Kelvin connections. If 10A is flowing through test leads, each with 0.1W resistance, the difference between the voltage at the DUT and the Load’s terminals will be 2V meaning it only sees 10V in this case, rather than the actual value of 12V. With additional sensing leads connected directly to the DUT terminals, if the sensing current is 10μA, even 5W resistance in the leads will only generate 50μV of error, giving a much more accurate reading of 11.9999V. 38 Silicon Chip Australia's electronics magazine siliconchip.com.au Parts List – WiFi-Controlled Programmable DC Load 1 WiFi control board (based on design from May & June 2021; see below for parts list) 1 double-sided PCB coded 04108221, 107 x 81mm 1 double-sided PCB coded 04108222, 67 x 81mm 1 270mm x 210mm x 140mm blue vented metal enclosure [eBay, Banggood, AliExpress] 1 12V DC 1.5A plugpack with centre-positive 2.1mm or 2.5mm ID plug 2 Hyper 103 coolers or similar [eg, www.umart.com.au] 3 120mm fan guards 1 30A relay module, 5V or 12V DC coil (see text) 1 470μH axial inductor (L1) [Altronics L7042A, Jaycar LF1542] 1 10kW lug-mount NTC thermistor (NTC1) [Altronics R4112] 1 2x10-pin IDC box header (CON1) 2 2x5-pin IDC box headers (CON2, CON3) 1 insulated coaxial DC panel socket to suit plugpack (CON4) [Altronics P0629] 1 red 30A binding post (CON5) [Altronics P9210, Jaycar PT0465 or PT0460] 1 black 30A binding post (CON6) [Altronics P9212, Jaycar PT0466 or PT0461] 1 red panel mount safety banana socket (CON7) [Altronics P9266, Jaycar PS0420] 1 black panel mount safety banana socket (CON8) [Altronics P9267, Jaycar PS0421] 2 4-pin PWM fan headers (CON9, CON10) [Molex 47053-1000, Cat SC6071] OR 2 2-pin polarised header (CON11, CON12) for non-PWM fans 1 4-way polarised header and matching plug with pins (CON13) 3 2-way polarised headers and matching plugs with pins (CON14, CON15, CON16) Hardware & wire 1 128 x 200mm sheet of 2mm-thick clear acrylic (front panel) or decal 1 250 x 130mm sheet of 3mm-thick clear acrylic, 5mm ply or aluminium sheet (for CPU cooler mounting) [Silicon Chip SC6514] 8 M4 x 12mm countersunk head screws and nuts (for mounting CPU coolers) 4 M3 x 25mm panhead screws (PCB mounting) 4 M3 x 12mm panhead screws (for mounting Mosfets) 14 M3 x 12mm countersunk screws (switches, TFT etc) 22 M3 hex nuts 4 M3 flat washers (for mounting Mosfets) 8 6mm M3-tapped Nylon spacers 1 1m length of twin 15A hookup cable [Altronics W2188, Jaycar WH3079] 1 1m length of light-duty figure-8 cable (eg, ribbon cable) 1 40cm length of red heavy-duty hookup wire 1 20cm length of blue heavy-duty hookup wire 1 1m length of green heavy-duty hookup wire 2 20-way crimp IDC headers 2 10-way crimp IDC headers 1 15cm length of 20-way ribbon cable 1 10cm length of 10-way ribbon cable 1 10cm length of 7-way ribbon cable (for encoder panel) 1 10cm length of 4-way ribbon cable (for switch panel) 1 small tube of thermal compound 4 35 x 16mm, 9mm-thick spacer blocks (eg, cut from MDF) siliconchip.com.au Semiconductors 2 LM358D dual single-supply op amps, SOIC-8 (IC1, IC2) 2 INA180B4IDBVT current sense amplifiers (B1 variant), SOT-23-5 (IC3, IC4) 1 MCP4725A0T-E/CH 12-bit DAC, SOT-23-6 (IC5) 1 ADS1115IDGS ADC, MSOP-10 (IC6) 1 SN74LVC2G02DCTR dual 2-input NOR gate, SSOP-8 (IC7) 1 CUI VXO7805-1000 5V 1A switching regulator module (REG1) 4 FQA32N20 800V 10A Mosfets, TO-247 (Q1-Q4) 2 BC807C or BC807-40 50V 500mA PNP transistor, SOT-23 (Q5, Q6) 1 SS8050-G 40V 1.5A NPN transistor, SOT-23 (Q7) 5 BAS70, BAS70-04, BAS70-05, BAS70S or BAT70C 70V 200mA schottky diodes, SOT-23 (D1-D5) Capacitors (SMD X7R ceramic, M2012/0805 size unless stated) 2 10μF 16V M3216/1206 size 1 1μF 200V polyester 4 1μF 16V 4 100nF 50V 6 10nF 25V 5 1nF 50V Resistors (SMD M2012/0805 size 1% 1/8W unless stated) 6 1MW 4 100kW 2 47kW 4 18kW 2 10kW 4 2.2kW 1 1.2kW 14 1kW 8 470W 1 820W 1 100kW 1/2W through-hole 2 100W 1/4W through-hole 1 4.7W 1/2W through-hole 4 0.02W 3W 5% wirewound through-hole WiFi control board 1 double-sided PCB coded 18104212, 167.5 x 56mm 1 Espressif ESP32-DEVKITC-compatible WROOM-32 WiFi MCU module [Altronics Z6385A, Jaycar XC3800, NodeMCU-32S] 1 3.5in 480x320 pixel SPI LCD touchscreen with ILI9488 controller [Silicon Chip SC5062] 1 2x10-pin box header (CON2) 2 19-pin header sockets (eg, cut from a 40-pin header) 1 rotary encoder (RE1) [Alps EC12E; Jaycar SR1230] 1 knob for rotary encoder [Altronics H6514 (23mm) or Adafruit 2055 (35mm)] 4 12mm SPST PCB-mount tactile switches with square actuators (S1-S4) [Altronics S1135, Jaycar SP0608] 2 black, white or grey switch caps [Altronics S1138] 1 red switch cap 1 green switch cap 1 10cm length of 6-way ribbon cable 1 10cm length of 4-way ribbon cable Semiconductors 1 7805 5V 1A linear regulator, TO-220 1 5mm green or red LED (LED1) Capacitors 1 47μF 10V X5R/X7R SMD M3226/1210 size 1 10μF 25V X5R/X7R SMD M3226/1210 size 13 100nF 50V X7R SMD M2012/0805 size Resistors (all SMD 1%, 1/10W M2012/0805 size) 3 10kW 2 1.8kW 1 1kW Kit (SC6399) – $85 It includes all the SMDs, the four FQA32N20 Mosfets, four 0.02W 3W resistors and the VXO7805-1000 regulator module. Australia's electronics magazine September 2022  39 If the specified thermistor isn’t available, you can use any 10kW NTC lugmount thermistor, as the temperature reading is also calibrated in software. Once the case temperature reaches 28°C, the fan speed increase beyond idling, reaching full speed at 35°C. If the case temperature exceeds 65°C, the Load disconnects the DUT. Provision has been made for threewire and four-wire CPU cooler fans or 12V DC two-wire fans. Q7 translates the PWM signal into current pulses at around 20kHz for two- and three-wire fans to avoid audible switching noise. If four-wire (PWM) fans are used, NPN transistor Q7 and its base resistor are not required. Q7 dissipates little heat as it operates in switch-mode, so an SS8050 is sufficient to operate two fans up to a total current of 500mA. Protection Protecting an electronic load is somewhat more complicated than a power supply, which mainly needs to be protected against short circuits and any reactive load characteristics that might cause the supply to oscillate. Electronic loads also need to be able to prevent damage when excess or reverse voltages are applied. As well as the microcontroller shutting down the Mosfets when the maximum allowed current or voltage is exceeded, a relay provides a final layer of protection, mainly for the DUT. If a reverse voltage is applied across the Load, the body diodes in the Mosfets will conduct. As the Mosfets are each rated at 32A continuous reverse current and pulses of 128A, huge currents could flow in this case. We take advantage of the fact that the ADS115 can measure voltages to 0.3V below ground. The relay is released when a negative input voltage greater than -0.1V is detected. The relay opens within 10ms, which should prevent damage to the DUT in most cases. A 30A relay module with NO contacts is employed to save on-board real estate. These are available from multiple internet sellers. Parts availability and substitutions We can supply a set of all the SMDs for this project (plus some other useful parts, like the Mosfets and regulator module) as many of them are currently hard to source. We also can supply the ESP-32 module and touchscreen; see the parts list. If you can’t get the ADS1115, if the ADS1015 is available instead, you could use it with a slight loss in reading accuracy. You might find it easier to source an ADS1115 based module and transplant the IC (eg, remove it using hot air). Different versions of the MCP4725, such as the A1, A2 or A3 version, could be used as the software scans all possible I2C address. That address is the only difference between those versions. The DAC7571 is a compatible replacement for the MCP4725, but there’s no guarantee it will be available either. Once again, the easiest way to get one of these chips might be off a prebuilt module. If you can’t get the SN74LVC2G02DCTR, the 74HC2G02DP or 74HCT2G02DP (or any other similar device) can be used instead. 40 Silicon Chip Australia's electronics magazine The contacts on these relays should be more than adequate, as contact ‘make’ will usually occur at zero load as the Mosfets ramp up to the set current, and ‘break’ activity will usually be in concert with the Mosfets switching off. Provision has been made for either 5V or 12V relay modules. A few different types of this module are available; the best kind has fairly large ‘terminal barrier’ style connections for the relay contacts. If a small terminal block is supplied instead, the power wires should be soldered directly to the PCB. As the remote voltage sensing pins are connected on the ‘wrong’ side of the protection relay, schottky diode D5 is connected across the ADC pins such that it is ordinarily reverse-­ biased. This keeps any negative voltage within the acceptable -0.3V limit. As there is a 100kW resistor in series with the diode, a small signal diode suffices to handle the few milliamps of potential current. siliconchip.com.au Fig.8: this control circuit was previously published in the May 2021 issue; the few changes are shown in red. While the original control board can be modified, we have an updated PCB that can be configured with a couple of solder bridges. It includes a simple power supply, ESP32 microcontroller module with WiFi, a colour touchscreen, SD card socket, rotary encoder and pushbuttons, plus a 20-pin DIL header (CON2) that connects to the Load circuit via a ribbon cable. siliconchip.com.au Australia's electronics magazine September 2022  41 Operating Mosfets in linear mode There are some challenges operating power Mosfets in linear mode. Most modern high-power Mosfets are optimised for switch-mode operation, where most of the time, they are fully on or off. This type of operation generates only moderate heat, as the internal resistance of the device in this mode is usually measured in milliohms. 10A through 5mW only generates half a watt of heat. When conducting 10A in linear mode, the dissipation is 10W for every volt across the device. While a Mosfet in a TO-220 package may well be able to handle 30A at a maximum VDS of 200V, it certainly will not be able to dissipate 6000W in lin- Fig.f: typical HEXFET Mosfet device geometry [Ref 2]. This is not the ear mode! As a rule of thumb, TO-220 devices can only type of Mosfet cell structure, handle 50W when closely thermally cou- but it is a fairly common scheme. pled to a large heatsink. TO-247 devices, with double the package footprint, can dissipate at least 75W. So, any design using Mosfets in linear mode will typically be limited by the ability of the package and heatsink to transfer heat away from the chip. The second challenge is that the architecture of most modern Mosfets, which works well for switch-mode operation, has disadvantages for linear operation. Modern Mosfets have multiple FET structures connected in parallel to han- Fig.g: hotspot damage in a Mosfet dle high currents. Close-packed hexagons [Ref 4]. This could cause the entire (Fig.f) or trench matrices are common. device to fail due to an internal Regardless of the structure, the goal is short circuit, but even if it doesn’t, to connect all the small Mosfets in paral- the device performance will certainly degrade. lel, so they operate like one large Mosfet. This is because Mosfet properties don’t scale well, so many small ones perform better than one big one. However, as all cells are not identical, one cell tends to carry the highest current. In the worst case, this can cause such a severe hot spot that the material melts, as shown in Fig.g. Even if the damage to the overall device isn’t catastrophic, after the first cell failure, the next weakest cell will follow and so on, degrading performance. However, if the hot-spot cells can cool between bursts of current, as in switch-mode operation, the possibility of failure is significantly reduced. For linear operation, it is therefore best to significantly de-rate the Mosfet. Early planar devices were better suited to linear operation. While some newer devices are designed for linear operation, they are expensive, and their total dissipation is still limited by their ability to transfer heat from the junction to the case and heatsink. Therefore, we are using four TO-247 general-purpose power Mosfets for this project, operated well below their maximum current and power ratings. References 1. Hüning, F. Using Trench Power Mosfets in Linear Mode. Power Semiconductors magazine 2012, Renesas 2. www.slideserve.com/harlow/mosfet 3. Williams, et al., The trench power Mosfet: Part I - History, technology, and prospects, IEEE Transactions on Electron Devices, March 2017 4. Nexperia Application Note AN11243: “Failure signature of electrical overstress on power Mosfets” 5. OnSemi (Fairchild) Cabiluna, et al., (2013), AN-4161 Practical Considerations of Trench Mosfet Stability when Operating in Linear Mode 42 Silicon Chip Australia's electronics magazine The reverse leakage current of the BAS70 is less than 20nA, small enough not to materially affect voltage measurements. Over-voltage protection for the ADC is provided by setting the ADC’s full-scale sensitivity to 2.048V, leaving a substantial safety margin before the VDD+0.3V absolute maximum is exceeded. This allows us to safely sense voltages up to 260V. Control circuitry The control panel reuses the microcontroller module/touchscreen design from the Hybrid Bench Supply project (May & June 2021, siliconchip.com.au/ Series/364). While the 3.5in touch screen version is preferred, software is also provided for the 2.8in version. Both of these screens are available from the Silicon Chip Online Shop. The circuit of this control board is shown in Fig.8. As this is very slightly different from the one previously published, a revised PCB is available that can suit either project. For this design, we need ADC-­ capable pin IO32 of the ESP32 to go to the CON2 Control header, rather than IO25 as initially designed, because IO25 cannot be used as an analog input. 100nF capacitors have been added from IO25 & IO32 to ground, to stabilise analog voltage readings made using those pins. Enclosure Finding a suitable enclosure was challenging, as the smallest dimension needed to be more than 92mm to fit the CPU coolers. The 270mm x 210mm x 140mm blue metal enclosure we ended up using is available from multiple suppliers on eBay and Ali­ Express, and is a cost-effective solution. It has ventilation slots in the sides and all panels are removable for easy access. While Mini-ITX computer cases could also be employed, few of those we came across had solid front panels on which to mount the control components. Next month In the second and last article in this series, we’ll have the assembly details for all the PCBs as well as the enclosure preparation, mechanical construction and final assembly. We’ll then go over testing, calibrating and using the Electronic Load. SC siliconchip.com.au Design, service or repair with our 100MHz Dual Channel Digital Oscilloscope Need more info than your DMM can display? Upgrade to this new and affordable feature-rich oscilloscope to get an accurate picture of your circuit's operation. 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 Creality CR-X Pro J aycar Electronics kindly lent us one of their new 3D printers – the TL4411 Creality CR-X Pro. We recently reviewed the Anycubic Photon Mono 3D Printer (July 2022; siliconchip.au/Article/15380), one of the newer resin-based 3D printers. So this seemed like an appropriate time to see what is the latest in the field of filament 3D printing. As times have progressed, nearly all recent 3D printer offerings are pre-­ assembled or require, at most, attaching a few parts here and there. The CR-X Pro requires some assembly, but nowhere near as much as the older kits. In the Anycubic review, we mentioned that we had previously looked at other filament-based printers going back around 10 years. Those were the UP! in August 2011 (siliconchip.au/ Article/1132), the RapMan in December 2012 (siliconchip.au/Article/450) and the Vellemann K8200 in October 2014 (siliconchip.au/Article/8040). The latter two were both sold as fairly involved kits, requiring a lot of work to get them going, both in construction and calibration. This Creality printer is very much easier to set up, as we shall describe. If you are unfamiliar with how 3D printing works, we recommend reading the article “From body parts to houses: the latest in 3D Printing” in our January 2019 issue (siliconchip. au/Article/11367). Also see the glossary later in this article. Technical specifications 3D Printer 3D printers have come a long way in recent years and we are spoiled for choice in the range of filamentbased 3D printers that are now available. Jaycar offered to loan us a Creality dual-filament printer for evaluation, so we took the opportunity to look at one of the newest ‘kids on the block’. Review by Tim Blythman 44 Silicon Chip Australia's electronics magazine The Creality CR-X Pro is a dual-­ filament 3D printer with a nominal build volume of 30cm wide, 30cm deep and 40cm tall. The unit itself measures around 80cm tall, 50cm wide and 60cm deep. It accepts widely-available 1.75mm diameter filament (the extruder has a 0.4mm nozzle aperture). The box includes two 1kg rolls of PLA filament in red and yellow. There is also a collection of tools and spare parts in the pack, which you can see in Fig.1. All of this is good to know when shopping for a 3D printer, but there is much more than just the bare specifications. The CR-X Pro Creality has been around for about eight years and has produced several 3D printer models, including both resin and filament types. The CR-X siliconchip.com.au One nozzle, two filaments The dual filament arrangement is siliconchip.com.au Fig.1: The included tools and spare parts are comprehensive. Not shown here are a pair of side-cutters (for cutting filament), a pair of spare Bowden tubes and a USB cable. We didn’t need any other tools during setup or operation. The needle-like object is a tool for unblocking nozzles and comes packed in a large block of foam. Frame Bowden Tubes X-axis Motor Extruder 1 Nozzle Extruder 2 BL Touch Print Bed Z-axis Motors Power Socket & Switch Pro is an update of the similarly-­ dimensioned CR-X, an older dual-­ filament design. The CR-X and CR-X Pro are so-called ‘Cartesian’ machines, meaning that the X, Y and Z axes operate independently and at right angles to each other. One stepper motor controls the printing head’s left-to-right motion, including the nozzle (the X-axis). The Y-axis is forward and back, achieved by moving the printing bed. The Z-axis is driven vertically by two lead screws, one on each side of the bed. Fig.2 shows the general arrangement. The X-axis is carried on the Z-axis, moving up and down with it. There are other arrangements for Cartesian-type printers; for example, some might move the bed up and down (instead of the printing head) to form the Z-axis. Non-Cartesian types might use linkages or pulleys to combine stepper motor actions to synthesise the axes that the printer uses internally. The arrangement used in the CR-X Pro means that the Y-axis stepper must have the power to move the weight of the bed, while the slower-moving Z-axis carries the weight of the extruders and the X-axis. Other arrangements have pros and cons, but the configuration used here is quite common and simple to design and manufacture. The frame is made of aluminium slotted channel, with the base covered by a black powder-coated folded sheet metal cover. The frame is powder-­ coated in a similar colour. The resemblance to older designs such as the K8200 is clear, but the execution and appearance have come a long way over the years. The CR-X Pro has cleaner lines and is sturdier. The extruder arrangement is pretty standard. The extruder motors are fixed to the Z-axis and feed the filament tubes to the nozzle on the moving X-axis via flexible Bowden tubes. This reduces the weight that the X-axis is required to move. The Bowden tubes introduce a small amount of slack in the filament path (compared to an extruder mounted directly to the nozzle), but this doesn’t appear to be a problem in this case; the Bowden tube is another prevalent design choice in filament-based 3D printers. Y-axis Motor Bed Adjustment Base Touchscreen Card Slot & USB Socket Fig.2: the general arrangement of the CR-X Pro, typical of many filament-based 3D Printers. The X- and Y-axis motors move the nozzle relative to the heated bed, with the extruders driving melted plastic out as needed. The model is built up layer-by-layer as the Z-axis travels upwards. The heated bed helps the lower layers adhere until the print is complete. Australia's electronics magazine September 2022  45 Creality CR-X Pro: features & specifications Printer type: dual filament extruder Print area: 300mm x 300mm x 400mm Power supply: 480W Nozzle aperture: 0.4mm Filament size: standard 1.75mm (2kg PLA included) Filament presets: PLA and ABS Software: two slicer programs included Print bed: textured glass (heated) Bed levelling: touch sensor for automatic bed levelling and compensation Other features: power loss resume, minimal assembly needed simple but functional. A Y-splitter combines the filament paths from both Bowden tubes into a single ‘hot end’ and nozzle. The filament paths merge where both filaments are still cold and solid. We’ve seen a few other nozzle arrangements for dual filament operation, and they too have various pros and cons. Some have two completely independent nozzles. This allows for independent extrusion, with the downside that the vertical and horizontal distance between them must be accounted for. Also, the available print area is reduced due to the distance between the nozzles. When printing with dual filaments, the CR-X Pro manual mentions a reduced print area (down to 27cm by 27cm in the horizontal plane). However, this is due to the purge tower, which we’ll explain later. We’ve seen other nozzles that combine the filaments in the hot zone, allowing the filaments to mix at varying ratios. This is great for combining colours, but we expect it would be more prone to being blocked. The large mixing area also means that cross-­ contamination is likely. One reason we have heard for using two different filaments is that a support filament (see glossary) can be printed in a different type to the main filament. For example, water-soluble filaments exist, allowing the supports to be washed away. We don’t think the CR-X Pro will be suitable for such a use as there is some mixing of filaments in the nozzle, meaning there will always be some filament cross-contamination. Different filament materials often require different nozzle temperatures, and this is not always practical with a single nozzle that would need frequent temperature changes to achieve this. 46 Silicon Chip We can see the appeal of the simplicity in the arrangement used on the CR-X Pro, although it only allows for printing in two different colours of the same filament type. For those interested, the CR-X Pro uses the open-source Marlin firmware. Out of the box We received the 3D printer in retail packaging from Jaycar and were thus able to experience the ‘out of the box’ journey. Assembly is not complicated, but we noticed some things along the way that might help you if you are thinking of buying this 3D printer. Like many 3D printers, the CR-X is knocked down inside the box and requires a small amount of assembly to complete. Fig.3 shows what we saw on opening the box. Some aspects might not be evident if you have not used a 3D printer before. For example, the print bed is not restrained in its travel and might slide around if care is not taken when removing the parts from the box. It’s all doable by one person but will be much easier with someone to help. Additionally, the Z-carriage, which moves vertically in the assembled printer, is fairly well fixed in place as it runs on lead screws. But unlike the photo in the manual, the Zcarriage is fully lowered, and we found that it came in contact with the glass print bed during assembly, marking it slightly. Attaching the two parts is fiddly. Each side of the vertical frame is attached to the base by a recessed machine screw via the holes under the base. Yet the machine does not lend itself to being rested on its side. We recommend that one end of the base be rested on the edge of a bench, with the other end held up by a willing assistant. This gives access to the screw holes in the middle of the base, leaving two hands free: one to hold the frame in place while the other fits the screw from underneath. The included tools are quite complete and include a hex key for tightening these screws. The frame is remarkably solid despite having no reinforcement apart from the machine screws holding the channel pieces together. Other designs require triangular reinforcement members, but the CR-X Pro is rigid enough without them. The filament roll holders are a bit tricky to install. They use T-slot nuts in the frame’s channel. We suggest leaving off the spools until after the brackets are secured. Some cables connect between the frame and the base. They are easy enough to fit, but we found that the two Z-axis motor cables came close to fouling the bed mechanism. So we pushed the cables back into the base slightly to minimise the amount of slack, then used the provided tape to secure the cables flush against the base, as shown in Fig.4. Fig.3: the CR-X Pro comes well-packed. We strongly recommend having an assistant to help with the unboxing and assembly, as the printer is large and unwieldy, although not too complicated. Australia's electronics magazine siliconchip.com.au While the printer is powered down, it is possible to move the bed by hand, so you can easily check the clearances before powering up the printer. Simply slide the bed back and forth to confirm that nothing will hit anything. You can do a similar thing with the X-axis and check that the nozzle can move freely left and right. The print bed is glass with a textured coating on one side. Glass is an excellent choice for its flatness, and we found that the textured coating worked very well to promote adhesion. We previously found that polyimide tape (such as Kapton) is one of the best bed surfaces for adhesion. We tried that on the CR-X Pro, and while we would say that it worked marginally better than the textured glass, it was not by much. Certainly not by enough to go to the trouble to apply and maintain the tape. controller if done while the printer is on. We tested the USB connection and found no fault with its operation otherwise. But experience has taught us that this isn’t the best way to run printing jobs. Any glitch in the connection can easily cause a print to fail, so we ran all our test jobs from a micro SD card, eliminating any chance of issues with the computer or USB cable. Amongst the included parts is a micro SD card loaded with some demo files that you can print, but the printer must first be levelled and have filament loaded. BL Touch levelling which sits next to the nozzle assembly and probes the bed itself. During probing, it lowers a pushpin to measure the bed position, which it does by raising and lowering the Z-axis. Thus, BL Touch can also scan the bed and detect variations in Z height at different locations. Manual bed levelling can be done using four thumbwheels under the bed to bring the four corners into true. The firmware on the CR-X Pro can also map the bed’s surface at 25 points to compensate for minor variations across the bed. The thumbwheel alignment is helped by the AUX levelling screen on the controller, which can quickly move the nozzle between the four bed corners for calibration. The first thing we found when we powered up the CR-X Pro was that it makes a lot of sounds. There is a startup chime, and most (but not all) button presses are accompanied by a loud beep. There doesn’t appear to be an easy way to disable these. So try to avoid any midnight 3D printing! The interface is intuitive enough, and the manual details each screen and where each setting can be found on the various subscreens. We connected the printer to a computer using the included USB cable and found that this resets the internal One of the biggest challenges to getting successful 3D prints is having a print bed that is properly levelled. This is more than just ensuring that things are square to the horizontal axis; every point in the X-Y plane should ideally be at the same distance from the nozzle when the Z-axis is at its home zero point. Being too far away can prevent the filament from adhering to the bed properly, while being too close will prevent the filament from being properly extruded and can distort the lower printed layers. It could even damage the bed surface. Most of the older printers we have used have a mechanical limit switch testing Z-axis movement against the frame to detect that the Z-axis is zeroed consistently and correctly. Instead, the CR-X Pro includes the BL Touch auto bed levelling sensor, Fig.4: there isn’t much clearance between the thumbwheels and the wires for Z-axis stepper motors, but it turned out OK with some careful adjustment of the wires and application of the provided tape. Fig.5: the Z-axis compensation can be found on the Adjustment screen, which only appears to be accessible during printing. If the nozzle is too far from the bed, increase the compensation to bring it closer. The best time to do this is during the first layer of a printing job. First power up siliconchip.com.au Australia's electronics magazine Settings One critical point not mentioned in the manual is a subtle deviation from how older sensors (like the mechanical limit switch) worked. This could be a trap for those familiar with this arrangement. The BL Touch acts against the bed, so it doesn’t have a fixed, external point of reference like a limit switch would. So simply adjusting the thumbwheels does not change the Z height offset, which would otherwise be done by a small screw adjusting the position of where the limit switch is triggered. Instead, there is a Z offset parameter which is not mentioned anywhere in the manual, but is what sets the offset between the BL Touch and the September 2022  47 nozzle. You can find it on the Adjustment screen (Fig.5), which can only be accessed during printing. So the only way to set the Z offset is to start a print job and change it during the print. It’s a bit awkward, but we’ve had excellent results once we found this. We simply adjusted the Z offset until the extruded filament firmly adhered to the bed. That might take a few attempts, but we’ve found that if the printer successfully lays down the first few layers, all is probably well. So at worst, you might get a few prints failing very quickly until this is dialled in. Once it was set, we found that occasional minor adjustments were all that were needed. Another setting we adjusted was to turn off the auto-levelling on the Levelling Mode screen. We didn’t notice any difference between prints, whether it was on or off, except for the extra time taken to do the 25-point bed probe during every job. Since that can be triggered manually, we didn’t feel it was necessary at the start of every print. We were happy with the results when running the auto-levelling around once in every ten prints. Filament handling Loading filament requires that the nozzle be heated, and since the CR-X Pro includes two rolls of PLA filament, we simply used the PLA preset from the TEMP screen. The built-in power supply is a healthy 480W, so heating is quick. The PSU has a fan that cycles on and off. We found that this fan was the loudest aspect of the printer during operation. We timed it at about two minutes for the nozzle to heat up to operating temperature from around ambient on a cold day. The bed took around the same time to heat up. Using the trick of cutting the tip of the filament to a point, we had no trouble loading the filament, although you do have to be careful not to force both filaments into the nozzle simultaneously. The included red and yellow filament made it easy to see when one was retracted back into the Bowden tube. That might be trickier with a white or clear filament. Another way to tell is that the filament coming down from the rolls is slacker on one side (where the filament has been retracted) and 48 Silicon Chip Fig.6: with the front cowl loosened, the filament splitter can be removed using the included hex key tools (shown removed here). This gives access to the filament path through the hot end and nozzle, allowing it to be unblocked if necessary. tighter on the side that is loaded to the nozzle. We had a blockage early on, which we suspect might have been due to us not retracting one filament before loading the other. Fortunately, it was quite easy to clear. Two hex head screws hold the cowl surrounding the nozzle assembly; it is easily loosened, although the wiring means it cannot be removed completely. Nor should it, as the front-most fan should remain running to keep the heat break cool. You can gain access to the top of the filament path by removing the Ysplitter, similarly secured by two screws. Fig.6 shows the cowl loosened and the Y-splitter detached. The nozzle tip is simply unscrewed from below. The necessary tools are included, although the spanner to suit the nozzle is a simple open-jawed type. Because the nozzle must usually be heated when removing the nozzle tip (otherwise, it is effectively glued in place with solid plastic), do it with care. We’ve seen different spanners that hold the nozzle tip captive in a cup, and we think that sort of tool would be a better choice for the job. When we had a blockage, we pushed it out with the nozzle cleaning tool and checked that the filament path was clear with a filament off-cut. We managed to start refitting the nozzle tip by hand before it got too hot, allowing us to tighten it with the spanner. It’s easy to forget that some parts of the printer get pretty hot, so take care when working on it. A quick tip: if you install the yellow filament on the left extruder and the red filament on the right, the preview Australia's electronics magazine display in the software (described below) is accurate. In use With the filament loaded and the bed levelled, the CR-X Pro was ready to print. While there are three sample G-code files on the included micro SD card, we found that they were sliced with different settings than the defaults used by the Creality Slicer program. This meant they did not work as well as they could when we first tried to print them. Firstly, the bed temperature should be set to 60°C, but the sample files used a 40°C setpoint which resulted in warping and peeling. Secondly, the initial raft layers in the samples were also set to print too fast, meaning that the extruder skips and there are gaps in the raft. This resulted in many loose filament ends that caught on subsequent layers, as shown in Fig.7. This, in turn, revealed just how close the nozzle fans are to the bed. Any loose filament strands that protruded even slightly would catch on the fans as the nozzle moved around. The clearance is about 2mm, much less than many other printers. Once we had overcome these problems, it worked well. Proper cooling of freshly extruded filament is critical to accurate printing, and the fan location is likely critical to the CR-X Pro’s success. With these settings in mind, we restarted the sample prints, then manually altered the bed temperature and print speed from the Adjustment screen and got much better results. siliconchip.com.au Fig.7: some of the sample prints printed too fast on the critical first layer, causing gaps in the extruded plastic. On its own, this is not necessarily a problem, but we found that the curled plastic caught on the fans which hang low near the nozzle, causing parts of the print to lift. We did not have this problem with files we sliced ourselves. Although not noted in the manual, Jaycar’s product web page describes a ‘Resume Print’ function that saves print progress and can resume after a power outage. The manual says, “Do not plug or unplug the power cord when power on”, but we did so to test this feature. When we restarted the printer, it did indeed prompt us to resume the previous job and could restart it. However, it did not load the correct nozzle temperature, which stalled the restart. Manually setting the nozzle temperature allowed printing to continue. Fig.8 shows the result of the interrupted print. You can see that there was at least part of a layer that the printer missed. Whether that is a critical failure depends on your specific print job. At least you have the option to resume and don’t always have to throw the partial print away if power is lost. Software The included micro SD card comes in a small USB card reader, and it includes the aforementioned sliced files for the printer plus four additional folders. One includes a PDF manual. There is also a software folder with drivers and two slicer programs. Another folder includes a troubleshooting guide, while the fourth has several different models in STL format. We did not need to install any drivers as the CR-X Pro simply uses a generic virtual serial port interface, Fig.8: the Print Resume function can successfully recover a print after a power failure, but we found that the printer did not automatically load the correct nozzle temperature. It appears that the exact printer state is not stored, as we also saw a partially missing layer in our test. which most modern operating systems support by default. Remember that it is unnecessary to use the USB connection for printing, and we do not recommend it. We first installed the Creality Slicer software. Initial setup requires selecting a printer; the CR-X Pro is not shown, so we simply chose the CR-X option. This worked without any problems that we noticed. Fig.9 shows a screen grab of the Creality Slicer program. The manual explains how to use it, but it should be clear enough to anyone who has used a similar program before. The program is simple and functional. We had no trouble loading a model and exporting it. Printing with two colours was easily done by loading Fig.9: the Creality Slicer program is similar to many others. It allows the model to be placed, scaled, rotated and previewed before generating a G-code file for the printer to process. Different filament presets can be selected at top left. We used the Creality PLA settings: 200°C for the nozzle and 60°C for the bed. Note the estimated print time of 44 hours for a print of this size. siliconchip.com.au Australia's electronics magazine September 2022  49 two models, one for each colour. Many dual-colour models are distributed in this fashion. A right-click on the viewing area brings up a menu, and the “Dual extrusion merge” option combines the two. The “Save Toolpath” button at top left exports a G-code file that can be copied to the micro SD card to be printed. If a card has been inserted into the computer, you can save this file directly to the card. In any case, you really don’t need to do much apart from loading a model such as an STL file (by dragging and dropping, or from the File menu) and then clicking on the “Save Toolpath” button. Creality Slicer gives an estimated print time which we found to be consistently 20-35% low. For example, a two-colour print that was estimated to take 4 hours and 11 minutes actually took 5 hours and 19 minutes. A large single-filament print that was estimated to take 32 hours actually took 47 hours. So it doesn’t appear to be due to the time taken to change between filaments. The latter was the largest job we attempted with the CR-X Pro; it was a hollow vase about 25cm in diameter and 30cm tall, shown opposite. Objects coming close to the full bed size will take a very long time to print. The default setting uses a so-called ‘raft’ for bed adhesion (see Fig.10), consisting of several extra printed layers between the bed and the model. It uses extra filament and adds to the print time. Other operating systems Fig.10: the default Creality Slicer settings print a raft under the model, helping adhesion and reducing the effects of unevenness in the bed. It takes extra time and filament, though. This print took about three hours; the raft alone took almost half an hour to print. The included programs, including Creality Slicer, are for Windows only (being .msi or .exe installers). We created a working profile for the opensource Slic3r slicing program (https:// slic3r.org/) that would allow Mac and Linux computers to create G-code files for the CR-X Pro. Still, despite a bit of tweaking, our basic profile did not produce results as good as Creality Slicer at its default settings, which is a credit to Creality in ensuring that the printer and its software simply work. We feel that the defaults resulted in slower printing than we were accustomed to with other printers we used. Still, successful prints are more important than fast ones. Getting good results without hours of tinkering and adjusting is critical to lowering the barrier to 3D printing for beginners. That was missing from the earlier 3D Printers, but Creality Slicer is easy to use and is an important part of this. Cura Slicer software Fig.11: print jobs requiring both filaments use a purge tower (at left) to change filaments. We found that one of the sample prints also created these blobs, which caught the nozzle and occasionally resulted in a horizontal offset in the printed object. That didn’t happen with the models we sliced ourselves. 50 Silicon Chip Australia's electronics magazine Creality Slicer is based on Cura Slicer, a different open-source slicer program that Ultimaker maintains. Cura Slicer is also on the included micro SD card and can be used instead of Creality Slicer. There is a preset for the CR-X, which we used; Cura Slicer also currently 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. J US T IN! • PRINT HUGE MODELS UP TO 300W X 300D X 400Hmm DUAL FILAMENT • HIGH QUALITY STEPPER MOTORS AND WITH QUIETER OPERATION • AUTOMATICALLY RESUMES PRINTING AFTER A POWER OUTAGE JUST 1299 $ • ALL-METAL DUAL EXTRUDER • DUAL FANS FOR IMPROVED HEAT DISSIPATION • TOUCH PROBE FOR 9-POINT AUTOMATIC BED LEVELLING • CARBORUNDUM GLASS PLATFORM FOR RELIABLE PRINT ADHESION • NEW QUALITY MEAN WELL POWER SUPPLY • UPGRADED SILENT MOTHERBOARD • NEW AUTOMATIC BED LEVELLING TL4411 GREAT VALUE! INCLUDES TOOLS & TWO 1KG ROLLS OF PLA FILAMENT • 4.3" COLOUR TOUCHSCREEN WITH EASY-TO-USE INTERFACE 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 AUTOMATICALLY SWAPS BETWEEN TWO COLOURED FILAMENTS SO YOU DON'T HAVE TO. BRILLIANT! Order yours today: jaycar.com.au/p/TL4411 1800 022 888 Glossary of important terms Axis Motor The X, Y and Z axes of a Cartesian coordinate system are driven independently by stepper motors in a typical 3D printer. The X- and Y-axes are typically coupled by toothed belts for speed, while the vertical Z-axis is often on one or more helical lead screws. Bed The surface onto which an object is printed. Depending on the printer, it may be stationary or move in one or more axes. It is usually heated to improve model adhesion. On the CR-X Pro, it is a textured glass surface that also aids adhesion. BL Touch A type of limit switch that uses a retractable probe detected by a Hall Effect sensor. On the CR-X Pro, it is used to measure the position of the bed relative to the nozzle moving with the Z-axis. You can also use it to map the bed to compensate for non-planarities. Bowden Tube A hollow, flexible tube that guides the filament from an extruder to the hot end and nozzle. It allows the extruder to be mounted remotely, so it doesn’t have to move with the nozzle, reducing the amount of moving mass. Extruder Usually a stepper motor driving a knurled shaft that grips the filament against a sprung roller. This allows the extruder to feed and retract the filament at a controllable rate. The spring allows the filament to be moved by hand if necessary, such as when loading and unloading filament. G-Code File A text file containing commands in the RS-274 CNC programming language. It is usually generated for a particular model of 3D printer by ‘slicer’ software and contains instructions that the printer follows to produce the object. Hot End The hot end is used to melt the filament. It sits directly above the nozzle and is typically a metal block heated electrically and monitored with a thermistor. It is accompanied by a heat break, such as a finned heatsink cooled by a small fan, to provide a sharp transition between the hot and cold parts of the filament path. Blockages can occur if hot plastic works its way into the cold part. Nozzle In the CR-X Pro, this is a pointed brass tip with a 0.4mm orifice through which the molten plastic is extruded. Its size dictates the smallest details that can be printed; it is mounted directly to the block on the hot end. Slicer A computer program that converts an STL file into a G-code file. This is known as slicing as the printed object consists of thin slices stacked vertically. Examples that are bundled with the CR-X Pro include Creality Slicer and Cura Slicer. STL File A file format commonly used for distributing 3D models. An STL file is usually generic enough that it could be printed on any 3D printer (within that printer’s limitations). Supports If any part of a model has an overhang (typically more than 45°), supports can be used to stop those parts from drooping during printing. The supports are printed plastic elements that can be broken away from the finished print. There is usually an option in the slicer program to enable supports for a given print job. 52 Silicon Chip Australia's electronics magazine lacks a preset for the CR-X Pro. The default settings are slightly different and present a few more options than Creality Slicer, but we did not find any significant differences in the printed results. In general, we found that the default supports Cura Slicer generated worked better and were more easily removed than those from Creality Slicer. On the other hand, the default brim (as opposed to raft) that Cura Slicer uses made for a rougher finish on the first layer. No doubt there are numerous settings to tweak all those things. We encourage new users to try both and see what they prefer; you might prefer Cura if you have used it previously or would like to delve deeper into the settings. Sample G-code Armed with better knowledge, we had another go at printing the sample G-code files. Even so, we don’t think they are a great showcase of the CR-X Pro’s abilities. There are three G-code files on the micro SD card. One is a yin-yang symbol (the file is named “taiji”), a great way to show off a dual extruder 3D Printer. Unfortunately, this was consistently affected by an odd but troubling glitch we didn’t see with any other prints. When the CR-X Pro changes between the two filament colours, it retracts the old filament and extends the new filament. It then runs what is commonly called a ‘purge tower’, visible on the left of Fig.11. An amount of the new filament is extruded onto the corner of the print bed. As this occurs on each layer, the result is like a tower. A large blob of filament is extruded on this tower for this particular model. We found that the nozzle would run into this lump (making a noticeable clunking noise). Occasionally, this would knock the nozzle off its position, meaning that subsequent layers were printed offset. With the smaller jobs we printed, the purge tower used at least as much filament as the printed object. So be aware when printing with two colours that the CR-X Pro will use substantially more filament. The purge tower is printed for every layer up to the full height of the model, whether a colour change is needed or siliconchip.com.au not. If it didn’t do this, there might not be a previous layer on the tower for the purge to attach, which would lead to loose filament and failed print jobs. The net result is inefficient filament usage. Fortunately, multiple models printed in parallel at the same time require only one purge tower, so you can save some filament by running many smaller jobs or copies simultaneously. The other two sample prints are so-called print-in-place mechanisms. That means there are interconnected moving parts that are printed in one job. A simple example of this is a gearbox. The individual gears and housing are printed together meshed, but are not fused. After being removed from the printer, they work as separate parts. One of the models (“tuzi”) is a rabbit head with jointed ears. The ears articulate quite well, but we noticed that despite the purge tower, the colours, especially the yellow, were not pure. The yellow was clearly reddened to varying degrees in different places. Some of the other files we sliced with Creality Slicer had a much larger (broader and deeper) purge tower. So we think the purge tower in this test print is simply not large enough. The third model is a folding cube (“fangkaui”) consisting of eight small cubes. It, too, is printed in one piece and can fold once removed from the bed. Like the rabbit, we found that it had inconsistent colouring. We also found that some of the joints did not work as expected, possibly because it has tight clearances. We also tried printing a pair of the included STL file models (from the “box3” folder) by running them through Creality Slicer with its default settings. That worked well, and we recommend that new users start with those models. Further observations We noted a few quirks while working with this printer. For example, the bed’s home position is at the front left, with the bed fully retracted to the printer’s rear. At the end of a job, the X and Y axes are homed, meaning that the bed needs to be moved forward to retrieve the print. Still, that is a minor point and could probably be fixed with some custom G-code. siliconchip.com.au This vase was the largest object we printed at around 25cm in diameter and 30cm tall. This print took a few days to complete, but large prints like this are a very good reason to get such a printer. At these sizes, printing artefacts are practically invisible. This heartshaped box is one of Creality’s provided STL files. It has printed well, capturing the detail of the flourishes within the resolution limits of the printer. The lid is a separate part that is a snug but neat fit for the base. Australia's electronics magazine September 2022  53 This is the test print that suffered printing errors (see Fig.11). You can see a step in the red part at the bottom. Despite the volume of plastic wasted in the purge tower, the colours still mix. You can see this in a comparison of the yellow of the top layer against the more pure yellow of the raft that is printed underneath it. Fig.12: the extruder mechanisms are solidly built but the filament feeds in at a sharp angle. This does not prevent smooth operation, but we saw these flakes of plastic being shaved off the filament as it passed through. 54 Silicon Chip Australia's electronics magazine As the filament feeds into the extruder, it turns sharply into its inlet, and we found that this caused fine flakes of filament to shave off. The sharp bend also places an added load on the extruder. Fig.12 shows the angle of the filament and the fragments that accumulate. This doesn’t seem to affect operation, but still could be eased by a guide wheel or perhaps another short length of Bowden tube. We saw one similar 3D printer where the owner had relocated the spools to the side of the frames instead of the top. That should be easy enough, as both parts are similar aluminium extrusions, and the sides should accept the T-slot nuts. That might help by bringing the filament in at a better angle, assuming you have the bench space to make the change. However, if you are using the full printer height, it might worsen as the extruder intake gets near its top. None of these points are major impediments to operation, but they are certainly opportunities for improvement. Conclusion Filament-based 3D printers have come a long way since our last review. We had no trouble printing in both single- and dual-filament modes. Even those who have not used a 3D printer previously should quickly find their way around the CR-X Pro, especially after reading this review. The common theme we have seen with the design choices in the CR-X Pro is that they are simple and effective, and they work. The Creality Slicer settings have been dialled in well and produce good results, although some users might find that they are wasteful of filament or slow. The included alternative of Cura Slicer is handy. 3D printers that just work are critical to ensuring that people new to 3D printing get the most from the experience. With some minor caveats, the CR-X Pro succeeds in this regard. Being based on solid hardware and the Marlin firmware means that the CR-X Pro is also adaptable. We expect experienced users will quickly refine a custom profile for the slicer program of choice. The CR-X Pro is available from Jaycar Electronics (catalog code TL4411) for $1299. SC siliconchip.com.au Keep your electronics operating with our wide range of replacement Power Supplies Don't pay 2-3 times as much for similar brand name models when you don't have to. Bring in your device and we'll help you find the right power supply for your needs. COMPATIBLE WITH MOST LAPTOPS ON THE MARKET SUITS COMPUTER & SURVEILLANCE SYSTEMS GENERAL PURPOSE WITH SELECTABLE 3-12VDC OUTPUT MP3310 MP3243 Multi-voltage • Full range: 7.2W (0.6A) to 27W (2.25A) • Output voltage: 3, 4.5, 5, 6, 7.5, 9, 12VDC • 7 x DC Plugs & USB Outlet MP3310 - MP3316 FROM 1995 $ MP3321 Low-Profile Desktop Style • Full range: 60W (5A), 120W (10A) • Output voltage: 12VDC • Termination: DC Plug MP3241-MP3243 Laptop FROM 4995 $ Specialty power supplies: MP3285 JUST 29 $ Suits Alarm Systems • 16VAC 1.25A unregulated • Terminated to bare ends MP3021 FROM 29 95 $ 95 For Industrial Applications • Full range: 35 to 320W / 5 to 24VDC • Ultra compact and 1U low profile • No load power consumption MP3285-MP3294 USED IN AUSTRALIAN NBN & NEW ZEALAND UFB NETWORKS JUST 39 $ 95 Suits NBN / UFB • 12VDC 2.5A • 8 Pin Molex connector MP3539 • Full range: 45W, 65W, 87W, 90W, 112W, 120W, & 132W • Output voltage: 5, 9, 12, 14, 15, 16, 18, 18.5, 19, 19.5, 20, 22, 24VDC • Fixed, auto and manual types • USB Type-C with PD available MP3319 - MP3471 FROM 4995 $ SUITS PORTABLE FRIDGE/FREEZERS ONLY 4995 $ For Your Automotive Devices • 12VDC 7.5A • Cigarette lighter socket MP3575 Shop at Jaycar for: • Wide range of AC & DC output adaptors • Mains and 12VDC laptop power supplies • Isolated stepdown transformers • Industrial Enclosed & DIN Rail Power Supplies • Don't forget our wide range of batteries too! Explore our full range of replacement power supplies, in stock at over 110 stores and 130 resellers or on our website. jaycar.com.au/replacementpsu 1800 022 888 of -S og oc GPS y h c n e d s i A n nal o r Cl Ge f a r G s ’ m ha k w it h l o n g b at t e ry e f li This GPS Clock Driver converts an ordinary wall clock into a highly-accurate timepiece that will keep exact time (within seconds) for up to eight years using a pair of C cells. You need not touch the clock during that period; it will automatically adjust for daylight saving by adding and subtracting an hour exactly when needed. This is a clock you can rely on to tell you the correct time. is amazing how useful it is to have it at least one highly accurate clock in the house. At a glance, you know the correct time without having to remember if that clock is running slow or fast and by how much. Most people would be happy with a wall clock that was accurate to the minute, but with this project, it will be accurate within a few seconds. Even better, any inaccuracy will not accumulate – the clock will remain that accurate for the life of its battery. Adjusting for daylight saving is an annoyance with traditional quartz wall clocks. Twice a year, it forces you to get up on a chair or step stool to take down the clock and adjust its hands. Our GPS Driver automatically makes those adjustments for you. At 2am on the day specified for the start of daylight saving, the clock will begin running fast until it has added the required hour. Then, at 3am on the day specified as the end of daylight saving, the clock will run slow or stop until it has returned to the non-­ daylight saving time. This is accomplished using a GPS module to get the precise time from the network of GPS satellites and some clever software to control the clock’s hands. We have published similar designs many years ago (the last was in February 2017), but they all had a relatively short battery life. By using ultra low power components and some extra tricks in the firmware, this design will run for about two years on a pair of AA cells and up to eight years with C cells. It will work with most wall clocks on the market. All that is needed is a modification to connect wires to the stepper motor in the clock’s movement. Luckily, that is usually easy. Scope 1: the output of the GPS Clock Driver for a stepping movement consists of alternating positive and negative pulses that make the rotor in the clock’s motor to make a 180° step with each pulse. Each pulse is about 40ms in duration, and they are delivered once per second. Stepping clocks Scope 2: the output driving a sweep movement; a continuous stream of positive and negative pulses at 8Hz. Each pulse is 31.25ms long with 31.25ms between pulses, resulting in 16 pulses per second. At low battery voltages, the clock driver lengthens the pulse time by 24% and reduces the idle time by the same amount, delivering more energy to the clock’s motor. There are two types of analog wall clocks: stepping clocks, where the second hand steps once a second, and sweep clocks, where the second hand moves smoothly around the dial. Stepping clocks are more common than sweep types. They have a Lavet-type stepping motor consisting of a small magnet that rotates between a coil’s magnetic poles. The clock driver delivers alternating positive and negative pulses to this coil, and the rotor rotates 180° with each pulse. Each pulse is about 40ms in duration, and one is delivered per second (as shown in Scope 1), causing the second hand to advance once per second. Stepping clocks vary considerably in quality and price. We purchased an example for testing from Kmart for the princely sum of $2.75 and, while it was not the best, it was also not the worst clock movement. Its accuracy was terrible but, as we are replacing its driving circuit with our own, that doesn’t matter. Typically, stepping clock movements have a coil resistance between 200W and 500W, with a higher siliconchip.com.au Australia's electronics magazine resistance indicating a longer battery life (the Kmart special was 375W). Sweep clocks Sweep clock movements, sometimes called silent or continuous movements, have a similar drive motor except that it is driven by a continuous stream of positive and negative pulses at 8Hz, as shown in Scope 2. This continuously spins the rotor, with its momentum keeping it moving between each pulse, so it does not make individual steps like the stepping type movement. September 2022  57 Einstein’s theory of relativity and GPS accuracy GPS satellites circle the Earth at an altitude of 20,000km and are used to ‘trilateration’ locations using precise onboard clocks. In their high-altitude orbits, the clocks experience a weaker gravitational field, so spacetime is warped differently for them compared to clocks on Earth. The effect is that the clocks speed up at a rate of 45μs/day. The satellites are also whizzing around at pretty high speeds (about 14,000km/h), and the time dilation predicted by Einstein’s special theory amounts to slowing the clocks by 7μs/day. Together, these effects amount to a net speeding up of 38μs/day. That doesn’t sound like much, but ignoring it would lead to a vast inaccuracy in the global positioning system within a few hours. Light travels over 10km in 38μs, and that sort of error in position per day wouldn’t make for accurate navigation. The solution is to slow the satellite clocks by a precise amount calculated using Einstein’s theory of relativity so that they match time measured on the Earth’s surface. This allows the system to work to accuracies of metres rather than kilometres. Edited excerpt from “Why does E=mc2” by Brian Cox and Jeff Forshaw, ISBN 978-0-306-81758-8 As a result, the second hand moves continuously (sweeps) around the dial, and the clock is silent. This contrasts with the stepping types, which make an audible tick sound every second. Each pulse is 31.25ms in duration with a dwell time of 31.25ms between pulses, resulting in 16 pulses per second. Because the motor is drawing current 50% of the time, you would expect the battery to be flattened in no time compared to a stepping clock. Sweep movements avoid this by utilising a coil with many more turns and a higher resistance (typically 5kW). Sweep clocks are more expensive, typically $50 to $150. However, we found an excellent example at IKEA (the “TJALLA”) for just $16, and it performed pretty well, rivalling a genuine Seiko sweep movement that we purchased for around $30. The only problem with the IKEA movement was that it was difficult to pull apart to modify, and even harder to reassemble. Keeping perfect time When the clock is running, the GPS Clock Driver will need to occasionally add or subtract a second to keep the hands accurate. This is easy for a stepping movement; the Driver delivers two pulses in one second to advance the clock by one second, or no pulses for a second to retard it by one second. With daylight saving, this is more noticeable. When daylight saving starts, the hands need to advance by one hour and to do this, the Driver generates two steps every second for an hour until the hands have reached the correct daylight saving time. At the end of daylight saving, the clock will stop stepping for an hour until the time catches up with the position of the hands. Sweep movements need a different approach because we must maintain the momentum of the spinning rotor; it cannot simply go twice as fast or stop/ start. So, the adjustment must be more subtle. To add or subtract a second, the movement is run 12.5% faster or slower for eight seconds. With daylight saving, this means that it will take eight hours to add the required hour and a similar time to retard by an hour. While this is a long time for the clock to be catching up, it only happens twice a year. Instead, you could disable daylight saving in the setup and manually adjust the hands when required. How the Clock Driver works Fig.1 is the GPS Clock Driver block diagram. Microcontroller IC1 generates a sequence of positive and negative pulses that are buffered by op amp IC2. IC2 drives the motor in the clock movement. A crystal oscillator running at 32768Hz (215) drives a 16-bit counter/ timer in IC1 to generate the precise timing required. Importantly, this timer can operate while the microcontroller’s core is in sleep mode, so it only consumes a few microamps. The microcontroller spends most of its time in this low-power sleep mode. When it is time to generate an output pulse, the timer wakes the CPU to drive the output pin to start the pulse, and it resets the timer to wake again when the pulse is due to finish. When it wakes again, it terminates the output pulse, sets the timer for the next pulse and goes back to sleep. This continues forever, with the microcontroller jumping in and out of sleep and toggling the output pin to generate the pulse train for the clock’s motor. The CPU’s running time is short compared to the sleep time, so the average current drawn by the micro is very low. Fig.1: the GPS Clock Driver uses a crystal oscillator running at 32768Hz and a 16-bit counter/ timer within microcontroller IC1 to generate the precise timing required to drive the clock motor. IC1 generates a sequence of positive and negative pulses that are buffered by op amp IC2 to drive the clock movement motor. IC1 spends most of its time in sleep mode to extend battery life. 58 Silicon Chip Australia's electronics magazine siliconchip.com.au The sequence of pulses to the clock’s motor alternate between positive and negative, with a dwell time in between. This is achieved by switching the pin between high, low and high-­impedance. Op amp IC2 buffers this signal to drive the clock by bringing its output to the positive terminal of the upper cell or the negative terminal of the lower cell, or the junction for the dwell time between pulses. This divides the load between the cells, with each providing half the power for the clock motor. GPS synchronisation Not shown in Fig.1 is the boost voltage regulator that powers the GPS module. Occasionally, after delivering a pulse to the motor, the firmware will not put the CPU to sleep but will keep running and enable the boost regulator, which delivers a regulated 4V to the GPS module. It will then get an accurate time from the constellation of GPS satellites. Generally, it takes less than a minute for the GPS module to locate sufficient satellites and return the precise time. When the microcontroller has received this time, it shuts down the regulator and makes some calculations to determine any timekeeping errors. After this, it reverts to its regular strategy of sleeping until the next pulse is due. Initially, the time between GPS synchronisations is set to 12 hours, but over time the firmware will increase this to five days. The average battery power required for GPS synchronisation is minimal, so this process does not materially affect the battery life. The firmware keeps track of the position of the clock’s hands as the number of seconds since 1st January 2000. The GPS time is also converted to this format, so it is easy for the firmware to compare the two and calculate any correction that may be required. The difference between the two numbers represents the error in the 32768Hz crystal oscillator, which is used to keep the time between GPS synchronisations. By working out this error, the firmware can correct for it over the next period between GPS synchronisations by occasionally adding or skipping a second as needed. This will start working following the second GPS synchronisation and will keep the clock accurate regardless of any error in the crystal, including siliconchip.com.au compensating for additional errors due to temperature and ageing of the crystal. The practical effect is that, apart from the first day, the clock’s hands will always be accurate within a few seconds between GPS synchronisations. Also, the next GPS synchronisation should not need a large correction; maybe only a second or two (or possibly none). When the boost regulator and the GPS module are initially powered, they can draw a lot of current, especially if the cell voltages are low. This cannot be sustained by a battery on its last legs, so the firmware measures the battery voltage when running the boost regulator. If it is below 2.25V (1.125V per cell), it will skip any subsequent GPS synchronisations. This will have little effect on the clock’s accuracy as it will only occur towards the end of the battery’s life, and by then, the firmware will have a good idea of any error in the crystal and will continue to compensate for it. Circuit details The full circuit, shown in Fig.2, is based around a Microchip PIC16LF1455 microcontroller. It is an extra-low-power device that can operate with a supply voltage as low as 1.8V (0.9V per cell in this case). Most clock movements will stop running between 0.9V and 1.0V per cell, so the microcontroller will run for as long as the clock’s motor can keep going. This microcontroller also has USB support, so a mini Type-B socket is provided for configuration (CON4). When a host is connected or removed, the microcontroller will detect the USB +5V voltage on its pin 9. The 5V is dropped to 2V by the 10kW/6.8kW resistive divider, so it will not damage the microcontroller when the battery is at 1.8V. It will still be recognised as a high logic level when the microcontroller runs from a fresh battery (3.2V). The GPS Clock Driver on the back of an IKEA “TJALLA” sweep clock. The movement has been modified to bring the connection to the clock motor’s coil out through a hole. The Driver PCB was designed to be small as there is often little space behind a wall clock. Australia's electronics magazine September 2022  59 Fig.2: the Microchip PIC16LF1455 microcontroller (IC1) runs the show. It steps the clock movement by driving its pin 8 high for a negative pulse, low for a positive pulse or setting it to high impedance during the idle time between pulses. Op amp IC2 buffers this signal and uses the centre point of the two batteries as its reference to drive its output either positive or negative. When the microcontroller needs to get the GPS time, it drives its pin 7 high, causing the boost regulator (IC3) to start running and power the GPS module. Any change in the voltage on pin 9 will cause the microcontroller to restart. If, upon restarting, the USB voltage is present, the firmware will set the microcontroller’s clock speed to 16MHz and enable the USB interface. LED1 will flash three times to indicate that the firmware is in configuration mode. If the USB voltage is not detected on startup, the clock speed will be set to 4MHz, and the USB controller will be disabled (both to save power). The firmware will go through the usual clock startup routine, flashing LED1 twice. The PIC16LF1455 has an unusual feature: it can use the host’s USB signalling rate to fine-tune its internal clock. The USB specification requires a high accuracy in this timing and that generally requires a 12MHz, or similar, crystal oscillator. But the PIC16LF1455 does not need this, which frees up two pins and makes for 60 Silicon Chip an easy-to-implement USB interface. The microcontroller steps the clock movement by driving its pin 8 high for a negative pulse, low for a positive pulse or setting it to high impedance for the idle time between pulses. This controls op amp IC2 (MCP6041), which uses the centre point of the two cells as its reference and drives its output either positive or negative relative to that. The MCP6041 has several desirable characteristics: its output will swing rail-to-rail, which means that little of the precious battery voltage is lost within the op amp. It also has an extremely low quiescent current (less than a microamp), so the battery is conserved between pulses, and it will operate at a supply voltage well below 1.8V (0.9V per cell). Boost regulator When the microcontroller needs to get the GPS time, it drives its pin Australia's electronics magazine 7 high, enabling boost regulator IC3, a Microchip MCP16251. It generates about 4V at its pin 5. This is set by the ratio of the 2.2MW and 1MW resistors; 4V was chosen so that the regulator will have some headroom to regulate the output voltage with fresh cells. The MCP16251 disconnects its output when it is disabled by a low voltage on its pin 3. This is unusual in a boost regulator, and is an important characteristic as it prevents the GPS module from draining the battery when it is not being used. The output from the GPS module (VK2828U7G5LF) is a standard asynchronous serial stream at 9600 baud with TTL signalling voltages. To protect the microcontroller when the battery voltage is low, BAT85 diode D1 clips its output to just a little over the battery voltage. The module comes with a connector and colour-coded flying leads, as shown in Fig.2. It also has two siliconchip.com.au indicator LEDs; the red LED, which indicates power, while the green LED will flash at one pulse per second. Battery life The main factors determining how long the batteries will last are the current drawn by the clock’s motor and the quality of the cells used. The Kmart stepping clock drew an average of 170µA while the IKEA sweep clock averaged 135µA (both with a drive signal of 1.5V peak-topeak), typical of these types of movements. Because the GPS Clock Driver powers the motor from both cells, the typical average current drawn from each is 70-85µA. The average current drawn by the microcontroller is about 18µA, which applies to both cells. The shutdown current of the boost regulator and a few other sources add about another 3µA per cell. Finally, there is the current consumed by the periodic operation of the GPS module. The peak current is up to 100mA, but it is only drawn for a short period every five days, so its long-term average is quite low at about 5µA. Adding all of this together means that a typical clock will draw about 100µA from each cell. To keep the clock running for longer on low battery voltages, the firmware changes the pulse train duty cycle if the battery voltage is less than 1.125V per cell. It lengthens the pulse time by 24% and reduces the idle period by the same amount. The waveform’s frequency is the same, so it does not affect the timekeeping accuracy, but it delivers more energy to prevent it from stalling. This allows a sweep clock to continue operating below 1V per cell, thereby using the last erg of energy in the cell and lengthening the running time. The effect on a stepping clock is not as significant, but most will last until 1V is reached. By the way, if you are testing the minimum running voltage for your clock, you need to mount it in a vertical position. The effort required to raise the second hand against gravity will cause the clock to stop early compared to if it is mounted horizontally. Also, if you are not concerned with having a second hand, you can remove it, and the clock should run for a few weeks longer because it siliconchip.com.au does not have to put in that additional effort. Good-quality alkaline AA cells have a capacity of 2000mAh or more with light loads (terminating at 1.0V) so, with a total current draw of 100µA, you could expect the battery to last about two years. Obviously, this can vary considerably depending on the quality of the movement and the cells, but it is a reasonable estimate. If there is room behind the clock, you could separately mount two C cells which have a capacity about four times that of the AA cell, so you could expect up to eight years of operation (see below). The limiting factor would be the quality of the cells and their rate of internal self-discharge. Sourcing the parts The easiest way to source the parts is to purchase a kit from the Silicon Chip Online Shop. This includes all the components needed except for the clock and cells (see the parts list for more details). The kit includes a pre-programmed microcontroller. However, if you have purchased the parts separately, you will need to program it yourself. There are six solder pads on the PCB for mounting a pin header. This is not usually populated, but if you want to program the chip in-circuit, you can install the header and connect a PIC programmer such as a PICkit 3 or PICkit 4. The firmware is available from the Silicon Chip website as well as http:// geoffg.net/gpsclockdriver.html It is worth checking for updates from time to time, as there is the possibility that a bug will be found and fixed. Besides the PCB and microcontroller, the other components are standard and can be purchased from the usual suppliers. However, you won’t find all the parts at Jaycar or Altronics (or likely any source), and ongoing parts shortages mean that you should check that you can get all the parts before you start ordering. The availability of the kit means you can avoid that hassle, though. Do not substitute the BAT85 diode with another type. It is a schottky type for a low voltage drop, but it also has a low reverse leakage, which is needed to extend the battery life. We have specified the V.KEL VK2828U7G5LF GPS receiver, a great performer that is readily available at a good price. If you want to use another module, that will probably be OK. Just make sure it uses TTL signalling and not RS-232 levels. The firmware will automatically try the typical communication speeds used by these modules (4800, 9600 or 19,200 baud). It uses the NMEA RMC A clock using separately-mounted C cells for power. C cells have a capacity about four times that of AAs, so a lifetime of up to eight years is possible. However, that will depend on the cells’ quality and their internal selfdischarge rate. The PCB is much smaller without the onboard cell holders. Australia's electronics magazine September 2022  61 Fig.3: assembly of the GPS Clock Driver is pretty straightforward. Start by soldering the three SMDs (IC3, L1 and CON4) and check carefully that they all have good solder joints before fitting the through-hole parts. The cell holder polarity is critical, while the LED needs to have its longer anode lead inserted into the pad labelled +. The ICs and diode also need to be orientated correctly. message generated by the GPS module, which is standard across all manufacturers. When purchasing the clock, you could choose a clock design that is attractive but swap out the movement for something else. Most highend clock manufacturers have standardised the physical dimensions of the clock movement and its mounting arrangement. However, this does not apply to cheap clocks, which do not follow any standard. You can also buy movements online with a wide variety of matching hands. So, making your own clock with a unique clock face is also an option. The fully populated Driver PCB. The tactile switch for adjusting the second hand is near the top edge, alongside the USB connector for configuring the firmware. On the far top right are the inductor and other components associated with the boost regulator that provides 4V for the GPS module. You will need a x10 or more magnifier to read these letters (some smartphone cameras will do it too). The first two should be “MB”, while the last two can be anything. Pin 1 is at lower left with the letters the right way up. To solder the chip, first coat the PCB pads with flux paste, then place a tiny solder bump on a corner pad. Position the chip and, while holding it down, apply the iron to that pad. With the first pin tack-soldered and the chip held in position, check and adjust the orientation of the other pins before soldering them. Always apply plenty of flux and use minimal solder on your iron. Next, fit the USB connector. This has two small plastic posts on the underside that go into two holes in the PCB to position it. Coat the pins and PCB pads with flux gel and, with a small amount of solder on your iron’s tip, slide it across the PCB pad to the connector’s pins. When the tip of the iron hits the pin, the solder should magically flow around it. With these small devices, it is easy to create solder bridges between the pins, but they can be removed using solder wick (braid). Finally, check all joints with a powerful magnifier (x10 or x20) to ensure that each joint is correctly soldered with no bridges. Don’t forget to solder the larger mounting tabs. The inductor is the last SMD. Start by placing a small solder bump on one PCB pad, and then, while holding the inductor in place, apply heat to that pad. That should secure it in place. Then, use rosin-cored solder wire to solder the other lug before refreshing the first solder joint. Australia's electronics magazine siliconchip.com.au Construction The GPS Clock Driver is built on 97 × 55.5mm PCB coded 19109221, shown in Fig.3. It was kept small as 62 Silicon Chip there is often little space behind a wall clock. You can cut off the end section of the PCB with two AA cell holders if you will use separately-mounted batteries. That results in a 64.5 × 55mm PCB that should fit almost anywhere. If cutting the board, do that before fitting any components. Use a metal ruler and a sharp craft knife to deeply score the PCB on both sides deeply, then snap the board apart and tidy up the edge with a file. The first component to solder is IC3, the MCP16251 in a 6-pin SOT23 package. It is quite small but not overly difficult with a steady hand. First determine its orientation. It has a laser-etched dot on the top near pin 1, but it is faint, so it is easier to read the four letters engraved on the chip and use them for orientation. The remaining components are all through-hole types; start with the low-profile items like resistors before moving on to higher-profile components such as the LED and cell holders. You can use IC sockets for IC1 and IC2 as these will make removing the device easy if you suspect it is faulty. Like the ICs, LED1 and D1 are polarised, so they must be orientated as shown in Fig.3. The GPS module can be secured to the PCB using double-sided adhesive foam tape. The ceramic antenna should be on top, with the module’s metal shield and label against the PCB. Typically, the antenna should be horizontal and facing the sky for the best sensitivity. If you have the space, you could separately mount the module with the antenna in this orientation. However, our tests showed that the module worked just as well when pointing to the horizon, mounted on the PCB and attached to the back of the clock. The GPS module is supplied with a connector and colour coded-leads which go to the solder pads on the right-hand side of the PCB. Trim the leads to length and solder them to the respective pads – WH means white, RE red, BU blue etc. If using external cells, wire them to the four “EXT BAT” solder pads. These can be used for terminating soldered leads or a 0.1” 4-pin header and socket. Modifying the clock movement The idea is to disconnect the clock’s stepping motor coil from its control board and connect two flying leads to the coil. All clock movements are different, so we can only give you general guidance here. The process involves freeing the clock’s movement from the clock housing, dismantling it, making the modification and reassembling it. First, remove the housing holding the front glass of the clock. Generally, this is held in place with screws accessible from the back. Then remove the hands. Generally, the second hand is a friction-fit on a pin in the centre of the shaft, so a gentle pull on this should free it. Next is the minute hand; in most high-end clocks, it is held down with a circular threaded nut. However, in cheaper clocks, it is often a friction fit on the minute hand shaft. The hour hand is likely a friction fit on the siliconchip.com.au Parts List – New GPS-Synchronised Clock 1 double-sided PCB coded 19109221, 97 × 55.5mm 1 V.KEL VK2828U7G5LF GPS module or similar (MOD1) [SC3362] 1 32768Hz watch crystal (X1) 1 4.7μH 4.3A 6×6mm ferrite-cored SMD inductor (L1) [eg, EPCOS B82464-A4] 1 4-pin low-profile tactile pushbutton switch (S1) [Altronics S1120] 1 2-way 2.54mm polarised right-angle header with plug and pins (CON1) 1 SMD mini type-B USB socket (CON4) [Altronics P1308] 1 6-pin header (CON5; optional) 2 PCB-mounting single AA cell holders (BAT1, BAT2) [Altronics S5029] 1 14-pin DIL IC socket (optional) Kit (SC6472 SC6472 – $55): 1 8-pin DIL IC socket (optional) includes the PCB and all onboard parts, Semiconductors including the VK2828 GPS module. 1 PIC16LF1455-I/P microcontroller programmed with 1910922A.HEX, DIP-14 (IC1) 1 MCP6041-I/P 600nA rail-to-rail input/output op amp, DIP-8 (IC2) 1 MCP16251T-I/CH DC-DC boost converter with disconnect, SOT-23-6 (IC3) 1 5mm red LED (LED1) 1 BAT85 30V 200mA schottky diode (D1) Capacitors 2 10μF 16V X7R multi-layer radial ceramic [eg, TDK FK26X7R1C106M] 1 100nF 50V X7R multi-layer radial ceramic 2 22pF 50V C0G/NP0 radial ceramic Resistors (all 1/4W 5% or better) 1 2.2MW 2 1MW 1 820kW 3 10kW 1 6.8kW 1 1kW hour hand shaft and should be gently pulled free. With the hands removed, you will find that the movement is held onto the clock face with a hex nut on the threaded shaft. Remove the nut and it should come free. Some cheaper clocks do not use a securing nut; instead, the movement is held in place by plastic clips on the rear of the clock. Take photographs of the movement and the layout of the gears before you start dismantling it, then take additional photos as you progress. It is very easy for the gears to fall out while you are handling the movement, and it will then be tough to reassemble it without a guide. In most cases, the movement will have a top cover held on by clips to the base. You can lever off these clips to remove the cover and gain access to the motor and gears. Inside, you need to identify the motor’s coil (this will be obvious) and the wires from the coil, which will be soldered to the PCB with the control chip (normally under a blob of black epoxy). The wires are very fine, so the best method of disconnecting the control chip is to cut one of the tracks leading from the coil’s termination on the control PCB. You can then solder your flying leads to the coil’s termination Australia's electronics magazine points and feed these out of the movement – you will probably need to drill a hole in the top cover to do this. Finally, reassemble the clock and terminate the flying leads on a 2.54mm-pitch 2-pin crimp plug. If you have a stepping movement, you can test your work by connecting a 1.5V AA cell across the leads and reversing it. Every time you reverse the cell, the clock should step by one second. Configuring the Clock Driver By default, the Clock Driver is set up for a stepping-type movement with no daylight saving compensation. If that is all you need, you can just insert the cells and start the clock running (see “Powering it up” below). Otherwise, you will need to configure the Driver. Plug the USB connector into a computer or laptop and insert the cells. The Clock Driver will connect to your computer as an asynchronous serial port over USB, and the LED will flash three times to indicate that the firmware is working in configuration mode. Ensure that fresh cells are installed; partially exhausted cells may not be able to deliver the correct USB signal levels, causing errors. The Driver imitates the Microchip MCP2200 USB/serial converter. September 2022  63 End Daylight Saving Month (1-12) ? 4 End Daylight Saving Day (1=Sun) ? 1 End Daylight Saving Day in Month (1 to 4=Last) ? 1 below). It will remember the settings you have entered, so you never have to re-enter them, even when replacing the cells. Daylight saving starts at 2:00am and ends at 3:00am. The one exception is the United Kingdom, where it needs to start/end one hour earlier. The firmware determines if the clock is running in the UK by checking the time zone offset, which is zero in the UK. Time Zone (-12.5 to +12.5) ? +10 Powering it up Configuration Saved Unplug USB ❚ All you need to do is set the hands to the next half hour or full hour (whichever is closest) and insert the cells, then hang the clock back on the wall. The clock will wait until the next half/ full hour is reached and automatically start running. From then on, it will keep precise time until the battery is exhausted. Do not put cells into the clock’s movement. The GPS Clock Driver wholly replaces the controller board inside the movement, so it does not need to be powered. The onboard LED informs you of the progress during the startup process. When the cells are inserted, the LED flashes twice to indicate that the microcontroller and firmware are running. The firmware then powers up the GPS module, flashing the LED briefly at 1Hz while it is searching for satellites. When the GPS module has a lock (ie, it has the accurate time), the LED will change to a long flash every second. Finally, when the clock starts running, the LED will turn off. With a new GPS module, it can take some time (up to 45 minutes) to find enough satellites. That delay might result in the clock starting at the wrong time. So, when you first use the clock, keep an eye on when it gets a satellite lock and readjust the hands if necessary. Once the GPS module has its first lock on the satellites, it is generally much faster, with GPS Clock Driver v1.0 Sweep Clock (Y/N) ? Y Use Daylight Saving (Y/N) ? Y Start Daylight Saving Month (1-12) ? 10 Start Daylight Saving Day (1=Sun) ? 1 Start Daylight Saving Day in Month (1 to 4=Last) ? 1 Screen 1: configuring the clock driver using the USB interface. In this case, sweep clock drive has been selected and daylight saving has been configured to suit NSW/Vic/Tas/ACT. These settings are remembered, so you never have to reenter the configuration details, even when replacing the battery. Windows 10 and 11 are delivered with the correct driver installed, but for other operating systems, you may need to load a driver. You can find this on the Microchip website: www. microchip.com/wwwproducts/en/ MCP2200 You will also need terminal emulator software to send your keystrokes to the clock driver and display anything sent back. For Windows, we recommended Tera Term (http://tera-term. en.lo4d.com), which is free to download and use. PuTTy is another popular emulator that will also work. The terminal emulator needs to know the number of the virtual serial port generated when the clock is connected. For Windows, you can find it using Device Manager. Other details such as the baud rate are unimportant and can be ignored. With everything set up, hit the Enter key on your keyboard, and you should see the configuration header as in Screen 1. The first question asked by the firmware is “Sweep (Y/N)”. If you type “Y” then Enter, you will configure the clock driver for a sweep movement. If you enter “N” instead, it will be configured for a stepping clock movement. The next question is “Use daylight saving (Y/N)”, and if you reply “N”, you do not have to do anything else; it will save the settings and you will be prompted to unplug the USB cable. If you replied “Y”, you will need to enter the specifications for the start and end of daylight saving. Configuring daylight saving The firmware can cope with the 64 Silicon Chip daylight saving requirements for most countries worldwide, although some are just too complicated or vague (for example, Iran’s). Table 1 shows the settings required for Australia and New Zealand. For both the start and end of daylight saving, you need to enter three numbers: 1) The month when daylight saving starts/ends (1 to 12, where 1 is January). 2) The day of the week when daylight saving starts/ends (with Sunday being day 1). 3) The week of the month it falls in, with 1 being the first week and 4 meaning the last week. Then you will be asked for your time zone. This should be entered as the number of hours before or after UTC. So, for example, Sydney and Melbourne are +10, Adelaide is +9.5 and Los Angeles is -7. When you press Enter after that, you will see “Configuration Saved, Disconnect USB”. Disconnect the USB cable and the clock driver will restart as if the battery has just been connected (ie, it will wait for the next precise half/full hour then start running, as described Table 1 – DST rules for AU & NZ (not observed in Qld, NT & WA) NSW, Vic, Tas & ACT South Australia New Zealand Start month 10 10 9 Start day 1 1 1 Start day in month 1 1 4 End month 4 4 4 End day 1 1 1 End day in month 1 1 1 Time zone offset +10 +9.5 +12 Australia's electronics magazine siliconchip.com.au subsequent attempts typically taking under a minute. Adjusting the second hand All clock movements allow you to adjust the hour and minute hands, but the second hand will probably not be at the 12 o’clock position and will be stuck somewhere around the dial. To correct this, you can hold down the tactile switch on the PCB while the clock is waiting to start, and the firmware will drive the second hand around the dial. Release it when it reaches the 12 o’clock position. That way, the clock will start with the second hand indicating the correct second. A problem with some movements is that when the clock starts running, the movement might start driving the hands a few seconds early or late. While not a big deal, you can adjust for even this slight error while the clock is running. Hold down the tactile switch when the clock is running until the LED illuminates. If you then immediately release the button, the firmware will advance by one second. On the other hand, if you keep holding down the button until the LED goes off again before releasing it, the firmware will retard the hands by one second. Remember that a sweep clock will need eight seconds to gain or retard its hands by one second. So, if using a sweep movement, you should wait for a while to check the effect of the last adjustment before making another one. You can verify your clock is accurate using a time source such as www. time.gov which will give you the exact time to the second – even compensating for delays over the internet. With this as your reference, you can use the tactile switch to bring the second hand to an exact agreement with this source and compensate for any starting error. You should correct for any startup error immediately after the clock has started running. This is so that you do not inadvertently adjust for an error in the crystal’s frequency, which will be automatically corrected by the firmware after the first 12 hours of running, following the second GPS synchronisation. All clock movements use a type of stepping motor that is locked to the pulse train delivered by the microcontroller. So, once the hands are accurately set, they will never lose or gain a siliconchip.com.au second unless the battery is exhausted or the movement is faulty. Therefore, in the normal scheme of things, you should never have to adjust the clock again after compensating for any initial startup error. Troubleshooting To test your clock, insert the cells and observe the LED sequence as described above. Hopefully, it will run through the starting sequence, and the clock will start running. If it does not work as expected, use the LED to help track down the problem. The LED should flash twice when the cells are inserted (and the USB is not connected). If that does not occur, the fault could lie with the cells, the microcontroller or the LED. Check that the LED is the right way around and that it works before looking for other causes. If you do not see the double-flash, check the voltage between pins 1 and 14 of the microcontroller. It should be the same as the battery voltage (3.2V with new cells). If that is OK, check the microcontroller. Is its orientation correct? Has it been properly programmed? If you used an IC socket, check that it is properly inserted, with no pins folded underneath. After the double flash, the firmware will power up the GPS module. Within a few seconds, you should see a brief flash every second on the LED indicating that data is being received from the module. If you do not see this flash, the problem could be with the boost voltage regulator or the GPS module. Check the voltage between ground and the red wire to the GPS (marked RE on the PCB). It should be about 4V; anything else indicates a problem with the regulator and its associated components. If the regulator is OK, the fault must be with the GPS module. Check that it is connected correctly and that it uses one of the supported serial communication speeds (4800, 9600 or 19,200 baud). GPS satellite lock After a while, the GPS module will get a lock on sufficient satellites to obtain an accurate time and when that happens, the boost regulator will shut down and the LED will change to a long flash every second. Usually this will be within a minute or two, but it could take some time. Australia's electronics magazine The inside of a typical wall clock movement modified for our GPS Clock Driver. The motor coil is at upper right while the blue control board is on the left, with a blob of black epoxy hiding the control chip. This has been disabled by cutting a PCB trace, and flying leads have been soldered to the motor coil termination points. There might not be a strong enough signal to get a lock. Take the clock outside and place it so that the antenna is pointing directly at the sky, and leave it that way for at least an hour. Typically, if the GPS module could gain a lock when you inserted the cells, it should be able to get a lock on subsequent synchronisations. However, a marginal signal level or moving the clock might change that. When the cells are inserted, the firmware will wait forever to get a GPS signal. However, after that first time, the firmware will wait for just 30 minutes to get a signal and then, if unsuccessful, it will give up and retry in 24 hours. To indicate this, the LED will then flash briefly every second until a subsequent attempt is successful and an accurate time is obtained. If you find that your clock is inaccurate, check the LED. If it is flashing, that indicates there was an insufficient GPS signal to get the accurate time. If you find that you are getting a short battery life, check the voltage of the exhausted batteries when you replace them. Most movements will keep going down to 1.0V. If it stops at a voltage significantly higher than that (say 1.2V), the movement has too much friction and should be replaced. We experienced this with a cheap movement that failed after a few years, so it might be prudent to purchase a spare movement (or clock) as a backup in case you need to swap out an old movement. That way, you are guaranteed a replacement that will fit your clock and accept the same hands. SC September 2022  65 The History of Last month, we described the rapid developments which took place after Silicon Chip was founded in 1987. That brought us up to 1993, by which time we were ticking along quite nicely and looking to grow the magazine as fast as we could. We even launched our Fifth Birthday Celebration in January 1993, culminating in the award of a brandnew Ford Festiva car to a lucky reader. Part 2 by Leo Simpson O ne small innovation we made around that time was the acquisition of a Polaroid scope camera. It was a DS-34 which used very fast Polaroid film and had a visor that fitted a standard oscilloscope screen (see siliconchip.au/link/abfl). All you had to do was to place the visor over the scope screen and pull the trigger. After a minute or so of film development, the result was a sharp, precisely-focused photo showing the signal traces on the screen. We used this quite frequently, to illustrate circuit operation for many of our project articles. However, digital scopes came out 66 Silicon Chip not too many years after that. It was then a simple matter to take a screen grab of whatever measurements you were doing, automatically saved in JPG (also called JPEG), PNG or TIF format, ready for inclusion in an article. So the relatively expensive Polaroid scope camera was made completely obsolete. Never mind, such is progress. I think it might still be gathering dust somewhere in the Silicon Chip workshop. Silicon Chip to be published in the USA In May 1993, there was a major business development that we had been Australia's electronics magazine working on for some time. We were very proud to announce that Silicon Chip was to be published in the USA and Canada, under licence to Gernsback Publications Inc, of New York. They were the publishers of Popular Electronics and Electronics (formerly Radio Electronics). This was a big coup for us. The arrangement was for them to initially publish four issues a year, with most of the editorial to be reproduced from the Australian issues of Silicon Chip. But soon after the agreement was made, the arrangement hit hurdles as Gernsback asked us for bromides for siliconchip.com.au their initial issue. That shocked us, as we had been producing Silicon Chip using Pagemaker for several years; it had not crossed our minds that they would still be using the old production methods. I cannot remember the details of how we solved those problems, but I do recall that they had to hastily acquire suitable computers and the necessary software. Apparently, very few magazines in the USA were using desktop publishing software at the time, and we were some way ahead of the curve. Ultimately, they only produced one issue, then decided it was all too hard. That was quite disappointing to us (apart from missing out on a revenue stream from the licensing agreement), as we knew from our experience that it took several years to establish a new magazine. In mitigation, the USA and Canada did not have the very efficient newsagency distribution scheme we have in Australia. Most large circulation American magazines were (and still are) primarily sold by subscription. Much later, around 2006, we signed another licensing agreement with Everyday Practical Electronics (EPE) magazine in the UK, now known as Practical Electronics (PE). That agreement continues today. In the meantime, our well-­appointed Mona Vale office had been a very pleasant place to work and we stayed there until January 1994. But I wanted to put the business on a more certain footing. By that time, I felt confident enough to buy into a very large industrial complex on Jubilee Avenue, in the Warriewood Valley. Above: a clipping from a local newspaper with Leo Simpson holding the new American version of Silicon Chip with the Studio Twin 50 Stereo Amplifier shown on the cover. Left: the Editorial from the first American issue of Silicon Chip. The American operation was based in Farmingdale, New York, with the publisher being Larry Steckler. Dolby Pro-Logic decoder Talking of licensing agreements, it was not long after moving to the Jubilee Avenue address that we were able to publish our Dolby Pro-Logic Surround Sound Decoder, in the December 1994 issue (siliconchip.au/Series/162). This was a big project for us, with all of the design work carried out by Technical Editor John Clarke. Significantly, it was sponsored by Jaycar Electronics, who did a lot of liaison work to get the design licensed by Dolby Laboratories. That was necessary for Jaycar to be able to obtain the Dolby chips for the subsequent kits for the project. (There was a second siliconchip.com.au Australia's electronics magazine September 2022  67 The Dolby Pro-Logic Surround Sound Decoder project was sponsored by Jaycar Electronics and our design was approved and licensed by Dolby Laboratories. version of this project several years later). The design prototypes had to be submitted to Dolby Laboratories in America to be approved and to my memory, they required several modifications before the approval was granted. It was a world-first for a technical magazine and was not repeated anywhere else in the world, as far as we know. Interestingly, there was another milestone in the same issue, with the publication of the first article in a series on Bob Young’s Radio Control unit that used surface-mount components (siliconchip.au/Series/198). Zoom magazine Throughout 1995, we featured many articles on car electronics and car modification projects, all generated by a very prolific and enthusiastic writer, Julian Edgar. The circuit designs were prepared by John Clarke. Those articles were so popular that I saw a place for a car magazine covering similar topics. And so it came to pass, with the publication of the first issue of Zoom magazine in April-May 1996. Julian Edgar produced and edited most of the editorial, and Ross Tester (who had previously worked at EA & Dick Smith Electronics) joined our staff to do all the layout and production. It was a bi-monthly magazine in full colour. Zoom was another big step forward for us. It was not only in full colour and more expensive to produce but also required much higher production standards. While we thought the first issue was pretty good, that illusion was soon shattered by Julian Edgar, who was utterly scathing in his assessment of picture quality. Well, that was pretty 68 Silicon Chip hard to swallow but we had to lift our standards substantially and quickly to meet the deadline for the next issue. Julian was a very fine photographer of cars, and he was used to seeing his photos reproduced in motoring magazines. So we, meaning Ross Tester and Greg Swain, had to learn how to get the same high-quality results from our desktop publishing equipment. It meant that we had to have our colour monitors properly calibrated and learn the subtleties of photo processing using Photoshop. With a few issues under our belts, the production standard became very good. But the magazine was not a financial success. While the circulation growth was satisfactory, we had a lot of difficulties in getting the many advertisers to pay us. They were mostly small businesses and their cash flow was often insufficient to justify their advertising commitments. Ultimately, I decided that the magazine was not financially viable for us and we sold it to a specialist publisher, Express Publications, in early 1998. Maybe I should have kept ownership of the Zoom name, though. In the light of “Zoom” meetings today, I might have become a multi-millionaire (or maybe not!). Giving up on Zoom was a setback, but one good aspect was that it meant Ross Tester could work full-time for Silicon Chip as a writer and layout artist. He would really come into his own when we went to full-colour production some years later. In addition, in about August 1997, our regular contract photographer, Glen Keep, decided to retire. So we acquired the key equipment of his studio set-up with flash gear and ‘soft Australia's electronics magazine boxes’. Ross Tester then took over all our photography, initially using his own Minolta film gear and later, Nikon digital cameras and lenses. As well as being a graphic designer, layout artist and clever advertising copywriter for many years at Dick Smith Electronics, Ross had also been a freelance wedding photographer – he was a man of many parts. His photography skills enabled us to achieve a long-term aim – high-quality, finely detailed pictures of all our electronics projects. These were so good that readers building projects could easily see the colour codes on tiny resistors, component numbers on semiconductors and so on. They could even determine if we had used a component that was not exactly the same as depicted in circuits and wiring diagrams. We had to be diligent, and readers loved it. We even tried to ensure that the colour codes on resistors in the diagrams ran the same way as in the photos, so as not to confuse our readers! The same comment applied to series connections of resistors and capacitors – ideally, they had to be in the same order on the circuit, PCB overlay diagram and in the assembled project, even if it didn’t affect circuit function. Otherwise, readers would complain that we had them back-to-front! The introduction of GenCAD The obvious next step in our continuing technology adoption was to go to CAD for our circuit diagrams and drawings, which we did in the latter half of 1995. The package chosen was an MS-DOS-based system called GenCAD, which ran quite well on the hardware of that era. It allowed us to send complete Postscript pages with everything in place to the commerical printers. A year or so later, we also moved from Windows 3.11 to Windows NT, which eliminated all those annoying operating system reboots. While GenCAD had been a great step forward for circuit diagrams, I was still dissatisfied with our wiring diagrams, particularly for large projects like stereo amplifiers, high-power inverters etc. Depicting multi-strand colour ribbon cables was a real challenge. I wanted to have the same standard as that achieved by the American Model Railroader magazine. They used to depict large model railway siliconchip.com.au layouts in full colour with detailed wiring. They would even do dioramas (ie, diagrams with a 3D perspective) of their layouts. That was far beyond the capability of GenCAD. But new software would eventually provide the answers. In 2000, we upgraded our operating systems to Windows 2000. At the same time, we ditched GenCAD and went to CorelDraw for our circuits, PCB overlays and wiring diagrams. Our draftsman devised a clever scheme of creating a component library with red bounding boxes, which all snapped into place on a grid so that everything lined up. We also developed an extensive component library which streamlined the process. Towards the end of 2003, we ditched Pagemaker (originally by Aldus, but by then owned by Adobe) and converted to Adobe InDesign. The latter was substantially more powerful and flexible, particularly when it came to type handling and special type effects. Incidentally, when we went to InDesign, the overwhelming majority of magazine producers, advertising studios and the like had standardised on Quark Express, again mainly on Mac hardware. Typical Silicon Chip – we went against the trend. Fast forward to today, and the vast majority use InDesign. After that, there were mainly just various upgrades to hardware, operating systems and the inevitable frequent software upgrades for InDesign, CorelDraw and Photoshop etc. Using that technique enabled us to provide incredibly sharp images. It would have been great when we were publishing those beautiful photos of cars in Zoom magazine. Moving to four-colour printing Initially, like the vast majority of magazines, Silicon Chip was printed with a four-colour (CMYK – Cyan▪ ▪, Magenta▪ ▪, Yellow▪ ▪ & blacK▪) cover. Still, the inside used ‘spot colour’, where certain pages could have a single second colour applied. As time went on, we printed one or two sections of the magazine in full colour, which allowed us to have photos in some articles in full colour, as well. But most sections of the magazine could still only have spot colour, which looked rather drab by comparison. The move to full four-colour printing came about due to a chance conversation between Ross Tester on a plant visit and the printer’s production manager. The bulk of their work – women’s magazines and catalogs – was printed in four-colour. The production manager was moaning that before Silicon Chip went on the press, they had to remove the C, M The cover of Zoom’s ninth issue, from August/ September 1997. Not long after its publication, in early 1998, Leo Simpson sold the magazine to Express Publications as it turned out to be too much trouble getting some advertisers to pay invoices. Unsharp masking Those software upgrades were often tiresome but they did bring production benefits. One of these was to be revealed when Ross Tester attended one of the many seminars discussing Photoshop’s latest features. It was called “unsharp masking”. While it sounds like something that would reduce photo sharpness, the process gets its name from a traditional photography darkroom technique initially developed in Germany in the 1930s. This was where a negative copy of the original photo is blurred, or “un-sharpened”, and then applied to the original image as a mask. As strange as it sounds, this blurring method actually results in a sharper image (there is a good description of the process on Wikipedia at https://w. wiki/5Vkz). siliconchip.com.au and Y stations and wash one of them down to use the special spot colour ink – then reverse the process to go back to four-colour. “Why don’t you guys print in four-colour? If you must have spot colour, you can get that from a CMYK ink mix”. We expressed the long-held belief that four-colour printing was too expensive. Up to that time, it had been, but when you took into account the press down-time, it came out line-ball. So the printers gave us a four-colour price which was very similar to the spot colour price – and Silicon Chip went all colour! Technology again came to the rescue here, with a technique known as computer-­to-plate or CTP. This digitised the plate-making process by using lasers to etch the plates directly, eliminating the expensive and cumbersome film process (one large piece of film for each CMYK colour). In addition, Kodak had developed the Photo CD process some years earlier – a cost-effective method of scanning 35mm film and placing the resulting files onto a CD. A special Kodak plug-in for Photoshop allowed the files to be retrieved from the CD and converted to JPEG files. Australia's electronics magazine September 2022  69 Pushing the boundaries of audio amplifier performance Leo Simpson operating the Audio Precision System One (bottom of stack), 1kW dummy load (above it, with a brick-wall filter in between) and digital scope (top) to test the 20W Class-A Amplifier. We still use a similar setup, albeit with an AP System Two. It was much cheaper than having colour slides digitised on a drum scanner, meaning it was cost-­effective for Silicon Chip to go to full-colour reproduction by the latter half of 1998. However, as noted above, we did not manage to incorporate full-colour circuits and wiring diagrams until several years later. The move to colour also required hardware upgrades. The Radius monochrome monitor had to be finally retired and high-end colour monitors substituted, and we invested in an expensive CMYK Postscript colour laser printer. The monitors had to be calibrated regularly so that what you saw on-screen matched the printed magazine page. State-of-the-art test equipment While we were grappling with Zoom magazine, other developments had been in train. We had spent quite a lot of money on desktop production equipment but we had also added to our laboratory equipment. In particular, we had acquired several oscilloscopes, including digital models, but we still did not have a really good distortion analyser. Those instruments we did have were quite old and certainly not state-of-the-art. That induced us to purchase the very best audio analyser available at that time, from US company Audio Precision. This represented a substantial outlay for us, but ultimately, I decided 70 Silicon Chip that the expense was justified. It would allow us to measure harmonic and intermodulation distortion down to previously unimaginable levels, as little as 0.0003% or even lower, along with commensurately low noise signal levels (to below -120dB). It brought the great time-saving ‘auto-nulling’ feature as a harmonic distortion test was run over a complete frequency sweep of the entire audio spectrum. That capability, and the ability to produce easy-to-read performance graphs of signal-to-noise ratio, frequency response and distortion curves, gave our audio designs a degree of credibility that could not be achieved in any other way. We started to feature performance graphs from this machine for audio equipment in the February 1995 issue. But the first significant design produced with the Audio Precision unit having been used as an actual design tool was the Plastic Power amplifier in the April 1996 issue (siliconchip.au/ Article/5015), shown above. This design used rugged new plastic-­ e ncapsulated power transistors from Motorola and it was an absolute joy to produce the excellent performance curves with the Audio Precision test set. The Plastic Power amplifier’s lowest distortion level was about 0.004%. It was good, but this amplifier was still far above the noise and distortion limits of the new test equipment. We were a long way above what we would achieve just two years later, in 1998. Australia's electronics magazine It was in July 1998 (siliconchip. au/Series/140) that we produced an amplifier with astonishingly low distortion, as low as 0.00025%. That’s only 2.5 parts per million! But making those extremely low harmonic distortion measurements was not solely due to the Audio Precision equipment, as we shall see. The amplifier in question was a 15W class-A module using “bog-standard” small signal transistors (BC547, 548, 556, 557 etc) and a pair of Motorola MJL21193/94 power transistors operating as current feedback pairs. The PCB was relatively unremarkable in appearance but was attached to an enormous heatsink, required to dissipate the standing quiescent power of 80W. Such high power waste is unavoidable for class-A amplifiers, which was the sole reason we had previously rejected requests from keen ‘audiophile’ readers for a high-­ performance class-A design. But we finally relented. So how did we make the measurements? Harmonic distortion measurements for hifi audio amplifiers are almost always presented as THD, meaning “total harmonic distortion”, ie, that the figure consists of the harmonic distortion plus residual noise (made explicit by writing THD+N). It is usually predominantly the various harmonics of the sinewave test signal, but there is always a noise component, including 50/100Hz hum, but mainly white noise. That wasn’t the case with the THD figures obtained from the class-A amplifier module. While the module’s absolute noise was incredibly low at -113dB (unweighted 22Hz to 22kHz; -116dB A-weighted) with respect to full power, it was still quite a significant amount of noise, often almost obliterating the harmonic components. This was clearly illustrated using a 100MHz analog oscilloscope that had on-screen measurements. We used this to show the noisy residual THD waveforms, as can be seen on page 61 of the July 1998 issue. So we knew that the actual harmonic distortion was actually much lower than the total THD figure. The question remaining was how to remove the noise to reveal the harmonic waveform. The solution was to use a technique described at about siliconchip.com.au that time in an article by noted audio designer Douglas Self in the British magazine Electronics World. It involved using a digital oscilloscope in averaging mode to remove the random noise from the low-level signals, to enable the buried harmonic content to be clearly displayed. And that allowed us to give precise estimates of the actual harmonic content. My Publisher’s Letter in the July 1998 issue has more on this topic. While kits for the design were ultimately not a big seller, the project did demonstrate what was and probably still is the “holy grail” of ultra-linear circuit design: the proverbial “straight wire with gain”. We will never quite get there, but that class-A amplifier is exceptionally close to ideal and far better than any present program source, analog or compact disc, or any audio transducer for that matter. We produced a 20W version of the class-A design in May 2007 and the following months. This had a simplified power supply, a shielded toroidal power transformer and other slight circuit changes and again resulted in some worthwhile performance improvements. Having seen what was possible with a great class-A design, we wondered what could ultimately be achieved with a really good class-AB design. Could we approach or even equal the performance of our class-A design? That was to become our benchmark. And up to that time, such a quest would have been seen as futile since class-AB amplifiers are, or were, inherently less linear. As it turned out, there were several design innovations to come which would help us in that quest. These did eventually allow us to achieve a major advance in class-AB amplifier design to go very close to class-A performance levels (and, in some ways, surpass them). But it took four attempts to get results which we think will now be almost impossible to improve significantly. The Ultra-LD series The first attempt was the Ultra-LD module presented in the March 2000 issue (siliconchip.au/Series/113), a 100W module that was essentially a refinement of the Plastic Power amplifier design featured in the April 1996 issue. The major differences were better output transistors (Motorola siliconchip.com.au MJ15030/MJ15031 and MJ1302A & MJ3281A) in compound current-­ feedback triples. Also, the input and class-A driver stages were fed with regulated supply rails to eliminate hum and noise on those rails. It was significantly better than the Plastic Power module, with lower harmonic distortion and less residual noise. But our next attempt, the Ultra-LD Mk.2 amplifier module in the August 2008 issue (siliconchip. au/Series/51), was considerably better. It had a greater power output (135W into 8W or 200W into 4W), much lower residual noise and again, much lower harmonic distortion. You will have to read the articles in the August & September 2008 issues to gain a full appreciation of all the changes we made. Briefly, they Australia's electronics magazine involved using new five-lead “ThermalTrak” power transistors which had integral power diodes for bias compensation, a modified input circuit with new low-noise transistors and significant modifications to improve the PSRR (power supply rejection ratio). That last innovation allowed us to eliminate the regulated supply rails for the input and driver stages, simplifying amplifier construction. Magnetic field cancellation This was a completely new circuit design compared to the March 2000 module, but the most significant improvement was the radically different double-sided PCB which introduced a break-through concept. The idea was to cancel the considerable magnetic fields generated by the class-B currents in the output stages, September 2022  71 The first Micromite series by Geoff Graham included two projects: the ASCII Video Terminal (at left); and the 44pin Micromite (below). which would otherwise induce distortion signals into the input stage transistors. Again, you will need to read the circuit description in the August 2008 issue to fully understand what we did. I was very proud of the magnetic field cancellation concept. It came about one day when we were trying to reduce the effects of currents in the power supply leads. The standard approach was to twist the positive, negative and 0V rail wires together and then dress them to avoid their deleterious effects on distortion performance. This process’s effect, or lack of effect, was clearly demonstrated by repeated testing with our Audio Precision test set. As we went through this futile process, I suddenly realised that it is impossible to cancel the magnetic fields generated by the positive and negative class-B currents in any amplifier. Why? Because they don’t flow at the same time! The positive rail currents are positive half-wave rectified versions of the signal waveform, while the negative rail currents are negative halfwave rectified versions of the signal. So twisting supply wires and playing with their routing was never going to work. It was utterly futile! But the new PCB did achieve magnetic field cancellation. John Clarke devised an ingenious layout for the top and bottom side power tracks. He carefully arranged the whole circuit to minimise the induction of distortion signals into the input stages and it worked brilliantly! However, a few years later, we had to revise the design again, mainly due to shortcomings in the claimed benefits of the ThermalTrak power transistors in preventing thermal drift and eliminating the need for adjustments. We presented the revised design in the July 2011 issue (siliconchip. au/Series/286). And again, the new design further improved the distortion performance. Could we do any better? At the time, I didn’t think so. Well, I was wrong. Again! In July 2015 up to the October 2015 issue (siliconchip.au/Series/289), Nicholas Vinen presented a radical re-design of the PCB using SMD transistors for the low signal level stages, SMD emitter resistors for the output transistors and a ground plane to shield the input stages. Notably, he also realised that the air-cored inductor in the output filter was generating a magnetic field that interfered constructively or destructively with the remaining magnetic field generated by the supply tracks on the PCB. This led to the idea of adjusting its orientation and value until maximum cancellation was achieved, then changing the other filter components so this did not impact the way the filter operated. That was the last change that got the distortion curve of the amplifier to track below that of the earlier 15W & 20W class-A designs. The result was quite remarkable. But none of these achievements would have been possible without our stateof-the-art test equipment. Mind you, while many of the solid-­ state amplifiers described above were undoubtedly popular, there was another design that was definitely not state-of-the-art, but it was nonetheless very popular. That was the Currawong stereo amplifier (November 2014-­January 2015; siliconchip.au/ Series/277), which was a real winner, and is still popular today. The attraction? The glowing magic of valves! I have detailed this epic quest for audio perfection because it illustrates the tireless work done by the Silicon Chip design team and many The Micromite Explore 100 was one of the more advanced Micromite-based projects (September-October 2016; siliconchip.com.au/Series/304) Australia's electronics magazine contributors over the years. The aim was to present the very best circuits we could, involving analog or digital technology, using the latest components and leading-­edge techniques. I also need to make special mention of the PIC32 microcontrollers and the Maximite (siliconchip.com.au/ Series/30) & Micromite (siliconchip. au/Series/261) series of projects developed by Geoff Graham to allow those micros to be programmed in BASIC. In terms of overall impact and popularity, these had far more impact than any of our audio projects. Indeed, a search of the internet will reveal countless mentions of Micromite, and it was all originally conceived by Geoff Graham (https:// geoffg.net/). Enter Nicholas Vinen In the latter years, Nicholas Vinen played a significant part in circuit design and most other aspects of Silicon Chip. He introduced himself sometime in 2009 and claimed that he had produced a digital-to-analog converter (DAC) that was a world-beater. Naturally, I challenged him to prove that it was as good as he said it was by putting it through a battery of tests with our Audio Precision gear while he looked on. It bombed out. That did not faze Nicholas in the least. He immediately got the message that unless you tested, tested and tested again, there was no way that you could make any changes to a design and hope for some improvement in results. He came back to our workshop quite a few times after that. He would go straight to the test equipment and run through another set of tests with the latest iteration of his design. In fact, he quickly became much more adept than I was at running the equipment. He learned very fast, the clever sod. And eventually, his DAC was a great design and we published it in the September-­November 2009 issues (siliconchip.au/Series/4). After that, we couldn’t keep him away from the place and he joined the staff in February 2010. I was very glad to welcome him on board, and his importance to the magazine grew continuously from that point until he took over Silicon Chip when I retired in July 2018. Postscripts All that remains in this story is to siliconchip.com.au The Ultra-LD Mk.4 Amplifier was the latest iteration of the Ultra-LD series. It was followed by the simpler SC200 (January 2017). briefly mention what happened to all our competitors. We started with three other electronics magazines against us in the market: Electronics Australia (EA), Electronics Today International (ETI) and Australian Electronics Monthly (AEM). Plus, we had trade and overseas magazines in the Australian market. Virtually every one of them has gone, with a few overseas exceptions. AEM dropped out relatively early, while ETI kept going until April 1990. But Electronics Australia kept going strong until 1999, finally fizzling out in January 2001. Federal Publishing then launched a hybrid publication called “EAT”. It lasted for five issues: April 2001, May 2001, June 2001, July/ August 2001 and September/October 2001. So Silicon Chip is now one of very few electronics magazines with DIY projects in the world. Funnily enough, seeing all our competitors fall by the wayside really did not give us a great deal of satisfaction. As far as we were concerned, they had ceased to be relevant years before, as the internet tidal wave rolled over everything. But there are a couple of satisfying postscripts. The first of these involved Jim Rowe. He was initially a long-time staff writer at EA from March 1960 (when it was Australia's electronics magazine still “Radio, TV & Hobbies”), becoming Technical Editor in 1965 when it was renamed to EA and Editor in April 1971. He left EA in 1979 and went to work at Dick Smith Electronics (DSE), becoming Technical Director. After Gary Johnston left DSE to start Jaycar Electronics in August 1983, Jim became marketing director of DSE but resigned shortly after, in March 1984. He then joined Federal Publishing as Managing Editor of their electronics and computer magazines (including EA, which they acquired later in the same year). In October 1985, he left Federal Publishing and worked at Applied Technologies (MicroBee) for a short time. Ultimately, he went back to run Electronics Australia after I was dismissed in early 1987. Lightning then struck again, and Jim Rowe and EA parted ways in August 1999. This was great for us. With some of us having worked with Jim Rowe in the 1960s and 70s, we knew him to be a highly qualified and extremely knowledgeable designer/writer. We invited him back, and he joined us in late 1999. That was a very significant development for the long-time staffers of EA and Silicon Chip. It meant that ...continued on page 75 September 2022  73 Leo’s early days at Electronics Australia Readers may wonder how Leo Simpson rose to the position of Managing Editor at Electronics Australia and then went on to start an entirely new magazine in competition to EA. Leo takes up the story... My first encounter with EA magazine was almost 60 years ago, involving the August 1963 issue. I was working as a clerk in my first full-time job after leaving school, at the Defaults department in the Australian Taxation Office. A fellow worker had just finished reading the issue, at that time called Radio, TV & Hobbies, and he threw it over to me, saying that I “might be interested”. That turned out to be an understatement. Until then, I had no interest or knowledge of electronics, although I had enrolled in a Science degree at the University of NSW (instead of doing a TAFE course in accountancy, the standard choice of my clerical workmates). I read that magazine from cover to cover that very day and then I read every back issue and any books that I could find on the subject. I became interested in hifi and then haunted the university library for every magazine on that topic and anything remotely related (to the detriment of my studies). In short order, I decided that I would change my degree course to Electrical Engineering at the end of the year. Also at the end of that year, I was extremely fortunate to gain a position as a cadet engineer at Ducon Condenser Pty Ltd, at their vast Leightonfield plant in Sydney’s western suburbs. I was one of only three cadet engineers taken on that year from about 600 applicants. The Ducon plant was a huge operation with over 2000 employees, making a vast range of passive electronic components such as all types of capacitors, resistors and potentiometers for Australia’s booming radio, TV and stereogram manufacturers. Ducon also made massive power engineering components for high voltage switch-yards at power stations, such as three-phase reactors weighing many tonnes. Over the next two years, I worked in most of the manufacturing and engineering departments of Ducon and enjoyed it immensely, learning a great deal. But that suddenly ceased when my university results came in, and I had failed two years running. I was out of a job, which really was 74 Silicon Chip a shock. I had no one to blame but myself since I was a hopeless student, utterly bored by the course subjects. Moving to EMI Only a few days afterwards, I started working at EMI (Electric Musical Industries, manufacturers of His Master’s Voice products) at Homebush, in Sydney’s west. Their products included TV sets, stereograms, radios and car radios. I was assistant to the Quality Control (QC) manager, Fred Stirk, and my job was to write QC procedures for all of the above products. To this end, I would spend time in all the production departments and, using specifications provided by the design engineers for the products, write the testing procedures to be used in each department and on the production lines. Because every radio, TV and stereo product was a unique design, each one had to have its own testing procedure and they would need to be modified each time there was a model or design change. While I was nominally under the supervision of Fred Stirk, I was pretty much a free agent and I was able to learn a great deal about manufacturing procedures. As well as very good design laboratories with very clever engineers, EMI had their own plating shop, transformer winding department and loudspeaker assembly (including magnetisation) department. Most punched steel chassis, PCBs and timber cabinets were outsourced, but everything else was made in-house. The labour force was predominantly female, and the production lines where the women assembled the chassis and soldered the circuitry ran like clockwork. All the supervision and testing staff were male. All the assembled TV chassis were powered and subjected to a full voltage heat soak test for several hours above the assembly lines on an elevated conveyor. Sometimes the TV sets had faults which resulted in spectacular bangs and the occasional fire. All assembled radios, TVs & stereograms had to be aligned and tested. To this end, suitable sweep alignment signals were distributed by 75W cables fed all around the factory. As well as spot frequencies for alignment of the antenna circuits on AM broadcast radios, there was a sweep frequency and marker test centred on 455kHz for IF (intermediate frequency) alignment. There was also a sweep and marker generator signal for alignment of TV IF strips and another sweep signal for alignment of ratio detector coils This photo of Leo Simpson was taken as he toured the A&R Electronics factory in Box Hill, Victoria, in 1977. He is being shown their new Arlec DMM 10, a 3-digit portable multimeter, with 7-segment red LEDs and powered by a rechargeable battery. He was a staff writer at the time (not Editor yet). The resulting article, titled “The A&R story”, started on page 20 of the March 1978 issue of EA. Australia's electronics magazine siliconchip.com.au in the 5.5MHz FM detector (for TV sound). All alignment tests were done using in-house oscilloscopes designed and manufactured by EMI with 5-inch CRT displays. That was really quite advanced for the time (the mid-1960s). Inevitably, some sets did not work properly as they came off the assembly lines. The men who fixed them became very adept at sussing out really weird faults caused by wrong value components or parts soldered to incorrect circuit points. Most products were entirely valve-based with point-to-point wiring, although there were some portable radios that used germanium transistors on PCBs. The car radios did use transistors, having just evolved to hybrid designs with transistors in the RF stages and valves in the audio output stages. HMV car radios were very good designs, with RF and audio performance far superior to any imported (mainly Japanese) designs of the time. Interestingly, there was also a large portable hybrid TV model which used the cathode voltage of the 6CM5 horizontal output valve (about 8V) to supply some of the small-­signal transistor stages. Working at EA It was mainly on the basis of my background at EMI and Ducon that I got the job at Electronics Australia magazine. I started in about March 1967 in a very junior capacity. My electronics knowledge at the time was quite sketchy, although I was very familiar with the circuitry of TV sets and radios. In most other respects, I regarded myself as a complete novice. My first project at EA was to assemble a transistor RIAA preamplifier to be installed in a valve amplifier. The circuit and PCB design came from the Technical Editor, Jim Rowe, who struck me at the time as a ‘god’ of design, having worked there for many years, producing myriad designs. After assembling it, I had to sketch out the circuit for the draftsman, Bob Flynn, and then write the article for the magazine, which would be edited by Neville Williams (another ‘god’). My next project was a rehash of an earlier valve-based stereo amplifier and was to become the Playmaster 118, with 6GW8 triode-­pentodes in the push-pull output stages. This project incorporated the previous transistor preamplifier, and it was then that I learnt about the difficulties of minimising hum in high-gain audio circuitry. siliconchip.com.au From there, I effectively had a project article published each month and I also reviewed a great many hifi stereo amplifiers, speakers, turntables, test equipment, records and books. By late 1971, I became dissatisfied with my progress at EA and realised that my chances of promotion were very limited. In May 1972, I got a job as a foreman at National Instruments Pty Ltd, at Kogarah. They made elevator control systems but their main product was jukeboxes, under license to an American manufacturer, Rowe-AMI. These were a very complex mechanical design with not much in the way of electronics, apart from the audio amplifiers. This change was a big culture shock for me. I missed the intellectual stimulus of the job and the people at EA. It was a big learning experience as I had to quickly become familiar with the mechanical complexities of the jukeboxes and, more importantly, learn about managing production staff, who were mostly women and all older than I was. I came to quite like the job, but I soon realised it was another dead end and started looking for another position. But in February 1973, I was ‘rescued’ by Neville Williams, who wanted me to come back as he had a staff vacancy. This was very opportune for me as I had become engaged to my future wife, Kerri, and we were looking to buy a house. It eventually happened with the purchase of our first home (at 74 Aubreen Street, Collaroy Plateau) in March 1973. We received the keys to our house on 16th March, the day before we were married. It would take another nine years before I was promoted to the position of Editor of Electronics Australia in March 1983. In that time, we had two daughters and had moved to a bigger house, also on Collaroy Plateau. In the meantime, I had enrolled in a Business Degree course at the New South Wales Institute of Technology and graduated in 1982. As I settled into the position of Editor, my long-time boss Neville Williams having retired in mid-1983, I had no inkling of what lay in the future, only five years ahead. Not in my wildest dreams could I have conceived of losing my treasured position as Managing Editor and then going out to start a brand new magazine with three members of my staff at the time: Greg Swain, John Clarke and Bob Flynn. Australia's electronics magazine what remained of the old EA team (ie, Leo Simpson, Greg Swain, John Clarke, Ross Tester and Jim Rowe) was together again, working on what really was “our” magazine. Right now, the only original people remaining from the EA days are John Clarke and Jim Rowe. All the rest who had connections with EA and Silicon Chip have moved on, retired or ventured up to that great hobby workshop in the sky. The final postscript involves the Electronics Australia archive. After the demise of EAT in 2001, we started getting requests from our readers wanting reprints of articles from EA and its earlier variants such as Radio, TV & Hobbies, Radio & Hobbies and before that, Wireless Weekly. We did not have the rights to do this, so I approached Federal Publishing and purchased the entire archive, with bound copies going all the way back, 100 years, to 1922. We still have regular requests for article reprints from this massive archive. We are proud to have been able to preserve it. Conclusion In writing this story, I have been very conscious that the long-term success of Silicon Chip has been due to the great teamwork of the staff over 35 years. Many people played their part, but I will single out four very special people. The first is Greg Swain, whom I have known and worked with very closely from 1973 until he retired in 2016. Second is the industrious John Clarke, who has worked with me since 1979 until I retired in 2018. He has produced a phenomenal body of work and countless ingenious designs. Third is Ross Tester, who came to work at EA in 1972 as a brash youngster whom I initially found quite annoying. He subsequently went on to work at Dick Smith Electronics and I have been friends with him now for many years. He was chaotic, creative and disorganised. He still is! To him, a tidy desk and office are anathema. He will turn his hand to anything and he helped to add life and humour to the magazine. And finally, there was Ann Morris, who provided the very special bond that held us all together from the time she started with us in 1990 to her retirement in 2020. I thank them all from the bottom of my heart. SC September 2022  75 mini By Tim Blythman LE river This small, low-cost module can drive relatively large 12V white LEDs from a USB or 5V DC power source. Sometimes you don’t need a floodlight; a modest amount of light is enough, and the Mini LED Driver is an economical way to deliver it. I n the June 2022 issue, we featured some 70W LED panels that are incredibly bright when run at their maximum power (around 6A <at> 12V). But those panels can still be handy when run at lower currents; they generate quite a bit of light even at 1A/12W, and there are plenty of other white LEDs out there which are designed to run at around 10W. This Mini LED Driver is perfect for them. The main motivation behind it is to safely power 12V LED panels from a 5V DC source. If you’re like us, you have many spare USB power supplies or power banks that can be pressed into service to supply 5V. This Driver can deliver enough current to drive most white LEDs to provide a handy light level. If they are large panels like the 70W types, as they are so under-driven, their lifespan will be significantly extended due to reduced heat production. The Mini LED Driver is based around the commonly-available, lowcost boost modules using the XL6009 IC, but it adds a few extra features. Those modules don’t have inbuilt current-­ l imiting except for short-­ circuit protection; our added circuitry provides an adjustable current limit. In the June LED Driver article (siliconchip.au/Article/15340), we explained why it’s preferable to run LEDs from a current-limited source. In brief, simply providing a fixed voltage to LEDs will not give consistent light output. Minor voltage variations 76 Silicon Chip can cause disproportionately large changes in current, perhaps even enough to damage the LEDs. The current limiting feature we’ve added will also protect the input supply, particularly if you’re using a small USB power supply to power LEDs that would draw too much current for it to handle at full brightness. The other feature the Driver adds is a low input voltage cut-out. This avoids the possibility that the boost module does not perform correctly with a low input voltage. Also, if the power comes from a battery, it will prevent excessive discharging of the battery, which could damage it. The XL6009 boost module Numerous DC/DC converter modules are available, both online and from stores like Jaycar and Altronics. They come in two main types, boost and buck, although some combine both capabilities. The buck types reduce the incoming voltage to a lower level. In contrast, buck/boost designs like the Altronics Z6337 (see the adjacent photo) contain two controller ICs (and duplicate many other parts) and can either reduce or increase the incoming voltage. These types of module are effectively a boost and buck module combined. But for this project, we’re specifically using dedicated boost type modules. To ensure that you can get the correct type, the Silicon Chip Shop will stock a boost module that we have tested to work, and that same module is included in our kit. That’s especially important given that there are quite a few different “XL6009” module designs floating around, and they do not all perform the same. These modules have a small PCB that includes a switchmode boost controller IC, a minimum of passive components, plus a trimpot to set the output voltage. The input and output connections are simply solder pads. We have used modules based on the MT3608 IC for some previous projects. In those cases, the module is soldered directly to another PCB and treated as though it were just another component, much like the Mini LED Driver. For example, the Water Tank Level Meter with WiFi from February 2018 (siliconchip.au/Article/10963) used such a module to provide 24V DC to a Features & Specifications ∎ ∎ ∎ ∎ Can drive 12V LEDs or LED panels from a 5V DC supply (eg, USB) Adjustable output current and voltage, up to 1A/20V Small and low in cost Input up to 4A/20V, subject to boost module capacity Australia's electronics magazine siliconchip.com.au Fig.1: the Driver circuit has two main sections. The first section provides the low-voltage cut-out function, using transistors Q2-Q4 and associated passives. The second samples the current between the boost module and the output at CON3 and injects a signal back into the boost module after diode D1 to limit the output current to a more-or-less fixed level. water depth sensor from a nominally 5V supply. Incidentally, this 5V supply was provided by another module that managed power from a solar cell and rechargeable battery. The Arduino-based Programmer for DCC Decoders (October 2018 issue; siliconchip.au/Article/11261) similarly used such a module to derive 12V power from a 5V USB supply. In that case, 12V was needed to correctly power and program the DCC decoders. For the Mini LED Driver, we have chosen a different boost module. The XL6009 IC makes it more capable than the MT3608-based module, giving headroom to operate the module comfortably within its limits. Implementing the current limiting feature with the XL6009-based module is also slightly easier. It’s somewhat larger, but the complete Mini LED Driver still measures just 72mm by 24mm. One caveat with these modules is that reader Jonathan Woithe wrote in to tell us that these modules do not always regulate their output voltage correctly under some input voltage conditions. This means that the module can produce up to 50V, even when set lower, which is clearly not desirable! His analysis is on page 8 of the June 2021 issue (Mailbag; siliconchip. au/Article/14875). This problem only occurs when the incoming supply voltage is below the minimum specified voltage for the XL6009 IC. So, for example, if the siliconchip.com.au module is powered by a battery that runs flat, it may be subject to these output spikes. We avoid this problem by shutting down the XL6009 module when the incoming voltage is low while also providing battery over-­ discharge protection. The Mini LED Driver is presented as a bare PCB and is intended to be used as an enhanced module as part of a larger assembly that might include a power supply and a LED panel or another device that uses power from the Driver. So the Mini LED Driver provides three main functions over a simple boost module: it’s easier to connect to, has current limiting and a low-­ voltage cut-out. We haven’t tested the Mini LED Driver in other applications. Still, it could be handy to help charge a 12V battery with the appropriate settings and a diode on the output, or anywhere a 12V DC source is needed at modest currents (up to about 1A). USB connectors will not handle more than about 2A, so the screw terminals are better for higher input currents. CON3 is another screw terminal block from which power can be drawn. If the low-voltage cut-out and current limiting are not operating, the Driver behaves just like a boost module. Circuit ground from inputs CON1 and CON2 is connected straight through to output CON3 and to the boost module’s ground terminals, IN− and OUT−. The low-voltage cut-out connects between the CON1 & CON2 inputs and the boost module, switching power to the module’s IN+ terminal. The low voltage cut-out works as follows. A divider formed by 10kW and 1.5kW resistors connects across the incoming supply. The junction of these two resistors connects to the base of NPN transistor Q3. When the voltage at this junction is above about 0.6V, Q3 Circuit details Fig.1 shows the circuit diagram of the Mini LED Driver. The input supply is wired to either CON1 or CON2 while the LEDs (or another load) connect to CON3. CON1 is a pair of screw terminals to which you can connect bare wires. This type of connector will handle up to 5A with ease. Mini-USB connector CON2 makes it convenient to power it from a USB power supply, but most Australia's electronics magazine The Altronics Z6337 buck-boost module uses two controller ICs and two inductors to provide separate buck and boost capabilities. The Mini LED Driver is intended to be used with a boost-only module. September 2022  77 The trimpot on the boost module is for changing the voltage, while the adjustment screw for the current trimpot can just be seen poking out below it. The wire just visible below the upper trimout here is critical for the Mini LED Driver’s operation. It is connected to a point on the boost module PCB that joins to the XL6009 IC’s feedback pin. is switched on, and it pulls the gate of P-channel Mosfet Q4 down, powering the boost module. The 10kW/1.5kW divider means that an input voltage of about 4.6V is needed to switch on Q3, along with Q2 and Q4. At the same time, Q3 sinks current from the base of PNP transistor Q2 via a pair of series-connected 10kW resistors, which serve both to limit the current sunk from Q2’s base and ensure it is held off when Q3 is not sinking current. These two resistors also hold Q4’s gate high when Q3 is off, so it is also switched off when appropriate. There are two resistors because Q4’s gate needs to be pulled more than 1V below the supply voltage to switch it on, while Q2’s base-emitter junction limits its base voltage to around 0.6V below the incoming supply. The 47kW resistor between Q2’s collector and Q3’s base provides some hysteresis for this voltage comparator. When Q3 switches on, Q2 supplies a small amount of extra biasing current into the junction of the 10kW/1.5kW voltage divider. This means that the input voltage needs to drop to around 3.9V before Q2, Q3 and Q4 switch off. This reduces the chance of the low-voltage cut-out oscillating when the input voltage is close to the cut-out point. The 100nF capacitor in parallel with the 1.5kW resistor also helps by further slowing down its response. The default resistors have been chosen to give correct operation with There are quite a few different modules with the XL6009 chip on them. This is the one we found worked best, and it’s pretty inexpensive. It will also be supplied as part of a complete kit for the Driver board. 78 Silicon Chip a nominally 5V USB supply and protect against such things as the USB supply’s voltage dropping. Although not explicitly designed for it, the Mini LED Driver can operate from higher voltages. We will mention some of the provisos and limitations later. By the way, the 20V maximum limit of this design is due to the maximum gate-source voltage rating of Mosfet Q4, while Q4 also limits the current fed to the boost module to 4A as its drain current limit is 4.2A. Still, the XL6009 module tops out at around 4A anyway, so using a beefier Mosfet wouldn’t gain us much. We have not added any input current limiting as most USB supplies will drop their bundle before delivering 4A. Current limiting The XL6009 IC on the boost module controls the output voltage by comparing an internal voltage reference to a fraction of the output voltage, and adjusting its operation to try to keep them the same. The trimpot on the boost module is part of a resistive voltage divider used to sample an appropriate fraction of the output voltage. So the output voltage can be set by adjusting the trimpot. We provide current limiting by injecting current into this voltage divider, making it appear to the switchmode chip that the output voltage is higher than it actually is, causing it to reduce its output. A 15mW shunt resistor is connected between the boost module’s output (OUT+) and output connector CON3. The voltage across this resistor is proportional to the current drawn by the load at CON3. The ZXCT1009 shunt monitor IC (IC1) amplifies this voltage difference and converts it to a current that flows from its pin 3 output. This current is 10mA for each 1V across the shunt. Note that the 15mW shunt resistor reduces the voltage applied to the load, Australia's electronics magazine but as its value is low, the difference is only a few millivolts (15mV <at> 1A), so it is not important. Since a 1A load current will induce 15mV across the 15mW shunt resistor, that will result in 150µA flowing from pin 3 of IC1 (10mA × 15mV ÷ 1V). The upshot is that IC1 produces a current that is 1/6667 (or, if you prefer, 3/20000) that of the output current. This current is fed to the FB (feedback) pin on the attached boost module through the 4.7kW resistor, trimpot VR1 wired as a variable resistor and schottky diode D1. This current will tend to reduce the output voltage in proportion to the current, but this is not the main factor in the current-­ limiting circuitry. There is also NPN transistor Q1 to consider. Q1’s base and emitter (with a 220W emitter degeneration resistor to moderate its gain) are connected across the 4.7kW resistor and VR1. If more than 0.6V appears across those two components, Q1 will start to conduct. This action forms the bulk of the current limiting feature, with the extra current being sourced into the FB pin through Q1’s collector and emitter. The 2.2kW collector resistor limits the maximum current that can be injected, helping to keep this arrangement stable. Since the voltage between the base and emitter of Q1 depends on both the load current and the setting of potentiometer VR1, based on Ohm’s law, that means that VR1 can be used to set the load current at which Q1 will start to conduct and therefore the maximum current that the whole device can supply. Note that if you use a supply voltage different to 5V, the current limit will change due to Q1’s collector resistor connecting to the incoming supply. But most sources of 5V DC are regulated, so this generally won’t matter. It is something to keep in mind if you’re going to power this circuit directly from a battery pack. Finally, there are two capacitors siliconchip.com.au connected across the output. We have used two smaller parts here as they fit the outline of the Mini LED Driver better. They smooth out the voltage across the shunt resistor, which would otherwise be quite peaky due to the upstream capacitors on the boost module. Due to this, the Mini LED Driver is not well suited as a current-­regulated source for dynamic loads, as these capacitors can only allow a slow response. If the load resistance suddenly changed, then these capacitors would need to charge or discharge before the system could settle at a new steady state. During this time, the current through the shunt would not represent what is happening downstream of CON3. Fortunately, LEDs present a slowly changing load. The Mini LED Driver just needs to cope with changes that occur as the LED forward voltage changes with slowly changing variables such as temperature. Keep in mind that this current limiting scheme is not effective as short-circuit protection, because the boost module cannot reduce its output voltage below its input voltage (except for the small drop due to its onboard diode). Basically, the Mini LED Driver cannot limit its output voltage to anything much below its input voltage and certainly not down to levels near zero. Current adjustment VR1 is wired such that the fully clockwise position corresponds to 0W between its two connected terminals. So the clockwise position sets a 4.7kW resistance between IC1’s Iout and the diode while the fully anti-clockwise position thus sets a 9.7kW resistance. Assuming a threshold of around 0.6V for a silicon base-emitter junction, Q1 will start to conduct at 127µA from IC1 when VR1 is set fully clockwise, and 62µA from IC1 when fully anti-clockwise. This means that the usable output current setting range is nominally from 0.85A down to 0.41A (recalling the factor of 6667 from previously), although these are not hard limits. During one of our tests, we started by setting the Mini LED Driver voltage to 12V with no load and with VR1 set to its minimum. We then connected one of the large 70W LED panels and measured a panel current of 0.48A at 11.1V. siliconchip.com.au Setting the current limiting to maximum gave 0.84A at 11.3V but the current could be increased to 1A by increasing the voltage setpoint (at no load) to around 12.6V. We measured close to 3A at the 5V input, so we don’t expect many USB supplies will work at these levels anyway. The fact is that the current limiting comes on gradually, which is necessary to keep the Driver stable. It also means that the LED operating point can be tweaked by careful adjustment of both the current and voltage settings. Fig.2 shows the effects of changing loads on the Mini LED Driver. We made these plots with the no-load voltage set to 12V and the current-limiting trimpot set to its lowest and highest positions, plus a third point near the middle. There is a limit to how low a voltage can be achieved by the current limiting circuitry; around 8.3V in this case. That is due to the 2.2kW resistor limiting the current injected into the voltage divider. Other boost modules that use different divider resistors for their voltage setting will behave differently as the injected current will change the setpoint by a different amount. This is one of the reasons we’re specifying and supplying a specific module, as shown in the photos opposite. This is the one that worked the best in our testing. If you must try a different boost module, we recommend thoroughly testing the combination before putting it to use. We used the Arduino Programmable Load from the June 2022 issue (siliconchip.au/Article/15341) for much of our testing, including plotting Fig.2. Efficiency We also measured the module’s efficiency and found that it did not reach the 96% figure claimed by the suppliers of many of these boost modules. They usually specify the efficiency for boosting 12V to 20V; boosting 5V to 12V is both a higher ratio and starting from a lower voltage, so efficiency will not be at its peak. With a regulated 5V DC input and 12V at the output, a helpful rule of thumb is to multiply the output current by three to work out the theoretical input current. This corresponds to an approximate efficiency of 80%. Australia's electronics magazine Fig.2: these curves show the behaviour of the Mini LED Driver when set to a nominal 12V and three different current limit settings. The curves correspond to VR1 at minimum (cyan/blue), maximum (red) and roughly halfway between the two extremes (green). Options You might decide to leave off CON1 or CON2 if you know that you will definitely only use one of them, but we’ll explain the construction procedure as if fitting both. Keep in mind that the Mini LED Driver will draw a considerable current with a 5V supply. Any significant sag in its input voltage could result in the low-voltage cut-out operating. A USB connector will have a noticeably higher resistance than the screw terminals. So we recommend fitting both in case this resistance turns out to be too high, and you need to use the screw terminal instead of the USB connector. Construction This board is not difficult to assemble, but it almost exclusively uses surface-­mounting parts. So ensure you have the necessary tools and supplies, including solder, flux paste, solder wicking braid, a fine-tipped iron (or at least not a huge one), tweezers, decent lighting and a magnifier. For more tips and tricks regarding SMD soldering, see our feature on the topic (December 2021; siliconchip.au/ Article/15138). The PCB is well-marked, but you can also refer to the overlay diagram (Fig.3) to see which parts go where. The PCB is coded 16106221 and measures 72mm x 24mm. Start with CON2, the mini-USB connector. Apply flux to the pads and rest the connector in place. It has locating lugs, so it should lock into the correct position. September 2022  79 Fig.3: the trickiest part of assembling the Driver is ensuring you don’t mix up the various SOT-23 parts. Check the PCB markings before soldering these components in place. The boost module sits over the top of this PCB, as you can see from our other photos. While the feedback connects electrically to pin 5 of the XL6009 IC, it’s usually easier to solder to a trimpot lead after checking for a low resistance between it and the IC feedback pin. Clean the soldering iron tip and apply a small amount of fresh solder. Touch the iron to the two extended end pads in the row of five – only these two are needed to supply power. If you bridge them to any other pins, use the solder wick to remove any excess before proceeding. Then apply a generous amount of solder to secure the four corner leads on the shell, which will ensure that the connector is mechanically secure. Work through the transistors, diode and IC next. They are all in identical-­ looking SOT-23 packages, but there are five different types, so take care that they are not mixed up. The PCB is marked with the part numbers as well as the designators. Check the types against the overlay, working with one type at a time. The SOT-23 parts are small, but the leads are pretty spread out, so they are quite easy to work with. Apply flux to the pads for these parts, then use tweezers to roughly place each part in turn. Tack one lead and check that the remaining leads are all within their pads. If not, adjust as necessary using the iron and tweezers. Then solder the remaining leads. Do the same with the eight small (3.2 × 1.6mm) resistors, checking their values against the silkscreen as you go. Much the same technique is used for these parts as for the semiconductors. Fit the larger (6.3 × 3.2mm) current shunt resistor next. It is harder to mix up with the other parts due to its unique size for this project. The solitary SMD capacitor goes next to the 1.5kW resistor and can be soldered similarly. That completes the fitment of the surface mounting parts. Clean the PCB of any flux residue before proceeding 80 Silicon Chip further and allow the board to dry thoroughly. You can test the low-voltage cut-out feature if you can connect a variable power supply to the CON1 or CON2 inputs. It’s best to do so now, before connecting the boost module, as it’s easier to fix any problems you find. Do not exceed 20V, and mind the polarity of the connections to CON1. Ramp the input voltage up and down. Check that the voltage between IN+ and IN− points is present when CON1 or CON2 is above the upper threshold (around 4.6V). When the input is below the lower threshold (near 3.7V), it should drop out. Completion The remaining parts to mount are CON1, CON3, trimpot VR1, the two electrolytic capacitors and finally, the boost module. Solder CON1 and CON3 first. They should sit far enough apart to allow the boost module to sit between the connectors on the ends. Fit VR1 next. While you could solder it in the standard vertical position, the boost module will sit over the Driver PCB, blocking adjustment. So instead, install it on its side, as shown in our photos. Ensure that the adjustment screw is positioned correctly. You should also adjust the trimpot to its minimum (fully anti-clockwise) in preparation for testing. The two electrolytic capacitors sit near CON3. The longer positive leads go into the pads marked with small + symbols. Push them down firmly against the PCB before soldering and trimming the leads. A warning before fitting the boost module; we have seen some boost modules that (confusingly) increase their voltage when the trimpot is Australia's electronics magazine adjusted counter-clockwise. If you are using a different module from the type we supply, check its voltage by powering it up and measuring its output with a multimeter before soldering it to the Driver board. Otherwise, you could cook those two capacitors the first time you power it up. Having checked that, solder the short length of wire to the feedback pin at the reverse of the voltage adjust trimpot on the underside of the boost module. It is intended to be connected to the middle pin, to align with the other PCB, but you might see that two of the boost module’s trimpot’s pins are connected together anyway. You can see where this connects in our photos. On the XL6009 modules that we are using, this should line up directly with the FBPIN pad on the Driver PCB, but it might be in a different location if you are using a different module. Since it lines up directly, a component lead off-cut might be adequate, but if you can’t run the wire directly, use a short length of fine insulated wire instead (eg, Kynar or wire wrap wire). Now solder component lead offcuts or short lengths of stiff wire to the four corners of the boost module at the IN+, IN−, OUT+ and OUT− pads. These should all face down in the same fashion as the wire going to FBPIN. We found a pair of tweezers or pliers handy to grip the wire while soldering it (to avoid burned fingers). Now you can join the two boards together with the boost module above the Driver PCB, ensuring that the pad labels match. Allow some clearance between the two PCBs if possible, and tack one lead in place. Adjust the boards to ensure that nothing is making contact where it siliconchip.com.au shouldn’t and check that they are square and parallel, then solder the four corner pads followed by the wire for FBPIN. Trim any wires that are longer than necessary. Testing During testing, remember that the Mini LED Driver is not short-circuit proof. So take care with the attached loads to ensure that there is no chance of a short circuit or very low resistance that might overload Mosfet Q4. As we mentioned earlier, the Arduino Programmable Load works well for testing, but you could use a fixed resistor (eg, 22W 10W or two 10W 5W resistors in series) or a high-power white LED. The following assumes a 5V supply and might not work if you have a much higher supply. Apply power without a load and adjust the output at CON2 to 12V using the trimpot on the XL6009 module. If you can’t smoothly adjust the voltage at the output, check the Driver assembly before proceeding further. Remember to not set the output above 20V! With VR1 on the Driver set to its minimum position, a 20W or lower resistance load should draw near 0.6A and cause the output to enter current limiting. Referring to Fig.2, check that your unit responds similarly to our prototype. If the output voltage or current seems to be dropping more than this, check that your USB supply is operating within its limits. It might have its own internal current limiting. If the voltage at CON1 is not being maintained near 5V, that is a sign that the supply you are using is not handling the load. It is a good idea to check the voltage going to the boost module at the IN+ and IN− pads. If this is much less than the voltage at CON1, the low-voltage cut-out is operating. That may be due to voltage drops in the cable or the USB supply sagging under load. Adjust VR1 and check that the current limit changes. You might need to increase the load (decrease the resistance) by adding extra parallel resistors. Set the current to your desired value and connect your desired load. Then, confirm that it works as expected. Using other boost modules We don’t recommend this unless you are experienced. Finding the siliconchip.com.au You can clearly see the wire from the FBPIN pad to the trimpot above. feedback (FB) pin can be tricky if your boost module is not labelled. A good place to start is the centre pin of the adjustment trimpot, although we have seen some modules that do not follow that trend. The FB pin is brought out on the XL6009 IC, and most boost controllers should have an external feedback pin, so it makes sense to start looking there. On the XL6009, it is the rightmost of the small pins (pin 5). On the modules we have tried, it is the smaller pin closest to the voltage adjustment trimpot. You could solder a wire directly to this pin, although it won’t be as neat as connecting to the adjustment trimpot terminal. Instead, you can use a multimeter set on continuity mode to find another more accessible (eg, through-hole) solder joint with a nearzero resistance to the feedback pin. If in doubt, look for a data sheet for the switchmode controller chip on your module. Using it We tried the Mini LED Driver with one of the large 70W LED panels we used in June with the Buck-Boost LED Driver (available from our Online Shop, Cat SC6307 or SC6308). We connected the LED panel after setting the output to 12V with no load and winding the current limiting to its minimum. It drove the panel at 480mA, with the output voltage being 11.1V. Slowly increasing the current limit increased the panel current and brightness. To confirm that the current is being adequately regulated, disconnect the LED panel and check that the output voltage rises by at least half a volt; this means that there is headroom for the Mini LED Driver to regulate its current. We found that the panel would dim and sometimes flicker after the current was set past a certain point, meaning that the USB power supply had reached its limit. Another symptom of overloading is a high-pitched sound from the boost module when under load. If this occurs, wind the current limit down to prevent SC damage to the USB supply. Parts List – Mini LED Driver 1 double-sided PCB measuring 72mm x 24mm, coded 16106221 1 DC-DC boost module based on XL6009 controller with red PCB (MOD1, see text) [SC6546] 1 2-way, 5.08mm screw terminal block (CON1) AND/OR 1 mini-USB socket (CON2) 1 2-way, 5.08mm screw terminal block (CON3) 5 20mm lengths of 1mm diameter solid core wire or component lead offcuts (see text) Semiconductors 1 ZXCT1009 high-side current shunt monitor, SOT-23 (IC1) 1 BAT54 (or BAT54C or BAT54S) schottky diode, SOT-23 (D1) 2 BC847B NPN bipolar transistors, SOT-23 (Q1, Q3) 1 BC857B PNP bipolar transistor, SOT-23 (Q2) 1 PMV50EPEA or AO3407 P-channel Mosfet, SOT-23 (Q4) Capacitors 2 100μF 25V electrolytic 1 100nF 50V X7R M3216/1206 SMD ceramic Resistors (all 1206/M3216 1/8W unless specified otherwise) 1 47kW 3 10kW 1 4.7kW 1 2.2kW 1 1.5kW 1 220W 1 5kW top adjust multi-turn trimpot (VR1) 1 15mW 2512/M6432 3W current shunt resistor [SC3943] Kit (SC6405 SC6405 – $25): has the PCB and all onboard parts, including the XL6009 module. Australia's electronics magazine September 2022  81 Wide-Range hmMeter This Wide Range Ohmmeter is more useful than a milliohm meter. It measures very low resistances, down to around 1mΩ, but it can also measure up to 20MΩ with an accuracy of around ±0.1%. That makes it handy in any electronics lab, and it's easy to use; just connect a device and read off its value. Having described how it works last month, we now move on to building it. C onstruction is relatively straightforward as most parts mount on a single modestly-sized PCB. The four binding posts/banana terminals mount on the case's front panel and are wired up via two figure-eight leads and two-way locking header plugs. The six AA battery holder is stuck to the base of the case and hard-wired to the on/ off switch, with power going to the PCB via another header plug. The rest of the parts are on the PCB, which mounts behind the front panel of the case. Several of these parts are only available in SMD packages, so some surface-mount soldering is inevitably involved. Still, we have tried to make it relatively easy. You need the right tools, including a temperature-controlled iron, a syringe of flux paste, solder wick, a good light and a magnifier. It’s also essential to exercise patience; it's easier to make mistakes if you rush into soldering these devices. A little practice soldering fine-pitched SMDs also wouldn’t go astray (eg, using our SMD Trainer from December 2021; siliconchip.au/ Article/15127). Don’t feel daunted; we believe most constructors with modest soldering 82 Silicon Chip Part 2 by Phil Prosser experience can build the Wide Range Ohmmeter without too much difficulty. So let’s start the assembly process. Construction The Wide Range Ohmmeter is built on a double-sided PCB coded 04109221, measuring 90.5 × 117.5mm. Fig.6 is the overlay diagram, which shows which parts go where. Start by checking the PCB, checking that you have all the required parts and tools. Commence by mounting the SMDs. The usual advice for soldering these goes: use plenty of flux, take your time, use a loupe or good handheld magnifier to check, then double-check for bridges between tracks and when you find them, use solder wick to remove them. Oh, and leave the quadruple espresso coffee until after you are finished. One of the most important things to do, and we can’t stress this enough, is to check that you have the right part in each location and that it is orientated correctly before you solder more than one or two pins. While it is possible to remove an SMD IC that has been fully soldered without damaging it or Australia's electronics magazine the board, then clean up the board to re-solder it, it is a lot of work! Some MAX11XXX ADCs have a chamfer along the pin 1 side and no dot to indicate pin 1. So if you can’t find the dot, look at the IC edge-on under magnification; hopefully, you can spot the chamfered edge. Pin 1 is on that side. It’s also an excellent idea to use your magnifier to check carefully that all of an IC’s pins are correctly located over its pads after soldering one pin in each corner, before soldering the rest. It’s easy for an SMD IC to shift slightly if you just tack one pin, and very hard to fix the alignment after soldering more than a few. Besides most ICs and regulators on the board being SMDs, there are also a handful of surface-mounted bypass capacitors and resistors, but they are much larger and easier to solder. It’s generally best to start with the finepitch ICs as that way, you have the best view and access to their leads. So fit IC1, IC2 and IC4 first (remember what we said about checking their pin 1 markings first!), then Mosfets Q2 & Q4, followed by IC3, REG2 & REG3 (don’t get the different types mixed siliconchip.com.au Fig.6: most of the components are mounted on the top side of the PCB. The only part on the underside is the 16×2 LCD. Take care to orientate the ICs, diodes, electrolytic capacitors, relays and TO-220 devices correctly and note how the relay footprints support two common styles of signal relay. Regardless of relay style, the striped (coil) end faces to the left. up). Follow with the five smaller 100nF SMD ceramics, the remaining 10µF SMD ceramics and then all the SMD resistors. Clean off any gross flux residue (using a special-purpose flux cleaner or pure alcohol), then, under good light, check every pin on the SMDs for bridges. Some phone cameras can zoom in for a really close-up photo; if yours offers that facility, take a picture or two and check them well. We have a reasonably inexpensive binocular microscope in our lab which is brilliant for finding pesky shorts. While you’re at it, also check that all the device pins and leads have a proper fillet from the lead down to the PCB pad. It’s relatively easy to get the solder to stick to a pin but not flow onto the pad, or vice versa, especially if you don’t use enough flux during soldering. If you find any problems, fix them up. You can fix bad joints by adding a dab of flux paste and then touching the tip of your iron to the junction of siliconchip.com.au the device lead and PCB pad. Some small solder bridges can be solved in the same way, although it can be better (and is usually advisable) to follow up the flux paste with some solder wick (if it’s saturated with solder, cut the end off and use a fresh section). Note that there are a few unoccupied pairs of SMD pads for optional parts that we determined aren’t required. Through-hole parts Move on to mounting all the remaining resistors. The 47W resistor in series with the LCD backlight can be reduced in value for more brightness, but that will reduce LED life. Or, for maximum battery life, select a higher value that provides acceptable brightness. Use quality resistors in the current source and references. We have provided some recommendations in the parts list, and they are what we supply in the hard-to-get parts set. Ensure that the high-precision 10kW resistor goes in the indicated location and not in place of one of the regular 10kW resistors. Australia's electronics magazine If you don’t have a 205W resistor, you can use 220W instead and replace the two parallel resistors (marked as 47kW and 1.5MW) with two 5.6kW resistors to get reasonably close to the required values. Next, fit the diodes, making sure that the cathode stripes face as shown in each case. Start with the 1N4148s, then the BAT85. Watch out as a BAT85 looks a lot like a 1N4148, but they are very different. Then install the 1N4004 and 1N5819 diodes. They are similar sizes, so don’t mix these up either. Now is a good time to mount the NE555 IC. It doesn’t need a socket, and once again, watch its pin 1 orientation. Follow with the two tactile switches, then all the through-hole ceramic and plastic film capacitors, which are not polarised. In case you’re wondering, two of the 10nF capacitors are PPS types (adjacent to S1 in Fig.6) rather than ceramic because these need to be low-leakage types. If you can't get PPS capacitors, use the best film capacitors you can September 2022  83 and check that they don't adversely affect high resistance readings. Install all the headers now. Most constructors won’t need to fit the programming and SPI monitoring headers, CON4 and CON6. Also, if you are using a programmed PIC, you can fit a wire link in place of JP1. If fitting JP1, simply place the jumper on it after soldering and, unless you need to reprogram the PIC, you can leave it on permanently. Next, fit the four BC547 (or BC546, BC548 or BC549) transistors, as well as the LM336. These are all in the same packages, so don’t mix them up. Follow with the two 10kW trimpots, orientating VR1 as shown in Fig.6. Then install all the electrolytic capacitors, with the longer positive leads going to the pads marked with a + sign on the PCB. The two near the top need to be laid over as shown. This is a good time to install the relays, for which we have provided two options. One is available from Altronics, while the narrower type is commonly available from major suppliers such as Mouser, Digi-Key and element14. The two different outlines are shown on the silkscreening; regardless of which type you use, ensure that the striped end faces to the left as shown. The LCD mounts via a header on the back of the board. Choose the right location for the LCD type you have. It is necessary to mount the LCD quite close to the PCB, but not so close that it touches the solder joints on the main board. We left about a 2mm gap and put a couple of dabs of neutral cure silicone under the screen to keep it from moving. Once set, the silicone will hold everything tight. Troubleshooting It is normal on the first power up for a message stating that default calibration values are being loaded. If the Meter is not working at all, check the following: ● The solder joints on all SMDs, looking for improperly formed joints or solder bridges. ● The battery voltage (you should have checked this earlier). ● The regulator output voltages (ditto). If the LCD is not displaying text: ● Can you adjust VR2 to get anything on the display? ● Is there about -2.2V at the anode of D10? If not, check around the 555 for faults. ● Check for activity on the LCD RS, RW, E and D7, 6, 5 and 4 lines (the rest are not used) on the LCD header. If these are not active, check the soldering on the microcontroller and verify that it has been programmed. ● If there is a problem with the ADC, there will be a message on the LCD telling you that. In this case, check the soldering on the ADC chip. Also check the SPI lines with a scope for activity. You should see activity on the CS, MCLK, SDI and SDO lines. The absence of activity suggests a short or similar problem. If it appears to be working, but the measurements are wrong: ● The connections for Sense+, Sense−, Force+ and Force−. If you have these swapped, the Meter will not make sensible measurements. ● Are the relays clicking? If not, look at the ADC connections again. Look at the four digital output lines and also make sure you have used proper BC54x transistors and the pinouts are correct. We have heard about some parts labelled BC54x that use the wrong pinout. ● Have you used relays with 5V DC coils? ● Are the reference resistors the correct values? ● Connect an ammeter on its 200mA range or similar from pin 3 of IC3, the LT3092 (the one closest to the top of the board) to the anode of D3, with the sense lines shorted (eg, using a jumper). You should measure very close to 50mA, then if you remove the short on the sense lines, it should drop to 0.5mA. ● Check that the 2.5V reference voltage is right; you should have checked this while adjusting it. ● Check that you put those push buttons in the right way around; if you rotated them by 90°, they would be shorted ‘on’ and you are probably stuck in calibration mode and keep getting calibration messages, but the buttons won't work! 84 Silicon Chip Australia's electronics magazine Reducing leakage paths At this point, the PCB should have all the parts on it. If you have a special-purpose flux cleaner such as our favourite, Kleanium Deflux-It G2, it's a good idea to start cleaning by spraying the board with that. Let it dissolve the flux, then dab it dry with a lint-free cloth before scrubbing it with alcohol. That will remove a lot of the residue in one easy pass, making the next step easier. Now get some isopropyl alcohol and a good scrubbing brush to clean the PCB (we used an old toothbrush). Thoroughly clean around the reference resistors, ADC and the input buffer, taking particular care to scrub away any residual flux around the ADC. After scrubbing, wet it again with alcohol and then dab it clean with a lint-free cloth to soak up any residue. Once you’re sure the board's critical areas are clean, liberally coat the ADC and reference resistor area with a clear, protective lacquer, being careful not to spray the headers. Ideally, you should use a purpose-­designed PCB conformal coating (the solder-through type is great in case you find a problem later). We want all sensitive parts of the PCB clean and sealed from moisture. Testing The first test is to apply power and check that the regulator outputs are correct. Prepare the battery of six AA cells. There are many options for this, but the parts list specifies two 3-cell holders, and you just need to connect them in series, negative to positive. Also cut and mount the side switch in the box, as shown in Fig.7. The switch can be mounted at any convenient location on one side of the case; Fig.7: the on/off slide switch can be placed along any convenient edge of the case. Apply this template (it can be downloaded from the Silicon Chip website and printed out), drill the two mounting holes plus 5mm holes at either end of the slot outline, then file away the material between those holes. siliconchip.com.au Front and rear shots of the Ohmmeter PCB. At the rear, two different types of 16x2 LCD modules can be fitted, as the ones found online typically come in one of two sizes. the photo overleaf shows where we placed ours. Use masking tape to mark the drill holes for the screws; 2mm holes are a good start. Also mark and drill two holes that define the ends of the slot. These are 5mm in diameter, and once you have drilled them, use a small file to join them into a slot. Mount the switch and then, ensuring the switch is off, wire up the battery to it (insulating any exposed joints with heatshrink tubing). Next, crimp and solder the two remaining wires into the plug housing that will go to the PCB. Don’t make the leads too short; ensure there is sufficient wire length to assemble and calibrate the instrument conveniently. Double-check the polarity as there is reverse polarity protection on the PCB, but it’s a bit brutal; if wired backwards, the battery will be shunted by a 1N4004 diode. Leave the PCB on the bench so you can make measurements easily, then plug in the battery/switch combination to the header and switch it on. Using a multimeter set to measure low DC voltage, measure between the ground test point right at the top of the PCB, and the output tabs of REG2 (3.45-3.75V) and REG3 (4.5-5.2V). If either reading is wrong, check the input voltage at the cathode of D9, in the lower left-hand corner of the board. This should be around 8-9V. If something is getting hot, switch off and figure out why. If one voltage is low, carefully check the soldering of the regulator and its surrounding components and verify that the components are the right types and orientated correctly. Verify that you have not put the LT3092 in place of a regulator. Assuming they check out, verify that the LCD backlight is on, then adjust 10kW trimpot VR2 until text shows on the screen. Now it is time to calibrate the 2.5V reference, which also optimises its stability. Monitor the voltage across TP1 and TP2, in between the holes for the test terminals on the PCB. Adjust 10kW trimpot VR1 to get a reading as close to 2.50V as possible. This does not need to be super precise, but get it close. At this point, all the adjustments on the PCB are finished, and when you switch it on, the relays should click, and a message saying “Over Range, Check Sense Conn” should come up siliconchip.com.au Australia's electronics magazine September 2022  85 Left: this shows where we mounted the on/off slide switch on our prototype. Above: here we are measuring a 3.3W enclosed wirewound ceramic core resistor. on the screen. You will find that the Meter is now working but not fully calibrated. Mounting it in the case The PCB is designed to fit into the Altronics H0401 instrument case. The front panel drilling and cutouts are in Fig.8. You will have already mounted the slide switch. There are four holes for the Kelvin probes binding posts/banana sockets. The specified binding posts include standard 3mm banana sockets. These holes line up with the large holes in the PCB, allowing the wiring to run straight through. There are also four countersunk holes for M3 screws used to mount the PCB. The front panel covers the PCB mounting holes, so we were careful to countersink the screw heads to be flush with the front panel. The smaller LCD cut-out shown matches the LCD we used. An alternative cut-out is shown for another common type. Before cutting, check which hole suits your LCD module. There could be a third option, in which case you’ll have to figure out the location and size of this cut-out. Internally, the case preparation is simple. By keeping the LCD mounted close to the PCB, the LCD will sit neatly behind the clear opening in the laminated label. Fix the cell holders inside the base with either a dab of neutral cure silicone sealant or double-sided tape. To allow the PCB to fit, we cut off the two standoffs at the top of the base so we could line up the battery holders 86 Silicon Chip along the top, as shown in the photo published last month. There is minimal wiring involved in preparing the case. The power, Force and Sense connections all use pluggable headers. Start with two pairs of red/black wires 150mm long, and crimp these to the pins that match the polarised header plugs. Note that the + and – pins are swapped between the Force and Sense headers. The easiest solution is to insert these in the plastic blocks last, ensuring they line up with the silkscreened markings on the PCB. We printed the front panel label onto thick paper and cut out the hole for the LCD. You can download the artwork as a PDF from the Silicon Chip website. There are two versions to suit the display window locations for two common types of compatible LCD screens, as shown in Fig.9. We then laminated this and used a sharp knife to cut out the holes for the banana plugs. The laminate makes a simple and effective window for the LCD. After that, we stuck it onto the front of the case with a very thin layer of neutral cure silicone sealant. Calibration The calibration procedure has been deliberately kept simple. There is one adjustment per range, which is stored in flash memory and loaded on powerup. As you need access to pushbutton switches S1 & S2 for calibration, it can only be done with the case open. Start calibration by pressing the ENTER key (S2) on the PCB until a calibration message comes up. The Australia's electronics magazine button press detection for the user interface is not terribly fast; buttons are checked after each ADC measurement, or about four times a second. Keep that in mind while calibrating the unit. The calibration process generates a correction for each range independently of all other ranges. Start by connecting a calibration resistor to the Meter as if you were measuring its value. The values used should ideally be close to the top of each range (as specified in the parts list last month and in Table 1). Once the resistor is connected, you adjust the calibration up/down until the Meter reads the correct value of the calibration resistor. You then accept the calibration value for that range. Once all ranges have been calibrated, the data is saved, and the Meter reverts to normal operation. The Meter has five ranges, shown in Table 1, along with the recommended calibration resistors. All but the 10MW types have ±0.1% tolerances, and most are less than a dollar (and are included in the set of hard-to-get parts). If you’re going to use different calibration resistors, they should ideally have tolerances of ±0.1% or better and temperature coefficients no higher than 50ppm/°C. On each range, the Meter will prompt you for a calibration resistor. Once you clip the resistor onto the Meter, it will present readings. Make adjustments as follows: 1. If no button is pressed, the Meter will continually update the measured resistances. siliconchip.com.au Fig.8: these drilling/cutting templates fit on the inside of the case front panel. Select the one which lines up with your LCD screen. Once again, you can download these and print them out, then cut them up and stick them onto the panel so you can accurately mark the hole locations. Table 1 – ranges and calibration Range Calibration resistor Suitable test resistor Notes 0-30W YR1B27R4CC (27.4W ±0.1%) YR1B10RCC (10W ±0.1%) A few test resistors in the 20mW220mW range would be handy 30W-3kW YR1B2K94CC (2.94kW ±0.1%) YR1B1K0CC (1kW ±0.1%) 3kW-100kW YR1B97K6CC (97.6kW ±0.1%) YR1B100KCC (100kW ±0.1%) 100kW-1MW YR1B976KCC (976kW ±0.1%) YR1B1M0CC (1MW ±0.1%) 1MW-20MW MF0204FTE52-10M (10MW ±1%) siliconchip.com.au Australia's electronics magazine High-precision resistors in this range are very expensive September 2022  87 2. When the SELECT button (S1) is pressed, a You will see either a < or > symbol to the right of the measured value. b The > indicates you will increase the calibration factor and the presented value. c Similarly, < indicates you will reduce the calibration factor. d To reverse the direction, hold down the SELECT button and then press ENTER (S2) briefly at the same time. e Pressing SELECT changes the calibration factor and thus the displayed value in the direction shown. The longer you hold the SELECT button, the faster the calibration corrections change. To slow the rate of change down, release the SELECT button for a second. There are three speeds – the slowest will allow tiny corrections, while medium and fast speeds let you get to the required value quicker. If the ENTER button is pressed alone, it will accept the current calibration value and move to the next range. After all adjustments are completed, the calibration data is saved, and the Meter goes back to normal. f 3. 4. Accuracy and precision Our tests show that the precision of this Meter between about 10mW and 10MW is entirely defined by the calibration precision. We calibrated the prototype using the recommended reference resistors and achieved precision close to ±0.1% across most of the range. The better calibration you can give it, the better performance you will achieve. Repeatability across our five prototype meters is excellent, indicating good linearity of the ADCs. We have gone to great lengths to ensure stability over time and temperature, so it should remain stable once calibrated. You will notice that the meter displays more significant digits than the precision would indicate. The Meter is very stable and, in most ranges, provides noise-free measurement to a resolution of much better than 0.1%. While the accuracy is limited to about 0.1%, the resolution and shortterm repeatability are much better than this. So if you want to match resistors to a high precision, the Meter provides the extra resolution you need for that. Using it WIDE-RANGE OHMMETER FORCE - + - + SENSE It’s just a matter of switching it on, connecting the device to be measured and reading off the value. At start-up, it shows the firmware revision and the measured battery voltage. If the battery falls below 6.5V, it will ask for a new set. Try not to leave the Meter on for hours at a time, as it does draw some current, especially in the low range. Aside from this, we trust this will become a handy tool for your workbench. We do not expect the Meter to need calibrating all that often. We went to a fair bit of bother to make sure things should stay stable. Still, keep those calibration resistors and clip them on once a year or so. If you are making a critical measurement, a quick check will only take you a second or two. When measuring low resistances, on the order of a few milliohms, component lead resistance can become significant. So connect the test clips as close to the body of the device as SC possible. Fig.9: while the instrument is simple enough that you might get away without a front panel label, it does make it look quite a bit nicer. Once again, select the one that matches your LCD panel position. Cutting out the LCD rectangle before laminating it produces a protective window for the LCD screen. 88 Silicon Chip Australia's electronics magazine siliconchip.com.au ONLY 249 $ QM1493 Specialty meters combined with multimeter functions. HIGH VOLTAGE INSULATION TESTING "MEGGER" • MULTIMETER FUNCTIONS • DIGITAL DISPLAY • ANALOGUE BARGRAPH • DATAHOLD ONLY 89 $ TAKE EASY ENVIRONMENTAL MEASUREMENTS • MULTIMETER FUNCTIONS • SOUND LEVEL • LIGHT LEVEL • INDOOR TEMP • HUMIDITY TEST WIRING INSULATION 95 ONLY 139 $ QM1594 TEST ALMOST ANYTHING! 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Specialty Function Display (Count) QM1632 QM1493 XC5078 QM1594 Clamp Meter up to 600A AC/DC Insulation Test up to 4000MΩ LAN Cable Test with pinout indicator Sound, Light, Humidity & Temp 4000 4000 2000 4000 Security Category Cat III 600V Cat III 1000V Cat III 600V/Cat II 1000V Cat IV 600V/Cat III 1000V Voltage 600V AC/DC 750V AC / 1000V DC 600V AC / 600V DC 600V AC / 600V DC 40MΩ 4000MΩ 20MΩ True RMS • Current 600A AC/DC Capacitance 100mF Resistance Frequency 200mA AC/DC 10A AC/DC 1000°C Non Contact Voltage • • 40MΩ 100µF 10MHz Temperature Relative Measurement • 10MHz 750°C • • • Explore our great range of multimeters, in stock on our website, or at over 110 stores or 130 resellers nationwide. • www.jaycar.com.au/specialtydmm 1800 022 888 SERVICEMAN’S LOG Being a gopher for a day Dave Thompson As a serviceman, I’m hard-wired to do most of the maintenance/ installation jobs around the house myself. It’s just the way things are – otherwise known as the Serviceman’s Curse. So when anything needs doing, I’m the go-to guy. However, if something is preventing me from completing any given chore, such as the requirements for compliance certificates or having actual knowledge of the subject, I (reluctantly) defer the task to a professional. Recently, we decided to get another heat pump installed at our home. We already have two downstairs, one in the office and one in the lounge area; both were installed when we moved in six years ago. The new one was for upstairs, to take the night chill off the bedroom areas during the darkest days of winter and provide some respite from the heat during the summer – at least, that’s the theory. Previously, the only heating in this house was from a few strategically-placed standalone fan heaters and a 30-year-old, inefficient Masport gas fire installed in the downstairs lounge. We knew this because we had been friends with the people who lived here for the past 25 years and had been to many a lunch and dinner here, so we were familiar with the vagaries of heating or cooling the house. Due to the somewhat oddball layout of the place (which 90 Silicon Chip has had rooms and bits added to it since it was first built as a single-story house in 1959), the heating arrangement was insufficient to warm anywhere but the lounge during the cold winters we experience in Christchurch. Even then, it didn’t warm things up very well, and certainly nowhere else in the house. The Masport gas fire was the only permanent heating source, and we already knew that it didn’t quite cut the mustard. So when we bought the place, our priority was replacing the Masport with a modern gas fire and installing other sources of heat; otherwise, we’d be constantly cold. Reusing perfectly good aircons When we moved in, we renovated the downstairs areas and, as part of that, had the two heat pumps installed. Both were reclaimed units. The bigger Daikin unit in our office area was initially installed in our computer repair workshop in the centre of town. Sadly, we were ‘quaked out’ of that space after the big shakes of 2011. That was the biggest non-commercial heat pump we could get at the time and did quite well to heat and cool that large, open-plan workshop. It was more impressive because the building was very prone to temperature extremes; it baked in the summer and froze in the winter, typical of commercial premises built here in the 1970s. When we finally had to leave that place (employees wading through liquefaction on a daily basis is not congruent with a happy work environment), we removed everything that we could take with us. That meant the heat pump, the alarm system, the compressed-air supply and any other plant we’d spent a small fortune on installing there. While I could have removed the heat pump myself, I had no idea what I was doing. Given that releasing refrigerant into the atmosphere is illegal, we thought it prudent to get someone in who knew what they were doing. How they capture the gasses, I don’t know. Editor’s Note: they usually use a pump to extract it into a cylinder for recycling and, ultimately, reuse. In all fairness, they could have just cut the pipes and bled the gas out, and we’d never have known, but either way, we ended up with the unit safely stowed away and ready to be used again. This heat pump sat in storage for about five years until we finally found a use for it when we moved into our current home. The second heat pump we had installed in the lounge downstairs (to supplement the existing gas fire) was also Australia's electronics magazine siliconchip.com.au but the pandemic came along and scuppered his plans once again. Can’t help but help out a quake casualty. We’d purchased it on a local auction site after the original owner salvaged it from his quake-damaged house. He had only installed it four months before the quake that ruined his house, and like us, he was loath to leave it behind, even though he had no immediate use for it. After moving into a new house with such systems already installed, he decided to sell it. As it was identical to another Daikin unit we’d installed and enjoyed in our previous house, we snapped it up when it appeared on the auction site. We got it for a fraction of its retail value, so we considered it a bargain. It was still in as-new condition and has given us faithful service ever since. Nudged into action by a cold snap Fast-forward six years, and after a particularly cold snap, we decided it was time to install another heat pump upstairs. Due to events in the meantime, we couldn’t use the original installers/removers. Instead, we hired a guy whom a builder friend of mine recommended. He was apparently very experienced with this type of work. As a know-nothing-about-aircon serviceman, all I could see were potential problems. Firstly, where to put the indoor and outdoor units; secondly, how to run the pipes and wiring required, especially to the downstairs compressor unit. To resolve these dilemmas, I decided to let the professional handle them. He is 15 years older than me (and I turned 60 the other day), and to still be active and doing this work is a testament to his character. I’ve actually done some low-level repair work for him over the years, mainly when he had a compressor PCB with a blown fan-motor fuse; all the fuses on those seem to be soldered in. When a fan motor goes (which I’ve written about before), it often takes the fuse as well. Replacing the motor is easy enough, but the rest of it is dead until the PCB fuse is replaced. You’d think they put in a socketed fuse, but no, they’d rather you buy a $600 replacement board. The guy confided in me that he has tried to retire a few times; the first time, he had trained someone who was all ready to buy his tools, van and plant, but that person got ill and couldn’t do it, so my guy had to carry on to fulfil obligations. Then he again decided enough was enough, siliconchip.com.au Anyway, he rocked up with a shiny new Mitsubishi heat pump. As I’m not the kind of person to sit around and do nothing while others work, I offered to help however I could. This is an interesting dilemma for a serviceman; do you like others looking on as you work? I get the odd customer who rocks up to my workshop unannounced and asks if they can wait and watch while I fix their computer. Usually, the answer is no, not only because I might not be able to get onto it straight away (despite their expectations that I drop everything else) but also because my workshop is small and has no room for people to hang around. I don’t care about revealing any trade secrets (I don’t have any; anything I do can be found on the Internet with even a rudimentary search). For me, it is more about not having someone hovering over my shoulder, possibly interfering with what I’m doing. I find jobs take twice as long if I have to answer a lot of questions from a curious onlooker. It’s even worse when I go to do something, and they claim: “I’ve already done that, and it didn’t work”. Explaining that I have my own methods and sequence of troubleshooting eats up on-job time, which they’d then likely complain about me charging them for anyway! In this case, I was happy just to be a gopher, tool collector, spare pair of hands (or eyes), coffee-maker or anything that might make his work a little easier. He was happy for me to hang around, and I made sure to never get in the way or interrupt his chain of thought, unless he wanted me to. For the first hour or so, we looked at prospective places to fit the units. The landing on the first floor was the obvious choice, but with so many doors leading off it, finding a suitable wall with enough free space to hang the indoor unit narrowed down the options considerably. It stood to reason that if we put the unit on one wall, we’d find a spot for the outside unit on the same side. Either way, it meant running the two insulated pipes required to connect the two units together through one of the rooms, the roof space, and down through the exterior walls or fascia to the ground outside. Then there’s the wiring to consider as well. All up, we had two choices, on opposite sides of the landing hallway, with neither being ideal. At this point, I felt like just flagging the whole idea because it just seemed to keep getting harder. To be an Items Covered This Month • • • Being a gopher for a day (installing a heat pump) “Blown” tail lights on box trailer Acer Aspire laptop repair 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 Australia's electronics magazine September 2022  91 Experience pays off installer, you’d have to have so much knowledge of how to traverse walls, roof spaces, cladding, insulation and other barriers, plus have the tools to do any of those things. No wonder tradies’ vans are so stuffed with different tools and fixings! Routing power and pipes Once we’d decided where the components would go, we had to work out how to get power to each unit. We didn’t have to run power between the two (though that is always possible); different circuits can feed the indoor and outdoor units. For upstairs, there was a nearby mains socket – he would piggyback off that to run the indoor unit. The compressor outside is a bit different – it has to be switched there, usually with one of those large, waterproofed on/off switches inline with the power feed. As the outdoor unit was going to sit outside the laundry, it made sense to take a feed from the washing machine circuit, which was just through the brick wall. The connecting insulated copper pipes (one for liquid, the other for gas) would run along the wall through a spare room on the other side of the indoor unit, then into the roof space, then down through the barge-board and the outside of the brick wall before ending up at the compressor. It would all be encased in a nice plastic conduit where visible and would end up looking quite sharp, even along the spare room wall. A drain is also needed to pipe away water condensate from either unit. Outdoors, that usually just means a drip tray or pipe leading to a garden, but the indoor unit must have a proper overflow pipe fitted into a suitable drain, running it down along with the insulated piping where feasible. Wow! That’s a lot of work to do. Given the number of different structural materials the installer would have to go through – plasterboard, concrete, fibreboard, brick, timber and even tiles, so many different tools are needed. I quickly gained a new appreciation and respect for the guys who do this kind of work all day! I was getting tired just thinking about it. Thank goodness he didn’t have to get under the house. He was getting a bit old for that sort of thing, so it would likely have been me crawling around under there, and that isn’t my favourite activity! 92 Silicon Chip The whole installation only took five hours, which amazed me. We had some guys install pre-built cabinets into our kitchen the week previously, and it took four guys three days. Even then, they didn’t finish it right off. They did an amazing job, though, and as a long-time woodworker and one-time furniture-maker, I also offered my services as a gopher at that time. They politely declined that offer, so I let them get on with it. They were quite disorganised, though, especially compared to the heat pump installer. He had several flexible tool bags, all set out with the specific tools he would need for certain phases of the installation. On the rare occasion that he didn’t have the right tool to hand, he knew exactly where the tool would be in his van, and I would fetch it while he worked on something else. It was a real privilege to be able to watch him work, especially as he seemed to know just what to do without having to think about it for ages (like I would have had to). He was methodical and didn’t waste time on anything but the task at hand. He also used a few tools I had seen but had never seen used, especially the pipe-related ones. He had a very nice pair of Vise-Grip branded wire strippers that he used to prepare the wiring. I tried them out and liked them a lot; I have several pairs of different types of strippers, but these ones worked remarkably well, even on thinner wiring. As a bonus, he very generously gave them to me because he had two identical pairs, and he kept the newer set. Tool score! Also quite intriguing was the pipe drying/evacuation process. He had a small vacuum pump with a couple of gauges mounted to it, and once the pipes had been flared and connected at both ends, he joined this into the system (via a purpose-made valve at the compressor end) and ran it for about 25 minutes. He explained this was to completely evacuate the pipes and dry out any condensation that might have gathered in them, and by noting if the readings on the gauges held firm, he’d know if the system was air-tight. I’d never seen that done before; I had assumed from what I’d picked up over the years that the installer ‘charged’ the systems with refrigerant from a tank they carried once it was all hooked up. However, these days the compressors come from the factory with the refrigerant pre-charged, so all the installer has to do is connect the pipework and open the valves once it is dried and evacuated. While all that was going on, I helped with the wiring, which required drilling a few holes through the walls and routing new cables to the existing power points. Fortunately, we reconfigured the main switchboard when we renovated this place just before we moved in. I made a map of which fuses ran which circuits then, so I knew straight away which breaker I had to pull to isolate the plugs we worked on. This map has come in extremely handy over the years; it meant that my wife could still work remotely from the office without us having to shut the whole kaboodle down. After everything was properly crimped and connected and the guy checked it, I buttoned it all back up. The only things left were to clean up, put batteries in the remote and test it. It works like a charm and makes a huge difference to living in the upstairs area. Australia's electronics magazine siliconchip.com.au Laboratory Power Supplies A GREAT RANGE of fixed and variable output power supplies at GREAT PRICES for hobbyist or industrial workbenches. CLUB OFFER 15% OFF LAB POWER SUPPLIES Not a member yet? 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Dual 0 to 16V 0 to 16V 0 to 5A 0 to 30V 0 to 15V 2 x 0 to 32V 0 to 27V 0 to 3A 0 to 36V 0 to 2.2A 0 to 5A 0 to 40A 2 x 0 to 3A 25A Current Limiting Display Single jaycar.com.au/laboratory-psu 1800 022 888 “Cleverly” blown lamps on a box trailer A. C., of Claremont, Tas had quite the experience with his box trailer... For many years, my vehicle of choice was a 1994 Mitsubishi Magna wagon. This car served me very well for about 25 years and was fitted with a standard Hayman Reese towbar and the obligatory 7-pin rectangular Australian trailer connector. When the wife and I bought our first house together, we invested in a 1.8 × 1.2m box trailer to assist with landscaping the property. The Magna hauled this for many years to and from the tip and landscape suppliers. About 18 months ago, I made the hard decision to finally let the old Magna go and upgrade to a brand spanking new Skoda Octavia wagon with all the bells and whistles. When I picked it up from the dealer, I arranged for them to fit the official Skoda tow pack, which came with a removable snap-in tow hitch and a connector that swung down from behind the rear bumper. Unlike the Hayman Reese kit, the Skoda one didn’t require cutting out a section of the bumper to pass the towbar tongue through. It also came with the bonus of having some smarts in it to know when you’d hooked a trailer up to it so it would automatically disable the rear parking sensors and collision avoidance systems – Simply Clevertm! Also unlike the Hayman Reese kit, however, the Skoda came with a European-style 13-pin round trailer connector. Thus, a 13-pin round to 7-pin rectangular adaptor was required to interface with the trailer. All appeared fine until the first time we needed to transport some green waste to the local tip. We hooked the trailer up to the Skoda and loaded it with pruned branches, grass clippings and leaves from the garden, then set off down the street. A couple of hundred metres down the road, the dashboard suddenly lit up with several warnings – “left turn lamp in trailer blown”, “right turn lamp in trailer blown”, “left brake light in trailer blown”, “right brake light in trailer blown”. We pulled over the car and checked the lamps in the trailer, but both the indicators and brake lights appeared to operate fine when we tested them. We got back in the car and proceeded further down the road, but the warnings on the dashboard persisted and wouldn’t reset, even after pulling over again, turning off the ignition and restarting the car. Satisfied that the trailer was safe to tow with a full set of operational lights, despite what the car was telling us, we completed our journey to the tip, dumped the gardening waste and returned home. Once back in the driveway, I contemplated the possibility that my nice, shiny new car was faulty, issuing false-­ positive warnings about the trailer lamps. A return trip to the dealer for a warranty repair wasn’t something I was looking forward to for a near-new vehicle. 94 Silicon Chip However, as it was the weekend and I only needed to tow the trailer once in a blue moon, I decided to sit on the problem for a bit. The car appeared to drive perfectly OK when the trailer wasn’t connected, so it wasn’t like I was stranded with no transport. I decided to look at the 13-pin to 7-pin adaptor that came with the car. The 13-pin connector end couldn’t be opened up as it appeared to be a sealed unit, but the 7-pin connector could be. With the help of the internet, I was able to deduce the standard pinout of a Euro 13-pin connector. I was then able to use the multimeter to verify the continuity of the relevant pins through the 7-pin connector. While the Euro standard trailer plug includes several functions that the Australian one doesn’t have (independent left/right tail lamps, switched 12V supplies and fog lamps, for example). Everything else appeared OK and lined up with the necessary signals required to make my trailer lamps illuminate. Once again, I hooked the trailer up to the Skoda and verified that all the lamps worked fine, but still, the car complained that the bulbs were blown. So what gives? At this stage, I was now willing to give the car the benefit of the doubt – it was new and Simply Clevertm, after all. Maybe I had some kind of obscure wiring fault in the trailer. I unhitched the trailer and popped the covers off the tail lamps. Everything seemed relatively clean for a 15-year old trailer, the wiring was nice and tidy, and the bulbs were all OK, even when temporarily hooked up to a 12V supply. When the indicators on the car were engaged, I could measure the pulsing 12V in the lamp sockets with the meter. On a whim, I plugged the trailer connector onto the car but left the trailer itself uncoupled from the tow ball, just resting on the ground. Not surprisingly, the dashboard still insisted that the bulbs were all out, but this time when I got out of the car to check if they were illuminated, none of the lamps were working! Like Dave Thompson, I decided to go right back to basics and did a full continuity check on the trailer socket through to the lamps. It took a fair bit of time to run a 3m wire around the trailer to all the measurement points without assistance. Australia's electronics magazine siliconchip.com.au Still, I eventually completed ‘belling out’ the trailer wiring and finally found the culprit – an open ground connection on the trailer plug. But why were the lamps working when the trailer was hitched up, and then not working when unhitched? Then the penny dropped. The ground return connection on the trailer plug is wired directly to the metalwork of the trailer, as are the negative sides of all the lamps. But with the ground wire in the plug open-circuit, as soon as the trailer is hitched up to the car, the ground for the lamp circuits is completed through the towbar to the vehicle body and back to the battery. And because the Skoda uses the trailer connector to monitor the integrity of the trailer bulbs, the returning bulb supervision current was being diverted through the car bodywork instead of back through the ground return pin on the trailer connector. The loss of the return supervision current fooled the car into assuming that all the bulbs were faulty, despite them all working correctly. To test my theory, I temporarily wired a dedicated ground wire from the trailer ground pin to the left indicator lamp. Not only was I now greeted with a blinking indicator, but the car suddenly announced that the left indicator bulb was OK. Re-running a new ground wire from the plug to the frame corrected this problem, and the Simply Clevertm Skoda finally admitted that all the bulbs were there. This kind of sneaky wiring fault would have gone unnoticed on the old Magna, as it did not have any lamp supervision circuitry. As long as the trailer remained hitched to the tow ball, the ground would have been connected through the bodywork, and the lamps would have all functioned correctly. Acer Aspire laptop repair B. P., of Dundathu, Qld is a prolific repairer, and this time, he has turned his attention to giving an old laptop a new lease on life... I have an old Acer Aspire 4315 laptop in very good condition for being 13 years old. I’d been working on others since I got that one, but I thought it was time to check it out. It originally had a single-core 1.86GHz Celeron CPU, 512MB of RAM, and an 80GB hard disk. It would have been underpowered and slow even when new. It came to me with no hard drive and no RAM, so I fitted two 2GB PC-2 RAM modules and switched it on. It behaved erratically, sometimes starting up, sometimes not. I got it to start up reliably by swapping the RAM for a different brand. I’ve previously encountered this problem, but this is the first time I’ve had it happen with a laptop. Because I’m using salvaged hardware, my first step is usually to run MemTest86+ to check the RAM, as I’ve found that some salvaged RAM can be faulty and cause all sorts of problems. When I booted from the MemTest CD, the laptop froze with a screen showing a pattern of squares with random characters in them. On rebooting, the same thing happened. I thought it might be a GPU problem, but the BIOS screen displayed correctly. I decided to fit an 80GB hard drive and try to install a ‘light’ version of Linux, as I’d previously done that for other old laptops with success. I initially tried Linux Mint, but it came up with a missing file error, so I tried Lubuntu. siliconchip.com.au Australia's electronics magazine September 2022  95 The Acer Aspire laptop, and a look at its BIOS (basic input/output system) screen. The installation proceeded to where I had to specify the locality, then it froze. I tried rebooting, but it froze again at precisely the same place. I wondered if the laptop was overheating, as I have encountered that previously and then found that the heatsink fins were blocked up with lint. With this particular laptop, the heatsink and fan are accessible by removing one of the back panels without completely dismantling the laptop, as is the case with most laptops. After removing the heatsink and fan, I could see that they were spotless and then I remembered that I had cleaned them when I’d first set this laptop aside for later testing. Seeing that I had easy access to the CPU, I thought I would try to upgrade it. I’ve dismantled a lot of old, broken and incomplete laptops that were beyond repair, so I have quite a collection of Intel CPUs available. I found six CPUs that would fit the PPGA478 socket. But just because a CPU will fit a socket does not necessarily mean that the CPU will work in the motherboard, as the chipset may not support it. I’ve encountered this a couple of times when attempting to upgrade a laptop, but I would see what happened. I had several ranging between 1.6GHz and 2GHz, so I picked the dual-core 2GHz CPU, fitted it in the socket, then refitted the heatsink and fan. The laptop started up, so I hit F2 and checked the BIOS screen. It now said that the CPU was a dual-core Intel CPU at 2GHz. Success. Sometimes, even if a CPU is partially supported, it will run at the correct speed, but the BIOS will not fully recognise it. Even with a BIOS upgrade, it still may show Servicing Stories Wanted Do you have any good servicing stories that you would like to share in The Serviceman column in SILICON CHIP? If so, why not send those stories in to us? It doesn’t matter what the story is about as long as it’s in some way related to the electronics or electrical industries, to computers or even to cars and similar. We pay for all contributions published but please note that your material must be original. Send your contribution by email to: editor<at>siliconchip.com.au Please be sure to include your full name and address details. 96 Silicon Chip up as an unidentified CPU at whatever speed. In this case, the CPU was fully supported by this motherboard. With the CPU upgraded, I started suspecting that this motherboard may not support 4GB of RAM, so I took one 2GB module out and reran MemTest86+. This time, the RAM tested as good. I decided to continue installing Lubuntu Linux, and this time it was successful, so my suspicion proved correct. Because this motherboard supports dual-channel RAM, I swapped out the single 2GB module for two 1GB modules, and I ran MemTest86+ again to verify that the RAM was good, which it was. A check of the specifications of this laptop online confirmed that it does only support 2GB of RAM. It was now time to have a good look at Lubuntu Linux. It has been many years since I last looked at Linux, and back then, Linux was quite difficult and technical to use. I was pretty impressed with what I found. It’s really easy to use and quite similar to Windows XP in many respects. It comes with many applications and has very good support and a large range of applications that can be installed. It came standard with Firefox and Abiword, which was a good start. I looked through the online list of applications available, and I installed Chrome browser, LibreOffice and several other applications. Then I checked that the hard drive and fully set up, Lubuntu had used under 10GB of space. Remarkable. The other impressive thing about these ‘light’ versions of Linux is their support for older hardware, particularly the touchpad on earlier laptops. So far, I have found that Linux supports the two-finger scrolling or one-finger side-­ scrolling features on the touchpads of all the older laptops that I’ve installed it on. This is in contrast to Windows 10, which often does not fully support touchpads on older laptops. It’s often difficult, if not impossible, to find a compatible driver that allows the full use of the scrolling feature of the touchpads on earlier laptops when running Windows 10. So now there’s a way to put those old XP and Vista era laptops and PCs to use instead of tossing them into the scrap heap because they are too old to run later versions of Windows. There are a wide variety of Linux versions available online, and unlike Windows, they are free. SC Australia's electronics magazine siliconchip.com.au Keep your electronics safe with our HUGE RANGE of Low Voltage Circuit Protection SAME GREAT RANGE AT SAME GREAT PRICE. ESPECIALLY HANDY IN A BOAT OR CARAVAN WHICH MAY NOT HAVE A CHASSIS GROUND TYPE SYSTEM CONTROL LIGHTING AND OTHER 12V GEAR AROUND THE BOAT & VEHICLE Blade Fuse Blocks with Bus Bar • Suits standard blade fuses • 30A per output, 100A combined • Red LED blown fuse indication • Negative bus bar 6 Way SZ2031 | 12 Way SZ2032 FROM 2995 $ PERFECT FOR HIGH END CAR AUDIO SYSTEMS, SOLAR INSTALLS AND OTHER HIGH CURRENT 12V APPLICATIONS Heavy Duty Circuit Breakers • Visible Trip / Circuit Breaker Button • Switchable / Manual Push-To-Trip Operation • Multi-wire gauge inputs and outputs 60A SZ2081 | 120A SZ2083 | 200A SZ2085 JUST 44 $ Marine Switch Panels with Circuit Breakers • 10A rated illuminated rocker switches • Push-to-reset 10A, 8A, 6A and 4A circuit breakers • Negative bus bar • Mount vertically or horizontally 4 Way SZ1902 6 Way SZ1903 FROM 4495 $ 95 EA Here's a small selection of our Fuses and Holders See our HUGE RANGE in-store or online SEE OUR STAFF IN-STORE FOR THE FUSE OR CIRCUIT BREAKER TO SUIT YOUR APPLICATION ANL In-line Fuse Holder • Suits ANL Wafer Fuses • Nickel plated • Protective cover SZ2078 JUST 14 $ 95 Gold ANL Wafer Fuses • 80A, 100A, 150A, 200A & 250A models • Screw down contacts SF1990-SF1999 JUST 7EA $ 95 Automotive Fuse Assortment • 20 x 5A, 10A, 15A, 20A, 25A & 30A ATO size fuses included • 120 pieces with storage case SF2142 Shop at Jaycar for Mains Voltage Circuit Protection: • Surge Arrestors • Transient Voltage Suppressors • Fuses and Fuse Holders • MOV & Noise Suppressors • PTC Fuses • Thermal Fuses and Switches Explore our full range of circuit protection products, in stock at over 110 stores or 130 resellers or on our website. jaycar.com.au/circuitprotection 1800 022 888 JUST 2695 $ 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. Using a PICAXE as an Arduino co-processor An Arduino Uno can handle most simple applications. But what if you have run out of input pins and your Arduino code is already too busy to handle more data? In my case, the solution was to use a PICAXE20X2 to perform serial stream ingestion. The Uno can then asynchronously read the data from the 20X2 over an I2C bus. The reason for using the 20X2 is that it can be configured to handle incoming serial data in a special ‘background’ mode while other functions continue to operate normally in the foreground. The 20X2 can also be configured as an I2C slave device, making it easy to interface it with the Uno. The 20X2 can process incoming serial data at ‘hserin’ (pin 12) in the background and write the relevant data to 20X2 scratchpad memory. The scratchpad memory is then accessed asynchronously by the Arduino Uno acting as an I2C master. This particular circuit allows the output of two remote temperature Simple USB power delay timer This timer was designed for use in a museum exhibit, where a Raspberry Pi Zero W plays a series of videos on an Android TV depending on the state of a switch. A button is pressed to switch power on when someone is at the exhibit, but the problem is that the TV takes some time to start up, so the Raspberry Pi needs to be powered up around 40 seconds later. This timer provides that delay. It is based on a 4093 quad schmitt-trigger 2-input NAND gate, IC1, and the time constant of a 270kW/47µF RC network. When 5V DC is first applied, or reset switch S1 is pressed, 98 Silicon Chip interrupting that power supply, the 47µF capacitor is discharged. With a low input at pins 1 and 2 of IC1a, the pin 3 output is high. This is inverted by IC1b, so its output pin 4 is initially low, and transistor Q1 is off. Thus, the coil of RLY1 is not energised and voltage is not applied to the USB-C socket that powers the Raspberry Pi. The 47µF capacitor slowly charges via the 270kW resistor. After 40 seconds, the voltage at pins 1 & 2 of IC1a is high enough to cause its output to switch low, and it stays low until reset because its input voltage will not otherwise decrease. With pin 3 of IC1a low, pin 4 of inverter Australia's electronics magazine sensors to be transmitted serially over a radio data link to an Arduino Uno. The two remotely-located DS18B20 one-wire temperature sensors are connected to a PICAXE14M2+. When the 14M2+ is polled by the 20X2 over an XBee wireless link, it generates a serial stream containing temperature information. The XBee link is configured to operate at a modest 2400 baud. Silicon Chip published a “PICAXE Goes Wireless” article in April & May 2006 IC1b is high, applying current to the base of Q1 via the 1kW current-­ limiting resistor and causing RLY1 to switch on, delivering 5V to the Raspberry Pi. The function of the timer could be inverted so that it’s on initially and then switches off after a delay by swapping the 270kW resistor and 47µF capacitor (+ lead to 5V). Also, you can change the delay time by varying the value of either component. It’s easiest to adjust the resistor unless its value would be over 1MW; in that case, increase the capacitor value. Higher values for either will give a longer delay, and lower values a shorter delay. Graeme Grieve, Bateman, WA. ($70) siliconchip.com.au (siliconchip.au/Series/73) with a lot of good information on PICAXE XBee interfacing. The XBee by itself is a 3.3V device. In this circuit, the XBees are mounted on a small SparkFun XBee Explorer Regulated WRL-11373 carrier card that has an onboard 3.3V regulator and level shifting, allowing it to interface with the 14M2+ and 20X2 micros running from 5V. The remote sensor 14M2+ is also configured as an I2C master that drives a 14mm diagonal (0.56-inch) fourdigit LED display module using the HT16K33 driver chip. This allows for the local display of temperature information. The 20X2 software autonomously polls the remote 14M2+/DS18B20 combination with two bytes of guard data (via the XBee) from ‘hserout’ (pin 10) every 30 seconds or so. On receipt of a valid two-byte poll, the 14M2+ responds with six bytes of data, including two check bytes and two bytes (one word) of temperature data from each DS18B20 sensor. The 20X2 parses the data and siliconchip.com.au places it in its scratchpad memory. The Uno then asynchronously reads the 20X2 scratchpad via its I2C bus to retrieve the temperature data whenever needed. The Arduino Uno is the main cog in my home automation, alarm and email notification system. I have one of the remote DS18B20 sensors monitoring a freezer in the garage and the other measuring outside ambient temperature. My Uno emails me when the freezer temperature exceeds a set value. That is beyond the scope of this article, so I have pared back the Arduino code just to retrieve the temperature data and display it on the Arduino IDE serial monitor. The circuit diagram also shows an MCP9808 I2C temperature sensor connected directly to the Uno that I use to monitor inside temperature. I have included the code Australia's electronics magazine needed to retrieve its temperature too. All the software can be downloaded in a single package from siliconchip. com.au/Shop/6/46 It includes the code for the PICAXE14M2+, PICAXE20X2 and Arduino Uno. Although I have shown the PICAXE20X2 in a remote temperature monitoring application, it could be used in other applications requiring serial-to-I2C translation or for other similar tasks. David Worboys, Georges Hall, NSW. ($100) September 2022  99 Vintage EQUIPMENT AVO Valve Tester Restorations By Ian Batty My article last month covered the history of AVO valve testers and described the seven different types that were made over the years and how they worked. I have some hands-on experience with five of those types. I have repaired or calibrated four, but there was some bad news regarding the original Valve Tester. I also have some general advice about repairing and calibrating these instruments. Warning: Electrocution Hazard All AVO valve testers apply AC voltages with peak values ~1.57 times the indicated voltage on the voltage selectors. From the MkI onwards, they can apply AC voltages with peak values exceeding 600V. Even the initial Valve Tester can apply peak voltages close to 400V. Exercise care with all AVO Valve Testers. Never touch any exposed contacts on valve socket panels. Be careful when measuring voltages. 100 Silicon Chip Australia's electronics magazine siliconchip.com.au T he five models I have personal experience with, in order of decreasing age, are the original Valve Tester, the VCM MkII, VCM MkIV, my CT160 and a VCM163. I have checked out each one, and here is what I found. Original AVO Valve Tester I was offered a Valve Tester to check out. It needed a good clean, but it’s one of those jobs where over-eager cleaning can damage finishes such as control paint markings from the late 1930s. I opted for a light touch on the basis that it was over 80 years old and should retain the marks of age. I tested several 6.3V valves: a 6J5 triode, a 6SH7 pentode and a 6V6 beam tetrode. As I was uncertain of its calibration, I set the mains tapping for 230V and adjusted my bench variac to give 6.3V on the heater of the valve under test. I got consistent readings, all low (Photo 8). As noted last month, all components are passive linear types except the backing-off rectifier. That means they can be easily tested. The general construction of the AVO is robust and reliable, so what might be wrong? Transformers can have open-circuit windings that give no output, high-­ resistance connections that allow the output to fall under load, or internal shorted turns that commonly lead to overheating and smoking. I couldn’t find any sign of these problems in T1 (the high/grid voltage transformer) and T2 (the filaments/heater transformer). There are just eight fixed resistors, and only the values of R1-R6 affect measurements. All tested good. There are two variable resistors, with RV2 being a dual-gang special type. All three sections tested good. It would be odd to find one of the switches, plugs or sockets causing a low-sensitivity fault (Photo 9). They all tested OK. I was really hoping there was nothing wrong with the meter (Photo 10) as it would be a nightmare to fix, and finding a replacement would be almost impossible without buying a whole new instrument. It moved freely, without hesitation going to full scale or coming back to zero. And it settled to the zero mark without any tapping or jiggling. So it seemed to be mechanically OK, but what about electrically? Disconnecting it, I found its coil resistance to be correct, but for siliconchip.com.au Photo 8: The meter scale on the original AVO Valve Tester. The 0-10 scale could read out either the gm directly or a proportional value where 10 represented the expected gm. Interestingly, valves with a gain as low as 56% of nominal were still considered ‘good’ – presumably due to the expense of replacing them. Photo 9: The inside of the socket panel of the Valve Tester. The wiring is quite busy, but the good news is that it rarely goes wrong. Note the copperplated springs used to create the detents on the thumbwheels. Photo 10: The meter movement is a highprecision instrument, but unfortunately, it’s exposed to the inside of the case in the original Valve Tester. So you have to be careful not to contaminate or damage it if you open the unit up. Note the magnetic adjustment tab visible at the back; this gives a 5% or so FSD adjustment range. Australia's electronics magazine September 2022  101 full-scale deflection (FSD), it needed just on 1mA. The movement is specified for a 700µA FSD, so it was giving only about 70% of its usual indication, explaining the under-reading of transconductance measurements. I chatted with some instrument tech mates, wondering whether the permanent magnet had weakened with age. They agreed that this was a possibility. I recalled a method of magnetising the small magnets in telephone earpieces from my training days. The iron polepieces were set into a jig containing a multi-turn, low-resistance coil. Then the coil was connected, in series with a fuse, across a 24V battery. The fuse blew, of course, but not before it had allowed a pulse of current that induced (via the coil) just the right amount of magnetism into the pole pieces. The idea of using this technique to restore the Valve Tester’s magnet seemed plausible. Still, I had two concerns: how was I to know which polarity I needed to increase the AVO’s magnetisation, and how large a current pulse was required to do the job? Having worked for an instrument company back in the late 1960s, I had some appreciation of the fine touch needed with moving-coil meters, so I wasn’t going to risk experimenting on a rare and valuable piece of gear such as the Valve Tester. The UK Vintage Radio Repair and Restoration has an informative thread on meter remagnetisation: siliconchip. au/link/abew The meter is a very fine piece of precision engineering. The internal photo of the meter shows a small moveable tab above the polepiece area. It’s a variable magnetic shunt that changes the movement’s sensitivity by some 5%. Regrettably, the loss of sensitivity in this example was well outside the meter’s adjustment range. VCM MkII clean-up I was also asked to check a VCM MkII out by a fellow HRSA member (see lead photo and Photo 11). This version has the high-­sensitivity meter most of us will come across. The VCM uses a fully-enclosed meter, making work on it much easier. This VCM’s meter appeared ‘sticky’. It showed some hesitancy in moving up to and down from full scale. It was also erratic in settling, not always returning exactly to zero without a gentle tap on the case. Another HRSA member, a former instrument technician, agreed to overhaul the meter for us. Removing the meter proved to be an adventure, demanding the removal of all control knobs and the front panel before I could draw out the meter Photo 11: the rear interior of the MkII. The only real problem with this sample was that the meter was ‘sticky’. It’s a sealed unit in this version and quite a bit of work to remove. Rather than open it up and risk damaging it, I handed it over to someone with experience to fix it and then I reinstalled it. 102 Silicon Chip Australia's electronics magazine forwards from the main chassis. As the similar photo of the MkIV shows (Photo 12), the VCM’s case is ‘well-­ populated’ with components. Repairs may demand extensive disassembly and desoldering. I also discovered that some of the control knob grub screws had slotted heads, others hex. Take your time to check before attacking them. They are not making spare parts anymore. When the former instrument technician returned the meter to me, it was much cleaner and in working condition. A quick check confirmed that it now smoothly reaches FSD with the appropriate current applied. Replacing the meter and carefully bringing the mains up on my variac, I was rewarded with a functioning MKII. That was, until I turned it off, then on again. Splat! As Euan McKenzie notes, selenium cartridge rectifiers have a high failure rate after ageing, and this one had gone out on me. I replaced both the grid circuit rectifiers with modern silicon diodes, and the AVO came back to life. With the meter in working order and the VCM re-assembled, I checked its calibration. Euan McKenzie’s excellent Radio Bygones article has the complete procedure. Here’s my shortand-sweet version. First, check the meter movement FSD is 410µA. Then check the meter reading near FSD. It was a bit low, but adjusting the RV7 pot (sensitivity) made it indicate correctly; the AVO’s meter reading of 100mA measures 50mA using a multimeter in series with the valve anode. Checking the grid voltage, its magnitude was too high at around -67V DC with the Grid Volts set to 100V. It should be -52V, but I couldn’t get it close enough to 0V by adjusting the VG calibration pot, RV6. I figured out that adding around 4kW in series brought the adjustment in range, so I connected two 8.2kW resistors in parallel between the ‘hot’ end of the grid supply and RV6. I could then set the grid voltage to -52V/-5.2V. With the TEST function activated, the grid voltage should become 0.52V more positive when the gm button is pushed, so the -5.2V reading should change to -4.68V. Adjusting RV5 (GM CAL) brought it into calibration. I then checked it using a calibration valve, and its measurements were good. Next, I checked the meter indication siliconchip.com.au on the CH(Cold) position. This is the Mains Adjust function, so a correct indication is the vital first step in any measurement. The reading was too low. With all presets in calibration and the test valve reading correctly, what could be wrong? Following calibration, the meter FSD (affected by the setting of RV7) was 549mA. Ohm’s Law shows that R4 (125kW) should be around 114kW to get the 84% deflection current of 455mA. Shunting R4 with a 1.8MW resistor brought the meter onto the calibration mark, at 84% of FSD. Given the repeated cautions about not messing with the Mains Cal circuit, why did I end up here? The inclusion of RV7 means that you cannot rely on AVO’s assumption that the meter’s sensitivity will be exactly 440µA as noted in the circuit diagrams. In providing RV7 to allow FSD adjustment as part of the calibration procedure, AVO did not foresee the need to make R4 adjustable to compensate for calibration adjustments in RV7. MKIV clean-up Another request from a fellow HRSA member was to clean up a MkIV VCM. The MkIV is the pinnacle of the design, but I found it the most difficult to use. I found it hard to get the expected results and finally considered the SET~ (mains voltage adjustment) indication. The manufacturer’s circuit drawing was confusing, and it took some effort to discover that the drawing did not show how the calibration circuit was connected. Rather than trace out the wiring, I persisted and found a revised circuit (still incomplete) that I could decipher. The photo of the MkIV interior shows that it’s built on a frame, with the bottom rails carrying the overload relay and three mains transformers. From left to right, these are the filament/heater transformer, grid supply transformer, overload relay and anode/ screen transformer. The SET~ calibration relies on the rectified, unfiltered supply taken off the high-voltage winding of T2 (grid bias/transconductance supply). This feeds to a voltage divider, with its top resistor being calibration pot RV4. The tap between RV4 and the rest of the divider then feeds to the meter via two series-connected 1.48MW resistors (confusingly marked as a siliconchip.com.au Photo 12: The VCM MkIV is a powerful instrument, but it’s challenging to work on because many of the components are packed close together or inaccessible. single 2.96MW resistor, R19). Accurate calibration relies on T2 working correctly, the setting of RV4 and the correct value of R19. As with the MkI, I accepted that the transformers would be the most reliable components in the instrument. T2 is fed from the 200V primary tappings of the multi-tap transformer T1, so I set my Variac for 230V and adjusted the mains input selectors to get 200V at T2’s primary. This gave an incorrect calibration indication, so I reasoned that the fault was in the calibration circuit. RV4 lacked sufficient range to correct the calibration indication, so I checked R19. Its value had gone high. Shunt resistors (to a final value of 23.9MW) brought the combination down to its correct value and brought the calibration within the range of VR4. Drift in the value of R19 (and its equivalents in other Marks) is a known cause of calibration errors. But don’t just head for R19 (or its equivalent in other models) if you have this problem. The MkIV circuit includes a number of our ancient enemies (capacitors) and some silicon diodes. I expect the diodes to be reliable, but they are early releases of silicon technology and are almost 60 years old. Also, be alert to ‘previous repairs’. Hopefully, the prestige and value of AVO VCMs have been enough to deter inexperienced repairers from just Australia's electronics magazine launching in with no understanding or respect for the subtleties and complexities of the AVO valve testers. CT160 calibration I bought my CT160 at a Defence clearing sale back in the 1990s, and it has served me well since then. I decided to check it out for this article. Later versions replaced the two duo-diode 6AL5s with silicon diodes for extended lifetime and reliability. These versions are easily identified: there is no warm-up time, as present with my 6AL5-equipped version (see Photo 13). I carefully checked the meter FSD and found it to be 30.4µA, accurate enough given that its most recent Navy calibration was in 1988. The instrument passed the manufacturer’s calibration procedure. Tested against a calibration valve, it was within 3%. VCM163 clean-up Another HRSA member loaned me this, the “ultimate AVO” (Photo 14). It had been repaired and only needed calibration. That is pretty straightforward: set the mains indication, set the grid voltage and adjust the transconductance measurement circuitry. To calibrate the mains indication, I set the incoming mains to exactly 240V AC using a variac, set the mains voltage selector to midrange and adjusted RV2. That was easily done. September 2022  103 corrected, the VCM163 was included in my talk at the Melbourne HRSA’s May meeting. It will be available on our website: https://hrsa.org.au Instrument accuracy AVO’s initial justification for using the valve to do rectification was that they could build transformers with much better regulation than any DC power supply. So, how true was this? The most likely error will be low heater voltage due to the high currents drawn by output/power valves. Correctly calibrated, the CT160 gave the following heater voltages for various heater currents. Photo 13: The interior of the CT160. For the grid voltage, I used RV3 to set the voltage at the top of the Grid Voltage potentiometer to -52V using an average-reading meter. I then checked that, for the Grid Voltage pot set to half-scale, the measured grid voltage is precisely half the pot’s full-scale indication, on all grid voltage ranges. While the full-scale voltage was correct, none of the half-scale voltages were. Close examination showed that the control knob did not sit exactly at the 10V mark when fully clockwise. The Grid Voltage pot’s shaft lacks the usual flat to allow a grub screw to lock the knob to the shaft. Instead, the pot’s smooth shaft is gripped by a collet inside the knob. While this does allow precise adjustment of the knob relative to the shaft, it can allow the knob-shaft relationship to drift, as had happened here. Realigning the knob so that full rotation settled exactly at 10V fixed the problem. Be aware that this problem is not described in the service notes. The final check confirms the transconductance measurement. My calibrated 12AU7 showed a lower gm than the 4.3mS I had found when setting it up. Remembering that transconductance is anode current dependent, I opened the anode current link and checked. For a test current of 16mA, I should have read an average current of exactly 8.0mA, but I measured 7.42mA instead. Adjusting the grid voltage to give a measured 8.0mA, my 12AU7 showed a gm of precisely 4.3mS. This could only mean that the anode current meter was too sensitive. I thought about this – I’ve noted that meter sensitivity can fall with age, as 104 Silicon Chip a field magnet weakens, but I could find no explanation for this meter’s increase. Online conversations led me to accept my guess. There is no way of altering the meter’s sensitivity, as it uses a conventional milliammeter circuit with fixed-value, switched shunts. I opted to add a small preset pot in series with the meter movement. This corrected the error, and could easily be removed if my repair method proves to be inappropriate. Be aware that the VCM163’s switch position numbering differs from all previous models. All valve data books give the correct voltage and current settings for all VCMs, but you will need to interpret switch settings if your book does not include the VCM163’s unique numbering scheme. With the anode current indication Valve Heater Voltage --- 0A 6.75V 6J5 0.3A 6.65V 6V6 0.45A 6.6V 6AG7 0.65A 6.5V 6DQ6 1.2A 6.35V EL34 1.5A 6.3V Most ‘receiving types’ draw 0.45A (6V6) or 0.3A (6SH7). These do not load the heater transformer heavily, so the applied heater voltage is higher than the nominal 6.3V. I reset the calibration to give 6.3V for these types. I found that this lowered the voltage for the high-current EL34 to only 5.95V. Testing a group of five EL34s gave an average gm about 20% low compared to readings for the same group with the correct 6.3V heater supply. Photo 14: the interior of the VCM163. Thanks to Jerry Aldrich – UK Vintage Radio Repair & Restoration Forum, & British Vintage Wireless Society Australia's electronics magazine siliconchip.com.au Taking a 6SH7, I found that, from a high heater voltage of 6.7V to a low of 5.9V, the gm reading changed by +5%/ -7%. The 6SH7’s ‘low heater’ gm reading has a much smaller error than for the EL34 (-20%). So high-power valves are more sensitive to heater voltage than receiving types, and high heater voltages give smaller reading errors than low voltages. Thus you should use the AVO calibration method unless your application demands highly-accurate readings. in the worst case, out of sight. Be really sure to get the full service manuals if you need to dive into the innards of any VCM, especially the MkIV. But with the VCM163, the backing-­ off circuit’s removal and the provision of simultaneous anode current and transconductance indications make it the instrument of choice. Its only downside is the removal of bases such as the UV/UV4~7 series. But you can either get or make adaptors. The long story short is that you should probably get one if you’re working with valves. How good are the Testers? Calibration The original Valve Tester is great for its day, but the application of zero grid bias means that it cannot give the comprehensive testing needed with modern valves. And you can only measure gm; there’s no indication of anode current. On the other hand, the VCM MkI to MkIII are winners on any day. You can set a valve up for the specified control grid, screen grid (tetrodes and pentodes) and anode voltages and measure the valve’s anode current. As mentioned above, it’s possible to chart a valve’s complete electrical characteristics on this instrument. But if you’re just testing valves for correct operation, you can get a direct readout of the transconductance. The MkIV, though, is not my favourite. As an instrument, it’s excellent, but its ergonomics/user interface is confusing. Both grid voltage and mA/V are set by the combination of a range switch and a pot. This does give quite precise adjustments, for example, over the range of 0~5V bias. If you need -17V, you select the 15V position on the switch and then set the variable dial to 2V. The Coarse Setting (grid volts, mA/V) indicator discs are set behind transparent covers. I found I needed to be looking pretty well perpendicularly at them – difficult to impossible if you are standing at a test bench of standard height. And the calibration marks are in red on a black background. The graphic artist in me was shouting ‘luminance values!’ until I went out and took a break. Also, AVO cut the use of terminal strips to the absolute minimum. So they mounted minor components such as resistors on inoperative wafers of the various switches (Photo 15). This puts some parts out of easy reach and, AVO recommend making up a calibration valve. You’ll find a description in AVO instructions and other places. One description calls for plotting the characteristics of a 12AU7 as follows. Strap both sections in parallel. Apply a grid bias of -7V with an anode supply of 200V. Measure the anode current, which should be around 16mA, and adjust the grid voltage to give exactly 16mA anode current. Increase and decrease the grid bias by 1V, measuring the anode current at each point. Divide the anode current swing by two, giving the transconductance in mA/V (mS). For example, observed anode currents of 13mA and 21.5mA give a total swing of 8.5mA for a gm of 4.25mS. You can use this method to create other calibration valves – you might want to use a 6L6/EL34 if you regularly test power output types. You will need to set the relevant voltages. For a 6L6, set the anode to 300V, screen to 200V, grid to -12.5V and the anode current should be about 50mA, giving a gm of about 5.3mS. siliconchip.com.au Place the calibration valve in the VCM, set the relevant voltages grid and check that the VCM gives a gm value matching that of your calibration valve. As mentioned above, the 12AU7 must have both sections connected in parallel when used to calibrate a VCM. Do this using switch settings 641 226 413, which connects the two anodes. Repair advice As touched on above, the meters used in the MkI-IV are highly-­ specialised, sensitive instruments with exacting specifications. Glomping any old ohmmeter into a low-­ resistance circuit can dump tens of milliamps through the test leads. That presents a real danger of damage to a VCM, especially those in the MkIII, MkIV and CT160, which have a fullscale sensitivity of only around 33μA. The electrode selector/roller switches are often hard to turn. Do not use oily lubricants on them, as these will further jam the mechanisms. Clean the instruments well with a totally evaporating cleaner that is safe on Bakelite and the painted lettering, then use a silicone lubricant. If you’re unsure which products are safe, spray a little on your fingers and rub them together. A safe lubricant will dry off rapidly, but your fingers will glide easily over each other due to the coating. Purchasing advice I have a CT160 that I bought at a Defence clearing sale back in the 1990s, so I’m happy with what I have. A recent HRSA auction saw a MkIV sell at $1400, so I’ll need to save up if I want one. Expect to pay at least $1000 SC for any working VCM. Photo 15: To save on tag strips, some of the components in the MkIV are soldered across unused contacts on the wafer switches. This only compounds the problem of difficult servicing! Australia's electronics magazine September 2022  105 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. 09/22 YES! 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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 DATE AUG19 AUG19 AUG19 SEP19 SEP19 SEP19 SEP19 SEP19 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 PCB CODE Price 07106191 $7.50 05107191 $5.00 16106191 $5.00 11109191 $7.50 11109192 $2.50 07108191 $5.00 01110191 $7.50 01110192 $5.00 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 For a complete list, go to siliconchip.com.au/Shop/8 PRINTED CIRCUIT BOARD TO SUIT PROJECT 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 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 DATE APR21 APR21 APR21 APR21 APR21 MAY21 MAY21 MAY21 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 PCB CODE 10102211 01102211 01102212 23101211 23101212 18104211 18104212 10103211 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 Price $7.50 $7.50 $7.50 $5.00 $10.00 $10.00 $7.50 $7.50 $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 WiFi PROGRAMMABLE DC LOAD MAIN PCB ↳ DAUGHTER BOARD ↳ CONTROL BOARD MINI LED DRIVER NEW GPS-SYNCHRONISED ANALOG CLOCK SEP22 SEP22 SEP22 SEP22 SEP22 04108221 04108222 18104212 16106221 19109221 $7.50 $5.00 $10.00 $2.50 $5.00 NEW PCBs We also sell an A2 Reactance Wallchart, RTV&H DVD, Vintage Radio DVD plus various books at siliconchip.com.au/Shop/3 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 Can the VGA PicoMite emulate a C64? I read the article in your magazine on the VGA PicoMite and am enquiring about the ability to turn it into a Commodore 64. Video support should be fine and joystick support OK. Keyboard support will depend on whether one uses a standard or a Commodore-­ 64-style keyboard. A sound chip and a few extra pieces like a serial port might need to be added. Does it sound possible? Many people have spare memory chips like DDR3 or older, which are now obsolete. Could a board be made that you could plug in or solder in a few DDR3 DIMMs and maybe a battery for memory retention and have it act like a small hard disk drive, or even a USB flash drive as a hard drive? Is that possible? (M. H., via email) ● Geoff Graham responds: It might be possible to make the VGA Pico­Mite run Commodore 64 programs, but it would not be easy. The main problem with emulating old hardware like this is correctly implementing the various ‘hacks’ where programmers could directly access the hardware (such as the PEEK and POKE commands that directly accessed the C64’s memory). For this reason, we do not have any plans to add Commodore 64 emulation. The RP2040 chip does not have support for adding DDR memory. You can use SD cards for storage anyway. VGA PicoMite keyboard choice I have constructed the VGA Pico­ Mite computer (July 2022; siliconchip. au/Article/15382) but cannot get the keyboard to work. I am using a USB to PS/2 adaptor, and it works with a USB numeric keypad but not with a full-size USB keyboard. The numeric keypad draws 40mA from the PicoMite but the full-size USB keyboard reads 0mA. I have tried three different keyboards, 108 Silicon Chip all from Dell. They all work with my laptop and draw 40mA of current from the laptop. Will the VGA PicoMite work with a USB keyboard and adaptor? Can you suggest where I can purchase a cheap PS/2 keyboard, or do I need a different adaptor? (J. B., Blackwood, SA) ● Geoff Graham responds: You cannot use a USB to PS/2 adaptor on just any USB keyboard – the keyboard must be designed to suit both USB and PS/2. The USB to PS/2 adaptor is a passive device that simply adapts the pin configuration and tells the keyboard to switch into PS/2 mode. The best way of telling if a keyboard supports both standards is to check if it comes with such an adaptor. While PS/2 compatible keyboards are not as popular as they used to be, there are still plenty for purchase, such as the PERIBOARD-409P from Amazon, Altronics Cat D2111, the Wiretek full-sized PS2 Keyboard from Kogan and many more on eBay. Multimeter Checker USB fussiness I have built the Multimeter Calibrator & Checker from the July 2022 issue (siliconchip.au/Article/15377). All went well with the construction and the board works as advertised in stand-alone mode. Still, I have a problem when connecting to it via USB. The USB driver is installed and the USB port shows up as a USB Serial Device in Device Manager. However, it will not open in a serial terminal emulator like PuTTY with the error message “Unable to open connection to COMx. Unable to configure serial port”. I have confirmed the continuity of both USB comms lines from the PIC through to the end of the USB cable “A” connector and checked the various supply voltage levels around the board. The signals on the USB lines look normal and are active when the PC connection is made. Any hints? (M. P., Belrose, NSW) Australia's electronics magazine ● PuTTY gave us the same error message when we tried to connect to the prototype, but it works fine using Tera­ Term Pro. It appears that the problem is that PuTTY tries and fails to set the baud rate. As it is a virtual serial port, the baud rate is essentially irrelevant, but it seems that PuTTY will refuse to connect if it can’t set it. We have modified the software to allow for the baud rate to be ‘set’, although it ignores the setting. Luckily, there was enough remaining flash space in the microcontroller to add that feature. After doing that, PuTTY successfully connects. All chips programmed (including in kits) that we now sell will use the revised 0410722B.HEX firmware. The new firmware is also available for download from siliconchip.com.au/ Shop/6/18 CD Welder design questions Thank you for publishing the Capacitor Discharge Spot Welder project (March-April 2022; siliconchip.au/ Series/379). As I get to this project’s assembly stage, I have a few questions. 1) The parts list shows six 100nF 50V X7R ceramics capacitors for the power supply board and seven 100nF 63V MKTs for the controller board. Why is there a difference in the type of bypass capacitors between the two boards? Looking at the board photos (pp26-27, March 2022), it seems like both boards have the same kind of (orange ceramic) 100nF bypass capacitors installed. 2) The 2.2μF capacitor in the power supply is listed in the parts list as a 2.2μF 50V X7R ceramic. On the board photo, it looks like the installed capacitor is electrolytic. What is the correct capacitor type for the 2.2μF? 3) The controller board contains two 220nF capacitors, one MKT and one ceramic. It is difficult to determine which capacitor in the circuit is the MKT and which is the ceramic. This is shown on the PCB silkscreen, but it siliconchip.com.au would be helpful to identify the capacitor type in the circuit diagram. Thank you for providing an excellent magazine with great content. (E. B., Wodonga, Vic) ● Phil Prosser responds: There are two significant concerns driving filtering and bypassing in this design. The fact that there is a switchmode power supply demands local attention due to the high currents with extremely fast rise and fall times. In the switchmode power supply, particularly around the switching regulator, we are concerned with the very high frequency performance of the parts, hence the choice of ceramic capacitors around the MC34167T. Around the linear regulator on this board, that is much less of a concern, and film caps are adequate. When building the prototype, my particular concern was around the switching part of the circuit; you can see the 0805 ceramic capacitor is ceramic, but the remainder are actually film caps. That was purely a consequence of my having a box of those capacitors to hand. So you could use MKTs around the op amp, current sense and linear regulator, and ceramic capacitors around the switcher. The fact that the 2.2μF cap bypassing the switcher is electrolytic in the photo was me being cheeky. You should use the X7R ceramic part as it will have better long-term reliability. I built this prototype on a weekend when the shops were shut, so I compromised. Don’t do this if you have a choice. There is a 220nF capacitor across the trigger input on the controller board purely to deal with high-frequency noise. This capacitor is right next to the trigger input, and the best part for this purpose is a ceramic capacitor, which I recommend you use. I am sure you will quickly point out that the prototype used an MKT cap. That is true, but a ceramic here is better. The second 220nF capacitor on the controller module is for timing pulse widths and is found between the NE555 timers. It should be MKT, as in timing circuits, the low leakage of these devices is of benefit, as is the typically better tolerance of ±5% to ±10% for film caps compared to ±10% to ±20% for ceramics. You are right that we should have marked which 220nF capacitor is an MKT type. siliconchip.com.au I hope the above helps explain the areas in the design where there are ‘absolute’ drivers and other areas where the choice is more ‘grey’. The final recommendation was us seeking to be conservative in the implementation. While we strive for prototype photos to match the final design, there can be slight deviations for various reasons. For example, we might specify all one type of capacitor on a board to keep the parts list simple (and allow you to buy in bulk) when it would be acceptable to mix capacitor types, and we might have done that. Variable speed motor controller blew up I have a three horsepower (2.25kW) Hitachi router with a burned-out speed controller. A replacement speed controller is no longer available, so I purchased a kit for your 230VAC 10A FullWave Motor Speed Controller (May 2009; siliconchip.au/Article/1434). I have had the router running on the unit while I adjusted VR2. The variable speed control worked quite well, but I haven’t yet tried it under load. However, when I switched it on today to show a friend how it worked, the speed adjustment didn’t work. It started at full speed, and I could not alter the speed. I intend to go to our local Jaycar shop and buy a replacement IGBT as there is zero resistance between the E and C legs. But before I do so, have you got any suggestions as to why this has happened? Is the router startup current too much for the Speed Controller to handle? There is an insulating pad between the casing and the IGBT but nothing to insulate the metal part of the IGBT from the 3mm bolt. Could this be the problem? (T. H., Wallington, Vic.) ● It might be better to soft-start the router by setting it initially at a low speed, then bring it up to speed more slowly, rather than switching it on with a high initial speed. The IGBT does not need extra insulation as it has a plastic area around the mounting hole, including on the back. Note that we upgraded our motor controllers over the years from the 2009 version to the latest Refined FullWave Motor Speed Controller (April 2021; siliconchip.au/Article/14814), which features a Triac that’s much more rugged than most IGBTs. Australia's electronics magazine Purpose of solder pads on I2C adaptor I am building the Wideband Digital RF Power Meter, but I am having some problems (August 2020; siliconchip. au/Article/14542). I purchased the PCB from Silicon Chip. I have a 16×2 LCD with a blue backlight and the I2C add-on. The software loaded OK. The I2C module has three vacant solder pads underneath labelled A0, A1 and A2. What do I do to these? The LCD just gives me bright squares, no information. I have altered the sketch for the PCF8574T (0x27). I’m unsure if the FDEBRANDER Arduino Liquid Crystal I2C program is the right one to use. Visiting GitHub, it seems that the author has withdrawn the Liquid Crystal sketch. (B. W., Longford, Tas) ● The three dual solder pads on the rear of the I2C LCD add-on are used to set its I2C address. Leave them open; that sets the address as 27 hex. If the LCD just displays bright squares of dots, you might need to adjust its contrast trimpot. If your sketch has been altered for an I2C address of 0x27, it should be compatible with your I2C adaptor as long as you haven’t soldered those three pads. If you are using the firmware sketch “RF_Power_Meter_sketch.ino” downloaded from siliconchip.com.au/ Shop/6/5594 and LiquidCrystal_I2C.h within the same ZIP at that link, you shouldn’t have any problems. We hope these suggestions help you get the Digital Power Meter going. LC Meter also shows inductance for caps I finally made the Wide-Range Digital LC Meter from the June 2018 issue (siliconchip.au/Article/11099), but I am a bit disappointed. It measured the capacitance of a 100nF capacitor accurately but also said it had an inductance of 28H. It also gave an inductance reading (along with the correct capacitance) for a 470μF capacitor. It measures inductors under 1mH accurately but measured a 300mH inductor as 500mH. Is there an update to the software, or have I done something wrong? (L. N., South Lake, WA) ● What you have described is consistent with how the LC Meter operates. We mentioned the difficulty distinguishing between capacitors and September 2022  109 inductors on p39 of the article. Both values are displayed so that the user is not bound by the LC Meter’s automatic detection algorithm and can make an informed interpretation of the data provided. Also note that the value of inductors can change markedly depending on the test frequency. The LC Meter uses very low-frequency pulses, so it might not give the same readings for inductors when their performance has been characterised at a higher frequency. In the June 2018 article (inside the panel on page 40), we noted that even a high-quality commercial LC meter gave values that varied by 10% for the same inductor. If you can send some photos of your construction (the PCB in particular), we can check them for problems in case something is wrong. But we suspect that this is just the nature of reading the values of multiple types of components over wide ranges with a relatively simple instrument. Calibrating DDS project touchscreen After I built the Touchscreen DDS Signal Generator, I found that the touchscreen worked but trying to use the on-screen keypad, pressing a key would result in a different letter or number being selected (April 2017; siliconchip.au/Article/10616). I queried this via email, and the response I got was that I needed to recalibrate the touchscreen using the Micromite LCD BackPack’s serial port. I have a CP2102-based USB/serial adaptor. I downloaded TeraTerm and the drivers for the CP2102, pointed it to COM3, opened TeraTerm and set the speed to 38,400. When I hit Control-C, I get the “>” prompt, then I type “GUI CALIBRATE” and press enter. I get an error message saying, “SPI is open”. I tried this several times; once I managed to get into the calibration routine where it said to press here at the four corners of the screen. Once I did that, it said, “GUI calibrate error”. Trying again, I always get the “SPI is open” message. How do I solve this? (B. L., Downers Grove, Illinois, USA) ● The “SPI is open” error is because you are interrupting the DDS program while it has the SPI port open. To work around this, after pressing Ctrl-C and before running GUI CALIBRATE, enter the command “SPI CLOSE” and press enter. That will force it to close the SPI bus before starting the touchscreen calibration. The GUI CALIBRATE ERROR can sometimes happen, especially if you don’t press targets with perfect accuracy. Try it again a few times and it should eventually work. Geoff Graham recommends using a toothpick and holding it on each target for around one second. Multi-amplifier noise problem As a subscriber to Silicon Chip, I am enjoying the magazine as much as ever, particularly the articles from Parts for High Temperature Thermometer/Thermostat I want to build the High-Temperature Thermometer/Thermostat (May 2012; siliconchip.au/Article/674). I have been trying to locate the AD8495 thermocouple amplifier IC and the OP747ARZ quad precision op amp, but the usual suppliers have nil stock. I’ve found a supplier for the voltage reference, but that’s all. Do you know of a supplier, or can you recommend alternative devices? (E. M., Capel, WA) ● Digi-Key and RS currently show the OP747ARZ as being in stock (look up catalog codes 505-OP747ARZ-ND and 412-854P, respectively). The AD8495 is more of a problem. You could get a module with the chip onboard and remove it if you know how to do that, eg, see www.tindie.com/products/nsayer/ ad8495-breakout-board/ If you must build it now, that’s your only real option. Other suppliers like Mouser and Digi-Key are taking back orders for the AD8495 for delivery in early-to-mid 2023, so you could also order one and wait. Given the difficulty of obtaining parts, we are planning to update the project using a different IC that is currently available. The revised project will likely be published early next year. Waiting for that might be slightly quicker than waiting for those ICs to arrive, depending on how long it takes us to develop the design and publish the article. It will likely be cheaper to build, too. 110 Silicon Chip Australia's electronics magazine prolific Phil Prosser and John Clarke. Keep up the great work! I have built several Ultra-LD Mk.4 amplifier modules (August-October 2015; siliconchip.com.au/Series/289). They are among the best sounding amplifiers I have ever heard. Recently, I used them to create a stereo four-way active speaker system. I made up two sets of four amplifier modules with one power supply per set, but with the 4,700μF capacitors replaced with 10,000μF units. The problem I have is that when I connect the four modules to the power supply, I hear the slightest noise when I place my ear right up against the midrange speaker. I have been careful to connect the amplifier modules to the +V GND -V of the power supply, so that no ground potential or loops are created. If I disconnect two amplifier modules, all I hear is the slightest white noise. Swapping each module around in this two-channel arrangement gives the same result. So I know there is no problem with any of the modules. But if I connect all four modules together, I get the slight noise again. The noise is not heard from 150mm away from the loudspeaker, let alone when seated on the sofa, but I find it annoying that it is present. The noise is not your typical ground loop hum, and I have been very careful to use screened cable to the amp module from my RCA connectors. Do you have any idea or explanation as to why this arrangement causes noise? (J. D., Endeavour Hills, Vic) ● When you have four amplifiers connected, try disconnecting the shield from the amplifier end of the shielded cable, or insert a 100nF capacitor in series with the connection from the audio signal lead shield to the amplifier. The problem is that the input cable shields can create an Earth loop, possibly destabilising the amplifiers. Disconnecting one ground, or adding the capacitor, may fix this. We assume you have been careful to connect the amplifier 0V leads in a ‘star’ configuration and not between the capacitor bank and rectifier, where significant AC currents flow. Doing this correctly with multiple amplifier modules can be tricky. So we think it’s most likely the input lead grounds that are the problem. continued on page 112 siliconchip.com.au MARKET CENTRE Advertise your product or services here in Silicon Chip KIT ASSEMBLY & REPAIR FOR SALE 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 SILICON CHIP LEDs, BRAND NAME AND GENERIC LEDs. Heatsinks, LED drivers, power supplies, LED ribbon, kits, components, hardware – www.ledsales.com.au 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 KEITH RIPPON KIT ASSEMBLY & REPAIR: * Australia & New Zealand; * Small production runs. Phone Keith: 0409 662 794 keith.rippon<at>gmail.com LEDs and accessories for the DIY enthusiast 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 Lazer Security 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 For Quality That Counts... QUALITY COMPONENTS + MORE The parts clearance sale continues, but stock is limited, this month check out the freebies – go to lazer.com.au Email for a postage quote, quote the number directly below the photo when referring to a book: silicon<at>siliconchip.com.au EAL Keep your copies VALUE A T $19.50* safe with these PLUS P& P handy binders R * increasing to $21.50 from October 1st 2022 Order online or call (02) 9939 3295 www.siliconchip.com.au/Shop/4 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 adverts<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 September 2022  111 Setting Ultra-LD Amp quiescent current I have a few questions about the Ultra-LD Mk.3 200W Amplifier Module (July & August 2011; siliconchip. au/Series/286). I have already built a module, and it works extremely well. I adjusted the quiescent current as described by you in the magazine. It says, “The voltage across one resistor is then monitored and trimpot VR1 adjusted for a reading of 9.5V – equivalent to a quiescent current of 70mA.” But by 9.5V, it is drawing about 160mA. It works, but then I have more dissipation, and the heatsink gets quite warm. If I lower the voltage on the test resistor to about 3.5V, I have a stable 70mA. Why do I have this discrepancy? I also noticed that the positive side draws a little more current. Is that normal? I have another question about the VAS transistors (2SC4793, 2SA1837) and 180pF capacitors. Is a replacement Advertising Index Altronics.................................25-28 Dave Thompson........................ 111 Digi-Key Electronics...................... 3 Emona Instruments.................. IBC Hare & Forbes............................. 11 Jaycar........................ IFC, 9, 13, 43, ............................. 51, 55, 89, 93, 97 Keith Rippon Kit Assembly....... 111 Lazer Security........................... 111 LD Electronics........................... 111 LEDsales................................... 111 Microchip Technology......... OBC, 5 Mouser Electronics....................... 7 Ocean Controls............................. 8 available? I tried BF470 and BF469 from CDIL, but the THD was much worse than the original transistor from Toshiba. What is the tolerance for the 180pF capacitors? Would 220pF be too high? I can’t find a 180pF polypropylene; currently, I am using ceramic. (B. G., Neu-Isenburg, Germany) ● A reading of 9.5V across each 68W safety resistor corresponds to 140mA per side or 70mA through each output transistor (two per side). We are unsure how you can obtain 160mA when there is 9.5V across a 68W resistor; perhaps your resistors are a bit low in value, closer to 60W. It would be best to check them with a resistance meter. If you can adjust for 140mA and the dissipation is reasonable, that’s good. The heatsinks will get a little warm but should not be too hot in free air. If you can’t handle that much idle dissipation, you can reduce the bias current, but you will have slightly higher THD+N than the figure we published. Once the fuses are in place, the quiescent current can be checked by measuring across each 0.1W emitter resistor. You should get 7-10mV. It is normal for the current to be different for each transistor and to differ between the positive and negative rails. One rail can draw slightly more current than the other, but they should be almost equal once the correct bias level has been established (within a few milliamps). You can replace the 2SC4793/­ 2SA1837 VAS transistors with FZT558 or FZT796A for the PNP transistor and FZT458 or FZT696B for the NPN transistor. However, since these are surface-mount types you need to mount them onto the small heatsinks using clamps, with connecting wires to the PCB. We don’t think using the BF469 and BF470 should be too detrimental to performance as long as they are quality Silicon Chip Binders................ 111 Silicon Chip Shop............ 106-107 Silvertone...................................... 6 The Loudspeaker Kit.com.......... 95 Tronixlabs.................................. 111 Wagner Electronics..................... 12 112 Silicon Chip Errata and Next Issue ROLEC OKW.................................. 4 transistors, but as those parts have been out of production for a while, those left on the market may not be great examples. The 180pF capacitor values are reasonably critical for stability and should be that value. Higher values should work but will slightly compromise the high-frequency performance. Ceramic capacitors are fine as long as they are NP0/C0G types; those are just as good as plastic film capacitors. You can reduce the value of the 220pF capacitor to 180pF by adding 1nF capacitors in series with each. Alternatively, you could use 100pF and 82pF capacitors in parallel, or other combinations that total close to 180pF. Plans for an updated headphone amp? Do you have any plans to present a new headphone amplifier project in the near future? I have the September/October 2011 issues (siliconchip. au/Series/32) and will build that one if there’s no plan to update it (which looks excellent and is by no means obsolete). I also note that you have some parts for that project available in your Online Shop. (P. H., Warwick, Qld) ● We will likely publish another headphone amplifier project eventually, but we don’t have any currently in development. As you say, the September/October 2011 design is still perfectly valid. If we publish a new one, it will probably be a simpler design that doesn’t necessarily perform as well (it still must be good, obviously!) but will be easier and cheaper to build. It’s doubtful we could exceed the performance of the 2011 design anyway. We certainly still have PCBs for that project and it uses standard components that should not be difficult to find. SC AM-FM DDS Signal Generator, May 2022: the 10nF capacitors connected to the A & B pins of rotary encoder RE1 should be increased to 100nF to provide more reliable operation with some encoders. Capacitor Discharge Welder, March & April 2022: in Fig.4 on p31 of the March issue, the 220nF capacitor connected to pin 6 of IC6 should be an MKT type while the other 220nF capacitor should be ceramic. Next Issue: the October 2022 issue is due on sale in newsagents by Thursday, September 29th. Expect postal delivery of subscription copies in Australia between September 26th and October 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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