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AUGUST 2022 ISSN 1030-2662 08 100 Years of Electronics in Australia The Histor y of Silicon 9 771030 266001 $ 50* NZ $1290 11 INC GST INC GST Chip Page 26 Wide-Range Ohmmeter measure from 1mΩ to 20MΩ Page 48 The HiFi isoundBar with a built-in woofer SPY-DER A 3D-PRINTED DIY ROBOT siliconchip.com.au Australia's electronics magazine Page 60 Reviewing the DH30 Max Li-ion spot welder Page 80 Assembling the August 2022  1 Secure Remote Mains Switch Want to build your very own Smart plug? Here’s a great project that lets you use your Smartphone to turn on/off any appliance such as a TV, computer, table lamp, etc. using Bluetooth® and directly from the power point without getting up off the couch or out of bed. SKILL LEVEL: Beginner For step-by-step instructions & materials scan the QR code. CLUB OFFER BUNDLE DEAL 6495 $ www.jaycar.com.au/bluetooth-powerpoint See other projects at www.jaycar.com.au/arduino SAVE 25% KIT VALUED AT $89.75 DON'T FORGET YOUR ESSENTIALS FROM 4 95 $ Prototyping Boards Transfer your breadboard design without having to rework it. Small 25 Rows/400 Holes HP9570 $4.95 Large 59 Rows/862 Holes HP9572 $9.95 100 $ gift card Awesome projects by On Sale 24 July 2022 to 23 August 2022 JUST 11 $ 95 Breadboard Jumper Kit Includes 5-pieces each of 14 different lengths, single core wires. PB8850 Got a great project or kit idea? JUST 1495 $ EA Acrylic Sheets General purpose perspex for hobby use. Clear or red available. HM9505/09 If we produce or publish your electronics, Arduino or Pi project, we’ll give you a complimentary $100 gift card. Upload your idea at projects.jaycar.com Looking for your next build? Silicon Chip projects: jaycar.com.au/c/silicon-chip-kits Kit back catalogue: jaycar.com.au/kitbackcatalogue 1800 022 888 www.jaycar.com.au Shop online and enjoy 1 hour click & collect or free delivery on orders over $99* Exclusions apply - see website for full T&Cs. * Contents Vol.35, No.8 August 2022 14 IC Fabrication, Part 3 Due to the increasing transistor density of ICs, newer manufacturing technologies are required. FinFETs, GAAFETs and now “multi-chip modules” are some of the methods used to produce ever more packed silicon dies. By Dr David Maddison Semiconductors 34 History of Silicon Chip, Part 1 Leo Simpson, the founder of Silicon Chip magazine tells the story of how and why Silicon Chip formed. It all started in 1984, while he was the editor of the magazine Electronics Australia. By Leo Simpson 60 DH30 MAX Li-ion Spot Welder Many new welders that use Li-ion batteries have been popping up online, at prices that you would consider reasonable. While the DH30 MAX has the beginnings of a good design, it wasn’t without its stumbles. By Phil Prosser Review 26 Wide-Range Ohmmeter, Part 1 This auto-ranging Ohmmeter measures just about any resistance you could want, from 1mW all the way to 20MW. It’s accuracy is better than ±1%, and it’ll run for ~24 hours of active use with its six AA cells. By Phil Prosser Test equipment project 48 isoundBar with Built-in Woofer Why spend over $1000 on a good commercial soundbar when you can build your own for less than half that! Just make sure you have enough room for it, as our isoundBar measures 1.24m wide. By Allan Linton-Smith TV & Audio project 64 SPY-DER: a 3D-printed Robot SPY-DER is a speech and web-controllable surveillance robot. It walks like a spider, and can monitor locations using its onboard camera. You can build it yourself by using a 3D printer, some servomotors and a few low-cost electronic components. By Arijit Das Raspberry Pi & Arduino project 80 Secure Remote Mains Switch, Pt2 We finish off our Remote Mains Switch by showing how you assemble, test it, and then register the transmitter(s). We also have a separate panel on how the rolling code system works. By John Clarke Mains power project Wide-Range OhmMeter Page 26 isoundBar Page 48 Page 64 SPY-DER A 3D-PRINTED DIY ROBOT 2 Editorial Viewpoint 4 Mailbag 23 Subscriptions 47 Product Showcase 70 Online Shop 72 Serviceman’s Log 88 Vintage Equipment 96 Circuit Notebook 100 Ask Silicon Chip 103 Market Centre 104 Advertising Index 104 Notes & Errata AVO valve testers, part 1 by Ian Batty 1. Mains timer / LED lamp dimmer 2. Hearing loop (telecoil) phone headset 3. Smoke, alcohol or LPG alarm SILICON SILIC CHIP www.siliconchip.com.au Publisher/Editor Nicholas Vinen Technical Editor John Clarke – B.E.(Elec.) Editorial Viewpoint 100 years of Australian electronics magazines 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: The first issue of Wireless Weekly was published on the 4th of August 1922 – almost exactly a century before you are likely to read this. You might be wondering what that has to do with Silicon Chip, besides both publications being Australian electronics magazines. There is a bit more of an association than just that. Wireless Weekly was started by Florence Violet McKenzie, Ron Marsden and William Maclardy. You might recall that I reviewed a biography of Violet McKenzie (aka Mrs Mac) titled “Radio Girl” in the February 2022 issue (siliconchip.au/Article/15203). They sold Wireless Weekly to Wireless Newspapers Ltd in 1923. It became a monthly magazine in April 1939 and was renamed “Radio & Hobbies” and then “Radio, Television & Hobbies” in 1955. Radio, TV & Hobbies once again changed its name to “Electronics Australia” in April 1965. Electronics Australia began to decline around April 2000, when it changed its name to “ea” (ugh) and not long after that, it ceased to be a hobbyist publication, simply describing the latest gadgets. It was renamed again to “Electronics Australia Today” (EAT) in April 2001. EAT only lasted five issues, the last being September/October 2001. Was that the end of the line for what started as Wireless Weekly? Not quite. Rewinding the clock to 1987, EA editor Leo Simpson was not satisfied with the magazine’s direction. He attempted a management buyout of the magazine and was immediately dismissed. After recovering from the shock, he took that as an opportunity to start a competing magazine. Other key staff members of Electronics Australia (John Clarke, Greg Swain and Bob Flynn) also felt that the magazine was in decline. They decided to leave too, ultimately joining him to start a new magazine: Silicon Chip. EA competed with Silicon Chip for a while under the editorship of Jim Rowe, but when he was let go in September 2000, he ultimately came to join the Silicon Chip team. Electronics Australia did not last much longer after he left. Silicon Chip subsequently bought the rights to all the EA material, including its earlier incarnations: Wireless Weekly, Radio & Hobbies and Radio, TV & Hobbies and even EA’s main competitor, Electronics Today International (ETI). Thus, “the loop was closed”. Silicon Chip is a true successor to Electronics Australia. Because many people don’t know the story behind Electronics Australia and Silicon Chip, we have a fascinating article by Leo Simpson this month (to be concluded next month), starting on page 34. This first article reveals some of what went on behind the scenes at EA and the transition to Silicon Chip. The second part next month will concentrate more on what happened until I took over Silicon Chip in August 2018. One aspect that many Silicon Chip readers probably don’t realise is that the magazine almost failed in its first year. You can read all about that (and more) in Leo’s article. It’s quite incredible to realise that all this was set in motion way back in 1922, when a few radio enthusiasts decided to start a weekly publication for their burgeoning community. I don’t exactly know what the future holds for Silicon Chip, but I certainly plan to keep it going for as long as possible. Another 100 years, perhaps! 24-26 Lilian Fowler Pl, Marrickville 2204 by Nicholas Vinen Technical Staff Jim Rowe – B.A., B.Sc. Bao Smith – B.Sc. Tim Blythman – B.E., B.Sc. Advertising Enquiries Glyn Smith Mobile 0431 792 293 glyn<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. 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”. Trouble seeing junctions in circuit diagrams I’d like to make a small point with your circuit diagrams. Would it be possible with Altium Designer 22 to increase the size of the junction dots on your circuit diagrams? I’m finding it very hard to see them. It is not a real problem for normal three-way (T) junctions because, after many years of reading circuit diagrams, I tend not to notice them anyway; I just assume that there is a join. However, with the four-way junctions (+), which seem to be creeping in a fair bit lately (p42 of the June issue, for example), the dots are really hard to see, and my old brain just skips over the join, as my old days, having a four-way junction was a bit of a no-no and I’m not used to them. Anyway, keep up the good work. Brian Playne, Toowoomba, Qld. Jim Rowe responds: thanks for your suggestions. We try to avoid four-way junctions, but sometimes it isn’t easy. Most readers don’t seem to have any problems with them, perhaps because when two lines cross without intersecting, we always use the ‘crossover’ symbol. This should make it clear when there is not a four-way junction. By the way, our diagrams are not drawn using Altium Designer but with CorelDraw. We use Altium’s “schematic capture” as part of our development process, but the resulting diagrams are not ideal for publication. Error in DDS Signal Generator PCB I have just built the AM/FM DDS Signal Generator (May 2022; siliconchip.au/Article/15306), but not without a couple of hiccups. There was a shorted track in the PCB I purchased from the Silicon Chip Online Shop. It appears to be a design flaw rather than a manufacturing fault, so I thought others might be up for the same. After construction, I had no display when powered, and the circuit only drew about 40mA. Checking the PCB, I found that both vias associated with the display data line to the OLED were shorted to the ground plane. I cut the shorted track at both ends before the vias, then soldered a short length of Kynar wire between the vias. Strangely, the photo on p50 clearly shows the track as intact. Maybe mine was a one-off. I noticed some other minor things: • The footprint for IC3 is slightly too small (or maybe I had the wrong package from AliExpress), but there was minimal land on the pads past the toe of the gull wing. • The mounting holes for the display do not match the dimensions of the display from Silicon Chip (although I was still able to mount it using the screws). • The PCB silkscreen has Q1, Q2 and Q3 designated as Q2, Q3 and Q4. • The 12mm M2 screws listed in the parts list are too short for 10mm untapped spacers. Despite what probably reads as lots of criticism, I am most impressed with the project and very much appreciate the effort put into developing it. Clearly, a lot of work went into designing it, and the article reads very well. I will be lining up for the companion attenuator and look forward to any future offerings you can contribute. Simon Smith, Zillmere, Qld. Comments: there was indeed an error in the PCB files we received for this project and subsequently sent to the manufacturer. We have discarded those PCBs and ordered a new lot with this error fixed, and most people who’ve ordered that board have received the corrected version. Apologies to anyone who received them before we were made aware of this problem. We purchased OLEDs that we believed matched the footprint that Charles used, but there are subtly different electrically-compatible versions available with slightly different mounting arrangements. That likely explains your observations. You are correct that the screws are too short; we should have changed them to 16mm. We did renumber some parts to remove gaps but didn’t modify the PCB as, ironically, we were concerned about introducing new errors if we did. “Supercap” batteries may not be what they seem I have a comment on the “Solar PV Update” article (January 2022; siliconchip.au/Article/15170) in the January issue (I’m a bit behind with my reading…). One widely-­ advertised and sold supposed “supercap” battery is probably a scam. Looking past the corflute, duct tape, hot glue and MDF The shorted track in the AM/FM DDS Signal Generator (left), and the wire link made to fix it (right). 4  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. 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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 construction, once you crack open the metal case, it’s controlled by Arduinos with Ethernet shields (on a device with a supposed lifetime of decades) and has current-­ carrying wires in tight bundles so they can heat each other up. People who have examined it say that it appears to use LTO cells, not supercaps. There’s a video analysing it at youtu.be/tD7MXTfumJs and a lengthy discussion at siliconchip.au/link/abfg It’s sold under a variety of different names and brands. So if you’re thinking of going with a supercap battery, make sure you do your research before sinking money into one. Peter Gutmann, Auckland, New Zealand. Comment: “LTO” cells are lithium-­titanium-oxide cells, a type of Li-ion cell that can charge and discharge much more rapidly than standard Li-ion cells but with a reduced maximum charge voltage. That means they have a lower energy density than standard Li-ion cells. Mixing LTO cells with Li-ion could give interesting results for ‘bursty’ loads, but they are certainly not supercaps. IoT devices wanted I’d like to see a bit more on IoT in Silicon Chip. I fiddle with computers and Arduinos these days, and I have a few devices sending data to my servers to display data graphs. I haven’t yet cracked secure serving (HTTPS) or common home automation, but I hope to do so eventually. I know there is a lot on the internet about all this stuff. And of course, a magazine will be rapidly out of date (like me). But I’m using cheap ESP8266 and ESP32 modules that have been available for a long time and still work well. Experimenting and blowing up a few isn’t an issue at $2 per ESP8266 in lots of 10 or 20. While I appreciate Raspberry Pi articles, I haven’t got into those. Arduinos have enough grunt for me, and old laptops do as home servers. As for the ‘mite’ and BASIC, you can keep those. Niche, pointless and limited. I don’t know if my circuits and code would be of any use to the magazine; it’s just what I’ve cobbled together off the internet, so I am loath to present anything. However, I have had some take-up of the weather station software I shared. I appreciate reviews like the resin-based 3D printer in July 2022 (I have a cheap 3D deposition printer). I also like the technical info/scientific articles, even if some are beyond me. Ken Wagnitz, Craigburn Farm, SA. Comment: we don’t receive many IoT project contributions. Part of the problem may be that many IoT applications are of limited use to the average person. It would be helpful to have a more concrete idea of what IoT projects people want to see since it’s such a broad area. Exporting firmware from a Raspberry Pi Pico I recently developed a program using the PicoMite (January 2022; siliconchip.au/Article/15177) with an LCD screen. I wanted to have a way of easily saving my work that is stored in the PicoMite’s flash memory. After communicating with Tim Blythman, who pointed me in the right direction, I worked out a method to do this if you have a Raspberry Pi. Mine is a Raspberry Pi 3B, and this is how I saved the 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 Create highly detailed prints with Our Newest 4K 3D Printer The new Anycubic Photon Mono 4K resin printer is great value and perfect for any maker, from hobbyist to professional. • MAKE MODELS UP TO 165(H) X 132(W) X 80(D)mm • FAST 1.5 SEC LAYER CURE • 10-50µm LAYER HEIGHTS • 2.8" TOUCH SCREEN • RESIN FILL INDICATOR • REPLACEABLE ANTI-SCRATCH FILM • COMPATIBLE WITH PHOTON MONO FEP SHEETS • 6.23" 4K MONOCHROME LCD • 35µm XY RESOLUTION BRINGS VIVID DETAILS • 400:1 CONTRAST RATIO FOR SHARP & CLEAR EDGES JUST 599 $ • UV BLOCKING COVER • AUTO PAUSE IF COVER REMOVED MID-PRINT TL4419 10% OFF SELECTED RESIN TL4425 - TL4550 NOW FROM $26.95 Promotion Date: 17.08.22 – 04.09.22 Shop Jaycar for your 3D Printing needs: • 2 Models of Resin Printers, with over 45 types of resin • 8 Models of Filament Printers, with over 50 types of filament and counting! • Massive range of 3D Printer spare parts & accessories • In-stock at over 110 stores or 130 resellers nationwide Order yours today: www.jaycar.com.au/resinprinters Phone: 1800 022 888 program. Saving the program is relatively easy, but the software installation is a bit involved. The following instructions are on page 4 of the following PDF found at siliconchip.au/link/aben At the Raspberry Pi console, type the commands: Helping to put you in Control Programmable Non Isolated Head Mount Module TT-500 is a non isolated 0-10VDC hockey puck head mounted Temperature transmitter. It accepts all kinds of thermocouple and PT100 RTD inputs and coverts them into an analog 0-10VDC signal. SKU: XMB-005 Price: $98.95 ea \ \ You will then have to wait about an hour for it to finish. After that, reboot and type the command: J Thermocouple Temperature Sensor J-type thermocouple in a stainless steel tube and 1/4” BSP thread with 2 meter glass fibre sheathed cable good for 0 to 400 ºC. SKU: XMS-020 Price: $43.95 ea LabJack T7 Data Acquisition Module LABJACK T7 Multifunction DAQ with Ethernet and USB. 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SKU: TOD-025 Price: $328.90 ea For Wholesale prices Contact Ocean Controls Ph: (03) 9708 2390 oceancontrols.com.au Prices are subjected to change without notice. 8  Silicon Chip $ sudo apt install wget $ wget https://raw.githubusercontent.com/ rasberrypi/pico-setup/master/ pico_setup.sh $ chmod +x pico_setup.sh $ ./pico_setup.sh $ picotool help You should see a list of about 20 lines with helpful commands to use picotool. The website at https://github. com/raspberrypi/picotool has much valuable information about picotool. Now connect a USB cable from the Raspberry Pi to the PicoMite while holding the BootSel button down, then release the button. A dialog box on the Linux screen should appear with the message “Removable medium is inserted”. Leave the box there but don’t push any buttons. To save the current program on the PicoMite, type the following command: $ sudo picotool save -p test_program.uf2 -t uf2 To test that the transfer went properly, disconnect the PicoMite and reconnect it in BootSel mode as before. Open the drive when the USB drive dialog pops up on the Linux screen. Drag and drop the file “test_program.uf2” onto the drive and wait for it to finish. Now disconnect the Raspberry Pi and connect your regular terminal such as Tera Term. You should be able to see your program run. You can easily develop a program and share it with your friends using this method. Grant Muir, Sockburn, New Zealand. Comments on Buck/Boost LED Driver You should consider adding a remote temperature sensor to the Boost/Buck LED Driver (June 2022; siliconchip. au/Article/15340). You want to limit the temperature of the LEDs to well under 100°C; 80°C is good and lower is better. You just need an NTC glued/attached to the back of the panel that ultimately causes a reduction in the drive current above a specific temperature. It might be able to be incorporated around IC2 in your design; however, I think a separate op amp is probably required as you don’t want the temperature limit to change with the current limit setting. This is probably obvious but I’ll point it out anyway – if a single LED goes open circuit in a series-parallel array that’s being run from a current source, suddenly, all of the other LEDs in parallel will have to absorb that extra current. Total array failure is likely at some time in the near future. These days, white LEDs are always blue with a yellow or orange phosphor on top. The resultant light is the sum of the light from phosphor compounds that have been excited by the blue light, plus some blue that goes through without hitting any phosphor. The mixture or Australia's electronics magazine siliconchip.com.au phosphor thickness is modified to change the colour temperature. On p43, under “Current limiting”, you say it could be run without the ground current returning directly to the module. This is a big no-no in an EMC sense – you risk having switchmode noise being radiated via the resulting loop. The load ground must return to the PSU directly if EMC isn’t to be a problem. David Timmins, Sylvania Southgate, NSW. Comments: we think it’s better to set the LED current and choose a heatsink so that they do not run at an excessive temperature rather than throttling them. However, an over-temperature shutdown would be a good idea. We think that could be implemented by attaching an NTC thermistor to the LEDs with a series resistor wired to JP1 such that it shuts down the LM5118 if the temperature is too high. A comparator would probably be necessary to implement this function, given the wide range between the on (3V) and off (0.5V) voltage thresholds. If we revise the design, we’ll incorporate such a comparator. If the power supply is regulated, it might be possible to use the thermistor to trigger under-voltage shutdown via pin 2 of the LM5118 without any extra active components. With 84 LEDs per group, we think there will be more variation due to internal LED forward voltage differences than the effect of removing one LED in a given series string. Still, you are correct that a single LED failure will increase the chance of more failures in the future. Regarding the phosphor, we were more intrigued by the use of a separate phosphor layer over the array of LEDs rather than the phosphor being part of each single LED. If a separate ground return is used, as long as that wire parallels the supply wires and passes directly across the driver PCB, there should not be excessive EMI as the current loop is still minimised. The return current doesn’t need to pass through the driver board, but it needs to closely parallel it to avoid EMC concerns. We should probably have mentioned that in the article. This is because the current consumed by the board itself is tiny compared to the LED driving current. The majority of that current will pass through the supply wire into the board, out of the board into the LED, then return directly to the power supply. Water-cooled amplifier – joke or not? When I saw the circuit for the new 500W Amplifier (siliconchip.au/Series/380) in the April 2022 issue (pages 30 & 31), with the number of output devices and the fact it was in the April issue, it brought back memories of an April Fool type article in Wireless World many years ago. The project was to build a 1kW amplifier. This was in the days of germanium transistors, so there were quite a few problems to be overcome. One of these was heatsinking. They accomplished this by using large numbers of output transistors mounted on hot water/steam radiators with cold water running through them, electrically connecting the output transistors together with car battery cables. Speakers were another problem; they had to be re-coned with steel sheets. These were days before digital audio, so great attention had to be given to housing the turntable/pickup. The final solution was to house them in a garden shed. 10  Silicon Chip Australia's electronics magazine siliconchip.com.au OUR SERVICES Take advantage of our local services Aglobalelectronicsdistributorthatprovides you with local support A high-service distributor of technology products, services and solutions for electronic design, maintenance and repair. In person, via phone or online Dedicated account management Account holders will be assigned an individual account manager to help with your queries, product resourcing and orders Quoting on volume requirements Dedicated team to assist in quoting you the best possible price Not in catalogue sourcing When a product is not available in our range, our team can help you source it directly from the manufacturer Contract pricing Special pricing is available for eligible customers Exclusive buffer stock arrangements Reserve stock now for a future order, available for qualified customers Flexible scheduled ordering Place an order now and opt to have it scheduled to be delivered at a later date Cable & Wire Assemblies Connectors Development Boards Passive Components Semiconductors Switches & Relays Test & Measurement Tools & Productions Supplies Contact us au.element14.com One had to be very careful when setting up to play a record, that in the haste to mate the pickup and record in time to get back to the house to hear the first notes of music, one did not drop the pickup. The resulting damage to the local glazing could produce substantial bills! I don’t recall the power supply details, but I hope the above brings a bit of a giggle. Bruce Bowman, Canberra, ACT. Comment: the idea of a water-cooled high-power linear amplifier is not such a silly one. For a start, the pump and fans could be in another room, so the listener would not hear the noise. A decent water-cooling system would also easily deal with the heat output of a 500W or even 1kW amplifier, possibly even several, depending on its size. It might have been an April Fool’s joke, but we’re tempted to try it! True RMS voltmeter observations I designed and built a dimmable power supply suitable for a microscope filament lamp. I used a phase-controlled, full-wave rectified, unsmoothed 12V supply. When I measured the voltage across the test lamp with one of my True RMS DMMs, I got a reading, at full brightness, of about 6.3V, which was strange because the light globe filament looked the correct colour for a 12V supply. Even stranger, when I dimmed the light, the DMM reading increased, peaked and then decreased. I tried my other True RMS DMM, and it did the same. I then tried my older DMM, which measures average, but is calibrated for a sinewave, also my trusty AVO 8. They both showed a similar response. I then got my real True RMS voltmeter, a Sangamo-­ Weston S68 AC-DC dynamometer voltmeter. Now I could get voltage readings that matched the filament brightness and colour temperature. The dynamometer family of meters all measure True S68 QM1320 QM1552 AVO 8 Mk3 Sinewave 10V 9.99V 9.98V 9.8V Full-wave rectified 8.67V 4.09V 4.16V 4.28V Half-wave rectified 6.56V 5.37V 5.10V 4.56V RMS. They consist of a moving and a fixed coil; there is no permanent magnet and no magnetic circuit. They rely on the attraction between the two coils, which like the moving iron meters, makes them AC-DC and True RMS reading. As a bonus, having two coils, you can also configure them as a wattmeter. I did some comparison measurements and plotted the results. I then did some further measurements using halfwave and full-wave rectified AC waveforms, summarised in the table above. These differences became evident when I looked at the waveforms with my oscilloscope. The first screen grab (bottom left) shows the voltage measurement with the waveform DC-coupled as 10.7V RMS. The second grab (on the right) shows the measurement with the waveform AC-coupled as 7.38V RMS. So it seems that the S68 meter is making DC-coupled RMS measurements while the others are AC-coupling the signal, which shifts its centre point and thus changes the RMS measurement. This illustrates why understanding how your test equipment works can be a great help when you get readings that don’t seem correct. Rodger Bean, Watson, ACT. Comment: some True RMS digital multimeters have a button to switch between pure AC and AC/DC voltage measurements for this reason. For example, our Agilent U1253B meter has that option. Neither of the manuals for the (now discontinued) QM1320 and (still available) QM1552 multimeters mention an AC+DC option, so we assume they don’t have that function. Running three-phase gear from single-phase mains Jon Hornstein writes in Mailbag (April 2022, page 8) of Charles Steinmetz. He is well known to many home metal machinists for the “Steinmetz Connection” (a great title for a Bond or Bourne movie!). Many industrial three-phase machines have been snapped up at closure auctions and snaffled off home into dingy, cramped spaces, but how to run them? Some have resorted to using phase-shift capacitors to crudely simulate three-phase power as described in his patent, to operate their new prized acquisitions. The results are a little rough and ready, but some swear by them. Andre Rousseau, Auckland South, NZ. Another ‘energy saving’ scam You might be interested in the Voltizer energy saver – https://getvoltizer.com/article/au Alan Ford, Salamander Bay, NSW. Comment: we mentioned the virtually identical Voltex scam on page 10 of the May 2021 issue. The laws of physics still apply, as does conservation of energy. In practically all cases, the only way to reduce the energy used by an appliance is to turn it off or replace it with a more efficient version of the same thing. SC 12  Silicon Chip 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/SC0822 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 29-08-22 06_SC_280722 LP-900P Industrial Louvre Wall Backing Panels Package Deal IC Fabrication AMD EPYC 7702 ES photographed by Fritzchens Fritz: www.flickr.com/photos/130561288<at>N04/49139472562/ from inception to cutting-edge technology Over the last two issues, we’ve described the history of integrated circuits (ICs), the manufacturing process, process nodes, wafer sizes and EUV lithography. Along with EUV, another technology that is just maturing and has fundamentally changed the way high-end ICs are made is multi-chip modules. We shall now investigate that and other cutting-edge chip technologies. Part 3 – finFETs, GAAFETs, chip stacking & multi-chip modules – By Dr David Maddison 14  Silicon Chip Australia's electronics magazine siliconchip.com.au IC technology is approaching the physical limits of feature size – ie, it is becoming almost impossible to make transistors smaller or increase density. In an attempt to overcome this, finFETs were developed and now gate-all-around (GAA) FETs are coming into use. After covering those, we will look at 3D ICs and chiplets. As density is not improving as quickly as it used to, multi-chip modules (MCMs) containing ‘chiplets’ are becoming much more widespread. Designs are no longer limited to what can fit onto a single, reasonably-sized silicon die. FinFETs and beyond A fin field-effect transistor (finFET) is a 3D Mosfet in which the gate is enhanced vertically to make a ‘fin’, forming three surfaces where the gate interacts with the channel, rather than just one (see Fig.57). This is helpful because the planar device can be made no smaller due to the scalability restrictions of a 2D plane. Also, the fins have a larger surface area. FinFETs are smaller than and have superior performance to planar CMOS devices. They were first commercialised in the mid-2010s and are the dominant devices in the 14nm, 10nm and 7nm process nodes. At the 5nm process node, undesired variations in channel width in finFETs can cause variability in behaviour and the loss of carrier mobility. 3nm is considered the limit of their usability. Therefore, the industry is now moving to a “gate-all-around” (GAA) technology in which the gate interacts with the channel on all four sides. GAAFETs and Moore’s Law Since about 2010, the rate of increase of transistors in a chip Fig.58: a cross-sectional image of an actual 2nm gate-all-around (GAA) device using nanosheets produced by IBM. This technology results in 333 million transistors per square millimetre. The cell height is 75nm, width is 40nm, individual nanosheets are 5nm high and separated by 5nm. The gate pitch is 44nm and gate length is 12nm. Source: IBM decreased below the original prediction by Moore. Instead of doubling every two years, it is now about two and a half years. The physical limits of transistor size with current technology are being approached due to increasing sourceto-drain leakage, limitations due to the metals used in gates and limited options for channel materials. The channel is where charge carriers such as electrons or holes flow between the source and the drain. In silicon, the smallest possible gate size for a Mosfet was thought to be about 7nm, although finFETs and GAAs have somewhat lowered this limit, perhaps to as low as 2nm for the IBM GAA (Fig.58). Any smaller and electrons can move between adjacent transistors by a process known as quantum tunnelling. If that happened, a transistor could unexpectedly change its state. By comparison, the diameter of a silicon atom is around 0.2nm, so we are discussing a structure of only about 10 to 35 atoms across. Presently, there is no point in making transistors any smaller in silicon than this. The processor in an iPhone XS uses 7nm technology, and it was stated that the active channel of a transistor gate in it would be 7nm long, 7nm deep and 20nm wide. Based on there being 5×1022 atoms/cm3 in a silicon crystal, there would be about 49,000 atoms in such a structure. The apparent discrepancy between the atomic radius of silicon and the volumetric density is due to the way the atoms are arranged in a crystal. According to Wikipedia (https://w. wiki/583Z), for the 5nm process node, there are typically over 130 million transistors per square millimetre. Options for the future include “spintronics”, which exploits the spin state of electrons, “tunnelling junctions”, which use the quantum mechanical process of quantum tunnelling, and the use of nano-scale wires in the channels. One advantage of spintronic devices, according to Professor Ian Appelbaum (then at the University of Delaware), STI stands for shallow trench isolation Fig.57: a comparison of planar, FinFET and gate-all-around FET devices. The gate operates at the interface shown in green. In the gate-all-around (GAA) structure, the channel may be constructed from either ‘nanowires’ or ‘nanosheets’ (shown here). siliconchip.com.au Australia's electronics magazine August 2022  15 Fig.60: a possible transistor of the future by Lawrence Berkeley National Laboratory with a 1nm gate size. It is fabricated from a carbon nanotube, zirconium oxide and molybdenum disulfide. Managing chip defects is that “silicon can now be used to perform many spin manipulations both within the space of thousands of devices and within the time of thousands of logic operations, paving the way for silicon-based spintronics circuits”. See Fig.59 and the video at https://vimeo.com/32338065 Another approach is to use different materials. Carbon nanotubes, molybdenum disulfide and zirconium oxide were used to make a transistor with a 1nm gate size in 2016. Ali Javey did that at the US Department of Energy’s Lawrence Berkeley National Laboratory – see Fig.60. By comparison, human hair is 50,000 nanometres thick. More recently, Tian-Ling Ren at Tsinghua University in Beijing made a transistor with a gate length of 0.34 nanometres. The materials used were a titanium-palladium alloy for the metal contacts, molybdenum disulfide and hafnium oxide. Fig.59: this early spintronics chip developed in 2007 contains 16 spintronics devices. It was built by Professor Ian Appelbaum and doctoral student Biqin Huang at the University of Delaware and Douwe Monsma of Cambridge NanoTech. Fig.61: schemes for 3D packaging as envisaged by AMD. TSV Pitch refers to the distance between the through-silicon vias used for vertical connectivity. IP refers to ‘intellectual property’ cores which are designs with a specific function produced by a third-party vendor. Uncore refers to parts of the CPU that are not part of the cores, such as cache memory and the memory controller. Source: Advanced Micro Devices (AMD) 16  Silicon Chip Three-dimensional ICs ICs can be 3D either by having many layers in a monolithic IC or by 3D packaging. In the latter, multiple dies are connected on top of one another using through-silicon vias (TSVs) or with solder bumps – see Figs.61 & 62. For example, V-Cache is a technology from AMD that allows a cache memory die to be stacked directly on top of the CPU core die. This triples the CPU cache memory without altering the size of the die or shrinking the feature size. This technology is related to chiplets, which we will discuss shortly. Australia's electronics magazine Not all silicon chips are made equal. When IC dies are tested, several things can happen. The worst scenario is that the die is unusable and must be discarded. Alternatively, a chip may not work reliably at the maximum design speed, but could work perfectly well at a lower clock rate. Such chips are usually marked and sold at lower prices, with a lower default clock. Some people try to increase the clock speed to see if they can find a higher speed that it will reliably operate at (“overclocking”), as manufacturer speed ratings are very conservative and chosen for maximum reliability. Another thing that can be done in the case of memory chips is if parts of the memory are defective, they are siliconchip.com.au Figs.63(a) & (b): an example of how chip defects and differences in performance between different sections of a die are managed. Each of the twelve CPU cores spread across two dies has its own characteristics, such as maximum stable operating frequency and power consumption. Clocks are controlled and tasks are allocated based on a profile made for each chip section after manufacture. permanently locked out, and the chip is sold as having less memory. Similarly, in CPUs or GPUs with multiple computing cores, faulty cores can be permanently locked out, and they are sold as lower performance devices with fewer cores. In other words, most chips come off the same production line. They are then “binned” and sold according to the speed, power consumption and other characteristics determined during testing (usually before packaging, as there’s no point in packaging a defective chip). Fig.63 shows some statistics we gathered from a computer CPU built with 16 cores but sold as a 12-core device. Presumably, those four cores were disabled because they either didn’t work or weren’t up to spec. The second-from-right column in each image shows the maximum readings seen during testing. Core 0 has run at a maximum of 5.15GHz, Core 3 at 5.10GHz, while Cores 4 and 9 only ran up to 4.475GHz. After manufacturing and testing, these limits are programmed into the chip based on the maximum speed that each core can reliably operate at. Also, note how Core 3 consumed up to 7.5W while Core 8 has never drawn more than 1.71W, even though it ran up to 4.525GHz (88.7% as fast as Core 3). Mobile chips are binned for power efficiency, whereas desktop chips like this one are mainly chosen based on their peak performance. Still, better efficiency does let the CPU run cooler under load. Core-to-core peak temperature Fig.62: how through-silicon vias (TSVs) in DRAM dies (top right) and solder bumps create a 3D package for a graphics processing unit. The whole assembly is mounted directly on a PCB. Source: Wikimedia user ScotXW (CC BY-SA 4.0) siliconchip.com.au Australia's electronics magazine variation is also high, with Core 3 recording a peak of 59.1°C, while the coolest core was Core 8, which only ever reached 44.8°C (it's also the one that uses the least power). All of these variations are despite the fact that the masks for each core are identical, and they were made in the same manufacturing process at the same time. Multi-chip modules (MCMs) So far, we have mainly described monolithic ICs that comprise only one chip or die in a package. “Multi-chip module” is a generic term. Wikipedia defines it as electronic assemblies that come in various forms and involve multiple components, such as IC dies (chips) and discrete components, all held together Fig.64: AMD’s EPYC SoC (system on a chip). Depending upon the model, there can be up to eight CCDs (core chiplet dies) plus one I/O chiplet. Each CCD comprises one or two CCXs (core complexes), depending on the generation. A CCX is a quad-core or octa-core CPU with a shared L3 cache. This can give a total of up to 64 cores. Source: AMD August 2022  17 Fig.65: a hybrid integrated circuit in the form of an operational amplifier, containing both discrete IC/transistor dies and thick-film resistors. According to the Wikipedia definition, it is a form of MCM, but we would refer to it as a hybrid IC. Source: Wikimedia user Mister rf (CC BY-SA 4.0) on a substrate and contained within a package. Substrates may be of various forms, such as printed circuit boards, ceramic substrates or IC base plates with other devices mounted on top. The entire package assembly can be treated and used as a component in the same manner as an IC. Other terms for these MCM packages include “heterogeneous integration” and “hybrid integrated circuits” (Fig.65). They are used to save space and avoid designing customised ICs because the desired functions can be produced using separate off-the-shelf components at a lower cost. But there is no strict definition of what an MCM is. We think it would be clearer to reserve the term MCM for assemblies containing monolithic ICs and no other components and refer to the other devices as hybrid circuits. So that is the terminology we will use in this article. Earlier examples of MCMs include IBM bubble memory (1970s), the IBM 3081 thermal conduction module (1980s), superconducting multi-chip modules (1990s) and the Intel Pentium Pro (1995) – see Fig.66. a standard “library” of such devices, and can thus be combined in a modular fashion to produce the desired functionality. Even chiplets from different manufacturers can be used. The use of chiplets in MCM devices is a way to dramatically reduce the cost of the design of large ICs. With a large enough library or catalog of chiplets, it would be possible to combine them to rapidly develop many custom applications, resulting in major cost savings. One estimate is that using chiplets leads to a 70% reduction in design and development costs and time to produce a given device. There are several advantages to using chiplets. One is that smaller dies with fewer components generally have better yields (a higher percentage of functional devices after fabrication) than single larger dies with more components. It may thus be more economical to use two or more individual dies tied together than one larger one with the same overall functionality and number of components. As chips get larger and larger, the yield drops naturally, as there is more likelihood of defects in larger devices. Sometimes it gets to the point that it becomes uneconomical to produce them. Chiplets are the most obvious way to overcome that. Also, dies can be “mixed and matched” with different technology nodes, production processes, materials (eg, some chiplets of silicon and some of another semiconductor such as gallium arsenide) and manufacturers. More advanced MCMs This use of chiplets to make MCMs is a developing idea in the IC industry. An important aspect of using chiplets is how they are connected together in the package, either horizontally or vertically (ie, when chiplets are stacked on top of each other). Individual chiplets are controlled and unified by input-output and communication controllers that coordinate the entire device as a single unified IC. See the section below on chiplet interconnect standards. Another advantage of MCMs is that chiplets in the same device can be fabricated with various process nodes. An example would be using a mixture of 7nm and 10nm process nodes depending on performance and component density requirements, plus factors such as cost. Fig.66: the Pentium Pro processor could be regarded as the first example of a consumerlevel ceramic multi-chip module (MCM). It contains both a CPU die and a separate cache memory die. Chiplets A chiplet (called a “tile” by Intel) is an IC with defined functionality that is designed to be combined with and connected to other chiplets in a single MCM. Chiplets can come from 18  Silicon Chip Australia's electronics magazine siliconchip.com.au For example, a chip for integrated connectivity such as USB, Wi-Fi, Ethernet or PCIe does not need the latest technology, but a GPU core will. The CPU tested to produce Fig.63 uses this approach, with two 7nm chiplets each with eight compute cores (two disabled in each, for a total of 12) plus an 8nm I/O chiplet that interfaces those cores to the outside world. A manufacturer can easily customise an MCM for different applications, such as having more graphics processing chiplets for more graphics capability and fewer memory chiplets for one application, or the opposite for another application – see Fig.70. Examples of MCMs that use chiplets on the market include AMD’s Ryzen, Ryzen Threadripper and EPYC CPUs (see Fig.64) and soon, Intel’s Ponte Vecchio (described in detail below). One clever aspect is that AMD produces consumer (Ryzen), workstation (Threadripper) and server (EPYC) CPUs using essentially identical core dies (CCDs). Ryzen chips have one or two CCDs totalling 6-16 cores, Threadripper chips have up to four CCDs for up to 32 cores (later versions up to 64), while EPYC chips have up to eight CCDs for up to 8/64 cores. Reusing the same chiplets saves a lot of R&D time and money and makes the end product more affordable. Layout of MCM integrated circuits with chiplets There are several possible physical configurations in which chiplets can be incorporated into a module. Some are shown in Fig.67, in increasing levels of advancement. (A) Shows four chiplets laid out side-by-side on an organic substrate Fig.68: details of an interposer showing internal connections in yellow on the lower diagram. TSV stands for through-silicon via which are vertical interconnects fabricated into the silicon. The micro bumps and C4 (controlled collapse chip connection) bumps are connection pads. such as a high-density PCB. (B) Shows chiplets laid out side-byside on a passive silicon interposer (see the description of interposer below). 2.5D refers to side-by-side chiplets with high interconnect densities to neighbouring chiplets. (C) Shows chiplets mounted on an electrically active interposer. The active interposer may contain parts of the system, such as a platform controller hub (PCH). (D) Shows chiplets connected via an active silicon bridge embedded in the package substrate. The bridge acts much like an interposer, but because it is embedded in the package substrate, the chip can be much smaller as it is level with the rest of the substrate material. (E) Shows chiplets mounted directly on an active silicon base using a bumpless bonding system developed by TSMC. This is distinct from (C), in which the attachment is via wafer bumps. An interposer (Fig.68) acts as an interconnection between chiplets and connects them to the external input/ output lines. An interposer can have a higher wiring density than an organic substrate. Bumps are a type of connection used on integrated circuits to eliminate wire bonding. In “wafer bumping” technology, solder spheres are attached to the chip’s input/output pads instead of wires. Advantages include better electrical performance, lower inductance, Fig.67: several manners in which chiplets can be laid out in a package, with a cross-sectional view at the bottom and plan view at the top. Original source: Jawad Nasrullah, Palo Alto Electron Inc (http://ieee-edps.com/archives/2021/ c/1100nasrullah.pdf). siliconchip.com.au Australia's electronics magazine August 2022  19 HBM2 HBM2 Compute Dies Rambo Caches 10 ESF Compute Dies Passive Die Stiffeners Passive Die Stiffeners Passive Die Stiffeners Passive Die Stiffeners Passive Die Stiffeners Xe Link IO Tile HBM2 Foveros 3d Packaging HBM2 Fig.69: Intel’s Ponte Vecchio GPU package with multiple individual chiplets/tiles. HBM is highbandwidth memory; ESF is enhanced SuperFin; EMIB is Intel’s embedded multidie interconnect bridge; Tile is Intel’s name for a chiplet. Source: Intel Compute Dies Rambo Caches 10 ESF Compute Dies Passive Die Stiffeners Graphics Compute I/O AI In-Package Memory Media Xe Link IO Tile HBM2 HBM2 HBM2 DRAM HBM2 EMIB under passive die & HBM2 greater current capacity, lower cost and a smaller footprint. Intel Ponte Vecchio The Intel Ponte Vecchio (see Fig.69) is an example of an advanced MCM device in the form of a GPU (graphics processing unit). It will be initially used in the USA’s Argonne National Laboratory's new ‘exascale’ supercomputer, Aurora and for artificial intelligence, machine learning and graphics applications. "Exascale" refers to a computing system capable of executing at least 1018 floating-point operations per second (>1 exaFLOP). Ponte Vecchio uses 63 ‘tiles’ (Intel’s name for chiplets) in total; 47 active tiles for computing functions and 16 for thermal management, with a total of 100 billion transistors in a 77.5 × 62.5mm package. The device is partly fabricated using “Intel 7”, which is their name for an enhanced 10nm SuperFin fabrication process. Some tiles use Intel 7, while others are fabricated by TSMC using their 7nm (N7) and 5nm (N5) nodes, plus some others. For more information on Intel’s SuperFin technology, see the video at https://youtu.be/ Y04yHqLKs4w Note that Intel’s 10nm chips are comparable to 7nm devices from TSMC or Samsung because, as we pointed out earlier, those figures no longer correspond directly to physical feature size. As mentioned earlier, mixing chiplets/tiles from different process nodes and manufacturers is one of the advantages of MCMs. The eight GPU tiles used in the device are manufactured by TSMC using their 5nm process, and each Persistent Memory Fig.70: Intel envisions a package made of standardised tile (chiplet) components with the combination adjusted to suit the needs of different users. Source: Intel of those tiles contains 128 Intel Xe GPU cores or “compute units” for a total of 1024 vector units, 1024 matrix engines and 128 ray tracing units per device. Each device also has 64MB of L1 cache memory and 408MB of L2 cache. The GPU tiles, memory and other tiles (eg, for I/O) are all mounted on the “base tile”. The base tile is a 646mm2 die with 17 layers. It includes a “RAMBO” memory controller, voltage regulators, a PCIe 5.0 interface and a CXL (Compute Express Link) interface. RAMBO (random access memory, bandwidth optimised) uses Foveros interconnection technology. RAMBO uses novel SRAM (static random access memory) and has four banks of 3.75MB memory groups for a total of 15MB per tile with eight tiles. There is also up to 128GB of HBM2e Chip development costs According to Handel Jones, CEO of International Business Strategies Inc (Los Gatos, CA, USA), it costs US$40 million to design a 28nm chip, US$217 million to design a 7nm chip, US$416 million for a 5nm device and a future 3nm design is expected to cost US$590 million. Chiplets in multi-chip modules (MCMs) are one way to reduce costs. The use of chiplets is expected to reduce the cost of new device elements because they can be produced as standard functional elements. Then, making a device means assembling standard chiplets together, perhaps with some custom fabrication work too. Physically, chiplets are much like any other chip, but they are designed to interface with other chiplets. Essentially, they are modular elements or building blocks, selected from a library or catalogue of such devices. Apart from chiplets, existing packaging solutions can integrate existing dies into existing packaging types. This includes 2.5D layouts (multiple dies inside the same package arranged in a planar or stacked configuration) or fan-out (dies placed on “redistribution layers” similar to circuit boards inside the package). 20  Silicon Chip Australia's electronics magazine siliconchip.com.au ADD MOTION DETECTION TO YOUR PROJECT PIR MOTION DETECTION MODULE ADD OBSTACLE DETECTION OR AVOIDANCE DUAL ULTRASONIC SENSOR MODULE • Adjustable delay times XC4444 $5.95 • 2 - 45cm 15° range XC4442 $7.95 Expand your projects with our extensive range of Arduino® compatible Modules, Shields & Accessories. OVER 100 TYPES TO CHOOSE FROM AT GREAT PRICES. ADDRESSABLE RGB LEDS DETECT WHEN PLANTS NEED WATERING SOIL MOISTURE SENSOR MODULE • Analogue output XC4604 $4.95 VIEW OVER 70 ARDUINO® PROJECTS YOU CAN BUILD AT: jaycar.com.au/projects Shop at Jaycar for: • Arduino® Compatible Development Boards • Display Modules • Servos, Solenoids & Motors • Wheels & Chassis 1.3" MONOCHROME OLED DISPLAY • 128x64 Pixel XC3728 $19.95 ADD AMAZING COLOUR TO YOUR NEXT PROJECT 5V LED STRIP WITH 120 ADDRESSABLE RGB LEDS HALL EFFECT SENSOR MODULE • 2m long, flexible, waterproof XC4390 $29.95 • Sense magnetic presence XC4434 $4.95 • Prototyping Hardware and Accessories • Project Enclosures • Servos & Motors • Switches & relays Explore our wide range of Arduino® compatible modules, shields and accessories, siliconchip.com.au Australia's electronics magazine in stock on our website, or at over 110 stores or 130 resellers nationwide. jaycar.com.au/shieldsmodules August 2022  21 1800 022 888 memory (according to Hardware Times) or 64GB (according to Tom's Hardware). Possibly there will be different versions of the chip with different memory sizes – not all specifications of the device have yet been confirmed. The memory is contained in eight HBM2e (high bandwidth memory 2e) ‘stacks’, each eight dies high. Ponte Vecchio's heat dissipation is 600W with water cooling or 450W with air cooling. The entire surface area of all 47 active tiles in the Ponte Vecchio is 2330mm2, or 3100mm2 including the thermal tiles. When fully packaged, the area is 4844mm2. The package has a staggering 4468 pins. Intel has devised two technologies to allow the tiles to communicate with each other. The first is their embedded multi-die interconnect bridge, and the second is Foveros die stacking packaging. EMIB is a method to connect adjacent dies via a small embedded bridge rather than the conventional, more complicated method of connecting dies via a silicon interposer and through-silicon vias (TSVs). For more on this, see the video titled “Intel EMIB Technology Explained” at https:// youtu.be/mRQFJFmYMak Foveros 3D die stacking packaging is an interconnection technology for vertical chip-to-chip bonding via Fig.71: Intel’s Ponte Vecchio GPU mounted on a PCB with the heat spreader removed. A large number of these modules would be used to construct an exascale supercomputer. Source: Intel microbumps. There is a video about this titled “Intel Foveros Technology Explained” at https://youtu.be/ eMmCYqN6KSs The Ponte Vecchio package is housed in a module, as shown in Fig.71. Chiplet interconnect standards For chiplets to come into common use, with the mixing of chiplets from different manufacturers and fabrication processes, they will need to use common connection standards. In March 2022, Advanced Semiconductor Engineering, Inc (ASE), AMD, Arm, Google Cloud, Intel Corporation, Meta (formerly Facebook), Microsoft Corporation, Qualcomm Incorporated, Samsung and TSMC announced a standard for chiplet interconnects called Universal Chiplet Interconnect Express or UCIe – www.uciexpress.org The objective is to have a single set of standards (initially, UCIe 1.0), similar to that for PCIe expansion cards (see Fig.72). Predating UCIe, the Open Domain-­ Specific Architecture (ODSA) from the Open Compute Project Foundation was released in 2019 (see siliconchip. au/link/abef). The objective was to “define an open interface and architecture that enables the mixing and matching of available silicon die from different suppliers onto a single SoC for data centre applications. The goal is to define a process to integrate best-of-breed chiplets onto a SoC”. SoC stands for ‘system on a chip’. It is unclear how or if this project relates to UCIe, as no specific public information is available. Conclusion Fig.72: example packaging options from the UCIe 1.0 standard for chiplets. MCM technology is very important at the moment. For example, it is a key reason that AMD’s laptop and desktop chips have been competitive with Intel’s products over the last few years. Intel is now using it too, as are Apple (with the M1 Ultra) and Nvidia (with the Hopper AI engine). MCM technology is now entrenched in the CPU market. It also appears that AMD’s new line of high-end graphics processors (RDNA3) will be based on MCMs, and Nvidia may follow suit. It probably won’t be long before all but the most basic computer chips are using MCM technology. SC Australia's electronics magazine siliconchip.com.au 22  Silicon Chip Subscribe to JULY 2022 ISSN 1030-2662 07 9 771030 266001 $ 50* NZ $1290 11 INC GST INC GST VGA PicoMite A Powerful, but siMPle rAsPberry Pi-bAsed coMPuter ANYCUBIC PhotoN MoNo 3D PrINter revIew Build our Multimeter Calibrator & Checker Australia’s top electronics magazine Silicon Chip is one of the best DIY electronics magazines in the world. Each month is filled with a variety of projects that you can build yourself, along with features on a wide range of topics from in-depth electronics articles to general tech overviews. Published in Silicon Chip If you have an active subscription you receive 10% OFF orders from our Online Shop (siliconchip.com.au/Shop/)* Rest of World New Zealand Australia * does not include the cost of postage Length Print Combined Online 6 months $65 $75 $50 1 year $120 $140 $95 2 years $230 $265 $185 6 months $80 $90 1 year $145 $165 2 years $275 $310 6 months $100 $110 1 year $195 $215 2 years $380 $415 All prices are in Australian dollars (AUD). Combined subscriptions include both the printed magazine and online access. Try our Online Subscription – now with PDF downloads! IC Fabrication; June 2022 VGA PicoMite; July 2022 Multimeter Checker & Calibrator; July 2022 An online issue is perfect for those who don’t want too much clutter around the house and is the same price worldwide. Issues can be viewed online, or downloaded as a PDF. To start your subscription go to siliconchip.com.au/Shop/Subscribe siliconchip.com.au Australia's electronics magazine August 2022  23 IDEAL FOR STUDENT OR HOBBYIST ON A BUDGET • DATA HOLD • SQUARE WAVE OUTPUT • BACKLIGHT • AUDIBLE CONTINUITY Don't pay 2-3 times as much for similar brand name models when you don't have to. ONLY 1995 $ QM1517 HANDY FOR THE HOME TOOLBOX AUTORANGING FOR EASE OF USE • TEMPERATURE • DUTY CYCLE • NON-CONTACT VOLTAGE ONLY 5995 $ QM1323 FOR THE TECH'S TOOLBOX FOR A STUDENT OR APPRENTICE ONLY 49 $ 95 QM1321 ONLY 2995 $ ACCURACY OF TRUE RMS MEASUREMENT • CAPACITANCE & FREQUENCY • TRANSISTOR HFE TEST • DIODE & AUDIBLE CONTINUITY • NON-CONTACT VOLTAGE QM1020 EASY TO READ MEASUREMENTS • MIRROR BACKED SCALE • TRANSISTOR LEAKAGE TEST • AUDIBLE CONTINUITY Test & Measure with our GREAT RANGE of multimeters at the BEST VALUE, to suit hobbyists and professionals alike. 24 Explore our wide range of multimeters, in stock on our website, or at over 110 stores or 130 resellers nationwide.  Silicon Chip www.jaycar.com.au/multimeters Australia's electronics magazine 1800 022 888 siliconchip.com.au LARGE BACKLIT DISPLAY AND IP67 WATERPROOF RATED • TRUE RMS • CAPACITANCE • FREQUENCY • RELATIVE MEASUREMENT TAKE EASY ENVIRONMENTAL MEASUREMENTS • MULTIMETER FUNCTIONS • SOUND LEVEL • LIGHT LEVEL • INDOOR TEMP • HUMIDITY ONLY 99 $ 95 QM1549 WIRELESS BLUETOOTH® FEATURE FOR DATA LOGGING • AUTORANGING • TRUE RMS • 6000 COUNT • IP67 WATERPROOF ONLY 139 $ QM1594 ONLY 149 $ QM1578 Use this colour coded selection guide to pick the meter that best suits your needs. GREEN labelled product suit hobbyists and those on a budget. BLUE suit makers familiar with multimeters and want more features. For all the bells and whistles and the highest ratings, choose from the ORANGE professional range. ENTRY LEVEL * QM1500 QM1517 QM1527 MID LEVEL QM1529 QM1321 QM1020 QM1446 Display (Count) 2000 2000 2000 2000 4000 Analogue Security Category Cat II 500V Cat III 600V Cat III 500V Cat III 600V Cat III 1000V Cat II 1000V • • Autorange True RMS PROFESSIONAL QM1323 QM1552 2000 4000 2000 4000 4000 2000 4000 6000 4000 Cat III 600V Cat III 600V Cat IV 600V Cat III 600V Cat IV 600V Cat III 600V Cat IV 600V Cat IV 600V Cat III 1000V • • • • • • QM1551 QM1549 • • • • • XC5078 QM1594 QM1578 • Voltage 1000VDC/ 750VAC 500V AC/DC 500V AC/DC 600V AC/DC 1000VDC/ 750VAC 1000V AC/DC 1000VDC/ 700VAC 600V AC/DC 1000VDC/ 750VAC 600V AC/DC 1000V AC/DC 600V AC/DC 600V AC/DC 1000V AC/DC Current 10A DC 10A DC 10A DC 10A AC/DC 10A AC/DC 10A DC 10A AC/DC 10A AC/DC 10A AC/DC 10A AC/DC 10A AC/DC 200mA AC/DC 10A AC/DC 10A AC/DC Resistance 2MΩ 2MΩ 2MΩ 20MΩ 40MΩ 20MΩ 20MΩ Capacitance 100mF Frequency 10MHz Temperature Duty Cycle 20MΩ 40MΩ 200MΩ 40MΩ 40MΩ 40MΩ 60MΩ 100μF 100µF 100mF 100µF 100µF 100µF 6000µF 10MHz 10MHz 10MHz 10MHz 10MHz 10MHz 10kHz 1000°C 760°C 1000°C 760°C 750°C 760°C • Continuinty • • • • • • Relative Min/Max/Hold • Non Contact Voltage • • • $24.95 $29.95 $49.95 • • • • • • • • • • Max Hold • • • $59.95 $69.95 $69.95 IP Rated Price • • • • siliconchip.com.au $19.95 *Lifetime warranty excluded on models: QM1500/QM1517/QM1527 $29.95 $49.95 Australia's electronics magazine 4000MΩ • • IP67 $9.95 1000VDC/ 750VAC • • Max Hold • QM1493 $99.95 IP67 $89.95 $139 $149 August 2022  25 $249 Wide-Range hmMeter Features & specifications Resistance measurement range: 1mΩ to 20MΩ Individual ranges: 1mΩ to 30Ω, 30Ω to 3kΩ, 3kΩ to 100kΩ, 100kΩ to 1MΩ, 1MΩ to 20MΩ Resolution: 0.1mΩ in milliohms range (usable resolution closer to 1mΩ) Accuracy: better than ±1%; typically close to ±0.1% Test current: 50mA up to 30Ω, 0.5mA from 30Ω to 3kΩ, <50μA up to 20MΩ Other features: auto-ranging, battery voltage display Power supply: 6 x AA cells; up to 100mA drawn during tests Battery life: around 24 hours of active use This auto-ranging ohmmeter will measure just about any resistance – from a handful of milliohms to many megohms! T here have been several occasions recently where I have needed to measure low resistances accurately. That includes some speaker projects, where I needed to accurately measure the DC resistance of a voice coil to estimate a driver’s Thiele-Small parameters or determine the resistance of an air-cored power inductor. Another time it was for the Capacitor Discharge Welder project (March & April 2022; siliconchip.com.au/ Series/379), where I wanted to check the resistance of the leads. Theory said they should be 8mW (spoiler alert – with the cables and handles, our welder leads measured 10mW). Your garden variety multimeter won’t measure anywhere near that low. Even my fancy, expensive meter was way off the mark. So what do you do when you want an accurate measurement of a really low resistance? You reach for your trusty old lowohms meter. Like many journeys in life, this design started on one path but ended up somewhere else. The initial plan was to update a previous Milliohm Meter design, adding a digital front end and making it easy to use. But halfway through, somebody said: why 26  Silicon Chip not make it measure up to 20MW? This added a bit of a spin on the design, but we think the result is a very handy and versatile device. So here we have a design for a meter that will measure resistances from a couple of milliohms to 20 megohms, with precision significantly better than 1% across that range. Using 0.1% resistors for calibration (which we recommend), we have seen precision in the region of 0.1% across most of its range. The trouble with multimeters The problem with a standard multimeter is that the lead and banana socket resistance is usually in the 0.2-0.5W range. The variability in these resistances are too high to zero them out. Ohm’s Law is one of the first equations you learn in electronics. It is therefore not surprising that this principal is used in most ohmmeters, with the resistance measured using a constant current source and a voltmeter. A typical multimeter combines these inside the meter and uses two leads, as shown in Fig.1. When measuring a low resistance this way, the constant current needs to flow through the banana plugs, leads Australia's electronics magazine Part 1 by Phil Prosser and from your lead tips into the device you are measuring, then back again. The voltage drops created by their inherent resistances all appear to the multimeter to be part of the measured resistance. This results in significant errors in low-resistance measurements. There are other ways to measure resistance accurately that don’t use this principle. For example, the Wheatstone bridge is a very elegant approach that can be highly accurate. But an automated meter based on one of those would be very complicated. If you are interested in this use for a Wheatstone Bridge, Wikipedia is a good place to find out more. Kelvin connections A four-wire measurement technique can be used to minimise these errors. Two wires deliver a known current through the device under test, while the second pair measure the voltage across the device under test (DUT), as shown in Fig.2. This neatly avoids the majority of errors above. By using a constant current source, even if there are lead and connection resistances, the current is always as expected. The voltmeter is chosen to have a high input resistance, so siliconchip.com.au Measured resistance R=V÷I Measured resistance R=V÷I Measured resistance Rdut = Rref × (V2 ÷ V1) Current = V1 ÷ Rref V2 = Current × Rdut Fig.1: a standard ohmmeter works by passing a known, fixed current through the device under test (DUT), measuring the voltage across it, then using Ohm’s Law to determine its resistance. The problem is that the test lead resistances are in series with the DUT and included in the result. Fig.2: two pairs of leads are used with Kelvin connections, one to feed the test current to the DUT and one to sense the voltage across it. The voltage drop across the leads supplying current no longer affects the reading, and the voltage drop across the other pair of leads is so tiny that it doesn’t matter. Fig.3: the problem with using the method shown in Fig.2 to measure high resistances is that the test current needs to be really low. So we use this method instead, where the DUT and a fixed resistor form a divider, and we measure the DUT resistance in proportion to the fixed resistor value. when the voltage measurement leads are connected across the DUT, even if the connection is a bit dodgy, we still read the correct voltage, and the R = V ÷ I calculation avoids the majority of errors. There is a bit more effort involved in making really accurate resistance measurements than just adding two wires, but they are necessary to measure values well under 1W accurately. You might wonder why all ohmmeters don’t work this way if it is so effective. Well, using a four-wire ohmmeter is fiddly. There are four wires and most of us only have two hands. Also, the errors are no longer significant above a few hundred ohms. Therefore, all but a few meters (mainly benchtop meters, but some are handheld) use the conventional two-wire approach. The four-wire connection is called a “Kelvin connection” after Lord Kelvin, who invented this to measure low resistances in 1861. While working on this meter, we noticed some nice ‘Kelvin clip leads’ available at reasonable prices. These are essentially crocodile clips with two connections, one for the current source and the other for the sense wire. We found that these worked well over the range of our meter, though for really low resistances, four separate wires will give better accuracy. and, as the voltmeter, an analog-to-­ digital converter (ADC) with a carefully designed voltage reference. These both provide good long-term stability for the meter and the ability to use 0.5mA and 50mA bias currents, which give measurements accurate into the low-milliohm range. Measuring down to about 1mW is practical with a reasonably simple meter. This is about the lower limit before other factors become problematic. Even with higher currents, low resistances mean we need to measure low voltages. Our design uses special very low offset and very low drift operational amplifiers. If we had chosen, say, a common TL074, the worst-case input offset of 4mV would introduce errors of up to 80mW on the low ohms range! The device selected has a worst-case offset of 8uV over its entire operating temperature range, which still could result in an offset error of up to 1.6mW (although we have not seen anything like this sort of error in our testing). This allows our meter to accurately measure a 5mW shunt resistor, which we feel is pretty good. To go beyond this, design approaches that null out these offsets are required – this is usually achieved by switching the current source on and off, allowing subtraction of the nil current offset. By using low-offset parts, we can avoid the need to do this in our design. low current and making the exact same measurement. This is true, provided you can generate a stable current source delivering about 0.1μA with an output resistance much greater than 20MW. But that is not easy to achieve. To avoid this, we use a slightly different technique for measuring higher resistances, as shown in Fig.3. We use a high-value precision resistor to establish the test current. Because this is in series with the DUT, the current flowing will depend on the DUT’s resistance. We do not try to control the current; instead, we measure the voltage across the reference resistor to measure the current flowing for every measurement. By also measuring the voltage across the DUT, we have all the information we need to determine its resistance in proportion to the sense resistor. For the 1MW range, we use a 1MW sense resistor. The current through this will vary. If we measure a 1MW resistor, the current will be Itest = Vsupply ÷ (Rref + Rdut), about 1.5μA. Keep in mind that Itest = V1 ÷ Rref. This relationship is handy, as we will see in a minute. Ohm’s Law tells us that the resistance of the DUT is defined by Rdut = V2 ÷ Itest, where V2 is the voltage across the DUT. Combining this and the previous equation: Rdut = V2 ÷ (V1 ÷ Rref) = Rref × (V2 ÷ V1). Our ADC does not have two channels, but it does have an independent reference (V1) and measurement input (V2). So by connecting our ADC reference across the reference resistor, we Other challenges We need to know the exact current through the DUT and the voltage across it. For DUTs with a low resistance, both of these are easily achieved. We use an LT3092 programmable current source siliconchip.com.au Megohms measurements Adding a megohm range would seem to be a simple matter of setting the constant current source to a very Australia's electronics magazine August 2022  27 can measure the ratio of V1 and V2 with the ADC, and it simply comes out as the measured value! An added bonus of this approach is that we don’t need to care about the exact supply rail voltage or exact current through the DUT. The catch here is that our measurement of the voltages across the reference and DUT resistors has been assumed to be ideal, ie, our ADC has no impact on the current flowing through the DUT. We already know that the current will be in the region of 0.1μA, so the ADC measuring the reference and DUT voltages needs to have very high input resistances and very low bias currents (the current flowing into or out of the input), or else the above assumption will fail. The ADC we have chosen, the MAX11207, only has a bias current of 30nA. The voltage 30nA will develop across a 10MW resistor is 30 × 10-9 × 10 × 106 = 300 × 10-3V, or 0.3V. This is a massive error, given that we will be measuring about 1.5V. So we had to add a buffer amplifier with a super low bias current. Our choice, the MCP6V64, has a typical input bias current of 20pA and a maximum offset current of 200pA (the difference between the bias currents for the + and – inputs). Given the current shortages, we have listed a few alternatives that we have tested in the parts list, but the MCP6V64 is our first choice. This reduces error with a 10MW resistor to 200 × 10-12 × 10 × 106 = 2 × 10-3V or 3mV, a much more manageable error. Circuit description Let’s look at how these decisions come together in our final design. The complete circuit is shown in Fig.4. The heart of this meter is the MAX11207 20-bit ADC. We have also tested this with the similar MAX11210 chip, and the MAX11206 and MAX11200 should also work just fine too. We chose this device as it is very linear, provides great resolution and is available in several pin- and software-compatible forms. It also has fully differential inputs for both the ADC and the reference, which can operate across the entire input range. This means we can pull some tricks and use the reference input in a somewhat unusual manner for high-resistance measurements. This device has a range of settings, the most important ones being internal calibration and internal buffering. The software looks after this, and you should only notice a slight delay at power-on as they are initialised. All the inputs to the ADC are buffered by the MCP6V64 quad operational amplifier. This device provides a very high input impedance, low bias current and low drift buffer for the ADC. All of its inputs and outputs can go close to the supply rails. Its key feature is bias currents in the pA range, and it can operate within 200mV of the rails. When you get to the construction stage, take note that the PCB must be A preview to part two, showing how the batteries and PCB are mounted. 28  Silicon Chip Australia's electronics magazine very clean around this surface-mount IC. Flux and residue from soldering can increase the leakage currents on these extremely high impedance inputs, degrading the performance of your meter. Thoroughly cleaning and coating this area with clear protective lacquer is an essential step in construction. We have included 10kW series protection resistors from the sense inputs to the buffers, and a 10nF capacitor across the sense inputs, providing modest protection to the circuit. That said, we strongly suggest that you do not connect the meter to live circuits, as the application of more than a few volts between the terminals could easily cause damage. On the milliohms range, the reference voltage going to the REFP input (pin 5) of IC1 via buffer IC2a comes from an LM336 2.5V shunt regulator, IC5 (lower left). We’re specifying the LM336B type as it has tighter tolerances. The LM336 is set up with series diodes and a trimpot, which allows us to set it to exactly 2.50V, and the diodes minimise its drift with temperature. The reference input is connected across a resistor of either 100kW, 1MW or 20MW resistors on the higher ranges. These can be found near IC5. The stability of these resistors is important for the accuracy of these ranges. Again, we will be calibrating the device, so initial precision is less critical than stability for these parts. The MCP6V64 buffers for the ADC (IC2b & IC2c) can drive to within a few millivolts of the rails, but not quite to the rails. To accommodate this, the 2.50V voltage reference and reference resistors connect to ground through D8, a BAT85 schottky diode. Similarly, the DUT connects to the positive rail through D4, a 1N5819 schottky diode. These drop about 0.3V at the currents we operate them. We use a constant-current device (IC3) to pass either 0.5mA or 50mA through the DUT on the milliohms and ohms ranges. The stability of the voltage and current references is essential to the accuracy of these ranges. But because we calibrate this meter against known resistors, absolute precision is less of an issue. With a 3.6V supply rail, the maximum voltage that we can handle across the DUT is 1.7V. This is calculated ...continued page 31 siliconchip.com.au Parts List – Wide-Range Ohmmeter 1 double-sided PCB coded 04109221, 90.5 × 117.5mm 1 189 × 134 × 55 sloping ABS instrument case [Altronics H0401] 2 3 AA cell battery holders with leads [Altronics S5033 + P0455] 1 backlit 16×2 character alphanumeric LCD screen with HD44780-compatible controller (LCD1) [SC5759] 2 4-pin tactile switches (S1, S2) 1 subminiature DPDT solder tag slide switch with mounting screws (S3) [Altronics S2010 + S2014] 3 Omron G6H-5V or G6S-5V telecom relays or equivalent (RLY1-RLY3) [eg, Altronics S4128B] 1 10kW top-adjust multi-turn trimpot (VR1) 1 10kW top-adjust mini trimpot (VR2) 1 2-pin header with jumper shunt (JP1) (optional; only needed for in-circuit programming) 2 2-way vertical polarised headers with matching plugs (CON1, CON2) [Altronics P5492 + P5472 + 2 x P5470A] 1 16-pin header (CON3; for mounting the LCD) 1 6-pin header (CON4) (optional; only needed for in-circuit programming) 1 2-pin right-angle polarised header with matching plug (CON5) [Altronics P5512 + P5472 + 2 x P5470A] 1 5-pin header (CON6) (optional; for monitoring SPI) 2 red captive head binding/banana posts (CON7, CON8) [Altronics P9252] 2 black captive head binding/banana posts (CON9, CON10) [Altronics P9254] various lengths of light-duty hook-up wire 1 pre-made set of Kelvin clip leads [www.ebay.com.au/ itm/263861879033] OR 1 DIY set of Kelvin clip leads (see section below) Hardware 4 M3 × 10mm tapped metal spacers 4 M3 × 6mm panhead machine screws 4 M3 × 6mm countersunk head machine screws 8 M3 shakeproof washers 1 small tube of clear neutral-cure silicone sealant 1 can of PCB conformal coating/protective lacquer Kelvin clip leads (if not using pre-made leads) 2 Kelvin alligator clips [Mouser 485-3313 or 510-CTM75K; Digi-Key 1528-2279-ND] 1 2m length of 17AWG (1.0mm2) black figure-8 cable [Altronics W4146] OR 1 2m length of two-core heavy-duty microphone cable [Altronics W3028] 1 1m length of 18AWG (0.75mm2) red silicone hightemperature hook-up wire [Altronics W2400] 1 1m length of 18AWG (0.75mm2) black silicone hightemperature hook-up wire [Altronics W2401] Semiconductors 1 MAX11207EEE+ 20-bit ADC, QSOP-16 (IC1) ● (alternatives exist – see text) 1 MCP6V64-E/ST quad low-drift rail-to-rail op amp, TSSOP-14 (IC2) ● ■ 1 LT3092EST or LT3092IST programmable current source, SOT-223 (IC3) ● siliconchip.com.au 1 PIC24FJ256GA702-I/SS 16-bit microcontroller programmed with 0410922A.HEX, SSOP-28 (IC4) ● 1 LM336BZ-2.5/NOPB voltage reference, TO-92 (IC5) ● 1 555 timer, DIP-8 (IC6) ● 2 AZ1117H-ADJTRG1, AMS1117 or equivalent adjustable 1A LDO regulators, SOT-223 (REG1, REG2) ● 4 BC547 100mA NPN transistors, TO-92 (Q1, Q3, Q5, Q6) 2 IRLML0030TRPBF N-channel Mosfets, SOT-23 (Q2, Q4) ● 7 1N4148 75V 250mA signal diodes (D1, D2, D5-D7, D10, D11) 2 1N5819 40V 1A schottky diodes (D3, D4) 1 BAT85 30V 200mA schottky diode (D8) 1 1N4004 400V 1A diode (D9) Capacitors 7 10μF 50V radial electrolytic 5 10μF 16V X7R SMD M3216/1206-size ceramic ● 5 100nF 50V X7R through-hole ceramic 5 100nF 50V X7R SMD M2012/0805-size ceramic ● 2 10nF 100V PPS [Kemet SMR5103J100J01L16.5C] ● 4 10nF 50V X7R through-hole ceramic Resistors (all axial 1/4W 1% metal film unless noted) 2 10MW 0.1% 25ppm SMD M3216/1206-size ● 1 1.5MW 1 1MW 0.1% 25ppm SMD M3216/1206-size ● 2 1MW 1% SMD M2012/0805-size ● 1 100kW 0.1% 25ppm SMD M3216/1206-size ● 1 47kW 1 33kW 1 22kW 1 10kW 0.1% 15ppm ● 7 10kW 4 4.7kW 3 3.3kW 1 2.2kW 2 1.2kW 1 820W 1 205W 0.1% 15ppm ● 2 100W 1 47W 2 1W 1% 50ppm ● Calibration resistors (not required if another highprecision ohmmeter is available) 1 27.4W 1/4W 0.1% 15ppm axial [YR1B27R4CC] ● 1 2.94kW 1/4W 0.1% 15ppm axial [YR1B2K94CC] ● 1 97.6kW 1/4W 0.1% 15ppm axial [YR1B97K6CC] ● 1 976kW 1/4W 0.1% 15ppm axial [YR1B976KCC] ● 1 10MW 1/4W 1% 50ppm axial [MF0204FTE52-10M] ● ● all these parts (with IC4 pre-programmed) are available in a set (Cat SC4663) for $75.00. ■ compatible op amps need to be rail to rail, unitygain stable with very low input offset voltages and input bias currents in a TSSOP-14 package. Good alternatives are the MCP6V79, MCP6V34 and OPA4317. Australia's electronics magazine August 2022  29 Fig.4: all measurements are made by IC1, the ADC, controlled by microcontroller IC4. IC4 switches relays RLY1-RLY3 to select the appropriate range and displays readings on the 16x2 LCD module. Voltage reference IC5 is used in the lower (milliohms & ohms) ranges while IC3 regulates the test current, with Mosfets Q2 & Q4 switching it between 0.5mA & 50mA. In ratiometric (high-range) mode, IC3 and IC5 are not used, and precision resistors of 100kW, 1MW or 20MW are connected in series with the DUT. 30  Silicon Chip Australia's electronics magazine siliconchip.com.au by subtracting the voltage drops from the supply rail due to diode D4 (0.3V) and IC3 (1.6V). Let’s say we can allow up to 1.5V across the DUT to be safe. This means a maximum reading of 1.5V ÷ 50mA = 30W on the milliohms range and 1.5V ÷ 0.5mA = 3kW on the ohms range. The maximum readings on the other ranges are limited by the values of siliconchip.com.au the 100kW, 1MW and 20MW reference resistors. The current regulator For the higher current (lower resistance) ranges (milliohms and ohms), we use IC3, an LT3092 constant current source. We have chosen this for its long term stability and ease of use. This device sources a constant 10µA Australia's electronics magazine from its SET pin, and the OUT pin is maintained at the same voltage as the SET pin. With a 10kW resistor from the SET pin to GND, there will be 0.1V across it (10kW × 10μA). The parallel combination of 205W, 47kW and 1.5MW resistors results in 204.08W between the OUT pin and ground, giving a current of 490μA. Therefore, the IN pin August 2022  31 sinks 490μA + 10μA = 500μA for these two currents combined, which is our goal (0.5mA). For the milliohms range, parallel Mosfets Q2 & Q4 switch on, so the two series 1W resistors are connected in parallel with the 204.08W resistance. But note that the on-resistance of the Mosfets (40mW || 40mW = 20mW) adds to the 2W from the resistors. With 2.02W in parallel with 204.08W, we get 2.0002W. Thus the current from the OUT pin will be 49.99mA + 0.01mA or 50mA. This way, the software can switch the constant current source between 0.5mA and 50mA to suit the resistance detected on the meter by controlling the gates of Q2 and Q4. We recommend using 0.1% 15ppm resistors for the 10kW and 205W parts, as specified in the parts list. We found 1W 0.1% resistors too expensive, so we used 1% parts instead. These are MF0207FRE52-1R, which have a 50ppm temperature coefficient, so they should be pretty stable. We have provided the current source with a good heatsink in the form of a large copper fill on the top layer of the PCB. The keen-eyed will also note that we have placed a guard track around the SET pin, which has an extremely low current flowing from it. This will reduce leakage currents interfering with our carefully-designed current source. The reference resistors We measure resistances in three ranges above 3kW: 100kW, 1MW and 20MW. Our measurement technique uses reference resistors at each of these values. We have specified parts that should provide a low temperature coefficient and long-term stability. We again recommend 0.1% parts where reasonable. 20MW tight-tolerance resistors are both expensive and uncommon, so we use two 10MW resistors in series. Stability is probably more important than actual precision, as the meter will be calibrated. Again, cleaning off all flux and residue around these is very important, as is coating it with a protective lacquer to optimise long-term stability. We used 3.2 × 1.6mm SMD parts here (M3216/1206) as our survey of suppliers found that 0.1% parts are more available and less expensive in these packages than in through-hole. 32  Silicon Chip Switching the ADC inputs Because we have five different ranges and can’t handle any additional bias currents, we need to do some switching, and that’s done with relays. The resulting switching arrangement might initially look complicated but there isn’t too much to it. Regardless, the auto-ranging feature means that the user doesn’t need to know the details. One relay, RLY1, switches the reference input between the fixed 2.50V reference and the three reference resistors. The other two relays, RLY2 and RLY3, connect either the constant current device (IC3) or one of the three reference resistors to the lower pin on the Force connector, CON1. The PCB has been laid out to handle two of the most common types of signal relays, conforming to the Omron G6H and G6S layouts. These are available from a range of electronic outlets. Just make sure you use 5V non-­ latching versions. Microcontroller and display We have kept the display and control circuitry simple. We see this as a utilitarian device, so it should put function over form, and seek to ‘do what it says on the box’ as simply, cheaply and reliably as possible. The LCD screen operates from the VDD rail of about 3.4V, but these displays are almost always powered from 5V. It turns out that the LCD bias between the VDD and VO pins on the LCD module needs to be about 5V, but the actual controller is specified to operate from 2.7V. Therefore, we can generate a negative voltage of about -2V for the VO bias reference and power the LCD from the same VDD rail used for the PIC micro. We need to do this because some LCDs are incompatible with the 3.3V CMOS outputs from microcontrollers. Annoyingly, it is very difficult to tell which LCDs work with 3.3V logic and which don’t. To avoid this frustration, we have arranged the circuit so that all LCDs should work. The negative VO bias is generated by 555 timer IC6, which oscillates at a couple of kilohertz. This drives a switched-capacitor voltage inverter comprising two 10μF capacitors and two 1N4148 diodes. This runs off the relay 5V rail and generates -2V or so. By using the 5V rail, we avoid running this ‘noisy’ Australia's electronics magazine circuit from a rail used for the sensitive current sources and ADC. User interface The goal of simplicity has led us to remove all buttons from the front panel and implement an auto-range function. There are two buttons on the PCB which are only used for calibration; we will discuss them later. Upon initial connection, the Meter will first check the DUT on the 100kW range. Depending on the result, it will increase or decrease the range appropriately until the optimal measurement range is found. We start with the 100kW range as most of the resistors we measure seem to be less than this resistance. The way the meter does auto-ranging means it will generally jump from the 100kW range straight to the final measurement range. The initial test current will be 30μA or less, and this will increase to 500μA for resistances between 30W and 100kW, or 50mA for resistances below 30W. The highest possible power delivered is 75mW for a 30W resistor. This should be safe for all bar the most sensitive devices. The microcontroller used is a PIC24FJ256GA702-I/SS. This is just right for the job in terms of pin count, though we also use four ‘free’ digital I/O pins provided on the ADC, as they were too convenient to ignore! We have used a simple schottky diode to drop the 3.6V rail to something closer to 3.3V for the ADC and the microcontroller, as 3.6V is right at their upper limits. The micro drives a 16 column, two-line alphanumeric LCD with an HD44780-compatible controller. These are bog-standard but, as a result, come in a bewildering variety of layouts. We have included two very common footprints on the PCB, which gives you some options for selecting a display. When you purchase the display, check the pin-out, as the LED backlight, in particular, seems to change around a lot. There are two headers that you probably won’t need. The first is the ICSP header, CON4. This allows the microcontroller to be reprogrammed on the board, which we used in development, but many readers will build the device with a pre-programmed PIC. There is also a footprint for CON6, siliconchip.com.au SPI_MON. You should definitely not need this unless you want to look at the SPI activity between the microcontroller and ADC. This sort of facility is super helpful when developing a project like this. We also have pads for an external 8MHz crystal and associated 22pF and 100W resistors, although these components are not required in this design as we use the PIC’s internal oscillator instead. The ADC, buffer op amp and microcontroller are all surface-mount parts. They are simply not available in through-hole packages in the first two cases. We also had a desire to fit this project into a handy instrument case. Power supply The circuit operates from six AA cells. We chose this approach to ensure the meter would have a good runtime and that the 5V rail stays up as the batteries discharge. The meter can draw close to 100mA when measuring low resistances. This should provide over 24 hours of runtime on a set of batteries, which will be fine provided you do not forget to switch it off overnight! There are two linear low-dropout regulators. One has a 5V output to power the relay coils, LED backlighting on the LCD screen and the -2V generator (REG3). The other has a 3.6V output (REG2) to power the ADC, buffer op amps and micro. Both regulators are specified as the AZ1117 type, but there are many pin-compatible LDO regulators (usually with 1117 in their part code) that will work fine too. We’ve provided all the components to allow two identical adjustable regulators to be used for REG2 & REG3. Still, you could use a fixed 5.0V output regulator for REG3, omitting the resistor between the OUT and ADJ pin and its series capacitor, and replacing the resistor between ADJ and GND with a 0W resistor (or a short piece of wire across the pads). You could theoretically do that for REG2 as well, but unfortunately, 3.6V is not available as a fixed output option on this type of regulator. So stick with the adjustable type for REG2. Kelvin leads We used Adafruit 3313 Kelvin clips leads with the prototype, which are amazingly cost-­ effective; certainly less expensive than a double espresso (let alone that smashed avo!). Availability from the usual suppliers is mixed. We also tried Mouser Cat 510-CTM-75K, which is a delight to use but rather more expensive. These are simple to wire up, as shown in the adjacent photo. All you need to do is wire the Force+ and Sense+ wires to either side of the “+” Kelvin clip (with the red wire) and the other two terminals to the remaining black wires of the “-” Kelvin clip. Keep in mind that the force and sense wires only contact either side of the DUT lead. Where you measure larger or more fiddly items, separate force and sense test leads might be better. Again, the force current must run through the whole item you wish to measure the resistance of, and the sense lines are connected to measure the part you desire, as shown in Fig.5. We made two sets of leads for our meter. One set had separate sense and force leads, and these are essentially conventional multimeter leads. We made them using 18AWG silicone-coated high-temperature hook-up cable (Altronics W240X), which is very flexible. We connected these wires to clips for the force and probes for the sense lines. We did not use these much in the end, as the Kelvin clips are excellent right down into the low-milliohm region. We used Altronics Cat W4146 sheathed figure-8 flex for our Kelvin Clips, though we feel that a lighter gauge would be easier to use if you can find it. We used coloured heatshrink tubing to clarify which wires are + and – (although this generally isn’t important when making measurements). One Kelvin clip connects to “Force -” and “Sense -” while the other goes to the “Force +” and “Sense +” sockets on the meter. The length of leads should not matter as the conductors are close, so any EMI picked up should mostly cancel out. We felt that 600mm was about right, but that is a matter of preference. If you don’t want to make up your own set of Kelvin clip leads, they are available to buy pre-made at reasonably low prices at sites like eBay. Search for “LCR clip leads”. For example, www.ebay.com.au/itm/263861879033 Next month We don't have space in this issue for all the construction, testing and set-up details, so they will be in a follow-up article next month. SC siliconchip.com.au Fig.5: when working with Kelvin probes, it doesn’t matter whether you connect the ‘sense’ leads closer to the DUT than the ‘force’ leads or not. Regardless, the section between the two connections on either side is not measured because there is no current flowing through it or the measurement point is further along. Australia's electronics magazine August 2022  33 The History of What was the genesis of Silicon Chip magazine? How did it come about? Why would anyone have had the foolhardy idea to launch a new electronics magazine in a crowded Australian market in 1987? Leo Simpson, the founder of Silicon Chip, tells how the seeds were sown several years before, in 1984, when he was editor of “Electronics Australia” magazine. B ack in July 1984, while I was editor of Electronics Australia magazine, I wrote a fateful editorial about the battle between the two competing videotape formats, VHS and Beta. Sony was the inventor of the Beta format but over the years, the VHS format had grabbed the lion’s share of the market. Both formats were quite similar in principle, using a rapidly 34  Silicon Chip spinning drum carrying the video heads and thereby helically scanning the videotape as it passed part way around the drum. Today, VHS would be regarded as ‘open system’ like the IBM PC, while Beta would be compared to a ‘closed system’ like Apple’s iPhone. But while Beta was regarded as technically superior (much like Apple products today), Australia's electronics magazine VHS had gradually whittled away that lead. And then big department stores started giving major price reductions for Beta machines. What was happening out there? Until then, readers would often write or phone to ask us which VCR format they should buy. I would tend to summarise the position outlined above but would never make a ‘buy’ recommendation. That all changed when I attended a major presentation by the German company BASF with the release of a premium grade four-hour tape for VHS machines. Significantly, they did not bother with a Beta version. I closely questioned the BASF people about this, and their verdict was clear: Beta had lost the battle. Hence, I decided to write that fateful editorial. I was telling the truth, but did not reckon on the financial consequences. Sanyo, a manufacturer of Beta format VCRs and a major advertiser in Electronics Australia, immediately cancelled all their advertising. That was drastic enough, but then they really upped the ante by cancelling all advertising in all magazines published by John Fairfax’s magazine subsidiary, Sungravure. In today’s money, that would have amounted to many hundreds of thousands of dollars! I was quite shocked, but the Sungravure management must have suffered apoplexy. And yes, I was absolutely right about Beta; sales of all Beta VCRs pretty much ultimately ceased worldwide. But not too long after that editorial, in November 1984, the ownership of Electronics Australia was transferred from Sungravure Pty Ltd to the Federal Publishing Company. My editorial may not have been the only factor in that transfer decision, but it must have been a major component. Looking back, I had been quite naïve; the editorial should have been vetted by senior management. To be honest, if Neville Williams had still been the editor-in-chief of EA, the editorial would probably not have seen the light of day. Having said that, it was quite a precipitous decision by the Fairfax senior management to then transfer EA to Federal Publishing. Electronics Australia was very successful and one the most profitable magazines in the whole group. If I had been the general manager siliconchip.com.au of Sungravure, I would have summarily fired the editor! Yep, I would have given that idiot editor his marching orders and then patched things up with the advertisers. Fortunately, that did not happen, and I managed to keep almost the entire staff together for the transfer: staff writers, advertising sales and even some of the production people came across. Why? I suppose they must have liked me, but the bigger reason was that we all loved working together on ‘our’ magazine! That delusion about ‘our’ magazine was part of the reason that I wrote that fateful editorial. And that delusion was very quickly erased as we started work for the new company in the new location at Rosebery. Talk about culture shock! Nobody liked it. Federal Publishing was the magazine division of the very successful Eastern Suburbs Newspapers group. But my judgement was that while their burgeoning local newspapers were highly prosperous, they did not treat their magazine journalists at all well. The company was beset by high staff turnover and that also affected EA and Electronics Today International (ETI), which had also been absorbed by the group some years earlier. So we started to lose staff. We also lost access to our very comprehensive library, but we did manage to have a spacious new laboratory built, which we shared with ETI. The situation worsened when the operation was transferred to a huge plant in Alexandria. This was formerly the CIG plant which manufactured an extensive range of industrial gases. Alexandria was far more remote, forcing most people to drive long distances, and more people in the company left, including our very experienced draftsman, Bob Flynn. We were forced to use non-technical company layout artists. So it was difficult to function as well as we had, and we ended up with a much smaller laboratory that was not as well-equipped. The magazine was in decline. Eventually, after a great deal of thought, I decided to make an offer to purchase Electronics Australia from Federal Publishing. My offer was based on a very significant amount of cash for which I would have needed to mortgage my home. In hindsight, it was a bold (rash?) decision, but I was prepared to take the risk. siliconchip.com.au The editorial from the July 1984 issue of Electronics Australia Well, it got very short shrift. I can’t remember the exact sequence of events, but within a day or two, I was called in to senior management and dismissed. They told me to hand over the keys to my company vehicle, to clean out my desk while a security guard looked on and I was escorted off the premises. Assistant editor Greg Swain kindly drove me home, and that was that. Shortly after, Greg Swain and project designer John Clarke also decided to move on. They both resigned and left some four or five weeks after my departure, having been released early from their mandatory 12-week notice periods. That was around the end of April or early May 1987, if my memory serves me correctly. At that stage, none of us really had a clue what we were going to do, and there was every chance that we would go our separate ways. We spoke often over the phone during the following weeks and explored various business ideas. But electronics and magazine publishing were what we knew. Eventually, Greg Swain and I decided to take a big risk, to start a new magazine. We might have been familiar with running an electronics magazine, but there would be an enormous difference between taking over a long-established magazine like Electronics Australia and starting a new one from scratch in a crowded market! There were already three electronics magazines on the Australian market: EA, ETI and Australian Electronics Monthly (AEM – founded by ex-ETI Australia's electronics magazine editor Roger Harrison), plus several competing trade electronics magazines. Any casual observer would have concluded that we would fail within very short order. That Silicon Chip continues as one of the very few electronics magazines in the world today proves that such a forecast would have been wrong. Forming the new magazine We basically started with nothing. Apart from a Fluke 77 multimeter, a couple of soldering irons, an IBM PC with two floppy drives and a few reference books, that was all I had. Oh, I did have a slide rule (an anachronism even then) and a scientific calculator. Greg Swain was in much the same boat but without a computer (it was 1987, after all; few people had the cash to buy an IBM PC). My computer skills were confined to knowledge of MS-DOS and WordStar and little else. While I did have a Business Degree, I had no experience running a business where I was the owner, not an employee. That was pretty daunting. But I did have a very good knowledge of how to run technical magazines. Before I had been given the boot, I had been Managing Editor of EA, ETI, Your Computer and Sonics magazines. I also had good knowledge of magazine printing and the role of a publisher. So, where to start? Fortunately, I was introduced to a very helpful solicitor (whom I still work with today). He, in turn, introduced me to a great accountant who helped me with a good connection to a bank manager at the ANZ. August 2022  35 The Playmaster 200 with its front panel attached. It was a very ambitious project. Then I had to seriously exercise some of my business and publishing knowledge and make use of my business contacts. I had to line up a commercial printer and typesetter (this was well before the days of desktop publishing) and a magazine distributor for Australia’s thousands of newsagents. And then I had to line up advertising support. The printer we selected was Masterprint Pty Ltd, based in the NSW country city of Dubbo. While this posed some logistical problems, they were well-versed in dealing with publishers from all over Australia, and the arrangement worked well. Ironically, just a few years later, Masterprint was bought out by Hannanprint Pty Ltd – the owners of Eastern Suburbs Newspaper and Federal Publishing, the company we used to work for! Funnily enough, that caused no problems at all, as we had developed very good relationships with the whole staff at Masterprint. Greg and I looked at several offices in which to start our fledgling business but decided to be very cautious and start in the basement of my home on Sydney’s Northern Beaches. In fact, it was in three very spartan rooms adjoining my garage, with little lighting and not much else. I purchased a PC-clone with a 5.25-inch floppy and a 20MB hard drive – wow! We also purchased a 300 baud dial-up modem. Greg set about learning about computers while I plastered the ceilings with Gyprock, installed lighting and set up an office. We had two desks, two computers, a few ordinary chairs and a portable typewriter. To provide more desk space, I had a table tennis table which split into two sections. We also had an electric jug to make tea and coffee. Oh, joy. Some time later, Jack O’Donnell of Altronics visited our ‘office’ and commented favourably on our “Readymix The interior of the Playmaster 200 Amplifier was faithfully reproduced in the cartoon on the opposite page. 36  Silicon Chip Australia's electronics magazine carpet”, ie, the concrete floor, since that was how he started out. In July 1987, we incorporated Silicon Chip Publications Pty Ltd and made a start on the contents of our first issue. In fact, it was only a few weeks before that we had decided on the name of the magazine: Silicon Chip. There were already too many companies out there, publishing and otherwise, with electronics in their name. We needed something different but which still encapsulated what the magazine was about. Out of a list of dozens of possible names, only one stood out: Silicon Chip. It was not evident to most people at the time, and most had the impression that the magazine must be about computers. Well, that was part of it, but I maintained then that silicon chips would become embedded in every aspect of human lives. I had no idea just how true that would turn out to be. If you looked through the first 96-page issue in November 1987, which featured a 7-digit frequency counter on the cover, there was little to indicate how just how small our operation was. There were just four of us on the staff: Greg Swain, John Clarke, Bob Flynn and me. We also had a list of “regular” contributors, which was quite funny, considering that we had just started. All those people were previous contacts that we had known for years and fortunately, they and quite a few others stuck with us for many years. Crucially, we had very good advertising support right from the beginning from three key companies: Altronics, Jaycar and Dick Smith Electronics. We could not have started without them, but fortunately, they had faith in us. Of course, we had no laboratory and virtually no test equipment; not even an oscilloscope. That came a little later when I purchased an old Tektronix scope that weighed a ton. Fortunately, John Clarke was quite well equipped with a 2-channel oscilloscope, a protoboard (for lashing up circuits) and his much-prized Beckman DMM – much better than a Fluke DMM, according to him! We designed our prototype PCBs using the old tape process and etched them ourselves. Later, my good friend Bob Barnes (now deceased) of RCS Radio Pty Ltd would make our prototype boards and also stock them for sale to readers. siliconchip.com.au One of Brendan Akhurst’s earliest works for Leo Simpson. This cartoon was reproduced from Electronics Australia, April 1985, page 48. That’s Jim Rowe wearing a barrel. Leo is shown working on the Playmaster Series 200 stereo amplifier design. The first article of this amplifier was published in the January 1985 issue of EA. Subsequent articles were delayed due to noise problems in the moving coil preamp, and the series wasn’t finalised until the May 1985 issue. Ultimately, the projects were very well supported with kits by our three key advertisers, Altronics, Jaycar and Dick Smith Electronics. Some of the initial project designs came from contributors. A few months later, we started getting letters from readers for Circuit Notebook contributions and letters to “Ask Silicon Chip”. Magazine format We had thought very carefully about the look and style of the new magazine. I wanted it to be clear and very easy to read. At that time, Dick Smith was running a brilliant new magazine, siliconchip.com.au Australian Geographic. Dick had set very high standards for page layout, outstanding photography, excellent writing and proofreading and lastly, excellent printing. I wanted to emulate his approach. As a first step, I used the same type font for the body copy as in Australian Geographic. It was Melior, a serif font with large lower case, making it very easy to read [we still use it today, including for this article – Editor]. We decided to use a similar circuit drawing style to that used in EA, but we would have to develop all our own circuit symbols and so on. That was to Australia's electronics magazine be Bob Flynn’s task – he was an excellent draftsman. The circuit diagrams were done by hand using stick-on bromide symbols and connections made with Rotring drawing pens. PCBs were designed using stick-down tape for tracks; the overlay components and wiring were drawn by hand and by tracing drafting templates. Very early in the piece, I had the brilliant idea of getting the late Brendan Akhurst to prepare cartoons for the Serviceman pages. While getting Brendan to do this work was a wonderful idea, I must admit that it was August 2022  37 This cartoon by Brendan Akhurst was published in the June 1988 issue of Silicon Chip as part of the regular monthly Serviceman column. pioneers in the field of drone technology, Bob Young. You can read his latest story on that subject in the March 2022 issue (siliconchip.au/Article/15245). This fitted with my belief that merely concentrating on small-scale electronics was to ignore some of the far-reaching major technology developments worldwide. Getting into financial strife not original; it came from the British magazine Television. But Brendan did it so much better, and his work was so much funnier too. Greg Swain did all the magazine layouts. All the editorial copy was written and edited on the PCs, and we received most contributed material via our 300 baud modem. We would watch the text coming in on a green-screen monitor at about 30 words per minute. That was state of the art! After all the editing had been done, we would squirt the text down the phone line to our typesetters in Chippendale and a day or so later, the type galleys (continuous proofs with the type in correct size, width, etc but not ‘laid out’ in any way) would arrive by courier. Greg would then do paste-ups of the page layouts, leaving space for photos, circuits and wiring diagrams. The 16-page sections of the magazine, together with advertising material, would then be couriered back to the typesetters and they would produce full-page bromides. We would then proofread and correct photocopies of these pages before sending the final bromide layouts to the printers at Dubbo. (There’s more on our editorial production systems later in this article). Many of the early Silicon Chip designs were model railway projects. This came from my own hobby interest, but they turned out to be very popular because there was virtually no other source of DIY circuit designs. My 38  Silicon Chip The first couple of years of the magazine were not smooth sailing. In fact, they were extremely difficult. While I had a great deal of experience in running and publishing technical magazines while working at Sungravure and then at Federal Publishing, I quickly realised after only three months or so that we would go out of business very soon unless I immediately changed tack. The problem? The print run was far interest in railways, large and small, too large. Unless I reduced it drastialso led to the first long series from cally, we would crash. Bryan Maher on “The Evolution of Stupidly (rashly?), I had assumed Electric Railways” (29 articles in total; that we would quickly match the magsiliconchip.au/Series/246). azine sales of EA and ETI, and I set Some readers sneered at the first the print run accordingly. But one of few articles because they were mainly the problems of publishing I was yet about steam locomotives. Funny that, to become fully aware of is that there but that’s where electric railways is typically a gap of about two months evolved from. As the series continued, or more between a magazine going on some of those readers admitted that sale at newsagents and getting the sales the articles had become very interest- figures, then there is more delay before ing and actually incorporated lots of the publisher is paid in full. very complex electronic engineering. So at least three issues had been on That included AC-DC converters, sale, and another was due to go to print extremely heavy-duty variable fre- before I realised the extent of the brewquency inverters for driving huge ing disaster. Of course, I had to pay the synchronous traction motors, diesel-­ printer for every single magazine that electric locomotives with inverter had been printed, whether they were drives, dynamic braking, radar-­ sold or not. So I was already looking controlled anti-slip traction control at a huge loss after only a few months. (before it became commonplace in Should I close the whole thing down cars) and so on. before our home was in jeopardy? The Anyone who ploughed through that situation was that dire. entire series would have gained a very Greg Swain and I then had a hurgood understanding of today’s very riedly arranged meeting with my high-speed trains in Japan, France, solicitor and one of my closest busiChina and elsewhere in Asia and ness friends to survey the wreckage. Europe. I went home shattered. I thought that After that series, I continued the Greg had probably concluded that we themes of electronics in diverse fields, would close down the whole thing. I whether they were in power engi- was facing the ugly possibility that this neering (eg, long-distance EHV DC was the only practical way out. links), medical technology (all sorts of But after a couple of long and sleepimplants) or defence with an empha- less nights over the weekend, I came sis on drone technology. to a different conclusion. First, I had In fact, we used to have a regular to immediately and drastically cut monthly column of remote control the print run, while bearing in mind which was introduced in the Octo- that too much of a reduction would ber 1989 and written by one of the mean greatly reduced distribution Australia's electronics magazine siliconchip.com.au to Australia’s huge network of thousands of newsagents – which would mean lost sales. I also had to produce a drastically different cash-management projection since my first effort had clearly been from la-la land. I also had to start paying Greg Swain. He had initially put money into the venture, but I had to acknowledge that he could not sustain the losses so far. Severely chastened by developments to that date, we decided to continue. I should also point out that we had not taken out a business overdraft with the bank to start our operations, so we were very much swimming out there in a big and savage ocean. After that process, false rumours arose that Gary Johnston of Jaycar had put money into the magazine to keep it going. I could see how those rumours might have arisen. After all, Gary was a very good friend of mine, but I was mortified nonetheless. If it had been true, it would have significantly impinged on our ability to sell advertising space to other companies. Having said that, he did surprise me with a generous gift very early in the piece. Having visited us in our ‘offices’, he decided that we really needed a fax machine and so one arrived by courier the next day. I was quite overcome and immediately phoned him at home, to thank him! It was almost two years before the magazine started to break even and I could start paying myself. It took quite a few more years to make up the losses, but we survived and eventually prospered. Along the way, I gained a great deal more practical knowledge about financial management and the realisation that there are no guarantees that any business will continue. And, of course, there would still be many hurdles to overcome. Those early days were really very tough and stressful for all four of us, and we worked much harder than we ever did at Electronics Australia magazine. My wife Kerri was also heavily involved, handling a lot of the work of packing the thousands of subscription copies; she continued to do that for well over 20 years before we put it into the hands of a mailing house in Melbourne. I should state that while producing the magazine was a lot of hard work, it was not all misery. There was siliconchip.com.au also plenty of humour and repartee. I remember one particular instance that was quite funny. Because we were working in pretty cramped conditions and were all anxious to get through the work, there was often a lot of swearing, usually over trivial matters. With my wife and three daughters (upstairs) in mind, I decided that it was all going too far, and I instituted the ‘swear jar’. Anyone who swore had to put 10c in the jar for each and every swear word. It got really frustrating. You would swear, realise that you had just sworn and then curse again, which entailed a double penalty. But Bob Flynn, initially one of the worst offenders, became quite insufferable. Instead of swearing, he would exclaim “Upon my soul” or “Oh, goodness me!” or some other mealy-mouthed expression. After about a week of this, I got thoroughly exasperated with the whole scheme and canned it. I should say that John Clarke was not there every day at that time, and he didn’t swear anyway. The saint. Bob Flynn admitted afterwards that he would swear almost continuously each time he drove home, until the process came to an end. The sod. I can’t remember what we did with the contents of the swear jar. We might have bought a cake for someone’s birthday. That was a tradition that we continued right up until the pandemic hit in 2020. Chocolate mud cake was always a popular choice. Editor: It didn’t end there – when I started working at Silicon Chip in 2010, my desk was between Leo Simpson’s and Greg Swain’s, and I often copped the swearing in stereo! I should explain about John Clarke not being present during the swearing saga. In about December 1988, John announced that he was resigning and was going on a lengthy world trip (including what was to be an arduous journey through Africa) with his newlywed wife Robyn, and he did not know whether he would ever return. That was a bitter blow, but we had to carry on as best we could. Shortly after that, a New Zealand student, Malcolm Young, joined us and filled in the gap left by John Clarke. Inevitably, his accent was the source of much mirth. Fortunately, he took it all in good spirit and gave as good as he got. John Clarke eventually returned in about May the following year and is still working on the staff today. Thanks so much, John. Sometime in 1988, I suffered severe back problems and ended up in hospital for a few weeks, during which I could barely walk. I wasn’t much better when I came home and would spend another couple of weeks slowly recovering. It was at that time that I had the idea for another project. Shut in the bedroom, I could not attract anyone’s attention, including that of my wife when I might have wanted a cup of tea or other ministration. The result was the “Remote Controlled Chimes Unit” designed by John Clarke, featured in the August 1988 issue. The idea was that you could The cartoon used as the lead-in for the Remote Alert/Doorbell project from the August 1988 issue of Silicon Chip (siliconchip. au/Article/7684). Australia's electronics magazine August 2022  39 This shows part of the mezzanine area of our first commercial premises. Greg Swain is in the foreground while our draftsman Bob Flynn is beavering away on his drafting board on a circuit diagram. All the circuits were hand-drawn. A computer and CAD software would come later. press the button on a keyring transmitter to attract attention. The project was a pretty good idea, but the real genius was in the pair of cartoons produced by Brendan Akhurst and reproduced in these pages. I should state here that the cartoons bore no resemblance to the persons depicted therein. Of course, mobile phones have utterly superseded the need for that project. That process would occur many times in the following years, whereby a useful magazine project would be made obsolete by the advance of electronic technology. Leaving the family home Ultimately, the time came to move our magazine operation out from the basement of the Simpson family home. After a few years, we had more staff, and I was fed up with working out of a cramped basement and the fact that it all impinged on the daily life of my wife and our three young daughters. I will never know how my wife coped with all the daily stress, but I am eternally grateful that she had faith in me. So in May 1990, we moved into a capacious industrial unit in Warriewood, also on Sydney’s Northern Beaches. I had vertical blinds and carpet installed, but apart from that, there 40  Silicon Chip were no creature comforts. It was cold in winter and hot in summer, but I had negotiated a very good rental agreement for the first year! By this time, we had more staff, more desks, filing cabinets, the start of a very good technical reference library, more test equipment and so on. We needed that space. It was also during that time that Ann Jenkinson (née Morris) joined the staff to provide all the secretarial duties. Among our many valued and loyal staff, Ann was crucially important to the whole team, eventually becoming office manager. She stayed with us right up to her retirement in March 2021. Desktop publishing During this first year in Warriewood, I wanted to streamline our editorial operations. I looked seriously at purchasing a large bromide camera; second-­hand, of course. But I quickly discarded that idea when we got some desktop publishing software. At that time, Quark Express was the standard for desktop publishing, but all its proponents were using Apple computers. You could also get Aldus Pagemaker for both Apple and IBM PCs, although PCs were disparaged by the cognoscenti. We disregarded all that; besides, we could not afford high-priced Apple Australia's electronics magazine computers and Quark Express, or rather, I refused to spend that much money. Eventually, we found a typesetter in Dee Why who agreed to work with Pagemaker files produced on (ahem, gag, splutter) a PC clone. But it all eventually worked! Our starting hardware for this comprised: 1. A PC-compatible computer with an Intel 386 processor, 120MB hard drive and 4MB RAM. 2. A 300DPI Postscript-compatible laser printer (probably a Hewlett-­ Packard). 3. A Radius 21-inch high-resolution monochrome monitor. 4. A 14.4kb/s modem (the good old dial-up days; a big jump from the 300 baud modem we had when the magazine first started). The software was: 1. Windows 3.1 (an unstable beast that required frequent reboots). 2. Aldus Pagemaker 3 for page layouts. 3. CorelDraw (for special type effects, to create fancy headings and to produce front panels). We used Pagemaker to make up the pages with spaces left for the B&W photos and diagrams (the latter were still hand-drawn). Once the Pagemaker layout was complete, it was printed siliconchip.com.au out and proofread. Pagemaker was then used to produce Postscript files, which were then sent via our modem to the typesetting house in Dee Why to produce a bromide of each page. These page bromides, the photos and the diagrams were couriered in batches to the compositor for final make-up. The photos and diagrams were photographed in a darkroom to produce correct-size images (halftones in the case of the photos), and these were then fed to a waxing machine that applied a wax backing. A compositor then trimmed the edges of each image and carefully stuck it in place on its designated page. The assembled pages were then photostatted and couriered back for final proofreading. The whole procedure was still labour-intensive, but the on-screen layout process saved a considerable amount of money. And there were other big advantages: 1. We could make corrections or additions on the spot after initial proofreading. 2. We could run a spell check over the made-up page before it went to the compositor. 3. It was easy to use special symbols like “W” and “µ” for the resistor and capacitor values. As far as I know, Silicon Chip was one of the first magazines to use desktop publishing on a PC clone. It worked well, and it was a significant achievement for our first year in our first proper premises. Temper tantrums I should mention our adventures with another printer used in our office. This was a large tractor-feed dot-­matrix machine that could be used to produce several different fonts. We used it for general correspondence, monthly invoices, pay slips and to produce the carrier sheets for the subscription copies. It was controlled via a small LCD panel and was quite frustrating to use, to the point where I sometimes felt like picking it up and hurling it off the mezzanine floor of the premises. Suffice to say that the cost of replacing that expensive machine stayed my hand, but only just. Quite a few years later, I had similar frustrations with a much cheaper and smaller dot matrix printer. Remembering the utter frustrations of those earlier times, temptation siliconchip.com.au These two shots show views of our lab set up which was quite spacious. By this stage (mid 1990) we had proper workbenches and gas-lift chairs and quite an array of test equipment, some of it secondhand. ultimately got better of me, and I threw it down the stairs at home – it smashed into smithereens. Sweeping up all the broken plastic cogs, bits and pieces in the aftermath gave me much satisfaction, knowing that I wouldn’t have to put up with it any longer. Yes, yes, I know I shouldn’t have done it, mea culpa, mea culpa etc etc. Editor: later there was a similar scene on a smaller scale when I received an extended call from a rude person on my corded desk phone. The phone somehow took to the air, flew Australia's electronics magazine across the room and came to an abrupt halt in a shower of parts. I put those parts back together, but the phone never quite worked the same after that. At least I didn’t have to deal with that bloke any more! That arrangement in the Warriewood industrial unit lasted slightly less than 12 months because most of the units in this complex of 36 were unsold, and the developer ran into problems with a Victorian bank (some readers may remember the Victorian banking crisis in 1991). August 2022  41 attach a front panel to a finished project if it had been photographed without a front panel in place. Call it skullduggery, but it made the projects look far more professional and also meant that the production panels looked far superior to our previous versions. CAD for PCB design This shot shows the ground floor of our first commercial premises, showing where Ann Morris used to sit, and where we processed subscriptions and mail orders. Leo Simpson lurked in the corner, behind the filing cabinets. The mezzanine floor above would have been the likely launching point for a large printer which caused a huge amount of frustration. The water board advised us that the water would be cut off in a few weeks because of unpaid rates. We had to break the lease and get out. Panic stations! Then, in short order, I had the very good fortune to lease a large office which had been previously used as part of the manufacturing plant for one of Australia’s leading boat builders, at Bassett Street, Mona Vale. After our previous spartan lodgings, this was very spacious and luxurious. The original office fit-out was still in place, with carpeted floors, glass partitioned offices, air-conditioning, a tea room and an attached small warehouse. What bliss. In fact, those premises were to set the standard for all the premises we leased or purchased in the future. We were always able to make use of an existing office fit-out with air conditioning and thereby save a heap of money. I was always conscious of keeping control of expenses. enhance our photos by using various tools to adjust the sharpness, brightness, contrast and shadows. It also allowed us to quickly deep-etch images (ie, remove the background from around an object), a previously labour-intensive task at the compositor. And it allowed us to produce drop shadows for any deep-etched object. Another advantage of Photoshop was that we could directly import and Another big step was to move to on-screen design for PCBs. This was done using Protel (from the company now known as Altium), and we had switched over to this method by June 1992. The parts overlay and wiring diagrams were still done by hand, however. Every year or so, there would be a new version of Protel with more features which we jumped on as soon as they became available. Altium continues that process today and Silicon Chip still uses this world-class software. Next month The story so far takes us up to the end of 1992. We’ll follow up next month with the remainder of the history of Silicon Chip, from 1993 to the present. That article will include details on the people involved and the technological and methodological changes that improved the magazine production process over those SC 30 years. More on magazine production We added an HP flat-bed scanner to our desktop equipment in 1992, shortly after moving to Bassett St, Mona Vale. That enabled us to scan and place the photos directly into our Pagemaker layouts, again saving time and money. We also invested in Adobe Photoshop. This enabled us to greatly 42  Silicon Chip Leo Simpson looks happy sitting in his office at the first rented premises for Silicon Chip, at Warriewood, on Sydney’s Northern Beaches. Unfortunately, we soon had to move from that building as the owner/developer of the complex ran into financial difficulties. Australia's electronics magazine siliconchip.com.au Build It Yourself Electronics Centres® Turn it up SAVE $40 199 SALE $ Demo in store! C 5064 Opus One® Bluetooth Bookshelf System get your Everything you need to August. projects cranking this Want top notch sound for your games, hi-fi listening or home theatre? These new active bookshelf speakers need no amplifier, just plug them in & connect via Bluetooth, digital S/PDIF or stereo RCA. Amazing sound for their price with a sleek oak grain finish - looks great with grilles on or off! Size: 146 x 164 x 240mm. NEW! 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Ideal for PCB assembly, cutting solid core wiring etc. 19.95 $ 6pc Soldering Helper Tools Tools for reworking solder joints, cleaning pads and removing debris. Your one-stop electronics shop since 1976. | Order online at altronics.com.au Secure your home & save. SAVE $100 P 8149 399 HOT PRICE! SAVE 24% $ 2 For 30 $ S 9901J IS PRICE! 20 SYSTEMS ONLY AT TH TOP DEAL! SAVE $10 69 $ S 9017A Automate lighting & appliances! Switch any connected appliance on or off remotely from anywhere in the world. Set schedules, monitor and control via the Tuya Android/iOS app. Maximum 10A 2400W. Works with Google Home and Alexa Pan & Tilt Wi-Fi Camera Makes a great baby or pet monitor, this indoor camera features intelligent tracking of moving objects within the frame. 2-way audio with mic and speaker. 5m IR night time coverage. Requires 5V 1A USB power supply. Affordable 5 Megapixel CCTV Surveillance System. Simple to install with instructions supplied. Cameras can be remote viewed on iOS/ Android. Each pack includes: • Hybrid digital video recorder (IP camera ready!) • Pro grade 5MP (2K equivalent) resolution weatherproof cameras • 20m connection leads • Power supply • HARD DRIVES TO SUIT: 1TB $98 (D 5514), 2TB $125 (D 5516). Genlamp® PIR Security Lights SAVE $40 Motion activated for instant light at night. Fitted with 240V 3 pin mains plug. Fully approved. Natural white. Rust free stainless steel brackets and hardware. IP65 rated. SAVE 24% 44 $ X 2340C 10W SAVE 24% 60 $ X 2315C 20W 149 $ 30 $ X 2312C 10W 45 $ X 2314C 20W 139 $ Covert Wi-Fi HD Camera Clock 1080p video or 20MP still shot resolution. SAVE 23% 77 $ X 2317C 50W Covert CCTV Camera Video Recorder Great for monitoring in remote locations, temporary CCTV monitoring etc. Runs off batteries, so its quick & easy to set up anywhere you need to keep an eye on things. Weatherproof case with LCD screen. Requires 8xAA batteries & DA0329 32GB SD card $12.50. Great for added security around the house, back shed or garage. Fitted with 240V 3 pin mains plug. Fully approved. Natural white. Rust free stainless steel brackets and hardware. IP65 rated. SAVE 24% SAVE $30 S 9446C Genlamp® LED Floodlights SAVE 24% No expensive cloud service required store footage on site. S 9850 Looks like an alarm clock but has a 1080p camera capable of streaming direct to your iOS and Android device via Tuya Smart Home app. Motion detect recording. USB or battery powered (S 4736 x 2 $18.50ea). *Note: We encourage this item be used responsibly for legitimate CCTV use. S 5322 SAVE 28% 35 $ Window/Door Open Alert SAVE 23% 69 $ Alerts you when a door or window opens with an alarm or chime. Adhesive backed, installs in seconds! SAVE 25% 15 $ Wireless Door/Entry Alert System S 5327 A handy motion activated chime unit for shops to notify staff when customers arrive. Also great for driveways. 120m range. Requires 3xAAA batteries & 3xC batteries. X 2318C 50W Our huge online clearance sale is on now. Click “Clearance Deals” <at> altronics.com.au Western Australia Build It Yourself Electronics Centres Sale Ends August 31st 2022 Phone: 1300 797 007 Fax: 1300 789 777 Mail Orders: mailorder<at>altronics.com.au » 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 0008 Find a local reseller at: altronics.com.au/storelocations/dealers/ PRODUCT SHOWCASE New N20K48 temperature and PID controller NOVUS Automation have released their new N20K48 controller family, and it’s available from Ocean Controls. Unlike other temperature and PID controllers with fixed I/O, the N20K48 is based on a compact, powerful core controller plus a growing family of clickNGo micromodules that enables it to expand its I/O and connectivity to meet your requirements. The base unit has the Process controller with both USB and Bluetooth communications, a single relay, pulse output and a 48x48mm LCD display. The plug-in clickNGo modules include: • CG-3D0 – three digital outputs • CG-1AO – one analog output • CG-485 – RS485 modbus RTU interface • CG-WIFI – WiFi module • CG-1R16 – one relay output, 16A • CG-3DI – three digital inputs • CG-2R5 – two relay outputs, 5A The native Bluetooth interface offers simple field diagnostic and commissioning through the QuickTune Mobile app, reducing downtime, while the USB interface provides a batch configuration option, optimising workbench series production. The QuickTune Mobile app provides the user an intuitive mobile platform for configuration management for all controllers and micromodules on the shop floor. The N20K48 controller has an elegant and distinctive design, featuring a large, bright and clear display, while coming in a compact enclosure, making it suitable for installation in restricted spaces. Visit Ocean Control’s website at www.oceancontrols.com.au for more information. Ocean Controls 44 Frankston Gardens Drive Carrum Downs VIC 3201 Phone: 03 9708 2390 info<at>oceancontrols.com.au https://oceancontrols.com.au/ 2 Series Mixed Signal Oscilloscope from Tektronix Meet Next Gen Tek. The 2 Series mixed signal touchscreen oscilloscope (MSO) – Tektronix’s biggest (actually smallest) benchtop innovation in years. Weighing in at just under 2kg, the 2 Series MSO travels light so you can take it from your benchtop to the field and back again. It can even come with an optional battery pack that will keep you going for up to eight hours of unplugged use. The 2 Series MSO is a highly portable full-featured scope for all your testing needs. With integrated software tools, and 1280 x 800 resolution, 10.1-inch touchscreen all in a compact package. It has a bandwidth range of 70-500MHz, two or four analog channels and 2.5GS/s max sample rate among many other features. Find out more at www.tek.com/en/ products/oscilloscopes/nextgentek Tektronix Inc. 1 Clementi Loop #06-02 Singapore 129808 Phone: 1800 709 465 www.tek.com Qorvo QPF4532 integrated WiFi 6 module now at Mouser Mouser Electronics is now shipping the QPF4532 WiFi 6 integrated front end module (FEM) from Qorvo. It is designed for the latest WiFi 6 (802.11ax) systems such as residential gateways, wireless routers, access points and Internet of Things (IoT). The QPF4532 integrates a 5GHz power amplifier, single-pole, two-throw switch and bypassable low noise amplifier into a single compact form factor device. siliconchip.com.au The QPF4532’s performance is focused on optimising the power amplifier for a 3.3V supply voltage to conserve power consumption, while maintaining the highest linear output power and leading-edge throughput. The receive path design maximises sensitivity with the noise figure performance as low as 2dB. The QPF4532 features integrated die-level filtering for second and third harmonics as well as 2.4GHz rejection for dual-band, dual-concurrent operation. For application feedback, a DC Australia's electronics magazine power detector is integrated into the halogen- and lead-free package to provide voltage that is proportional to the output power from the transmit path. An evaluation board is stocked by Mouser for rapid prototyping. Visit www.mouser.com/new/qorvo/qorvoqpf4532-wifi-6-front-end-module/ to learn more about the QPF4532. Mouser Electronics Inc. 1000 North Main St, Mansfield, TX 76063 USA Phone: (852) 3756 4700 www.mouser.com August 2022  47 isoundBar with built-in woofer Many of us spend an enormous amount of time watching TV, movies and playing video games. Even if you only use your TV occasionally, life’s too short to put up with the lousy sound quality of typical TV speakers. Commercial soundbars cost a bomb and often aren’t that much better. Why not build this awesome soundbar and enjoy your favourite programs in high fidelity? By Allan Linton-Smith A soundbar is a set of speakers in a wide, slim package that’s ideal for putting just under or in front of your TV. There are two big problems with these: the ones that are any good are usually unjustifiably expensive (sometimes more than the TV they’re paired with!), and the requirement to be slim usually limits the amount of bass they can produce. Cheap soundbars abound and are best avoided; many of these have cheap external subwoofers (if they have one at all), which can be very boomy and annoying. In some households, these end up being switched off entirely due to ‘subwoofer fatigue’. On the other end of the scale, decent hifi soundbars from well-respected audio manufacturers are now around the $1000-2000 mark, which can be hard to justify when 65-inch (165cm) 4K TVs start at around $700! Hence this design – a DIY soundbar with excellent frequency response, decent bass and low distortion that won’t break the bank. The soundbar is punchy and will suit many listeners, but if you want to go all-out, we’ve designed a matching sub that rounds out the sound with plenty of bass. It’s a fairly cost-effective design, so even with the sub included, the whole thing will cost a fair bit less than that cheapo 65-inch TV. The total cost of all the drivers used in the isoundBar is around $260, so even when you add in the amplifier module, timber etc, you will probably be able to build it for under $400. You can buy a soundbar for that, but we doubt it will sound anywhere near as good. Design I spent considerable time designing this self-contained system with an internal woofer in a small box that is just 1240mm wide, 70mm tall and 200mm deep. There were significant (and unexpected) challenges, not the least of which is that the slim design restricts us to forward-facing drivers no larger than 55mm in diameter. Also, the internal volume has to be shared by the separate left and right channels and the internal woofer. The solution was to create three isobaric chambers (see side panel overleaf) using four 5cm (2in) drivers for the left & right channels (two each) and two 9cm (3.5in) drivers for the woofer, mounted horizontally. The use of isobaric chambers is critical because this halves the required internal volumes for a good low-­ frequency response. The double isobaric design enables good upper bass from the small L & R inner enclosures, leaving just enough space for an internal woofer, also in an isobaric configuration. The final design added 2.5cm (1in) Vifa tweeters to the 5cm and 9cm Vifa drivers, giving outstanding performance! The isoundBar has spectacular highs from its small tweeters and includes Bluetooth connectivity. A critical aspect of the drivers chosen is that we have checked that they are all available in reasonable quantities, and hopefully should remain available for some time after this article is published. The whole design is tri-amped, with separate amplifiers for the left and The isoundBar uses four TC6FD00-04 drivers (left), two TG9FD10-04 (centre) and two BC25SC55-04 tweeters (right). Not shown to scale 48  Silicon Chip Australia's electronics magazine siliconchip.com.au Fig.1: the frequency response of the isoundBar is quite smooth up to 20kHz (blue curve). It has a very acceptable bass response, which is significantly enhanced with the woofer (red curve) and even further by the optional subwoofer (green). While it might look like the subwoofer creates a bass peak, in practice it sounds good, with strong bass that isn’t boomy or annoying. right channels and the internal woofer. In fact, there is a total of five separate amplifiers: two for the left and right main drivers, two for the left and right tweeters and one for the woofer, each with a maximum output 50W RMS and each with its own volume control for balancing. To do this, I used a Yuanjing class-D 4.1 amplifier module, which I previously reviewed in the May 2019 issue (siliconchip.au/Article/11614). The module has three Texas Instruments TPA3116D2 high-efficiency class-D audio amplifier ICs with two 50W channels per IC. If you refer to that article, you will see that it dedicates one whole TPA3116D2 for the subwoofer channel to theoretically deliver 100W RMS. However, testing showed the actual maximum output to be closer to 60W. Nevertheless, we selected that module for its low cost and ease of use. It provides plenty of power to handle the vast dynamic range from modern signal sources such as streamed movies, CDs, DVDs, Blu-rays etc, with sufficient headroom before clipping. The sound quality is also pretty respectable for a low-cost class-D amplifier module. Many movie soundtracks feature realistic whispers and then instantly impose super-loud sounds from bombs, jets and vehicles, so you need a substantial dynamic range. Any clipping in the amplifiers could siliconchip.com.au Fig.2: total harmonic distortion for the isoundBar is generally less than 2% above 120Hz and well under 1% across much of the critical midrange. This is excellent when you consider that the amplifier’s distortion is much higher than most Silicon Chip amplifiers. It’s less than 10% down to 40Hz, which is exceptional for tiny 9cm (3.5-inch) drivers! quickly damage these little speakers, especially the small tweeters. So you need more power in reserve than you might think. These ICs also have short-circuit/ overload protection, over-voltage and under-voltage protection and are around 90% efficient. So they only need a tiny heatsink each and run from a 12-24V high-current plugpack, meaning no mains wiring is required. The tiny amount of heat generated means that special cabinet ventilation is unnecessary. This module also has a built-in Bluetooth receiver which activates a relay when pairing occurs. A signal can also be fed in via the onboard 3.5mm socket. The signal priority is set up to select whichever input is active first. If you require a bigger sound, we’ll also describe an external subwoofer output to interface with the subwoofer. As we said earlier, the sound has plenty of punch without it, but the subwoofer adds a whole new dimension and is required if you want an authentic hifi experience, or are just a bass fiend! the 60-80Hz region, and adding the external subwoofer extends it further, to about 35Hz. That might not ‘sound’ like the external woofer would make a big difference, but trust us, it does! The overall sound quality goes from good to great when you add the subwoofer. Still, the internal woofer is pretty good for watching ordinary TV programs. When you want to listen to music or watch a movie cinema-style, the extra bass is really worthwhile. Fig.2 shows the measured distortion Performance The frequency response of the system without the internal woofer and that of the woofer on its own are shown in Fig.1. Without the woofer, it has a pretty flat response from around 120Hz to 20kHz. Adding the woofer extends the bass response down to Australia's electronics magazine The optional sub adds plenty of bass and only measures 45 × 30 × 15cm. August 2022  49 What is an isobaric speaker? Two identical drivers are used with the isobaric box speaker design, but only one radiates sound. The other is coupled to the first one by a small sealed enclosure where the pressure remains constant as the speakers move in the same direction, by the same amount, at the same time – see Fig.3. Harry Olson invented this configuration in the 1950s. It uses speaker drivers (usually bass units) mounted in a sealed enclosure and driven in parallel or series to ensure they move in ‘lock step’. This configuration lowers the effective Vas by half. In other words, it effectively doubles the speaker enclosure volume and extends the bass frequency response beyond what would be possible for otherwise identical speakers in the same sized box. Although the power handling capability doubles, the efficiency and sound pressure level do not increase. The main disadvantage is the doubling of driver cost without a corresponding increase in sound output. Fig.3: the isobaric arrangement has two drivers connected in series, driven with the same signal. at one watt. Importantly, it’s quite low (below 1%) in most of the region between 150Hz and 3.5kHz, where the majority of the most critical sounds like the human voice and many instruments lie. That results in a clear sound with excellent dialog intelligibility. Layout and calculations Similar to what’s shown in Fig.3, the woofers are set up in an isobaric box in opposite positions. However, the cones are wired to move in the same direction. The sound output from underneath the drivers travels to the woofer port at the front, which is designed so that only a 32mm hole is required. There is no extended port tube, simplifying construction. This isoundBar uses Vifa/Peerless drivers throughout (Vifa and Peerless merged in 2000). The main left and right speakers are 5.5cm TC6FD00-04 drivers, with two 9cm TG9FD10-04 drivers as the woofers. All are available in Australia via Wagner Electronics (www.wagneronline.com.au). The majority of the sound from the soundbar comes from the four TC6FD00-04 drivers, two on each side. They are wired in series because the amplifier cannot handle the 2W load they would present if wired in parallel. These little speakers have a very smooth frequency response in the midrange, but lose a bit at the top end frequency due to their isobaric positioning, which damps them somewhat. Hence, the inclusion of one Vifa BC25SC55-04 25mm tweeter on either side. These tweeters are rated at 6W and are driven by a separate amplifier with its own volume control. They are mounted on the ends of the soundbar and are fed via 6.8μF capacitors. These add some nice treble which tends to bounce off the walls adjacent to your All drivers must be sealed with a selfadhesive foam weather stripping. TV room to create a spaced-out effect. Their cut-off frequency (-3dB point) is close to 4kHz due to the capacitor value. The volume control for these tweeters offers very easy adjustment of the amount of treble, which is especially useful for those with some HF hearing loss. Their independent amplifier also means that there is no interference with either the mid-range or the bass speakers, significantly reducing the overall distortion. Because of their natural roll-off at high frequencies, the main 5.5cm drivers do not need any choke, as would be the case in a typical speaker arrangement. This reduces the overall cost of the system. The woofers are wired in series for a total impedance of 8W and fed from the subwoofer channel of the class-D amplifier. The LEAP program predicts a -3dB point at 39Hz, although We mounted the drivers using 3mm nuts and bolts, although wood screws would work too. All gaps must be sealed with weather stripping or filled with silicone sealant. The woofer mounted to the mezzanine points downward while the one mounted to the top panel folds over and nestles neatly beside it. Make sure the wiring to the subwoofers does not interfere with the cones. 50  Silicon Chip Australia's electronics magazine siliconchip.com.au our Audio Precision measurements indicate a somewhat higher roll-off at around 55Hz. Still, this is quite impressive, considering the small space allocated and the low sensitivity of these drivers at 84dB/W <at> 1m. The woofers are rated at 10W, but with the two in series, we can drive them at up to 20W. The class-D amplifier subwoofer channel can deliver more than 50W; so the speakers will audibly distort well before the amplifier clips, so the voice coils should not overheat even if they are over-driven (within reason). The design includes a switchable output for driving an external passive subwoofer, and it can drive just about any speaker with an impedance of 4W or higher. The optional subwoofer presented later works very well when connected to this output. Soundbar construction The isoundBar is a fair bit more challenging to build than, say, our Concreto Loudpeaker System (June 2020; siliconchip.au/Article/14463), although, to be fair, it doesn’t get much simpler than the Concretos. Bear in mind that we have to jam everything into a relatively small box, and the result has to offer quality performance from small speakers. The more expensive hifi commercial soundbars also use pretty complex designs, which is part of the reason they are so costly. But if you DIY, you can eliminate a lot of that cost. As long as you work steadily, you will find that the construction is easier than it might look from the diagrams. In fact, the average DIYer should be able to build it using minimal power tools. The pieces of timber you need to cut and drill are shown in Figs.4 & 5, while the way they go together is shown in Fig.6. Start by cutting the pine boards into the required lengths, then cut the holes for the speakers and the ports with hole saws or a jigsaw. Next, assemble the outer frame by screwing and gluing the four outer pieces together, followed by the internal pieces. Drill small pilot holes for the screws, so they don’t split the timber. Fig.4: here are the larger panels you need to cut for the top, bottom, back and front of the isoundBar. The top and bottom are cut from 4mm ply, while the front and back are 19 × 64mm DAR pine. siliconchip.com.au Australia's electronics magazine August 2022  51 Fig.5: there are also 11 smaller panels to cut. The mezzo baffle is cut from 3mm MDF, while the other pieces are from 19 × 64mm or 12 × 40mm DAR pine. 52  Silicon Chip Australia's electronics magazine siliconchip.com.au Those who are more advanced at woodworking may prefer to use better joining techniques such as dovetailing, but whatever method you choose, make sure you keep the frame square. You can do this by clamping, or you can just nail a piece of scrap timber diagonally to keep it square until the glue dries. Next, build the woofer box and mount the timber strips flush with the bottom using screws and glue. Glue the mezzanine baffle to the side strips and then mount one of the 9cm speakers as shown. All drivers must be sealed with self-adhesive foam weather stripping, as previously shown. The next step is to mount the remaining drivers using timber screws into pilot holes, or nuts and bolts through 3mm holes drilled right through. Make sure you use the weather stripping because the whole arrangement needs to be airtight. Mount the tweeters in the holes on each side of the frame, then mount the second 9cm speaker to the hole in the top panel. Fill any gaps that air might be able to pass through using silicone sealant. For the amplifier panel, cut a piece of blank copper laminate or unclad FR4 and drill holes for the potentiometers, the power socket, the 3.5mm jack socket, the external subwoofer terminals and the selector switch. Paint it black, then screw and glue this panel to the rectangular cut-out at the back of the soundbar. Our prototype used 3mm nuts and bolts, although you could use self-tapping wood screws. Mount the class-D amplifier to the panel and then mount all the other ancillary sockets. Solder/attach the speaker wires as per the wiring diagram, Fig.7, and mount the amplifier in the soundbar. Once everything is in place, it is time to test it. You can either connect the 3.5mm input to an audio source (eg, via a 3.5mm stereo jack plug to 2 x RCA lead) or just pair your smartphone, tablet or another device via Bluetooth. The amplifier will simply select the source you choose. Run the unit at a low volume initially to avoid overloading the speakers before they are fully enclosed with the top and bottom panels. Ensure all the speakers are operating; dial in the tweeters slowly until you achieve enough volume to verify that they are working. Similarly, dial in the woofers last to ensure there are siliconchip.com.au Fig.6: a plan view of the isoundBar along with a detailed view of a crosssection of the woofer chamber. Australia's electronics magazine August 2022  53 no unwanted vibrations from their mounts. Once you are happy that all is good, cut the acoustic wadding into rectangular pieces that fit into each section and place them loosely inside. There is not enough room in the small woofer chamber, but fill the rest. You can then mount the bottom panel with screws or glue. We attached the top and bottom panels to our prototype using screws with thin weather stripping to seal it, so that we could easily open it up again to make changes during the development phase. Once the bottom panel is in place, you can seal the joins with a silicone caulking compound. Also seal the holes that wires pass through to ensure everything is airtight. Mounting the top panel can be a little tricky because the top woofer needs extra wire length (slack), and this needs to be carefully nestled inside the soundbar so that nothing touches the cones. It is a good idea to locate the top panel in position and hold it in place with weights, then test it out with an audio signal to ensure nothing interferes with the cones before permanently attaching it. Now screw and glue the top panel in place. Test everything again to ensure the soundbar gives a clean sound; then, you are ready to finish it off with grille cloth. We painted it black before covering it with speaker grille cloth for a ‘stealthy’ appearance, so you won’t notice it sitting under the TV. To do this, simply cut the grille cloth to the right size, wrap the soundbar, then glue it with a hot melt glue gun. You are now ready to enjoy some beautiful sound from your TV! Subwoofer construction As stated earlier, the isoundBar has punchy bass by itself but lacks the deep bass that makes sound super realistic for both movies and music listening. As this subwoofer doesn’t cost the earth to build, we highly recommend it as an add-on. Subwoofer design This little sub is really easy to build as a sealed enclosure and can be screwed or glued from 18mm melamine. Its slim design means it can easily be hidden from view. The class-D amplifier in the isoundBar can put out more than 50W RMS, so it will drive this mini-sub to generate pretty generous amounts of bass. The class-D amplifier (bottom right) is mounted to the back panel after the woofers are in place. Allow some slack in the wiring for easy removal or replacement of the drivers. Our prototype used felt weather stripping to seal the top and bottom panels, which were screwed on for easy access, but you can glue them instead. Fig.7: here’s how to wire up the various drivers to the amplifier module. Don’t forget the capacitors in series with the tweeters, or they could easily be damaged. 54  Silicon Chip Australia's electronics magazine siliconchip.com.au The selection of a driver for this subwoofer was inspired by the JBL Club WS1000, a 25cm (10in) speaker which has a really low resonance (26.62Hz) combined with a low VAS of 40.37L. This means you can achieve great bass in a little sealed box of around 15L; that’s tiny for a subwoofer that can reproduce such low bass! This driver cost us $148 (including shipping) at the time of building and comes with a full data sheet and brochure, plus a JBL sticker! The 18mm HMR melamine we used to build the cabinet was from an offcut we already had, the acoustic innerbond filling was also left over from other speaker projects, and the wire was also from the junk box, so it was a budget project. To make it look nice, we covered it with a 2mm-thick black felt carpet that’s explicitly sold for use with subwoofers, costing $19.99 for a 1m x 1m square. So the total cost to build the sub was just $168 in our case. Even if you have to buy all the materials new, you’re probably only looking at around $200. While the driver is powerful, it is also very shallow at 80mm deep, allowing for a very slim box design. An earlier JBL W10GTi MkII 25cm woofer we tried was 232mm deep, so JBL have made their designs significantly more compact over time! We tried using the W10GTi MkII as part of our Senator loudspeakers (May & June 2018; siliconchip. au/Series/300) but found it to be too expensive and heavy and not suitable for a slim enclosure. The new WS1000 design is much lighter and thinner, with an easier wiring system, yet it performs almost as well! This JBL driver was designed mainly for use in cars, so it has a “selectable smart impedance” (SSI) switch allowing it to present either a 2W or 4W impedance. For the isoundBar, the class-D amplifier is not suitable for driving a 2W load, so the 4W option is the one to use. JBL recommends a 14.15L sealed enclosure. They also have recommendations for larger ported enclosures, but the smaller sealed box is much easier to make and can be put together quickly. Subwoofer performance Parts List – isoundBar 2 Vifa/Peerless TG9FD10-04 9cm/3.5-inch drivers [Wagner Electronics] 4 Vifa/Peerless TC6FD00-04 5.5cm/2-inch drivers [Wagner Electronics] 2 Vifa/Peerless BC25SC55-04 2.5cm/1-inch tweeters [Wagner Electronics] 1 100 × 45cm piece of acoustic wadding [eg, www.ebay.com.au/itm/185046067357] 1 TPA3116D2-based class-D 4.1 amplifier module [eg, www.aliexpress.com/item/32911419084.html] 1 5m length of figure-8 medium-duty speaker cable 2 6.5-6.8μF 250V metallised polypropylene crossover capacitors [Jaycar RY6956] 1 24V 5A power ‘brick’ with DC barrel plug 1 panel-mount barrel socket to suit the power supply 1 panel-mount speaker connector [Jaycar PS1082] 4 knobs (to suit amplifier module; most likely fluted types) 1 bottle of wood glue 1 tube of neutral-cure silicone sealant Timber & hardware 3 1.24m length of 64 × 19mm DAR pine 1 1.24m length of 40 × 12mm DAR pine 1 2400 × 1200mm sheet of 19-20mm plywood 1 1240 × 900mm sheet of 4mm plywood 1 600 × 900mm sheet of 3mm MDF 1 5m roll of 9mm-thick, 9.5mm-wide grey closed-cell foam weather-seal tape [eg, Bunnings 0077668] 50 8G × 15mm button-head wood screws (for mounting drivers) OR 50 M3 × 25mm panhead machine screws with flat washers and hex nuts 50 7G × 30mm or 8G x 30mm countersunk head wood screws (for joining pieces) 20 small Nylon cable ties (P-clamps; optional) 4 M3 tapped Nylon standoffs & 6mm M3 machine screws (for mounting amp module) 1 300 × 100mm sheet of clad or unclad FR4 1 1m x 1.5m piece of dark speaker grille cloth [Jaycar CF2752] Parts for optional (but recommended) subwoofer 1 JBL Club WS1000 24cm/10-inch subwoofer driver [eBay] 1 100 × 45cm piece of acoustic wadding [eg, www.ebay.com.au/itm/185046067357] 1 1200 × 596mm (or larger) sheet of 18mm-thick plywood, MDF or similar 1 pair of panel-mount speaker terminals (optional) 1 1m+ length of heavy-duty twin loudspeaker wire (to suit installation) 8 8G x 15mm button-head wood screws (for mounting the driver) OR 8 M3 × 25mm panhead machine screws with flat washers and hex nuts 20 7G x 30mm or 8G x 30mm countersunk head wood screws (for joining pieces) 1 tube of neutral-cure silicone sealant external − Sub Sub O/P 12-24V DC CTR+ + internal Master Volume Tweeters Volume Front Volume Sub Volume 3.5mm input The control panel for the isoundBar. You might find it useful to make your own label so others can easily see what each connection does. The frequency response for our subwoofer is very smooth down to a very siliconchip.com.au Australia's electronics magazine August 2022  55 Fig.8: the subwoofer frequency response has a modest peak at around 65Hz and produces usable sound down to about 30Hz. It combines nicely with the isoundBar’s sound output and gives it more oomph! Fig.9: the subwoofer distortion plot. It might seem quite high, but subwoofers are notorious for having high distortion levels; around 2% in the middle of its range is actually quite decent. Fig.10: despite being nominally a 4W driver, the subwoofer impedance doesn’t dip below 5W, and its resonant peak is 25W at around 46.5Hz. 56  Silicon Chip Australia's electronics magazine respectable 30Hz, with a peak around 60Hz, as shown in Fig.8. The upper cut-off frequency can be as high as 300Hz, but the setting on our class-D amplifier is fixed at 150Hz (-6dB). That turns out to work quite well with this sub. As shown in Fig.9, distortion from the subwoofer is below 5% from around 35Hz to 120Hz. The higher distortion below 35Hz is due to the output level decreasing, while above 200Hz, it is due to the high moving mass of the driver. While 5% might sound high, it is a pretty clean response for a subwoofer, with low harmonics that are troublesome with many subwoofers. The final impedance of the JBL driver mounted in the little box shows an impressive resonance peak at 46.62Hz – see Fig.10. The speaker was set to 4W, but the actual measurements are higher, with a minimum of 5.3W at 83.1Hz, because of the added resistance of the speaker wire and the connectors. Construction Since this is a sealed enclosure, it is much easier to build than a ported design which would have been three times the volume as recommended by JBL. We used 18mm HMR melaminecoated particleboard, but any material at least 18mm thick is suitable, including plywood, timber or MDF. Remember that the finished enclosure must be airtight, so make sure you cut the pieces for a tight fit and seal all joints well with silicone sealant. Start by cutting the pieces as shown in Fig.11, then glue and screw the box together as shown in Fig.12. We fitted the front panel using foam weather stripping and screws so that we could open it up later if necessary. Given the simplicity of the sub, you could easily glue and screw it instead, like the rest of the box. Covering the sub Depending on the type of material you used to make the box, you can varnish it, paint it or cover it. We chose the last option and used a 1m x 1m piece of 2mm-thick black subwoofer felt fabric, attached using hot melt glue. You can use contact adhesive if you prefer. If you loosely wrap the bare speaker box, sausage-roll style, with a 1m-long siliconchip.com.au Fig.11: the subwoofer is a simple box made from six pieces, with only two holes that need to be made. 240mm hole saws are not that common, but you can trace the circle with a nail, pencil and string and then carefully cut it out with a jigsaw. siliconchip.com.au Australia's electronics magazine August 2022  57 The finished isoundBar (not to be confused with the bar it’s sitting on) is quite a large unit at over 1m long, so make sure you’ve got enough room to actually fit it! piece, it should overlap about 4cm at the back and extending at least 16cm past the top and bottom of the box Before starting, read the following instructions and ensure you understand them. The whole process has to be done fast, before the hot-melt glue sets. Ensure you use a decently-­sized hot melt glue gun and let it warm up fully before starting to give you as much time as possible. Check that it overlaps sufficiently, then use a hot melt gun to first glue down just one edge, at the back (top to bottom). Allow it to set, which will take a few seconds, then unwrap it to expose the bare box. Glue around the circumference of the speaker hole and quickly put a few stripes down the front and sides, then roll the carpet back around the wet glue. Tension it slightly and press the material around the front and sides and over the speaker, then tension it so that it overlaps at the back. Apply glue to the back and fold the carpet over, then press it down until dry. If all has gone well, you should be ready to affix the top and bottom. Cut the material at the top in line with the corners, then cut the side and back flaps to allow about 3cm overlap, but don’t cut the front flap yet. Glue down the sides and back flaps, then fold over the front flap, cut it to size and glue it down. Repeat this at the bottom, and the entire box should be covered, including the speaker hole. Using a sharp blade, cut out the speaker hole. Drill or cut a hole at the back for the speaker wire or terminals. Mounting the driver Start by checking that the driver is set for 4W operation. We soldered heavy gauge speaker wire to the JBL driver terminals, fed that through a 4mm hole at the back of the box and stuffed a 40 × 30cm piece of “innerbond” acoustic wadding The amplifier module is mounted to the back panel opening using blank PCB material, including the 3.5mm panel-mount line input jack. A selector switch for an optional external subwoofer and 12-24V barrel power socket is included. The banana sockets are for the external subwoofer. Keep all wiring secured using ties and silicone sealant to prevent unwanted vibrations. 58  Silicon Chip Australia's electronics magazine siliconchip.com.au Fig.12: the subwoofer box assembly is not difficult but make sure it’s properly sealed, and note that you’ll need more than the handful of screws shown here. loosely into the box. We then lowered the driver into place, sealing around the edges with an adhesive gasket, and attached it using wood screws. You could use speaker terminals, but making the wire captive is easier – there are terminals at the amplifier anyway. The only disadvantage of this approach is figuring out how much wire you need in advance. Either way, ensure the wire exit hole/terminals are sealed airtight. We filled the hole with silicone sealant. Remember to leave a bit of slack in the wiring inside the box in case you need to remove the driver later for inspection, repair or replacement. With the acoustic wadding sitting loosely in place, screw the driver firmly in place, and you are now ready to test it and run it in. Having already built and tested the isoundBar, you just need to switch it over to external subwoofer mode, connect the subwoofer wires to the appropriate terminals on the back and adjust the subwoofer level to match the rest of the system. Then you’re ready to rock and rumble! SC siliconchip.com.au We made our subwoofer out of some melamine-coated MDF kitchen cabinet cutouts. It doesn’t need to be pretty, just square, since the carpet covering hides the material it’s made of. Note the acoustic wadding and slack wiring. Australia's electronics magazine August 2022  59 Review by Phil Prosser DH30 MAX Li-ion Battery Welder It is a simple idea, and it should work well. How did it go so wrong? I was asked to review one of the Li-ion battery based welders that are cropping up on internet sites of late. Having just finished the Capacitor Discharge Spot Welder (March & April 2022; siliconchip.com.au/Series/379), my reaction was: why not? This might be a cost-effective alternative. So I proceeded enthusiastically. The prices of these welders seem to reflect the capacity of the battery used, which in practice consist of one or two cells paralleled inside the welder. That translates to costs broadly in the range of $50-100. As noted in the CD Welder article, one challenge battery-based welders face is getting enough energy into the weld quickly enough. So to be fair in this review, I chose a welder at the high end, the DH30 MAX, which claimed to have a 10.6Ah battery for about $100 plus shipping. After a relatively long wait (a bit over a month), it turned up, and I must say it both looked and felt the part. The case is 150 × 28 × 80mm and has substantial heft. It is an aluminium extrusion, and it is clearly packed full of batteries and stuff. Using it Plugging the welding cables in was a delight. I wish I knew where I could buy these connectors as they are great (shown below), and I would have been tempted to try fitting some to our CD Welder. I was initially bemused at how they were insulating that connector from the front panel (it is an unclad PCB). I will get into that more shortly. Also in the pack was a length of 0.12mm “nickel” strip and a USB charging cable. I had a prototype milliohm meter sitting on my bench (to be described in an upcoming issue), and I used it to quickly determine that the leads have a resistance of 1.5mW. This is consistent with 300mm-long 10 gauge (8mm2) leads. I noted that these leads are inconveniently short, even on the first weld. Checking the maths, though, they need to be short for the welder to work. The user interface is colourful but fiddly. It took me a little while to get it to do what I wanted. With the pack fully charged, I was off to the workshop and ran a couple of test welds on flat AA cells. Three welds in, and everything went pear-shaped. After the third weld, “magic smoke” started erupting from the welder case! With some concern about the device catching fire, I moved outside. A “minor” setback With a large coffee to calm my nerves, I reassured the wife that the house would clear of the acrid smoke. This was not going to plan! The DH30 MAX welder comes with the batteries installed into an aluminium enclosure. It has a rated welding output of 4.2V at 650A. Note that the charging port is USB Type-C. 60  Silicon Chip Australia's electronics magazine siliconchip.com.au ► The DHT30 MAX welder uses a 0.91inch OLED screen. I channelled the Serviceman and took to the case with screwdrivers and pliers. Having extricated the PCBs and lithium-ion cells from the box without shorting anything dangerous, the trail of smoke and cinders was something of a dead giveaway to the fault. Ignoring the minor fact that it blew up for the moment, I will provide some comments on the construction of the unit. The cells look the part for 10Ah, weigh enough and have very wide tinned connections to the ‘power board’. The actual part numbers have all been wiped off, but without running a capacity test, I assume they are up to the task. The controller PCB has a microcontroller with the top ground off, USB Type-A and Type-C connectors, the front panel control switch and OLED and two capacitive switches that use springs from the PCB to the display panel. The construction looks OK, if not excellent. This unit can double as a USB phone charger when not welding, which is handy. The ‘power board’ connects to the two Li-ion cells, the ‘control board’ via a header, the front panel and the welding lead connectors. It has four 4N03LR8 power Mosfets rated at 30V, 240A. They are quite appropriate for this job, though I would have been tempted to use more of them. The PCB layout has footprints for six smaller devices; I would rather see them all present, given the currents involved. There are a lot of vias on the power PCB, and for the most part, both sides of the board have large copper fills carrying the current with vias connecting between them on the top and bottom layers. The left side of the PCB has VBAT running up to the output connector. The right-hand side of the PCB carries GND, the battery negative terminal. This connects to all the Mosfet source pins, with the drain on the tabs connected to the “Out-” connector on the front panel. This switching method is the same concept used in my CD Welder, but on a baby scale. Take note of those vias running right down the right-hand side of the PCB; they are connected to GND. Repairs required I found that the PCB trace for VBAT had overheated and fused. The Mosfets were OK, as was the controller. All in all, it is a credible design except for the catastrophically narrow length of track on the left-hand side trying to carry 600A or so. After scraping the charred material and solder mask away, I soldered three lengths of copper braid (solder wick) over this section. Solder wick is nice and flat and can carry an awful lot of current. While doing this, I also noticed that the Mosfets were barely soldered to the The welder ‘blew’ up on both sides of the PCB, marked with red arrows. ► ► siliconchip.com.au Australia's electronics magazine August 2022  61 board. So I soldered down the floating pins while muttering many a salty oath along the lines of “you were so close to getting this right; what were you thinking?” With the sort of conviction that you can only have when something is about to go wrong, I started reassembling the unit. Halfway through the reassembly, I had a minor conniption. The only thing stopping a dead short across those beefy batteries was the solder resist on the PCB! Remember those vias (shown directly above)? They are actually inside the slots in the extrusion! My muttering turned to the question: “Are you for real? This will burn my house down!” To fix this, I took my trusty Dremel and ground back the VBAT fill up to the solder braid I had added, giving a gap of about 0.5mm between the case extrusion and the VBAT trace. I allowed the GND side to touch the case since that would no longer be harmful. some more measurements and got the following readings: • 2.5mW from the positive battery tab to the tip of the positive probe • 1.5mW from the drain of the Mosfets to the tip of the negative probe • the Mosfet specification is 0.79mW each with VGS = 4.5V, or about 0.2mW for four in parallel • the resistance from the negative battery tab to the Mosfet sources is about 1mW This gives a total of 5.5mW or so, resulting in 650A into a short circuit. This jibes with the spec on the box. For a 200ms pulse, this would be in the region of 400J. The problem is that little of that goes into the workpiece, as that is counted as 0W in this calculation. Basically, the workpiece needs to have a resistance of at least 5.5mW between the probe tips to get even half of that energy into it, and ideally considerably more for it to take the bulk of the energy. During tests, the leads got quite warm after half a dozen welds or so, as did the tips. As you can see in the photos, while I made reasonable welds, there was significant heating around the weld spot. Is it worth it? I guess the main question is: can you use it to make good welds? A decent weld to an AA cell is shown opposite. I did that in gear 13. I found that was the minimum to get a reliable weld that would not pull off easily. But that put a lot of heat into the battery. I welded three times in succession on one battery and literally melted the plastic insulation. So you need to be very careful using this welder! So, in summary, does it work? Yes, Back to the review With that done and everything buttoned back up, it was back to the task at hand: reviewing this comedy of errors. I took a more gingerly approach, starting with a 3W resistor and testing the welder in “gear 1” through “gear 20”. These equate to power levels, which are implemented by variable pulse widths of 26ms to 300ms (see Scope 1). Using levels up to about gear 8-10 gave unreliable welds with the strip they provided. I achieved decent welds in gears 11-13. The welds were OK, but because of the 200ms weld time, things got really hot making them. To check if this made sense, I did 62  Silicon Chip Scope 1: a scope grab of the output at the “gear 11” setting. I found this gave OK welds; the pulse width is 182ms. There are a couple of short pulses at the start, which are present on all settings. Australia's electronics magazine siliconchip.com.au this device will weld after significant repairs. Is it reliable? For welding, I would give a qualified answer. It can weld, but puts a lot of heat into your workpiece. So it depends on your application. I would be very cautious using it to weld anything very sensitive, like Li-ion cells. Will it remain reliable? This device is marginal. Other similar devices could be better. The Mosfets are OK on spec; however, the manufacturing had several serious flaws. Also, an increase of a milliohm or two in battery impedance would severely impact weld quality, and that could easily happen over time or with use. I would recommend the DH30 MAX only to technically confident people willing to check it thoroughly before use, and only if you intend to undertake small/non-professional jobs. There is a world of difference between this and my CD Welder design, in terms of weld repeatability and heat in the workpiece. Granted, there is a significant price difference. I’d like to comment on how I think that the design flaws in this unit came about. My day job is in engineering in Defence, where “engineering governance” is an integral part of life. It is tedious, but it is there for good reasons! This device has all the hallmarks of a design that was originally very good, relatively simple and fit for purpose in its original embodiment. Looking at the problems I found, my guess is: • The packaging was changed and, in this process, somebody neglected to check the VBAT and GND trace clearances to the case extrusion slots. I imagine this was done by a different person than the original designer, and they didn’t even think to check. • The PCB manufacturing was cost-optimised, perhaps too much so. Six devices were reduced to four. Looking at the solder mask, it actually extends under the four Mosfet source tabs! It is hard to see the original designer finding this acceptable, but I doubt they reviewed this change. • The PCB uses lightweight copper foil. It is much cheaper to use this than heavier (eg, 2oz) copper – again, a change that I suspect occurred in manufacturing without return to design and qualification. • Someone had reworked all the Mosfets, but only fixed soldering on two of the five pins. This procedure would never get past a review or the original designer; doing it right would take a second or two extra! Also, the need for rework is indicative of a deeper manufacturing problem. All these faults could be fixed at marginal or nil cost. They might even get away with the lightweight foil with a better PCB layout. As it stands, each of these faults could lead to catastrophic failure. Therefore, I recommend that you avoid purchasing this particular unit (and be wary of other similar units) unless you will personally open it up and check that it is safe to use before powering it up. I must also admit that I have a bit of concern that one of these could go up in smoke during transportation, depending on how it is handled, given the proximity of those ‘live’ vias to the SC metal case. Improved SMD Test Tweezers Complete Kit for $35 Includes everything pictured (now comes with tips!), except the lithium button cell. ● ● ● ● ● ● Resistance measurement: 10W to 1MW Capacitance measurements: ~10pF to 150μF Diode measurements: polarity & forward voltage, up to about 3V Compact OLED display readout with variable orientation Runs from a single lithium coin cell, ~five years of standby life Can measure components in-circuit under some circumstances siliconchip.com.au SC5934: $35 + postage siliconchip.com.au/Shop/20/5934 Australia's electronics magazine August 2022  63 By Arijit Das SPY-DER A 3D-PRINTED DIY ROBOT SPY-DER is a speech and web-controlled surveillance spider robot. It walks like a spider and acts as a spy using its camera, hence the name “SPY-DER”. The best aspect of it is that you can make it yourself using some 3D-printed parts, a bunch of servos and some low-cost off-the-shelf electronic modules! Y OU CAN CONTROL THIS ROBOT IN TWO WAYS — USING VOICE COMMANDS OR ITS WEB-BASED CONTROL INTERFACE. For example, I have nicknamed mine “Bumblebee”. Whenever I call it by that name, it starts listening to me, and it will then act on voice commands. I am using two main technologies to enable this: hot-word or wakeword detection and speech recognition. The speech recognition also involves intent detection, so that I can give it the same command in different ways. For example, if I say “wave your hands” or “say hello”, either way, it will wave its legs. For the web control part, one can simply open a particular URL in any browser and use it to control the SPY-DER. The web-based interface contains all the control options as buttons. You can open another URL to watch the live video feed from this robot’s camera. You can see a short demonstration video that shows what SPY-DER can do at https://youtu.be/3edXTxIZ_2U 64  Silicon Chip Developing SPY-DER Initially, I built a simple Bluetooth-controlled spider robot using an Arduino Nano, but it could only be controlled using an Android or iOS app. Thus, I added speech recognition, web control and surveillance features. Implementing all these features using an Arduino was impossible; I needed a small computer. That’s why I decided to add the Raspberry Pi Zero. The whole system could have been implemented using just the Raspberry Pi Zero, but it would be too time-consuming to rewrite all the spider movement control code. So I decided to keep the Arduino and add the Raspberry Pi and have them communicate over a serial link. The Arduino controls all the spider’s movements while the Raspberry Pi sends commands to the Arduino. This also means that I don’t have to worry about the Raspberry Pi being so busy doing speech recognition that it loses control of the limbs! Australia's electronics magazine siliconchip.com.au Fig.1: this diagram shows all the wiring required for the SPY-DER robot. The order in which the servos are connected is important; see Fig.2, and note that the wire colour coding can vary between models. Also, be careful to check the labelling on the other modules as they might not precisely match what we’ve shown. All the Raspberry Pi code is written in Python. For the web-based control part, I used the Flask framework and built the web page using HTML, CSS and jQuery. For the live video streaming, I used RPi-Cam-Web-Interface (see https://elinux.org/RPi-Cam-Web-Interface) because it has very low latency. For speech recognition and hot word detection, I used Picovoice (https://picovoice.ai/) and modified the code in Python. I tried using local speech recognition, but as the RAM and processing power of the Raspberry Pi Zero is very limited, the accuracy was not that good, and the latency was also very high. The physical robots parts are based on an existing robot that I found at thingiverse.com/thing:2901132 (but it has since been removed). I redesigned a few parts in TinkerCAD (www.tinkercad. com/) and made all of the relevant parts available online at thingiverse.com/thing:4815137 I 3D-printed all those parts siliconchip.com.au using an Ender 3 3D printer (see Photos 1 & 2). Starting assembly If you prefer to watch a video, I have made a video just over one hour long going over the project in detail at https:// youtu.be/KkZiZggtvIU which is definitely worth watching before you start assembly. Also see the parts list later in the article for what you will need to build it. I have created another video just under 30 minutes long that concentrates on the steps for building SPY-DER, which you can view at https://youtu.be/fnMmnd9k6q8 Step 1 – 3D printing the parts First, if you haven’t already done so, print all the 3D parts that make up the robot. Step 2 – attach the servo motors Next, you need to attach the twelve SG90 servo motors Australia's electronics magazine August 2022  65 #1 #2 using M2 screws, as shown in Photos 3 & 4. Four of the 12 servo motors connect to the body while the other eight connect to the legs. Attach them with screws, but don’t add the ‘horns’ yet. Plastic gear servo motors are used for this project as the robot is pretty light. I have some details on attaching the servos, along with the following Steps 3, 4, 5 & 6 in the video at https://youtu. be/fnMmnd9k6q8 shield. While attaching the servo motors, make sure you have attached them according to the numbering shown in Figs.1 & 2 and with the black wires to the side marked “G” (for ground). The I/O shield also needs to be wired up to the power supply which powers the servo motors and the Arduino. Make sure the power switch is off when you connect it. Photo 7 shows what the Nano looks like once placed inside the robot’s body. Step 3 – join the body parts Step 6 – servo calibration Then connect all the 3D-printed body parts through the servo motors – see Fig.2. Don’t attach the horns just yet. Step 4 – connect the battery and BMS As the power requirements of the 12 servo motors are pretty high, I used two 18650 Li-ion cells in series. The Arduino, servo motors and Raspberry Pi all require a 5V DC supply. An LM2596 buck converter is used to convert the 7-8V output of the battery to a regulated 5V, which is then fed to all the components. For safety, a battery management system or BMS is also used. Fig.1 shows how these parts are connected, including some other parts we’ll get to shortly. Make sure that when you join these, it can still fit within the robot’s body, as inserting it is the next step. Photo 5 shows how I wired these parts up (including the on/off toggle switch), while Photo 6 shows it installed in the robot body. Note how the servo power/control leads have been fed into the main cavity. Now you need to upload the code to the Arduino Nano. The code is available to download from https://github.com/ Arijit1080?tab=repositories (a copy of this is also available from the Silicon Chip website). The first step is to calibrate the robot legs. The program to do this is in the “Legs” folder (named “legs.ino”). Before calibrating the servo motors, check that their connections are correct and they are appropriately powered. After running the legs.ino calibration sketch, screw the horns that hold the legs to the body. Step 7 – initial functional testing First, plug the Arduino Nano into the socket on the Prototype Shield – make sure it’s the right way around. Next, plug all the servo motors into the headers on the I/O To check the basic functionality of the robot, there is another Sketch named “program1.ino” in the program1 folder of the GitHub repository. After uploading this, when you power the robot up, it will automatically start testing all the features in the following order: • Stand up • Move forward • Move backwards • Move left • Move right • Hand wave • Dance #5 #6 Step 5 – setting up the Arduino 66  Silicon Chip Australia's electronics magazine siliconchip.com.au #3 #4 Any deviations from the above movements need to be checked as they suggest an incorrect connection or component that is not working correctly etc. To know more about this and the last step, you can watch my videos. Arduino with the 3.3V I/Os on the Raspberry Pi. The Arduino connects to the 5V (“HV”) side of the level shifter while the Pi goes to the 3.3V (“LV”) side. I have a general video about using a level shifter like this for serial communication between different boards at https://youtu.be/e04br5J4UpQ To connect a microphone to the Raspberry Pi Zero, there are three options: 1) Connecting a USB microphone using an OTG cable 2) Connect a microphone with a 3.5mm jack plug using a Raspberry Pi sound card and OTG cable 3) Using a Raspberry Pi audio hat. I suggest you connect a USB microphone using an OTG cable as I did. The Raspberry Pi supports most standard USB microphones. For the camera, use a standard Raspberry Pi camera (www.raspberrypi.com/products/camera-module-v2/) and plug it in as per the instructions. I have a video on using the Raspberry Pi Camera with a Raspberry Pi Zero at https:// youtu.be/oo0A_yRrIxQ Step 8 – uploading the final Arduino code Now you can upload the final code to the Arduino. This will work with the Raspberry Pi. The code is available from siliconchip.com.au/link/abd3 (and the Silicon Chip website). Upload the “SPY-DER_Arduino.ino” file to the Arduino. This program takes commands from Raspberry Pi and acts accordingly. Step 9 – preparing the Raspberry Pi Start by installing the latest version of the Raspbian operating system on the Raspberry Pi. You can use SSH or a direct HDMI connection while working with the Raspberry Pi. Step 10 – Raspberry Pi microphone & camera The Raspberry Pi needs to have the mic, camera and logic level shifter attached, as shown in Photo 8. This logic level shifter is needed to interface the 5V Step 11 – setting up the Raspberry Pi The remaining setup steps are as follows: Fig.2: match these servo numbers up with the connections shown in Fig.1. siliconchip.com.au Australia's electronics magazine August 2022  67 #7 #8 1) Set up VNC Connect on the Raspberry Pi so that you can remotely access and control it from your computer. 2) Switch on the camera in the settings or use raspi-­config from the command line. Check that the camera works; RaspiStill can be used to test it. 3) Enable the microphone and then test recording from the terminal. You might need to modify the “.asoundrc” file to set up the mic. 4) Test serial communications between the Raspberry Pi and Arduino. 5) Clone all the code from my GitHub repo (siliconchip. com.au/link/abd3) onto the Raspberry Pi (say, into the home folder). 6) Clone the Picovoice (https://picovoice.ai/) repository from https://github.com/Picovoice/picovoice and then launch the Picovoice program in my GitHub repository (see the README file). 7) Install RPi-Cam-Interface for video streaming. You can get it from https://elinux.org/RPi-Cam-Web-Interface and see the video at https://youtu.be/yzpqEw1kEGo for more details 8) Train the Rhino speech-to-intent model so that for a single task, you can use different commands; Rhino is contained in the Picovoice repository. To train the model, open a web browser and go to https:// console.picovoice.ai/rhn and input different kinds of commands and their intentions – see Screen 1. Depending on the intentions you use here, you need to change the “picovoice_demo_mic.py” file. After writing down all the commands and intents, follow the prompts on the webpage to train the model by using the microphone, then upload the trained model to the Raspberry Pi. 9) For web control, you need to install the Flask framework in Python; all the Python & HTML files are in my repository. Step 12 – finishing the build & controlling the robot Fit everything inside the body (Photo 9) and glue the microphone and camera into the holes provided in the lid (Photo 10). Attach the lid, power it up and then use VNC to connect to the Raspberry Pi wirelessly from your computer. Photo 11 shows the completed robot with the lid attached. To start the web control interface, open a console inside the SPY-DER GitHub repository root folder and enter the following commands: cd web_control python3 web_control.py After running these commands, you can access the web control interface from any browser using the URL http://<raspberry_pi_ip_address>:5010 (insert the current IP address of your Raspberry Pi) – see Screen 2. From here, the robot can be controlled using all those buttons. You can modify the control interface by changing the code in the “web_control” folder. Step 13 – Speech control Go into the “picovoice” folder to run the speech control system. There are three files there you will need. The first one is the main code file named “picovoice_demo_mic. py”. Modify this code according to your speech to text model training. The next file needed is the porcupine keyword file. This is the keyword that you will use to call the robot. There are many pre-trained files available in the Picovoice repository. You can choose any of the keywords to use as your robot’s wake word. #11 68  Silicon Chip Australia's electronics magazine siliconchip.com.au #9 #10 Finally, you need the speech-to-text model, which you have already trained and downloaded. Then you can run the code with these two files using the following commands: cd picovoice python3 demo/python/picovoice_demo_mic.py \ --keyword_path resources/porcupine/resources/ keyword_files/raspberry-pi/bumblebee_raspberrypi.ppn \ --context_path your_rhino_model In this example command, I have used “bumblebee_raspberry-pi.ppn” as the keyword file, so “bumblebee” is the wake word for my robot. Step 14 – Video streaming You can enable live video streaming either using voice commands or the web control interface. After turning on the live video surveillance, to access it, open the URL http://<raspberry_pi_ip_address>:80 in a web browser. Conclusion & future improvements There is plenty of room for modifications to this project. For example, if a local speech recognition system could be designed that would perform well on a Raspberry Pi, that would speed up its response to voice commands and remove the need for an internet connection. Snow-boy hot-word detector is an open-source hot-word detector that works pretty well on the Raspberry Pi. It provides several image processing features like object detection, face recognition etc. It could potentially be added to this project. Maybe I will upgrade it in the future! SC Parts List – SPY-DER Robot 3D printed robot parts 1 Arduino Nano microcontroller module 1 Raspberry Pi Zero W embedded computer 1 Raspberry Pi camera 1 5V to 3.3V logic-level shifter [AliExpress siliconchip.au/link/abdk] 1 Nano 3.0 Prototype Shield [AliExpress siliconchip.au/link/abdl] 12 SG90 mini servo motors [AliExpress siliconchip.au/link/abdm] 1 LM2596-based buck converter module [Silicon Chip Cat SC4916] 1 Lithium-ion 2S battery (nominally ~7.4V) [eg, from Hobby King or two 18650 Li-ion cells in series] 1 Li-ion 2S battery management system 1-2 bright LEDs (eg, 5mm blue types, for eyes) 1-2 current-limiting resistors for LEDs (eg, 220W 1/4W) 1 USB microphone 1 USB OTG Micro-B cable or adapter 1 SPST/SPDT switch (eg, toggle or slide) rated 5A DC 4 M2 x 50mm machine screws and nuts 1 pack of DuPont jumper wires (mostly short femalefemale types) 36 No.2 x 6mm self-tapping screws (may be included with servos) various lengths and colours of medium-duty hookup wire ► Screen 1: the Picovoice Rhino training console. Here you can teach it how you say the different words that you will later use to control the robot. You’ll need to sign up for an account on the Picovoice website to allow you to do this. Screen 2: the SPY-DER web ► control interface is quite simple, and all the functions of the buttons are pretty obvious. This works in parallel with voice control, assuming you have voice control up and running. siliconchip.com.au Australia's electronics magazine August 2022  69 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. 08/22 YES! You can also order or renew your Silicon Chip subscription via any of these methods as well! The best benefit, apart from the magazine? Subscribers get a 10% discount on all orders for parts. PRE-PROGRAMMED MICROS For a complete list, go to siliconchip.com.au/Shop/9 $10 MICROS $15 MICROS 24LC32A-I/SN ATmega328P ATmega328P-AUR ATtiny85V-10PU ATtiny816 PIC10F202-E/OT PIC10LF322-I/OT PIC12F1572-I/SN PIC12F617-I/P Digital FX Unit (Apr21) Si473x FM/AM/SW Digital Radio (Jul21), 110dB RF Attenuator (Jul22) RGB Stackable LED Christmas Star (Nov20) Shirt Pocket Audio Oscillator (Sep20) ATtiny816 Development/Breakout Board (Jan19) Ultrabrite LED Driver (with free TC6502P095VCT IC, Sep19) Range Extender IR-to-UHF (Jan22) LED Christmas Ornaments (Nov20; versions), Nano TV Pong (Aug21) Refined Full-Wave Universal Motor Speed Controller (Apr21) Model Railway Level Crossing (two required – $15/pair) (Jul21) Range Extender UHF-to-IR (Jan22) PIC12F617-I/SN Model Railway Carriage Lights (Nov21) PIC12F675-I/P Motor Speed Controller (Mar18), Heater Controller (Apr18) Useless Box IC3 (Dec18) PIC12F675-I/SN Tiny LED Xmas Tree (Nov19) PIC16F1455-I/P Digital Interface Module (Nov18), GPS Finesaver (Jun19) Digital Lighting Controller LED Slave (Dec20) PIC16F1455-I/SL Ol’ Timer II (Jul20), Battery Multi Logger (Feb21) PIC16F1459-I/P 20A DC Motor Speed Controller (Jul21) Fan Controller & Loudspeaker Protector (Feb22) Secure Remote Mains Switch Receiver (Jul22) PIC16F1459-I/SO Multimeter Calibrator (Jul22) PIC16F15214-I/SN Improved SMD Test Tweezers (Apr22) PIC16F1705-I/P Flexible Digital Lighting Controller Slave (Oct20) Digital Lighting Controller Translator (Dec21) PIC16LF15323-I/SL Secure Remote Mains Switch Transmitter (Jul22) ATSAML10E16A-AUT PIC16F18877-I/P PIC16F88-I/P High-Current Battery Balancer (Mar21) USB Cable Tester (Nov21) UHF Repeater (May19), Six Input Audio Selector (Sep19) Battery Charge Controller (Dec19 / Jun22) Railway Semaphore (Apr22) PIC24FJ256GA702-I/SS Wide-Range Ohmmeter (Aug22) PIC32MM0256GPM028-I/SS Super Digital Sound Effects (Aug18) PIC32MX170F256D-501P/T 44-pin Micromite Mk2 (Aug14), 4DoF Simulation Seat (Sep19) PIC32MX170F256B-50I/SP Micromite LCD BackPack V1-V3 (Feb16 / May17 / Aug19) RCL Box (Jun20), Digital Lighting Controller Micromite Master (Nov20) Advanced GPS Computer (Jun21), Touchscreen Digital Preamp (Sep21) PIC32MX170F256B-I/SO Battery Multi Logger (Feb21), Battery Manager BackPack (Aug21) PIC32MX270F256B-50I/SP ASCII Video Terminal (Jul14), USB M&K Adaptor (Feb19) $20 MICROS ATmega644PA-AU PIC32MX470F512H-I/PT PIC32MX470F512H-120/PT PIC32MX470F512L-120/PT PIC32MX795F512H-80I/PT AM-FM DDS Signal Generator (May22) Stereo Echo/Reverb (Feb 14), Digital Effects Unit (Oct14) Micromite Explore 64 (Aug 16), Micromite Plus (Nov16) Micromite Explore 100 (Sep16) Touchscreen Audio Recorder (Jun14) dsPIC33FJ64MC802-E/SP dsPIC33FJ128GP306-I/PT 1.5kW Induction Motor Speed Controller (Aug13) CLASSiC DAC (Feb13) $25 MICROS $30 MICROS PIC32MZ2048EFH064-I/PT DSP Crossover/Equaliser (May19), Low-Distortion DDS (Feb20) DIY Reflow Oven Controller (Apr20), Dual Hybrid Supply (Feb22) KITS, SPECIALISED COMPONENTS ETC WIDE-RANGE OHMMETER (CAT SC4663) (AUG 22) VGA PICOMITE KIT (CAT SC6417) (JUL 22) MULTIMETER CALIBRATOR KIT (CAT SC6406) (JUL 22) 110dB RF ATTENUATOR SHORT-FORM KIT (CAT SC6420) (JUL 22) BUCK-BOOST LED DRIVER KIT (CAT SC6292) (JUN 22) Partial Kit: Includes the PCB, programmed micro, all SMDs, most semiconductors, PPS capacitors and calibration resistors $75.00 - 16x2 alphanumeric LCD with blue backlighting (Cat 5759) $10.00 Includes the PCB, programmed micro, OLED and all other on-board parts Complete kit with everything needed to assemble the board SPECTRAL SOUND MIDI SYNTH KIT (CAT SC6261) Complete kit including all programmed PICs (no case or power supply) (JUN 22) SLOT MACHINE (MAY 22) 500W AMPLIFIER HARD-TO-GET PARTS (CAT SC6019) (APR 22) IMPROVED SMD TEST TWEEZERS KIT (CAT SC5934) (APR 22) RASPBERRY PI PICO BACKPACK KIT (CAT SC6075) (MAR 22) CAPACITOR DISCHARGE WELDER (MAR 22) - Micromite Plus BackPack kit without touchscreen (Cat SC6211) - DFPlayer Mini module (Cat SC4789) - Set of laser-cut 3mm acrylic pieces for front panel & coin slot (Cat SC6181) (FEB 22) $75.00 SMD TRAINER COMPLETE KIT (CAT SC5260) (DEC 21) $80.00 USB CABLE TESTER KIT (CAT SC5966) (NOV 21) $200.00 MICROMITE LCD BACKPACK V3 KIT (CAT SC5082) (AUG 19) $45.00 $45.00 $5.00 $10.00 All the parts marked with a red dot in the parts list, including the 12 output transistors, driver transistors, VAS transistors, input pair (2SA1312), BAV21 & UF4003 diodes, TL431 ICs, 75pF capacitor, E96 series resistors and 10kW 1W resistor $200.00 Complete kit with PCBs, all onboard parts, new microcontroller and gold-plated header pins to use for the tips. Does not include a lithium coin cell $35.00 Complete kit, includes all parts except the optional DS3231 IC Parts for the ESM – includes one ESM PCB, IC8, Q3 & Q4 (IRFB7434G), D9 plus the SMD capacitors and resistors (Cat SC6225) → 8-14 sets typically needed $20.00ea INTELLIGENT DUAL HYBRID POWER SUPPLY Complete kit with everything needed to assemble the board, you just require a few external parts such as a power supply, keyboard and monitor $35.00 Complete kit with everything needed to assemble the board siliconchip.com.au/Shop/ $80.00 Parts for the Power Supply – includes the power supply PCB, IC1-3, D1, the 1W shunt and sole SMD capacitor (Cat SC6224) $25.00 Hard-to-get parts for the regulator module – all the ICs & regulators ◉ needed to build one module, plus the schottky diode, 10μH inductor, 4700μF 50V capacitors, 1W shunts and SMD capacitors – does not include PCB (Cat SC6096) $125.00 ◉ does not include the LM2575T as it comes with the CPU module parts Hard-to-get parts for the CPU module – most of the required parts, including PIC32MZ, EEPROM, LM2575T, LM317 & LD1117V regulators etc. You just need the PCB, headers, a ferrite bead, trimpot and electrolytic capacitors (Cat SC6121) $60.00 Includes PCB & all on-board components, except for a TQFP-64 footprint device Short form kit with everything except case and AA cells $20.00 $110.00 Includes PCB, programmed micros, 3.5in touchscreen LCD, UB3 lid, mounting hardware, Mosfets for PWM backlight control and all other mandatory on-board parts $75.00 Separate/Optional Components: - 3.5-inch TFT LCD touchscreen (Cat SC5062) $35.00 - DHT22 temp/humidity sensor (Cat SC4150) $7.50 - BMP180 (Cat SC4343) OR BMP280 (Cat SC4595) temp/pressure sensor $5.00 - BME280 temperature/pressure/humidity sensor (Cat SC4608) $12.50 - DS3231 real-time clock SOIC-16 IC (Cat SC5103) $7.50 - 23LC1024 1MB RAM (SOIC-8) (Cat SC5104) $6.00 - AT25SF041 512KB flash (SOIC-8) (Cat SC5105) $1.50 - 10µF 16V X7R through-hole capacitor (Cat SC5106) $2.00 - MCP1700 3.3V LDO regulator (suitable for USB M&K Adapator, Feb19) $2.00 VARIOUS MODULES & PARTS - 70W LED panel (cool white, SC6307 | warm white, SC6308) - 0.96in SSD1306-based yellow/blue OLED (AM-FM DDS, May22, SC6421) - Pulse-type rotary encoder (AM-FM DDS, May22, SC5601) - DS3231 real-time clock SOIC-16 IC (Pico BackPack, Mar22) - DS3231MZ real-time clock SOIC-8 IC (Pico BackPack, Mar22) $19.50 $10.00 $3.00 $7.50 $10.00 *Prices valid for month of magazine issue only. All prices in Australian dollars and include GST where applicable. # P&P prices are within Australia. Overseas? Place an order on our website for a quote. PRINTED CIRCUIT BOARDS & CASE PIECES PRINTED CIRCUIT BOARD TO SUIT PROJECT GPS SPEEDO/CLOCK/VOLUME CONTROL ↳ CASE PIECES (MATTE BLACK) RASPBERRY PI SPEECH SYNTHESIS/AUDIO BATTERY ISOLATOR CONTROL PCB ↳ MOSFET PCB (2oz) MICROMITE LCD BACKPACK V3 CAR RADIO DIMMER ADAPTOR PSEUDO-RANDOM NUMBER GENERATOR 4DoF SIMULATION SEAT CONTROLLER PCB ↳ HIGH-CURRENT H-BRIDGE MOTOR DRIVER MICROMITE EXPLORE-28 (4-LAYERS) SIX INPUT AUDIO SELECTOR MAIN PCB ↳ PUSHBUTTON PCB ULTRABRITE LED DRIVER HIGH RESOLUTION AUDIO MILLIVOLTMETER PRECISION AUDIO SIGNAL AMPLIFIER SUPER-9 FM RADIO PCB SET ↳ CASE PIECES & DIAL TINY LED XMAS TREE (GREEN/RED/WHITE) HIGH POWER LINEAR BENCH SUPPLY ↳ HEATSINK SPACER (BLACK) DIGITAL PANEL METER / USB DISPLAY ↳ ACRYLIC BEZEL (BLACK) UNIVERSAL BATTERY CHARGE CONTROLLER BOOKSHELF SPEAKER PASSIVE CROSSOVER ↳ SUBWOOFER ACTIVE CROSSOVER ARDUINO DCC BASE STATION NUTUBE VALVE PREAMPLIFIER TUNEABLE HF PREAMPLIFIER 4G REMOTE MONITORING STATION LOW-DISTORTION DDS (SET OF 5 BOARDS) NUTUBE GUITAR DISTORTION / OVERDRIVE PEDAL THERMAL REGULATOR INTERFACE SHIELD ↳ PELTIER DRIVER SHIELD DIY REFLOW OVEN CONTROLLER (SET OF 3 PCBS) 7-BAND MONO EQUALISER ↳ STEREO EQUALISER REFERENCE SIGNAL DISTRIBUTOR H-FIELD TRANSANALYSER CAR ALTIMETER RCL BOX RESISTOR BOARD ↳ CAPACITOR / INDUCTOR BOARD ROADIES’ TEST GENERATOR SMD VERSION ↳ THROUGH-HOLE VERSION COLOUR MAXIMITE 2 PCB (BLUE) ↳ FRONT & REAR PANELS (BLACK) OL’ TIMER II PCB (RED, BLUE OR BLACK) ↳ ACRYLIC CASE PIECES / SPACER (BLACK) IR REMOTE CONTROL ASSISTANT PCB (JAYCAR) ↳ ALTRONICS VERSION USB SUPERCODEC ↳ BALANCED ATTENUATOR SWITCHMODE 78XX REPLACEMENT WIDEBAND DIGITAL RF POWER METER ULTRASONIC CLEANER MAIN PCB ↳ FRONT PANEL NIGHT KEEPER LIGHTHOUSE SHIRT POCKET AUDIO OSCILLATOR ↳ 8-PIN ATtiny PROGRAMMING ADAPTOR D1 MINI LCD WIFI BACKPACK FLEXIBLE DIGITAL LIGHTING CONTROLLER SLAVE ↳ FRONT PANEL (BLACK) LED XMAS ORNAMENTS 30 LED STACKABLE STAR ↳ RGB VERSION (BLACK) DIGITAL LIGHTING MICROMITE MASTER ↳ CP2102 ADAPTOR BATTERY VINTAGE RADIO POWER SUPPLY DUAL BATTERY LIFESAVER DIGITAL LIGHTING CONTROLLER LED SLAVE BK1198 AM/FM/SW RADIO MINIHEART HEARTBEAT SIMULATOR I’M BUSY GO AWAY (DOOR WARNING) DATE JUN19 JUN19 JUL19 JUL19 JUL19 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 PCB CODE Price 01104191 $7.50 SC4987 $10.00 01106191 $5.00 05106191 $7.50 05106192 $10.00 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 For a complete list, go to siliconchip.com.au/Shop/8 PRINTED CIRCUIT BOARD TO SUIT PROJECT BATTERY MULTI LOGGER ELECTRONIC WIND CHIMES ARDUINO 0-14V POWER SUPPLY SHIELD HIGH-CURRENT BATTERY BALANCER (4-LAYERS) MINI ISOLATED SERIAL LINK REFINED FULL-WAVE MOTOR SPEED CONTROLLER DIGITAL FX UNIT PCB (POTENTIOMETER-BASED) ↳ SWITCH-BASED ARDUINO MIDI SHIELD ↳ 8X8 TACTILE PUSHBUTTON SWITCH MATRIX HYBRID LAB POWER SUPPLY CONTROL PCB ↳ REGULATOR PCB VARIAC MAINS VOLTAGE REGULATION 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 DATE FEB21 FEB21 FEB21 MAR21 MAR21 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 PCB CODE 11106201 23011201 18106201 14102211 24102211 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 Price $5.00 $10.00 $5.00 $12.50 $2.50 $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 WIDE-RANGE OHMMETER AUG22 04109221 $7.50 NEW PCBs We also sell an A2 Reactance Wallchart, RTV&H DVD, Vintage Radio DVD plus various books at siliconchip.com.au/Shop/3 SERVICEMAN’S LOG Spy games and super-villain gadgets Dave Thompson It’s no secret that I like gadgets and I suspect many electronics enthusiasts do too. In my case, the weirder the gadget, the better, and even more so if the device is something I can make myself. However, some gadgets move beyond weird and into worrying territory, and this time I had a chance to repair one. As a kid, I was always fascinated with Maxwell Smart’s shoe-phone. Not so much that it was a phone, but that it was hidden in a shoe. Throughout the 80s and 90s, I used a couple of space-age Ericofon Cobra phones with the dial on the bottom as my home telephone as an homage to that shoe phone. (I have three in my collection and they all still work!) The fascination extends to spy gadgets in the slightly less silly spy movies: rotating number plates, oil slicks at the push of a button, rockets mounted behind the headlights and so on. Of course, all those things are faked, made for the big (or small) screen, but they are no less cool, and they sparked my lifelong interest in such things. I get the same feeling when I see a wall safe concealed behind a hinged picture frame, a secret door to a passage behind the fireplace, or a bookcase operated by a hidden lever. A long time ago, I messed around making ‘bugs’, tiny radio transmitters that broadcast to a transistor radio. Of course, in the spy movies I grew up on, bugs are tiny little things that can be stuck anywhere with the press of a finger and transmit several kilometres, even without a prominent antenna. In reality, they need to be a little bigger and, even then, can reach out only a few dozen meters, even if they are relatively sophisticated. Someone needed to be nearby with a receiver to pick up the signal, which of course, was also detectable by the bad/good guys with electronic bug sniffers. Spy games indeed! Editor: for some fascinating related stories, see our articles on Cyber Espionage in the September & October 2019 issues at siliconchip.au/Series/337 As time went on, I made more advanced projects, though I would still build any ‘bug’ that appeared in any of the magazines of the era. Some worked OK, some very well, but regardless of performance, I loved experimenting with them. I never used them in any surveillance role, but they gave me hours of fun. This is how I learned; by doing. A little while ago, I wrote about an old-school night-vision device a customer brought in (April 2022; siliconchip.au/ Article/15283). That device was featured in a late-1970s project magazine, and around the same time, another gadget was advertised in those publications as a “pain field generator”. At the time, I was very curious as to what this thing was and how it worked but never looked into it any further. It turned out that a friend of the guy with the night-vision scope had purchased a short-form kit and plans for one of these ‘generators’ years ago and, had tried to put it all together, without much luck. He contacted me after the night-vision thing worked out and wondered if I would like to look into it for him, and perhaps get it working. I sure would! Pain in the wotsit The plans he’d imported included a reproduction of the original magazine project article featuring this device, explaining how it worked and what to expect from it. It turns out that this project (or one very similar) is also featured in one of those ‘Evil Genius’ project books that were popular a few decades ago. On the face of it, it seemed straightforward; it is essentially a high-frequency oscillator that could be manually varied in frequency and modulation to produce some very annoying high-level sounds that could potentially be damaging to humans and animals. I suppose this is the “pain” they are alluding to in the blurb. There are several iterations of the project, from a ‘pocket’ version up to one you could mount on a perimeter fence. The main difference was the output power and the speaker array used. The parts used in the project (or their modern 72  Silicon Chip Australia's electronics magazine siliconchip.com.au Items Covered This Month • • • • Spy games and super-villain gadgets An overloaded Onkyo receiver Intermittent lights in a trailer tow bar Fixing washing machine PCBs 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 equivalents) are still widely available, and I saw no reason not to have a go. However, I was initially a bit cautious because I didn’t know these guys or what they would use something like this for, and I was unsure of the legalities of even owning/ building something like it. A bit of research on the topic showed that something very similar in theory – though much more powerful – is already in-use at a military level by the USA and shipping companies (against pirates, among other possible uses). The Israeli Army developed another version for use in the Middle East. Called LRAD, or Long-Range Acoustical Device, they consist of a large, focused speaker array that can emit sounds at very high levels to make the ‘listener’ very uncomfortable, theoretically without doing any permanent damage. Another similar ‘civilian’ unit is marketed and used worldwide to prevent groups of young people from congregating around shopping malls or other areas where loitering kids could potentially cause problems. Older people cannot usually hear the high-frequency sound these devices emit and are mostly unaffected, but it is apparently quite uncomfortable to younger ears. Of course, the kids soon learned that by wearing earpods or headphones, they could easily defeat the system. Even so, these devices are apparently still deployed in many countries for this very purpose. I suppose it would be like anything else – a stereo system can be used as a sound weapon (ask annoyed neighbours!), so it matters what something will ultimately be used for as to whether it is deemed dangerous or not. I asked the customer, and he said that for him, it was only about curiosity and experimentation – much like my own motivations for wanting to make one. Perfidious perfboard With that dealt with, I looked at what he’d done already. And the answer was “not much”. The ‘kit’ came with some of that older-style perfboard prevalent in the days before DIY PCBs. The project required component leads to be put through holes and then routed underneath and soldered together to create pseudo ‘tracks’, creating a facsimile of a hand-wired printed circuit board. This construction method is fine when done correctly – however, this one wasn’t; it was a bit of a mess. I thought it best to salvage what components I could and replace those I couldn’t. siliconchip.com.au Australia's electronics magazine August 2022  73 happened. Cranking the pots and toggling the sweep switch did nothing. No pain, no gain For example, the project used a couple of 555 timer ICs, and I couldn’t easily extract them from the rats’ nest. It would take way more effort (and potentially do more damage) to try to remove them, so instead, I reached into my parts box for a couple of new ones. I recovered an IRF540 Mosfet, a custom-wound transformer/choke and a couple of other inductors; the rest I just replaced with new components. I used Veroboard for this build. I know it isn’t very popular among some out there, but for something like this, it is (relatively) cheap and easy to work with. The voltages and currents involved are well within the limitations of a construction method like this. I have used the excellent open-source VeeCAD software (veecad.com) in the past for complex layouts on Veroboard, but this would be a reasonably straightforward build, so I just ‘winged it’. If push came to shove, I could easily redo it using the CAD program. Almost all the components mount on one board, with two Motorola piezo tweeters mounted externally in a suitable enclosure. Those tweeters have off-board inductors mounted directly on their terminals. Two pots are mounted into whatever case is used and these, along with a modulation setting and a power switch, are the only controls. The first 555 in the circuit is configured as a free-running oscillator with variable frequency control. In contrast, the second 555 is configured to produce a sweep voltage that modulates the output of the first oscillator. This sweep is controlled by the second pot and can be switched in and out. The output is fed to a Mosfet and then on to the LC network of the tweeter array. The whole thing actually reminds me of the Barking Dog Blaster project from the September 2012 issue of Silicon Chip (siliconchip.au/Article/529); that is far more advanced, but the output section is very similar. I also made one of those ‘blasters’ back in the day and, with it, successfully ‘trained’ a dog a few doors down. It learned that if it barks constantly, some uncomfortable sounds would come its way! I assembled the project and fired it up on the bench. I powered it using a benchtop power supply (it runs from 9-12V DC) and flicked the power switch on. Nothing 74  Silicon Chip Now, it could be that I am so deaf after years of racing model aircraft and playing in bands that I just couldn’t hear it. Still, as I also didn’t experience any of the disorientation, dizziness or headaches they claimed in the promotional material, I was pretty sure it wasn’t working. Time to dig a bit deeper. The first thing I did was check my layout and make sure I’d cut all the tracks that needed cutting, ensuring I hadn’t cut any that didn’t! Tracing through the circuit diagram and comparing it to my layout, it all looked fine to me. The next easiest thing to check was the Mosfet. The IRF530/IRF540 used in the project needs a heatsink fitted, but even though I hadn’t added one yet, the component wasn’t getting warm. I didn’t bother checking it; I have many types with similar specs in my parts bins that would work in this circuit (N-Channel, 100V 30A 100W in TO-220). I found a suitable alternative and soldered it in. The only other thing was the choke, which the customer wound himself. I know from my own experience of winding transformers and inductors that they can be tricky things to get right. Since the bobbin and E-cores the guy used came as part of the kit, I knew they were at least the correct types. As it has only 50 turns of “#24 magnet wire” on the bobbin (24 gauge, or 0.51mm diameter enamelled copper wire), it was easy enough to strip it off and rewind it myself using nice new wire. Fortunately, using one of the winding jigs I’ve made up over the years made this a simple, though laborious, task. One anomaly I did spot redoing this choke was that the original plans called for three six-thou (0.006-inch or 0.15mm) shims to be placed between the two E cores. No such shims fell out when I pulled the cores apart, so I created some from plastic and tacked them to the prongs of one of the cores with superglue before putting it together. According to the component description, it should measure 1.5mH (millihenries), and my Peak LCR meter tested it as 1.71mH, which was close enough for me. After taping everything up, I scraped the enamel from the two flying leads and soldered it back into the board. After another quick check-over, I powered it on once again. This time I could hear noise from the tweeters. It almost sounded like white or pink noise until I started messing around with the frequency and modulation controls; then, all hell broke loose! This thing was loud! I powered it off, closed the workshop doors and put a pair of earmuffs on. I also buried the tweeters under a couple of folded-up drop-cloths. I tried it again and ran it at a reasonable level, noting the current draw and onboard temperatures. It was almost unbearable at the audible (for me) end of the range. At the upper end, all I could hear was that slight hiss, but I could feel a kind of pressure in my skull, a very odd and uncomfortable sensation. This sound pressure level is still likely to cause hearing damage if I was exposed to it for long enough, even though I couldn’t hear the actual output. Australia's electronics magazine siliconchip.com.au The Mosfet was now starting to get warm, and as I knew the unit was going to work, I powered it off and set about prepping to mount it in a case of some sort. As I was fixing a heatsink to the Mosfet, there was a knock on the workshop door; it was our nearest neighbour wondering if our alarm was going crazy. I apologised and assured him everything was fine and that it was just a project I was working on. I also apologised in advance, explaining I would have to test this thing again once I’d built it into an enclosure. I told him I would try to keep any noise to a minimum (if that was really possible)! I found a plastic Jiffy box that would accommodate the circuit board, though it would require the usual drilling and chopping around to fit all the stuff into it, and I’d still have to find some way to mount the tweeters. Looking around my workshop, my eye settled on an old set of computer speakers under the bench. These were reasonably large, with timber backs and sides and a moulded plastic front. I reckoned the whole shebang would fit into one of them, and the pots and switches could poke out of the back side – this way, they could be manipulated with the speakers pointing the other way! There was plenty of room, and all I’d need to do was remove the plastic front (held on by four screws) and the old drivers with it, and replace it with one made from Thinline MDF. The tweeter holes were easy enough to mark out and cut in the timber, and with a quick sand and a spray with matte black paint, it looked like a bought one. I used the original mounting holes to fix the tweeter array to the rest of the cabinet. The project was designed to be portable and run on batteries; the customer was not keen on this and asked if it could be mains-powered; he’d only be playing with it around his home anyway. I dug out a 12V 1A ‘wall wart’ type power supply from my bins and simply added a socket to the back of the unit to match the plug on the supply. That should be ample. The finished device looked pretty good. I once again packed bunched-up material in front of the tweeters, put on earmuffs and switched it on. And again, I was greeted with a lot of noise, and after playing around with the controls found I could get some hugely annoying sounds out of it. I could see it would be very disorientating if someone were suddenly exposed to it. With earmuffs off, it was literally unbearable to be around, with even my teeth feeling as if they were vibrating when the sweep was set just right. Nasty! The guy was very happy with it and looked forward to his ‘experiments’. I don’t think his neighbours will be that happy, though! I almost feel sorry for the real-life pirates at the receiving end of the ‘big daddy’ LRAD devices. Almost. Those guys are not quite as affable as Jack Sparrow, and the AK-47s they carry are a bit more menacing than a single-shot flintlock pistol... An overloaded Onkyo receiver R. S., of Fig Tree Pocket, Qld repairs a wide variety of devices. This time it’s an old Onkyo TX-SR506 7.1 AV Receiver which would have cost a pretty penny new. Here’s what he found... The Onkyo receiver would not switch on, indicating an overload. It has seven amplifiers, and one of them had shorted output transistors. Q6053 and Q6063 (visible in this section of the circuit diagram overleaf) had failed short-circuit. Replacing the output transistors with new ones, protected by 100W 5W resistors in the collector circuits (to siliconchip.com.au Australia's electronics magazine August 2022  75 NAAF-941 U01 AMPLIFIER PC BOARD R6093 0.22 (1/4W) Q6013 -0.6V P6083 ID+ ID- R6103 0.22(3W) Q6063 LIST R6173 VPRO 47K R6183 Q6043 2SA1930 -1.1V 33K R6163 SPSL D6013 220K C6043 +47/50 IDLING CHECK Q6073 2SC2240 C6053 103J R6143 22K VOLH D6003 47K D6003, 6013 : KDS4148U R5193 10 (1/4W) -52.5V A close-up of the power amplifier section of the Onkyo TX-SR506 receiver circuit. Q6004, 6014 : 2SC1740S-S R5184 SR IPRO Q6053 LIST R6193 Q6033 2SC5171 R6083 0.22 (1/4W) Q6003 + C5053 47/50 R6043 2K -0.4V 3.3K 22K R5133 C5093 101K Q5043 2SC2229-Y R5173 LIST +52.5V R6153 12K 470 -0.3V +0.6V R6073 LIST R5203 +1.0V 3.9K 5.6K R6013 R6003 R6033 Q5033 2SA949Y R5163 LIST 2.2 (1/4W) IDLING ADJ. C5113 + 22/100 Q5053 LIST R5063 R5073 1.2K 100K C5023 + 10/50 R5103 D5003 MTZJ5.6B -51.5V R5233 120K R6023 +1.1V R5033 120K C5083 040D C5103 + 22/100 Q5013 R5053 4.7K -46.5V 10 (1/4W) C5043 + 220/25 -0.65V 470 56K 330 NC R5083 R5043 0V 2.2K R5013 R5023 221K C5003 1K R5113 Q5003 Q5003, 5013 : 2SC2240 R5003 C5013 47/50 1K + +50.5V 100K R5093 Surround Left ch +51.5V +52.5V R6026 0 +1.1V R6164 33K R6165 33K D6015 220K R6195 Q6005 + C5055 47/50 Q6015 siliconchip.com.au Q6006, 6016 : 2SC1740S-S 36 Y R5166 LIST 1K 10 (1/4W) D6014 220K C6054 103J C6055 103J R6194 R6154 12K C6044 +47/50 C6045 +47/50 R6155 12K R6074 LIST Q6014 R6075 LIST Q6004 + C5054 47/50 470 3.9K 5.6K 3.3K 470 22K 22K R6015 R6005 R6035 R6055 C5095 101K Q5045 2SC2229-Y R5175 LIST 3.9K 5.6K R5204 R5134 22K 22K R6054 R5205 R5135 C5094 101K C5085 040D Q5035 2SA949Y R5165 LIST R5174 LIST Q5044 2SC2229-Y C5114 + 22/100 470 C5105 + 22/100 C5045 + 220/25 C5115 + 22/100 470 3.3K R6014 R6004 R6034 Q5034 2SA949Y R5164 LIST C5044 + 220/25 Q5054 LIST Q5015 R5186 +51.5V R5116 Sorround Back NC R5085 R5065 R5075 1.2K Q5055 LIST 56K 2.2K NC R5084 R5064 R5074 1.2K R5115 R5015 R5045 Q5005 100K R5095 1K 100K C5024 + 10/50 R5104 D5004 MTZJ5.6B D5005 MTZJ5.6B C5025 + 10/50 R5105 100K Australia's electronics magazine  Silicon Chip SBR C5084 040D Q5014 Q5004 R5014 56K 2.2K R5044 C5004 221K SBL 76 C5104 + 22/100 1K 100K R5094 R5114 R6024 (1/4W) the supplies), did not work. The output of the 10 amplifier cosmetic panelling of the boot. This picks up the various 2.2 (1/4W) Q6034 +1.1V Sorround Right ch 2SC5171 went to the positive rail immediately. The driver transis- signals (brakes, turn indicators, taillights and soIPRO on) and R6084 Q6054 tors, Q6033 and Q6043, were also +50.5V shorted, as was the Vbe drives the trailer lights putting any load on the 0.22without +1.0V LIST (1/4W) multiplier Q6013, and 100W resistor R6073 (between the car’s internal electronics. Otherwise, the trailer connec+0.6V Q6074 R6144 2SC2240 22K driver emitters) was burned and open-circuit. I replaced tion could interfere with, say, flasher timing or blown Q5004, 5014 : 2SC2240 all of these. globe detectors. R5034 IDLING C5014 R5004PNP The transistorR5024 Q5033 controlling the driver120K transis- -0.3VI took my car to the trailer dealer and tow bar installaCHECK 47/50 1K 0V SPSR + tors seemed OK, but 330 I have had trouble before with tran- tion experts, which involved a round trip of about 200km. P6084 R6104 -0.65V R5234 sistors in this part of the circuit, as they can be leaky. So After spending a day wandering around shopping centres, 0.22(3W) ID+ 120K R5054 IDI replaced it as well. I returned to be shown everything working correctly. 4.7K IDLING This time the amplifier worked, and the output centred So I drove the hundred or so kilometres home and ADJ. R6094 close to 0V. Maybe what happened was that Q5033 leaked R6044 thought, this is pretty0.22 good; I’ll just have a look at the (1/4W) Q6064 2K -0.6V enough current to destroy Q6013, then the voltage between lights before putting the trailerLIST away. Oh, dear! Some of -46.5V -0.4V R6174 the bases of the driver transistors rose high enough to the lights didn’t work or were intermittent. A phone call VPRO 47K the destroy them, and the output transistors as well. to the dealer later, we decided that job had VOLH to go back R6184 The circuit is unusual as it has two Vbe multipliers, with to be fixed. D6004 47K Q6044 -1.1V Q6013 in contact with driver Q6063 and Q6003 in contact After a fair bit2SA1930 of fiddling with multimeters and test D6004, : KDS4148U with the output transistor heatsink. I have not seen lamps, the mechanic decided that the 6014 electronic control R5194this 10 (1/4W) -52.5V -51.5V before; perhaps it offers better quiescent current stability. unit must have a faulty ground (connection to the chasI recently discovered that the quiescent current set- sis). Rather than pull the boot lining out again, he decided ting trimmer pot R6043 pin goes run a separate wire from the+52.5V trailer plug to the vehicle Q6005,to 6015 : 2SC1740S-S +51.5V was faulty. The wiper R5185 open-circuit as the control is adjusted. This would stop chassis. Lo and behold, everything worked again. Problem 10 (1/4W) R6025 Q6035 +1.1V Q6013 from working correctly and possibly destroy the solved. Oh yeah!2SC5171 IPRO Sorround Back 2.2 R6085trip home, I decided to check the output and driver transistors. This +50.5V small, low-cost part has After the 100km return (1/4W) Q6055 +1.0V Left ch 0.22 (1/4W) why; ILIST caused a lot of trouble. lights again. I don’t know guess IQ6075 didn’t have much +0.6V R6145 2SC2240 confidence in the system. Of course, it isn’t necessary to 22K Intermittent lights in trailer tow bar Q5005, 5015 : 2SC2240 tell you what I found, is it? R5035 IDLING R. G. B., of Ararat, Vic had that frustrating experience that I had to fix it myself. Like the 120K R5005 C5015 -0.3VThat’s when I decided CHECK 47/50 R5025 1K 0V of taking +something to the so-called experts, and it still Serviceman, I found that the quality of the wiringSPSBL was atroP6085 R5235 -0.65V you need to take R6105 comes back broken. 330 Sometimes these cious. I have a license to test and tag, so I did have some 120K ID+ 0.22(3W) R5055 things into your own hands, and doing so saved him quite idea of what I was dealing with. It was very difficult to get ID4.7K a bit of hassle... at anything to check if the various circuits were intact, but IDLING R6095that all was well with the wiring. I just finished reading the December 2021 Serviceman’s ADJ. eventually, I determined 0.22 R6045 (1/4W) story about his problems with trailer wiring (siliconchip. 2K The lights were sealed LEDs,Q6065 so that had to be taken on LIST -0.6V -46.5V au/Article/15141). Apparently, the demon affecting trailer -0.4V faith; they worked before, and R6175 it was unlikely they had VPRO wiring has international relatives. The Serviceman could suddenly failed. 47K R6185 VOLH have been talking about the wiring on a new trailer I bought So, I phoned the dealer again and47K told them there was D6005 Q6045 recently. still a problem. For some reason, I was now talking to an 2SA1930 -1.1V When a tow bar is fitted to a modern vehicle, some older man whom I doubted was D6005, a qualified electrician or 6015 : KDS4148U R5195 sort of electronic device a mechanic. There was a bit of silence on the other end, 10 (1/4W)the -51.5V is installed, hidden behind -52.5V C5005 221K P6902A Q6003, 6013 : 2SC1740S-S R5183 +51.5V R6053 SL WHITE 22K 902B 2.2 +52.5V Q6036 2SC5171 IPRO A selection of our best selling soldering irons and accessories at great Jaycar value! 25W Soldering Iron TS1465 $14.95 Build, repair or service with our Soldering Solutions. We stock a GREAT RANGE of gas and electric soldering irons, solder, service aids and workbench essentials. 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By now, I was nearly at the point of rudeness, but fortunately, I only thought to myself, “of course I checked the wiring to the plug, you fool”. After mildly telling him I had done so, he said, “No, check the plug itself”. When I looked at this device from a mechanical viewpoint, it consisted of several brass holes into which brass pins were inserted. The pins were slit lengthwise, allowing them to make a springy contact with the holes. Inserting a screwdriver into each pin and spreading the contacts slightly fixed the problem. I still check the lights each time I use the trailer, but so far, this simple repair has lasted over two years. Fixing washing machine PCBs N. B., of Taylors Lakes, Vic runs a laundry repair business, so he sees a lot of broken washing machines. Here are some repairs he’s undertaken lately... The first one is an obvious fault, but at first glance, it looks like a write-off. There was a giant scorch mark and significant damage to the PCB around the relay pin that connects to the mains-potential “FS1” spade lug. Replacing the relay and repairing the board was the challenge. The relay switched mains to a high-current resistive heating element to maintain the desired wash temperature. So the repair insulation had to be good, and the resistance had to be low. After removing the relay, I cleaned the soot off the damaged area on both the top and bottom sides of the board 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. 78  Silicon Chip using an old toothbrush and PCB cleaning spray. I had to ventilate the room well while doing this. After I scraped through and removed the charred area, I filled the hole left with epoxy resin from both sides. When it was set, I marked and re-drilled the hole. Then I soldered in a new relay. The hole I had drilled was large enough to feed a crimp pin through it and onto the relay pin and flow solder through to the relay pin. I had enough clearance between the pin and the PCB, so there would be no problems with arc-over (especially as it’s a non-inductive load). I soldered two strands from a 2mm2 mains cable between the spade connector and the extended pin of the relay, snipping off the excess pin length. A quick insulation test between the spade terminals told me the job would be reliable. After testing it under load, I sprayed plumber’s clear rubber pipe sealant on both sides to seal the deal. On another similar PCB, I had a problem with the door sense circuit not recognising that the door was closed. The circuit for this is a simple series circuit comprising a mains source, a dropping resistor, a 1000V 1A diode, an optocoupler and the return Neutral. The diode tested open-circuit between the diode side of the resistor and the opto-coupler input pin. Still, it seemed OK when I tested the diode directly in both directions. I removed the surface-mount diode, and there was the remnant of the solder mask under one of the pads (the coating applied to PCBs to prevent solder from sticking in unwanted areas and forming solder bridges). I removed the coating and re-soldered the diode, and it tested OK. I then found that the opto-coupler internal LED was shorted, so I had to replace that too. I’ve also come across PCBs with breakdowns in high voltage areas, where white streaks can be observed running between components. This is high-voltage arcing in the intermediate layers of the board. The cure is to drill a hole wider than the arcing track but, of course, not through any internal or external traces on the PCB unless you bridge them out by another path. The sides of the hole and the edges of the PCB can then be sealed with lacquer. Moisture ingress into the PCB can cause this and can also affect layer capacitance, affecting the performance of tracks carrying high-speed digital signals. SC Australia's electronics magazine siliconchip.com.au Huge Range of Project Enclosures A hand-picked selection of our plastic and metal type enclosures for projects big or small. SAME GREAT RANGE AT SAME GREAT PRICE. SEALED PLASTIC ENCLOSURES • IP65 Rated • ABS & Polycarbonate types • Flanged & Clear Lid options DIECAST ALUMINIUM • Standard, IP65 Rated & Flanged Options Easy to mount with cable entry Protects against dust and moisture General purpose and easy to cut or drill HANDY JIFFY BOXES BULKHEAD BOXES Ideal for harsh, hot or outdoor conditions IP65 RATE D • ABS IP65 RATE D • ABS FROM 3 $ FROM 3 25 HB6006-HB6082 10 sizes available $ Clear lid option FROM 6 45 HB6004-HB6025 11 sizes available $ Flange options 95 HB6120-HB6251 29 sizes available Flange options FROM 1095 $ HB5029-HB5064 15 sizes available Flange options Shop at Jaycar for: • Over 100 types of plastic & metal enclosures • Enclosure cooling fans • Great range of rubber feet, cable glands & grommets • Huge range of panel mount plugs & sockets • Special selection of fasteners, spacers & standoffs Explore our wide range of enclosures, in stock on our website, or at over 110 stores or 130 resellers nationwide. jaycar.com.au/enclosures 1800 022 888 Secure Remote Receiver 68m line-of-sight range Up to 16 remotes per receiver Mains-powered, quiescent power typically 0.8W Relay contact rating: 30A at 250V AC, meaning it can switch large mainspowered devices like pumps Relay on-timer ranges: 250ms to 60s or 60s to 4.5h (see Tables 3 & 4) Brownout protection: 192V AC switch off, 220V AC switch on DC supply current: 17mA with relay off, 100mA with relay on Part two: by John Clarke T HE SYSTEM COMPRISES ONE RECEIVER AND UP TO 16 KEY-FOB TRANSMITTERS. You can build multiple receivers if you have different equipment to control. There is no possibility of a transmitter triggering the wrong receiver due to the secure rolling-code system. The assembly of both modules is relatively straightforward due to the use of mostly standard parts. The transmitter PCB is small (30 x 45mm), and the onboard microcontroller is in an SMD package (SOIC-14). Still, anybody with reasonable soldering skills and proper equipment should be able to build it. Transmitter construction All the parts for the transmitter mount on a 30 x 45mm double-sided PCB that’s coded 10109212 – see Fig.3. Once assembled, this will be housed in a 65 x 25 x 17mm remote control case. This enclosure is designed for use with a 12V N battery, but we are using a button cell instead. So you will need to remove the curved plastic mouldings inside the front lid of the enclosure at the key ring end that locate the N-sized battery, using side cutters, to provide space for the cell holder to fit. 80  Silicon Chip Most of the parts except for the UHF module are mounted on the top of the PCB. The IC and 220W resistor are surface-­mount devices. IC1 will need to be programmed before soldering it in place. This IC can be obtained pre-programmed from Silicon Chip, or you can program it yourself if you have a suitable programmer. Start by soldering the 220W resistor in place. Tack solder one end of the resistor and remelt the solder to straighten it, if necessary, before soldering the opposite end. Then add a bit of fresh solder (or flux paste) to the first joint and heat it to reflow it so that it is nice and shiny. Next, fit IC1, making sure it is orientated correctly. Solder pin 1 to the PCB and check the alignment to ensure the IC pins all line up with the pads on the PCB before soldering the remaining pins. If any pins have a solder bridge, you can remove it with a bit of flux paste and some solder wick. Next, install the three switches, S1-S3. These are installed close to the PCB. Then fit LED1, ensuring its polarity is correct (the longer lead is the anode [A]) and positioned with the top of the LED lens 7.5mm above the top surface of the PCB. Australia's electronics magazine Mount the two 100nF ceramic capacitors next. The capacitor adjacent to S3 needs to lie over toward IC1. The UHF transmitter can now be installed on the underside of the PCB, with its pins bent so that it lies flat against the back of the PCB with 1mm of clearance. Check that it is correctly orientated before soldering its pins. Then mount the cell holder on the top of the PCB. The board assembly is completed by fitting the antenna. Make it from a 162mm length of 0.5mm diameter enamelled copper wire. Strip the insulation from one end by about 2mm using a sharp hobby knife, emery paper or sharp side cutters. Close-wind it on a 3mm mandrel (eg, a 3mm drill bit) and then stretch it out to 28mm overall length. Install the wire coil from the underside of the PCB with the stripped end into the antenna hole. Place the PCB assembly into the enclosure base before attaching the lid. The assembly is held together with the two self-tapping screws supplied with the key-fob enclosure. Then affix the front panel label that came with the enclosure to the lid. Note that the switches may not siliconchip.com.au MAINS SW TCH Transmitter Powered by a 3V CR2032 lithium cell, 200mAh+ recommended, giving more than two years of life with typical use Standby current: typically 60nA (526μAh/year) Active (transmitting) current: 10mA average over 160ms (900nAh / transmission) Registration current: 10mA average over 2.75s (15.5μAh per registration) Transmission rate: 976.5 bits/s (1.024ms per bit) Data encoding: Manchester code with a transmission time of 82ms Unique code generation: secure UHF rolling code control with 48-bit seed, 24-bit multiplier and 8-bit increment value This Remote Mains Switch uses a high-security rolling-code system, so it is suitable for triggering motors that open doors or gates. It’s also very robust, allowing it to switch motor-based appliances like pool pumps and water pumps. Last month, we described the circuitry; this article concentrates on its construction, testing, set-up, and use. initially all be operable; some adjustments might be required. In particular, switch S2 may not be able to be pressed due to the corner of the cell holder adjacent to S2 being a little too high to allow the bending of the enclosure lid lever for S2. In this case, file down that corner of the cell holder a little so the switch can be pressed (as seen below). Additionally, you might find that the switches are pressed in when the lid is attached. To avoid this, we will be supplying PCBs that are thinner than usual (1.0mm instead of 1.6mm). This thinner PCB should prevent the switches from being pressed by the lid. But if you still experience this problem, you will need to trim the tops of the plastic pins on the lid of the enclosure that press on the switches with a file, sharp side cutters or a craft knife. Take care not to remove too much material, and test the switch operation after shaving off some of this plastic. Note that if you touch the junction of the two halves of the coin cell (the + and – contacts), that will cause a higher than expected leakage current due to oils from your skin being deposited on the insulating surface. This will discharge the cell quicker than expected. If you touch it like that, clean the cell with methylated spirits or isopropyl alcohol and avoid making contact across the cell halves your fingers. Receiver construction Many of the parts (but not all) fit on the PCB coded 10109211 that measures 159 x 109mm – see Fig.4. The off-board parts are the IEC mains input socket, GPO mains output socket, pushbutton switch S1, power switch S5 and the neon indicator lamp. Install the resistors first, taking care to place each in its correct position. The resistor colour codes are shown in the parts list, but you should also use a digital multimeter to check each resistor before mounting it in place. Fig.3: the top and bottom view of the PCB overlay and actual prototype PCB for the Transmitter half of the Secure Remote Controlled Mains Switch. siliconchip.com.au Australia's electronics magazine August 2022  81 Diodes D1-D5 are next. Make sure these are orientated correctly before soldering their leads. Then install a socket for IC1, ensuring its notched end matches the position shown in Fig.4. Do not fit IC1 yet – that step comes later, after the power supply has been checked. Regulators REG1 & REG2 are both mounted horizontally on the PCB. The first step is to bend their leads down through 90° so that they will go through their PCB holes. In each case, the regulator’s two outer leads are bent down 8mm from its body, while its centre lead is bent down 5mm from the body. Secure each regulator to the PCB using an M3 x 10mm machine screw and nut. Be careful not to get the regulators mixed up – the 7805 (REG1) is on the right-hand side. Tighten each assembly firmly before soldering and trimming the leads. Do not solder the regulator leads before tightening the mounting screws, as that could stress the soldered joints and fracture the board tracks. Next, install trimpots VR1 and VR2 (VR2’s screw adjuster toward the top of the PCB), transistor Q1 and the BCD switch. This must also be orientated as shown. The capacitors can then be mounted. The electrolytic capacitors are polarised and must be installed with the polarity shown (the longer lead is positive). You can install the two 100nF MKT polyester capacitors either way around. The two LEDs (LED1 and LED2) are mounted with the tops of the lenses 12mm above the surface of the PCB and the anodes (longer leads) to the holes marked “A”. CON1 and CON2 are 4-way and 3-way screw terminals. CON1 is made of two 2-way screw terminals dovetailed together by sliding them together along the side mouldings. Orientate CON1 with the wire entry toward RLY1. CON2 has connections made only to the two outside terminals. This is to increase the separation between the Active and Neutral connections. On our prototype, we removed the centre pin from the terminal. But if you find it difficult to remove, it can be left in place. The wire entry for this connector is on the left. Then fit the headers for jumpers JP1, JP2 and JP3. Now install the 433.9MHz receiver module, again ensuring it goes in the right way around. The pin designations are all clearly labelled on the back of the module, and you can also match the orientation of the module against the photographs. The antenna is made from a 170mm length of 1mm diameter enamelled copper wire. Form it into a spiral by winding it over a 6mm (or similar diameter) mandrel, such as the shank of a 6mm or 1/4-inch drill bit. As shown in Fig.5, it extends from the antenna PCB pad to another pad adjacent to REG1. Be sure to scrape away the enamel insulation from both ends of the antenna wire before soldering it into position. For safety reasons, the antenna must be fully enclosed in the plastic case. Under no circumstances should it be mounted externally, nor should any part of the antenna protrude from the enclosure. Otherwise, if a mains wire comes adrift inside the case, it could contact low-voltage circuitry and the antenna might also become live at 230V AC. The transformer mounts on the PCB and is held in place using two cable ties that are joined to provide a sufficient length wrap around the transformer body and PCB via holes provided on the board. The cable ties prevent the transformer from coming Fig.4: the overlay diagram for the receiver section of the Secure Remote Controlled Mains Switch. 82  Silicon Chip Australia's electronics magazine siliconchip.com.au Rolling Code Systems – frequently asked questions One question that’s often asked about rolling code systems is what happens if one of the switches on the transmitter is pressed when the transmitter is out of range of the receiver. Will the receiver still work when the transmitter is later brought within range, and the button pressed again? This question is asked because the code the receiver was expecting has already been sent (but not received), and the transmitter has rolled over to a new code. How does the system get around this problem? The answer is that the receiver will process a signal that is the correct length and data rate, but it will not trigger the relay unless it receives the correct code. So if the signal format is valid, but the code is incorrect, the receiver then calculates the next code that it would expect and checks this against the received code. If it matches, the receiver will trigger the relay; that means it missed one button press. If the code is still incorrect, the receiver calculates the next expected code, and it will do this up to 10 times, to handle cases where there have been multiple transmitter button presses out of range. If none of these are correct, the receiver then changes its operation to allow for a possible valid signal more than 10 codes ahead. The receiver waits for two valid separate transmission codes before restoring correct operation. On the first receipt of a valid transmission, it looks ahead up to 200 codes, so it is more likely the required valid code will be found, but it doesn’t trigger the relay. The Learn LED lights during this look-ahead operation. If a valid code is found, the receiver waits for the next code sent by the transmitter. This following code must also be correct before the receiver will operate the relay. If only one or neither code is correct, the receiver will not take action. If it’s more than 200 codes ahead, the transmitter will need to be re-registered to operate the receiver. You can test this process by switching the receiver off and pressing one of the remote control switches 10 times or more. Then switch on the receiver and press one of the switches again. siliconchip.com.au The Learn LED will light, indicating that the look-ahead feature beyond the initial 10 times is activated. The selected function on the remote should operate on the next press of the switch, and the Learn LED extinguishes. While two successive transmission codes could be intercepted, recorded and re-sent in an attempt to activate the receiver, these codes will not be accepted by the receiver. That’s because they have presumably already been received and processed, and the receiver has already rolled past those codes. It will look forwards but not backwards. Another transmitter with a different identity will still operate the receiver (provided it has been synchronised in the first place). That’s because the receiver tracks each transmitter’s rolling codes separately. Calculating the code Another question that’s often asked is how the receiver knows which code to expect from the transmitter since it changes each time. The answer is that the transmitter and the receiver both use the same series of calculations to determine the next code. They also both use the same variables in the calculation; unique values that no other transmitter uses. Without going into too much detail about how the actual rolling code works, here are the basics. We use a linear congruential generator (LCG) in conjunction with a 31-bit pseudo-­ random number generator (PRNG). The LCG uses an initial seed value, an addition value and a multiplication factor to produce a nominally random result. For example, if consecutive codes have the number 3 added and then multiplied by 49, with the same starting number, both the transmitter and receiver will go through the same sequence. But the actual numbers used are very large, making it difficult to predict the next code by peeking at a few values in the sequence. The code is 48 bits long, with 281,474,976,710,656 possible values (that’s over 281 quintillion or 2.8 x 1014). One problem with the LCG is that it can produce recurring values; depending on the factors, it can produce the Australia's electronics magazine same number more than once within a few hundred rolling code calculations. To prevent this, we include a second layer of randomisation. So once we have the value from the LCG calculation, this value is used in the PRNG to generate a pseudo-random number for the rolling code. The PRNG randomisation runs between one and 256 times before providing the ‘random’ number for the rolling code value. The number generated is then used as the seed in the LCG for generating the next number in the sequence. Using the PRNG makes it difficult to predict the rolling code sequence even if the multiplier or addition value for the LCG is known. We throw further complications by also using code scrambling. The calculated code is not sent in the same sequence each time. There are 32 possible scrambling variations that are applied to the code, so predicting the next code becomes very difficult. What if the transmitter rolling code is identical for two consecutive codes, and the first of these identical codes is intercepted and re-transmitted to open the lock? Our system has safeguards to prevent the same code from appearing twice in succession. There is a check for the same code repeating itself for consecutive codes. If the code is the same, the duplicate is effectively skipped, preventing this possibility. Multiple transmitters Wouldn’t the receiver lose its synchronisation if several transmitters were used? No, because each transmitter operates independently. Each of the 16 possible transmitters used with a given receiver has its own different identity from one to 16. The codes sent by each transmitter are different due to the unique identifier within each transmitter IC that sets the rolling code calculation. Also, the code includes the transmitter identity value that differs between each transmitter. The receiver stores up to 16 different rolling code and calculation parameters, one for each identity, so each transmitter is treated independently. Therefore, even if one transmitter is not used for months while other transmitters are used frequently, its rolling codes will remain synchronised with the receiver. August 2022  83 adrift if the assembled unit is dropped. Without them, the transformer is only held by small pins that are secured in the plastic of the transformer body. The next step is to install the relay with its coil terminals toward CON1. Secure the relay to the board using M4 machine screws and nuts. Final assembly The Secure Remote Controlled Mains Switch is housed in an ABS enclosure measuring 171 x 121 x 55mm. You will have to drill and shape holes in one end of the case for the mains switch and IEC connector. The lid also needs holes drilled for the GPO socket, the neon indicator and pushbutton switch S1. A template for these cut-outs is shown in Fig.6. This can also be downloaded from siliconchip.com.au/ Shop/11/6418 and printed out. The large cut-outs (for the mains GPO and IEC connector) can be made by drilling a series of small holes around the inside perimeter, knocking out the central piece and filing the job to a smooth finish. The switch hole must not be oversized so that it stays clipped in when inserted into the cut-out. So take care with shaping it. Once the drilling and cutting is finished, install the PCB and power switch in the case. The PCB is secured using the integral brass inserts and four M3 x 6mm screws. The IEC connector must be secured using Nylon M3 x 10mm screws, although you can use metal nuts. The Nylon screws avoid the possibility of ‘live’ screws should a mains wire inside the enclosure come adrift and contact them. Before attaching the mains GPO, switch S1 and the neon indicator, you can print out the front panel label shown in Fig.7. Again, this is available for download from our website. Print it onto photo paper and cut out the holes for the switch, neon and GPO with a sharp craft or hobby knife. The panel will be held in place by the switch and the GPO. If the label is prone to drooping, use a small amount of clear tape to affix the corners or dabs of clear neutral-cure silicone sealant or glue. The wiring marked in Fig.5 must be run using 10A mains-rated cable. That includes the wires for switch S1. Note that brown wire is used for Active while the light blue wire is Fig.5: the wiring diagram for the receiver section of the Secure Remote Controlled Mains Switch. Note how the antenna is wound on the right-hand edge of the PCB. You can do this by winding it over a 6mm drill bit. 84  Silicon Chip Australia's electronics magazine siliconchip.com.au for the Neutral leads. The green/yellow-striped wire is for Earth wiring only, and the Earth lead from the IEC connector must go straight to the GPO. For the wiring not marked as 10A (for switch S1 and the relay coil), you can use lighter-duty 7.5A rated mains wire. Be sure to insulate all the connections with heatshrink tubing for safety, and cable tie the wires to prevent any broken wires from coming adrift. Secure the Active and Neutral leads to the GPO using cable ties passing through the holes in its moulding. Use neutral-cure silicone (eg, Roof & Gutter silicone) to cover the Active bus piece that connects the active pin to the fuse at the rear of the IEC connector. Take great care when making the connections to the mains socket (GPO). In particular, be sure to run the leads to their correct terminals (the GPO has the A, N and E terminals clearly labelled) and do the screws up nice and tight so that the leads are held securely. Similarly, make sure that the leads to CON2 are firmly secured. Testing Before applying power, check your wiring carefully and ensure that all mains connections are covered in heatshrink tubing. Then install the 10A fuse inside the fuse holder. Leave IC1 out of its socket for the time being. The Remote Mains Switch will be operated with the lid open when testing and making adjustments. During Fig.6: the lid needs to be drilled for the GPO socket, neon indicator and switch S1, while one side of the ABS enclosure needs to be drilled and shaped for the mains switch and IEC connector. siliconchip.com.au Australia's electronics magazine August 2022  85 Assembling the receiver is not difficult, but make sure you use mains-rated wire in the correct colours and add insulation and cable ties, as shown here and in the wiring diagram. this procedure, you must not touch any of the 230V AC wiring. This includes the transformer primary leads plus all wiring to the mains socket, neon lamp, switch S1, the IEC connector, the relay and CON2. Although all connections are insulated, it’s wise to be careful. In particular, note that the relay’s contact connections, the fuse holder’s terminals and switch (S2) could potentially all be at 230V AC. That applies whenever the device is plugged into the mains, even with switch S2 and the relay off. If your premises does not have a safety switch (Earth leakage detector, residual current detector or RCD) installed, consider using a portable safety switch for this part of the test. Rotate the timer trimpot (VR1) fully clockwise and apply power. Use your DMM probes to check for 5V DC (4.95.1V is acceptable) between pins 1 & 20 of IC1’s socket. If this is correct, switch off, disconnect the mains plug from the wall socket and install IC1. Take care to ensure that IC1 goes in the right way around – refer to Fig.4. 86  Silicon Chip Power the circuit back up and, with your DMM set to read DC volts, adjust multi-turn trimpot VR2 so that the voltage between TP2 and TP GND is around 3V. This ensures that the relay can switch on so that you can proceed with calibration. Next, set the DMM to a high AC voltage range suitable for measuring mains voltage and carefully check the voltage between the Active and Neutral sides of the CON2 screw terminal Australia's electronics magazine block. Press switch S1 to turn on the relay, set your DMM to read low DC volts again and adjust multi-turn trimpot VR2 until the DC voltage between TP2 and TP GND is 1% of the mains voltage reading you got earlier. For example, if you measured 250V AC, adjust VR2 for a reading of 2.50V DC at TP2. Alternatively, if the mains voltage was 230V AC, set VR2 for a reading of 2.30V at TP2. This sets the brownout cut-out level to 192V AC. siliconchip.com.au The Acknowledge LED will light continuously during a brownout. The relay can only be switched on again via a (registered) remote transmitter or the switch on the receiver once the mains voltage has recovered after a brownout. Now that you’ve calibrated the unit, you can set jumper options JP1-JP3 and adjust the timer with VR1 (see Tables 1-4). Fig.7: you can either copy the front panel label from here, or download it from siliconchip.com.au/ Shop/11/6418 Registering a transmitter When registering a transmitter and for regular use, it is essential to have the transmitter and receiver apart by at least 1.5 metres. If the transmitter is closer than this, it could overload the UHF receiver and corrupt the signal, leading to incorrect registration or intermittent remote control operation. To register the transmitter with the receiver, press Learn switch S2 on the receiver. The Learn LED (LED1) will light. On the transmitter, remove the cell from its holder and reinsert it while pressing and holding switch S1. This will set the transmitter to Synchronisation mode (with the acknowledge LED lit) and send the registering code when S1 on the transmitter is released and then pressed again. The rolling code is continuously updated during the synchronisation time between when S1 is released and it is pressed again. This randomises the rolling code generation sequence to an undetermined point, due to the rapid rate that the code is recalculated – on average, around 500 times per second. The rolling code sequence is then well into its generating sequence. This makes it hard to guess the code based on possible MUI values, even if the initial seed value for the code generation is known. The acknowledge LED on the receiver will flash twice, and the Learn LED will extinguish once registration is complete. Test the transmitter and check that the receiver responds by switching the relay on and off. It will take a couple of attempts before the transmitter and receiver start working together. De-registering a lost transmitter Any transmitter that has been registered can be prevented from operating the receiver, for example, if a transmitter is lost and you don’t want it to be used by an unauthorised person. Deregister the lost transmitter by selecting the transmitter identity using BCD switch S4. The switch is labelled 0 to F; the labels A-F correspond to identities 10-15. Then press and hold the Clear switch (S3) for more than one second. The Clear LED will light initially, then extinguish after S3 is Table 1 – JP3 settings released and the transmitter is deregistered. If you are unsure of the identity of the lost transmitter, you can deregister all the registered transmitters, one at a time, then re-register the required transmitters again. Jumper options There are three jumper positions on the receiver board, and we’ve reproduced Tables 1 – 4 from last month, so you can recall what they do. JP1 selects the timer length multiplier (see Table 3). The range is 250ms to 60s with JP1 out (the x1 range) or 60s to 4.5 hours with JP1 in (the x255 range). Table 4 shows typical timeouts versus TP1 voltages as trimpot VR1 is adjusted. JP2 affects the function of the buttons on the remote control, as shown in Table 2. JP3 affects the function of switch S1 on the receiver, as shown SC in Table 1. Table 3 – JP1 timer settings JP3 in/out Receiver switch S1 function JP1 in/out Timer period Out Off if already on, otherwise on with a timer, range per JP1 Out 0.25-60s (1x) In Toggle on/off In 1m-4.5h (255x) Table 2 – transmitter switch functions Table 4 – Nominal period versus TP1 voltage Switch Function with JP2 out Function with JP2 in TP1 Time with JP1 out Time with JP1 in S1 Relay on with a timer, range per JP1 Relay on with a timer, 0.25-60s 0V 0.25s 1m S2 Relay on continuously Relay on with a timer, 1m-4.5h 1.25V 15s 1h 7.5m 2.5V 30s 2h 15m S3 Relay off Relay off 3.75V 45s 3h 22.5m 5V 60s 4h 30m siliconchip.com.au Australia's electronics magazine August 2022  87 Vintage EQUIPMENT AVO Valve Testers and Valve Characteristic Meters By Ian Batty The ultimate evolution of the AVO Valve Characteristic Meter – the MkIV. “I checked it on the AVO.” For decades, AVO valve testers were the standard for testing valves (their multimeters were also extremely popular). This article explains the differences between the various AVO meters and describes how they work. 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. 88  Silicon Chip Australia's electronics magazine siliconchip.com.au A VO was typically used to refer to the AVO Valve Characteristic Meter (VCM), based on a design first made by the Automatic Coil Winder & Electrical Company in the late 1930s. This company would become the famous AVO, best known for (and named for) its most prolific product, the Amp-Volt-Ohm meter. With its initial patent lodged in 1922 by Donald MacAdie, the AVOmeter would become the sub-standard meter of choice, with the final one made in 2008 (Photo 1). Note that I wrote sub-standard and not substandard; in measurement circles, a sub-standard is an instrument second only to the physical examples stored at the National Standards Laboratory. But there wasn’t just one “AVO”. The initial release was the 1936 Valve Tester, registered as British Patent 480,752: “An Improved Method and Apparatus for Testing Radio Valves”. Lodged by Sydney Rutherford Wilkins on August 26, 1936, the patent describes the AVO Valve Tester circuit and gives the design principles described below. Notably, there is only one non-­linear component, the rectifier in the SET ZERO circuit, which applies pulsating DC to the meter circuit in opposition to the valve’s pulsating anode current. It’s the balancing of these two currents that allows the meter to settle to zero in readiness for the gm measurement. It’s a remarkably elegant design, so let’s look into how the problem of valve testing was definitively solved. Valve testing basics Simple valve testers heat the filament or cathode and measure the emission between the filament/cathode and the anode (in a diode) or the first grid (in all other valves). You can use an ordinary ohm-meter for this job. You would need a list of various valves types and their expected resistance readings, and such charts were the manufacturer’s specified anode current. 2. Shift the grid voltage up and down by half a volt each way and observe the swing of the anode current. Using a 6V6 with 250V on the anode and screen, reducing the bias voltage of -12.5V to -12V and increasing it to -13V should give a total anode current swing of 4.1mA, confirming a gm of 4.1mA/V or 4.1mS. But that would demand up to three adjustable, regulated supplies, and the Valve Tester hails from the 1930s. Regulated supplies of the day were bulky and prohibitively expensive. Imagine designing and building two indepenPhoto 1: an AVOmeter (amp/volt/ dent 0~400V, 100mA supplies before ohmmeter) Mk8, the multimeter. the invention of the 6L6 beam tetrode. supplied with some multimeters, such Knowing that they could design and as Hansen’s FN/SU models. build mains transformers that would This is emission testing, useful deliver well-regulated AC supplies, for sorting out dud valves and mak- the engineers at ACWEC decided to let ing like-for-like comparisons. How- the valve under test do the rectifying. ever, emission testing does not test With the valve performing rectificathe entire valve’s performance under tion, the anode current is pulsating DC. typical applied voltages, doesn’t test The indicating meter would simply be at the valve’s full rated voltage or (for calibrated to respond to the pulsating power valves) typical operating cur- DC and give a reading equivalent to a rents, and doesn’t check for inter-­ steady direct current. electrode shorts or leakages such as The applied anode (and screen) heater-­cathode leakage. supplies would effectively be half The emission tester also fails to test sinewaves since the valve would not a key valve characteristic: its mutual conduct during negative half-cycles. conductance (gm), now commonly A simple implementation would called transconductance. This is the see the indicating meter settle to, say, ratio of anode current change to grid 45mA for a 6V6, rising to 49.1mA voltage change. It was initially mea- when the grid voltage is made 1V more sured in microamps (of anode cur- positive. That would work, but you’d rent) per volt (of grid voltage), with have to observe, accurately, only about the unit of the micromho (“mho” is a 10% change in the meter reading. ohm backwards). Fig.1 shows the problem. It looks It is now measured using the SI unit like the standing current is about of microsiemens (µS). It’s a form of 45mA, and the on-test current is about conductance (G = I ÷ V) because it’s 49mA, so the valve’s gm is maybe about the inverse of resistance (R = V ÷ I). 4mS (49mA − 45mA). So, the question then is – how to We’d prefer a direct indication: a gm measure it? In principle, the steps are: of zero means the meter does not move 1. Apply the correct grid bias, at all, a gm of 4.1 gives a meter indiscreen voltage (tetrodes/pentodes) cation of 4.1, and so on, as shown in and anode voltage, and trim to get Fig.2. This requires two supplies: the Fig.1: the difference in reading you would expect applying a 1V signal or step to the grid of a 6V6 with the specified bias of -12.5V. It’s hard to read this with any precision. siliconchip.com.au Fig.2: by increasing the meter’s sensitivity and offsetting the reading so that it’s at zero with the specified bias of -12.5V, it becomes easier to read the difference in current accurately. Australia's electronics magazine August 2022  89 Read the instruction manual before operating an AVO meter This article includes basic lists of steps for using each type of AVO meter. This is mainly to give you an idea of how they work. I recommended that you read the full instructions before using any of the valve testers. Note that in each case, the recommendation is to set the switches with the power off or, where available, with the FUNCTION set to CHECK. Doing it this way prevents accidental short circuits and valve damage. selected anode voltage & the backing-­ off supply, which adds to it. This is depicted in the simplified circuit of Fig.3. Although it’s not shown, S1’s SET position is applying a sinewave causing an effective -0.5V grid bias. The anode current flows through the mA/V pot, which acts as a variable shunt, controlling the meter’s full-scale sensitivity. Let’s say we have selected an anode voltage of 250V, and the backing-off control is adjusted for minimum effect. The valve will draw a current of Ia, so there will be some voltage drop across the mA/V pot. The meter will deflect, with the indication depending on the shunting effect of the mA/V pot’s setting. Let’s say the valve draws 45mA. Adding current from the backing-off supply will raise the voltage at the anode end of the mA/V pot, reducing the total current through the mA/V pot. If the backing-off supply is adjusted to give enough current to raise the anode back to 250V, there will be no voltage drop across the mA/V pot, and the meter needle will fall to zero. Now, applying the test bias to the valve will increase the anode current, but the backing-off supply is still set to 45mA and cannot entirely cancel the new anode current. The difference between the new anode current and the backing-off current will be shown directly on the meter scale, as in Fig.2. The “SET M. A./V.” (referred to as “SET mA/V” for future references) can be adjusted to the expected gm value; in our example, 4.1mS. This control is a continuously-­variable current shunt across the meter movement, so this setting gives the meter itself a full-scale deflection of 4.1mA. After doing that, the key switch is set to the mA/V position. This inverts the sinewave voltage on the grid, replacing the effective -0.5V with +0.5V. This step will push the total anode current to about 49.1mA. But, as there is a counteracting current of 45mA from the backing-off supply, the meter will indicate 4.1mA (49.1mA − 45mA). 90  Silicon Chip And that is the sensitivity we set using the mA/V control, so the meter will show 100%. Alternately, setting the “SET mA/V” control to the “mA/V” position gives 10mA full-scale. In this case, our 6V6 will deflect the pointer to the 4.1 mark. This confirms the previous measurement, but it also allows a direct reading for any valve without having to look up a table of specs and adjust the “SET mA/V” accordingly. So that’s the principle used in the AVO Valve Tester. A description of how the follow-on Valve Characteristic Meter operates will come later. The AVO Valve Tester The AVO Valve Tester (Photo 2) used a case similar to their existing multimeters, with an extension board carrying the selector switches and valve sockets. It could test valves with anode voltages ranging from 30-250V and screen voltages from 60-250V. The test range was either a direct reading of 0~10mA/V or by setting a dial for the specified gm and reading the valve’s merit (“goodness”) from the scale. Heater/filament voltages matched common valves of the day, with selections of 2, 2.5, 4, 5, 6, 7.5, 10, 13, 16, 20, 26, 30, 35 and 40 volts provided. The test panel added a ÷7 switch so that, for example, 1.4V valves could be tested with a selected supply of 10V, reduced to 1.4V by actuating the ÷7 switch. The Tester also offered a heater-­cathode insulation test. The instrument’s accuracy depended on the mains voltage, with an internal selector panel allowing settings of 200V AC to 250V AC in 10V steps. The Valve Tester set an instrumentation standard that saw “the AVO’s” widespread use in civilian and military contexts. I recall using a CT160 at the Williamtown Air Force Base near Newcastle in the mid-1960s, and in Darwin. The photo opposite (Photo 3) shows the interior. From top to bottom, the major components are the high-­voltage transformer, meter, function keyswitch and low-voltage transformer. The dualgang Set Zero (backing off) pot can just be seen at lower left. The socket panel’s connector is at top right. For all its brilliance, the Valve Tester had a serious drawback: it tested with 0V of standing bias. This meant that the anode current under test might not be that recommended by the valve manufacturer. This matters, as transconductance is anode-current dependent. It’s low for low anode currents, and increases Fig.3: a greatly simplified circuit for the original AVO Valve Tester. The twogang potentiometer at upper left is used to zero the meter before starting the test, while the pot below the meter adjusts its sensitivity so that FSD (full scale deflection) can be set to the expected reading. A good valve will then provide FSD, while a weak valve will give a somewhat lower reading. Australia's electronics magazine siliconchip.com.au as anode current increases to the permitted maximum. Let’s consider the 6AU6. With zero grid bias, it draws around 17mA to give a gm around 5.5mS. But it’s often used in audio amplifiers at anode currents as low as 300µA. What is its gm at such a low current? The Valve Tester cannot apply variable bias (and we’d need around -4.5V to get such a low anode current), so it’s impossible to find out. The Valve Tester also swings the grid positive, with possible grid emission effects giving false readings. To explain the remaining features of Fig.3, diode D1 rectifies the backing-off supply to balance the anode current indication back to zero for testing. In the SET position, S1 applies an AC voltage to the grid. Setting S1 to the TEST position reverses the polarity of the grid signal, causing the anode current to rise, and allowing the meter to indicate the change in anode current as a transconductance reading. Diode D2 ensures that the screen cannot go negative during the valve’s non-conducting cycle. Allowing this could disrupt the instrument’s measurement accuracy. This diode is not included in all diagrams; I have included it in case you find a Valve Tester with it fitted. So, while the Valve Tester gave reliable indications for valves (mostly triodes) that specified low (essentially zero) grid bias voltages, it could not be relied on for those that required a negative grid bias for normal operation. That’s pretty much everything with an oxide-coated cathode. Also, one had to trust that the calibration was accurate. Valves are specified for a range of filament/heater voltages, and it was luck whether the Valve Tester actually applied the correct voltage on any one particular test. While manufacturers allow as much as ±10% variation of heater voltage, deviations from the nominal voltage affect results. On test, an ECC82/12AX7 returned gm values of 2.05mS and 1.5mS for heater voltages of 6.9V (+10%) and 5.7V (-10%), with a reading of 1.8mS at the specified 6.3V. That’s a variation of +14%/ -17% over the recommended operating range. Basics of operation 1. With the power off, consult the AVO data book and set the roller switches to the required positions. Set the filament/heater voltages. Be careful with 1.4V valves; you need the ÷7 setting on the socket panel with the 10V setting on the Tester. 2. Set the mA/V control to the value shown in the data book to get an indication of relative functionality, or to 10 to get an actual transconductance reading. 3. Push the key switch to the mA/V position and read off the meter indication. The Valve Characteristic Meter (VCM) The Valve Characteristic Meter was a significant rework of the design. First, it was unitised and made more ergonomic. The meter and controls were mounted on a sloping front panel, making operation and observation much easier. The socket panel was located on the top surface, removing the previous connecting lead, plug and socket. Sockets that had been recently invented were included. The socket panel was protected against debris intrusion by a flip-up cover. Second, the mains voltage selector was brought out to the front panel, with an indication on the test meter. Third, they added a variable grid bias control. Operators could set up all of the valve manufacturer’s specified parameters. Fourth, the VCM incorporated a short-circuit relay which appears to have been included in some issues of the Valve Tester. This needed to operate at any anode/screen current selection. To achieve this, the relay’s core held enough residual magnetism to stay latched in with no current flow. In regular operation, the anode/ screen current is pulsating DC due to the rectifying action of the valve under test. The resulting uni-directional magnetisation added to the residual magnetism, holding the relay in. But a short circuit would draw current on both half-cycles of the internal Photo 2 (above): the original AVO Valve Tester. The part on the right was an expanded version of their AVOmeter ‘multimeter’ (a term that hadn’t been coined yet), while the part on the left houses all the valve sockets plus some extra controls. Photo 3 (right): the inside of the AVO Valve Tester is busy but there are very few actual components. Most of it is (very neat) wiring! The meter movement is right in the middle, while the transformers are at the top (HV) and bottom (LV). siliconchip.com.au Australia's electronics magazine August 2022  91 Fig.4: the Valve Characteristic Meter (based on the MkIII/IV VCM) is a refinement of the original concept that added a great deal of flexibility. Its main advantages are the ability to test the valve over a wide range of bias voltages and a built-in overload/short circuit protection relay that ends the test if too much current flows. Fig.5: the final evolution of the AVO Valve Tester, the VCM163, included a solid-state sinewave generator and amplifier/rectifier to provide even more accurate results. 92  Silicon Chip Australia's electronics magazine alternating voltage supply. The relay might hold in on the first half-cycle (depending on polarity) but would be thrown out as the opposite-­polarity half-cycle began. Once thrown out, it was reset by pushing the RESET button on the control panel. Fig.4 shows the basics of the VCM circuit. The backing-off/zero circuit has been modified: it now applies the opposing current directly to the meter, but with the same effect. Notice that the meter now reads the voltage drop across the fixed 200W resistor (R36). You can regard the meter as a sensitive, multi-range voltmeter calibrated in transconductance when testing. The overload relay (RLYA) senses anode and screen currents in separate windings. As described, the alternating current resulting from a short circuit will throw the relay out, demanding that the operator reset it manually. As with the Valve Tester, diode D2 ensures that the screen never has negative voltage applied. The bias supply is in two parts. In SET mode, the operator uses potentiometer VR5 to apply the specified grid voltage. Switching to TEST mode makes the grid voltage 1V more positive. This causes the anode current to increase above the balanced value when the backing-off was set. That extra current will be read as the valve’s transconductance. Along with this, the design rework provided for anode current measurement. The name “Valve Characteristic Meter” is a clue. This rework allows the operator to record the anode current for any combination of control grid bias, screen voltage and anode voltage. It was possible to plot the entire set of grid-anode characteristics for any valve that would fit the extensive set of sockets. In effect, the VCM offered a complete test bench for any valve, of any kind, for any test conditions. Operators could also identify weak valves, which would work fine at low anode currents, but lacked the emission to deliver full performance at full current. Matching valves to each other (important for high-performance push-pull operation) was also made much easier. A manufacturer aiming to operate a particular output valve from a lower-­ than-specified high tension (HT) supply could easily measure that valve’s characteristics and could refine a siliconchip.com.au design to suit. The venerable 6V6, for example, can give up to 4.5W of output. But a small mantel set can get by with just one or two watts to the speaker. Could an ‘economy’ set do this using a 6V6 with just 150V HT? Sure, and the VCM could confirm that. Basics of operation 1. With power off or the function setting in the CHECK(C) position, consult the AVO data book and set the roller switches to the required positions. If the VCM was off, switch on in the CHECK(C) position and adjust the SET~ control for the correct mains indication. 2. Set filament/heater voltages. 3. Set grid, screen & anode voltages. 4. Set the METER SELECTOR (MkI-II) or METER SWITCH (MKIII-IV) to 100(mA). 5. Switch to C/H.ins to warm the valve up before testing. 6. Switch to TEST and read the anode current. Set the METER SELECTOR/SWITCH to a lower range if needed. 7. Set the SET mA/V control to the expected gm value and set the METER SELECTOR to mA/V. 8. Adjust the SET ZERO (MkI-II) or BACKING OFF (MkIII-IV, COARSE and FINE) to bring the meter to 0. 9. Press the mA/V button or switch to mA/V and read the valve’s merit from the coloured scale. 10. To get the actual gm value, repeat the above, but with the SET mA/V control at 10. Press the mA/V button and read off the valve’s actual gm value, treating the calibrations as a 0~10mS scale. The CT160 The ‘clamshell’ CT160 used the same basic electronic design. While it did not offer laboratory testing capability, it became the standard ‘quick, accurate and ready’ instrument used in many workshops and service centres. The CT160 only operates as a gm tester; it does not give anode current readings. The electrode voltage settings (grid, screen and anode) work as for the MkI-IV and the VCM163. But the anode current settings take the place of the backing-off controls in all previous models. A simplified version of its circuit diagram is shown in Fig.6. The CT160’s meter is fixed at 700μA FSD. Perhaps confusingly, the 1mA/V mark, at around 74% of FSD, is a DC siliconchip.com.au Fig.6: a simplified circuit diagram of the CT160. It doesn't provide all the features of its predecessors (eg, it lacks anode current readings), but it is still a useful instrument and was widely used. equivalent of 520μA. With the SET mA/V control at 1mA/V, the applied grid voltage decrement is 0.52V. Using the formula ∆Ia = ∆vg x gm, a valve with a gm of 1mS will give an anode current increment of 520μA, resulting in a scale indication of 1.0. So, while a 0.52V decrement would give a 1.0 indication for a valve with a gm of 1mS, applying the 0.52V decrement to a valve with any higher mutual conductance would overswing the meter. The SET mA/V control does, indeed, give a 0.52V decrement on its 1mA/V position, but it gives proportionately less for each higher dialled-in gm value: 260mV for gm = 2mS, 130mV for gm = 5mS and so on. I was, again, awed by the elegance of this instrument’s design. As with the previous VCMs, the CT160 is calibrated with simple DC values, so this preceding complexity is hidden from the operator. Basics of operation 1. With the power off or the function Australia's electronics magazine setting in the SET~ position, consult the AVO data book and set the roller switches to the required positions. There are plug selectors and a switch beneath the transparent lid just below the meter. Be aware that these are at mains potential. Adjust for the correct mains indication. 2. Set filament/heater voltages. 3. Set grid, screen & anode voltages. 4. Set the anode current’s coarse switch and fine potentiometer controls to the specified values. 5. Switch to C/H to warm the valve up before testing. 6. Rotate the mA/V control to the Cal position and set the function switch to TEST. 7. Be ready to adjust the anode current, as the meter may swing wildly back past 0, or forward past full scale. I find it easier to adjust the grid voltage when the meter overswings – it has the same authority as the two anode current controls combined, but it’s a single control and is easier to manage. Once the meter gives a safe indication, August 2022  93 trim the grid voltage and anode current controls. Aim to get the specified anode current, even if the grid voltage is not close to the specified value. Anode current has the most effect on gm, so the correct setting of anode current has priority. Be aware that a very low grid voltage implies a valve with poor emission. The VCM163 Finally, the VCM163 introduced a solid-state measurement design (Fig.5). This revolutionary instrument uses a transistor oscillator to generate a sinewave signal that is applied to the grid of the valve under test. This high-frequency signal modulates the half-wave 50Hz applied to the grid. The VCM163 uses a high-pass filter in the anode circuit to pick off the amplified high-frequency modulation from the anode current. This signal is further amplified and rectified to drive the transconductance meter. Since the transconductance is measured by the amplification of a high-frequency signal, AVO removed the entire backing-off section. This allowed continuous measurement of anode current by a dedicated meter. No longer did operators need to set anode current, back off, measure transconductance and then remove the backing-­off setting to check that the anode current had not drifted. Half-wave rectification is now done by silicon diodes, removing the possibility that high-voltage negative half-cycles applied to valve electrodes will affect the instrument’s accuracy. The VCM163 retains the fundamental AVO principle: mains transformers can deliver sufficient regulation to permit accurate valve testing without the need for regulated DC supplies. Setting the valve up as a signal amplifier gave the highest accuracy. It also took the gm meter out of the valve’s current path, meaning that overloads caused by incorrect settings, or shorts, would not pass damaging amounts of current through the meter’s delicate moving-coil winding. Basics of operation Set the CIRCUIT SELECTOR to CHECK(C) and LEAKAGE to ~. Check that the meter settles to the calibration mark. If the front-panel SET~ control won’t adjust, remove power, open the voltage selector panel on the left side and adjust the coarse mains tapping. 2. With power off or the function setting in the CHECK(C) position, consult the AVO data book and set the roller switches to the required positions. 3. Set filament/heater voltages. 4. Set grid, screen & anode voltages. 5. Set the anode current and mA/V controls to the expected values. 6. Switch to C/H to warm the valve 1. up before you start testing it. 7. Switch to TEST and read off the anode current from the left-hand meter. Read the transconductance value from the right-hand meter. Model identification The Valve Tester is immediately identifiable by its two-part construction. Valve Characteristic Meters can be identified as follows: ] MkI: Grey aluminium exterior case, unitised design, flip-top lid over valve sockets, side carry handles, sits flat on the bench. ] MkII (Photo 4): Similar to the MkI with added front handles, standup runners raising the instrument off the bench and a valve data book tray underneath. ] MkIII (Photo 5): Revised design with ‘roll-over’ handles, panels over the frame, black front panel, large dials for grid voltage (left) and transconductance (right). ] MkIV (see lead photo): Revised design with combined grid voltage variable/range switch and transconductance variable/range switch. ] CT160 (Photo 6): clamshell design, transconductance only. ] VCM163 (Photo 7): has two meters. Special handling Never tap any meter on the glass. Be aware that the original Valve ► Photo 4: the AVO VCM MkII looks similar to the MkI, also having a flip-top lid with extra handles fitted to the front. Photo 5 (above): the AVO VCM MkIII has roll-over handles. Its grid voltage and gm controls are on the front panel, while the MkIV has them behind protective windows. Source: Rodney Champness 94  Silicon Chip Australia's electronics magazine siliconchip.com.au Tester meter movement is not enclosed, as the interior photo shows. Opening the back of the Valve Tester exposes the meter movement, making ‘clean room’ maintenance essential. The instrument is well-constructed but my example had a two-wire power lead. I did notice that slight ‘tingle’ that you get (due to mains leakage) when I ran my fingers over the front panel. I recommend the fitting of a three-core power lead to provide Earthing. You would need to make connections to the metal frames of the two power transformers. If you decide to take on an AVO to repair, get all the info you can first. All VCMs are compact, and the MkIV is tight to the point of inaccessibility/ invisibility for some components. Further reading The available circuit drawings are often difficult to interpret. I welcome discussion and corrections regarding my simplified illustrations. I have not found a single, easily-­ comprehensible circuit for any AVO. An example is the calibration circuit – the critical first area to examine when repairing or calibrating. I found the original AVO documentation hard to understand, mixing operating instructions with technical descriptions. If you’re a newcomer to the AVO, consider getting help from an experienced owner. You can find the detailed manufacturer’s instructions online, so I have not attempted to make this article comprehensive. You can find out a lot more Differences between voltage readings and applied voltages AVO valve testers rely on the tested valve’s self-rectification, so the applied voltages and currents are not the same as those selected on the controls, or indicated on the meter. On their DC ranges, meters commonly display average values, so they indicate 0.637 of a half-sinewave’s peak value, rather than the correct RMS factor of 0.707 for AC. The conversion factor from average to RMS is (0.707 ÷ 0.637) = 1.11, so with a selected anode voltage of 400V – the DC-equivalent mean – the instrument applies 444V RMS to the valve anode. While you won’t usually measure it, this is a peak value of some 630V. AVO’s meter is calibrated to deflect to twice the valve’s anode current. The grid voltage is even stranger. Selecting -10V bias on the Grid Voltage setting measures as -5.2V on an average-reading meter. This is a bit confusing, but you only need to consider it if you’re testing or calibrating an AVO valve tester. In the main part of the article, I treat all currents and voltages as DC values, unless the AC values are critical to description or calibration. Just to reiterate, the controls and the meter are calibrated for the equivalent DC values. by reading those instructions. See the links to just some of the many valuable references at the end of this article. Next month In the follow-up article next month, I’ll describe three AVO Valve Testers/ VCMs that I was given to test (plus my own CT160) and some of the problems that I encountered. In some (but not all) cases I was able to fix the problems and get them working properly again. Useful links Martin Forsberg’s excellent entries on the UK Vintage Radio Repair and Restoration Discussion Forum, in collaboration with Euan MacKenzie and permissions from Yutaka Matsuzaka: siliconchip.au/link/abeh (be aware Photo 6: the CT160 is the only AVO Valve Tester in a clamshell case. While it’s a later design, it only offers direct measurement of gm. siliconchip.com.au these texts are copyrighted). For the MkIV, see Guido Pedrali Noy’s thorough reconstruction of the user manual at: siliconchip.au/link/ abe5 Frank Philipse’s extensive list of resources for the MkII/III/IV, CT160 and the VCM163: https://frank. pocnet.net/instruments/AVO/ Extensive discussions for AVO products at: siliconchip.au/link/abei A must read (!) article on the VCM163 at: www.schmid-mainz.de/ Radio-Bygones_140.pdf Even more information on the AVO MkIV, including meter replacement: siliconchip.au/link/abe8 For information on servicing and repairs, see pages 3-10 of the PDF at: SC siliconchip.au/link/abeg Photo 7: the VCM163 is the only one with two meters! They show DC anode current and transconductance. Source: Jerry Aldrich, UK Vintage Radio Repair Forum Australia's electronics magazine August 2022  95 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. Simple mains timer/LED lamp dimmer If you need a low-power night light, for example, in a child’s bedroom, you usually have to buy a specialised light. But I realised that a high-power mains lamp could be configured to also act as a night light. So, I designed this circuit and put it in a box with a plug and socket so it can be connected inline with an LED desk or floor lamp. When the mains is switched on at the wall (or the switch on the box), the lamp comes on at full brightness. After a while (approximately 35 minutes), this lamp is automatically converted to a low-power light as the X2 capacitor is connected in series with it, limiting the current that it can draw. The circuit is based on a transformerless power supply (at lower left), generating a 24V DC rail. The timing circuit is based on schottky diode D6 (a BAT85) and a 100µF capacitor. While a schottky diode is reverse-biased, it has a higher leakage current than standard diodes, around 0.2-0.5µA. That slowly charges the low-leakage 100µF capacitor. Capacitance Lamp Current 100nF 5.9mA 220nF 12.7mA 330nF 19.5mA 470nF 27mA 680nF 39mA 1μF 57mA 96  Silicon Chip As the capacitor voltage increases, so does the voltage at the collector of buffer transistor Q2; Q1 & Q2 form a complementary (or Sziklai) pair that acts like an NPN transistor with a very high gain, so the timing capacitor is not discharged. Eventually, after about 35 minutes, enough voltage is applied to the relay coil to pull it in, disconnecting the direct path to power the lamp. Then, current must flow through the X2 capacitor. The value of this capacitor can be changed to alter the dimmed output current, as shown in the table on the circuit diagram. Note that not all LED lamps will work well with a lower-than-nominal voltage/current. Some will flicker. You might have to test several LED globes or lamps before finding one that works well with this circuit. Those with a simple linear driver are more likely to dim fully and not flicker. The RC low-pass filter after the mains switch (47W/100nF) limits the inrush current when the mains switch Australia's electronics magazine is closed. Dissipation in the 47W resistor will be around 355mW for a 20W lamp load. This resistor limits the maximum load to around 30W, but the rest of the circuit isn't designed for more than that anyway. This circuit isn’t just for bedrooms, either. You could have such a light in a place like a basement, so you can see well enough to reach the switch, then flick it off and on again to turn the light on to full brightness. As a bonus, you can’t forget to turn the light off – it will automatically dim some time after you leave. Note that this needs to be built into an Earthed metal case (eg, a sealed diecast aluminium box) with fully insulated mains wiring. You could cut an extension cord in half and feed in the wires via two cord grip grommets, or use an IEC mains input socket and a GPO mounted on the box, as shown in the circuit diagram below. Hichem Benabadji, Oran, Algeria. ($80) Editor's note: a 1N4004 can be used instead of a 1N4007 for D5. siliconchip.com.au Hearing Loop (telecoil) phone headset In the October 2020 issue of Silicon Chip, I wrote an item for Circuit Notebook (siliconchip.au/Article/14603) about making induction headphones for cochlear implants and hearing aid telecoils (T-coils). Ironically, I used hearing protectors bought at a local hardware store at a very modest cost. I am profoundly deaf and have bilateral cochlear implants that allow me to hear pretty well. Coming from a professional electronic background starting in the early 1960s, I find today’s highly integrated electronic technologies absolutely stunning. For various reasons, landline phone communications can still present difficulties for cochlear implant users, probably more so than for hearing aid users. That's because cochlear implants provide direct electrical stimulation of nerves in the cochlea, bypassing most of the ear mechanics. In contrast, a hearing aid uses all of the ear mechanics as well as a vast array of nerves in the cochlear by amplifying sound pressure and applying it to the eardrum. Thus, hearing aid acoustic stimulation tends to provide a fuller acoustic spectrum than cochlear implant stimulation. Sometimes, bilateral cochlear implants can have different left-right pitch perception, making accurate sound perception difficult, especially with the limited landline bandwidth and telephone handset's poor sound reproduction. So a cochlear implantee may have some difficulty using a standard single-sided acoustic phone handset. An improvement for both implantee and hearing aid users can be achieved with a bilateral “call-centre” style headset and microphone, eliminating ambient acoustic noise and reverberation while also feeding sound to both ears equally. Further clarity can be achieved by eliminating acoustic coupling and having the landline audio electromagnetically coupled to the cochlear implant or hearing aid with a T-coil. While a standard call centre headset will have some level of magnetic field leakage, maintaining stable coupling to the leakage magnetic field can be problematic. Headsets accompanying consumer phones have small receivers and are prone to moving around on the head. Also, the placement of the magnetic siliconchip.com.au receiver coil in the cochlear implant sound processor, or hearing aid, may not align well with the headset’s magnetic field. So, the problems are with magnetic field strength, proximity and stability. Fortunately, while not particularly elegant, industrial hearing protectors can provide some solutions to these problems. They can be used as a coil former to give a sizeable magnetic field distribution around the hearing devices’ T-coil, irrespective of location. They are also robust and provide a range of positional adjustments that are stable. My noise protectors had a conveniently shaped plastic profile behind the soft earmuffs, almost like a bobbin. This shape made a good coil former on which I previously wound 24 turns of 0.25mm diameter enamelled copper wire. I then glued light-duty figure8 cable to the headband using hotmelt glue to connect the left and right induction coils in series, as shown in the photo. I terminated the windings inside the plastic ear-cup through a 1mm hole drilled for the purpose. I then drilled more holes in the left-hand ear cup, one for the incoming two-core shielded cable plus one for a small screw to anchor an internal solder lug. To turn these into a headset, I just had to add a boom microphone. My Uniden landline handset has a three-pin jack socket with contacts for common (sleeve), ear (ring) and microphone (tip). I thought about using an electret mic insert and making a boom fitting, but instead ordered a Uniden call centre headset with one earphone and a boom mic for about $40. This solved two problems; it provided an elegant microphone solution, and I was able to determine the resistance of the single earpiece at 150W. I then added a ¼-watt 150W resistor in series with the two earphone coils, presenting a total resistance of 157W to the handset. The mic’s boom attachment point was a 5mm diameter plastic post held down with a small self-­threading screw. I drilled a 5mm hole low down in the left earmuff, with two 2mm holes close by to feed the fine mic wires through. Fortuitously, the length of the plastic post was the same as the depth of the hole through the earmuff. On completion of the mechanical assembly, I performed the wiring. Apart from the figure-8 wire connection to the right-hand induction coil across the headband, all the solder connections are in the left-hand ear muff. With very little space in which to make soldered connections, I extended the length of the microphone wires by soldering to them and insulating them with heatshrink tubing. I used a solder lug to anchor several common connections and then fixed The headset makes phone conversations much easier for those with a hearing aid or cochlear implant. Australia's electronics magazine August 2022  97 Smoke, alcohol or LPG alarm This circuit raises an alarm if it detects smoke or LPG cooking gas leakage, or even alcohol vapours. This is achieved by using the same circuit with one of several sensors designed to detect smoke, LPG or alcohol. So different alarms can be made by simply changing the sensor. For a smoke alarm, use the MQ2 sensor; to detect alcohol, use the MQ3; or use the MQ6 sensor for LPG. The MQx sensors each have six pins. The heater filament, between pins H-H, is powered from the 5V rail. Two pairs of A-B pins connect across the sensing element; it doesn’t matter which pair you use. Half of the LM358 dual op amp the lug using a screw in a hole already drilled for the purpose. The wiring is hidden under foam acoustic pads inside the ear cups. The cable connecting to the phone has two wires, pink and white, plus a screen braid, with a three-way jack plug on one end. Do not mix up the microphone’s white return wire with the white wire in the cable back to the phone. If necessary, put a label on the microphone's white wire, change its colour with a marking pen, or solder it to the common lug first. Circuit Ideas Wanted 98  Silicon Chip (IC1) is wired as a comparator. A reference voltage set using potentiometer VR1 is applied to the inverting input (pin 2) while the sensor voltage goes to the non-inverting input (pin 3). The sensor produces a current that is converted to a voltage by the 10kW resistor between the B pin and ground. Output pin 1 of the op amp swings high whenever the sensor voltage goes above the reference voltage. A small amount of hysteresis is provided via positive feedback using a 10MW resistor so that the output doesn’t vacillate when the sensor voltage hovers around the trigger threshold. When pin 1 of IC1 goes high, The centre (ring) contact on the jack plug connects to one side of the string of two induction coils and the 150W resistor. The opposite end of that string goes to the common solder lug. The third and longest contact (sleeve) at the base of the jack plug is returned via the screening braid, which you should also connect to the common lug. When finished, check for around 157W between the jack plug ring and sleeve contacts. Depending on the probe polarity, there should be around 1.2-2.5kW between the tip transistor Q1 releases the reset signal on 555 timer IC2, which is configured as an astable multivibrator, so it starts oscillating. The frequency depends on the value of the capacitor connected to pin 6 and the two resistors connected to pin 7. The resulting square wave is AC-coupled to a small 8W speaker to produce the alarm tone. After switching on the 5V supply, wait about ten seconds for the filament to heat up. Then adjust VR1 until the alarm just stops sounding. Enclose the PCB in a suitable box with vents so that fumes can circulate near the sensor. Raj K. Gorkhali, Hetadu, Nepal. ($75) and sleeve. If all indications are OK, plug your induction headset into a suitable phone and press talk to hear a dial tone. Using my Silicon Chip Hearing Loop Tester/Level Meter (November & December 2010; siliconchip.au/ Series/15), I found that the dial tone was smack bang on 0dB or 0.1A/m. The phone also has a volume control that can reduce the volume below that level. Anthony Leo, Cecil Park, NSW. ($90) Got an interesting original circuit that you have cleverly devised? We will pay good money to feature it in Circuit Notebook. We can pay you by electronic funds transfer, cheque or direct to your PayPal account. Or you can use the funds to purchase anything from the SILICON CHIP Online Store, including PCBs and components, back issues, subscriptions or whatever. Email your circuit and descriptive text to editor<at>siliconchip.com.au Australia's electronics magazine siliconchip.com.au Ventilation Fans We stock a wide range of DC and AC powered enclosure fans to keep your projects cool. A GREAT RANGE AT GREAT PRICES. 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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 How to convert 12V AC to 24V DC I want to add low-voltage LED retro festoon string lights to an existing garden lighting system. All the units that look good and are robust require 24V DC, whereas the garden lighting is 12V AC. Additional cabling would require lifting up pavers & digging up an established garden. So I am keen to know whether I can use a small 230:115V AC transformer in reverse to step up the voltage and then regulate it to DC. The 12V transformer has plenty of spare capacity as originally sized for 12V halogens which have been replaced with 12V LED units. (T. H., Batehaven, NSW) ● It’s possible that the step-up transformer would work; it depends on the details of the transformer, but likely it would give you double the AC voltage. You would still have to convert that to DC. However, there are simpler/ easier ways. To start with, a simple full-wave voltage doubler feeding a pair of 4700µF 16V electrolytic capacitors will give you pulsating DC averaging around 25V DC with a 2A load. Using pairs of diodes in series would drop that to be very close to 24V DC, as shown in Fig.1. The capacitors need to be low-ESR types with a high ripple current rating, ideally at least 2A. There will be a few volts of ripple across the LEDs (6V peak-to-peak according to our simulation). We suspect that won’t bother them, but it depends on their exact design. The output voltage of that circuit is somewhat load-dependent; for a 1A load (say), you would just need to reduce the filter capacitors to 2200µF and eliminate the extra series diodes to get much the same output voltage. If you need the DC supply to be ripple-free, there are a few ways to achieve that. Fig.2 shows a similar circuit with a very basic linear regulator based on an NPN transistor and zener diode. Simulation shows it delivers a smooth ~24V DC output. The transistor should be a type with decent gain up to a few amps (such as the KSC2334Y shown). Q1 will dissipate close to 10W, so it will need a decent heatsink; an IP65 sealed metal case could be used to house the circuit and also as a heatsink, with an additional finned heatsink bolted to the outside directly opposite the transistor. The output ripple with this version is a fraction of a volt. With a linear design like this, it’s hard to avoid dissipating a few watts if you need a mostly ripple-free output. For a more efficient approach, try using a rectifier/filter circuit like those shown here with Tim’s Blythman’s Buck/Boost LED Driver (June 2022; siliconchip.au/Article/15340) to convert the pulsating DC to a smooth, regulated DC. We have a kit for that project (siliconchip.au/Shop/20/6292). Because that board can deal with an input voltage above or below the output, the exact voltage being fed to it isn’t critical. However, it’s better to arrange for the input voltage to be above, or at least close to, the output voltage. That will give maximum efficiency. It can deliver around 5A in this configuration, given sufficient filter capacitance on the output of the rectifier. Dimming for Buck/ Boost LED Driver I ordered the Buck-Boost LED Driver kit (SC6292; June 2022, siliconchip. au/Article/15340) and LED panel from you last week, and the package arrived promptly early this week; thank you. It’s now assembled and running nicely. Compliments to whoever laid the PCB out, as it’s obviously been designed for ease of assembly. Having most of the smaller components lined up across the board’s edges with large pads made it quite easy to place and solder them. One comment about the assembly instructions: nowhere did I see any mention of soldering the ground pad of the LM5118 to the PCB. I heated the via on the underside of the PCB with a hot iron and fed a quantity of solder into the via. It seemed to wick in, so hopefully that worked. Fig.1 (left): the full-wave voltage doubler will give close to 24V DC from 12V AC, but with substantial ripple. Fig.2 (below): adding a very basic linear regulator applies a smooth 24V DC to the load, but with about 10W dissipation. Using the Buck/Boost LED Driver instead would result in much lower losses. 100  Silicon Chip Australia's electronics magazine siliconchip.com.au Getting to the point of my email, Can you suggest a modification to add a dimmer control? I want to make a work light with the LED, but it’s very bright. I’d thought the current limit adjustment pot might work, but it only reduces the current to 1.5A, which is still very bright. (D. S., East Melbourne, Vic) ● Thanks for the kind words about the layout. We must admit that the LM5118 is well suited to a convenient layout. You are correct that we should have mentioned the thermal pad on IC1 – we soldered it on our prototype. We have published an erratum to make readers aware of this. With hand soldering, the process you used is about the only practical way to solder such a pad. Unfortunately, the current control does not lend itself well to a minimum value near zero as it depends on the current rising high enough to overcome the diode threshold above the 1.23V reference voltage. If you are comfortable with a proportionally lower maximum current, substituting a higher-value shunt resistor than 15mW (the one between TP4 and TP6 only) should work. Another option is to apply a PWM signal across JP1, which should effectively PWM the output. We haven’t tested this; you might need to remove (or reduce) the 100nF capacitor labelled C14 attaching to IC1’s pin 7 (7th component from the left along the bottom) to cut out the soft-start ramping. We think a relatively low PWM frequency would give the most linear response. Finally, you could simply add an external voltage control pot. It won’t give perfect control but should let you cut the brightness way down, while the current limiting will prevent any damage to the LED at the upper end of its range. With the current limit at 4A, the voltage pot range from off to full will be about 700W to 400W. So a 500W pot with a 750W parallel resistor between the wiper and one end, plus a 390W resistor in series with both, should give a suitable adjustment range. This combination can be wired up in place of the onboard 5kW multi-turn trimpot. Solar PV (photovoltaic) water heating What is the strategy to connect solar panels (in series or parallel) to a water heater with a resistive element, say about 2.4kW? I expect you need to interface with maybe an inverter and batteries. Perhaps you have covered this previously in the magazine. (F. C., Maroubra, NSW) ● We have covered this previously in the magazine on several occasions. There are various ways to do what you are asking, all of which have problems. For example, see: • September 2013, pages 98 & 99 • September 2014, pages 98 & 99 • October 2017, page 96 • December 2017, pages 4 & 5 The bottom line is that if you’re going to use solar power to heat water, you ideally want an electric water heater with dual elements (a main element and a ‘booster’) so that you can power one from the mains and the other from solar power. That way, you’ll always have hot water. The problem with feeding solar power to an inverter with the output of the inverter driving one of the water heater elements is that it likely won’t deliver any power unless there is enough solar power available to drive the element at its full power rating (eg, 2.4kW). So that approach is generally not going to work well. That leaves the idea of arranging the panels so that they produce around 240V DC in peak sun under load and driving the heater element with DC. This has the advantage that it will provide whatever power is available, even if your panels cannot deliver enough power to achieve the full rated element power. It’s also going to be the most efficient method. However, using DC will promote corrosion, so it is necessary to arrange for a contactor or similar to reverse the polarity periodically (eg, every 12 or 24 hours). Also, it is unclear whether the thermostat will last long if it’s switching DC rather than AC. Finally, you would probably need to get a licensed electrician to do the wiring if the heater is also mains-­powered, and it’s unclear whether your average electrician would want to do this sort of work. In conclusion, you’re probably better off installing a standard solar hot water system as they are designed for the job. Help to find a Coilcraft part I am having trouble finding one of the Coilcraft items for the Precision AM/FM DDS Signal Generator (May 2022; siliconchip.au/Article/15306). Please verify the part number for the Coilcraft 1206CS-121XJEC 120nH chip inductor. It does not appear to exist on either the Coilcraft site or Tricomponents site. (J. S., Avondale, Qld) ● It seems like a valid part number. Here it is on Coilcraft’s website: siliconchip.au/link/abff We don’t think that using that particular part is especially critical; Raspberry Pi Pico BackPack With the Raspberry Pi Pico at its core, and fitted with a 3.5inch touchscreen. It's easy-to-build and can be programmed in BASIC, C or MicroPython. There's also room to fit a real-time clock IC, making it a good general-purpose computer. This kit comes with everything needed to build a Pico BackPack module, including components for the optional microSD card, IR receiver and stereo audio output. $80 + Postage ∎ Complete Kit (SC6075) siliconchip.com.au/Shop/20/6075 The circuit and assembly instructions were published in the March 2022 issue: siliconchip.au/Article/15236 Australia's electronics magazine August 2022  101 many manufacturers have 120nH chip inductors that could be used instead and might be easier to get. Note that element14 stocks the XGLC and XJLC versions of those chip inductors, and they would be fine in this application. Yet another version of the R80 Receiver kit I refer to the review of the R80 Receiver kit in the November 2021 issue (siliconchip.au/Article/15101). I have built this unit but am having problems with the modifications on page 43. The BC548 emitter is connected to pin 9 of the display PCB plug (GND), while the collector is connected to the junction of R18 and D3, not the junction of D2 and CP5 as shown. The BC548 is mounted with the flat towards the board, not away from it as shown in the article. I have checked for errata in later editions but could find nothing on this. Was this a later modification? (J. P., via email) ● Andrew Woodfield replies: your kit appears to be an earlier (!) version than the one we reviewed, most likely V6 (the review was of V7). Most readers who reported discrepancies between their kits and our review had later versions of the kit. We aren’t sure if you need to make the squelch modifications to the V6 kit. It may help, but it will have to be done differently as the design is obviously not the same. It would help if you had a circuit for your version of the kit to compare to the one for V7 posted on the Silicon Chip website (siliconchip. au/Shop/6/5950). Flight level is based on pressure, not altitude I am reading the “Advanced GPS Computer” by Tim Blythman (June & July 2021; siliconchip.au/Series/366), and I hope you’ll indulge me in clearing up an uncertainty. The Computer can show flight levels (FL) as well as altitude, but I missed seeing how barometric pressure is measured (which is necessary to convert altitude to FL). Many thanks for pointing this out to me; I hope I haven’t missed the obvious. (G. M., aircraft museum curator, London, UK). ● The Advanced GPS Computer uses the altitude data from the GPS receiver 102  Silicon Chip module, so it does not calculate an altitude or flight level based on barometric pressure. So it is more correct to say that it can display the altitude in the same units as flight level, but does not display a true flight level based on pressure. We’re considering an update to the project which adds a barometric pressure sensor like the BMP280 so that it can show the proper flight level. Design for density altitude meter wanted Have you published a design for a density altitude meter? (L. B., via email) ● We have not, but we have published hardware designs that could be used as a density altitude meter with some relatively simple changes to the software. For example, the Touchscreen Altimeter and Weather Station (December 2017; siliconchip.au/Article/10898). It has an onboard barometric pressure sensor and temperature sensor. Those provide the two values that you need to compute the density altitude. The BASIC software is available online (siliconchip.au/Shop/?article=10898), so it should be relatively simple to modify the software to calculate and show the density altitude, then upload that to the BackPack. Transducer power for Ultrasonic Cleaner I am interested in building the “Large Ultrasonic Cleaner” featured in the August 2010 issue (siliconchip. com.au/Article/244) but with some modifications. First of all, I am wondering if it’s possible to use a 35W transducer instead of 50W as the larger unit is somewhat hard to get at the moment, and the smaller unit can be had for a very good price on sale. If so, I imagine that some changes may need to be made to the drive circuit to avoid over-driving the transducer. Secondly, to compensate for the lower-power transducer, I was thinking of running two in parallel. I imagine this achieved not by simply running both transducers from one circuit, but by duplicating the drive circuitry (Mosfets and transformer), running both sets from one microcontroller. Is that feasible? Or would two transducers on the same cleaning tank Australia's electronics magazine interact negatively with each other? (A. C., Auckland, NZ) ● You can use the 35W transducer at a reduced power level. We don’t recommend using more than one transducer, even if the driver section is duplicated. That’s because each transducer needs to operate at the correct frequency for the selected output power. Individual transducers will have slightly different resonances, so one transducer will be delivering the majority of the power output if two are used. Note that we published a revised version of that project in September & October 2020 (High Power Ultrasonic Cleaner, siliconchip.com.au/ Series/350). Altronics sell a kit for the newer design, Cat K6022. BWD power supply circuit diagram wanted In the Serviceman’s log column in November 2010, you detailed a repair to a BWD 207B power supply and mentioned that you had obtained several versions of the service manual. I have tried various methods to try and obtain a service manual for this power supply but to no avail. Are those manuals available on your website, and if so, where? (P. A. S., via email) ● We haven’t uploaded the BWD 207B manual or circuits to our website but we can supply them upon request. 2010 DAB+ Tuner has limitations I have had this DAB+/FM Tuner (October-December 2010; siliconchip. au/Series/13) running for many years now (I built it from the Jaycar kit) without any problems. The ABC has recently updated (reassigned bandwidth) to their DAB+ transmissions. They recommended re-scanning the stations, so I did, but the scan did not complete. I turned off the unit and found that it only found 62 stations of the 72 available in Melbourne. I did this at least three times with the same result each time. I did notice that some but not all of the ABC stations were scanned. Once, it left out ABC Melbourne. I have the latest firmware of 7.71. Do you know why it is not picking up all the channels? (A. L., Watsonia, Vic) ● It turns out that the 2010 DAB+/ FM Tuner firmware has a hard-coded continued on page 104 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 PCB PRODUCTION PCB MANUFACTURE: single to multilayer. Bare board tested. One-offs to any quantity. 48 hour service. Artwork design. Excellent prices. Check out our specials: www.ldelectronics.com.au LEDs and accessories for the DIY enthusiast 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 Email for a postage quote, quote the number directly below the photo when referring to a book: silicon<at>siliconchip.com.au Issues Getting Dog-Eared? Keep your copies safe with these handy binders Order online from www.siliconchip.com.au/Shop/4 see website for overseas prices or call (02) 9939 3295. REAL VALUE A T $19.50* PLUS P&P ADVERTISING IN MARKET CENTRE Classified Ad Rates: $32.00 for up to 20 words (punctuation not charged) plus $1.20 for each additional word. Display ads in Market Centre (minimum 2cm deep, maximum 10cm deep): $82.50 per column centimetre per insertion. All prices include GST. Closing date: 5 weeks prior to month of sale. To book, email the text to silicon<at>siliconchip.com.au and include your name, address & credit card details, or phone Glyn (02) 9939 3295 or 0431 792 293. WARNING! Silicon Chip magazine regularly describes projects which employ a mains power supply or produce high voltage. All such projects should be considered dangerous or even lethal if not used safely. Readers are warned that high voltage wiring should be carried out according to the instructions in the articles. When working on these projects use extreme care to ensure that you do not accidentally come into contact with mains AC voltages or high voltage DC. If you are not confident about working with projects employing mains voltages or other high voltages, you are advised not to attempt work on them. Silicon Chip Publications Pty Ltd disclaims any liability for damages should anyone be killed or injured while working on a project or circuit described in any issue of Silicon Chip magazine. Devices or circuits described in Silicon Chip may be covered by patents. Silicon Chip disclaims any liability for the infringement of such patents by the manufacturing or selling of any such equipment. Silicon Chip also disclaims any liability for projects which are used in such a way as to infringe relevant government regulations and by-laws. Advertisers are warned that they are responsible for the content of all advertisements and that they must conform to the Competition & Consumer Act 2010 or as subsequently amended and to any governmental regulations which are applicable. siliconchip.com.au Australia's electronics magazine August 2022  103 limit of 64 stations in total that it can store. We are unsure of the reason for this limitation as the designer of that project left Silicon Chip many years ago. We assume it is due to the limited amount of flash memory or RAM available. It’s possible that could be changed, but we no longer have a prototype to test new firmware, nor are we confident that compiling the source code with a current compiler will necessarily produce working code without being able to test it. Our much more recent Touchscreen DAB+/FM/AM Tuner design (January-March 2019; siliconchip.au/ Series/330) does not suffer from this problem. It must have an upper bound on the number of stations it can tune, Advertising Index Altronics.................................43-46 Dave Thompson........................ 103 Digi-Key Electronics...................... 3 element14................................... 11 Emona Instruments.................. IBC Hare & Forbes............................. 13 Jaycar.......................... IFC, 5, 7, 21, ..............................24-25, 77, 79, 99 Keith Rippon Kit Assembly....... 103 LD Electronics........................... 103 LEDsales................................... 103 Microchip Technology.................. 9 Mouser Electronics..................OBC Ocean Controls............................. 8 SC Pico BackPack.................... 101 but nobody has run into it yet. Also, the source code is available (it’s written in BASIC), so it could easily be fixed if such a limitation existed. While the parts for that project are somewhat hard to come by, we do have a handful of Si4689 ICs on hand for anyone who wishes to build one, and the PCB, Explore 100 kit and other associated parts are still available – see siliconchip.au/Shop/?article=11369 Consider, though, that this newer project requires some fairly small SMDs to be soldered. But we think that is a better situation than the old tuner, which needed a module that wasn’t available to purchase (it only came as part of the now-discontinued Jaycar kit). Replacement pot for Class-A amp My 20W Class-A amplifier (MaySeptember 2007; siliconchip.com.au/ Series/58) is in need of a new volume pot as it has gone all scratchy. It is an Alpha dual-gang 20kW log motorised pot, previously sold by Altronics as Cat R2000 but no longer available. Do you know of a suitable replacement? Is it possible to retrofit one from another brand? (N. M., Sunbury, Vic) ● We suggest you try spraying some contact cleaner into the wiper assemblies first as that might resolve your scratchiness with much less expense and hassle than replacing the pot (eg, try Jaycar Cat NA1012). If you do need to replace it, the pot value is not so critical (eg, you could use a 10kW or even 5kW dual-gang log pot). The main concern is it fitting on the existing preamp PCB. Bourns Pro Audio PRM162-K420K103A1 is a 10kW dual gang logarithmic pot with dimensions very similar to the Alpha unit Altronics sold. The PCB SC SMD Test Tweezers.............. 63 Silicon Chip Shop.................70-71 Silicon Chip Subscriptions........ 23 Silvertone...................................... 6 The Loudspeaker Kit.com.......... 10 Tronixlabs.................................. 103 Wagner Electronics..................... 73 104  Silicon Chip Errata and Next Issue Silicon Chip Binders................ 103 probably would need some slight modifications to make it fit (due to slightly different motor mounting posts) but we think it would not be too hard to retrofit. Unfortunately, it is somewhat hard to find anyone with this in stock. Verical list 142 in stock at the time of writing and we have purchased from them before, so we think that is a reasonable option (siliconchip.au/ link/abdh). Master Electronics also say they have 147 in stock but we have no experience with them – see siliconchip.au/ link/abdi Stereo Compressor kit wanted Is the Stereo Compressor kit still available? It used to be sold by Jaycar, but they no longer supply it; I hope you can help. (A. B., Christchurch, NZ) ● We designed two different Stereo Compressors that were made as Jaycar kits, one in June 2000 (siliconchip.au/ Article/4328; Jaycar Cat KC5291) and one in January 2012 (siliconchip.au/ Article/809; Jaycar Cat KC5507). Jaycar makes their kits based on our articles; we do not make them for Jaycar. It does look like both Jaycar kits are no longer available. You might be able to get a kit for the January 2012 design from Altronics (Cat K5526). It is still listed on their website; it looks like they are very low on stock, but they have kits in a few stores. Perhaps if you contact them, they can get one back to their warehouse and deliver it to you. Failing that, we can supply PCBs and panels for the January 2012 design, see siliconchip.au/Shop/?article=809 You would need to get the rest of the parts yourself. It looks like they are still available; the critical part is the SA571 IC (in DIP), and they are for sale on eBay. SC Spectral Sound MIDI Synthesiser, June 2022: the orientation of diode D2 in Fig.9 is incorrect. Install it with the cathode stripe facing to the right, as shown on the PCB silkscreen. Digital FX (Effects) Pedal, April & May 2021: Fig.2 in the April issue shows incorrect connections for op amp IC3b. Its pins 5 & 6 are swapped. Pin 6 (−) should be at the top, connected to the 4.7μF capacitors, while pin 5 (+) should be at the bottom, connected to Vcc ÷ 2. The PCB has the right connections. Next Issue: the September 2022 issue is due on sale in newsagents by Monday, August 29th. Expect postal delivery of subscription copies in Australia between August 29th and September 16th. 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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