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AUGUST 2023 ISSN 1030-2662 08 The VERY BEST DIY Projects! 9 771030 266001 $ 50* NZ $1290 11 INC GST INC GST Watering System Controller A ‘smart’ WiFi watering system with season-based schedules that can check the weather forecast The Australian Electrical Grid Electricity is distributed locally and via inter-state ‘interconnectors’ and sold on an energy market Arduino-based LC and ESR Meter Built using all through-hole parts, it’s ideal for checking suspect capacitors and inductors Calibrated Measurement Microphone An affordable phantom-powered, balanced microphone that’s calibrated against a reference mic ...plus much more inside high-altitude Aerial Platforms long-endurance aircraft for observation and communication Design, service or repair with our 100MHz Dual Channel Digital Oscilloscope Need more info than your DMM can display? Upgrade to this new and affordable feature-rich oscilloscope to get an accurate picture of your circuit's operation. 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Jaycar reserves the right to change prices if and when required. Contents Vol.36, No.08 August 2023 14 High-Altitude Aerial Platforms High-altitude platform stations (HAPS) fly above most planes and are utilised for observation and communication. They are especially useful when it would be too prohibitive to organise a satellite, and they can even be launched by amateurs/hobbyists. By Dr David Maddison Technology feature 46 The Electrical Grid Australia’s electrical grid operates as several isolated systems rather than a single distribution network. This article covers how the grid is managed between the states via the interconnectors and the role of the NEM. By Brandon Speedie Electricity generation & distribution 66 RadioFest 2023 The Historical Radio Society of Australia (HRSA) is hosting Australia’s largest radio exhibition in Melbourne this year on September 16th and 17th. By Kevin Poulter Vintage radio event 80 An interview with DigiKey We had the opportunity to interview DigiKey’s Vice President of the AsiaPacific region, Tony Ng, about the future and history of the company. By Silicon Chip Interview 30 The WebMite The WebMite is a Raspberry Pi Pico W with MMBasic, WiFi and regular internet connectivity. It can be used to implement a web server, check the weather, send emails, transfer files using TFTP and more. By Geoff Graham & Peter Mather Raspberry Pi Pico W feature 36 Watering System Controller By using the WebMite, you can build an advanced Watering System Controller that does it all! It has individual scheduling depending on the season, checks the weather forecast before running and can alert you to a burst pipe or blocked sprinkler. By Geoff Graham Reticulation system project 54 Arduino-based LC & ESR Meter This project is an enhanced version of our previous LC Meter allowing it to also measure capacitor ESR. It can be built as a standalone PCB, or as an add-on to the original project. By Steve Matthysen Test & measurement project 68 Calibrated Measurement Mic If you can’t justify the cost of a fancy microphone, or need several tailored mics, then this phantom-powered, balanced and calibrated microphone is for you! You can choose from multiple different microphone capsules that can be calibrated to produce an almost flat response. By Phil Prosser Audio project Watering System Controller Page 36 Arduino–based LC and ESR METER Page 54 Page 68: a low-cost, calibrated Measurement Microphone 2 Editorial Viewpoint 5 Mailbag 29 Subscriptions 82 Serviceman’s Log 90 Circuit Notebook 94 Vintage Radio 1. dsPIC-based audio spectrum analyser 2. USB power board 3. Cases for the Advanced Test Tweezers Replacing Vibrators, Pt3 by Dr Hugo Holden 104 Online Shop 106 Ask Silicon Chip 111 Market Centre 112 Advertising Index Cover Photo: the solar-powered Centurion by NASA (www.nasa.gov/centers/armstrong/news/FactSheets/FS-054-DFRC.html) SILICON SILIC CHIP www.siliconchip.com.au Publisher/Editor Nicholas Vinen Technical Editor John Clarke – B.E.(Elec.) Technical Staff Jim Rowe – B.A., B.Sc. Bao Smith – B.Sc. Tim Blythman – B.E., B.Sc. Advertising Enquiries (02) 9939 3295 adverts<at>siliconchip.com.au Regular Contributors Allan Linton-Smith Dave Thompson David Maddison – B.App.Sc. (Hons 1), PhD, Grad.Dip.Entr.Innov. Geoff Graham Associate Professor Graham Parslow Dr Hugo Holden – B.H.B, MB.ChB., FRANZCO Ian Batty – M.Ed. Phil Prosser – B.Sc., B.E.(Elec.) Cartoonist Louis Decrevel loueee.com Founding Editor (retired) Leo Simpson – B.Bus., FAICD Silicon Chip is published 12 times a year by Silicon Chip Publications Pty Ltd. ACN 626 922 870. ABN 20 880 526 923. All material is copyright ©. No part of this publication may be reproduced without the written consent of the publisher. Subscription rates (Australia only) 6 issues (6 months): $65 12 issues (1 year): $120 24 issues (2 years): $230 Online subscription (Worldwide) 6 issues (6 months): $50 12 issues (1 year): $95 24 issues (2 years): $185 For overseas rates, see our website or email silicon<at>siliconchip.com.au Recommended & maximum price only. Editorial office: Unit 1 (up ramp), 234 Harbord Rd, Brookvale, NSW 2100. Postal address: PO Box 194, Matraville, NSW 2036. Phone: (02) 9939 3295. ISSN: 1030-2662 Printing and Distribution: 24-26 Lilian Fowler Pl, Marrickville 2204 2 Silicon Chip Editorial Viewpoint High inflation and price changes While I previously said to expect an update on magazine pricing in September, since the new prices have been decided, I’m revealing them now. The last price increase was in October 2021 and I was planning to make a small adjustment two years after that. Unfortunately, that small adjustment has gone out of the window given the current economic environment. Still, we are not passing on all the cost increases because I think it would be too much in one go. The cover price will go up by $1 from the October 2023 issue, to AU $12.50 and NZ $13.90. Subscription rates will increase by a lesser proportion on the 1st of November 2023 – see below. For example, the 12-month Australian print subscription price will increase 6.3% compared to the 8.7% cover price change. As I wrote last month, we greatly value subscribers and want to ensure that subscribing is as attractive as possible while also staying in business long-term. To put the price increase into perspective, annual CPI inflation is hovering around 7%, so I could have argued that an increase greater than 10% was justified. That means, when adjusted for inflation, the magazine price is actually decreasing over time (although I understand that might provide little consolation). On the 1st of July, the electricity tariff for our office went up from 28.956¢/ kWh to 41.515¢/kWh, a whopping increase of 43.4% in one go! I’m sure many of our readers are facing similarly unreasonable price increases. Then there are our printing costs. Between July 2021 and July 2023, our per-copy printing cost went up by 42%. The online version doesn’t involve printing, so we are not increasing online subscription prices as much as the others. Also, print subscription prices outside Australia and New Zealand are not changing this time, as we already had to increase them substantially last time. Since subscription rates are not going up until later this year, you can lock in the current rate for the next few years by renewing or extending your subscription before then. Or, if you don’t have a subscription, by taking one out. We’ll review the prices in another couple of years. I hope that inflation has settled down to a more normal level by then! by Nicholas Vinen Online 6 months $50 → $52.50 Online 12 months $95 → $100 Online 24 months $185 → $190 Australia print 6 months $65 → $70 Australia print 12 months $120 → $127.50 Australia print 24 months $230 → $240 Australia combined (print + online) 6 months $75 → $80 Australia combined 12 months $140 → $147.50 Australia combined 24 months $265 → $275 New Zealand print 6 months $80 → $82.50 New Zealand print 12 months $145 → $150 New Zealand print 24 months $275 → $285 New Zealand combined (print + online) 6 months $90 → $92.50 New Zealand combined 12 months $165 → $170 New Zealand combined 24 months $310 → $320 New Prices Print (AU) Combined (AU) Print (NZ) Combined (NZ) Online 6 months $70 $80 $82.50 $92.50 $52.50 12 months $127.50 $147.50 $150 $170 $100 24 months $240 $275 $285 $320 $190 All the prices above are in Australian dollars (AUD) 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”. Switching to reading the magazine online After all these years (and filing cabinets full of magazines), I have decided to try the online version. I will not miss the torn covers from our mailman jamming them in the letterbox. I really enjoy the magazine and the many entertaining and inspirational articles. The advanced components and software needs of projects are beyond my fading grey cells now, but it is always interesting to keep up with technology. Keep up the good work. David Humrich, Greenwood, WA. LC Meter is very sensitive to inverter chip used I would like to add a quick comment and thank you to Charles Kosina for his detective work on his LC Meter (November 2022; siliconchip.au/Article/15634). I also had problems and experienced the same symptoms during the calibration phase that he described in his letter in the May 2023 issue (Mailbag, p6). My unit seemed to work about 50% of the time after forcing a calibration, but rarely from a cold start. At the time, I had put this down to a bug in the software (because it worked some of the time) – another case of barking up the wrong tree. So I thought I would wait it out and expected to see something in the notes and errata about it at some stage. After reading his Mailbag letter, I promptly ordered a replacement Fairchild 74AC04 from eBay. I swapped it out, and now it works every time. My original 74HC04 was indeed the Toshiba IC supplied with the kit, so I suspect there may be more of us out there... Simon Smith, Zillmere, Qld. Reminiscing about the Y2K bug Y2K again! (June 2023; “The Y2K38 Bug”) I get a bit antsy when I keep hearing that it was all a hoax. In 1999, I was computer support in the graphics department at the Perth station of one of the major TV networks. For the year prior, we had gone through, identified and checked every computer on the station for susceptibility to the ‘bug’. All of them passed OK except one, and if I had still been there (I took a voluntary redundancy on the 29th of October 1999), I would have had to go in on New Year’s Day 2000 to correct this one computer. It was a stills/slide store that used a 486 motherboard. Yes, it would have rolled over to the wrong date on 1/1/2000. It was a real thing, this Y2K bug. It wouldn’t have been a big deal if it hadn’t been fixed; it would only have meant that stills would have been saved with an incorrect date. No aircraft would have crashed. I remember that time clearly. Not a day went by without at siliconchip.com.au least one article in every newspaper or magazine, repeated endlessly and boringly for that year. But it was not a hoax or false alarm; it was real. Peter Croft, Butler, WA. Comment: no doubt it was seriously overblown in the media, but there probably would have been some serious consequences (to airlines, banks etc) had nothing been done in the lead-up to the year 2000. Many dud CR2032 cells these days I just finished building the Advanced SMD Tweezers kit (February & March 2023; siliconchip.au/Series/396). There was no display when I inserted the 3V coin cell. I checked over the board for any shorts and checked the orientation of the PIC24 IC; they were fine. I then tried to connect a PICkit 3 to the PIC24 with the OLED and coin cell removed, but MPLAB IPE timed out. I suspected the PIC was faulty. Luckily, it turned out to be a dud coin cell battery. I measured the battery voltage at 2.98V with no load, but everything started working after replacing the battery. I think the Advanced Tweezers will be a pretty handy bit of kit with all the different functions in one compact device. Tim must be quite proud of the project. Nick Sibbald, Ipswich, Qld. Comment: we have also had many problems with dud CR2032 cells from various sources of late. They work fine initially in car keyfob remotes etc but then need replacing in six or twelve months. We’ve had to resort to buying the more expensive cells (eg, Energiser Ultimate Lithium) to get something that lasts. We aren’t sure why you couldn’t connect to the PIC24 using a PICkit 3. It should work; did you enable target power in the software settings? We suspect a bad connection with the ICSP header if it doesn’t work with that enabled. Tim spent a fair bit of time developing the software for this project, which has been pleasingly popular. Are AIs already masquerading as people? I found Nicholas Vinen’s May 2023 editorial on the “AI Revolution” interesting, but I thought I might provide another perspective that I hope will interest your readers. For quite some years, I have been reading stories taken from the website Reddit that generally involve some self-­ entitled person or group getting their ‘comeuppance’. I have noticed an interesting trend in the stories over the past year or less. The first thing I noticed was that some stories ended with a moral message so ‘pat’ that it sounded like it was written to be read to toddlers. Australia's electronics magazine August 2023  5 The second thing I noticed, and others are beginning to notice, is that many stories, including stories that lacked the moral message ending, had bizarre inconsistencies. What is most interesting about these inconsistencies is what they’re inconsistent about. The inconsistencies revealed that the writer had little to no idea of how the real world works. They involve such things as police not following the correct procedures or important information being unstated in the story when any average person would never forget to include such information. This is happening so frequently that I have concluded that some people ask an AI writer to write stories for them and then post them to Reddit as though they are true. This trend exposes the real problem with any AI: it has no real experience to draw upon. An AI has never experienced life. It has no real emotions and does not actually know how real people behave or what real people want. It is incapable of understanding the subtleties of human interactions or knowing anything about how the real world works. Although the differences between a human-written and an AI-written story are subtle, they are also very evident to anyone who is well-read (which I consider myself to be). In summary, while allowing an AI to perform certain limited tasks may be a good option, ultimately, they will still require human oversight for a very long time due to this one significant shortcoming. It is a shortcoming that I believe will not be overcome unless true robots with truly general AI (AGI – artificial general intelligence) become a reality. But that will come with its own set of problems which I won’t go into. Thanks for making Silicon Chip magazine. I especially enjoy Serviceman’s Log and Circuit Notebook, although most articles in each issue get at least a look from me. Jonathan Waller, via email. Treadmill/lathe motor controller design I noticed a question on page 102 of the July 2023 issue about high-voltage DC motor control for a treadmill. A while back, I completely reverse-engineered the DC motor controller in my Sieg mini-lathe. I did that as there is no detailed manufacturer data on it and nothing useful on the internet either, aside from some glib descriptions of how it is supposed to work. The lathe uses the same type of 180-200V DC motor that is popular in treadmills. I found that the designers at Sieg had done a very clever job on it, using op amps to PWM control the Mosfet. The servo system they created does not require a CPU and could be generalised to very high-power motors simply by selecting the appropriate current sensing resistor and a suitably heatsunk and rated power Mosfet. It also has adjustable overload protection and synthetic torque [sic]. I went into plenty of detail on the operating theory in the PDF available from my website at siliconchip.au/link/abmn A controller like that could be made into a compact, generic type that could work for new projects. It could also replace failed treadmill and lathe controllers, where there is no original manufacturer replacement or for other high-voltage DC motor applications/projects. Sieg did make a replacement for the one in my lathe using SCRs, but for a few reasons (as explained in the PDF), it is not as good as the PWM Mosfet unit. 6 Silicon Chip Australia's electronics magazine siliconchip.com.au The 150-180W version is all on one PCB and pretty compact. They used surface-mount op amps on a small vertical board to save some PCB space. It gives smooth motor control down to low speeds. I discovered that two board versions exist, one a fourlayer type while the original has two layers. Both versions have become very rare. There are a few disappointed people with C1 lathes that could not get their boards repaired or get a replacement. If any motor controller is worth cloning, this is the one! Dr Hugo Holden, Minyama, Qld. Comment: we’re investigating what it will take to design a compatible PCB and test the resulting speed controller. Mains speed controller is working well I successfully built and incorporated the Refined FullWave Motor Speed Controller (April 2021; siliconchip.au/ Article/14814) into an inexpensive magnetic-based drill that was running far too fast for our liking. The magnetic base requires full voltage, so the controller couldn’t go in series with the whole unit. Fortunately, it was pretty easy to connect the controller in series with one of the wires going to the motor itself. I 3D printed a ‘flange’ to replace the rear plate of the drill control box and fitted the controller to that, with the appropriate wiring going out through a grommeted hole in the rear of the controller box. The controller was initially tested The Refined Motor Speed Controller permanently wired to a magnetic drill press. 8 Silicon Chip with the plug and socket arrangement carefully wired in. It worked very well the first time on several appliances; I then wired it into the drill’s electrics (see the adjacent photo). I saw your response in the Ask Silicon Chip section of the July issue, where you advised D. K. of Wynnum on this kit. I had no trouble obtaining the parts to build it. The only thing that I got wrong was initially purchasing the incorrect fuseholder. I’m glad you are going to keep the printed edition going. Keep up the good work. Brian Playne, Toowoomba, Qld. Questions about crickets Am I correct that the pet cricket project (Silicon Chirp, April 2023; siliconchip.au/Article/15738) is another reincarnation of Cudlip Cricket published back in the early eighties (I think)? I’ve built several Cudlips since its original publication for my own use and as gifts. At least one is still in use in Ohio, USA. I regard Cudlip as superior to its first reincarnation, which lacked a response to noise. I found that being responsive to both noise and light made Cudlip far more difficult for the intended victim(s) to locate. Of course, once the circuit board is spied, the jig is up; that will be even more so with this latest incarnation with a PCB resembling a cricket. So I suggest enhancing the difficulty of location by keeping the PCB out of sight in a suitable enclosure. I habitually disguised the Cudlips by placing each inside an innocuous box with strategically located holes cut to facilitate the admission of sound and light. The microphone, LDR and even the piezo sound emitter can be attached to the inside of the box using flying leads to the PCB. The trick is to select a box that doesn’t look out of place. For example, I found that a cardboard paper clip box featuring black brand lettering on the outside isn’t an unusual item in a kitchen or office. A suitably sized hole cut in the lettering cunningly disguised the black face of the electret microphone, fixed in place against the inside surface of the box. The LDR face was located just as cunningly in a hole cut elsewhere in the box graphics. Such trickery adds to the amusement factor as you watch the victim open the cupboard or drawer, then pick up and move the box in search of the cricket, then put it back again without ever finding the source of the chirping! After deploying one of my disguised crickets in his bedroom, one of my workmates reported that he’d had the greatest difficulty preventing himself from shaking with laughter as his wife searched in vain for the cricket, only to have it commence singing again every time she climbed back into bed. Moreover, he reckoned that when he finally owned up, it came close to breaking up his marriage! Ron, East Oakleigh, Vic. Comment: Cudlip was published in the February 1982 issue of Electronics Australia. Our latest Cricket is similar but detects light to start or stop chirping (it chirps in darkness unless set to canary mode). The April 2023 cricket incorporates far more convincing cricket sounds and has variable timing gaps between chirps and between chirp bursts. We have not updated any of these types of cricket projects that detect sound or lack thereof, mainly because of the resulting high battery drain. Light sensing can be performed using a brief sample every few seconds instead of continuously, as required for sound detection. Australia's electronics magazine siliconchip.com.au Keep your electronics operating with our wide range of replacement Power Supplies Don't pay 2-3 times as much for similar brand name models when you don't have to. Bring in your device and we'll help you find the right power supply for your needs. 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Explore our full range of replacement power supplies, in stock at over 110 stores and 130 resellers or on our website. jaycar.com.au/replacementpsu 1800 022 888 Prices correct at time of publication but are subject to change. Jaycar reserves the right to change prices if and when required. DC transmission losses were vastly overstated This is a reply to the letter on the New Zealand DC transmission system (part of pumped hydro) by John Tewkesbury from the UK (June 2023, Mailbag, p5). The article from NZ Engineering from April 1966 (PDF; siliconchip.au/link/abmj) states that the losses in the cable amounted to less than 10%. In my younger days, I attended a lecture by one of the engineers on this DC project and I don’t remember anything about using motors and generators. The DC-to-AC conversion was by mercury vapour thyristors. If there had been an 80% loss, I am certain the project would not have gone ahead. Bill Bool, Westown, New Zealand. Storing energy in mineshafts is impractically expensive I was prompted to write in after reading Dick Smith’s letter in the July issue (page 6) stating that pumped hydroelectric storage for electricity is not practical. I recently read an article from the ABC on the potential of using Australia’s legacy mineshafts to store renewable energy (siliconchip.au/link/abmi). With a background in the mines and drilling rigs, the concept naturally intrigued me. The report described a system known as a Mineshaft Electricity Storage System (MESS), designed to harness the gravitational force of heavy weights suspended in disused mineshafts to store power. Given the abundance of around 100,000 potential sites across Australia, the proposition seemed attractive at first glance. However, upon closer scrutiny and calculations, I have concluded that MESS might not be as promising or feasible as it initially appeared. I am open to the possibility that I might have erred in my analysis, and I invite readers and experts alike to scrutinise my findings and point out any inaccuracies. By comparison, a popular energy storage method these days is the Tesla Powerwall battery, with a storage capacity of 13.5kWh of electricity, costing around $8000. Considering an average life span of eight years, the daily storage cost amounts to $2.80, excluding the cost of the electricity itself. The energy generated by a 10-tonne mass falling 500 meters yields 13.6kWh, but storage, movement, and regeneration losses reduce the net stored power to approximately 12.24kWh. This crude comparison reveals that the MESS system doesn’t deliver significantly more storage than its battery counterparts. The actual feasibility of such a project appears even less favourable when considering the practicalities involved. The significant costs and potential hazards associated with a site survey for an old mineshaft cannot be understated. Besides the physical challenges and dangers, factors such as accessibility for heavy engineering vehicles, the need to reconnect a long-disused mine to the power grid, and the sheer complexity of the engineering works involved, all combine to make MESS a challenging proposition. By my estimates, based on experience and some generous assumptions, the minimum cost for a single 10-tonne system would be in the region of $2.6 million, calculated as follows: • Site survey including access, inspection, safety and support costs, equipment hire and report preparation: $120,000 10 Silicon Chip • Plans, permits, building works, earthworks, foundation, mineshaft restitution, pumping (if needed), building structure to house the plant, equipment, electrical switchboard: $2,000,000 • Electrical works and mechanical equipment, including three-phase installation, cable, drum, winch, motor, gearbox, mass, alternator and control system: $480,000 Even if I’m off by an order of magnitude, it will still be much more expensive than the Tesla Powerwall, which can store a similar amount of energy. My estimates don’t even begin to cover the costs associated with larger systems or the daily operational costs for maintenance and supervision, which would be needed for larger, more complex systems. Even at its maximum theoretical output, a larger, 100-tonne MESS system would barely provide sufficient power for an average two-person Australian household and would surely cost many millions of dollars! While the idea of using existing infrastructure to generate renewable energy seems compelling, the costs, complexities, and inefficiencies seem to outweigh the potential benefits of the MESS system as it currently stands. Gerard Dean, Glen Iris, Vic. Earlier LC Meter troubleshooting Many thanks to Tim Blythman for helping me troubleshoot my Wide-range LC Meter (June 2018; siliconchip. au/Article/11099). He told me there was a problem with the oscillator and to check the passive components around the LM311. He was absolutely right, although it wasn’t the passive components; it was the LM311 itself! After repeatedly checking everything, I decided to remove and replace the LM311 and voila, the LC Meter started working! As I am obsessed with this kind of instrument, I have a few of the most advanced ones produced during the last 30 years. You have done an excellent job. My only complaint is that there is always a random capacitor indication on the screen as soon as any component is connected. Still, it shows the component value with accuracy, depending on adequate calibration. Symeon, Wales, UK. Another message of appreciation I have to agree with the letter on p106 of the June issue from the man in the USA about the quality of content in Silicon Chip. The engineering knowledge is deep and real. The feature articles make no attempt to dumb down topics. That’s its uniqueness. Thank you. Paul Howson, Queensland. SportSync stereo update wanted Watching the current Ashes series on commercial TV, it has just occurred to me that your SportSync (May 2011 issue; siliconchip.au/Article/996), which has saved me from hours of inane commentary, could benefit from an upgrade a total redesign to stereo in time for the upcoming Australian summer of cricket. Rob Chandler, Clayton, Vic. Comment: that is a good idea. Ideally, We’d like to develop a solution that doesn’t require an external RAM chip, but we have yet to figure out how. Failing that, we have a stock Australia's electronics magazine siliconchip.com.au of 4MB RAM chips that might be suitable if paired with the right microcontroller. More on solar power for sheds The email from K.C. you published in Ask Silicon Chip, June 2023 (page 106) on a solar lighting system for a shed prompted me to write to you. In December 2019, I sent you details of my solar shed, which you published in a letter to the editor (February 2020 issue, page 8). The shed has since evolved, with a second solar panel and a much better battery replacing the SLA batteries. I also Earthed the shed to the correct standard with a long copper-coated rod. I’m sending you a schematic diagram of this new arrangement plus a photo. Adding the Victron Battery Protect module may have been overkill, as the LiFePO4 battery apparently includes under-voltage protection. However, I was wary as I destroyed the SLAs by over-discharging them. They bulged and spilled chemicals, which was not good. The issue of the LED lighting is tricky, as you say. I indulged and used the Jaycar “1600 lumen Solid 30W LED Marine Deck/Interior Light” (SL3480). It cost $99 at the time and was an excellent light, but it is sadly discontinued now. The ability to generate good 230V standby power and charge a device in the shed or run a long lead into the house if needed is useful too. This setup worked well but we eventually sold the house, so I left it there for the new owners. Rick Arden, Gisborne, Vic. SC siliconchip.com.au Australia's electronics magazine Above: the module and wiring details for Rick Arden’s solar shed. Left: many of the components of this sytem as installed in the shed, including the 100Ah LiFePO4 battery (bottom), 1500W pure sinewave inverter (middle) and Victron MPPT charge controller (top). August 2023  11 Explore our GREAT RANGE of Filament 3D Printers Create amazing 3D prints with our great selection of 3D printers. The best brands at great prices, stocked with spare parts, great service and advice. FROM 349 $ ONLY 599 $ TL4256 TL4750/52 CREALITY ENDER-3 NEO & V2 NEO FLASHFORGE ADVENTURER 3 Common features: • Prints up to 220x220x250mm • Auto bed levelling • Prints up to 150x150x150mm • Built-in camera for remote monitoring NEO^: • 128x64 Mono screen TL4752 • Carborundum glass bed • Easy to assemble V2 NEO: (Shown) • 4.3" Colour screen • PC Spring steel bed • Quick & easy to assemble GREAT VALUE! 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Special balloons and fixed-wing aircraft can act as long-endurance aerial platforms for observation and communication. Known as high-altitude platform stations/systems (HAPS), they fly above most planes but below satellites. Weather, scientific and military balloons are similar; they also ascend to great heights but do not necessarily stay there for a long time. Image Source – Airbus 2023 – https://mediacentre.airbus.com/mediacentre/media?mediaId=604534 A pplications for HAPS include communications, military or civilian surveillance, scientific observations and even amateur/hobbyist uses. They are especially useful when a satellite would take too long to organise or be too expensive, as these applications can often be effectively served by some other type of platform located within the Earth’s atmosphere. HAPS are sometimes called ‘pseudo-­ satellites’ or ‘atmospheric satellites’. Such platforms are uncrewed and fly at the highest possible aircraft altitudes or above. They are either special aeroplanes designed for high-altitude flying or lighter-than-air craft (a balloon or an airship) that rise due to a buoyant gas like hydrogen (H2) or helium (He). The lowest practical orbital altitude for a satellite is around 160km, while the highest any aircraft can fly is 26km (85,000ft) for the retired SR-71 ‘Blackbird’. The currently flying aircraft with the highest maximum altitude is the U2 surveillance plane at around 21km (70,000ft) sustained, although the CIA version of that same plane could cruise at 22.7km (74,600ft). By comparison, the Concorde could cruise at a mere 18.3km (60,000ft) above sea level. Current commercial jets typically fly at altitudes of 9-12.5km (30,000ft to 41,000ft) with a maximum service 14 Silicon Chip ceiling of up to 13.1km (43,000ft). That includes aircraft like the Airbus A380, Boeing 787-8 and 787-9. Military jets such as the F-35A in service with the RAAF have a service ceiling of 15.2km (50,000ft). This leaves a large gap from around 20km to 160km, unreachable by satellites due to too much atmospheric drag, and aircraft due to a lack of lift and oxygen to power their engines. The Fédération Aéronautique Internationale (FAI) considers space to start at the Kármán line, which is defined as an altitude of 100km. However, there is still too much air at that altitude for satellites to realistically orbit. The stratosphere is an area of the atmosphere that starts at around 7km at the poles, 10km at mid-latitudes and 20km at the equator and extends to an altitude of 50km (see Fig.2). This is the area in which HAPS platforms usually fly, most typically at around 20km (65,600ft). Part of the region from 20km to 160km can be accessed by ‘aerostats’ such as balloons or airships. The highest ever balloon flight was 53km (173,900ft), by the BU60-1 in 2002. Rockets can also access that region, but they usually don’t stay there for long! Why fly in or near the stratosphere? Fig.1: the US Air Force Project Manhigh gondola from 1955-58. Source: www.thisdayinaviation. com/2-june-1957/screen-shot2018-06-01-at-11-53-55/ In the stratosphere, there is little or no turbulence. The air is almost still, so it provides a stable platform for surveillance; it is ‘above the weather’. Winds are minimal at around 20km up. As the air is still, less structural mass is required to deal with turbulence and less engine power (for powered Australia's electronics magazine siliconchip.com.au vehicles) is required to overcome it. Because the air is so thin in the stratosphere, it is difficult to generate lift, so the aircraft has to be as light as possible. That usually means limited propulsive power, so they must fly slowly. But as the air gets thinner with altitude, the aircraft has to fly faster to maintain sufficient lift. Studies find the best balance for the lowest power consumption to maintain lift and altitude is around 20km (65,600ft). These light aircraft are naturally fragile, and the limited power means they take a long time to reach the target altitude. They must take off and land under calm conditions, which precludes launches in places like the UK, where it usually is too windy for such launches. Another consideration is that wherever a solar-powered HAPS aircraft is launched, there must be enough daylight hours for the solar panels to charge batteries for night-time operation, precluding launches at the poles in winter (for example). Lighter-than-air HAPS aircraft The first hydrogen balloon was made in France in 1783 by Jacques Charles and the Robert brothers. The first crewed free-flight in a lighter-­than-air aircraft was an untethered hot air balloon invented by the Montgolfier brothers and demonstrated in 1783. It was flown over Paris by Pilâtre de Rozier and the Marquis d’Arlandes. Manned high-altitude balloons were launched in the 1930s in pursuit of altitude records. For example, Explorer II ascended to 22,066m (72,395ft) in 1935. The US Air Force’s Project Manhigh (Fig.1) was undertaken in 195558 and achieved the following altitudes for manned balloons. Manhigh I: 29,500m (96,800ft); Manhigh II: 30,942 m (101,516ft); and Manhigh III: 29,900 m (98,100ft). In 1960, under the auspices of the US Air Force Project Excelsior, Joseph Kittinger skydived from a balloon at 31,300m (102,960ft), a record not beaten until Felix Baumgartner’s descent in 2012 from an estimated 39km (around 128,000ft). Project Moby Dick Project Moby Dick was a Cold War era project of the USA to fly espionage siliconchip.com.au balloons with cameras over the then Soviet Union. The Soviets protested when they found the remains of one in 1956. Project Skyhook Project Skyhook balloons were launched by the United States Navy Office of Naval Research from 1947 until the late 1950s, for atmospheric research at very high altitudes. The first such balloon carried a 29kg payload to 30km (100,000ft). About 1500 such balloons were launched. Some highlights of this project are as follows. In 1948, a three-balloon cluster was launched. In 1948 and 1953, Skyhook balloons measured radiation in the atmosphere between 27km (90,000ft) and 32km (105,000ft). In 1949, a manned launch took place. In 1954, two balloons with telescopes were launched to photograph a solar eclipse from a high altitude. In 1957, a 30cm telescope was launched to photograph the sun, providing the sharpest photographs of the sun taken to that date. Project Genetrix Project Genetrix, also known as WS-119L, was a US program of the 1950s to send surveillance balloons over China, Eastern Europe and the Soviet Union. They flew at 9-18km (30,000ft to 60,000ft). Soviet surveillance balloons The Soviets also had their own fleet of surveillance balloons they sent towards the West. Quoting from the website at siliconchip.au/link/abl1: ...in 1956, the OKB-424 design bureau — also known as the Dolgoprudny Automatics Design Bureau (DKBA) — was established, especially for the task of making new military aerostats... ...The first task of OKB-424 was to copy a US photo-reconnaissance balloon that had come down on Soviet territory. Over the next 60 years, DKBA produced around 20 types of free-­floating balloon envelopes, with volumes ranging from 11,500 cubic feet [326m3] to 21,190,000 cubic feet [600,000m3], each of which could carry various kinds of mission equipment. The largest of them was the Ukolka series of balloons from the 1960s, Australia's electronics magazine Fig.2: HAPS typically reside in the upper part of the troposphere or lower part of the stratosphere. Original source: https://w.wiki/6doG (author Kelvin Case, CC BY-SA 2.5) August 2023  15 Cannon Cosmic Ray Plates Parachute which had a capacity of 21,190,000 cubic feet and could lift a 660-pound [300kg] payload to an altitude of 147,600 feet [45km]. Project Mogul Radio Beacon Gondola Ballast Project Mogul was a US program conducted during 1947-1949 that launched balloons carrying microphones to listen for the noises of Soviet atomic blasts. When one of these balloons went down, the result was the “Roswell Incident”, which was claimed to be a UFO. Since Project Mogul was highly classified at the time, the object’s true nature was never disclosed. Project Strato-lab Fig.3: Operation Stratomouse, 1955. The cannon was to sever the payload at the end of the mission. The temperature and pressure inside the gondola were transmitted via a radio beacon, and ballast could be dropped or the payload separated by radio control. Source: https://academic.oup.com/milmed/ article/119/3/151/4933143 Fig.4: a Google Loon launch in New Zealand in 2013. Source: https://w. wiki/6dpb (CC BY 2.0). Project Strato-lab was developed from Project Skyhook (see above) and ran from 1954 to the early 1960s. They were manned balloons that contributed significantly to the space flight program by measuring radiation at altitude and testing pressure suits. The maximum altitude achieved was 34.7km (113,740ft). Operation Stratomouse (1955) In 1955, the US Air Force undertook a balloon flight program to determine if primary cosmic rays, which are strongly present at high altitudes, were hazardous to humans. Mice were chosen as the experimental test subjects, along with tissue cultures and cosmic ray measuring equipment. Helium balloons of 56,600m3 (Fig.3) were constructed by a company called Winzen Research (https://w. wiki/6dpT), a pioneer in high-altitude scientific balloons. The balloons were made from polyethylene and, uninflated on the ground, were 76m long. Fully inflated in the stratosphere, they had a diameter of 53m. An altitude of 40km (131,500ft) was reached on one of the flights, with flight durations of up to 26 hours. For a fascinating full account of this project, see https://academic.oup.com/ milmed/article/119/3/151/4933143 Google Project Loon Project Loon (https://x.company/ projects/loon/) was a project of Google’s parent company, Alphabet, to use HAPS balloons (Fig.4) at an altitude of 18-25km (59,000-82,000ft) to provide internet access in remote areas. Manoeuvring was to be achieved by altitude control to move the balloons into layers with different wind directions. One test balloon achieved a flight duration of 312 days in 2020. The balloons used were Raven Aerostar Super Pressure Balloons (see below) composed of polyethylene about 0.076mm thick. They were around 15m across and 12m tall. They also carried an electronics box weighing 10kg plus a 100W solar panel. The project was terminated in January 2021 due to a lack of profitability. Aerostar Aerostar (https://aerostar.com/­ products/balloons-airships) is a US manufacturer of high-altitude, long-duration stratospheric balloons (Fig.5), some of which are steerable, such as the Thunderhead model. The Thunderhead exploits different wind directions at different altitudes to provide directional control. Aerostar was previously associated with Google and their Project Loon, now discontinued, despite making significant technical advances. Sceye Fig.5: an Aerostar super pressure balloon at launch with the payload in the foreground. Note the solar panels. Source: https://aerostar.com/products/ balloons-airships/super-pressure-balloons 16 Silicon Chip Australia's electronics magazine Sceye (www.sceye.com) is a Swiss company (also with offices in Roswell, New Mexico, USA) developing an airship (Fig.7) for applications such as broadband delivery, atmospheric monitoring, agricultural monitoring and security surveillance (eg, border protection). It uses a hull fabric of unspecified composition that is said to be five times stronger and 1500 times more gastight, UV-resistant and ozone resistant than existing materials. Its advanced lithium sulfur batteries have an energy siliconchip.com.au Helium or hydrogen for balloons? Fig.6: the Czech Stratosyst Skyrider can stay aloft for weeks or more. Source: www.stratosyst.com Helium is extremely expensive for balloons, and the supply is very limited. Hydrogen is cheap and of unlimited supply, but flammable. Hydrogen is not considered suitable for human flight in balloons or airships ever since the Hindenburg disaster. Still, it can be used in uncrewed balloons, provided proper safety precautions are taken during filling. Hydrogen is typically used in weather balloons, including those launched by Australia’s Bureau of Meteorology (BoM). Nevertheless, many organisations still prefer to use helium, even for unscrewed balloons. Our recent report on the Australian International Airshow in Avalon Airport (May 2023; siliconchip.au/ Article/15773) included mention of the Sierra Nevada Corporation (www. sncorp.com) developing an LTA-HAPS (lighter-­than-air higher altitude platform station) for long-term ISR (Intelligence, Surveillance, Reconnaissance) for military missions. It is designed to fly for up to 60 days at 23km (75,000ft) with a 50kg payload. To do this, they partnered with balloon maker World View Enterprises (https://worldview.space/), as described in the news article found at: siliconchip.au/link/abl2 World View Enterprises use their balloons for remote sensing with what they call a Stratollite (Fig.8), a portmanteau of stratosphere and satellite. A Stratollite flies at 15-23km (49,00075,000ft) and can be launched as a constellation. These tandem balloons have an upper balloon containing helium or much cheaper hydrogen, and beneath that, a ballast balloon for altitude control. Winds often blow in different directions at different altitudes, so by varying its altitude, it is possible to have a limited ability to control the position. Technically, this type of balloon is known as a ‘variable altitude air ballast balloon system’ (VAABBS). The lifting balloon is known as a zero-­pressure Fig.7: a Sceye airship climbing. It can reach 20km altitude and is expected to go into commercial operations in around one year. Source: www.sceye. com Fig.8: the Stratollite can alter its course by varying its buoyancy and thus altitude. Source: World View. density greater than 400Wh/kg. An ultra-thin laminated solar cell ‘cape’ covers much of the airship’s surface that is 50-85% lighter than conventional solar cells. One such airship was launched in New Mexico in June 2022; it took two hours to ascend into the stratosphere and then maintained its position for 24 hours. Commercial operations from 20km (65,600ft) up are expected in about 9-15 months. Stratosyst Stratosyst (www.stratosyst.com) is a startup company from the Czech Republic developing the Skyrider HAPS. It is expected to take a payload of 12kg, have a power supply that can deliver up to 5kW, fly at an altitude of 20km and have a mission duration of weeks to months (see Fig.6). World View Enterprises (2012 – present) siliconchip.com.au Australia's electronics magazine balloon (ZPB), while the ballast balloon (one or two) are super-pressure balloons (SPBs). Beneath the ballast balloon is a ‘ladder’ that contains solar panels to charge the batteries. Beneath that is the gondola or “Stratocraft”. The ZPB is made of UV-resistant polyethylene with a volume of about 23,000m3. The SPB beneath it has a pumpkin shape and operates at a higher pressure than the surrounding atmosphere. Its pressure is varied to alter buoyancy and thus altitude by a compressor in the Stratocraft. The concept of using both a lifting balloon and a ballast balloon (one or more) or tandem balloon originates in the “Sky Anchor” system developed by Texas A&M University in 1976. The orientation of the ladder can be changed to ensure the solar panels have maximum exposure to the sun; the orientation of the Stratocraft can also be altered to suit requirements. The Stratocraft can carry a payload of 50kg. Continuous power of 250W and instantaneous power of up to 1000W are available. At the end of a flight, the Stratocraft separates from the structure and August 2023  17 Figs.9 & 10: the human-powered AeroVironment Gossamer Penguin (left) and 2kW AeroVironment Solar Challenger (above). They and their predecessors pioneered techniques of lightweight construction, low drag and solar power that were later used in HAPS aircraft. Source: www.nasa.gov/centers/ armstrong/news/FactSheets/FS-054-DFRC.html descends via a steerable parachute, guided to a designated landing location. Stratollites have sensor packages that can photograph the surface with a 5cm/pixel resolution (5cm GSD) vs 25cm GSD for a commercial satellite. Plus, they can take infrared imagery, radar imagery and RF signals can be received and processed. Word View has an online portal for customers to examine the data that has been collected. World View is also developing nearspace tourism and has produced a pressurised gondola (with restroom!) with the intention of launching at various locations around the world, including Australia. Passengers will be taken to 30km (100,000ft) and flights are expected to take place from 2024 – see https:// worldview.space/space-tourism/ on human-powered aircraft turned out to be valuable research put towards building HAPS aircraft. An athlete such as a Tour de France contender can sustain a continuous power output of a few hundred watts for several hours, so that is how much power is available for sustained human-powered flight. A HAPS aircraft such as the Zephyr (see below) uses around 100-200W of power to cruise, so it’s arguably more efficient than early human-power aircraft. HAPS aircraft have the advantage that they don’t have to carry the weight or volume of a human, although the battery, motor and other electronics might come close to that. Some milestones were: ● 1974: NASA Sunrise II was the first radio-controlled solar-powered aircraft. ● 1977: the first human-powered flight in the AeroVironment GossaHeavier-than-air mer Condor. Its empty weight was HAPS aircraft 31.75kg. Similar ultralight construcHAPS aircraft must be lightweight, tion techniques were later used on have very low drag and fly with lit- HAPS aircraft. tle power. Those parameters are ● 1979: the AeroVironment Gosall also requirements for human-­ samer Albatross became the first powered flight; hence, the past work human-powered aircraft to cross the English Channel with an empty weight of 32kg. ● 1980: the AeroVironment Gossamer Penguin (Fig.9) was the first solar-powered aircraft capable of carrying a human with an empty weight of 30.8kg. ● 1981: the AeroVironment Solar Challenger (Fig.10) was the first solar-powered aircraft to cross the English Channel with an empty weight of 90kg. NASA ERAST program The NASA Environmental Research Aircraft and Sensor Technology (ERAST) program that ended in 2003 produced UAVs that could perform long-duration science missions at 18km (60,000ft) and above. Among other vehicles, it resulted in the solar or fuel-cell-powered Pathfinder, Centurion and Helios aircraft (see Fig.11). NASA Pathfinder (first flight 1995) The NASA Pathfinder by AeroVironment (see Fig.12) was the first aircraft built under NASA’s ERAST Program to develop long-duration, high-altitude aircraft for science missions. Fig.12: the solar-powered NASA Pathfinder over Hawaii Fig.13: the NASA Centurion first flew in 1998. Source: www. on the 28th of August, 1997. Source: www.dfrc.nasa.gov/ nasa.gov/centers/armstrong/news/FactSheets/FS-056-DFRC. Gallery/Photo/Pathfinder/HTML/EC97-44287-2.html html 18 Silicon Chip Australia's electronics magazine siliconchip.com.au Fig.11: the planform evolution of the NASA solar-powered aircraft designed under the Environmental Research Aircraft and Sensor Technology (ERAST) program. Original source: https://w.wiki/6doD In 1995, it set an official record altitude for solar-powered aircraft of 15.4km (50,567ft). It also set an unofficial altitude record of 21.8km (71,500ft) and had a ground speed of 24-40km/h. In 1998, it was modified into the Pathfinder Plus (more on that later). It had a wingspan of 29.5m. It weighed 252kg and could carry a payload of 45kg. Endurance was 14-15 hours with 2-5 hours on battery power. NASA Pathfinder Plus (first flight 1998) The AeroVironment Pathfinder Plus is a modification of the Pathfinder that climbed to 24.4km (80,206t) altitude in 1998. It was the second NASA ERAST aircraft with a wingspan of 36.3m, a Fig.14: the NASA Helios in its HP01 high-altitude configuration. Source: www.nasa.gov/pdf/64317main_helios. pdf siliconchip.com.au weight of 315kg and a payload of up to 67.5kg. The solar array produced up to 31kW at high noon in summer. It had 14 electric motors of 1.5kW each and flew at around 27-34km/h. Like the original Pathfinder, its endurance was 14-15 hours with 2-5 hours on battery power alone. In 2002, it was involved in atmospheric satellite tests from 20km (65,600ft), transmitting HDTV and 3G signals. Only 1W of transmission power was required. NASA Centurion (first flight 1998) The NASA AeroVironment Centurion (Fig.13) first flew in 1998 and Fig.15: this dramatic image demonstrates the fragility of this type of aircraft as it disintegrates and falls into the Pacific Ocean. Source: www. nasa.gov/pdf/64317main_helios.pdf Australia's electronics magazine was the third ERAST aircraft. It was designed to fly to 30.5km (100,000ft), although no official altitude attainment was recorded. It had a wingspan of 63m, weighed 529kg and could carry a payload of 45-270kg. Its endurance was, once again, 14-15 hours with 2-5 hours powered by its lithium battery alone. NASA Helios (flights in 1999 – 2003) The NASA Helios (Fig.14) was the fourth aircraft of the ERAST program and a modification of the Centurion. A 12m wing section was added to the Centurion for a new wingspan of 75.3m. In 2001, it achieved a world record for sustained horizontal flight by a winged aircraft of 29.524km (96,863ft). It had two possible configurations. HP01 was optimised for altitude and used solar cells and a battery to power 14 motors. HP03 was optimised for endurance and used solar cells, a battery and a fuel cell to power 10 motors. The HP01 weighed 600kg empty weight and could carry a payload of 329kg. It was lost in a dramatic accident in 2003 – see Fig.15. You can read the accident investigation report at www. nasa.gov/pdf/64317main_helios.pdf Solar Impulse 1 (2009) Solar Impulse 1 by André Borschberg August 2023  19 Fig.16: an artist’s impression of the Titan Aerospace Solara 50. Source: https://w.wiki/6doE and Bertrand Piccard of Switzerland first flew in 2009. As the name suggests, it was solar powered and used LiPo batteries so it could continue flying at night. In 2010, they took it for a manned flight over a complete night/ day cycle (26 hours). Solar Impulse 2 (2015 – 2016) Solar Impulse 2, also by André Borschberg and Bertrand Piccard, completed a manned circumnavigation of the world in 2015-16, although it involved 16 stops (17 stages). Titan Aerospace Solara 50 concept (2015) Titan Aerospace was a US company that existed from 2013-14 before being acquired by Google. Google planned to use the Solara 50 (Fig.16) and subsequent models as atmospheric satellites to deliver services such as internet, real-time Earth images, voice, navigation and mapping. The aircraft was expected to fly at around 20km (66,600ft) and spend five years continuously in the air. It had a 50m wingspan, was 15m long and could carry a payload of 32kg. The ground area to be serviced was expected to be 17,800km2. Fig.17: an illustration of one aircraft from the DAP concept. It has a wingspan of 39m, a wing area of 64m2 and a gross weight of 192kg. Source: www.nasa.gov/ sites/default/files/thumbnails/image/niac_engblom_phii.png Unfortunately, the aircraft crashed due to structural failure early on its maiden flight in 2015, and Google shut down the company in 2016. Dual-Aircraft Platform (DAP) concept (2015) This is a very unusual idea from Embry-Riddle Aeronautical University. It involves two powered aircraft tethered together that take off from a runway and ascend to around 60,000ft using both solar and battery power. The lead aircraft is called SAIL, while the towed aircraft is called BOARD (Fig.17). At about 60,000ft (18.3km), the two aircraft separate by around 1km and utilise the difference in wind speeds at the two locations in an analogous manner to kite surfing (Fig.18). The SAIL aircraft provides lift for both aircraft, while the BOARD aircraft provides directional control, like a keel. The propeller can be used as a wind turbine to recharge batteries under certain conditions, and missions of up to several months or years are thought possible. However, it has yet to be flight tested. For more information, see the video titled “DAP Configuration” at https://youtu.be/fidiDPaLWWw Facebook Aquila (2016 – 2018) Facebook Aquila, developed by Ascenta in the UK, was a HAPS intended to provide Internet access in remote areas (see Fig.19). It was designed as a flying wing about the size of a Boeing 737, with a wingspan of 43m, but weighed just 399kg. It was to fly at 27km (90,000ft) during the day, dropping to 18km (60,000ft) at night. The planned endurance was three months, to provide internet access to an 80km radius below the flight path. The project was cancelled in 2018. Airbus Zephyr (2001 – present) Zephyr is a solar electric HAPS platform that uses solar during the day Fig.20 (left): the Airbus Zephyr. Source: https://mediacentre.airbus.com/mediacentre/media?mediaId=604534 Fig.21 (right): the Zephyr 8/S in flight, presumably soon after launch, during 2021 tests in the United USA to demonstrate wireless broadband service delivery. It undertook 18 daytime flights. Source: https://mediacentre.airbus.com/ mediacentre/media?mediaId=557935 20 Silicon Chip Australia's electronics magazine siliconchip.com.au Fig.18: the dual-aircraft platform (DAP) aerodynamic concept, analogous to kite-boarding. Source: www.nasa.gov/sites/default/files/thumbnails/image/ engblom_sail_board.jpg Fig.19: the Facebook Aquila drone in flight. Source: Meta – http:// siliconchip.au/link/ablk and batteries at night – see Fig.20. The Zephyr was initially conceived and designed by Chris Kelleher for QuinetiQ around 2001 (QuinetiQ is an offshoot of the UK Ministry of Defence). In 2013, the project was sold to Airbus Defence and Space and is now under the Airbus business unit AALTO HAPS (www.aaltohaps.com). Zephyr went through a series of models, and in 2004, the Zephyr 4 was demonstrated in Australia. In 2010, the Zephyr 7 achieved a flight duration record of 14 days, 22 minutes and eight seconds, which was longer than any other unrefuelled aircraft flight at that time. It flew as high as 21.5km (71,000ft). In 2018, a Zephyr 8/S broke another record with a flight of 25 days, 23 hours replacing 250 terrestrial mobile phone towers and providing coverage over a 7500km2 area. Other possible applications include military reconnaissance, communications relay and environmental monitoring. Zephyr is optimised for operations at around 20km, the ideal balance between power required for propulsion and altitude. At this altitude, the line-of-sight (LOS) is about 500km, so a radio reception area of 1000km diameter could be established (eg, using UHF). Zephyr can travel up to 1852km (1000nmi) if it is not kept on station in one area. It takes about eight hours to ascend to its usual altitude of 20km and, due to its highly efficient aerodynamics, it takes about 24 hours to descend from that altitude. and 57 minutes. In 2022, a Zephyr 8/S was lost due to a mechanical failure after flying for 64 days. The Zephyr 8/S (Fig.21) has a wingspan of 25m, weighs 62-65kg, has a service ceiling of 23km (76,000ft), a rated endurance of 624 hours (26 days) and can carry a 5kg payload. Another variant, the Zephyr T, has a wingspan of 32m, weighs 145kg and can carry a payload of 20kg. The Zephyr can be used for various HAPS applications. One example is surveillance with the Airbus OPAZ Earth observation payload. OPAZ has an electro-optical (EO) sensor that provides an 18cm resolution and an infrared sensor for night and day operations. It can also be used as a ‘mobile phone tower in the sky’ (Fig.22), Fig.22: the ‘mobile phone tower in the sky’ concept for Zephyr. Coverage is expected over an area of 7500km2, equivalent to 250 ground towers. D2D is short for direct-to-device. Original source: www.aaltohaps.com/mobile-connectivity siliconchip.com.au Australia's electronics magazine August 2023  21 Fig.23: an artist’s concept of the Stratospheric Technologies aircraft, to be launched from a balloon and then use a plasma engine to stay aloft. Source: https://stratospherictechnologies.com/technology Fig.24: the Hawk30 (in 2020, renamed Sunglider), a product of HAPSMobile. Source: NASA / Carla Thomas During ascent and descent, it is vulnerable to bad weather because of its light structure, so the weather must be carefully monitored (this applies to all HAPS). duration of several months. It can provide a phone service area 200km in diameter for use by smartphones and IoT devices. It is envisaged to use it in areas with no existing coverage, such as islands or remote areas, for natural disaster relief or to provide communications links for drones. The Sunglider is a development of the NASA Pathfinder and NASA Helios. In 2020, a demonstration flight lasted for 20 hours and reached 19.1km (62,500ft). Its operational altitude is intended to be 20km. Stratospheric Technologies (2016 – present) Stratospheric Technologies (web: https://stratospherictechnologies. com/overview) is developing a HAPS (Fig.23) that is launched by balloon and then released at an altitude of around 30km (98,000ft). After that, it is powered by plasma engines that derive their power from solar panels and ascends to 35km (115,000ft). We don’t have specific details of the plasma engines, but Fig.25 shows how atmosphere-breathing electric propulsion works. Electric power ionises atmospheric gases and then accelerates them to generate thrust. At night, the platform gradually glides down to around 20km; when it becomes light again, the panels can again produce power for the engines so it can ascend. The plasma propulsion system is unaffected by low air density and is said to be the first plasma propulsion system that operates in the atmosphere. When the platform needs to return to Earth for maintenance, it glides to a landing area. The company says that potential use cases for the platform include telecommunications, weather forecasting, imaging and surveillance, including civil and military applications. It is not in commercial use at the moment. For more details, see the video titled “Stratospheric Technologies” at https://youtu.be/4D1TAV_aocc Hawk30/Sunglider (2018 – present) The Hawk30, renamed Sunglider in 2020, is a product of the Japanese company HAPSMobile (website: www. hapsmobile.com/en/) – see Fig.24. It has a wingspan of 78m, a cruise speed of 110km/h and is designed for a flight Kraus Hamdani Aerospace Kraus Hamdani Aerospace (also called KHA; https://krausaerospace. com/) has developed the K1000ULE Rev-P 4.8m wingspan drone, demonstrating a powered flight duration of 26 hours so far. However, this drone is designed to fly like a glider or bird and extend its mission time using thermals. Fig.25: how atmosphere-breathing electric propulsion works. Original source: https://w.wiki/6doF (CC BY-SA 4.0). 22 Silicon Chip Australia's electronics magazine siliconchip.com.au This aircraft is not strictly a HAPS as it is only intended to fly to 6.1km (20,000ft) to perform various observation and communication functions. Balloons of uncertain origin and purpose Mysterious balloons over the United States were in the news recently. One was ultimately shot down by US Air Force planes. Fig.26 shows one of these balloons from a US Department of Defense U-2 high-altitude reconnaissance aircraft. While parts of the balloon were recovered, at the time of publishing, the origin and purpose of these balloons are not known for certain. The Chinese government said it was a civilian weather balloon that was blown off course. BAE Systems PHASA-35 (2020 – present) Promoted as having the “wingspan of a 737 and weight of a motorcycle”, and being able to carry a 15kg payload, the BAE Systems PHASA-35 (www. baesystems.com/en/product/phasa-35) is described as a high-altitude long-endurance (HALE) unmanned aerial system (UAS). It is solar-­powered and can operate over an area of interest for several months – see Fig.27. It provides a persistent, stable platform for monitoring, surveillance, communications and security for military and civil applications. It can also be used in disaster situations, for agricultural monitoring, environment monitoring, Earth observations and border monitoring. It can potentially deliver 5G communications in a disaster or remote area. Its wingspan is 35m; it weighs 150kg and flies at 20km (65,600ft). It can also be used as part of a constellation of identical aircraft. For more information, see the video titled “PHASA-35 - Persistent High Altitude Solar Aircraft” at https:// youtu.be/Z7NE-rcDtGs What to do if you find a downed weather balloon If you find a weather balloon, it should be considered dangerous if it is still inflated, even partially, as it likely contains flammable hydrogen. The advice from the BoM is to call the Fire Brigade. Secondly, it will have a radiosonde. The BoM says these can be disposed of in regular household garbage or recycling; you do not need to return them. We suggest a better use. You can use and reprogram the radiosondes for amateur radio purposes, including tracking any balloons you may launch (subject to appropriate laws). That balloon has likely been for a journey into HAPS territory; they typically achieve 16-35km altitude, according to the BoM. You can view the video by Australia’s Peter Parker, VK3YE, titled “A mystery package from a mystery sender” at https://youtu.be/_-cwbIiinkA Also check out “Repurposing Vaisala RS41 radiosondes for amateur radio high-altitude balloon tracking” by 0xfeed at siliconchip.au/link/ablg Fig.26: “A U.S. Air Force pilot looked down at the suspected Chinese surveillance balloon as it hovered over the Central Continental United States February 3, 2023” – from US DoD. Source: www.dvidshub.net/ image/7644960/u-2-pilot-over-central-continental-united-states Fig.27: BAE Systems’ PHASA-35. Source: www.baesystems.com/en/product/ phasa-35 Tethered drones While not strictly speaking HAPS, tethered drones such as quadcopters and multi-rotor drones can provide persistent aerial observation, surveillance, reconnaissance and communications at altitudes up to a few hundred meters. Tethering a drone involves connecting a power and data cable from a ground station to a drone. siliconchip.com.au Fig.28: launching a tethered Teledyne FLIR Skyranger drone. Source: www.flir.fr/news/pressreleases/flir-acquirestethered-drone-assetsand-technology-fromaria-insights/ Australia's electronics magazine August 2023  23 The flight duration is then limited only by the power available and how long the drone can last before requiring a motor overhaul etc. Existing drones, including consumer types, can be converted to tethered operation. However, dedicated tethered drones are available, designed for particular commercial or military applications (see Fig.28). Tethering can be done from a stationary position, a moving vehicle such as a ship at sea, a land vehicle or even a person carrying the ground station in their hands or, more likely, in a backpack. One potential use for a tethered drone is for aerial filming in areas subject to commercial airspace restrictions, where untethered drones can’t be used; for example, near airports. One example is the LIFELINE tethering system (www.lifeline-drone. com) that works with consumer DJI drones like the Phantom 4 Series V1 & V2, Mavic Pro, Mavic 2 Pro, Zoom & Enterprise, Inspire 1, and Inspire 2. UAVOS Inc. We can’t tell you too much about the UAVOS product as our Malwarebytes software warns us not to visit their website at the time of writing. However, you can safely view the video titled “HAPS (High Altitude Pseudo Satellite) by UAVOS” at https://youtu. be/1YsloiRVEzs PICO balloons PICO balloons are a form of amateur HAPS that anyone with an amateur radio license can participate in. We first mentioned these balloons in the February 2015 issue (“Reach for the Sky”, siliconchip.au/Series/281). They are basically standard helium-­ filled Mylar party balloons that you can buy at any party supply shop carrying a tiny transmitter, solar panel and GPS module. The payload can weigh 13g or less but relays the balloon’s position using weak signal protocols such as JT9, JT65 and WSPR at 10-25mW. These balloons can stay aloft for Wind direction varies with altitude The wind speed and direction usually change with altitude, not only in the stratosphere but at any height – see Fig.29. By altering the altitude of a balloon, it is possible to achieve some directional control. Smart software and information from weather resources can help a lighter-than-air HAPS platform stay on station. many weeks and even circumnavigate the Earth several times, see: • https://picospace.net/ • www.picoballoons.net Balloon tracking website You can track amateur balloons at https://amateur.sondehub.org/ If you want to track scientific and weather balloons such as from the BoM, check out: • siliconchip.au/link/able • siliconchip.au/link/ablf Links and videos ● “B-Line to Space: The Scientific Balloon Story”: https://youtu.be/ sPQ-tMoAHkY ● “China’s Balloon: One Question NO ONE Is Asking!”: https://youtu.be/ eeAFCclFXUY ● More about the Chinese balloon over the USA: https://stratocat.com. ar/2023-03-e.htm ● L.E. Epley (1990) “A system architecture for long duration free floating flight for military applications”: www. osti.gov/biblio/6525013 ● “Stratosphere: The Uncharted Territory in Networks | Halim Yanikomeroglu | IEEE YP Ottawa | 14Mar2023”: https://youtu.be/ XyGGQoCt5M0 ● A website about Stratospheric balloons: https://stratocat.com.ar/ indexe.html ● Information about high-altitude balloons: farleyflightaerospacellc. SC space/FFA.html Distance to the horizon by altitude To indicate the desirability of using HAPS, this table shows the distance to the horizon as a function of altitude. Theoretically, a radio beam could reach the horizon from a HAPS at the indicated altitude. Altitude Distance to the horizon 1km 113km 5km 252km 10km 357km 15km 438km 20km 505km 25km 565km 30km 619km Fig.29: how a balloon can control its direction of travel by varying its altitude. 24 Silicon Chip Australia's electronics magazine 50km 800km 160km 1438km siliconchip.com.au DEALS OVERSTOCK Build It Yourself Electronics Centres® You get a bargain. We get warehouse space. It’s win win - only until August 31st. C 5160 SAVE $50 X 7063 SAVE $54 199 $ 225 $ FIRE THE WEATHER MAN! Get live, local weather at home every day. With outdoor sensors & smartphone app! This fantastic weather station displays your local weather data - great for boaties & gardeners. Bright & clear base station provides readings for indoor/outdoor temperature, humidity, air pressure, rainfall, wind speed and direction. Plus handy weather trends. You can even connect it to wi-fi for monitoring readings & data with your phone. 100m sensor range. 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To start your subscription go to siliconchip.com.au/Shop/Subscribe where the PicoMite meets the Web The WebMite a Raspberry Pi Pico with MMBasic, WiFi and Internet Connectivity | Article and MMBasic by Geoff Graham | WebMite firmware by Peter Mather | M ost readers will be familiar with the PicoMite, which we introduced in January 2022 (siliconchip. au/Article/15177). It is a Raspberry Pi Pico programmed in the MMBasic language and is a very capable microcontroller at an extremely low price. Following that, the Raspberry Pi Foundation released the Raspberry Pi Pico W, which is very similar to the original Pico but with the addition of a WiFi module. In theory, you could take any Pico project and then add an internet connection… but it is not quite that easy. The internet and its protocols are complicated, with many protocol layers. That means it takes an experienced programmer to accomplish even the simplest task. That is where our new WebMite comes in. We have added to the Pico­ Mite firmware support for the wireless capability of the Pico W and the protocols (802.11n, DHCP, WPA-PSK, TCP, IP, TLS, HTML etc) that are necessary to access the internet. With the WebMite, you can easily: ; Connect to a WiFi network with a specified SSID and password. ; Implement a web server with advanced features. ; Query websites for data. ; Get the current time/date. ; Check the weather. ; Send emails. ; Publish and retrieve data from MQTT broker services (for IoT messaging). ; Remotely edit BASIC programs. ; Transfer files to and from the Pico over WiFi using TFTP. These features have been implemented using an easy-to-use programming framework with the flexibility to handle the unusual aspects of accessing internet resources. Later in this article, we will present an example of a simple web server that uses just 12 lines of BASIC code – that is all it takes to serve up a web page for your projects. The MMBasic language is an easyto-use programming environment. With the WebMite, you can easily add internet features to complex gadgets with touch-sensitive LCD panels, SD card support for storing files, connection to various sensors and so on. Loading the firmware As the hardware is already built for you (the Raspberry Pi Pico W, available for under $10), all you have to do to create the WebMite is load the appropriate firmware onto that module. Luckily, that is easy. The WebMite firmware c a n b e All that you need for the WebMite is an affordable Raspberry Pi Pico W. Australia's electronics magazine downloaded for free from the Silicon Chip website or the author’s website at http://geoffg.net/webmite.html It comes with a comprehensive 178-page user manual that includes a tutorial on BASIC programming for beginners. Loading the WebMite firmware on the Raspberry Pi Pico W is the same as with the original Raspberry Pi Pico and is described in the user manual. Essentially, you plug your Pico W into a USB port on your computer while holding down the button on the top of the module. The Pico will then create a pseudo USB drive on your computer, and you just drag and drop the WebMite firmware into that. When the transfer has been completed, the Pico will restart running the WebMite firmware and create a serial connection via its USB port. Once it has done that, you can use a terminal emulator like Tera Term (http://tera-term.en.lo4d.com) to access the WebMite’s console. If you then hit the Enter key on your keyboard, you will see the MMBasic prompt, a greater-than character (>). You can configure the WebMite, test commands, edit programs, and run them at this command prompt. Internal file system Before we get into the internet capabilities of the WebMite, we need to introduce the internal file system. It looks like an SD card to the programmer, but files are actually stored in the flash memory chip of the Raspberry Pi Pico W. You can open files for reading and writing, create and navigate directories and do all the things you can do with a physically attached SD card. That includes using the normal BASIC file commands such as OPEN, CLOSE, FILES etc. If you connect a removable SD card to the WebMite, it is accessed as drive “B:” while the internal file system is drive “A:”. siliconchip.com.au This internal file system has a capacity of about 600kB, and it is automatically created by the firmware when MMBasic is loaded onto the Raspberry Pi Pico (W). This is especially useful on the WebMite because, to set up a web server, you need somewhere to store the web pages and images to serve. The internal file system is perfect for the job. This feature was introduced in the last release of the PicoMite firmware, so if you are currently using the Pico­ Mite or the VGA PicoMite, consider upgrading to get this feature. Connecting to WiFi The WebMite can connect to any WiFi network running 802.11n (2.4GHz) with WPA-PSK security. The encryption must be either TKIP or AES (or both) and DHCP must be enabled on your router. These are standard requirements for most WiFi-enabled gadgets, so most routers are set up like this by default. To log into your network, use the command OPTION WIFI at the WebMite’s command prompt. For example, if your network is called MyNetwork and the password is secret, you would use this command at the command prompt (the quote characters are required): OPTION WIFI “MyNetwork”, “secret” This will be remembered and will be automatically reapplied on every reboot. It will also cause the WebMite to restart and drop the USB connection, so you will have to reconnect to access the command prompt again. You can check the IP address that your router gave to the WebMite with the command: PRINT MM.INFO(IP ADDRESS) Most routers will allocate the same address to the WebMite on every reboot. However, if you want to ensure the address will not change, go into your router’s configuration and allocate a static IP address to the WebMite. Incidentally, you can have many WebMites on your network with different IP addresses and they will not conflict. Remote connection via Telnet The WebMite could be installed in some inaccessible place, so the firmware allows you to use Telnet over your WiFi network to access siliconchip.com.au Screen 1: You can connect to the WebMite using Telnet over WiFi via Tera Term. This lets you do everything that you can do via a USB cable, including editing and running programs. the MMBasic console. This feature is enabled with the command: OPTION TELNET CONSOLE ON As before, this command will be remembered and automatically applied on every reboot. It will also cause the processor to restart, so you will have to reconnect to regain the command prompt. The recommended terminal emulator, Tera Term, supports Telnet, so all you need do is select that in the new connection dialog box and enter the WebMite’s IP address, as shown in Screen 1. You can do everything you can via a physical USB connection using Telnet, including editing and running programs... all over the WiFi! You can also use PuTTY in Windows or the telnet command in Linux or macOS (it is no longer part of the macOS by default, but you can install it via Homebrew). File transfers Another handy feature is the ability to transfer files to and from the WebMite over WiFi. This is done using TFTP (Trivial File Transfer Protocol) from a Windows, Mac or Linux computer. In Windows, this is built into the operating system; however, you must enable it first by going to the Control Panel, selecting “Programs and Features”, then “Turn Windows features on or off”. Finally, scroll down the list and tick TFTP Client. You can then send a file to the WebMite’s internal file system (drive A:) Australia's electronics magazine using the following command in a Command or Power Shell window: TFTP -i ipaddress PUT filename This protocol can also be used to retrieve files from the WebMite, eg: TFTP -i ipaddress GET filename Long string support Another new feature of the WebMite that needs explaining is long strings. Regular string (text) variables in MMBasic can store a maximum of 255 characters. However, most data transferred between an internet client and server is much longer than that. The WebMite has a series of routines called long strings to address this need. These work with strings of any length, limited only by the available RAM. Using them, you can pull long strings apart, search for specified text, copy parts of the text and so on. They mimic what the standard string functions do in MMBasic, although they are slower and clunkier (which is why they are only used when required). To allocate RAM for holding a long string, you need to declare an array of integers with a size (in bytes) that will fit the longest string expected. While declared as integers, the string routines do not store numbers in these; they are just used as memory blocks. For example: DIM INTEGER StrA(512),StrB(512) Each array is 512 integers, and an integer is eight bytes, so each array occupies 4KB of RAM (512B × 8). A August 2023  31 character is one byte, so each can store strings of up to 4,096 characters. These arrays are passed to the long string routines using empty brackets. For example, to copy StrB to StrA, you can use the command: LONG STRING COPY StrA(), StrB() Long strings are documented in the user manual. It is worthwhile to familiarise yourself with them as they are invaluable when dealing with the large amount of data sent over the internet. Web server functions Assuming that you have connected the WebMite to your WiFi network as described above, the next step in implementing a web server is to tell the firmware to start a TCP server. This is done with another OPTION command as follows (it must be entered at the command prompt): OPTION TCP SERVER PORT 80 Port 80 is the standard HTTP port, normally used for serving web pages. As with the other OPTION commands, this only needs to be entered once and will be remembered. It will also cause the WebMite to restart. In your program, you tell the server what to do if an incoming request is received with the command WEB TCP INTERRUPT. This specifies a subroutine that the firmware will call (interrupting the main program) whenever a request is received. Within your interrupt subroutine, you can retrieve the remote request using the command WEB TCP READ. This command needs a long string buffer for holding the text of the remote request (see above for a description of long strings). The request from the remote browser will look something like that shown in Screen 2. In this case, the browser is requesting a web page called “page. html”, but it could be the name of an image file or even a single forward slash (/), which is a request for the default page of the website (typically called “index.html”). The request could also be a notification that the user has clicked on a button or control on the web page and is expecting the WebMite to take some action. In that case, the text between the keywords GET and HTML will indicate the control involved and the user’s action. Some queries may use the keyword POST instead of GET, but the intention is the same; whatever is between the first keyword and HTML is the request from the remote browser. Sending a web page If the request is for a web page, you can send it using WEB TRANSMIT PAGE. This specifies a file formatted in HTML residing in the internal file system of the WebMite (described above) or on an SD card (if connected). When the firmware transmits the web page, it will scan the page for any embedded BASIC variables surrounded by curly brackets. It will substitute these with the current value of the variable. This facility lets you insert data your BASIC program has collected into the web page. For example, if your program had a variable called Humid which had the value of 42 and represented the current humidity, the following text in your HTML file: The current humidity is {Humid}% Screen 2: a web request from a remote browser will look like this. The important part is the text between the keywords GET and HTTP. In this case, the browser is requesting a web page called “page.html”, but it could be an image file or some text indicating that the user has clicked a control on the web page. 32 Silicon Chip Australia's electronics magazine Displays in the client’s browser as: The current humidity is 42% You can also send non web pages using the WEB TRANSMIT FILE command, which will send images, audio files and much more (without substituting for variables). Using these commands, you can create a web server that will serve up pages displaying whatever data you have collected. This server could also respond to remote commands from the user to turn on/off motors, pumps etc, as required. Whatever the WebMite can do locally, it can also do remotely! A simple web server This example will display the temperature and humidity in a fictional greenhouse. From the comfort of your living room, you could call up the web page on your phone, tablet or computer and see the current conditions for your plants, even though they may be located at the bottom of your garden. The whole program is shown in Program 1 and is about as simple as it gets at just 17 lines. The web page is even smaller, at only three lines. The first line of the program starts the web server and specifies the interrupt subroutine to be used for any incoming requests (“WebInterrupt”). The next four lines implement a simple loop where a DHT22 sensor (connected to the GP28 pin, as shown in Fig.1) is queried for the current temperature and humidity ten seconds. The command specifies that the results should be saved in CurrentTemp and CurrentHumid variables. The WebInterrupt subroutine, starting at line 7, is where the work is done Fig.1: here’s how to connect the DHT22 temperature/humidity sensor for the sample web server program in Program 1. siliconchip.com.au WEB TCP INTERRUPT WebInterrupt DO BITBANG HUMID GP28, CurrentTemp, CurrentHumid PAUSE 10000 LOOP SUB WebInterrupt LOCAL INTEGER a, p, t, b(512) FOR a = 1 To MM.INFO(MAX CONNECTIONS) WEB TCP READ a, b() p = LINSTR(b(), “GET”) t = LINSTR(b(), “HTTP”) If (p > 0) And (t > p) Then WEB TRANSMIT PAGE a, “index.html” ENDIF NEXT a END SUB in serving up the web page. Whenever the TCP server receives a request, it will call this subroutine, interrupting whatever the BASIC program was doing at the time. This subroutine first defines several local integer variables, including an array of integers called b(), used as a long string variable to hold the incoming data. The web server can handle multiple simultaneous requests, so the program starts a loop stepping through all possible connections. The WEB TCP READ command will read whatever is available on each connection and save any received data in the long string buffer b(). The following two lines look for GET and HTTP keywords in the received request. The next line checks that these keywords are present and in the correct order. In that case, we send the default web page, “index.html”. Note that we don’t care what file the remote browser actually requested; we just send the default page for every request. This web page is shown in Program 2 and consists of just three lines. The first line is the heading, and the next two define the text on the page. When the page is transmitted, the firmware will substitute the text {CurrentTemp} and {CurrentHumid} with the current values of those variables. “<BR />” in HTML is an instruction to the web browser to insert a new line (line BReak). Screen 3 shows the result displayed in a browser. This is a functional program, and if you have a Raspberry Pi Pico W handy, you can copy the files to it and have it working immediately. To make it easy, the WebMite firmware download includes both these files and a ‘readme’ file with detailed instructions. Give it siliconchip.com.au Program 1: this simple web server program displays the temperature and humidity in a fictional greenhouse. It is just 17 lines; the WebInterrupt subroutine starting at line 7 is where the work is done in serving up the web page. <H3>Greenhouse Monitor</H3> The temperature is {CurrentTemp}&degC <BR /> The humidity is {CurrentHumid}% Program 2: this is the web page HTML source for the program shown in Program 1. The first line defines a heading and the next two specify the text in the page. When the page is transmitted, the firmware will substitute the text {CurrentTemp} and {CurrentHumid} with the current values of those variables. a go and be prepared to be amazed at what the WebMite can do. Advanced server features Web infrastructure is a rich environment, so you can add many more features to your web pages. These include images, textured backgrounds, multiple pages and more. For example, you might want to display a graph of past temperatures and humidity for your hypothetical greenhouse. That can be done by defining a virtual LCD panel in the WebMite. This does not have an attached physical display, but regardless, you can draw your historical data on it using the graphical drawing commands built into MMBasic: line, pixel, text etc. You can save this image as a BMP file to the internal file system in the WebMite. Then, when a remote browser requests the web page with this embedded image, the browser will also ask for this file, and the user will see an image representing the graph of past temperatures and humidity that your program recorded. Screen 4 illustrates what it could look like. Even more useful is the ability to define HTML forms in the web page, including embedded controls such as Screen 3: how the simple web server appears to a user on a phone, tablet or computer. Screen 4: with a little more programming effort, you can extend the simple web server to display a graph of past temperatures and humidity readings for your greenhouse. Australia's electronics magazine August 2023  33 buttons, checkboxes, radio buttons, input text fields and much more. Using these, the user can, via the web page, send commands to the BASIC program running on the WebMite to do things like turn devices off/on, set parameters and so on. Screen 5 provides some examples of these. A wide range of controls is available but be warned that the HTML code can get complicated. The web page at www.w3schools.com/howto/default. asp lists these controls and their features, and has plenty of examples that you can copy into your web pages. This ability means that many projects that generally need an LCD screen with associated buttons and switches (or a touchscreen) can be converted to a web interface with the same functions and more. An excellent example is the Watering System Controller starting on page 36 of this issue. It uses the WebMite and there are no controls on the physical box. All the controller’s functions are configured and controlled exclusively via web pages in a browser. TCP client As well as acting as a web server, the WebMite can act as a client and get data from web servers on the internet. Three commands will do this for you: WEB OPEN TCP CLIENT, WEB TCP CLIENT REQUEST and WEB CLOSE TCP CLIENT. For example, if you wanted to get the default web Screen 5: you can include embedded controls such as buttons, checkboxes, radio buttons, input text fields and much more on a web page using HTML forms. The user can use these to send commands to the BASIC program running on the WebMite to turn devices off or on, set parameters and so on. 34 Silicon Chip page from a website called example. com, you could do it this way: DIM INTEGER b(512) WEB OPEN TCP CLIENT “example.com”, 80 WEB TCP CLIENT REQUEST “GET / HTTP”, b() WEB CLOSE TCP CLIENT Editor’s note: the WEB OPEN and WEB TCP commands should all be on a single line; the commands are shown split here due to limited column width. The web page would be saved in the long string buffer b() and you could pick it apart to get the data you wanted using the long string routines. There are many services available on the internet that can be accessed with the TCP client. Two that are documented in the WebMite user manual are getting the weather and sending emails. You need an account with a weather service to get the weather. The user manual describes how you can connect to Open Weather Map; you can get a wealth of data using their service, such as the current temperature and weather for a city or suburb, plus a forecast for the next day or two. Open Weather Map is free for the basic service and is accurate and comprehensive. Sending emails is a little more complicated, as most email relay services have protection to stop them from being used to send spam. To send an email, you need to connect to an SMTP relay service that will then send your email to its destination. The example in the user manual uses SendGrid for this task, as they allow a free account to send up to 100 emails a day (plenty for the WebMite). Sending an email is handy as it allows your WebMite-based gadget to alert you to errors and faults, provide regular status updates etc. For example, your greenhouse monitor could send an email if the temperature went too high or low. Many internet services now require a secure (encrypted) connection, so the WebMite also implements an experimental version of TLS (Transport Layer Security), an extra protocol layer above the TCP layer that supersedes the SSL protocol. Client-server applications use TLS to communicate across a network in a way designed to prevent eavesdropping Australia's electronics magazine and tampering; many sites insist that this protocol is used. Network Time Protocol Getting the current time and date is such a common task that the WebMite has a dedicated command for just this purpose using the Network Time Protocol (NTP) as follows: WEB NTP timeoffset With this command, the WebMite will get the date/time from a public time server pool and set the internal clock of the WebMite accordingly. This means that you do not need a realtime clock in your project; you don’t need a mechanism to adjust the time or date either. The parameter “timeoffset” is the local time zone as a floating point number. For example, “WEB NTP 9.5” will get the current time and set the clock in the WebMite to Adelaide time. Note that daylight saving compensation is not included in the NTP service. Another handy inclusion is a series of commands to post and retrieve data from an MQTT broker. MQTT (Message Queuing Telemetry Transport) is a protocol that enables a client to post data on a server (called an MQTT broker) for later retrieval by another client. It is rather like a bulletin board service for small computers. An example would be our greenhouse monitor. Say it was battery-­ powered; it could power up once an hour, measure the temperature/humidity, post the results to an MQTT broker and power down to save the battery. Separately, a client program on a PC could later read these messages, display the results and graph them. Conclusion In this summary of the WebMite firmware, we have not mentioned all the features that the WebMite inherited from the PicoMite. That includes the high-performance CPU, fully-­featured BASIC programming language, built-in program editor, support for touch-­ sensitive LCD panels, playing sound and music, external SD cards and an extensive range of communications protocols like serial and I2C. The Raspberry Pi Pico W costs little (~$10) and is readily available, so why not have a go? 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Jaycar reserves the right to change prices if and when required. jaycar.com.au/shieldsmodules 1800 022 888 WebMite-based Watering System Controller By Geoff Graham This advanced Watering System Controller does it all. It can change the watering schedule depending on the seasons, check the weather forecast before watering and even alert you to a burst pipe or blocked sprinkler. Best of all, it is very easy to set up and use. Image: www.pexels.com/photo/sprinkler-on-a-grassy-field-3351909/ W atering system controllers, often known as reticulation or irrigation controllers, are notoriously difficult to program. They generally have a small LCD screen and an array of tiny buttons or switches to configure the watering schedule. Our Watering System Controller has no LCD or buttons; it is entirely set up and controlled via a web browser on your smartphone, tablet or computer. The web pages are easy to understand and provide everything you need to set it up. The key component is the WebMite, a Raspberry Pi Pico W microcontroller running the MMBasic programming language, starting on page 30 in this issue. Here it delivers the web pages, gets the time, date and weather from the internet and follows the watering schedule you have configured. The only other significant components in this design are a small power supply and the solid-state relays (SSRs) that drive the solenoid watering valves. The program running on the WebMite is written in BASIC, so you can read it and edit it if you have special requirements. This project was partly developed to demonstrate what you can do with the WebMite. Even if you do not want to build a Watering System Controller, this project can be helpful by providing the code and techniques you can use in other projects. The program will even run on a bare Raspberry Pi Pico W. That means you can explore the program and try it yourself without building anything; you just need the Pico W module. Watering system layout Fig.1 shows a typical reticulation layout. The water supply is connected via a master valve to a series of valves that control individual sprinklers (or sets of sprinklers). The Controller The finished controller in a weatherproof enclosure mounted on an exterior wall. We decided to mount the status LED on the lid along with a waterproof power switch. 36 Silicon Chip Australia's electronics magazine opens the master valve, then steps through each sprinkler valve in turn, opening them for the specified time. The master valve is important as it provides a backup if one of the sprinkler valves is stuck open (it happens). The master valve will still cut off the water supply, limiting the damage caused by the permanently-open valve. Some systems have a pump as the water supply; in that case, the Watering System Controller would switch that on and off instead of a master valve. Either way, the Controller will switch it on half a second before the first sprinkler valve is opened and switch it off half a second after the last has been closed. That is to ensure that the water pipes leading to the sprinkler valves are kept full of water, avoiding the situation where a sprinkler valve closes after the master valve, letting water out of the pipes. Otherwise, when the master valve next opens, the water rushing through the empty pipes could act as a hammer and damage the joints in the pipe and the valve. The flow sensor is an optional but worthwhile addition. It is usually fitted at the outlet of the pump or master valve and tells the Controller the amount of water flowing through the system. The Controller records this and, over time, builds up an average flow rate for each valve. The Controller can then easily detect an abnormal flow rate when it opens a valve, either over or under the average. This is invaluable as an excessive siliconchip.com.au Fig.1: a typical watering system layout. The water supply is connected via a master valve (or pump if using rain water) to a series of valves that control the sprinklers. The optional flow sensor allows the Controller to detect a burst pipe (above-average flow) or blocked valve (below-average flow). flow indicates that a pipe has burst and it might be digging a hole in your garden. A lower-than-normal flow rate means a sprinkler or valve is blocked; if left unfixed, that could cause your plants to die. When an excessively high flow is found, the Controller immediately shuts off that valve to stop any damage. In the case of underflow, it will continue with the watering time in the hope that some water is getting through, but it will also inform you of the problem. The rain sensor is also optional. The Watering System Controller can check the weather forecast for you and skip watering if rain is predicted, but connecting a rain sensor provides a backup specific to your garden. The Controller will check the sensor before it starts a watering run, and if it indicates that it is currently raining, the schedule will be skipped for that day. Controller capabilities To set up the Controller, you use a web browser to access its web page, siliconchip.com.au shown in Screen 1. It lists all the possible watering schedules, with a button to configure each. It also has a RUN NOW button that can be used to start the watering schedule at any time. These schedules are set to start at a certain date in the year and terminate at another. For example, you can set up a schedule for the summer months tailored to the demands of hot weather, another for autumn when less watering is required, another for winter and so on. You can set up the watering requirements for the whole year and, Features & Specifications » » » » » » » » » » » » » » » Configured using a web interface from a smartphone, tablet or computer Controls a master valve plus up to eight sprinkler valves Up to eight independent watering schedules Schedules can be customised for different requirements during summer etc The active schedule can be skipped if rain is forecast or detected Sprinkler times can be increased on hot days Flow sensor support for detecting burst pipes, blocked valves or sprinklers A rain sensor can be connected to avoid watering during rain Schedules can run on certain days of the week or at intervals in days Schedules can start at a fixed time or a period before/after sunrise/sunset Time and date are set from the internet with automatic daylight saving compensation No battery-backed clock is required Schedules continue if the WiFi or internet is down Schedules automatically restart after a power failure Powered by 24V AC at 1A Australia's electronics magazine August 2023  37 unless you change your mind, it will be repeated year after year. Typical Watering System Controllers require you to change the watering characteristics at the start of each season, and that can quickly become tedious, something that our design eliminates. That page includes buttons to configure each schedule. After clicking one, you will be presented with a web page similar to that shown in Screen 2, which provides all the schedule details. The first field on the configuration page allows you to enter a meaningful title to be displayed on the main page. You can also enable or disable the schedule with a checkbox. The next four fields let you set the start and stop dates in the year for the schedule. Schedules can overlap and, if you want the same watering scheme for the whole year, you can set the start to 1/1 and the end to 31/12. The following section allows you to set the days of the week for watering or specify a watering interval in days. This is a case of one or the other but not both. Following this, you set the time for the watering to start. Screen 2 shows Screen 1: the main web page you see when you connect to the Controller. It lists all the watering schedules and their start and stop dates. The CONFIGURE button lets you change the associated schedule, while the RUN NOW button immediately starts that program. Screen 2: this allows you to modify a schedule, including the start and stop dates, the time to start watering, the watering time for each valve and the actions to take based on the weather forecast. 38 Silicon Chip Australia's electronics magazine this set to 6 hours 0 minutes after midnight (ie, 6am). However, using the dropdown list, you can also specify a number of hours and minutes before sunrise, after sunrise, before sunset or after sunset. That gives you a lot of flexibility in setting the start time. In the next section, you can configure each solenoid valve’s watering time in minutes. The Controller will step through each valve in the sequence, opening it for the specified time. It can drive up to eight valves (plus the master valve), but you do not need to install that many if you need fewer. The program will skip any valves with a zero or blank watering time. If you have entered some watering times in these fields, the RUN NOW button will appear on the main page, even if the schedule is disabled and the other fields have not been filled in. That means you can create a watering sequence that can only be started on demand from the web page. The final section allows you to change the watering schedule for that day depending on the weather forecast. You can skip watering entirely if rain is forecast, and you can increase the watering times if the forecast for the next 24 hours predicts a maximum temperature over a certain threshold. The former can avoid wasting water, while the latter can prevent plant death on unusually hot days. At the bottom of the page is a button to save the changes that you have made. The BASIC program saves the configuration and settings to a file called “settings.dat” in the internal file system of the WebMite. On power-up or a reboot, the program reads that file so that all the details are in memory. General settings The GENERAL SETTINGS button at the bottom of the main page (in Screen 1) takes you to the web page shown in Screen 3. On this page, you can tell the program your location, connected sensors and details for sending emails. The location data is used for many features of the Controller, including its time zone, daylight saving compensation, the times for sunrise and sunset and the weather forecast. You need to enter the name of your city and the country code, which is AU for Australia and NZ for New Zealand (a full list of the Alpha-2 codes can be found at https://w.wiki/Gb$). After that, you siliconchip.com.au Screen 3: this screen lets you change the settings for the Controller as a whole. You can tell it your location, the connected sensors and how to send emails. The location is particularly important as it is used to determine the time zone, daylight saving compensation, times for sunrise and sunset and the weather forecast. can click on the TEST button, and you should see a response similar to that shown in Screen 4. For large cities, you can also enter a suburb (eg, “North Sydney”); if that is found, it will provide you with a more specific weather forecast. The database has over 200,000 cities and towns, so you should be able to find your location. If you cannot, try for the nearest larger city or town within the same time zone. The weather predictions might still be accurate enough, depending on how close it is to you. These functions use data from Open Weather Map (http://openweathermap.­ com). It uses that service to look up the latitude and longitude when validating your location. The program can then use that information to query Open Weather Map for your time zone (including DST) and the sunrise and sunset times. If a schedule depends on the weather forecast, the program will query Open Weather Map for the 24-hour forecast before running the watering schedule. With that data, the program can determine if the schedule should be skipped or modified. If you do not enter a location, the Controller will still operate but will use the AEST (GMT + 10 hours) time zone or whatever is set in the BASIC program. You can still set a watering schedule and start times, but compensation for daylight saving will not be included, and you will not be able to set times based on sunset/sunrise or modify the schedule based on the weather. Screen 4: you can test the location you entered and if it is found, you will see a message like this. When you test the email function, you will see a similar message confirming that it worked OK. Sensors There is a section below the location data where you can configure the flow and/or rain sensors (if fitted). The flow sensor will alert you if the water flow for a particular valve is significantly over or under its average flow rate. Either case will cause the status LED to flash and add a warning message on the main web page of the Controller. However, these can be missed, so an email alert (see below) should also be configured to ensure you are notified of the fault. If the fault is not corrected, the Controller will, over time, add this abnormal flow into its average flow rate for the valve and eventually stop treating it as a failure. So, if you get an email indicating a fault, make sure that you siliconchip.com.au attend to it. When you fix the fault, click the button to reset the average so that the BASIC program knows to build a new average for fault detection (it will do that for all valves). You can connect a rain sensor and, if configured, the Controller will not run a watering schedule if it is currently raining. That is in addition to checking the weather forecast. Most rain sensors Australia's electronics magazine have normally-closed contacts that open in the case of rain, which is what the Controller is designed for. You just need to connect it to the screw terminal on the Controller and tick the box to enable this function. Sending emails This is an invaluable feature as you would not normally check the August 2023  39 Controller’s status LED or web page daily. Because sprinklers are usually run before sunrise, critical faults can remain unnoticed for months, by which time they could have done a lot of damage to your garden. To send emails, you need to open a free account with SendGrid (http:// sendgrid.com). Opening the account is a little tedious because they need to verify your identity to prevent spammers from abusing their service. However, with the account created, you can get a free API key (a 69-character string) that you can enter in the API key field. When you get the key from SendGrid, you must also provide them with a matching “from email address”, which should be entered in the next field (From Email Address). Finally, you need to provide an email address to receive emails. This can be the same as the From Address or different. To test your settings, click on the TEST button. After a few seconds, you should see a confirmation message telling you that a test email has been successfully sent. You can then check your email inbox to confirm you have received it. Circuit details The circuit diagram for the Watering System Controller, Fig.2, is dominated by the Raspberry Pi Pico W (ie, the WebMite). The only other significant components are the power supply and the solenoid drivers. All valves use a single common return connection. The Controller is designed for the typical solenoid valves used in domestic reticulation systems that are controlled by 24V AC. These solenoids usually draw a surge current of 350mA when energised, then drop to a holding current of about 220mA. Photo 1: The fully populated Watering System Controller PCB (shown smaller than actual size). Along the bottom edge are the screw terminals for the power input, the master valve plus eight sprinkler valves and the inputs for the optional flow and rain sensors. The board has plenty of space below the screw terminals to route the wires. 40 Silicon Chip Australia's electronics magazine An IXYS CPC1965 solid-state relay drives each valve. These switch on the zero crossing of the AC waveform, so there are no problems with inductive kickback from the coils in the solenoid valves. These are controlled by an inbuilt LED that provides isolation between the input and output. The drive current for the LED is about 5mA (limited by the 470W resistor), well within the drive capability of the microcontroller’s digital outputs. Only two solenoid valves can be energised at once: the master and the currently open sprinkler valve. These are protected by separate PPTC (polymeric positive temperature coefficient) ‘fuses’, which increase in resistance if there is an excessive current through them, limiting the maximum current. When the fault is removed, they revert to regular operation. They protect against short circuits in a solenoid or the solenoid wiring. The power supply is a switching buck (step-down) regulator providing 5V DC to the WebMite and the flow sensor (if fitted). This comprises switching regulator REG1, inductor L1, diode D1, a feedback voltage divider that sets the output to 5V and a couple of bypass/filter capacitors. The power requirement of the Controller is modest at 60-100mA. However, the relatively high input voltage of around 34V DC from the rectified 24V AC would result in 3-4W of heat being generated by a linear regulator. In a sealed enclosure, that could lessen the life of the electrolytic capacitors. With the switching power supply, dissipation is less than 1W. The life of the electrolytic capacitors is a major consideration, as the Watering System Controller should ideally last for 10-20 years or more. For this reason, we have specified high-­ voltage, high-temperature capacitors with higher capacitances than strictly necessary. Those factors together should extend the life of the capacitors considerably. 5V power to the WebMite is supplied via schottky diode D2. This is to isolate the Controller’s power supply from the USB 5V provided by your computer if you have plugged that into the WebMite, letting you use the USB port to debug and test the software on the WebMite even while the Watering System is powered. The flow and rain sensor inputs are pulled up to 3.3V (from the Pico) by siliconchip.com.au Fig.2: the Watering System Controller circuit is dominated by the Raspberry Pi Pico W (ie, the WebMite). The power supply at upper left is a switching design to reduce heat generation. The solenoid drivers on the right switch on the zerocrossing of the AC waveform to avoid inductive spikes from the solenoid valves. 3.3kW resistors and clamped to stay within the supply rails by pairs of schottky diodes. The diodes are for protection from miswiring, nearby lightning strikes etc. In both cases, the input is pulled to ground by the sensor, which is detected and processed by the WebMite’s BASIC program. There are two LEDs and two tactile switches mounted on the PCB. The red LED indicates the controller status; when it is solidly lit, the Controller is operating without fault. If it is siliconchip.com.au flashing or off, that indicates a fault like an abnormal flow detected by the flow sensor, an inability to connect to the internet etc. The green LED illuminates when the Controller is running a watering cycle; the abort button below it can terminate this cycle. The reset switch will force the WebMite to reboot, which is useful if you are upgrading the firmware. Circuit board design The fully-populated Watering Australia's electronics magazine System Controller PCB is shown in Photo 1. This is intended to be mounted in a RITEC RP1285BF 186 × 146 × 75mm waterproof sealed enclosure. Altronics stocks this (Cat H0310F) and there are others of a similar size, some with a clear lid. Note the screw terminals along the bottom edge of the PCB. The first on the left is the 24V AC power input. While a capacity of 1A is specified, a source capable of providing 750mA or more should work OK. August 2023  41 Further along the bottom are the outputs for driving the eight sprinkler valves plus one master valve. Also on the bottom edge are the inputs for the optional flow and rain sensors. The flow sensor should be a Hall effect type that can be powered by 5V DC. The parts list gives a typical example, although there are many other suppliers. The rain sensor does not need power and should be a type with normally-closed contacts; again, the parts list gives a typical example. The board is designed so there is plenty of space between the screw terminals and the bottom of the case, allowing you to route the wires easily. On the top of the PCB, there is space for a small toroidal transformer that can be installed by a qualified electrician if the Controller is to be permanently wired to a power circuit. Before you decide on the placement of the Controller, check that the WebMite can reach your WiFi network at that location. As described later, you can do this by loading the firmware onto the WebMite and powering it with a 5V USB power bank or portable computer. If you can call up its web page from that location, you are good to go. 24V AC power source 24V AC is the standard power supply for domestic watering system controllers and if you are replacing an existing controller, it might already be available. We mounted the prototype Watering System Controller next to the house fusebox, which had a mains GPO socket inside, then used a 24V AC plug pack to power the Controller. This is the best and most economical solution; suitable plug packs are inexpensive and easy to find. Typical examples are Jaycar MP3032 and Altronics M9379A. If you want to power the Controller from the mains, you will need a qualified electrician to run the cables and connect them to a power circuit. This is expensive, so we do not recommend it, but if you must, the PCB has space for a small toroidal transformer at the top, such as Jaycar Cat MT2112 or Vigortronix VTX-146-030-212. The Controller does not have facilities for terminating and fusing the transformer primary as that would be done by the electrician. Construction The Controller is built on a 132 × 152mm double-sided PCB coded Fig.3: this shows where to place the components on the PCB. Note that many parts are optional and could be left off if you don’t need them. Take care with the orientation of the IC, diodes, SSRs and electrolytic capacitors. 42 Silicon Chip Australia's electronics magazine siliconchip.com.au 15110231, with the components mounted as shown in Fig.3. Before you start, you need to decide what options you will include or exclude. The first is the number of valves to control. Most reticulation schemes only need two, three or four sprinkler valves, but the Controller can control up to eight to accommodate large layouts. Most constructors will choose one of the options mentioned in the parts list: four, six or eight valves. The two sensor inputs are also optional. You can omit the associated components if you do not plan to install a rain or flow sensor. Still, you might want to fit them in case you decide to use them later. The two LEDs and tactile switches are also optional. They are helpful if you are fault-finding or setting up the Controller, but they will be of little use once the box is sealed. You could mount them on the front panel using waterproof LEDs and switches with flying leads, where they would be much more useful. We mounted a waterproof power switch and status LED on the front panel of our prototype. If you see the LED flashing, you can visit the Controller’s web page to determine the cause. All the components are throughhole types, so construction should be easy and there are no particular tricks. Follow Fig.3 and the silkscreened text on the PCB and start with the low profile components, working towards the taller components. The WebMite (Pico W) can be soldered directly to the PCB, but we strongly recommend using sockets on the PCB and pin headers on the WebMite to make it a plug-in device. That way, you can easily remove it for testing and fault-finding. Loading the firmware Before you plug the WebMite into the board, load the firmware via the USB port on a computer (Windows, Mac or Linux). Starting with a factory-­ fresh Raspberry Pi Pico W, you first need to load the WebMite firmware (MMBasic). The process is described in detail in the WebMite User Manual, but we will summarise it here: 1. While holding down the white button on the top of the Pico, plug it into your computer. The Pico should appear as a pseudo USB drive on your computer. siliconchip.com.au Parts List – Watering System Controller 1 double-sided PCB coded 15110231, 132 × 152mm 1 Raspberry Pi Pico W microcontroller module (MOD1) 1 RITEC RP1285BF 186 × 146 × 75mm sealed enclosure [Altronics H0310F, DigiKey 164-RP1285BF-ND, Mouser 546-RP1285BF] 1 330μH 0.5A bobbin-style inductor (L1) [Altronics L6227] 1 IXYS CPC1966Y or CPC1965Y solid-state relay (SSRLYM) [Mouser 849-CPC1966Y or 849-CPC1965Y] 2 500mA hold current, 1A trip PPTC resettable fuses (PTC1-2) [Altronics R4550A or Bourns MF-RX050/72-AP] 2 PCB-mounting momentary tactile switches (S1, S2) [Altronics S1120] 2 two-way 5/5.08mm 45° PCB-mounting terminal blocks (CON1, CON2) [Altronics P2044A] 2 20-pin headers, 2.54mm pitch (for MOD1) 2 20-pin header sockets, 2.54mm pitch (for MOD1) 2 3AG PCB-mounting fuse clips (F1) [Altronics S5980] 1 3AG slow-blow 500mA fuse (F1) 4 No.4 × 6mm panhead self-tapping screws Semiconductors 1 LM2574(Y)N-ADJ buck regulator, DIP-8 (REG1) 1 W04 400V 1.2A bridge rectifier (BR1) [Altronics Z0073 or Z0073A] 2 1N5819 40V 1A schottky diodes (D1, D2) 1 3mm red LED (LED1) 1 3mm green LED (LED2) Capacitors 2 220μF 63V 105ºC radial electrolytic caps Resistors (all ¼W 5% axial) 1 10kW 1 3.3kW 3 470W Extra parts for a four-, six- or eight-valve controller 4, 6 or 8 IXYS CPC1966Y or CPC1965Y solid-state relays (SSRLY1-SSRLY8) [Mouser 849-CPC1966Y or 849-CPC1965Y] 4, 6 or 8 470W ¼W 5% axial resistors 2, 3 or 4 two-way 5/5.08mm 45° PCB-mounting terminal blocks (CON3-CON6) [Altronics P2044A] Extra parts for the flow sensor 2 1N5819 40V 1A schottky diodes (D3, D4) 1 10kW ¼W 5% axial resistor 1 3.3kW ¼W 5% axial resistor 1 three-way 5/5.08mm 45° PCB-mounting terminal block (CON7) [Altronics P2045A] 1 5V-powered flow sensor, TTL output [Valves Direct siliconchip.au/link/abmg] Extra parts for the rain sensor 2 1N5819 40V 1A schottky diodes (D5, D6) 1 10kW ¼W 5% axial resistor 1 3.3kW ¼W 5% axial resistor 1 two-way 5/5.08mm 45° PCB-mounting terminal block (CON8) [Altronics P2044A] 1 rain sensor with NC contacts [Valves Direct siliconchip.au/link/abmh] 2. Locate the WebMite firmware (with a name like WebMiteV5.07.07. uf2) and drag and drop that into the USB drive. 3. When it finishes copying, the WebMite will reboot and reconnect to your PC as a serial port over USB. The green LED on the top of the Pico W should slowly flash. 4. Determine the name of the serial Australia's electronics magazine port used by the WebMite (ie, COM12), then use Tera Term (http://tera-term. en.lo4d.com) to connect to that port. 5. Press return/Enter and you should see the MMBasic command prompt (the > character). Next, you must set the WebMite options for accessing the WiFi network. These are entered at the command prompt and each will cause the August 2023  43 Modifying the BASIC program While the Controller is configured via its web pages, you can also change some minor settings by editing the BASIC program. To do this, use Telnet to connect to the WebMite’s console (eg, using Tera Term), then press CTRL-C to interrupt the running program. Enter EDIT at the command prompt to run the editor. Scrolling down, you will see part of the program labelled “User changeable constants”, as shown in code below. These are the parameters that you can easily change. The status LED will flash continuously if you have not entered a location on the general setup page. To avoid this, you can turn off the warning by setting DisableLocationWarning to 1 instead of 0. You might want to change the default time zone from AEST (+10 hours). To do this, change the line CONST DefaultTimeZone = 10.0 to your time zone. For example, Adelaide is 9.5. Note that the program will not be able to correct for daylight saving in this case. The program will signal a fault from the flow sensor if the value is 50% above the long-term average. This can be changed by changing the entry Const UpperFtolerance = 50 to another value. For example, if you wanted the Controller to be much more sensitive to excessive flow, you could change the value to 20 (20%). Similarly, for the lower tolerance (reduction in flow), change the entry Lower­ Ftolerance on the line below. We have registered an account with Open Weather Map and used the associated API key in the Watering System Controller program. Their free account provides us with everything we need. The only significant restriction is that users of the key are limited to 60 queries per minute or a million in a month. That means that all users of this program will be using the same API key, but that should be fine as it is unlikely for 60 users to all make a call in the same minute. However, you can get your own access key if you want to be independent. If you open an account with Open Weather Map, they will provide you with an API key. The key is a 32-character-long string of letters and numbers that acts like a password. To replace the key in the code, edit the program line starting with “Const OWMKey =”. When the program gets the weather forecast from Open Weather Map, the chance of rain is returned as a percentage, with 0 representing no chance of rain and 100 indicating certainty. If a schedule is configured to skip watering on a forecast of rain, the program will do this if the chance of rain is at least 90%. You can change this threshold to anything you want by changing the line “Const RainThreshild = 90”. For example, if you only want to skip watering if it is certain to rain, you can set the value to 100 (ie, 100% chance). ''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' ' User changeable constants ''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' ‘ set this to 1 to disable the location warning Const DisableLocationWarning = 0 ‘ this is the default time zone if the location is not set Const DefaultTimeZone = 10.0 ‘ the Const ‘ the Const % increase in flow rate to trigger a fault UpperFtolerance = 50 % decrease in flow rate to trigger a fault LowerFtolerance = 50 ‘ % forecast % chance of rain required to skip a schedule Const RainThreshild = 90 ‘ API key for accessing Open Weather Map ‘ This key is shared between all users of this program and is ‘ limited to 60 queries/minute. This should not be a problem but ‘ you can easily get your own key and be inderpendent. To do this ‘ goto https://openweathermap.org/ and open a free account, then ‘ generate a key and replace the key below with your own key. Const OWMKey = "73cd207244614965fc5ca3646bdd10ab" 44 Silicon Chip Australia's electronics magazine WebMite to reboot, so you will need to reconnect the Tera Term session after each (the double quotes are required for the SSID and password values): OPTION WIFI “SSID”, “password” OPTION TCP SERVER PORT 80 OPTION TELNET CONSOLE ON The following command will show the IP address that your router has allocated to the WebMite: PRINT MM.INFO(IP ADDRESS) Now you need to copy some files to the WebMite’s internal file system. The best way to do this is by using TFTP on your computer. Follow these instructions for Windows: siliconchip. au/link/abmf The files are in the download for the Watering System Controller and are named “retic.bas”, “config.html”, “index.html” and “setup.html”. Use the following TFTP commands to transfer the files (ipaddr is the IP address of the WebMite): TFTP TFTP TFTP TFTP -i -i -i -i ipaddr ipaddr ipaddr ipaddr PUT PUT PUT PUT retic.bas config.html index.html setup.html You can check that the files have copied correctly by using the command FILES at the MMBasic prompt. That will list the files in the internal file system. Now you can run the BASIC program using the following command and the Watering System Controller should start up: RUN “retic.bas” When the program starts, it will print a series of status messages on the console. The program does this whenever it takes some action; it is useful for debugging and understanding what is happening. You can now fire up your web browser and enter in the address field the IP address of the WebMite that you determined earlier. When you press Enter, you should then see a web page similar to Screen 1 (without the configuration data entered). Note that it’s possible to skip all the steps above apart from setting the WiFi options and running the program by instead loading the all-in-one “WaterCtrl.uf2” file that’s included in the download package. Now you can install the WebMite on the Controller PCB, place the siliconchip.com.au Controller in its final location and attach the case lid. You can then set up the Controller as described earlier by accessing it via WiFi, configuring each watering schedule, completing the basic setup section to enter your location etc. Fault-finding If the Controller does not work as expected, first check the status LED. If it is off or flashing, that means a fault has been detected; if it is permanently illuminated, that means that everything is working correctly (as far as the program is concerned). While the Controller is starting up, the LED will turn off or flash for a while, but if it is still flashing after a minute or two, something is wrong. If the LED indicates an error, log into the Controller web page and check for a message in red at the bottom. This could be an incorrect configuration, inability to access the internet, excessive water flow etc. When you correct this error, the message should vanish and the status LED will stop flashing. If you cannot log into the web page or the Controller appears dead, unplug the WebMite and plug it directly into the USB port on your computer. Then use Tera Term to access the serial-overUSB console to diagnose the problem. You might have to press CTRL-C to terminate the running program so you can access the MMBasic console. Try restarting the BASIC program with the command RUN “retic.bas”. As the program starts, you should see a series of messages in your terminal emulator describing the progress. The first will be concerned with connecting to your WiFi, then connecting to the internet, followed by more messages detailing the progress in getting your location and time zone from Open Weather Map. The success or failure of these should give you some pointers as to where to look. Typical problems that can trip you up include: ● Not programming the Pico W with the correct WebMite firmware. ● Incorrect SSID or password in the OPTION WIFI command. ● Your router is not configured for WPA-PSK security and DHCP. ● Your router is blocking the WebMite from reaching the internet. ● You have not set the options correctly. Use OPTION LIST to check them. siliconchip.com.au Photo 2: the Controller mounted in a waterproof sealed enclosure. This shows it with an onboard 24V mains transformer, but note that it must be installed by a qualified electrician who will terminate the primary and connect it to a suitable power circuit. ● You have not copied the program files to the WebMite. Use the FILES command to check that all four files have been copied correctly and are not zero bytes. If the WebMite seems fine while plugged into your computer but not in the enclosure, it could be something as simple as a wire inside the controller box draped near the WebMite’s WiFi aerial, reducing its sensitivity. If the fault appears to be with the control board, you will have to revert to traditional fault-finding procedures like checking that the power supply is working correctly and 5V is on the Australia's electronics magazine VSYS pin of the WebMite. Also check the component values and examine your soldering in detail. Hopefully, your Watering System Controller will work the first time, and you can relax knowing that your plants will have all the water they need. For future software updates, check the Silicon Chip website or the author’s website at http://geoffg.net/retic.html Consider joining the Back Shed Forum (www.thebackshed.com/ forum/Microcontrollers), where many enthusiastic WebMite and MMBasic users are happy to help newcomers with advice and hints. SC August 2023  45 Feature by Brandon Speedie The Electrical Grid Australia’s Electricity Distribution Networks and Markets Many readers may understand the basics of the ‘grid’ and its role in distributing energy from generators to end users. But how is supply managed to match demand? How are voltages kept within tight tolerances? And how is our grid changing as we transition away from centralised generation? Image source: https://w.wiki/6o9T A ustralia’s grid operates not as a single large transmission and distribution network, but as several isolated systems. The largest system is the National Electricity Market (NEM), covering most of the densely populated areas across the eastern seaboard – see Fig.1. The NEM is one of the longest networks in the world, stretching from Port Douglas in Queensland to southern Tasmania, and west as far as Ceduna in South Australia. Fig.2 is a close-up of the South Australian (SA) portion of the NEM. We don’t have space to show such maps for all states in this article. You can download PDF maps for all states in the NEM from the AEMO: siliconchip. au/link/abm8 Smaller grids operate in Western Australia and the Northern Territory. The South West Interconnected System (SWIS) supplies the populated areas from Geraldton through Perth to the south coast and as far east as Kalgoorlie – see Fig.4. The SWIS is sometimes also referred to as the Wholesale Electricity Market (WEM), a reference to the market that administers power in that system. 46 Silicon Chip The North West Interconnected System (NWIS) operates in the Pilbara, predominantly supplying the extensive mining operations on the North West coast of WA near Karratha and Port Hedland – see Fig.5. The Northern Territory’s primary grid is called the Darwin Katherine Interconnected System (DKIS) and extends from Darwin through to well south of Katherine – see Fig.6. Interestingly, the Northern Territory has some of the most abundant solar irradiance on Earth. A site near Tennant Creek has been earmarked for development by “Sun Cable”, an ambitious project to build the world’s largest solar farm (20GW), the world’s largest battery (40GWh), and the world’s longest submarine power cable (4500km, HVDC) – see Fig.7. The generated energy would supply Table 1 – VIC energy generation mix Table 2 – NSW energy generation mix Type Avg Price Contribution ($/MWh) Type Contribution Avg Price ($/MWh) Brown coal 65.8% $105.59 Black coal 61.3% $156.33 Wind 21.9% $69.77 Solar (rooftop) 9.1% $75.28 8.9% $25.10 Solar (rooftop) Wind 8.0% $135.70 Hydro 6.3% $186.99 Gas 2.5% $284.00 Solar (utility) 7.2% $85.25 Solar (utility) 3.2% $50.68 Hydro 4.6% $212.59 Gas 2.1% $252.92 Battery 0.3% discharge $189.06 Battery 0.03% discharge $264.03 Imports 4.8% $98.02 Imports 9.1% $108.05 Exports 13.7% $124.02 Exports 1.6% $154.07 Australia's electronics magazine siliconchip.com.au Darwin, Singapore, and later, Indonesia. Interconnectors The NEM states (SA, Vic, Tas, NSW & Qld) share a single electricity network, but commercially they operate as isolated systems, with interconnectors stretching across state boundaries to share power. They are summarised below; you can get more information on them from siliconchip.au/link/ abm7 Basslink (Victoria – Tasmania) Basslink connects George Town on the north coast of Tasmania to Victoria’s brown coal generator Loy Yang A in Gippsland via a 400kV DC cable – see Fig.8. Much of the cable (290km of the total 370km) runs undersea in Bass Strait. Loy Yang can supply up to 478MW (megawatts) to Tasmania or import 594MW for use in Victoria. We have published an article on Basslink in the September 2008 issue (siliconchip.au/Article/1943). A failure of the undersea cable in December 2015 (see Fig.3) left Tasmania isolated from the rest of the NEM. That was one factor leading to the Tasmanian energy crisis of 2016. Hydro Tasmania had largely depleted its storage from low rainfall and above-­ average generation (to maximise revenue before the repealing of the carbon tax). The state was forced to recommission a gas-fired power station and deploy temporary diesel generation to firm up supply until the interconnector was repaired, six months later. Table 3 – QLD energy generation mix Type Contribution Avg Price ($/MWh) Black coal 70.8% $146.40 Solar (rooftop) 11.4% $54.95 Solar (utility) 8.4% $64.87 Gas 8.1% $210.61 Wind 3.5% $133.38 Hydro 2.0% $203.80 Battery 0.07% discharge $256.35 Imports 0.9% $132.62 Exports 5.4% $111.87 siliconchip.com.au Fig.1: the High Voltage Transmission infrastructure in the NEM, one of the longest electricity networks in the world. This map was pieced together from individual state maps supplied by the AEMO and shows Tasmania closer to the mainland than it really is (with the Bass Strait islands removed) for compactness. Australia's electronics magazine August 2023  47 The failure was caused by heat stress due to mismanagement by the interconnector’s operators. 30 Olympic Dam West Olympic Dam North LeighCreek Coalfield LeighCreek South Heywood (Victoria – SA) Woomera TRANSMISSION INFRASTRUCTURE Pimba Mt Gunson 500 kV Transmission Line 330 kV Transmission Line 275 kV Transmission Line Neuroodla 220 kV Transmission Line 132 / 110 kV Transmission Line 40 Wudinna Middleback DC Link Regional Reference Node Davenport 212 77/201 280 Cultana 66 kV Transmission Line 110 110 Baroota 309 Stony Point Whyalla Central Mt Lock 150 150 Whyalla Belalie Port Pirie Bungama 132 Terminal Clements Gap 70 Yadnarie Kadina East Brinkworth Waterloo Waterloo East 66 130 154 Port Lincoln 10 127 250 30 Dalrymple 1 2 3 4 5 6 1080 210 232 529 204 150 Key to Adelaide 8 9 10 11 12 13 3 62 4 1 58 8 7 65 8 91 Kilburn Northfield Parafield Gardens West Magill East Terrace City West 196 201 200 90 200 Templers West Munno Para 20 Roseworthy 78 71 Blyth Clare West North Hummocks Adrossan West 240 53 Canowie 119 Red Hill 60 Snowtown 99 144 126 95 245 57 123 21 111 4 6 Robertstown Murraylink (Victoria – SA) 100 4 North West Bend Monash Berri 50 Templers Dorrien Millbrook Para Angas Creek 12 10 13 9 100 Tungkillo 11 Mannum 29.99 MBH3 Mobilong 1312 10 MBH1 Mt. Barker Mt. Barker South Morphett Vale East Cherry Gardens Happy Valley 15/6 4 87/41.5 Also known as Directlink, the Terranora interconnector links Laverty’s Gap in NSW to Bungalora in Queensland. The cable consists of three buried bipolar DC circuits at ±80kV, able to operate at up to 107MW from New South Wales to Queensland and up to 210MW in the opposite direction. 35 Keith 7 171 Black Range GENERATION SYMBOLS WIND SOLAR OCGT HYDRO PUMPED HYDRO STORAGE DIESEL COAL Kincraig CCGT BIOMASS Queensland to NSW Interconnector BATTERY SUBSTATION Application Pre-Registration Registration Commissioning Operational 63 100 South 46 Mayura East Blanche 25 279 Mt Gambier This map is intended to be a high-level representation only, interested parties should always consult with their relevant network service provider (or equivalent) for more information. Fig.2 (above): a more detailed view of the South Australian part of the NEM state, showing transmission infrastructure and large generators by type. Due to South Australia’s large makeup of renewable energy you can see lots of windfarms and solar generation on the map. Maps of all the other NEM states can be found at siliconchip.au/ link/abm8 (AEMO). Fig.3 (right): the Basslink cable section that failed in 2015. It was pulled out of the sea onto a ship for repair. Basslink was out of service for around six months. 48 Silicon Chip This one connects Berri in SA to Red Cliffs in Victoria via an underground bipolar ±150kV DC link. It can transfer power at 220MW from Victoria to South Australia and 200MW in the opposite direction. Terranora Interconnector (Queensland – NSW) Tailem Bend 95 This connects the Heywood substation in Victoria with SA’s southeast substation (near Mt Gambier) via 275kV AC overhead lines. Power can flow at up to 600MW from Victoria to South Australia and 500MW in the opposite direction. The interconnector infamously tripped due to an overcurrent condition at the start of the 2016 South Australia blackout; this was incorrectly cited as the cause by some. The real culprit was severe weather causing transmission line damage, and the subsequent loss of wind generation, possibly due to conservative ‘fault ride through’ settings. Australia's electronics magazine This joins Dumaresq in NSW with Bulli Creek in Queensland via two overhead 330kV AC lines and two 275kV AC lines between Braemar (NSW) and Tarong (Qld). The power rating is 1078MW from Queensland to New South Wales and 600MW in the opposite direction. Victoria to NSW Interconnector The Vic-NSW interconnector is made up of four separate lines, as well as a 132kV bus tie at Guthega, which is usually not used. There are two 330kV AC lines linking the Victoria and NSW parts of the Snowy Hydroelectric Scheme (Murray – Upper siliconchip.com.au Fig.4: the transmission infrastructure in the SWIS, which serves Perth and the surrounding area. Source: www. westernpower.com.au/media/3258/annual-planning-report-2018-19-overview-20190418.pdf Tumut and Murray – Lower Tumut), as well as a 330kV AC line from Jindera and Wodonga, and a 220kV AC line between Buronga and Red Cliffs. The scheme can operate at up to 1600MW from Victoria to New South Wales and 1350MW the other way, though these power limits are highly constrained when Snowy Hydro is generating. is from generators to the transmission network, then the distribution network, the retailer, and onto the end user – see Fig.9. The Transmission Network is the high voltage ‘backbone’ that carries Pilbara network facilities Please note: this map is indicative only and should not be relied upon for non-Horizon Power network information. Supply chain Broadly speaking, electricity flows through four ‘service providers’ before reaching the end user. The basic flow siliconchip.com.au FMG PLUTO 50MW (Load) 500MW EnergyConnect (proposed: SA – NSW) An interconnector currently under construction will link Robertstown in SA to Wagga Wagga in NSW via a 330kV above-ground transmission line. EnergyConnect aims to ease network congestion in the so-called “rhombus of regret”, a problematic area in North East Victoria that sees generators curtailed by as much as 100 days a year due to capacity constraints. the bulk of the supply capacity into metro areas. These networks typically operate at AC voltages such as 500kV, 330kV, 275kV, 220kV, 132kV and 66kV, connecting large generators to local substations. G KGP 280MW Dampier Pilbara Iron 220MW CP G ATCO G 80MW Cape Lambert TransAlta 158MW 220Kv KARRATHA Roebourne HP 65MW Goldsworthy BHP 2MW (Load) 66Kv Alinta 210MW RTIO Marble Bar 250MW 132Kv Onslow EXMOUTH gas Pannawonica 10MW (Load) Shay Gap HP 65MW Load (East Pilbara) 220Kv 132Kv 450MW PORT HEDLAND 66Kv BHP 70MW G G Millsteam NWIS 220Kv NEW M Nullagine 100MW FMG 100MW Tom Price 30MW (Load) Horizon NWIS Network Pilbara Iron owned BHPB owned FMG owned Alinta owned G Connected generation Isolated generation BHPB Yandi Yandicoogina 220Kv RTIO 150MW G Paraburdoo G 150MW 20MW (Load) 90MW West Angelas 7MW (Load) 132Kv G Alinta Newman BHP 250MW Fig.5: transmission infrastructure in the NWIS in the Pilbara. Source: https://nwis.com.au/media/jqcniluy/nwis-network-map-2020.pdf Australia's electronics magazine August 2023  49 Table 4 – SA energy generation mix Table 5 – TAS energy generation mix Type Contribution Avg Price ($/MWh) Type Contribution Avg Price ($/MWh) Wind 46.6% $79.25 Hydro 73.7% $123.88 Gas 25.4% $244.37 Wind 15.4% $91.96 Solar (rooftop) 18.2% $25.76 Solar 2.5% (rooftop) $75.41 Solar (utility) 5.3% $55.26 Gas 0.7% $150.34 Imports 14.4% $81.74 The Distribution Network consists of the low-voltage poles and wires that connect the substations to most loads in the grid. This includes the low-­ voltage supply to residential and commercial properties (230V single-phase, 400V three-phase) as well as medium voltages (11kV, 22kV, 33kV) for primary distribution and to directly supply larger industrial loads, plus 66kV for sub-distribution. Exports 6.8% $181.89 Generation Battery 0.5% Discharge $270.34 Imports 9.9% $122.64 Exports 6.2% $37.11 Fig.6: Northern Territory gas, water, and electricity infrastructure. Source: www.powerwater.com.au/__data/assets/pdf_file/0017/90602/FINAL_Powerand-Water-Annual-Report-2021_web.pdf 50 Silicon Chip Australia's electronics magazine Generators supply energy to the network. Australia generates the bulk of its power from large coal power stations, with transmission infrastructure built to distribute the power into the population centres. This model is beginning to change as coal power stations are retired and smaller decentralised generators connect to the grid. Victoria’s generation (Table 1) is centred around the brown coal deposits in the Latrobe Valley, with an increasing contribution from wind, and to a lesser extent, solar. Victoria also has some hydroelectric generators, mainly situated in the Kiewa scheme on the slopes of Falls Creek Ski Resort and the southern part of the Snowy Hydro scheme. The latter is located in NSW but allocated to Victoria. New South Wales (Table 2) relies heavily on the black coal deposits in the Hunter Valley near Newcastle, with smaller contributions from solar, wind and hydro. Two of the three existing pumped hydro projects in the NEM are in NSW: the northern part of the Snowy Hydro scheme (Tumut) and Shoalhaven, near Nowra. Queensland (Table 3) predominantly uses black coal from two main areas, west of Brisbane and near Rockhampton. Solar is a small but growing generation type, with smaller contributions from gas, hydro and wind power. South Australia (Table 4) is somewhat unusual in that it is heavily reliant on renewable energy, and almost none of it is hydro. South Australia also has no coal-fired power stations (though it does import power from Victoria). Wind power is the largest contributor, with sizeable generation also coming from solar and ‘firming’ (filling in the gaps in variable generation) using turbines powered by natural gas. siliconchip.com.au Fig.7: the proposed Sun Cable route from Darwin to Singapore. Source: Sun Cable. Tasmania (Table 5) is also mainly a renewable grid, using predominantly hydroelectric power for its needs, with smaller contributions from wind and solar. Western Australia (SWIS; Table 6) is pretty typical by Australian standards, with the largest generation coming from coal and gas, and smaller but equal contributions from solar and wind. The source of data for these tables is https://opennem.org.au/energy/ nem/?range=1y&interval=1w Demand trends The load on the grid is variable but follows predictable cycles. Across the course of a day, the load is lowest around 3am and grows steadily throughout the day, typically peaking around 7pm. In recent years, the increased proliferation of ‘behind the meter’ generation (mainly rooftop solar) has had the effect of reducing grid demand across the middle of the day. The resultant demand graph is known as the “duck curve”, a reference to its shape similar to the aquatic bird – see Fig.10. There are also longer-term trends. The load is typically higher on weekdays, lower on Saturdays and even lower on Sundays. There is also seasonal variation. In spring and autumn, the weather dictates lower loads from HVAC (heating, ventilation, air conditioning) systems, which are the main drivers of the seasonal variation. Winter has a higher demand, driven by heating, particularly during a cold snap where there is a sustained period of cold weather. Summer typically has the highest load due to heavy air conditioning use, particularly during a heat wave. However, this ‘peak demand’ is somewhat offset by increases in solar generation; hot weather generally coincides with good irradiance. The wholesale energy market This section focuses on the operation of the NEM energy market (the largest in Australia), although its operation is similar to markets in other regions. Loy Yang Power Station Table 6 – Western Australia (SWIS) energy generation mix Type Contribution (March 2022 – March 2023) Average Price ($/MWh) Gas 37.3% $85 Black coal 27.2% $80 Wind 16.8% $69 Solar (rooftop) 16.4% $38 Solar (utility) 1.9% $57 Biogas 0.4% $73 siliconchip.com.au Australia's electronics magazine George Town Substation Fig.8 (above): the Basslink route from Gippsland, Vic to Georgetown, Tas. Source: https://w.wiki/6nyX August 2023  51 Fig.9: the electricity supply chain. Original source: AEMO. The Australian Energy Market Operator (AEMO) is responsible for keeping the lights on by matching supply with demand. Every five minutes, AEMO predicts grid demand for the next five-minute interval. They ingest data from various sources, including historical data, market conditions and weather forecasts, and produce a prediction. Simultaneously, generators submit bids to AEMO. These bids offer a quantity of generation at a particular price; for example, 10MW <at> $50/ MWh (megawatt-hour) or 40MW <at> $70/MWh etc (see the later section on generator bidding strategies). AEMO orders these bids from cheapest to most expensive, then works its way up the ‘bid stack’ (Fig.11) until it has met its required generation capacity. This cut-off point sets the price that all generators get paid for their contribution, regardless of their initial bids. Frequency Control Ancillary Services (FCAS) There are also ancillary markets focused on maintaining grid stability. If the grid has balanced supply and demand, its frequency is maintained at 50Hz. If there is excess generation (insufficient load), the frequency will tend to rise, while if there is a lack of generation (excessive load), the frequency will fall. The FCAS markets work to maintain 50Hz across the region. The regulation FCAS markets are used to fine-tune supply and demand. There are two: raise and lower. Raise Fig.10: the average wholesale electricity spot price in South Australia for April 2023. Note the negative price in the middle of the day, where generators pay, and loads are paid, instead of vice versa. This is called a “duck curve” because it looks a bit like a duck! 52 Silicon Chip Australia's electronics magazine works to increase the frequency by increasing generation or shedding load. Lower is the opposite, reducing frequency by increasing load or shedding generation. Generators bid into the FCAS markets in the same way as for energy, offering a quantity of generation at a desired price. AEMO decides how much reserve capacity is required and works its way up the bid stack. Generators below the marginal price are ‘dispatched’ in the form of an operating setpoint. AEMO updates this setpoint every four seconds to match changes in demand or correct any errors in AEMO’s prediction when predicting the next five-­minute interval. The contingency FCAS markets provide standby capacity in the event of a shock to the system, such as a large generator tripping offline or a transmission line collapsing. Market participants monitor their local system frequency and operate if they see an excursion outside the normal operating range (typically 49.8550.15Hz). Participants are paid for being available, regardless of whether they actually respond. There are six contingency FCAS markets: fast raise, fast lower, slow raise, slow lower, delayed raise and delayed lower (see Fig.12). In the same way as regulation FCAS, the raise markets are for increases in generation (or reductions in load), while lower markets are for decreases in generation (or load increases). Fast services must be able to respond within six seconds, slow within 60 seconds and delayed within 5 minutes. siliconchip.com.au Generator bidding strategies The price that generators bid into the market typically reflects their ‘short-run marginal cost’ (SRMC), which is the price of producing an additional unit of power. In theory, this is based on their fuel cost, though their bidding strategies are more complicated than that would suggest. Wind and solar generators benefit from having a $0 fuel cost. Therefore, it is not unusual to see these types of generators bid into the market at or near $0/MWh. Hydroelectric generators are a little more complex. While the rain is free, they have limited storage, so their bid strategy tends to consider the opportunity cost of dispatching at other times. Many hydro generators also have environmental constraints (for example, limits to prevent downstream flooding). Black coal generators’ bids are largely a function of their coal price. Coal generators tend to be slow to ramp up or down, which must also be considered in their bidding strategy. It is not uncommon for a coal generator to bid below their SRMC in the hope that the price will increase in the short term and they won’t have to back off. Brown coal power stations are slower to ramp than black coal, so they tend to primarily consider the avoided cost of turning off when bidding. Gas generators are fast responding, so they don’t have the same constraints as coal. Their SRMC is typically based on the costs of burning natural gas. Because gas is often the marginal generator, they play a central role in setting the wholesale price, despite often only being a small fraction of the overall generation mix. Fig.11: an example bid stack showing how generators get dispatched by merit order to meet demand. At 4:25, Generator 1 gets paid $100 despite only bidding $20. Original source: AEMC. storage; a battery could charge for low cost (or free) during the middle of the day, then discharge into a high-price market during the evening (see Fig.10). The retailer The primary function of the retailer is to meet their end-user electricity demand by purchasing supply from the wholesale markets. They will then on-charge that energy at a fixed rate; say, $300/MWh ($30¢/kWh), or perhaps two or three different rates for peak/shoulder/off-peak. This is much higher than the average wholesale price of $93/MWh (for the fourth quarter of 2022), which might make you feel ripped off as a consumer. But consider that during periods of high demand and low supply, the wholesale price can go as high as the market cap of $15,500/ MWh! So you are paying for not just retail margin but also financial hedging and other costs such as metering, network fees, administration etc. The wholesale market also has a price floor of -$1000/MWh. When the price is negative, the grid is oversupplied, and your retailer receives a credit for any load you provide (and if you have solar, a bill for any generation). Traditional peak/shoulder/off-peak electricity tariffs price energy more expensively during the day, with offpeak periods at night. Arguably, these off-peak periods should be shifted to the middle of the day, to help align customer behaviour to grid supply and ease our transition SC to renewables. Price trends Because the forces of supply and demand drive the wholesale energy market, and supply is naturally limited, the price tends to follow demand. Across the course of a day, it is typical to see moderate prices at night, with a small peak at dawn as demand increases. Solar drives the price down once the sun is up, sometimes even into the negative region. The evening peak usually experiences the highest prices, as solar generation drops, but demand remains high. This cycle shows the value of siliconchip.com.au Fig.12: the contingency FCAS response times. Fast generators must be able to ramp within six seconds, slow within 60 seconds and delayed within five minutes. Australia's electronics magazine August 2023  53 Steve Matthysen’s Arduino-Based T LC and ESR METER This enhancement to our Wide-Range Digital LC Meter (June 2018; siliconchip.au/Article/11099) allows it also to measure capacitor ESR. That is extremely useful for diagnosing faulty equipment because increasing ESR over time is one of the most common ways electrolytic capacitors fail. im Blythman presented an LC Meter with excellent performance, range and accuracy in the June 2018 issue. The meter is based on a custom Arduino shield and is easy to build. Its accuracy is optimised by auto-calibration features and compensation for the inherent capacitance of the leads and even the Arduino pins. While it’s undoubtedly useful for checking suspect components, for electrolytic capacitors, it is important to know whether it has a low impedance to alternating currents. That requires it to have a low equivalent series resistance (ESR). The last full ESR meter published in Silicon Chip was the Mk.2 Meter by Bob Parker (March-April 2004 issues; siliconchip.au/Series/99), who created its original design some 27 years ago! The project articles include additional information expanding on the design of capacitors and the importance of measuring their ESR values. I thought it would be worthwhile to incorporate both the LC and ESR functions in a single device. Why is ESR so important? Electrolytic capacitors are used where high charge storage is required. In many applications, current must flow efficiently into and out of the capacitor to charge or discharge it. ESR acts like a resistor in series with the capacitor, losing energy each time current flows in or out. That ESR also prevents the capacitor from doing its job properly, which is usually stabilising voltage. Say the capacitor is being charged at 1A and then starts discharging at 1A. If it has an ESR of 1W, the voltage seen by the rest of the circuit will suddenly shift by 2V ([1A + 1A] × 1W). For example, that would add to the ripple on a power supply storage capacitor. High ESR values also lead to heating within the electrolytic capacitor, possibly changing the capacitance and reducing the integrity of its electrolyte. One of the most common indications of failed or failing electrolytic capacitors is a sudden or gradual increase in their ESR values. Increased ESR values can introduce a wide range of mysterious circuit failures that are sometimes difficult to pin down. For a switch-mode power supply, these include decreased voltage regulation, filter failures, elevated noise levels, signal losses, or failure to start. 54 Silicon Chip Australia's electronics magazine siliconchip.com.au Therefore, it makes sense when testing electrolytic capacitors to confirm that their capacitance and ESR values are in the appropriate ranges. Revised design The March 2004 Mk.2 ESR Meter is based on a Z86E0412 microcontroller driving two seven-segment displays. It (and its predecessor) were extremely popular. In this version, rather than redesign the wheel, we adopted the same frontend circuitry used in the Mk.2 meter, but we feed the signals into an Arduino Uno driving an LCD. The benefit of doing this is that the ESR front end can be built on a relatively small circuit board and integrated with the LC meter presented in the June 2018 issue (siliconchip.au/Article/11099). That makes it a great general-­ purpose instrument that can not only check the ESR of capacitors but also their values (up to a certain limit), plus it can be used to measure inductors and more. Alternatively, you could simply attach the front end to an Arduino Uno (or clone) with a 4-line I2C alphanumeric LCD to produce a standalone ESR meter. The code for both the LC-integrated and standalone versions is available from siliconchip.com.au/ Shop/6/234 Electrolytic capacitor construction In their most basic form, capacitors have two conductive plates (the anode and cathode) separated by an insulating material called the dielectric. There are three main types of electrolytic capacitors based on the material used for the anode and the associated dielectric used in their design: aluminium, niobium oxide and tantalum. Capacitance is directly proportional to the total surface area of the plates but inversely proportional to the distance between the plates. Hence, the thinner the dielectric, the more efficient capacitors become. Dielectrics have a high resistance; for low-value capacitors, examples include various polymers, mica, ceramics and even some liquids and gases, including air. In all three types of electrolytics, the anode consists of the primary material (aluminium, niobium oxide or tantalum) and the dielectric is a very thin layer of the respective oxide (pentoxide for niobium) deposited on the face of the anode. This very thin dielectric must be in close contact with the cathode, which is the electrolyte’s purpose. In essence, the electrolyte is the actual cathode, except that we also require a physical connection that allows the device to be soldered into a circuit. To ensure a high-quality coupling with low resistance, the electrolyte is a highly conductive liquid, gel or solid. In aluminium electrolytic capacitors, an efficient way to ensure a high-quality coupling between the two is to sandwich a thin electrolyte-soaked sheet of paper between the dielectric and the cathode. Manganese dioxide is a solid electrolyte typically used in niobium and tantalum capacitors to connect the cathode to the dielectric. For more details, see our article “All About Capacitors” in the March 2021 issue (siliconchip.au/ Article/14786). If you have already built the LC meter and want to attach the ESR module, you could do that, although starting from scratch is possibly easier. Measuring ESR Fig.1 shows a simplified diagram representing the theory of operation. S1 and S2 are electronic switches Fig.1: S1 repeatedly discharges and then briefly applies current to the DUT. The pulses are too short to charge the capacitor, so the resulting voltage is proportional to the ESR. The pulse amplifier then feeds an amplified version to the comparator, along with a linear ramp, and by counting the number of output pulses, we can accurately determine the ESR. siliconchip.com.au Australia's electronics magazine controlled by the Arduino. When no measurement is underway, both S1 and S2 are in the discharge position to ensure the capacitor being tested and the C-Ramp capacitor are maintained in discharged states. At the start of a measurement cycle, the Arduino code places S2 into the Charge position and charges C-Ramp with a constant current of 9.4mA. The resulting voltage at the inverting input of the comparator increases at a steady rate of 20mV/ms (ie, 20V/s). After 480µs, S1 is switched to the charge position for 20µs, connecting a constant current source to the capacitor being tested. Depending on the range, the applied current is either 0.5mA, 5mA or 50mA. The test current pulse is kept very short to minimise charge build-up on the capacitor plates; we only want to measure the momentary pulse that develops across the capacitor’s equivalent series resistance. Per Ohm’s law, the magnitude of the resulting voltage pulse is directly proportional to the ESR of the capacitor. The test pulse voltage is amplified by a factor of 20 and fed into the non-­inverting input of the comparator. It compares the magnitude of the test pulse to the reference ramp voltage, and if the magnitude of the test pulse is greater than the latter, the comparator produces a 5V pulse at its output. The Arduino code increments a counter August 2023  55 and then waits another 480µs before closing S1 again for 20µs to produce another test pulse. Since the ramp voltage increases at a constant rate, it will eventually exceed the magnitude of the test pulses. The Arduino code detects the missing pulse and stops the measurement process, placing both S1 and S2 in the discharge position. The Arduino uses the total number of pulses and the test current to calculate the ESR figure and displays it on the LCD screen. Circuit details Fig.2 shows the circuit diagram of the original LC meter (on the left) with the ESR add-on on the right. However, note that some extra components are shown on the left, such as mode switch 56 Silicon Chip S1 and ESR input protection diodes D5 & D6. While only one connection is shown passing between them – the added ESR+ terminal connection – there are 10 further connections between the corresponding pins of CON5 and CON6. GND is shared between both sides via pin 8 of those connectors. There are two versions of the PCB. The smaller version that is an add-on to the existing LC Meter design only has the added circuitry on the right (with a few components mounted offboard, such as D5 & D6). The larger version incorporates everything shown in Fig.2 and simplifies the wiring, especially as CON5 & CON6 are not required. The ESR circuit on the right has Australia's electronics magazine three sections: a set of current sources used to pulse the capacitor being tested (upper left), the pulse amplifier (lower left) and the reference voltage ramp generator (upper right). Pulse current sources Transistors Q1, Q2 and Q3 are driven by Arduino Uno digital outputs D12, D11 and D10 when the respective output is pulled low. The Arduino Uno will switch on one of the transistors depending on the measurement range. The 10kW, 1kW & 100W collector resistors set the current pulse to 0.5mA, 5mA or 50mA. There is no current regulation; we rely on the fact that the 5V supply is regulated, and the DUT is initially discharged when the current is applied. siliconchip.com.au Fig.2: the original LC Meter circuit is on the left (with a few additions), while the added ESR-sensing circuitry is on the right. Headers CON5 and CON6 are not present on the combined PCB we’ve designed; instead, the ten connections are run via PCB tracks. Otherwise, a ribbon cable joins all pins between the two connectors. Therefore, close to 5V appears across the selected resistor and the current is determined by Ohm’s law. The current pulse is applied to the capacitor being tested via the parallel 100nF and 47µF capacitors which block any DC components. The ESR of this combination of capacitors is inconsequential, given the relatively high values of the current source resistors. Critically, the measurement is taken directly from the DUT terminal, so the circuit is not measuring the ESR of those two capacitors as well. The 100nF capacitor keeps the impedance low at high frequencies, as required by the nature of the short current pulses. Whenever Q1, Q2 and Q3 are turned off, the Arduino Uno digital output siliconchip.com.au D13 switches Q4 on by supplying current to its base. This ensures that the two AC-coupling capacitors are maintained in a discharged state, ready for the next current pulse. Inverse parallel diodes D1 & D4 protect Q4 from potentially high currents should a charged capacitor be connected to the test leads. The maximum pulse voltage for an ESR value of 100W is typically under 500mV, so D1 and D4 have minimal effect on the pulse voltage. Pulse amplifier The pulse voltage developed across the capacitor being tested is fed to the pulse amplifier via a 33nF capacitor and a 1kW series capacitor. The pulse is amplified by a two-stage transistor Australia's electronics magazine amplifier formed by Q5 and Q6. The ratio of the 6.8kW feedback capacitor to the 150W fixed resistor and VR1 (adjusted for about 200W) sets the gain to 20 (1 + 6.8kW ÷ [150W + 200W]). Diodes D2 and D3 protect Q5 if a charged capacitor is connected to the test leads. The amplified pulse voltage goes to the non-inverting input of the Arduino Uno’s comparator via a 270nF capacitor, which blocks the DC voltage across the 680W resistor at Q6’s collector. This resistor keeps the 270nF capacitor discharged in the absence of a pulse. Voltage ramp generator PNP transistors Q7 and Q9 operate as a current mirror circuit to charge the 470nF ramp capacitor at a constant August 2023  57 rate. When the Arduino pulls pin 4 of CON6 low, Q9 switches on, causing about 9.4µA to flow through the 470kW resistor. At the same time, Q8 switches off, allowing the ramp capacitor to charge. Q7 mirrors the current through Q9, so the capacitor begins to charge from 0V at 9.4µA. The rising voltage across the 470nF capacitor is connected to the Arduino Uno’s internal comparator (inverting input) via pin 1 of CON6. The Arduino Uno disables the ramp generator by setting pin 4 of CON6 high, turning off the charging via C9 while switching on Q8 to discharge the ramp capacitor. Integration with the LC meter The LC meter used the Arduino’s analog comparator inputs (D6 and D7) as digital outputs to drive the coils of relays RLY1 and RLY2. It was necessary to move those functions to D3 and D4 (by modifying the LC Meter code) to allow the ESR function to use the comparator. The larger, combined PCB design includes this rerouting. At the same time, D3 and D4 are shared with the ESR meter as digital I/Os via the selector switch, S1, that chooses between the LC and ESR modes. This was necessary since there were insufficient spare I/Os available on the Uno. As the original LC Meter shield lacks CON5, the wires from CON6 go to the Arduino/switch pins on my prototype. Additional input protection If the ESR meter were accidentally What is a normal ESR value? Electrolytic capacitors include reactive elements, so the ESR value will change depending on the frequency of the applied voltage (there is also an equivalent series inductance or ESL). Temperature changes also affect the reading, as do different manufacturing processes. Manufacturer data sheets typically give the expected ESR values at 20°C and 100Hz, 120Hz or 100kHz, although many do not include such information (or give it differently, eg as a dissipation factor). Thus, providing definitive expected ESR values for all electrolytic capacitors is impossible. Still, we do not expect to see the values exceeding several ohms, and higher-value capacitors should generally have lower ESR values. Capacitors designed for use in switch-mode supplies (often labelled “Low ESR”) should have values of a fraction of an ohm or less. For example, the data sheet for the Panasonic FM-A series of aluminium capacitors gives values from 0.012W to 0.34W ohms varying with the voltage rating (6.3V to 50V) and capacitance (22μF to 6800μF). The data sheet for the RubyCon YXF series for similar capacitance and voltage ranges lists the maximum expected ESR values to be between 0.025W and 1.3W. Table 1 shows the tabulated typical ESR values from the Mk.2 ESR Meter. These are generalised expected readings, so manufacturer data sheets should be used as a reference. However, it should be apparent that a capacitor is faulty if the measured ESR value exceeds tens or even hundreds of ohms! Table 1: typical ESR readings for good capacitors 10V 16V 1μF 35V 63V 160V 250V 5 4 6 10 20 2.2μF 2.5 3 4 9 14 4.7μF 6 3 2 6 5 1.6 1.5 1.7 2 3 6 10μF 58 25V 22μF 3 0.8 2 1 0.8 1.6 3 47μF 1 2 1 1 0.6 1 2 100μF 0.6 0.9 0.5 0.5 0.3 0.5 1 220μF 0.3 0.4 0.4 0.2 0.15 0.25 0.5 470μF 0.15 0.2 0.25 0.1 0.1 0.2 0.3 0.15 1000μF 0.1 0.1 0.1 0.04 0.04 4700μF 0.06 0.05 0.05 0.05 0.05 10mF 0.04 0.03 0.03 0.03 Silicon Chip A version of Table 1 that can be downloaded as a PDF will be available from: siliconchip. com.au/ Shop/11/238 Australia's electronics magazine connected to a charged capacitor, the energy dumped into this circuit could still damage it despite the protections mentioned above. As with the original project published in 2004, we have included two high-current diodes (1N5404s) connected back-to-back directly across the input sockets: D5 and D6. Despite this, remember to discharge capacitors before testing them! Software The ESR measurement code is based on Bob Parker’s algorithm published in the March 2004 issue, with minor changes to the pulse timings to better suit the Arduino Uno. The original design uses a pulse width of 8µs with an off-time of 492µs. Such settings resulted in a slight fluctuation in the readings. For example, a 0.6W resistance would show a reading fluctuating between 0.59 and 0.61. A pulse width of about 20µs improved the stability with no impact on accuracy, so a 480µs off-time was adopted to maintain the overall 500µs period. The program starts in the high range by setting D12 low and D13 high. This sets the pulse current to 0.5mA. At the same time, the reference voltage generator is initiated by setting D3 low. If the pulse at the Arduino’s non-­ inverting input exceeds the reference voltage, the comparator’s interrupt-onchange feature sets a flag indicating a pulse was detected. Consequently, a counter is incremented, the interrupt flag is reset, and another pulse is applied to the capacitor being tested. This process repeats until the code detects that the flag was not set after applying a current pulse. This signifies that the reference ramp voltage has reached a level greater than the pulse voltage, and counting is complete. After each count cycle, if the total number of pulses is below 10, the next lower range is selected, and the measurement is repeated until the count produced is between 10 and 100. In the low range, a count between 10 and 100 equates to an ESR reading of between 0.1W and 1W; in the medium range, it represents 1W to 10W; or 10W to 100W in the high range. If the count exceeds 100, the program automatically tries the next higher range until the count is between 10 and 100. If the count remains above 100 on the highest range, the display shows “Over range!”. siliconchip.com.au The prototype Meter was made using a specialised case to suit the display module. While you can use multiple PCBs as shown above, a single board design using the PCB shown in the lead photo requires much less wiring. Test lead resistance Since we aim to measure ESR values well below 1W, the resistance of the test leads and banana socket connections can introduce errors. Therefore, if the Zero button (S2) is pressed, the Arduino notices its D4 input pulled low and shows the message “Short test leads and press zero…”. Once the leads are shorted, the Arduino repeatedly measures and displays the lead resistance in ohms on the fourth line of the LCD. The code waits for the zero button to be pressed again and saves the lead resistance in the Arduino’s EEPROM. The result is then subtracted from the subsequent capacitor ESR measurements. In addition to displaying ESR measurements on the LCD, the Arduino also produces a serial stream of the measurement data via its USB port. The incremental count is displayed for each current pulse, followed by the final count, the final range selected and the number of range changes made during a measurement. The accumulated count includes the effects of test lead resistances. Combined LC / ESR Meter When the LC Meter and ESR Meter siliconchip.com.au are combined, a contact on the LC/ ESR selector switch, S1, signals which mode has been selected to the Uno via its digital input D2. With D2 low, it is in ESR mode. Switching from one mode to the other happens after the program completes the current procedure being processed by the Arduino. As previously mentioned, Arduino pins D3 and D4 are shared between the LC and ESR modules. D3 serves as a digital output in both modes; however, D4 is a digital input for the ESR module (for the Zero switch) but an output for the LC meter (driving RLY1). When switching modes, D4 is reconfigured by the code as required. could be removed), the Arduino and control board stack should fit, as should mode switch S1, but it will be a bit of a squeeze. Alternatively, you could use just about any rectangular case. It would need to be at least 175mm tall internally for a 20×4 LCD module to fit at the top with the combined control PCB and Arduino below it. The LCD Case selection The case used for the prototype is available from Mouser Electronics (563-HH-3421) or Digi-Key (HH-3421-ND), although stocks are limited. An optional tilt stand is available separately from Digi-Key (3771171-ND). Because the combined board is considerably narrower than the ESR-only board, it should fit in that case. With an internal depth of 37mm (excluding things like mounting bushes, which Australia's electronics magazine If you decide to build the ESR meter as separate PCBs, you might also need a mounting arrangement for the banana sockets as shown here and in Fig.8. In this case diodes D5 & D6 are located inside the white heatshrink. August 2023  59 will be around 87mm wide, defining the minimum internal width, while a depth of at least 30mm is required to fit the Arduino Uno, the shield on top of it, and the body of switch S1. The Altronics H0401 sloped case specified in the parts list should have plenty of room. Because of the sloping lid, you will need to mount the LCD and other PCBs to the inside of the lid. The screws and spacers in the parts list are intended to allow you to do this; the nut for switch S1 can also be used to hold the board in place. Remember to position the board so that the banana sockets will be accessible (or mount the chassis socket off-board). Construction First, you need to decide if you will build the original LC Meter design and wiring in the add-on ESR module or the combined PCB. We reckon the latter is a lot simpler. Fig.3 shows the wiring required with separate boards, while Fig.4 shows the combined PCB. For the combined version, the only part you need to add externally to Fig.4 is the LCD screen, via CON4. If you want to build the add-on board, it is shown in Fig.5, while the LC Meter board, without the sockets (as we’re using off-board sockets), is shown in Fig.6. We’ll describe the assembly process for the combined board; the two smaller boards are similar, you just need to skip the parts that are not onboard. The combined PCB measures 64.5 × 115.5mm and is coded 04106182. It’s essentially a larger-­ than-normal Arduino shield. Fit the resistors first, checking their values with a multimeter as you install each one. Follow with the smaller diodes (1N4148 & 1N4004), taking care to check their orientations; face the cathode stripes as shown in Fig.4. Next, mount IC1 (which can be soldered to the board or socketed, but watch its orientation), followed by trimpot VR1 (ideally a multi-turn type, although universal pads are provided) and pushbutton switch S2. ► Fig.3: this is the wiring needed to add the ESR feature to the existing LC Meter design by simply adding another small board (at the bottom). We think most constructors will prefer the much easier method of building the single combined PCB! 60 Silicon Chip Australia's electronics magazine siliconchip.com.au Follow with the transistors. There are nine, of four different types, so make sure to get the right types in each position and orientate them as shown. Bend their leads with small pliers if necessary to fit the pads. The next job is to install the capacitors, starting with the non-polarised MKTs/ceramics (the values should be printed on them, possibly as codes like 102 = 1nF, 104 = 100nF etc) and then the electrolytics. The latter are polarised, so insert the longer positive leads into the pads marked + (the striped side is negative). Remember that the 47µF non-polarised type goes at lower left. If you’re unsure about the values, check each component with a multimeter. Now is a good time to fit the bulkier components like the reed relays (watch their orientation), diodes D5 & D6 (ditto), the banana sockets and inductor L1. That just leaves the headers and the 3PDT mode switch. The CON4 header needs to be fitted as we’ll use it to connect to the LCD later, unless you plan to solder the LCD wires directly to its pads. CON1 is only needed if you plan to mount the banana sockets off-board and will not solder the wires directly (although you will need to do so for CON7 regardless). The remaining headers mount on the underside of the board. Use standard pin headers for the four SIL connections to the Arduino Uno (or similar) since we will not stack anything on top of this board. However, they need to be fitted using a particular method due to the height of the USB Fig.4: the combined PCB is basically the LC Meter shield (top section) with the ESR circuitry added below. Toggle switch S1 selects between the two functions. Some extra mounting holes have been added to increase mounting flexibility, although they unfortunately are not in a rectangle. connector on the Arduino Uno board that will fit below. First, apply some insulation to the top of the USB socket on the Uno, such as electrical tape or Kapton tape. Next, insert the Arduino headers into the shield board from the underside. Place a scrap of perfboard, protoboard or similar on top of the header pins that stick out the top of the board, then use a flat object to push the headers down so the tops of the pins are flush with the perfboard. Carefully remove the perfboard without moving the headers, then solder the pins at either end. This Figs.5 & 6: if you want to build the separate ESR board (left), either to use it as a standalone ESR meter or to add to an existing LC Meter (right), here is where all the components go. Besides the 10-way ribbon cable from CON6 (which could be left off & the ribbon cable soldered to the PCB), you also need to wire up the COM− and ESR+ test terminals. siliconchip.com.au Australia's electronics magazine August 2023  61 will mean there is a gap between the underside of the PCB and the plastic spacer on the headers. That’s so the pins project out further to reach the Arduino sockets despite the USB socket not allowing the shield to be pushed fully down. Finally, the 3PDT toggle switch mounts on the top side of the board into slotted holes designed to suit its rectangular solder lugs. This avoids the need to run nine flying leads, although you could do so if you want to mount that switch elsewhere. If doing so, use a short length of ribbon cable. Testing Make a final inspection of the soldering to ensure there are no solder bridges between tracks and that all the components are in their correct position and correctly orientated. If you have built the separate ESR board, you can do some testing before you wire it up. Connect pin 5 of CON6 to a +5V supply with pin 8 at 0V. Measure the current draw, which should be about 1mA. If the current is significantly higher (or zero), disconnect the supply and look for assembly errors. When plugging the shield into the Arduino, we recommend using 12mm tapped spacers and short machine screws to hold the two boards together due to the fact the headers won’t plug fully into the sockets. Attach the four spacers to the mounting holes on the Arduno, but only one needs to be screwed in through the shield to hold it down. The rest just set it at the correct height. If there is a solder joint touching the top of the USB socket that prevents you from tightening the screws, trim it flush to the extent possible. Wiring When the Meter is switched to ESR mode, a splash screen is briefly displayed showing the ‘Zero value’, which is effectively the offset due to the resistance of the leads and anything else that might be in the measuring circuit. 62 Silicon Chip Australia's electronics magazine If you are building the combined PCB, there isn’t much to the wiring. You just need to make up a 4-way cable to go from CON4 to the I2C LCD header. Make sure the connections are made per the labelling on the two PCBs, ie, GND to GND, SDA to SDA etc. If in doubt, refer to Fig.3; using a 4-way ribbon cable will keep it tidy. If you haven’t already soldered the I2C adaptor to the LCD screen, do that now, as the 4-way cable from the main board connects to that. If you’re adding the ESR board to an existing LC Meter, or building the boards separately for some other reason, wire them up as per Fig.3. The ten wires from CON6 are shown separately for clarity but again, it’s best to use a 10-way ribbon cable and only split out the individual wires as much as necessary to reach the appropriate pads. Note how, in Fig.3, the LC Meter shield no longer plugs directly into the Arduino as many pins are rerouted. Also note that diodes D5 & D6 are mounted off-board in this case. Loading the software To upload the firmware for the Uno board, you need to have the Arduino IDE (Integrated Development Environment) software installed on your computer. If you don’t have it, get it from www.arduino.cc/en/main/software The program that runs on the Uno requires an external library to interface with the I2C LCD. Open the IDE and select Sketch → Include Library → Manage Libraries... , then search for “liquidcrystal_pcf8574” and install the version by Matthias Hertel. siliconchip.com.au Now open the sketch file: “ESR. ino” for the standalone version or “LC_ESR_Meter.ino” for the combined version. Select the board type as Arduino Uno (Tools → Board Type → Arduino AVR Boards), then use the Tools → Port menu to select the serial port that the Arduino is plugged into. Most versions of the Uno will display as COMx: (Arduino Uno or similar) in the dropdown menu. If you’re using a 16×4 LCD rather than the 20×4 LCD recommended, change the line “lcd.begin(20, 4)” to “lcd.begin(16, 4)”. Compile and upload the sketch by pressing Ctrl-U. If you see the message “Done Uploading” at the bottom of the window, then all is well. If you get an error message, check that the LCD I2C library is installed correctly and that the correct serial port is selected. LCD adjustment If the LCD backlight is not lit, check that the backlight jumper is fitted on the I2C adapter board. If the backlight is working, but there is no text, adjust the contrast pot on the back of the I2C adapter board. Zeroing the test leads The program first checks to see if the resistance of the test leads has been saved in the EEPROM; if not, you will be prompted to perform the Zero process. Follow the instructions requesting the test leads to be shorted, and once the displayed resistance is stable, press the zero switch (S2). The display should briefly indicate that the zeroing process is complete before changing to the regular measurement display. The code expects the total resistance of the leads to be less than 1W or it won’t accept the result and briefly display the message “Invalid reading or bad leads” before aborting the zeroing process. In normal measurement mode and with the test leads separated, the display should indicate “Over range”. Calibration Calibration is straightforward, using a known resistance of about 68W or 82W. Verify the resistor’s actual value beforehand with a multimeter (deducting the multimeter lead resistances measured when shorting the leads together). Switch S1 (if present) to ESR mode. With this resistor connected via the probes, the screen should display a siliconchip.com.au Parts List – Arduino ESR Meter 1 suitable case [Altronics H0401] 1 Arduino Uno or equivalent microcontroller module 1 20×4 blue backlit alphanumeric LCD with I2C interface [SC4203] 1 double-sided PCB coded 04106182, 68.5 × 115.5mm 1 100μH bobbin-style or high-current axial RF inductor (L1) 4 5V DC coil DIL reed relays (RLY1-RLY4) [Altronics S4100, Jaycar SY4030] 1 200W top-adjust multi-turn trimpot (VR1) 1 3PDT solder tag toggle switch (S1) [Jaycar ST0505] 1 vertical tactile pushbutton switch (S2) 3 PCB-mount right-angle banana sockets; one black, two red (CON2, CON3, CON7) [Silicon Chip SC4983] OR 3 panel-mount banana sockets; two black, one red (CON2, CON3, CON7) 1 4-pin right-angle polarised header with matching plug and pins (CON4) 1 set of Arduino-style regular headers (1×10-pin, 2×8-pin, 1×6-pin) 1 100mm length of 4-way ribbon cable terminated with DuPont sockets at one end 8 M3-tapped 12mm spacers 9 M3 × 6mm panhead machine screws 4 M3 × 6mm countersunk head blackened machine screws Semiconductors 1 LM311 high-speed comparator, DIP-8 (IC1) [Altronics Z2516, Jaycar ZL3311] 3 BC327 or BC328 500mA PNP transistors (Q1-Q3) 2 BC337 or BC338 500mA NPN transistors (Q4, Q8) 1 BC548 or BC547 100mA NPN transistor (Q5) 3 BC558 or BC557 100mA PNP transistors (Q6, Q7, Q9) 2 1N4004 400V 1A diodes (D1, D4) 2 1N4148 75V 200mA diodes (D2, D3) 2 1N5404 400V 3A diodes (D5, D6) Capacitors 1 220μF 16V electrolytic 1 100μF 16V electrolytic 1 47μF 16V non-polarised electrolytic 1 22μF 16V electrolytic 2 10μF 6.3V tantalum or ceramic 1 470nF 63V MKT 1 270nF 63V MKT 3 100nF 50V multi-layer ceramic or MKT 1 33nF 63V MKT 2 1nF 1% NP0/C0G ceramic, MKP or polystyrene [Silicon Chip SC4273] Resistors (all 1/4W 1% axial) 1 470kW 1 220kW 5 100kW 2 47kW 7 10kW 2 6.8kW 1 4.7kW 4 2.2kW 1 1.3kW 3 1kW 1 680W 1 220W 1 150W 1 130W 1 100W Extra parts if building the ESR Meter with separate PCBs 1 double-sided PCB coded 04106181, 68.5 × 53mm 1 3PDT solder tag slide switch (S1) [Mouser 502-50209LX] 1 2x5 IDC header with matching socket (CON6) Ribbon cable and heatshrink tubing value close to the resistor value. Adjust VR1 until the reading matches the resistor value. Now try a resistor in the medium range (1-9.9W) across the leads and verify that the reading is close to expected. Similarly, a 0.1-0.9W resistor should give a very close measured result. With calibration complete, you can Australia's electronics magazine test a selection of electrolytic capacitors to get a feel for the meter’s operation. The screen shows the measured ESR on the first line, the range (High, Medium or Low) on the third line, and the saved lead resistance on the fourth line. There is no need to subtract the lead resistance from the displayed ESR August 2023  63 value, as that has already been done. If you’ve built the combined LC/ ESR Meter (as we think most people will), now would also be a good time to switch over to LC mode and verify that the unit changes modes when you flick the switch and that inductor and capacitor measurements are correct. Final assembly If you are building the unit as a standalone ESR meter, all that remains is to place the Arduino and ESR shield into an appropriate enclosure, with the LCD visible and the test lead terminals (and possibly S2) accessible. We have not shown the wiring to achieve this but it is similar to what is shown in Fig.3 without the LC Meter shield. The main differences are that the two connections from pins D3 & D4 on the Arduino to the ESR PCB via S1 should be run directly, while pin D2 should be tied to GND. The 5V and GND supply connections also connect from the Arduino to the ESR board rather than via the LC Meter Shield. If you have built the combined PCB, fitting it into an enclosure is a bit more straightforward. Again you will need a cut-out to view the LCD screen (unless your case has a clear lid) and possibly a way to access S2 (eg, a small hole in the case). The toggle switch will fit through a hole in the lid of your enclosure, but the board should be mounted against the left edge so that the banana sockets will fit through holes in the side (unless you’ve decided to mount them elsewhere and connect them to the socket pads via flying leads). You could use panel-mount banana sockets mounted just off the left edge of the board and attached via short wires. As in the prototype, you would typically mount the LCD screen near the top of the case with the main PCB below. Power for the prototype was fed in via the Uno’s power connector, with the plug going through a cut-out in the left-hand side of the case. You could use a similar arrangement, or use a chassis-mounting DC barrel socket mounted elsewhere and wired to the VIN and GND pins of the Uno. If your enclosure doesn’t have a ► Fig.7: while not recommended for the combined PCB, here is how the separate PCBs were mounted on an acrylic baseplate for the prototype. 64 Silicon Chip Australia's electronics magazine siliconchip.com.au clear lid, cut a piece of clear acrylic or other plastic for the display window. You can either glue this onto the underside of the enclosure cover or mount it on top of the LCD. Prototype mounting details Some constructors may wish to use a similar mounting arrangement to the prototype. However, this is not suitable if you are using the combined PCB; it’s only relevant if you have separate PCBs. The boards, mounting brackets and display were mounted on a 4mm-thick acrylic base plate, as shown in Fig.7. Fig.8 shows the reinforcement bracket used for mounting the banana sockets to the case. Depending on your case, you may not need this; you can mount the sockets directly to it, or use the onboard ones. If you are chassis-mounting mode switch S1, you might want to make a similar bracket for it if mounting it directly to the case isn’t suitable. Consider that you should drill a hole about 3mm in diameter in the case for accessing Zero switch S2 later should you need to recalibrate the lead resistance. Having to open up the case to do that could be a nuisance. Table 1 can be printed onto adhesive paper or printed, laminated and glued onto the case as a guide. That is what I did for the prototype. Keep in mind that if you’re using the Combined PCB, the mode switch toggle will be in the middle of where I attached it on my prototype. Depending on where you’ve put the banana sockets, you may be able to attach it higher up to clear that switch. Here is another view of the combined PCB we designed, plugged into an Arduino Uno, at actual size. Note how as well as the banana sockets projecting off the left-hand side, the USB and DC power inputs of the Uno do too. This allows you to make holes in the side of the case for all of those connectors. Conclusion Don’t forget to discharge the capacSC itors before testing them! Fig.8: while also not necessary for the version built with the combined PCB as described, this shows the mounting bracket used to hold the banana sockets in the prototype. siliconchip.com.au Screen 1: This screen is seen when no component is connected, or when a resistance over 100W is detected. The bottom line continues to display the lead resistance. If you see this when a capacitor is connected, it's probably not good anymore! Screen 2: Pressing and holding the ZERO button brings up this screen. You should short the ESR measurement terminals using the leads you would use for measurement and confirm that a low value as seen is displayed before pressing the ZERO button again. Australia's electronics magazine August 2023  65 RadioFest 2023 MELBOURNE, SEPTEMBER 16-17 – CELEBRATING 100 YEARS OF BROADCAST RADIO The Historical Radio Society of Australia (HRSA) is staging Australia’s largest vintage radio exhibition in Melbourne on September 16th & 17th this year. By Kevin Poulter T he exhibition includes displays of rare radios and accessories, plus the sale and auction of highly collectable vintage radios. RadioFest is held every two to three years, rotating between Canberra and Melbourne. Members travel from all over Australia for the best historical radio event in years. This year, it’s being held in Melbourne. It is a fantastic opportunity to see over one thousand restored or restorable radios from all eras, including early last-century crystal sets, to radios and televisions made up until the 1980s. Some of the radios at the show are rarely seen in public, with stunning designs and technology, or are believed to be so rare that they may be the only ones in existence. For example, we have seen a sealed set from 1923. Then there’s the universally admired green AWA Bakelite radio, 66 Silicon Chip nicknamed the “Empire State”. Where and when RadioFest will be held in the Southern Community Centre at 27 Rupert Drive, Mulgrave Victoria, on Friday September 15th (setting up), Saturday 16th and Sunday 17th. Members can access all days, sales, auctions and the dinner. The general public is invited to the exhibition between 10am and 3pm on Sunday September 17th. Taking part in all activities If you would like an ‘access all areas’ membership, including the ability to purchase at sales or the auction, the annual fee is just $50. That price includes a subscription to the quarterly Radio Waves magazine. See the www.hrsa.org.au website for more details on HRSA membership, RadioFest and the Radio Waves magazine. 100 years of radio This QR code will lead your mobile phone to the RadioFest Web pages, or visit www.hrsa.org.au Australia's electronics magazine RadioFest 2023 coincides with the Australian centenary of broadcast radio (100 years since the first radio broadcast in the country). siliconchip.com.au Radio Waves magazine includes “how-to” features on restoring radios to top working condition and near-new appearance. There are also many pages with parts for sale and advertising restoration services. It’s interesting to note that the date of the first licensed public broadcast was misreported many times. So radio historians, including this author, had to research original newspaper stories and advertising before, during and after 1923 to determine the actual date. It was confirmed as November 23rd 1923, followed by commercial broadcasting (with advertising) the following year. About the HRSA The Historical Radio Society of Australia (HRSA) is one of the largest vintage radio organisations in the world, with nearly 1200 members in various states and regions, including ex-pats overseas. Members share a passion for collecting and restoring radios, mainly Australian. However, many early radios sold here in the 1920s were from overseas, like Atwater Kent radios, imported from the USA but built for Australian mains power and reception specifications. HRSA groups have monthly meetings in major areas like Sydney, Melbourne and Canberra. The non-profit group has been dedicated to Australia’s radio heritage since the HRSA’s founding in 1982. The aim is to bring together individuals who share an interest in preserving and collecting vintage radios, broadcasting equipment, military radios, TVs, radiograms and related items. The society’s members include radio enthusiasts, historians, collectors and individuals with a great interest in early radio. There are over 30,000 AM radios in HRSA members’ collections. wiring looms, transistors, circuit manuals and much more. A circuit service assists members in finding the circuit they want, from thousands of circuits, within the HRSA and other sources like online. Member-to-member trading is encouraged in the magazine’s “yellow pages” classifieds, auctions and at monthly meetings. The radios offered by members for sale range from those which have been restored to others awaiting your expertise to bring an old original radio up to display standard, even fully operational. You don’t need to be a technician – members can learn many techniques along the way. Radio Waves magazine The HRSA publishes a regular magazine called “Radio Waves” that features articles, stories, and news related to radio history and preservation. The magazine provides a platform for members to contribute their research, experiences, and discoveries. Learn vintage restoration techniques and fascinating radio history in the quarterly colour magazine. See you at RadioFest 2023 Come and join us to see more than 60 tables of radios and meet members who will share their knowledge, display their collections, and engage in discussions about radio history. This event provides opportunities for networking, learning, acquiring radios and exchanging information among SC members. Two radios of the hundreds to be seen at RadioFest 2023. The green AWA “Empire State” (left) is highly collectable and most collectors want to have at least one Astor “Mickey Mouse” (above). Resources Members have access to 50,000 valves, plus other parts like 1920s siliconchip.com.au This world-class magazine is typically 68 pages and includes 20 “yellow pages” of member advertisements and announcements. Silicon Chip also publishes restoration stories from HRSA members in most issues, again to impart knowledge and encourage restorations. Overall, the HRSA plays a crucial role in preserving Australia’s radio heritage, fostering a sense of community among radio enthusiasts, and promoting the understanding and appreciation of radio history in Australia and overseas. Australia's electronics magazine August 2023  67 Build a low-cost, calibrated Measurement Microphone If you have ever wanted to characterise or build loudspeakers but couldn’t justify the cost of a fancy microphone, or you want several microphones you can tailor for performance or recording, this project is for you. It’s a phantom-powered, balanced, calibrated microphone you can build for much less money than a commercial equivalent. Project by Phil Prosser T his project aims to build a lowcost measurement microphone using an inexpensive electret condenser microphone (ECM) and a few other bits and pieces. The WM61A and alternative ECM capsules listed below are only a few dollars each. If you recycle parts for the housing, you can make a good microphone for under $40, which is ideal for getting started. With the calibration files we provide, it will let you measure frequency response to within about ±2dB from 20Hz to 20kHz. This Microphone uses phantom power, where the power for the microphone is provided over the signal lines from your microphone preamplifier or mixer. Our Speaker Test Jig (published in the June 2023 issue; see siliconchip. au/Article/15821) can provide this, as can several other Silicon Chip projects and most commercial microphone preamps. This avoids the need for batteries and is widely supported. If you want to build this as a measurement microphone, plenty of ECM capsules with calibration files are available from the Silicon Chip Online Shop at a modest cost. The capsules are numbered and you just need to match up your number with the downloaded file to get accurate calibration data for that capsule. We also have instructions to tailor the frequency response of a microphone for vocal or instrumental use. Aiming for a flat response How well does it work? Fig.1 compares the raw performance of two $2 WM61A capsules to our reference Dayton EMM-6 microphone. This is before the application of the calibration file. The curves’ 10-12dB offset is simply due to these capsules being more efficient than the EMM-6; note how the responses barely go outside the 9-11dB/11-13dB ranges that represent ±1dB from the average. To achieve this comparison, we placed the microphones within a couple of millimetres of the same point as the reference microphone. We feel the performance shown is pretty good for such a simple and low-cost design. Here’s a collection of the types of Measurement Microphones you can build. 68 Silicon Chip Australia's electronics magazine As mentioned earlier, the capsules we’re offering come with calibration data that allows the 1-2dB error to be corrected. The calibration accuracy is limited by our Dayton reference microphone, although we are confident that above 50Hz, it is flat within a couple of decibels. A Behringer ECM8000 runs about $80, while the Dayton EMM-6 starts at around $140. As mentioned earlier, you can probably build the Microphone described here for around $40, possibly a bit less. Note that the ECM8000 doesn’t come with a calibration file, while this one does, making it even better value. So you can achieve pretty good performance at a very competitive cost with this project. To get the best from your Microphone, the design incorporates a phantom-powered preamp and a balanced output buffer based on an industry-standard design, the ‘Schoeps transformerless design’. This harks back to the 1960s and is used in a vast range of professional and The Panasonic WM-61A microphone. siliconchip.com.au Fig.1: a comparison of the performance of two of the $2 WM61A microphones capsules to our reference Dayton EMM-6. This is uncalibrated performance; we can supply ECM capsules with calibration files that will reduce these errors. The offset of about 10dB/12dB for the two samples means those capsules are significantly more sensitive than the Dayton EMM6, which is rated at -40.3dBV/Pa. measurement microphones. We have added an input and filtering section to suit the ECM capsules we present here. The design is quite conventional, so you can make a general purpose phantom powered electret condenser microphone using this project. As you will see later, we have included the ability to tune the Microphone’s response. In our application, this is to get a flat response, but nothing is stopping you from using that capability to adjust the microphone response to suit vocals or instruments. So, how can you really get a good electret microphone for two bucks? ECMs are very simple devices and are made in huge volumes. As shown in Fig.2, they work by sound moving a very thin diaphragm relative to a backplate that is connected (typically) to the gate of a FET. A charge is created between these, and the capacitance between the diaphragm and backplate changes as the sound moves the diaphragm. The formula is C = ε0 × A ÷ d, where d is the separation between the diaphragm and the backplate, A is the area of the plate and ε0 is a mathematical constant. The charge between the plates Q is constant, and since C = Q ÷ V, as the capacitance changes due to the sound, so does the voltage between them (V). This drives the FET. As the capsules are tiny, and the siliconchip.com.au diaphragm extremely light, these devices can have excellent frequency response to very high frequencies with little resonance. The Panasonic WM-60A and WM-61A microphones are legendary examples and have an exceptionally usable frequency response from 20Hz to 20kHz. In the past, they were the mainstay of DIY measurement microphones. They were a workhorse component used in a wide range of devices, including telephones, which meant they were made by the million and thus cheap. Panasonic stopped making these in the early 2000s, which some ascribe to the demise of the old-fashioned ‘phone. Panasonic capsules can still be found, but many sellers list generic 6mm capsules as WM-61As. We bought a large quantity of real ‘new old stock’ (NOS) parts, all from a single batch, measured their response, and are offering them for sale – see Table 1. Before we found a batch of old stick WM61As, we bought and tested a huge number of microphone capsules. Our experience has been that ECM capsules that are ‘flat’ to 20kHz tend to be 6mm diameter units; they are pretty small. The larger 10mm ones generally exhibit a significant peak in the response between 5kHz and 10kHz, making them less than ideal for measurement applications. Therefore, all our recommended Australia's electronics magazine Fig.2: the structure of an electret condenser microphone (ECM). The internal FET amplifies the small AC voltage generated by the diaphragm moving in relation to the charged backplate. ECM capsules are 6mm. We also learned that the majority of capsules available cannot be used in this project as they exhibit peaks or dips, many over 10dB, that we are not comfortable addressing by calibration. Virtually all the satisfactory mics we found will be available from the Silicon Chip Online Shop, including the required SMD calibration components, all for similar prices. Another thing we learned is that there is no ideal ECM capsule that will give acceptable performance without calibration or at least some equalisation of the native response of the capsule. The old Panasonic WM61A capsules tend to be more consistent than most modern alternatives, but there can still be significant differences in frequency response from batch to batch. Manufacturers present typical frequency response plots for their ECMs, but there is significant variability in their response above 10kHz between batches. The Primo EM258 capsules are excellent, but at £6.10 (around $11.25) plus shipping, they are starting to defeat our goal of a low-cost design. We eventually concluded that calibration of each ECM capsule is essential. So we have done a couple of things: ● We designed a circuit that allows you to add a peak or dip and either a ramp up or down to the frequency August 2023  69 response. We have determined the required combination for each type of ECM we tested to get a reasonably flat response. ● Each ECM capsule we supply has a serial number matching a set of calibration corrections to make it perform even better than just with the frequency response adjustment. The calibration file can be loaded into the Room Equalisation Wizard (REW) or Speaker Workshop software to get your measurements as close as possible to ideal. For those who want to build a vocal or instrument microphone, we will show you how to tune the circuit’s response to get the ‘colour’ you want in the microphone you build. If you are making a vocal microphone, you don’t need one of the calibrated ECM capsules from our store; you can save money by buying a similar one from an internet vendor. Which capsule do we prefer? The NOS Panasonic devices still stand out. The best still-officially-available type is the Primo device. The CMC2742PBJ-A is pretty good with compensation (and still available). With compensation, all the types we’re selling are within a decibel or so of our reference mic to at least 10kHz, and with calibration, will be within ±2dB (or better) of our reference mic. Performance We are proud of the performance achieved, especially in a low-cost project. Fig.3 shows the compensated (but not calibrated) frequency response of 10 of the ECM capsules we tested. Some things we noticed are: ● The CMC6027-24T family of devices are very sensitive. That could be beneficial under certain circumstances, but using these for very close measurements or in very loud settings will result in potential compression and distortion. ● All microphones are within ±3dB of their average before the application of calibration over the range of 50Hz-20kHz ● All are pretty flat through the region where you would put a bassmid and midrange-tweeter crossover (although the JLI61A has a bit of a bump). So you could use these mics for such purposes even without calibration. ● The WM61A lot 4A14 microphones are brilliant. The great news 70 Silicon Chip is that we have lots of these available for constructors! Circuit description The electronics to drive the microphone capsule is not complex, as shown in Fig.4. The circuit has three main parts: buffers for driving the balanced output lines, a gain stage which includes some cunning frequency compensation and a power supply for the gain stage. The first thing to keep in mind when looking at this circuit is that pins 2 & 3 of CON1, the XLR socket, act as both 48V DC power inputs and AC signal outputs. The 48V DC is ‘phantom power’ from the upstream equipment like a mixer or microphone preamplifier. It is dropped across the 6.8kW resistors in the phantom power source, allowing the Microphone to vary the voltages on these pins to feed the signals back. PNP transistors Q1 and Q2 are emitter-­ follower buffers with 6.8V zener diode clamps between their collectors and emitters. The DC bias point for Q1 and Q2 is established by the 150kW resistors between their bases and collectors. The current flowing from their emitters to their collectors provide the supply current to the rest of the circuit via R12. Once power is applied, as the collector voltages of Q1 and Q2 increase, the base current through the 150kW resistors falls until DC equilibrium is established. For AC signals, Q1 and Q2 act as emitter-followers with the AC signals being coupled to their bases through 1μF electrolytic capacitors. Is this really balanced audio? By driving the hot pin with the microphone output and the cold pin from ground, we provide a differential output from the Microphone. The balanced line receiver for the Microphone will subtract any signal on the cold line from the hot, providing the immunity from noise pickup in the cable we seek. The 48V DC phantom supply is dropped across the 6.8kW series resistors in the microphone preamplifier and 5.6kW resistor R12 to the 6.8V limit set by zener diode ZD2. The collectors of Q1 & Q2 will sit at around 32V, as exlained below. This voltage (and the current that establishes it) supplies power to the amplifying NPN transistor, Q3, and the ECM itself, in both cases via 5.6kW resistor R12. The circuit includes 1nF and 2.2nF capacitors from pins 2 & 3 of CON1 to ground, with 47W resistors between them, to increase the immunity of the circuit to radio-frequency interference (RFI). These parts do little to affect the low-frequency audio signals or phantom power but will heavily attenuate ultrasonic signals. Additionally, 470pF ‘Miller’ capacitors across the base resistors of Q1 & Q2 roll off the frequency response of these buffer transistors above audible frequencies. Fig.3: the frequency responses of a selection of ECM capsules, including their recommended frequency correction parts, but without calibration corrections. These curves themselves form the calibration correction files. The vertical offsets represent differences in sensitivity, but we are mainly interested in the flatness of each curve (flatter is better from a measurement perspective). Australia's electronics magazine siliconchip.com.au Power supply The power supply for the ECM is very simple but includes plenty of filtering to get a stable DC supply from the hot and cold lines carrying our audio signal. We mentioned the 6.8V derived from the phantom power across ZD2. This is low-pass filtered to remove noise by the 100µF capacitor across ZD2, in combination with the source resistances (6.8kW & 5.6kW). It is further filtered by another lowpass filter (330W/10µF) before being applied to Q3 and the ECM. This is because the signal from the ECM is so low in amplitude that any noise getting through could seriously degrade our signal-to-noise ratio (SNR). Table 1 – Tested Microphone Capsules Model Source Notes Panasonic WM-61A – AliExpress 1005004118951415 – Silicon Chip SC6760 Gives the flattest response overall. Panasonic WM-61A – eBay 164187904055 – Silicon Chip SC6761 “Lot 4A14” – large quantity available; also gives a very flat response. JLI-61A – www.micbooster.com – www.jlielectronics.com – Silicon Chip SC6762 “Lot 3” – needs compensation for good performance. JLI-61AY-102 – www.micbooster.com – www.jlielectronics.com – Silicon Chip SC6763 Better than the JLI-61A but still needs compensation. CUI CMC-6027-24 – Mouser – Silicon Chip SC6764 Can have suffixes “T” or “L100” (same performance). They are the most sensitive of the tested types and among the flattest response with compensation applied. Frequency compensation Finally, we have the ECM interface and frequency compensation. This part of the circuit can be as simple as a bias resistor (R8 or R14) and an amplifying transistor (Q3). During our tests, we found several microphones that required either boosting their output at high frequencies, attenuating at high frequencies, or a little of both to give a flat response. Therefore, all our compensation is targeted at higher frequencies. Boost is achieved by R10/C12. These parts are in parallel with the emitter resistor of Q3 and thus increase the gain of Q3 at higher frequencies. We can set the corner frequency and the ultimate boost level by choosing the values of these parts. CUI – Mouser CMC-2742PBJ-A – Silicon Chip SC6765 Requires compensation and calibration, giving a reasonably flat response but with roll-off below 50Hz & above 15kHz. Kingstate KECG2740PBJ – element14 Requires compensation for good performance. Kingstate – element14 KECG2742TBL-A Requires compensation for good performance. Primo EM258 Excellent performer; expensive, no compensation required. – www.micbooster.com High-frequency attenuation is achieved by R13/C14, which are effectively in parallel with Q3’s 2.2kW collector resistor. Again, these parts can set the corner frequency and ultimate attenuation. This modification of the simple transistor amplifier (Q3) provides a powerful tool to tailor the response of a capsule. By implementing these corrections inside the Microphone, we achieve a respectably flat frequency response and leave only ‘fine-tuning’ to a calibration file. Fig.4: pins 2 & 3 of CON1 supply DC power (nominally 48V with source resistances of ~6.8kW) and are also the balanced audio signal outputs. PNP transistors Q1 & Q2 drive the audio signals onto those pins; their collector-emitter currents (and any current shunted by parallel zener diodes ZD1 & ZD3) also provide a power supply for amplifier transistor Q3 and the electric mic. The transistors shown are for the SMD version. Note that R8 is only fitted with 3-wire ECMs. siliconchip.com.au Australia's electronics magazine August 2023  71 Fig.5 shows how the compensation works. The green trace is the frequency response of the circuit using a JLI61A ECM with no compensation; note the ~7dB peak at about 7.5kHz. The red curve shows the compensation achieved with R10 = 220W, C12 = 12nF, R13 = 2.2kW & C14 = 15nF, and the blue curve is the much-flatter ultimate frequency response achieved. There is still a small peak of about +3dB, but we can’t knock it down further without overly attenuating signals at about 2-6kHz and 10-20kHz. It isn’t much bigger than some other peaks after compensation, anyway. Most ECM capsules within a batch behave similarly. During our calibration process, we set aside any parts that were outliers. Thus, you are guaranteed to get a pretty good response without the compensation file, and a very flat response with it. If you source your own ECM capsules, you will need to optimise the response and generate a calibration file. This project provides everything you need to do that, except a calibrated microphone against which to make the required measurements. Two PCB options If possible, we recommend you build the SMD version where all parts are on the top side. However, we have also laid out a through-hole version and managed to squeeze it into a Why bother with analog frequency compensation? If we are supplying a calibration file, why not just leave all the corrections to that file, and omit R10/C12 and R13/C14 from the circuit? If the microphone would only be used in a measurement system with a calibration file installed, there would be no reason to care that the Microphone itself had significant errors in its inherent frequency response. However, we wanted to make a microphone that, in itself, was quite respectable, leaving calibration via the associated file for fine-tuning. That means you could use it with other software without calibration support and still get reasonable performance. We also wanted to make a microphone that could be used for recording, with the possibility of tailoring it for vocal and instrumental use. By including these parts, we can do both. Because our calibration files are generated with the specified frequency compensation parts installed, if you use one of our ECM capsules and calibration file, you must load the recommended parts to get optimal performance. 13mm wide PCB, but it is 99mm long rather than the 64mm of the SMD version. The two versions are shown in Figs.6 & 7. Both these boards have been made thin enough to fit in a ‘skinny’ microphone case. Neither is hard to assemble, but we reckon the SMD one is less fiddly than the through-hole version due to all the parts mounting on one side. The smallest parts on the SMD board are the SOT-23 transistors and zener diodes, which are not that hard to solder. We hand-built about 20 prototypes and, without a doubt, soldering the ECM capsule pins is fiddlier than anything on the SMD PCB. So, unless you have plenty of room to house the Fig.5: the frequency compensation for a JLI61A microphone. Here we have set the compensation (red curve) to push down the peak in its response (green curve) while limiting attenuation at high frequencies. This is not perfect, as we need to match a batch of microphone elements with these parts, but we reckon ±2dB across most of the band is a good result for a microphone. 72 Silicon Chip Australia's electronics magazine through-hole PCB, we recommend you make the effort to build the surface mount version. SMD board assembly The SMD version of the board is coded 01108231 and measures 64 × 13mm. Start by fitting the resistors and ceramic ‘chip’ capacitors. There are variations depending on whether you have a 2-pin or 3-pin ECM and what compensation components are required. If you have a 2-pin ECM, fit R14 (2.2kW, near CON2) and leave off R8 (10kW). If you have a 3-pin ECM, fit R8 (10kW) and leave off R14 (2.2kW, near CON2). The compensation components are R10, R13, C12 and C14; they are all between Q3 and ZD2. Refer to Table 2 to determine which of these you need to fit for your ECM (if you purchased it from our shop, it will come with these components). Next, mount the three transistors (one NPN, two PNP) and three zener diodes. Watch out as these are all in SOT-23 cases. If you get them mixed up, you will find a code engraved on the top of the devices that identifies each. Unfortunately, this can vary depending on the manufacturer, so you might need to check the data sheet. Still, they will probably be one of these (a question mark ‘?’ represents any letter or number): BC849C: 2C?, 49C or 8DC BC860: 9EA/B/C, 4F? or 4G? BZX84C6V8: Z5, ?61, D4P, WC or KB Failing this, you can use a DMM on diode test mode or our SMD Test Tweezers (siliconchip.au/Series/396) to find siliconchip.com.au Fig.6 (left): this is the SMD version of the PCB. Note that the values (and presence) of R10, R13, C12 and C14 are varied to match your ECM capsule. Either R8 (10kW) or R14 (2.2kW) is fitted depending on whether you have modified your capsule; for an unmodified (2-pin) capsule, leave off R8 but fit R14. Fig.7 (right): to avoid making it too much bigger than the SMD version, the through-hole (TH) PCB has parts mounted on both sides. In most cases, the solder joints are still accessible should you need to make changes or repairs. It is the same width as the SMD version but about 50% longer, meaning it won’t fit in the inexpensive plastic case described in the article. the base/emitter pins of the devices. With the single pin at the top, the base will be at lower left and the emitter at lower right. If you get a ~0.65V reading with the red probe on the left, it’s an NPN transistor (BC849), or on the right, it’s a PNP transistor (BC860). If you get neither, it’s likely a zener diode. They will give a similar reading with the red probe on the lower left pin and the black probe on the top pin (that forward-­biases the zener diode). The three remaining SMDs are the three non-polarised 1µF electrolytic capacitors. These come in metal cans mounted on plastic bases. Like polarised electros, the bases have chamfered edges on two corners that normally indicate the positive end. Because they are not polarised here, it doesn’t matter which way around you mount them. Since two of these capacitors could be polarised types, we’ve left polarity markings on the PCB, but we’ve specified all three as NP caps to make things a bit easier. In terms of components on the board, that just leaves the two throughhole capacitors, which are both 100μF parts but with different voltage ratings. Solder them laid over on their sides, as shown in our photos, so that the assembly will fit in a small-diameter tube. The striped negative end must go towards the bottom of the PCB, with the longer positive leads to the pads marked with + symbols. Through-hole assembly The through-hole version of the board is coded 01108232 and measures 99 × 13mm. This can be assembled as usual, but it’s easier to fit all the components on one side (ideally the top side) before starting on the other. Fit the axial parts first (resistors and zener diodes, watching the zener diode’s cathode stripe orientation), then the MKT and ceramic capacitors with some laid over, as shown in Fig.7. Leave the electrolytic capacitor off initially to provide better access to the remaining solder joints. Table 2 – microphone capsule calibration component values Manufacturer Part R10 C12 R13 C14 Panasonic WM61A (AE) N/A N/A 100W 5.6nF Panasonic WM61A lot 4A14 N/A N/A 100W 6.8nF JLI JL61A 220W 12nF 2.2kW 15nF JLI JL60A-V02 220W 12nF 10kW 6.8nF CUI Devices CMC-6027-24T 220W 18nF 3.9kW 18nF CUI Devices CMC-6027-24L100 220W 18nF 3.9kW 18nF CUI Devices CMC2742PBJ 820W 4.7nF 2.2kW 8.2nF Kingstate KECG2740PBJ 10W 12nF 3.9kW 6.8nF Kingstate KECG2742TBL-A 100W 8.2nF 3.9kW 6.8nF Primo EM258 N/A N/A N/A N/A siliconchip.com.au Australia's electronics magazine Refer to the section above regarding which of the optional resistors and capacitors to install (R10, R14, C12 & C14). Next, fit the transistors as shown, pushing them fully down before soldering and trimming their leads, then flip the board over and solder the axial components (resistors & zener diode) on that side. Again, see the section above for what to do about R8 and R13. Follow with the single 1µF MKT on this side of the board, laid over, then the two electros, laid over and orientated as shown. Note that the 100µF 50V electrolytic capacitor is specified in the parts list as having a maximum diameter of 8mm. A 47µF 50V electrolytic capacitor is also fine to use, as long as its 8mm in diameter. Finally, flip the board back over and fit the last electrolytic capacitor (100µF) on that side. Capacitor selection Like the other low-value capacitors What if your phantom power is <48V? Phantom power for microphones is an old standard. Like many standards, it is not particularly well followed. Most phantom power systems operate at 48V. For 48V, your preamplifier/mixer will have 6.8kW series resistors from the 48V supply. However, if it has a 24V supply instead, they will be 1.2kW, or 680W for a 12V supply. R12 should be 5.6kW to suit 48V systems or 1.5kW for systems delivering 24V DC bias or less. Our calculations show that the Mic will work with 12V & 24V DC supply systems with R12 set to 1.5kW. August 2023  73 The SMD (left) and through-hole (below) versions of the Calibrated Measurement Microphone shown enlarged. Both have their XLR sockets fitted. (<1μF), the compensation capacitors, which range from 4.7nF to 18nF (if present) must be plastic film (eg, MKT) types for the through-hole board or NP0/C0G ceramics for the SMD board. Don’t be tempted to use cheaper X5R, X7R or Y5V ceramic capacitors. They have a high voltage coefficient and thus are highly non-linear; definitely not what we want as part of a filter network! The microphone housing Regardless of which PCB you’ve assembled, the remainder of construction proceeds in much the same manner. The connection to the XLR socket will depend a lot on the approach you have to construction. In many cases, you can push the PCB between the XLR pins and simply solder the PCB to the pins directly. How this fits depends on your chosen connector and how you house the PCB. If you are using a metal housing, add a wire link from the PCB ground pin on the XLR to the housing. We want the ECM insert in ‘free space’ and with minimal reflections to get flat performance. All the ECM inserts we recommend are 6mm in diameter. We will present two ways to achieve the required mounting, one based on metal pipe hardware and the other using plastic pen cases. Photo 1 (below) shows the collection of metal parts we used to build our Microphone, while Photo 3 (overleaf) shows the parts to make the plastic version. How you go about this comes down to what you can find in your shed and parts drawer. The three key goals are: ● We want the ECM insert mounted at the end of a 100-150mm tube that it just fits inside. ● We want a section that can house the PCB. Both PCBs are just under 13mm wide, but the electros are quite thick, so a tube with an inner diameter of 18-20mm is ideal. ● We want an XLR connector at the other end. If you have a vocal or musical instrument application, you might take an alternative approach to the housing. Copper housing We used a K&S #9825 brass tube for the ECM, which is 7mm outer diameter with 0.45mm wall thickness. An alternative is K&S #8132 brass tube, which is 9/32 inches (7.14mm) in diameter with 0.014-inch (0.36mm) wall thickness. These are available from hobby shops in 305mm lengths for about $7, enough to make two or three microphones. The challenge is to expand from the 7mm tube to the 20mm or 3/4-inch (19mm) tube that houses the PCB and XLR connector. You will likely find your own approach by looking through your parts bin. We adapted between the two different diameter pipes by first using the backshell from an Altronics P0192 RCA socket, which the brass tube just squeezes into, then fitting this to the small end of a 15mm to 20mm copper capillary adaptor. This might sound complicated, but it is not hard; Fig.9 and the photos show how it came together. The SMD version of the PCB fits into the 20mm tube easily; the throughhole version is no wider, but it is quite a bit longer. In more detail, the 7mm tube was a tight push-fit into the RCA backshell. We then wrapped the backshell in 1mm bare copper wire, making it a tight fit into the 15mm to 20mm reducer. Because these parts are all copper and brass, we simply soldered them together. There are many ways to do this, but after some thought, we assembled the parts using liberal amounts of solder paste (see Photo 2) and baked it in our reflow oven at 230°C for a few minutes. You could use any oven you don’t cook food in. We also successfully made microphones using a butane torch to heat the parts and literally soldered them using regular solder wire. We won’t present exact instructions here, as your parts will likely vary. Some ingenuity and finding surplus or recycled parts from your shed will save you a lot of money and hopefully be a fun challenge. The key parameter is that you adapt the XLR section to the 7mm tube 100-150mm long. Photo 1: we made our ‘high-end’ microphone housing from a 150mm length of 7mm brass tubing with a collection of copper pipe fittings, 3/4-inch (19mm) copper pipe and an XLR male-to-male adaptor. 74 Silicon Chip Australia's electronics magazine siliconchip.com.au Tuning your microphone response Photo 2: we pushed the 7mm tube through the RCA backshell, which was a tight fit. We then wrapped 1mm copper wire around this, which makes this a close fit to the 20mm to 15mm capillary reducer. The grey substance is solder paste. The assembly process was to pull the microphone wiring through the 7mm tube, with the ground and output wires soldered to the ECM capsule (see Fig.8). We felt confident nothing would short, so we simply tacked the tips of the hookup wire to the pads/ pins on the ECM capsule. At the plug end, we snipped the microphone wires off about 30mm past the opening and connected them to the PCB. The green (ground) wire goes to the ground pin, and the black wire (microphone output) to the middle pin. We then wrangled the wires into the microphone housing, and once everything was lined up, we fixed the plug to the housing. If you are using the Altronics XLR male-male adaptor, it is a simple matter of pushing the board in until the Fig.8: how to wire up a regular two-wire ECM (left) and modified 'Linkwitz' three-wire ECM (right); note the differences in R8 & R14. The arrangement is the same for the through-hole board. Our goal with a measurement microphone is a reasonably flat response before calibration and a flat response after calibration. If you purchase a calibrated ECM capsule from the Silicon Chip Online Shop, we will provide the necessary parts to load for response tuning. You will also get a calibration file, giving as close to a flat response as we can achieve with our equipment. Alternatively, you may want to tailor the response of your Microphone. In that case, you can download an LTspice model from the Silicon Chip website (associated with this article). This can be used to model your response while varying the tuning components. The following is a general guide to tweaking the response: ● C12 and R10 provide control over high frequency gain, with C12 setting the corner frequency. C12 increases the gain with frequency by reducing the emitter resistance, which is initially 1kW. R10 allows the ultimate gain of this combination to be set. Conceptually, if R10 is set to 1kW, then, at very high frequencies, this results in two 1kW resistors in parallel for a final gain of two times or 6dB. ● R13 and C14 set the gain roll-off at high frequencies. While these go to ground, they are effectively in parallel with the 2.2kW collector resistance. This is reduced by R13, which directly reduces the gain of this stage. R13 sets the ultimate attenuation of this stage, and C14 the corner frequency. You will also find the gain model in our “Analysis.odt” spreadsheet. While this is simpler to work with than LTspice, this spreadsheet is very much an engineering tool, so use it with caution. While the concept of how R10, R13, C12 and C14 interact is simple, getting the response you want can be tricky. The values shown in Table 2 are what we found to be effective with batches of capsules we purchased. These will be a good starting point for you to experiment if you have the ability to check your calibration. Reflowing the solder on the enclosure can be done with any regular oven by baking at 230°C. However, you shouldn’t use an oven that you cook food with. The final result is shown in the photo on the right. Fig.9: we used an Altronics XLR adaptor for the plug, which is a decent fit into a 20mm diameter copper pipe. We then used a capillary reducer and RCA socket shell to adapt that to the 7mm brass tube for the ECM. They came together very well with a few shims and some solder. siliconchip.com.au Australia's electronics magazine August 2023  75 A close-up of the interior wiring required for the microphone. Photo 3: the very inexpensive microphone housing is made from a whiteboard marker and Biro pen case. An epoxy glue (Araldite) was used for the XLR housing joint. screw hole in the plug lines up and inserting the screw. You are then ready to go. Plastic pen based housing As mentioned at the start, a major driver of this design was to keep the cost low. Copper pipe is great if you have off-cuts in the shed, but buying it is pretty expensive. So we looked for a cheap and accessible way of mounting the 6mm capsule at the end of a thin tube, and something suitable for housing the electronics. During one of the author’s less lucid moments, likely due to ingesting an How we generated calibration data for hundreds of ECMs Our calibration process generates a calibration file for Speaker Workshop that allows us to measure the error of an ECM capsule from a flat response. To do this we: ● Measure the SPL of a speaker at an exact location relative to that speaker using our calibrated Dayton EMM-6 microphone (without its calibration coefficients). ● Subtract the calibration coefficients for our Dayton microphone from the measured values and export the result as a “CAL file”. Using this as this synthetic calibration file, we will generate the calibration correction file for the connected microphone if we measure at the same location. We verified that this worked by running a measurement on the same Dayton EMM-6 microphone and confirmed that it produced the expected calibration values. We can then substitute our ECM capsules, and providing we get them in the exact same spot, generate suitable calibration files for those capsules. By labelling each ECM with a number that matches the file saved, anyone who purchases that module can find and use the calibration data we generated. We made a special spring-loaded jig that allows ECM capsules to be popped in and measured easily, speeding up this process. We also created a simple jig to ensure we always made the measurements at the exact same location relative to the speaker. 76 Silicon Chip Australia's electronics magazine unhealthy amount of coffee, the seemingly silly idea of using a mix of plastic pens popped into his head. He found some cheap Biros at Officeworks and some whiteboard markers that, with a bit of drilling and gluing, made an inexpensive microphone housing. If you use whiteboards (eg, at work), you will likely have a ready supply of dried-up markers. The SMD version of the board fits in these perfectly, although the through-hole version is too long. Even better, if you take an Altronics P0823 XLR plug and throw away all but the plug section, it fits perfectly into our whiteboard marker case, as shown in Photo 4. The assembly process is similar to that for the copper tubes but quite a bit easier. First, strip the whiteboard marker apart and clean it out. Cut the tab off the XLR connector with side cutters to allow you to solder to the An example setup of the Measurement Microphone with our previous projects, the Super Codec and Loudspeaker Test Jig. siliconchip.com.au Parts List – Calibrated Measurement Microphone SMD version – electronic module The XLR socket wiring on the SMD version of the Microphone. PCB. Cut the top of the whiteboard marker off and drill the end so you have a tight fit for the Biro tube, then fix the Biro in place with super glue. See the first and last pages of this article for the final result. Testing and using it Using the Calibrated Microphone should be as simple as plugging into a microphone preamplifier that supplies phantom power. We suggest that you check it out before gluing the case shut. If you don’t get a signal on power-up, here are some things to check: 1. Check your solder joints and that you have the PNP and NPN transistors and zener diodes in the right places and with the correct orientations. 2. Apply power by plugging it into the preamp or providing 24-48V DC from a power supply with equal resistors in series with the Hot and Cold (+ 1 double-sided PCB coded 01108231, 64 × 13mm Semiconductors 2 BC860 45V 100mA low-noise PNP transistors, SOT-23 (Q1, Q2) 1 BC849C 30V 100mA low-noise NPN transistor, SOT-23 (Q3) 3 6.8V ¼W zener diodes, SOT-23 (ZD1-ZD3) [BZX84C6V8] Capacitors (all SMD M2012/0805 50V X7R unless otherwise noted) 1 100μF 50V radial electrolytic (maximum 8mm diameter) 1 100μF 10V low-ESR radial electrolytic 1 10μF 16V X5R 3 1μF 50V non-polarised SMD electrolytics, 4mm diameter [Altronics R9600; Würth Elektronik 865250640005] 2 2.2nF 5% NP0/C0G 2 1nF 5% NP0/C0G 2 470pF 5% NP0/C0G Resistors (all SMD M2012/0805 size 1%) 2 150kW 1 100kW 1 39kW 1 10kW 1 5.6kW 2 2.2kW 1 1kW 1 330W 2 47W Through-hole version – electronic module 1 double-sided PCB coded 01108232, 99 × 13mm Semiconductors 2 BC560 45V 100mA low-noise PNP transistors, TO-92 (Q1, Q2) 1 BC549C 30V 100mA low-noise NPN transistor, TO-92 (Q3) 3 6.8V 400mW or 1W axial zener diodes (ZD1-ZD3) [eg, 1N754] Capacitors 1 100μF 50V radial electrolytic (maximum 8mm diameter) 1 100μF 10V low-ESR radial electrolytic 1 10μF 35V radial electrolytic 3 1μF 63V/100V MKT 2 2.2nF 63V/100V MKT 2 1nF 63V/100V MKT 2 470pF 50V C0G/NP0 ceramic Resistors (all axial 1/4W 1%) 2 150kW 1 100kW 1 39kW 1 10kW 2 2.2kW 1 1kW 1 330W 2 47W 1 5.6kW Copper-housed version 1 assembled electronic module (SMD or through-hole) 1 ECM capsule with calibration components [Silicon Chip SC6760-5] 1 60mm length of 20mm or 3/4-inch diameter copper pipe 1 150mm length of >6mm inner diameter brass tube (eg, K&S #8132 brass tube) [hobby store] 1 20mm straight capillary coupler [Bunnings 0252161] 1 20-15mm reducing capillary coupler [Bunnings 0252162] 1 RCA backshell [Altronics P0192] 1 XLR male-male adaptor [Altronics P0972] 1 200mm length of 1mm diameter bare copper wire (stripped from some spare solid-core mains wire) 1 300mm length of two-way ribbon cable or light-duty figure-8 Plastic pen-housed version 1 assembled electronic module (SMD version) 1 ECM capsule with calibration components [Silicon Chip SC6760-5] 1 whiteboard marker [Officeworks] 1 ball-point pen with unscrewable ends [Officeworks] 1 XLR plug [Altronics P0823] 1 300mm length of two-way ribbon cable or light-duty figure-8 siliconchip.com.au Australia's electronics magazine August 2023  77 What is this “Linkwitz Mod”? Most Electret Condenser Microphones use a FET in a common-source configuration. In this arrangement, the source is connected to the capsule case, and the 2.2kW resistor in series with the drain is the load across which the output voltage is generated. Linkwitz realised that if you can cut between the FET source pin and ground (a track that is accessible on the outside of the capsule), it is possible to rearrange the circuit as a source follower. This gives less gain but a lot more headroom. We tested it using our mics and found that all the frequency correction parts remain valid. This modification is very fiddly indeed, and it is easy to kill a mic doing this. We feel this is for ‘power users’ and something you might try once you are confident in making measurements. There are various references on the internet regarding this. A good place to start is at Siegfried Linkwitz’s own web page: www.linkwitzlab.com/images/ graphics/microph1.gif Assembled Calibrated Measurement Microphones in both the copper and plastic-type housings. Kits & Capsules SC6755 SMD Kit ($22.50) Includes the PCB and all onboard parts besides the XLR socket. and −) lines. Use 6.8kW for a 48V supply or 1.5kW for 24V. With this applied: a. Check the voltage on the microphone side of the resistors. This should be well over 10V, and the voltages should be about equal. If not, check for shorts and correct part locations on the board. b. Check the voltage across the power supply zener diode, ZD2. It should be close to 6.8V. Check the voltage at the collectors of Q1 and Q2, which should be well above 10V. If not, check the base voltages of these transistors. Also verify that each has a 0.6V base-emitter voltage drop. c. Check that you have installed R14 fitted (or R8 in if you’re using a “Linkwitz Mod” on the ECM) but not both. d. Check the voltage at pin 2 of CON2, the ECM output for two-wire mode. This should be somewhat less than 6.8V, and if you look with a ‘scope, you should be able to see the microphone signal. If not, check that you have the ECM connected the right way around. Also check for shorts on the capsule. e. If you still have no signal, but the DC voltages at the input and capsule are OK, check the voltage at the base of NPN transistor Q3. This should be about 1.9V, and the voltage on its emitter about 1.3V. The voltage at its collector should be around 3.9V. If these don’t make sense, check that you have the right transistor in the circuit. Using the calibration files Calibration files for all the ECMs we sell are available for download from the links in the ECM shop items. Your ECM will come in a bag with a number on it. Download the file for that specific type of ECM, then look for the files tagged with that number. The calibration files match specific capsules. You cannot use them for similar microphones and expect a great outcome. The file with the FRD extension, starting with your ECM serial number, is in the Speaker Workshop format. You can import it into Speaker Workshop and select it as the microphone calibration. This file contains 4096 rows with Frequency, Gain and Phase figures (the Phases are set to zero). Load this, and you are all set! 0dB in the calibration files equals -40.3dBV/Pa. Given that 1Pa is 94dB SPL, that means that 0dB is 53.7dB SC SPL. Happy measuring. SC6756 Through-Hole Kit ($25) Consists of the PCB and all onboard parts besides the XLR socket. SC6760/1/2/3/4/5 ECMs ($12.50) See Table 1 for the various options. Each comes with the required SMD compensation components, as shown in Table 2. If building the through-hole version, you can source the compensation components (resistors & MKT or greencap capacitors) from Jaycar or Altronics. 78 Silicon Chip Photo 4: the SMD board fits a treat into the whiteboard marker case after it has been stripped apart and cleaned out. The XLR connector will need the tab cut off with side cutters to allow you to solder to the PCB. Photo 5: the assembled Biro-cased Microphone, ready to have the ECM pulled in and glued to the tip. Australia's electronics magazine siliconchip.com.au Power your projects with our extensive range of Arduino® compatible power supply modules, batteries and accessories. A GREAT RANGE AT GREAT PRICES. LED VOLTAGE DISPLAY USB OUTPUT POWER YOUR PROJECT FROM A LOWER VOLTAGE POWER YOUR 5V PROJECT FROM BATTERIES BOOST MODULE Converts 2.5-5VDC from a single Li-Po or two Alkaline cells up to 5VDC. 500mA max. XC4512 ONLY 5 $ 95 DC-DC Boost Module with Display Converts 3-35VDC up to 4-35VDC. 2A max. 2195 $ XC4609 USB OR SOLDER TAB INPUTS EASILY ADJUSTABLE BY MULTI-TURN POTENTIOMETER MAKE YOUR PROJECT BATTERY POWERED RUN ARDUINO BOARDS OFF HIGHER VOLTAGE POWER LITHIUM BATTERY CHARGER MODULE Charges a single Lithium cell from 5VDC. XC4502 ONLY ONLY 5 $ 95 DC VOLTAGE REGULATOR Accepts any voltage from 4.5-35VDC, and outputs any lower voltage from 3-34V. XC4514 ONLY 7 $ 95 Batteries not included SINGLE 18650 BATTERY HOLDER SWITCHED 4XAA BATTERY ENCLOSURE WITH USB PORT PH9205 $3.50 MP3083 $5.95 SWITCHED 4XAA BATTERY ENCLOSURE WITH DC PLUG PH9283 $6.75 3.7V 18650 2600MAH LI-ION BATTERY SB2308 $22.95 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 Prices correct at time of publication but are subject to change. Jaycar reserves the right to change prices if and when required. INTERVIEW WITH We had the opportunity to conduct an interview about the future and history of DigiKey with their Vice President for the AsiaPacific region, Tony Ng. DigiKey just celebrated 50 years in business. Tell us a bit about the company’s history. Q Like many great companies, DigiKey evolved from a passion, in this case, ham radio. In the early 1970s, Dr Ronald Stordahl started selling the “Digi-Keyer” – a kit for ham radio operators that helped transmit Morse code. That led to selling components – first to electronic hobbyists and then to the commercial market. For 50 years now, we’ve built upon that initial passion, thanks to the hard work, commitment and entrepreneurial spirit of our more than 5000 employees worldwide, 929,000+ customers, 2400+ suppliers and myriad global partners. DigiKey now not only distributes electronic components but provides digital solutions and tools to engineers, designers and makers in more than 180 countries. A A lot must have changed in the electronics industry over the last 50 years. What are some of the latest changes and innovations you have undertaken? Q Over the past 50 years, the people of DigiKey have consistently had their fingers on the pulse of the industry, reacting to changing needs and offering a vast spectrum of components to fuel production into the future. We’re excited about industries like healthcare, automotive, energy, 5G and IoT, as they continue to drive innovation in 2023 and for many years to come. The electrification of everything is another key trend that will drive significant growth this year and beyond. Every forecast indicator suggests that the long-term demand outlook for the upcoming decade is very robust. DigiKey’s significant increase in capital infrastructure investments over the last three years puts us in a strong position to service those anticipated customer needs. Those investments include our Product Distribution Center expansion, more robust and predictive web search, higher inventory levels and the start of more self-serve order management tools aimed at providing a frictionless digital experience. The impact of the recent economic cycles on DigiKey and the industry has proven that A we have the resiliency, perseverance and grit to overcome obstacles. While the shortages we’ve experienced since early 2020 have eased somewhat, many products remain out of stock or available in limited quantities. How much longer will it be before the vast majority of products are in stock and lead times are more reasonable? Q While the availability of semiconductors is improving, long lead times are still plaguing certain product segments. DigiKey’s goal is to make it as easy as possible for customers to find alternative solutions that may fit their needs. When a customer tries to order a part number from our website and it is out of stock, DigiKey automatically presents potential alternatives from our database of nearly 60 million part number cross-references. Our customers have spent the past few years pivoting and embracing agile decision-­ making processes. While it has been an incredibly challenging time, we believe that those who have embraced and accepted these challenges will come out stronger on the other side because it is through challenges that we grow the most. A Those shortages also caused quite considerable price increases in some product lines, well above the rate of inflation (which is pretty high these days). Will those items that experienced significant price increases come back down any time soon? Q The supply chain disruptions and inflation in materials, labour, transportation, and energy costs forced many suppliers to raise prices in 2022 and early 2023. It is impossible at this point to say whether those price increases will continue. A What new suppliers are you working with that you’re particularly excited about? Q 80 Silicon Chip Australia's electronics magazine siliconchip.com.au Some of the key new products now available through DigiKey include: ROHM’s GNP1070TC-Z and GNP1150TCA-Z Gallium Nitride FETs Knowles’ V2S200D Digital Voice Vibration Sensor Renesas Electronics’ RZ/T2L ARM® Cortex®-R52 Microprocessor EAO’s Series 09 Universal modular key switches/joysticks Molex’s PowerWize Blind-Mate Interface (BMI) connectors A ◘ ◘ ◘ ◘ ◘ We’ve noticed that you can sometimes ship orders within a couple of hours of us having placed them. How do you achieve such quick turnaround times? Q That speed is all thanks to our amazing Product Distribution Center (PDC) staff! They are dedicated to ensuring that any order received by 8pm Central time (about 11am AEST or 8am AWST) are shipped that same day to the 180+ countries around the world that DigiKey currently ships to. The team now receives a bit of assistance from our new, fully automated Product Distribution Center expansion (PDCe) warehouse that we opened last year. Our distribution centre was designed to handle broken-pack quantities to support engineering and low/mid-level production requirements. The PDCe is nearly fully automated to achieve that purpose, with products stored in trays that can be configured in various means to support bulk, tube, reel or other manufacturer packing conventions. That tray is brought to a pick station and the targeted product is highlighted with a light to minimise errors. In addition to utilising available third-party systems, DigiKey has also designed its own systems that further automate the picking process and improve traceability and more accurate pick quantities. The largest component of our new automated system is the KNAPP Order Storage and Retrieval (OSR), which provides the right parts to the picker every time, eliminating walk time and providing an ergonomic environment for the picker. This high level of automation improves efficiency by up to 35% for picking and greatly improves packaging quality and efficiency. The PDCe features two primary sorting systems to provide redundancy in the case of a breakdown and provide for future growth. The new facility has over 27 miles (43km) of automated conveyor belt, and an average order will travel more than 3200 feet (975m) inside the building. The new PDCe also provides additional A siliconchip.com.au DigiKey recently opened its 2.2 million square foot/204,400m2 Product Distribution Centre expansion (PDCe) to keep pace with growing demand. room for our carrier partners to grow and incorporate their own automation on-site, allowing for ongoing and improved delivery options to customers. Are there any interesting component trends specific to the Australian/New Zealand market that you can tell us about? Q To begin with, the Australian/New Zealand market is not small. The countries are packed with lots of smart engineers, innovations and R&D activities, plus domestic manufacturing capabilities. These are all critical to supporting the domestic demands from smart cities, factory automation, agriculture, mining, personal healthcare and more. Due to the relatively smaller volume and competition on time-to-market, we are seeing more and more demand shifting to modules in sensor and RF applications. These really work in compliment to our new franchise addition in recent years. As we continue to expand our product portfolio, we are not limiting ourselves in the fields of electronic components. We are also expanding our sourcing globally for new technologies and products that our customers search for. A How do you decide what products to carry to ensure you meet customer needs as closely as possible? Q A Certain industries have become hot topics and will continue to drive the Australia's electronics magazine demand in the coming years: healthcare, new energy, EVs, industrial automation, telecom/5G/6G, IoT etc. Together with our website traffic and keyword monitoring, these fuel the new franchises as well as SKU count addition. The more customers utilise our web tools, the more we will be able to help them in the short and long term. You say that you have a commitment to innovation. Besides supplying components, what else do you do to support that aim? Q We see 2023 as the year that engineers are finally getting back to innovating and creating new designs. While we acknowledge there are still some supply chain challenges, on the whole, engineers have better inventory access than they’ve had for several years now. We see them taking that to their advantage and really digging into the next phase of innovation in the space. All indications are that 2023 is shaping up to be a good year of new product development for our engineering customers. DigiKey is looking forward to the continued innovation of our customers that will come in 2023, and we are excited to enable the world’s ideas. As a company, DigiKey has invested in innovations, including cut tape printing, providing more products and services within the ecosystem and expanding the DigiKey Marketplace, providing customers around the world with even more reason to make DigiKey their first stop in the design process. SC A August 2023  81 SERVICEMAN’S LOG The Wild West of Central Europe Dave Thompson Let’s face it, when the serviceman goes on holiday, all he can really expect is to do less servicing than usual – not none! This time was no different, but luckily, I had some seat-of-their-pants, wing-and-a-prayer helpers that did most of the heavy lifting for me. What’s the old saying? All good things must come to an end. Nothing is truer than the end of an extended holiday. Seven weeks is a long time to be out of the loop, and the older I get, coming home and returning to my old routine is becoming an increasingly strange experience. The only benefit of the long flights home is that they give pause to reflect on what was an amazing experience of seeing people, palaces, castles, cathedrals and art. I’m not into art by any means (unless we’re talking about a Fender Stratocaster), but I did see five original van Goghs, dozens of Klimts, a few Monets, a Rembrandt, a Sargent and a Whistler. It is hard even for a philistine like me not to be moved by seeing them. I have hundreds of photos to sort through, but of course, photos don’t show what I actually saw; at least, my photos don’t. I’m very much a ‘point-and-shoot’ photographer. I can also reminisce on a few occasions where my serviceman’s skills were needed (beyond those already covered last month!). In a household where the guy who used to do all the regular maintenance has long since passed on, things gradually decline to the point of needing some TLC. Many widows there rely on others with DIY skills, or they call in ‘a man from the village’ to do it as paid work. Some of these guys are capable, while some aren’t, which makes for interesting repairs. Evolving infrastructure As mentioned previously, the power to one of the apartments my mother-in-law and her late husband built years ago up around the coast (that we 82 Silicon Chip were soon to be staying in) had gone out, so I needed to look into that. I protested that I didn’t know much about the local system and regulations, but my protests fell on deaf ears. My brother-in-law said that nobody cared about that stuff anyway, and we could do pretty much what we wanted, as long as nobody got hurt! From some of the installations I saw later, I believed him! This particular town is essentially a centuries-old fishing village with some newer holiday homes tacked onto each end of it around the coastline. The infrastructure is creaky at best, with power, sewers and plumbing an afterthought and sometimes crudely implemented. Given the country’s typical cold-war era love of concrete, there’s a lot of it about. It isn’t always nicely-done concrete either, as we know it at least; much of it looks poorly mixed, cracked, crumbly and roughly applied. I even took some photos of ‘patches’ some local had done; while I’m no expert, it appeared to me to have been mixed with a garden fork and applied with a mop. The relevance here is that the concrete foundations for this place and the two garages were poured in the 1970s. Sewers, water pipes and power cables were simply pushed through plastic conduits embedded in the concrete. The water supply initially was a rainwater catchment system with the water collected and stored in a large concrete cistern built into the house. A pump ran automatically when a tap was turned on, pumping the water through a filter system and stopping when the tap was off. A separate mains-powered boiler mounted above a sink or bath (that looks similar to an old Zip, if anyone still remembers them) still provides hot water to most Croatian homes today. If the stored water ran out, residents would chip in to pay for a water truck to come over the hill from a bigger town to top up their cisterns. It stayed this way from the 1970s until around 2007, when a water pipe was installed from that town over the hill, at the residents’ expense. I remember helping clean and overhaul that water pump a few times on my early visits, and I have also helped replace several old boilers with much more modern, efficient ones. So, everything is buried in concrete these days, and in the newer areas, this makes for a neat and tidy system. However, given that the country and this area, in particular, is about as earthquake-prone as my hometown (we had a decent quake while there), things tend to sink or shift over the years, which can cause problems. Australia's electronics magazine siliconchip.com.au Items Covered This Month • • • Servicing in the Wild West of Central Europe Repairing a Lenovo laptop A sticky situation with Reveal 6D monitor speakers 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 Most residents regularly have to deal with problems like water leaks, broken sewer pipes and, of course, power supply problems. Power distribution The mains power to each property comes from now-­ buried cables that run under the access road leading to the beach houses. For those interested, Croatia has a standard mains voltage of 230V at 50Hz. They use the typical continental European two-pronged (round pin) plugs and mains sockets, types C and F. Without a meter, I couldn’t confirm those voltage figures, but I assumed it would be like many countries, where the voltage fluctuates slightly. There is a junction box at each driveway, similar to our water mains shutoff valve boxes, with a closeable metal cover that splits the feed off to another switchboard-type setup. This is usually in a garage, carport or other structure close to the road. The cable coming in might be run up the outside of the wall or buried in a conduit beneath the surface. If multiple properties are sharing the driveway (very common due to the housing density there now), the mains feeds to those homes are added in new conduits dug into existing concrete paths and structures. Sometimes, the property switchboard junction box is utilised for these feeds, and sometimes the feed is taken from the buried box at the roadside. How it is installed depends on who does the hook-up. The switchboards near the road are similar to those used everywhere and are either old and open to the elements (not great right next to the sea!) or more modern and enclosed in a covered, grounded (and usually rusted) metal box. Pole fuses and breakers are common; sometimes, there is a mixture of both. Each apartment also has its own smaller switchboard, where the outside mains feed terminates, and this is where I started my troubleshooting process. Oh, to have a multimeter! I physically checked the fuses and breakers – they all looked sound. The mains switch itself seemed to be working, or at least toggling correctly. There was just no power. My next stop was down to the breaker box where the mains entered the property. There was power here because I could hear it, and the pole fuses arced a little when I removed and replaced them. I also noted that there were two other feeds off to houses behind this one. They had their own pole fuses, and I didn’t touch them. Fortunately, someone years ago had labelled them, and the owner knew which ones were hers. siliconchip.com.au So, I had power to there, but not to the apartment in question. There are three apartments, each on separate floors of the three-storey building. This was the top-floor apartment, the newest one built, about 10 years old. The others had power, and their pole fuses were also on the main switchboard downstairs. Flying blind The second-floor apartment was empty, so I pulled both pole fuses and swapped them into each other’s sockets. The third floor was still without power. The second floor still had power, so the pole fuses were both working. That didn’t bode well because it meant there must be a break in the mains feed to the third floor, somewhere between this switchboard and the one upstairs. The obvious thing now was to remove the screws from the upstairs switchboard, fold it down and have a look behind it. Maybe a connection there had shifted? At this point, I was really missing having any tools with me. The family has a few random tools collected over the years, but nothing aside from a flat-blade screwdriver and a shonky Phillips one that was already chewed out and looked to have a shaft made of lead. I managed to remove the overly-long screws so I could lift the panel away from the wall. Everything looked to be connected securely, so that was another dead end. I could have done the same thing at the street switchboard, but with live power coming into it, and not wanting to shut down three households, I wasn’t about to mess with it. I replaced the upstairs panel and went to break my news to the owner. Between the two connections, there was about 20 meters of cable – somewhere along it, something had happened and had killed the power. Where was anyone’s guess. My serviceman’s brain was already spinning with the potential fixes for something like this, and none looked very appealing. I was thinking by this time that we’d have to get a proper sparky in to resolve it because, without proper tools, I’d just be winging it and likely doing it badly. The professionals must be used to dealing with this sort of thing all the time. Australia's electronics magazine August 2023  83 The only way I could see to repair this would be to cut into the concrete somewhere along the track, if we knew where it was, and rummage around until we found the cause. Hired guns My mother-in-law made the call, and two likely lads duly turned up. They were your typical tradies – a van packed to the roof lining with tools and whatever else and the ‘nothing is a problem’ attitude. They initially did essentially what I’d done, checking the obvious and conferring a lot before coming to a similar conclusion. Like many of these places, there were no real plans available of where anybody put what and because the apartments had been built over a span of almost 50 years, what drawings or plans there might have once been around at the time were long gone. We discussed it and determined that the cables must run in the shortest line between the two structures – the garage downstairs and the apartment upstairs. We knew where the cables ended and guessed the people who put them in would follow the natural path between those points. The guys had to go away and get even more tools. They returned the next day with some hired concrete-cutting gear and longer extension leads. They drew out some lines on the path about a third of the way from the bottom junction and set about cutting in. There was a decent crack running through the concrete around that point, and they (like me) assumed that might be where the problem was. It was as good as any place to start. Who needs health and safety? One thing I noticed in Croatia with workmen is that it’s like the Wild West. Workplaces don’t appear to be as highly regulated as they are in New Zealand, with health and safety briefings, licensed operators on specialised machinery, that sort of thing. On a job site there, you won’t find anyone wearing safety boots, high-vis vests, ear defenders or safety glasses. 84 Silicon Chip One renovation project going on a few hundred metres from the house I was staying in has a huge crane perched half on the road and footpath. It was being used to lift pallets of white rock cladding tiles to install on an old municipal building which, like many there, had been built in the 1960s and hadn’t had a thing done to it since. This crane had sunken into the footpath, probably because that hadn’t been made properly either, and yet it was there when we got there and still there when we left, a bit cock-eyed and still being used. Not one guy on that site had a hard hat or any safety gear, with other workers using big, gas-powered cutters to shape these tiles right by the thin wire fence they’d built to seal off the site. The noise was deafening (literally!) all day, and dust and other rubbish were being blown all over the footpath and road. Pedestrians and motorists were going about their business as if nothing was out of the ordinary. I crossed the street because I didn’t want to walk anywhere near that noise, the flying debris or under that wonky crane! These guys were the same. No regard for safety; they just lit up this concrete saw and got stuck in. They probably sneered at the foreigner standing way back with his fingers in his ears, but I didn’t care; I’m still able to hear (albeit not perfectly) at 61! They made short work of the concrete and made a 150mm/6in-wide cut over some guidelines they’d drawn. A few good hits with a hammer and chisel had the chunks out, and there was a partial view of a conduit underneath. Good guess! Dodgy work revealed They made another cut, widening the slot and when the concrete was clear, they cut carefully into the conduit. The cables were all in there – phone and power. One of the guys hooked the power cable and gently pulled it. It kept coming, from the road end, until it cleared the conduit. There it was, a break. On closer inspection, we could see that the cable had been joined, and the joint had failed. It was poorly done, and by the disgust on these guys’ faces, they thought so too. Here it is against the code to join a mains cable; from what I understand, it must be a single piece between the house and the street junction. Whoever put this in originally had not done it correctly, so we now had to restore it. After much discussion, including joining the cable again, they decided – at our insistence – that the whole thing should be replaced. That meant disconnecting the cable at the apartment end, behind the switchboard, and after tying some strong twine to it, carefully pulling it back through the conduit to the hole they had made. This they did without too much fuss. They then retrieved what we call a ‘fish stick’ from their van. This extendable, flexible fibreglass rod can be fed down walls and conduits to catch wires and pull them through. Sections are added as necessary. The cut was only about six meters from the bottom switchboard and with just one bend, so it wasn’t too much work to get the rod through to the hole. The new cable was measured out and pulled back with the twine to the apartment end. Once terminated there, the remaining length was attached to the fish stick, and that end was pulled to the board at the road. It was terminated there carefully because the board was still live! Australia's electronics magazine siliconchip.com.au Brave men. The pole fuse was put in, and the apartment finally had power. All that remained was to tidy up the switchboards, re-­ attach the cut section of conduit with lots of silicone and fill in the hole with concrete. These guys did it all. It was a fun job to be part of and to see how others do it. Holidays! Repairing an obsolete Lenovo tablet B. D., of Mount Hunter, NSW encountered the pitfalls of repairing a device when you aren’t familiar with how it comes apart and goes back together again. Still, he overcame that, albeit at a higher cost than anticipated... I purchased a Lenovo MIIX 510-12ISK Windows tablet about six years ago to use as my main computer. It is quite a good unit, similar to a Microsoft Surface but cheaper. It has an i5 processor, 8GiB of memory and a 250GB SSD. I used it for a couple of years with no problem when I noticed the power switch no longer had a positive click when operated. I tended to use it often to shut the computer down rather than using the software controls. Not long after, the computer started to shut down and reboot spontaneously. This went on for a while until it got so bad that it was in a continuous reboot cycle, and the tablet was no longer usable. I tried a few things, but realised after a while that the power switch must be faulty. I thought I might try to fix it myself and managed to remove the screen and look inside. I found the power switch was on a small circuit board together with the volume control that would not be easy to replace. I rang Lenovo, who had a repair service (no longer operating). They quoted $200 and I would have to post it etc. I decided it was all too hard, and as the battery had also lost capacity, I purchased a HP Spectre as a replacement. It has virtually identical specifications and performance. I put the Lenovo tablet away in the cupboard and left it there. Later, when I had spare time, I decided to have another look at it. At the time, I didn’t realise that when removing the screen, it is better to lift the top and not the bottom to avoid disturbing the connecting cables attached to the screen. I managed to dislodge both cables (for the display and touchscreen) from the back of the screen. So I decided it was still too hard to fix. At this stage, I hadn’t worked out how to determine the correct way to reattach the cables. So naturally, I managed to reconnect the main display cable the wrong way around when putting the screen back and was greeted with a burning smell and a small column of smoke rising from the system board. The tablet was then dead. I returned it to the cupboard as it still had usable memory and the SSD, so I was reluctant to throw it away. About a year ago, I was browsing on eBay and noticed second-hand system boards for my exact model were available for a reasonable price. I also found a very good teardown manual on the Lenovo website for this model. It gave clear step-by-step instructions on removing each part, such as the battery, hard drive etc. However, it doesn’t give small details, such as the correct way to remove the screen or that the small gates on most connectors must be lifted before removing or connecting the cables. It also doesn’t mention that a white line on the end of the cable must be visible when reconnecting it to ensure it is the correct way around. siliconchip.com.au Australia's electronics magazine August 2023  85 The two cables that caused the problem are circled in red. Hard-to-see horizontal white lines on the cables under the connectors show the correct orientation. The power switch and volume control are in the top right-hand corner. The touchscreen control board with the broken connector (CN1) in the bottom right-hand corner. I was still unsure whether the screen had been damaged, and with no way to test it, it would be a gamble if I purchased one of these boards, as a screen replacement would make the whole exercise non-viable. I explained this to the vendor and told him that these tablets were now obsolete, and he accepted my offer of $60 plus postage for the system board. He also threw in a used power switch and other useful bits and pieces. When the parts arrived, I commenced the repair slowly and carefully. Everything came apart pretty well as described in the manual. Just about everything has to come out to replace the system board, including the SSD, wireless card, cameras, battery and switch. I was also helped by a YouTube video on a heatsink paste renewal for this tablet, which showed most of the steps. I installed the replacement system board and also replaced the troublesome power switch with the one supplied. It seemed OK, with a positive click. I put everything back in reverse order and then reattached the screen. The battery had to be charged after so long in the cupboard. While reattaching the screen, as I hadn’t worked out the best way to do that yet, the touchscreen cable was stretched beyond its limit, and the plastic connector on the back of the screen broke away beyond repair. It was attached to a small circuit board on the back of the screen, called the 86 Silicon Chip touchscreen controller. I carried on and managed to put the screen back. With some trepidation, I pressed the power switch, which needed to be held down for some time. To my great relief, the Lenovo logo appeared on the screen after about ten seconds. However, I had no keyboard and no touchscreen, just a mouse. This made logging in (which required a password) rather tricky. I removed the screen again and checked the keyboard connector to the system board. This was when I realised that the small locking gates must be pressed down. After doing that, I reassembled the screen and had a working keyboard. I was able to log in and connect to WiFi. Everything seemed to be working OK, except for the touchscreen. The part number was clearly written on the part, so I typed it into Google, as Lenovo no longer carried this control board. Google returned an AliExpress page with the control board listed, albeit quite expensive at $60, but having no alternative, I ordered the part. I also ordered a replacement battery to complete the package. The touchscreen controller eventually arrived, and by then, I was well-practised at removing the screen. The board is attached with double-sided tape and reconnecting the multi-pin connector to the panel was not as difficult as I had anticipated. I put it back together and switched on the tablet. To my dismay, there was still no touchscreen. I went into Device Manager, where it was listed as not working. Fortunately, when I clicked on one of the options there, it suddenly came to life, and everything then worked. The tablet was now pretty good; however, Windows Update insisted on installing the latest version of Windows. After that, I noticed that the tablet took about 15 seconds to wake from sleep, whereas with the old version of Windows, it woke up straight away. I went to the Lenovo Users’ Board and found that this tablet is incompatible with the latest version of Windows, so I reverted to the old version, and the problem went away. However, as the slow wake-up seemed to be the only problem, I decided to upgrade again and live with the slow wake-up. I now use the tablet quite a bit as a spare or when the HP is not available. It has a removable keyboard and is lighter than the HP. I am glad I persevered with the repair as it was satisfying to achieve a result, and electronics is my hobby, after all, so it was time well spent. All up, the parts cost around $200. Speaking about a sticky situation N. B., of Seven Hills, NSW discovered how much more difficult a repair becomes when the circuit boards are covered in glue. It also didn’t help that multiple assemblies were packed into a small space... I empathise with Dave Thompson’s wrestle with a perfectly functional carpet cleaner in his March 2023 column. I’ve also once or twice found myself disassembling and testing something under the assumption that something was broken, when it was just simple operator error. When I bother to read them, I often think that the ‘troubleshooting’ sections of most appliance manuals usually only cover the ‘bleeding obvious’ operator errors and generally give little if any advice on what to do when there is a real problem with the device, other than “contact the service agent”. But I suppose operator errors are much more common than real failures. Australia's electronics magazine siliconchip.com.au My write-up of the following repair saga has already helped a colleague fix another pair of similar speakers. The Tannoy Reveal 6D monitors are compact two-way active, bi-amped near-field speakers. The 6D is one of the second-generation Active Reveals, built from about 20052010, with a 6-inch (150mm) low/mid driver and 1-inch (25mm) dome tweeter, each driven by its own amp after the active crossover and filter circuitry. They have a digital input (hence the “D”) and cost about $1200 each when new. This pair started making odd noises and didn’t sound right. I asked for a fault description, and it was reported that they made a great pair; one had no HF driver output, and the other had no LF driver output! (The failed LF driver sometimes worked intermittently). I decided to make them a personal project and took them home. I had no idea what I was in for, but I like a challenge. The tweeter producing no sound had a resistance under 1W and connecting a battery resulted in an extremely quiet click. I then noticed a smoke stain on the front panel above its mounting hole. I also removed the low-frequency driver and powered it up with DMMs on the speaker leads. About half a volt of DC appeared on both speaker outputs, increasing to 5-6V. Not good. I would have to pull the amplifier module from the back. Everything is mounted on a 3mm aluminium backplate, with a large finned heatsink occupying about half its outside area. Inside, things were quite packed. The power input and transformer were at the bottom. Above them was the main board with the power supply and power amps, then the filter board, with the analog input, crossover and EQ circuits. It has a level control pot and a line-up of switches, including 20 DIP switches for setting the EQ characteristics. Finally, the digital input board is at the top, with a few surface-mounted devices on it. Almost everything was coated in glue to stop things from vibrating and rattling. Fasteners were covered in hard, clear glue, while connectors received tough black glue to ensure they didn’t separate. Components of any size had brown glue added to brace them. A bead of it was also used between each board and the backplate. There was evidence that an electrolytic capacitor had vented all over the main boards and filter boards in both speakers. There were 11 small electros on the main board, plus two large filter capacitors for the modular power amps. Half of those caps were related to the ±15V supply for the filter and digital boards, with others for the mute circuitry. All electros measured at least 10% low, including the power amp supply caps. But a few were very low in value, and not surprisingly, the vented cap was open circuit. Getting to the main board to replace the capacitors was almost impossible, with it sandwiched between the transformer and the other boards above. I found a forum thread on repairing the Reveal 6Ds, which helpfully included schematics of the main and filter boards. There were several comments about access difficulty and problems from all the glue, including that the brown glue can be corrosive and conductive, so you should try to remove it as much as possible. Great. Removing the digital and filter boards was relatively straightforward, other than the time to chisel, cut and scrape off glue as I went. After doing that, a couple of the caps were still in awkward places, under an aluminium heat conductor from the 7815 regulator to the backplate and heatsink. siliconchip.com.au Access to the bottom of the board was also quite limited, and two end-mounted power resistors below the board were just a few millimetres from the transformer. The whole assembly would have to be dismantled to obtain good access to work on the board, or I would at least have to remove the power transformer. The amplifier modules were clamped to the backplate by a steel bracket that also supported the board, with the heads of the screws fixing it under the heatsink. Most of the screws mounting the heatsink were accessible with their heads on the inside, although glue had to be removed from each. But one heatsink screw was under the power transformer. The transformer was mounted on screws coming through the backplate, with nuts on the inside, but the heads of two transformer screws were under the heatsink. Australia's electronics magazine The tightlypacked Reveal 6D amplifier assembly. The dreaded brown glue, with the exploded capacitor visible in the centre. The Reveal 6Ds with replacement tweeters installed. August 2023  87 The transformer sat on an adhesive pad, which did the job so well that the screws seemed almost redundant. I could loosen the nuts on the transformer screws, but the remaining glue in the threads presented so much resistance that the screws started turning once there was some slack. Clearly, the transformer was going nowhere, so I gave up on that idea; the board would have to be fixed in situ. I removed the power resistors to improve access to the bottom of the board, then proceeded to replace all the small electros, chiselling off all the brown glue I could. Clearing the plated through-holes is not easy when you can’t get a solder sucker onto them, but solder wick saved the day. After remounting the power resistors, I connected meters and prepared for a smoke test of the main board. When I powered it up, the +15V output was only about 8V, and one cap started to smoke and bulge. I quickly turned it off and checked it. Oops, I’d installed it back-to-front. The overlay showed the polarity for most of them, but a few had to be carefully checked, and I’d gotten that one wrong! After replacing it, the main board passed the smoke test, the supply voltages were all good, and with no input, the speaker output voltages were only a couple of mV AC and DC. So far, so good. I mounted and connected the filter board and performed another test. Now the speaker outputs were showing about 30V DC. Not so good! The ±15V supply was going to the filter board, but the output lines were obviously DC-biased. I hoped it wasn’t a failed op amp, as there were 22 of them on the board. I decided to put that one aside and work on the second speaker, figuring that if that one could be more easily brought to a functional condition, it would be a good reference to diagnose the problem with the first one. Now that I’d learned what not to attempt, work on the second module proceeded a bit faster. However, the power resistors didn’t want to move as easily as those on the first board, and there was more glue under their bases. When they finally moved, each took a solder pad and a section of track with it. The glue stuck the solder pad to the resistor better than the pad was fixed to the board! I also accidentally broke a zener diode mounted across the inputs of the 15V regulator ICs when I tried to move it to give better access to clean the capacitor mounting pad it was soldered to. So, extra repairs were required when reinstalling the components. I laid down the lead of the 88 Silicon Chip capacitor next to each power resistor to replace the missing tracks. It passed the initial smoke and voltage test. I cleaned the filter board a bit more and reinstalled it. Again no smoke, and the voltages were OK, so I fed a pink noise source to the analog input, and the speaker output voltages did the right thing. I connected it to the speakers in their box, and both drivers produced suitable sounds, so that was one win. Back to the first speaker. On the filter board, I fitted component lead off-cuts to the bottom of the connector pins for the cable from the main board. That enabled me to selectively plug the cable into the leads on the power pins and leave the signal leads bent out to monitor what was going on. The power amps would then not be stressed by a DC signal input while I diagnosed the problem. On power-up, the supply voltages were good, but the signal outputs of the filter board were around 13V DC. Further probing found that the +15V supply pins on each op amp were also around -13V. I powered it down and started doing resistance checks on the +15V rail. Connections between all the op amp VCC pins were all good, but there was about 60kW between any of them and the +15V input pin and filter cap on the board. The filter board’s supply caps were a pair of 100µF electros right next to the cable connector, which measured better than the others. Like on the main board, there was a liberal dose of brown glue on them. I removed some of the glue, but it was between and under the caps and cable socket. I removed the filter caps and chiselled off as much of the glue as I could. I could then see that the +15V track ran on the top of the board, back under the edge of the cable socket, came out the opposite end, and onto the first op amp. I’d found earlier that the cable sockets are not too well fixed to their pins, as one of them came off the pins because the connector bodies were stuck together by glue I could not access. So I got a small sharp screwdriver under it and levered it off the pins. Once that was out of the way, I chiselled off the remaining glue to clean up the area. With the area all clean, I saw a 2mm-wide charred spot on the +15V track where it ran under the socket. It seems that the glue had eaten away at the track until it heated and turned a small area of the board into a carbon resistor. I used the tip of a small drill to excavate the carbonised material, replaced the socket and fitted new caps. I added a bit of old telephone (solid-core) wire on the bottom of the board to bypass the broken track. On reinstalling the filter board, its supply and the speaker output voltages were all good. It now passed sound well, and connecting speakers showed it worked like the second module. I reinstalled the digital input boards but did not connect them, as we have not found them useful. The audio outputs from the sound cards in our studio computers have better sound quality than the digital-to-analog converters in the 6Ds. Tannoy seemed to agree, as the digital input was omitted in later Reveals. The original tweeters are no longer available, but similar drivers from Jaycar with a differently-shaped mounting plate could be made to work. Their differing sensitivity was not a problem as a trimpot sets the tweeter level. So with some front panel work, I replaced the tweeters, and they are working again as a pair of utility speakers. SC Australia's electronics magazine siliconchip.com.au Keep your electronics clean, lubricated and protected. Service Aids & Essentials. GREAT RANGE. GREAT VALUE. In-stock at your conveniently located stores nationwide. 4 2 1 5 3 BUY IN BULK & SAVE!!! 1 Isopropyl Alcohol 99.8% 250ml Spray NA1066 BUY 1+ $11.95 EA. BUY 4+ $10.45 EA. BUY 10+ $9.45 EA. 99.8% 300g Aerosol NA1067 BUY 1+ $13.95 EA. BUY 4+ $12.45 EA. BUY 10+ $10.95 EA. 70% 1 Litre Bottle NA1071 BUY 1+ $19.95 EA. BUY 4+ $17.95 EA. BUY 10+ $15.95 EA. 2 Electronic Parts Cleaning Solution 1 Litre Bottle NA1070 BUY 1+ $15.95 EA. BUY 4+ $13.95 EA. BUY 10+ $12.45 EA. 3 Liquid Electrical Tape 28g Tubes, Red or Black NM2836-NM2838 BUY 1+ $21.95 EA. BUY 4+ $19.45 EA. BUY 10+ $17.45 EA. 4 175g Aerosols Contact Cleaner Lubricant NA1012 Electronic Cleaning Solvent NA1004 BUY 1+ $12.95 EA. BUY 4+ $11.45 EA. BUY 10+ $9.95 EA. PTFE Dry Lubricant NA1013 BUY 1+ $15.95 EA. BUY 4+ $13.95 EA. BUY 10+ $12.45 EA. 5 J-B Weld Products J-B Weld Epoxy 28g NA1518 BUY 1+ $22.95 EA. BUY 4+ $20.45 EA. BUY 10+ $17.95 EA. SuperWeld Extreme 15g NA1539 BUY 1+ $14.95 EA. BUY 4+ $13.45 EA. WaterWeld 57g NA1532 BUY 1+ $23.95 EA. BUY 4+ $21.45 EA. BUY 10+ $18.95 EA. Shop at Jaycar for even more service aids & essentials: • Adhesives & Insulation Tapes • Solder & Soldering Aids • Wire & Heatshrink Tubing Explore our full range of service aids, in stock at over 110 stores, or 130 resellers or on our website. • Fasteners & Cable Ties • Ultrasonic Cleaners • Tools & Workbench Accessories jaycar.com.au/serviceaids 1800 022 888 Prices correct at time of publication but are subject to change. Jaycar reserves the right to change prices if and when required. 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. dsPIC-based Audio Spectrum Analyser This Audio Spectrum Analyser uses the fast Fourier transform (FFT) to convert a time-domain signal to the frequency domain. The FFT is much faster than a standard Fourier transform. The development time for the software was shortened by using the MikroC PRO compiler for dsPIC by Mikroelektronika. It includes the FFT routine and a graphic LCD library, both used in this design. You can download the code-size-limited demo version to see the compiler’s features; if you like it, you can buy the license. The circuit is straightforward, with a 5V linear regulator providing power to the microcontroller and monochrome graphical LCD. The microcontroller updates the LCD screen contents over an 8-bit parallel bus with five control lines. Incoming audio is attenuated using VR1, then AC-coupled to analog input AN0 with a half-supply bias provided by a pair of 100kW resistors. That keeps the signal centred within the 0-5V range of the ADC. If VR1 is set too high, the signal could have an amplitude greater than 5V peak-to-peak, but it will be clipped by the ESD protection diodes within IC1. The remaining pins of IC1 are broken out into two pin headers, CON4 & CON5, in case an application is developed that needs the additional pins. The audio signal is digitised using the dsPIC’s built-in 10-bit ADC. The conversion time is set to the highest setting, and it uses the Timer1 interrupt to sample audio 38,400 times per second. According to the Nyquist theorem, it can handle frequencies up to 19.2kHz. The FFT algorithm turns this data into a series of vectors, with the magnitude representing the amplitude of the signal components with various frequencies. The more ‘bins’, the more frequencies are analysed. We can increase the number of samples to get more bins, but it is limited by the resources of the dsPIC microcontroller and the compiler. During operation, trimpot VR1 is adjusted to get a displayed amplitude that is ¾ the height of the graphic LCD. The rectangle in the graphical LCD is only drawn once, at power up, as otherwise, it will slow down the screen update rate. Trimpot VR2 is provided to adjust the contrast of the graphic LCD. You can test the Spectrum Analyser by applying sinewaves of 1kHz to 16kHz in 1kHz increments and checking that they form a series of peaks on the display, moving from left to right. The software for this project (C source code and HEX file) plus PCB Gerber files are available for download from siliconchip.com.au/Shop/6/226 Noel A. Rios, Manila, Philippines ($100). USB “Power Board” is just a PCB This simple PCB provides an inexpensive way to power up to four USB devices from a single upstream power source. The connectors are formed from exposed copper traces on the circuit board itself. Both genders are supported: they can be held between the pins and chassis of a female socket, or jammed into the end of a male plug. This arrangement ensures that the polarity is correct for both genders. If older connectors are a loose fit, you can add solder to the contacts 90 Silicon Chip to firm them up. Jumpers JP1-5 are initially closed to short the USB data lines (D+ & D−) together. For most devices, this signals to the device that maximum current can be drawn. You can open these jumpers with a sharp knife should the current drawn need to be limited to 500mA, perhaps to charge multiple phones or tablets from an undersized upstream supply. I have also found that charging a phone overnight at this lower current seems to offer better battery Australia's electronics magazine life. If cut, the solder jumpers can be closed again using 0W M2012/0805 SMD resistors or a blob of solder. The PCB needs to be 2mm thick for the best fit. Two 1mm thickness PCBs are typically cheaper to manufacture, so some plated through-holes are provided to mechanically bond two boards together using solder. You can download the Gerber files for the PCB from www.siliconchip. au/Shop/6/130 Brandon Speedie, Alexandria NSW. ($80) siliconchip.com.au Circuit Ideas Wanted 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 Editor’s note: a 1N4004 diode can be used in place of the 1N4001 (D1). siliconchip.com.au Australia's electronics magazine August 2023  91 3D-printed and laser-cut cases for the Advanced Test Tweezers After building Tim Blythman’s Advanced Test Tweezers (siliconchip. au/Series/396), I thought it a pity that they didn’t have a case to protect and enhance the project. Two approaches came to mind: 3D-printed and lasercut acrylic. To make the cases as small as possible, the display is mounted slightly closer to the Tweezers’ legs than the 1mm mentioned in the construction notes in Tim’s article. When soldering the display, I used a thin piece of cardboard as a spacer, providing a 0.25mm air gap above the Tweezers’ legs. The laser-cut case is made from 2mm-thick clear acrylic. The finished case has two parts – the top and sides making up one assembly and the back and a half-side making the other. After laser cutting the shapes, the top and sides are superglued together, leaving the back and one-half of the section that goes between the Tweezers’ legs separate. The parts are arranged as shown in Fig.1. The untabbed end of the sides points toward the Tweezers’ arms, and the half-side piece with the extended ends belongs with the top section of the case. The remaining case piece is superglued to the back, on the end away from the screw hole. To ensure uniform support across the back of the Tweezers’ PCB, two small blocks are glued onto the inside of the back, diagonally across from the screw hole. The precise position isn’t important as long as they do not interfere with the Tweezers’ arms. 4mm inside the edges of the case (6mm inside the edges of the Perspex) is a good location. Leaving the protective film or paper on the outside surfaces until after gluing is completed minimises the amount of superglue that finds its way to where it shouldn’t be. Holding the panels in place with masking tape can make alignment easier for gluing. Once the parts are taped up, use a piece of wire to touch a small drop of superglue to every visible join on the outside. When these have thoroughly set, strip off the tape and dab glue on any remaining outside joins. Avoid gluing on the inside of the case, as it will be difficult to correct any errors. Remove the remaining protective film, and you should have a cleanly finished case. Any white ‘glue haze’ left after gluing can often be polished off with a wet cotton bud. If that isn’t sufficient, try a little Brasso. The three buttons are made by laminating two base and two stem pieces, as shown in Fig.2. To simplify alignment, holes have been cut through the centre of each button piece, allowing them to be threaded onto a piece of 1mm wire for gluing. As the wire will become glued to the acrylic pieces, the ends can be cut off and filed flat. If you intend to paint the buttons, use the wire protruding from the bottom of the button as a handle for painting and cut it off afterwards. Finish the buttons by rounding off the tops with a fine file or sandpaper. The case is just a little larger than the tweezers; a small piece of thin foam or felt in the back of the case may be needed to stop the Tweezers from rattling. The two sections of the case are secured using a 19mm-long screw and nut through the hole in the PCB that Tim thoughtfully provided for the purpose! My screw had a countersunk head, so I countersunk the top screw hole so that the head was flush with the case. Don’t overtighten the nut, as acrylic is prone to stress fractures. You can make an alternative version of the case if you have a 3D printer. For those with access to 3D printing facilities, I have designed a somewhat more elegant two-part case that snaps together and is readily split to change the battery. In the top part of the case, the screen’s PCB rests on lands near the edge, reducing the likelihood of damage to the fragile cover glass. As the Tweezers’ programming pins are optional, I made two versions of the rear part of the case: one with a slot for the programming pins to fit through and one without. 3D-printed buttons fit in the front of the case. My case was printed with PLA filament, which can have a slightly rough surface. To smooth the case’s exterior, spray the raw 3D print with a can of automotive composite body filler and primer and sand the case to a smooth finish with wet and dry sandpaper. Single-pack epoxy spray paint provides a more robust finish than regular spray paint. The buttons may be painted with ordinary coloured spray paint, as they are less likely to get knocked about. The laser-cutting details are available for download from siliconchip. com.au/Shop/6/228 as an SVG file, while the 3D-printed case is included as several STL files. Richard Palmer, Murrumbeena, Vic. ($100) Fig.1 (left): the laser-cut clear case. Fig.2 (below): how the acrylic buttons are made. The finished acrylic version of the Advanced Test Tweezers case. 92 Silicon Chip Australia's electronics magazine siliconchip.com.au Laboratory Power Supplies A GREAT RANGE of fixed and variable output power supplies at GREAT PRICES for hobbyist or industrial workbenches. 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Dual 0 to 16V 0 to 16V 0 to 5A 0 to 30V 0 to 15V 2 x 0 to 32V 0 to 27V 0 to 3A 0 to 36V 0 to 2.2A 0 to 5A 0 to 40A 2 x 0 to 3A 25A Current Limiting Display Single jaycar.com.au/laboratory-psu 1800 022 888 Prices correct at time of publication but are subject to change. Jaycar reserves the right to change prices if and when required. replacement bipolar transistor units Can a very simple circuit replace a mechanical vibrator in a vintage radio? Could early germanium power transistors from the 1960s be used in a design that would have been economical then? The answers to both questions are yes; here is how it would work. Part 3: by Dr Hugo Holden T his is the fourth & final full vibrator replacement design I’m presenting; the other three were described in the June and July 2023 issues and were based on Mosfets or Darlington transistors. This one is based on bipolar transistors; while it has an extremely elegant circuit, it’s the most difficult to build as it involves a custom-wound transformer and custom housing. As with the other designs, two rectifiers formed from four diodes replace the secondary switching contacts. Power switching circuits that use bipolar junction transistors (BJTs) without driver transformers have large energy losses in the base bias resistors. Fig.1: the vibrator primary replacement circuit comprises just two germanium PNP transistors, two resistors and a transformer. The transformer converts the 24V peak-to-peak output to a much lower voltage signal for driving the transistor bases and limits the base current, while the external transformer controls the oscillation. 94 Silicon Chip The required transistor base-­emitter current is in the order of 0.21A (210mA) because the maximum collector current (the primary side switching current) in this application is in the order of 2.1A (with my ZC1 Mk2 in transmit mode), and the transistors must be operated in saturated switching mode. As a rule of thumb, a 1:10 ratio of base current to collector current is required to ensure saturation. Here we can see one of the significant advantages of Mosfets in such a role, with their high-impedance (capacitive) gates. If the 0.21A base current is sourced from the fellow transistor’s collector, which is transformed up to 24V in use, the power dissipation is around 5W total in the two bias resistors. More efficient transfer of power to the transistor bases involves using a feedback transformer, as shown in the circuit diagram, Fig.1. The ASZ17 germanium PNP transistors I’m using have a collector-emitter saturation voltage drop of only 0.15V at 2A, which is favourable compared to its silicon transistor counterparts like the 2N3055, with a C-E drop of around 0.3V. Modern silicon power transistors can do a little better than this, but the ASZ17s are pretty close and undoubtedly impressive for their time. The transformer is a small ‘feedback transformer’ that fits inside a similar housing to the original vibrator. The configuration is a version of the Royer Oscillator. The feedback transformer transfers the appropriate amount of drive current to each transistor base on consecutive half-cycles from a potential that is stepped down from the 24V peak collector voltage to about 3.6V. So the total transistor base power for the two transistors is about 800mW. The power loss in the 680W bias resistors is about another 850mW (425mW each). The transistor losses are about 0.3W due to their low collector-­emitter saturation voltages. Fig.2: this shows how the vibrator replacement (including the four BY448 diodes for the secondary) connects to the external transformer. This is important to understand since the properties of that transformer are responsible for causing oscillation and determining the operating frequency. Australia's electronics magazine siliconchip.com.au The power losses in the four HT rectifiers (in transmit mode output current around 80mA) are about 200mW. So the total power loss is only about 2W, which, coincidentally, is practically identical to the original mechanical vibrator. Notice how pin 4 of the socket, the 12V power supply connection, is not used. The circuit is powered by the ZC1 unit’s main primary power transformer connections. No DC voltage is applied across this small coupling transformer’s primary, even if the oscillations stop due to an extreme overload. The transformer wire lead colours are also shown in Fig.1 since they match those on the physical transformer. Fig.2 shows the electrical configuration when the unit is plugged into the ZC1 Mk2 radio’s power supply. Starting from the premise that one transistor is conducting, the circuit oscillates because, as time passes, the main power transformer’s primary current begins to magnetically saturate the transformer’s core, suddenly increasing the transistor’s collector current. The induced voltage is proportional to the current’s rate of change with time or dI/dt, and this rate of change falls away with core saturation. Therefore, the voltage via the feedback transformer directed to the conducting transistor’s base drops rapidly, along with the base current, as magnetic saturation begins. This process is accelerated via positive feedback, and the transistor rapidly comes out of conduction. The drive voltages at the base-emitter junctions reverse polarity, and the other transistor is driven hard into saturation. The process repeats for another half cycle. On switch-on, due to the inexact matching of the transistors, the asymmetry in the current encourages initial small sinusoidal oscillations, which rapidly grow to establish stable saturated switching in less than half a second. The switching frequency is determined by the magnetic saturation properties of the main transformer core and works out to about 60Hz. That is a little slower than the original V6295 vibrator, which ran at about 100Hz. This does not matter, provided the 10µF filter electrolytic capacitors in the radio’s power supply circuit are in good condition. siliconchip.com.au While Fig.1 might appear to show the load being driven by the emitters, from an electrical perspective, the load is actually in the collector circuit with the power supply circuit acting in series. This is because the drive voltage is applied by the feedback transformer directly and independently to the transistor base/emitter connections. Some people have become confused, thinking that the transistors are being used as emitter-followers and therefore could not act as saturated switches. An actual emitter follower circuit is unsuited to saturated switching or for use in a Royer-style DC/DC converter application. Regarding diodes D1-D4, it is necessary to have a very high PIV diode rating. That’s in case the unit is plugged in and out while running (or has a bad connection to one of its socket pins). In that case, the undamped collapsing field of the main vibrator transformer can produce a peak voltage high enough to break down and destroy a single 1N4007 rated at 1kV. Two series 1N4007s are required to prevent this. BY448s are 1.5kV rectifiers for modern switch-mode power supply applications and are even better. Construction This transformer-based version is the most challenging vibrator replacement for the home constructor to build. The easiest to make is the self-­ oscillating Mosfet version described previously. The first step is manufacturing the tools required to make a UX7 base. This is done with two solid aluminium cylinders. I traced the original UX7 base pattern from a scan to create a template to mark the position of the pins. There are two fat pins and five thin pins. The tool makes both a carrier for a disc of circuit board material and a template to mark the holes. This can be rotated in the lathe to set its outer diameter to 36mm – see Photo 1. I made another aluminium piece to support the pins while I pressed them into the PCB discs (Photo 2). I set the hole for the fat pins at 3.95mm and 3.1mm for the thin pins. The pins are pressed as an interference fit into the PCB using the drill press and the carrier, with a small socket to do the pressing – see Photos 3 & 4. It is not necessary to rivet the Australia's electronics magazine Photo 1: I cut and etched these PCBs as a starting point for the 7-pin bases. The tool above them masks the areas where copper is to be preserved during etching. Carrier to support 7 pins Photo 2: I made this tool to press the pins onto the etched PCB disc using a drill press. Photo 3: the pins being pressed in. Note the socket mounted in the drill press chuck for that job. Photo 4: the completed custom UX7 bases. August 2023  95 ◀ Photo 6: a small lathe with an RPM indicator and revolution counter is a handy aid in winding transformers. Photo 5 (left): the BY448 diodes have been soldered in series across the appropriate pairs of pins, and the three extra wires (tinned copper wire surrounded by silicone insulation) have also been soldered in place. pins in as the press fit and soldering to the copper laminate on the PCB material impart the required strength. One reason I didn’t rivet the pins is that it can split the thin brass material they are made from. The above method creates a very stable and reliable UX7 base into which the BY448 diodes can be fitted (Photo 5). Only three wires pass from the base up into the unit, made from 0.71mm tinned copper with silicone rubber insulation. One is the Earth connection, while the other two go to the transistor emitters. You might be wondering why I didn’t use a prefabricated base like the Amphenol UX7 base I used in my previous vibrator replacement designs. The Amphenol bases are pretty thick, and there was a limit to how tall the unit could be and still fit in my ZC1 Mk2 transceiver. The space needed inside the canister to fit the transformer makes this more difficult. The Amphenol base could probably be made to work for a taller unit. The housing would need to be adjusted to be the right size to accept such a base. transformer core must be well away from magnetic saturation. It must also have a precise DC secondary resistance to avoid the need for additional resistors in the transistor’s base circuit. It must fit inside the machined aluminium housing (34mm internal diameter) that replaces the original V6295 vibrator. The transformer must also provide a good base drive current to the transistors’ bases to ensure they are saturated with a 2A collector current. This base current is around 150-250mA, a typical value being 210mA. A suitably-­ sized core is 1cm2 inside the bobbin with grain-oriented steel laminations. In this operating mode, the feedback transformer’s secondaries are effectively shorted out on each half cycle by the base-emitter voltage of about 0.45V. The DC load resistance is of the transformer wire itself. The electrical equivalent circuit for this somewhat unusual arrangement is shown in Fig.3. This indicates that the transformer naturally limits the base current to around 227mA. For this calculation, the primary value DC resistance is reflected onto the secondary winding by the impedance ratio, which is the square of the turns ratio. The drive voltage for the feedback transformer during operation is a 24V square wave at 60Hz. The diodes with forward voltages of 0.45V represent the base-emitter junctions of the ASZ17 transistors. The RMS current in each secondary winding is about 160mA, which is over the upper limit for the current carrying capacity of 32AWG wire (using the 500 circular mils per amp specification of 126mA for 32AWG wire). However, in this case, the total power dissipated in each winding is only about 270mW. Also, because of its physical size and external location on the bobbin, the winding barely gets warm, and there is no threat to the grade-2 enamel insulation. The generally accepted flux density (Webers/m2 or Teslas) for iron-cored low-frequency transformers is in the vicinity of 1T. The higher this value, the greater the chance of pushing the iron core into magnetic saturation. Transformer requirements and design The transformer must have specific properties. It must have an iron core due to the low operating frequency and a primary winding designed for a low core flux density. This is because the core saturation properties of the main power transformer determine the operating frequency, not the driver transformer. During each half of the squarewave cycle (about 8.3ms), the driver 96 Silicon Chip Fig.3: Rp, Rp’ and Rs are resistances inherent to the driver transformer; Rp is the primary winding resistance, Rp’ is that resistance reflected into the secondary and Rs is the secondary winding resistance. These limit the current into the transistor bases (shown as diodes) to about 227mA per the calculations. Australia's electronics magazine siliconchip.com.au Estimating transformer winding resistances ◀ Photo 7: the completed windings on the bobbins with clear Kapton tape over the top. This also depends on the magnetic properties of the iron core; some materials saturate before others. As noted, the feedback transformer mustn’t come anywhere near saturation. By selecting a modest value of 0.5T, we ensure that the core is well below saturation. I performed some calculations to verify this would be the case, but they are a bit long and complicated to present here. I also won’t go into other aspects of transformer design here, like leakage reactance, core losses, winding capacitances etc. Making the transformer Improved wire enamels and factors of economy have meant that the configuration of the typical power transformer has changed over the last century. Until the mid-1960s, even those transformers with very fine wire and thousands of turns were wound in perfect layers, with very thin rice paper like insulation between each layer. This had disadvantages as residual salts in the paper could, in conjunction with water vapour, cause corrosion of the copper wire. They also had higher inter-winding capacitances. Still, one can’t help but admire the winding perfection seen in these vintage transformers. Such windings are still used in oil-filled car ignition coils. The primary winding is wound onto the bobbin first with 2000 turns of 36AWG (0.125mm or 0.127mm diameter) enamelled copper wire. Then the secondaries are wound on bifilar, ensuring they have identical DC resistances of about 10.6W. This means that enough DC bias can be developed, in conjunction with the 680W resistors, for self-starting and to limit the base current to the correct value. The wire sizes and numbers of turns siliconchip.com.au You can estimate transformer winding DC resistances from the number of turns and the geometry of the bobbin. The number of turns per layer is closely approximated by the diameter of the wire (including its enamel) divided into the bobbin width. Dividing this number into the total number of turns gives us the number of layers, which is then multiplied again by the wire diameter to calculate the winding height. Once that is known, it is simple to calculate the average length of a turn bisecting the centre of the windings, assuming 90° turns (ie, a square bobbin). We can then multiply this value by the number of turns to calculate the length of the wire, then multiply that by the resistance per length for the wire used to get the actual resistance. Let’s go through this exercise for the primary winding of the feedback transformer. The bobbin is 16.55mm wide (measured) and the 36AWG wire diameter is 0.135mm, including its enamel (measured with a micrometer), so there are 122.6 turns per layer (16.55mm ÷ 0.135mm). A 2000 turn winding is 16.31 layers high, or close to 2.20mm (16.31 × 0.135mm). The inner bobbin, where the winding starts, measures 11.35 × 11.35 mm. Therefore, with a 2.2mm high winding, we have the geometry shown in Fig.4. The average turn length is 54.2mm (13.55mm × 4) and with 2000 turns, the wire length is 108.4m. 36AWG wire has a resistance of 1.361W/m, so the expected primary resistance is 147.5W (108.4 × 1.361W). The measured resistance of the actual wound transformer primary is very close, at 144W. So this method of estimation was within 3% of the actual value. Let’s apply the same principles to the two secondaries, which total 600 turns (two bifilar-wound 300-turn windings). The 32AWG wire on the micrometer measures 0.23mm in diameter. There are 71.95 turns per layer (16.55mm ÷ 0.23mm) and 8.34 layers (600 ÷ 71.95), for a thickness of 1.92mm (8.34 × 0.23mm). Adding this on top of 0.1mm insulation tape on top of the primary gives the geometry shown in Fig.5. The average turn length is therefore 71.48mm (17.87mm × 4), and there are 600 turns total, making the wire length 42.9m. 32AWG wire has a resistance of 0.5383W/m, so the total secondary resistance is expected to be 23W (0.5383W/m x 42.9m). This makes the calculated DC resistance of one 300t winding 11.5W, compared to a measured value of 10.6W, within 8.5%. The calculations slightly overestimate the DC resistance, more so on the secondary, because the windings are modelled as rectangular. In practice, the corners become more rounded as the winding height increases, shortening the wire length of each turn. Figs.4 & 5 show the total height of the windings as 4.22mm (2.2mm + 0.1mm + 1.92mm). The plastic bobbin is about 5.75mm high, so there is enough room for the outer coat of insulation seen in the photos. Fig.4: we can estimate the winding thickness and average turn length by assuming the primary windings are square. are such that the full bobbin volume is used with just enough room for the required insulation. I used a small lathe with an added turns counter and RPM meter (Photo 6) to wind the transformer. With practice, Australia's electronics magazine Fig.5: we assume the secondary windings are square and stacked on top of the primary and insulation, allowing us to estimate their thickness and average turn length. it is possible to make the windings very even, as shown in Photo 7. The 2000-turn primaries have been wound on, and two layers of polyimide (Kapton) tape have been applied. In general, when winding transformers, it August 2023  97 Photo 8: fibreglass tape makes connecting flying leads to the fine wire of the windings much easier. Photo 9: after adding more wires and fibreglass tape, the bobbins are complete and ready for the cores. Photo 10: Another layer of fibreglass tape covers the soldered wire connections. is important to keep the windings as regular and orderly as possible. The secondaries are then wound on bifilar and again, two layers of Kapton tape. Then add some special fibreglass tape (Scotch number 27, made by 3M and available from Hayman’s Electrical) to assist in terminating the wires to their flying leads, as shown in Photos 8 & 9. This fibreglass tape is also used to finish the bobbin as it is far superior to the usual yellow plastic transformer tape. The 32AWG secondary wire used here is insulated with nonself-fluxing tough grade 2 enamel that must be carefully scraped before soldering. The 36AWG primary wire has self-fluxing enamel. Photo 10 shows some finished bobbins. The bobbins can then be stacked with their laminations, the edges of which are lightly painted with Fertan organic rust converter. This deactivates any surface rust crystals on the cut lamination edges. I prepared transformer brackets to allow them to be mounted inside a 34mm diameter cylinder, made from ¼in-wide, 0.8mm-thick brass strip and ½in-wide, 0.6mm-thick brass strip (stocked in model shops). I folded the brass and soldered it to create the brackets shown in Photo 12. The transformer stack is a firm press-fit into the bracket and is also effectively glued to it by the varnishing process. Photo 13 shows the transformers ready for vacuum varnishing. While the transformers could simply be dipped in varnish, it is better to apply a vacuum. A full vacuum removing most of the ‘standard’ air pressure (1013hPa) is good, but it requires a pump. A vacuum of about two-thirds that can be attained with a simple syringe, a strong arm and a jam jar, as shown in Photo 14. This shows one of the transformers inside the jam jar full of polyurethane varnish, subjected to a partial vacuum. This causes the air to exit the small spaces in the transformer windings and the varnish to pass in. Pulling the syringe upwards expands a tiny air bubble into a large volume. As it is hard to hold it there for long, you can use a brass rod to lock the syringe plunger and allow 15 minutes for the multitude of fine air bubbles to exit the transformer. Finally, I hung the transformers up to air dry (Photo 15). This process could be sped up with an oven; however, I simply left them for one week. which is very close to 1mm in diameter and has a springy quality. If wound around a 22mm diameter cylinder, it springs back to about 42mm (Photo 17) and fits into the 0.5mm-deep groove in the housing. The top cover attaches with four countersunk 1/2in-long 1/8in BSW screws. Photo 18 shows the holes I drilled and tapped for the TO-3 (ASZ17) transistors and transformer brackets. The transformer mounting holes are tapped for 1/8in BSW and countersunk. The transistor collectors connect to the case and ground (negative), so there is no need for any insulating washers. Photo 11: the E-cores have now been slipped into the bobbins after coating them with rust converter. Photo 12: I fabricated the transformer brackets from brass strips of two different sizes (12.7 × 0.8mm and 6.35 × 0.6mm). 98 Silicon Chip Aluminium housings UP-Machining in Shenzhen, China, made the high-quality housings based on my drawings (Photo 16 & Figs.6-10). The UX7 base is retained by a wire clip made from #17 piano string wire, Australia's electronics magazine Assembly The 7-pin base is retained in the housing by the spring clip. As it is such a close fit, after applying polyurethane varnish on its edges and over the clip, it is extremely strong and impossible to rotate the base in the housing. The varnish could still be dissolved one day if disassembly was required. The base must be rotated to the correct position before the varnish dries to accommodate the rectangular top of the housing when plugged into the radio – see Photo 19. Photo 20 is a view into the unit before the transformer is inserted. Only three wires rise out of the base. The transformer is retained in the housing by two 1/2in-long 1/8in BSW Photo 13: some of the completed transformers, ready to be varnishimpregnated. siliconchip.com.au Parts List – Bipolar Vibrator Replacement 1 UX7 base (see text) 1 machined housing with hardware (see text) 1 custom-wound transformer (see below) 2 ASZ17 60V 10A PNP germanium transistors, TO-3 2 680W 1W resistors 4 BY448 1.5kV 2A axial diodes 1 300mm length of 0.7mm diameter tinned copper wire 1 300mm length of 1-2mm diameter heatshrink or spaghetti tubing 1 200mm length of #17 piano string wire (~1mm diameter spring wire) 4 ⅛in BSW × 10mm or ⅜in panhead machine screws 4 ⅛in x ½in BSW or 12mm countersunk head machine screws 2 10mm lengths of 1-2mm diameter green heatshrink tubing 2 10mm lengths of 1-2mm diameter blue heatshrink tubing 2 solder lugs various lengths of light-duty hookup wire Photo 14: drawing a partial vacuum on a transformer dipped in varnish allows the varnish to fill in all the gaps. Note the brass rod used to keep the plunger up against the force of the vacuum pulling it down. Transformer parts 1 EI-core transformer bobbin and lamination set, initial winding size 11.35 × 11.35 × 16.5mm 1 110m length of 0.125mm (36AWG) diameter enamelled copper wire 2 22m lengths of 0.2mm (32AWG) diameter enamelled copper wire 1 30cm length of ¼in (6.35mm) wide, 0.8mm-thick brass strip 1 30cm length of ½in (12.7mm) wide, 0.6mm-thick brass strip 2 ⅛in BSW × 10mm or ⅜in countersunk head machine screws and hex nuts 1 small roll of 0.1mm thick polyimide (Kapton) insulating tape 1 small roll of Scotch number 27 fibreglass tape 1 small tin of polyurethane varnish Photo 18: I drilled holes for mounting the TO-3 transistors, the transistor leads and the transformer mounting holes in the cases. The transformer mounting holes are countersunk. Photo 15: the transformers were hung for a week to let the varnish fully cure. 42 mm Photo 16: the aluminium housings and lids, ready to accept the electronic components. siliconchip.com.au Photo 17: after bending 1mm diameter piano wires around a 22mm cylindrical former, they spring back to around 42mm in diameter. They can then be recompressed to fit into the groove in the housing and will expand to prevent the base from falling out. Australia's electronics magazine Photo 19: after placing the UX7 base that I made and inserting the spring clip, I applied varnish and let it cure so the clip couldn’t be accidentally knocked loose. August 2023  99 Photo 20: an inside view of the housing with the plug in place. slot head countersunk screws with nuts and spring washers. Solder lugs are placed between the transformer mounts and the inside of the aluminium housing as the solder tie points for the two 680W 1W resistors and ground, and the black ground wire from pin 7 on the base. The transistors can then be screwed to the case with 3/8in-long 1/8in BSW panhead screws. The transistor base and emitter leads have a protective silicone rubber insulating sleeve applied, green for the base and blue for the emitters. The emitters connect to the blue wires leading to pins 1 and 6 in the base, as shown in Photo 21. It is best to use a 1W resistor for reliability, as the dissipation in each resistor is 426mW, and then taking into consideration the enclosed space they operate in. The top cover can then be fitted, as shown in Photos 22 & 23. Photo 24 shows the unit working in a ZC1 Mk2 communications receiver. It looks the part and suits the rugged character of the radio. Performance Scope 1 is a dual-trace recording of the emitter waveforms of the two ASZ17s (ie, the ZC1’s primary transformer connections) with the unit running in receive mode. It oscillates at close to 60Hz, with a very clean switching waveform. The 12.4V across half of the transformer primary plus the 12.4V supply voltage results in about 24.8V appearing on one transistor’s emitter while the other is conducting. After a time, due to the magnetic saturation of the ZC1’s transformer core, the induced voltage suddenly starts to fall. This takes the conducting transistor out of conduction, and the other goes into conduction for the next half-cycle. The base drive current for each ASZ17 transistor is around 210mA and the collector current in receive mode is about 1A. To see how well the Photo 21: the electronic components are now in place; only a few junctions need to be soldered. One end of each resistor goes to ground via a transformer mounting screw to the case (along with the ground lead), and the transistor collectors are in intimate contact with the case. Six solder joints are required, four on the transistor base and emitter leads. Photo 23: the completed bipolar transistor vibrator units look rugged, with the two TO-3 package germanium PNP transistors mounted on the outside of a machined aluminium case. Photo 22: the completed vibrator replacement ready for testing and use. Photo 24: the industrial look of the vibrator replacement unit suits the appearance of my ZC1 Mk2 communications receiver very well! 100 Silicon Chip Australia's electronics magazine siliconchip.com.au Fig.8: isometric view of the machined housing. Fig.6: a side view of the machined aluminium housing for the vibrator replacement. The holes drilled into the sides for mounting the TO-3 transistors and transformer are not shown. Fig.9: plan view of the lid for the machined housing. Fig.10: details of the grooves in the base of the housing. The square inner grooves are for the UX7 base, while the rounded outer groove engages clips in the radio to retain the unit. Fig.7: a top view of the machined housing. siliconchip.com.au Australia's electronics magazine August 2023  101 +25V Emitter Voltage ASZ17 (1) +100mV 0V 0V ASZ17 C-E saturation voltage Collector current 1A, Receive mode ZC1 XFMR Core Saturation begins +25V Emitter Voltage ASZ17 (2) +100mV 0V 0V Transistor Collector – Emitter – Saturation Scope 1: the transistor emitter (external transformer primary) voltages during operation. The switching frequency is measured as 60.4Hz. transistors were saturating, I wound the scope gain up to 100mV/div on DC, giving the result shown in Scope 2. This shows the very low collector-­ emitter saturation voltage of the ASZ17 germanium power transistors. In transmit mode, the collector current is about doubled to 2A, and the saturation voltage increases slightly to 150mV (Scope 3). If these were Mosfets, that would correspond to an RDS(on) of 75mW. The oscillation frequency slows a little bit due to the additional loading. In transmit mode, the power loss in each transistor is about 0.3W (2A × 0.15V). The base-emitter power is 0.0945W (0.21A × 0.45V), so the dissipation in each transistor is only about 400-600mW (there are some additional losses during the switching transitions). So the whole assembly runs very cool on account of the size of the metal housing. The waveform in Scope 4 was taken with an isolated scope across Scope 2: by increasing the sensitivity of the oscilloscope compared to Scope 1, we can see the transistor collectoremitter saturation voltages are just over 100mV at just over 1A. That’s good for an obsolete germanium transistor. the coupling transformer primary, between pins 1 and 6 of the device. It is a 48V peak-to-peak rectangular wave. The radio’s HT measures +243V DC with only 70mV of ripple (see Scope 5). My radio has been upgraded with 25µF filter capacitors, so with the original 10µF capacitors, the ripple would be a little higher. Still, this is a very low figure for this type of power supply. The electronic vibrator replacement gives an HT of about 10V or 4% higher than the original V6295 vibrator in receive mode (with the sender switch on). This is to be expected, as the mechanical unit can’t quite reach a full 50% duty cycle due to its contact gaps and the time that neither contact is closed. In transmit mode, the output voltage from the electronic unit is about 14-15% higher than the original unit. So this electronic unit is superior overall to the electromechanical V6295. RECEIVE MODE VOLTAGES WITH ELECTRONIC V6295: +244.6V DC AC Ripple, 120Hz Approx. 3Vpp NOTE: -68V rail is ZERO in transmit mode and main output voltage at junction of L9B and L20A is +288V ELECTRONIC V6295 L20A +12.1V 0V +243V DC AC Ripple, Approx. 70mVpp Scope 4: connecting an isolated ‘scope across the two emitters, we see that they are generating a relatively clean 48V peak-to-peak square wave. 102 Silicon Chip -68.3V DC AC Ripple, Approx. 100mVpp Scope 5: three views of the ripple out of the transceiver’s power supply with the vibrator replacement operating. The amplitude is low and will not interfere with the set’s operation. Australia's electronics magazine siliconchip.com.au +150mV ASZ17 C-E saturation voltage drop, transmit mode, Collector current 2A 0V VIBRATOR TRANSFORMER 3/IT/9 47W 5W +150mV 12V 1.5W 400μF 2N3055 Scope 3: the same scenario as Scope 2 but with the ZC1 Mk2 in transmit mode, where the transistor collector current is a little over 2A. The saturation voltages have increased to a little over 150mV. Note that the 470nF tuning capacitor used in the oscillator-driven Mosfet-­ based vibrator replacement presented last month is not required here. Scopes 6 & 7 show the switching transients with this unit. Likely, because the transistors in the self-oscillating version do not switch-on as abruptly, or switch-off as quickly, as the oscillator-driven versions, there is more damping during the change-over time, suppressing the switching transients on the transformer primary. Also, should the oscillation stop for some reason (perhaps due to an overload), the base and collector currents Another BJT-based vibrator replacement Fig.11 shows a circuit for a 2N3055 silicon bipolar transistor-based vibrator replacement, originally published in Electronics Australia magazine, October 1975 (pages 58-61). As presented then, it was built on tag strips mounted on a large metal plate – much bigger than the original vibrator, making it a bit impractical. Notice the R-C snubber networks on the transistor collectors. Without these, because of the high transition frequency of the silicon transistor EM401 150W 16μF (compared to a germanium transistor), the circuit is unstable and bursts into oscillation at a high frequency. However, those snubber networks can be omitted if each 2N3055 has a 100nF collector-to-base feedback capacitor. Since the base drive is acquired from the opposite transistor’s collector, the dissipation in the 47W resistors is very high at around 5W and only just below the resistor ratings. So it is substantially less efficient at acquiring the transistor’s base drive than the ASZ17 circuit and much less efficient overall. This is why I did not use the EA design, but came up with SC my own. ASZ17/TRANSFORMER UNIT Scope 6: even without a tuning capacitor across the radio’s transformer primary, overshoot and ringing are well under control thanks to the gentle transition characteristics of the ASZ17 transistors in this configuration. siliconchip.com.au 150W 1.5W Fig.11: the EA October 1975 Solid-State Vibrator circuit. It works but is very inefficient, with each base resistor dissipating almost 5W. This shows why the transformer is necessary for my version. are too low to cause any trouble. ASZ17/TRANSFORMER UNIT 47W 5W 2N3055 EM401 16μF 0V 400μF Scope 7: a close-up of Scope 6 with a faster timebase showing the transition in detail. The overshoot is only a few volts and dampens out after just a couple of cycles. Australia's electronics magazine August 2023  103 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 194, MATRAVILLE, NSW 2036 (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. 08/23 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 Digital FX Unit (Apr21) Si473x FM/AM/SW Digital Radio (Jul21), 110dB RF Attenuator (Jul22) Basic RF Signal Generator (Jun23) ATmega328P-AUR RGB Stackable LED Christmas Star (Nov20) ATtiny85V-10PU Shirt Pocket Audio Oscillator (Sep20) PIC10F202-E/OT Ultrabrite LED Driver (with free TC6502P095VCT IC, Sep19) PIC10LF322-I/OT Range Extender IR-to-UHF (Jan22) PIC12F1572-I/SN LED Christmas Ornaments (Nov20; versions), Nano TV Pong (Aug21) PIC12F617-I/P Model Railway Level Crossing (two required – $15/pair) (Jul21) Range Extender UHF-to-IR (Jan22), Active Mains Soft Starter (Feb23) Model Railway Uncoupler (Jul23) PIC12F617-I/SN Model Railway Carriage Lights (Nov21) PIC12F675-I/P Train Chuff Sound Generator (Oct22) PIC16F1455-I/P Digital Lighting Controller Slave (Dec20), Auto Train Controller (Oct22) GPS Disciplined Oscillator (May23) PIC16LF1455-I/P New GPS-Synchronised Analog Clock (Sep22) PIC16F1459-I/P Cooling Fan Controller (Feb22), Remote Mains Switch Receiver (Jul22) PIC16F1459-I/SO Multimeter Calibrator (Jul22), Buck/Boost Charger Adaptor (Oct22) PIC16F15214-I/SN Tiny LED Icicle (Nov22), Digital Volume Control Pot (SMD; Mar23) Silicon Chirp Cricket (Apr23) PIC16F15214-I/P Digital Volume Control Pot (through-hole; Mar23) PIC16F1705-I/P Flexible Digital Lighting Controller (Oct20) Digital Lighting Controller Translator (Dec21) PIC16F18146-I/SO Digital Boost Regulator (Dec22) PIC16LF15323-I/SL Remote Mains Switch Transmitter (Jul22) W27C020 Noughts & Crosses Computer (Jan23) ATSAML10E16A-AUT PIC16F18877-I/P PIC16F18877-I/PT High-Current Battery Balancer (Mar21) USB Cable Tester (Nov21) Dual-Channel Breadboard PSU Display Adaptor (Dec22) Wideband Fuel Mixture Display (WFMD; Apr23) PIC16F88-I/P Battery Charge Controller (Jun22), Railway Semaphore (Apr22) PIC24FJ256GA702-I/SS Ohmmeter (Aug22), Advanced SMD Test Tweezers (Feb23) 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 AM-FM DDS Signal Generator (May22) dsPIC33FJ64MC802-E/SP dsPIC33FJ128GP306-I/PT PIC32MX470F512H-I/PT PIC32MX470F512H-120/PT PIC32MX470F512L-120/PT 1.5kW Induction Motor Speed Controller (Aug13) CLASSiC DAC (Feb13) Stereo Echo/Reverb (Feb 14), Digital Effects Unit (Oct14) Micromite Explore 64 (Aug 16), Micromite Plus (Nov16) Micromite Explore 100 (Sep16) $25 MICROS $30 MICROS PIC32MX695F512H-80I/PT Touchscreen Audio Recorder (Jun14) PIC32MZ2048EFH064-I/PT DSP Crossover/Equaliser (May19), Low-Distortion DDS (Feb20) DIY Reflow Oven Controller (Apr20), Dual Hybrid Supply (Feb22) KITS, SPECIALISED COMPONENTS ETC CALIBRATED MEASUREMENT MICROPHONE (AUG 23) SMD version kit: includes the PCB and all onboard components except the XLR socket. You also need one ECM set (see below) (Cat SC6755) $22.50 Through-hole version kit: includes the PCB and all onboard components except the XLR socket. You also need one ECM set (see below) (Cat SC6756) $25.00 Calibrated ECM set: includes the mic capsule and compensation components; see pages 71 & 73, August 2023 issue, for the ECM options (Cat SC6760-5) $12.50 ARDUINO ESR METER (AUG 23) - 20x4 blue backlit LCD with I2C interface (Cat SC4203) - red & black PCB-mount banana sockets (two sets are needed; Cat SC4983) - two 1nF ±1% capacitors (Cat SC4273) DYNAMIC RFID/NFC TAG (JUL 23) RECIPROCAL FREQUENCY COUNTER KIT (CAT SC6633) (JUL 23) Smaller (purple PCB) kit: includes PCB, tag IC and passive parts (Cat SC6747) Larger (black PCB) kit: includes PCB, tag IC and passive parts (Cat SC6748) (JUN 23) Kit: includes everything but the case, battery and optional pot (Cat SC6656) - 0.96in SSD1306-based yellow/blue OLED (Cat SC6421) GPS DISCIPLINED OSCILLATOR (MAY 23) - CH340G-based USB/serial module with panel-mount USB ext. (Cat SC6736) - NEO-7M GPS module with SMA connector (Cat SC6737) - GPS antenna with 3m cable and SMA connector (Cat SC6738) - DD4012SA 12V to 7.5V buck-converter module (Cat SC6339) SONGBIRD KIT (CAT SC6633) (MAY 23) Includes all parts required, except the base/stand (see page 86, May 2023) DUAL RF AMPLIFIER KIT (CAT SC6592) (MAY 23) SILICON CHIRP CRICKET (CAT SC6620) (APR 23) TEST BENCH SWISS ARMY KNIFE (APR 23) Includes the PCB and all onboard parts (see page 34, May 2023) Complete kit: includes all parts required, except the coin cell & ICSP header Does not include ESP32 module, case, 10A relay or connectors (Cat SC6589) - ESP32 DevKitC module with WiFi and Bluetooth (Cat SC4447) - 3mm black laser-cut UB1 Jiffy box lid (Cat SC6337) WIDEBAND FUEL MIXTURE DISPLAY (CAT SC6721) (APR 23) DIGITAL VOLUME CONTROL POTENTIOMETER (MAR 23) $5.00 $7.50 $100.00 $10.00 $15.00 $20.00 $10.00 $5.00 $30.00 $25.00 $25.00 Short-form kit: includes PCB, all onboard SMDs, boost module, SIP reed relay & UB1 lid. $50.00 $10.00 $10.00 Short-form kit: includes the PCB and all onboard parts. Does not include the case, O2 sensor, wiring, connectors etc (see page 47, April 2023) $120.00 SMD version kit: includes all relevant parts except the $15.00 universal remote control and activity LED (Cat SC6623) $6.00/set Through-hole version kit: includes all relevant parts (with SMD PGA2311) $2.50 except the universal remote control and activity LED (Cat SC6624) Includes all parts, except the case, TCXO and AA cells (see page 57, July 2023) $60.00 BASIC RF SIGNAL GENERATOR siliconchip.com.au/Shop/ ACTIVE MAINS SOFT STARTER (FEB 23) ADVANCED SMD TEST TWEEZERS KIT (CAT SC6631) (FEB 23) Q METER SHORT-FORM KIT (CAT SC6585) (JAN 23) RASPBERRY PI PICO W BACKPACK (JAN 23) $60.00 $70.00 Hard-to-get parts: includes the PCB, transformer, relay, thermistor, programmed micro and all other semiconductors (Cat SC6575; see page 41, February 2023) $100.00 Includes all parts (except coin cell and CON1) (see page 51, February 2023) $45.00 Includes the PCB, all required onboard parts (excluding optional debug interface) and the front panel. Just add a signal source, case, power supply and wiring $100.00 Complete kit: includes all parts in the parts list, except the DS3231 real-time clock IC (Cat SC6625; see page 56, January 2023) - DS3231 real-time clock SOIC-16 IC (Cat SC5103) - DS3231MZ real-time clock SOIC-8 IC (Cat SC5779) DUAL-CHANNEL BREADBOARD PSU $85.00 $7.50 $10.00 (DEC 22) Power Supply kit: complete kit with a choice of red + green, yellow + cyan or orange + white knob colours (Cat SC6571; see page 38, December 2022) Display Adaptor kit: complete kit (Cat SC6572; see page 45, December 2022) NEW GPS(/WIFI)-SYNCHRONISED ANALOG CLOCK $40.00 $50.00 (SEP & NOV 22) GPS-version kit: includes everything in the parts list with the VK2828 GPS module (Cat SC6472; see September 2022 p63) $55.00 WiFi-version kit: includes everything in the parts list with the D1 Mini module instead (Cat SC6472; D1 Mini is supplied not programmed, see November 2022 p76) $55.00 *Prices valid for month of magazine issue only. All prices in Australian dollars and include GST where applicable. # Overseas? Place an order on our website for a quote. PRINTED CIRCUIT BOARDS & CASE PIECES PRINTED CIRCUIT BOARD TO SUIT PROJECT ULTRASONIC CLEANER MAIN PCB ↳ FRONT PANEL NIGHT KEEPER LIGHTHOUSE SHIRT POCKET AUDIO OSCILLATOR ↳ 8-PIN ATtiny PROGRAMMING ADAPTOR D1 MINI LCD WIFI BACKPACK FLEXIBLE DIGITAL LIGHTING CONTROLLER SLAVE ↳ FRONT PANEL (BLACK) LED XMAS ORNAMENTS 30 LED STACKABLE STAR ↳ RGB VERSION (BLACK) DIGITAL LIGHTING MICROMITE MASTER ↳ CP2102 ADAPTOR BATTERY VINTAGE RADIO POWER SUPPLY DUAL BATTERY LIFESAVER DIGITAL LIGHTING CONTROLLER LED SLAVE BK1198 AM/FM/SW RADIO MINIHEART HEARTBEAT SIMULATOR I’M BUSY GO AWAY (DOOR WARNING) BATTERY MULTI LOGGER ELECTRONIC WIND CHIMES ARDUINO 0-14V POWER SUPPLY SHIELD HIGH-CURRENT BATTERY BALANCER (4-LAYERS) MINI ISOLATED SERIAL LINK REFINED FULL-WAVE MOTOR SPEED CONTROLLER DIGITAL FX UNIT PCB (POTENTIOMETER-BASED) ↳ SWITCH-BASED ARDUINO MIDI SHIELD ↳ 8X8 TACTILE PUSHBUTTON SWITCH MATRIX HYBRID LAB POWER SUPPLY CONTROL PCB ↳ REGULATOR PCB VARIAC MAINS VOLTAGE REGULATION 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 DATE SEP20 SEP20 SEP20 SEP20 SEP20 OCT20 OCT20 OCT20 NOV20 NOV20 NOV20 NOV20 NOV20 DEC20 DEC20 DEC20 JAN21 JAN21 JAN21 FEB21 FEB21 FEB21 MAR21 MAR21 APR21 APR21 APR21 APR21 APR21 MAY21 MAY21 MAY21 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 PCB CODE 04105201 04105202 08110201 01110201 01110202 24106121 16110202 16110203 16111191-9 16109201 16109202 16110201 16110204 11111201 11111202 16110205 CSE200902A 01109201 16112201 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 Price $7.50 $5.00 $5.00 $2.50 $1.50 $5.00 $20.00 $20.00 $3.00 $12.50 $12.50 $5.00 $2.50 $7.50 $2.50 $5.00 $10.00 $5.00 $2.50 $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 For a complete list, go to siliconchip.com.au/Shop/8 PRINTED CIRCUIT BOARD TO SUIT PROJECT CAPACITOR DISCHARGE WELDER POWER SUPPLY ↳ CONTROL PCB ↳ ENERGY STORAGE MODULE (ESM) PCB 500W AMPLIFIER MODEL RAILWAY SEMAPHORE CONTROL PCB ↳ SIGNAL FLAG (RED) AM-FM DDS SIGNAL GENERATOR SLOT MACHINE HIGH-POWER BUCK-BOOST LED DRIVER ARDUINO PROGRAMMABLE LOAD SPECTRAL SOUND MIDI SYNTHESISER REV. UNIVERSAL BATTERY CHARGE CONTROLLER VGA PICOMITE SECURE REMOTE MAINS SWITCH RECEIVER ↳ TRANSMITTER (1.0MM THICKNESS) MULTIMETER CALIBRATOR 110dB RF ATTENUATOR WIDE-RANGE OHMMETER WiFi PROGRAMMABLE DC LOAD MAIN PCB ↳ DAUGHTER BOARD ↳ CONTROL BOARD MINI LED DRIVER NEW GPS-SYNCHRONISED ANALOG CLOCK BUCK/BOOST CHARGER ADAPTOR 30V 2A BENCH SUPPLY MAIN PCB ↳ FRONT PANEL CONTROL PCB AUTO TRAIN CONTROLLER ↳ TRAIN CHUFF SOUND GENERATOR PIC16F18xxx BREAKOUT BOARD (DIP-VERSION) ↳ SOIC-VERSION AVR64DD32 BREAKOUT BOARD LC METER MK3 ↳ ADAPTOR BOARD DC TRANSIENT SUPPLY FILTER TINY LED ICICLE (WHITE) DUAL-CHANNEL BREADBOARD PSU ↳ DISPLAY BOARD DIGITAL BOOST REGULATOR ACTIVE MONITOR SPEAKERS POWER SUPPLY PICO W BACKPACK Q METER MAIN PCB ↳ FRONT PANEL (BLACK) NOUGHTS & CROSSES COMPUTER GAME BOARD ↳ COMPUTE BOARD ACTIVE MAINS SOFT STARTER ADVANCED SMD TEST TWEEZERS SET DIGITAL VOLUME CONTROL POT (SMD VERSION) ↳ THROUGH-HOLE VERSION MODEL RAILWAY TURNTABLE CONTROL PCB ↳ CONTACT PCB (GOLD-PLATED) WIDEBAND FUEL MIXTURE DISPLAY (BLUE) TEST BENCH SWISS ARMY KNIFE (BLUE) SILICON CHIRP CRICKET GPS DISCIPLINED OSCILLATOR SONGBIRD (RED, GREEN, PURPLE or YELLOW) DUAL RF AMPLIFIER (GREEN or BLUE) LOUDSPEAKER TESTING JIG BASIC RF SIGNAL GENERATOR (AD9834) ↳ FRONT PANEL V6295 VIBRATOR REPLACEMENT PCB SET DYNAMIC RFID / NFC TAG (SMALL, PURPLE) ↳ NFC TAG (LARGE, BLACK) RECIPROCAL FREQUENCY COUNTER MAIN PCB ↳ FRONT PANEL (BLACK) PI PICO-BASED THERMAL CAMERA MODEL RAILWAY UNCOUPLER MOSFET VIBRATOR REPLACEMENT DATE MAR22 MAR22 MAR22 APR22 APR22 APR22 MAY22 MAY22 JUN22 JUN22 JUN22 JUN22 JUL22 JUL22 JUL22 JUL22 JUL22 AUG22 SEP22 SEP22 SEP22 SEP22 SEP22 OCT22 OCT22 OCT22 OCT22 OCT22 OCT22 OCT22 OCT22 NOV22 NOV22 NOV22 NOV22 DEC22 DEC22 DEC22 DEC22 JAN23 JAN23 JAN23 JAN23 JAN23 FEB23 FEB23 MAR23 MAR23 MAR23 MAR23 APR23 APR23 APR23 MAY23 MAY23 MAY23 JUN23 JUN23 JUN23 JUN23 JUL23 JUL23 JUL23 JUL23 JUL23 JUL23 JUL23 PCB CODE 29103221 29103222 29103223 01107021 09103221 09103222 CSE211002 08105221 16103221 04105221 01106221 04107192 07107221 10109211 10109212 04107221 CSE211003 04109221 04108221 04108222 18104212 16106221 19109221 14108221 04105221 04105222 09109221 09109222 24110222 24110225 24110223 CSE220503C CSE200603 08108221 16111192 04112221 04112222 24110224 01112221 07101221 CSE220701 CSE220704 08111221 08111222 10110221 04106221/2 01101231 01101232 09103231 09103232 05104231 04110221 08101231 04103231 08103231 CSE220602A 04106231 CSE221001 CSE220902B 18105231/2 06101231 06101232 CSE230101C CSE230102 04105231 09105231 18106231 Price $5.00 $5.00 $5.00 $25.00 $2.50 $2.50 $7.50 $5.00 $5.00 $5.00 $7.50 $7.50 $5.00 $7.50 $2.50 $5.00 $5.00 $7.50 $7.50 $5.00 $10.00 $2.50 $5.00 $5.00 $7.50 $2.50 $2.50 $2.50 $2.50 $2.50 $2.50 $7.50 $2.50 $5.00 $2.50 $5.00 $5.00 $5.00 $10.00 $5.00 $5.00 $5.00 $12.50 $12.50 $10.00 $10.00 $2.50 $5.00 $5.00 $10.00 $10.00 $10.00 $5.00 $5.00 $4.00 $2.50 $12.50 $5.00 $5.00 $5.00 $1.50 $4.00 $5.00 $5.00 $5.00 $2.50 $2.50 CALIBRATED MEASUREMENT MICROPHONE (SMD) ↳ THROUGH-HOLE VERSION ARDUINO ESR METER (STANDALONE VERSION) ↳ COMBINED VERSION WITH LC METER WATERING SYSTEM CONTROLLER AUG23 AUG23 AUG23 AUG23 AUG23 01108231 01108232 04106181 04106182 15110231 $2.50 $2.50 $5.00 $7.50 $12.50 NEW PCBs We also sell the Silicon Chip PDFs on USB, RTV&H USB, Vintage Radio USB and more at siliconchip.com.au/Shop/3 ASK SILICON CHIP Got a technical problem? Can’t understand a piece of jargon or some technical principle? Drop us a line and we’ll answer your question. Send your email to silicon<at>siliconchip.com.au GPS Analog Clock Driver time errors I had a problem with a sweep clock fitted with the GPS Analog Clock Driver (September 2022; siliconchip. au/Series/391) not keeping time, so I built another board with a standard tick mechanism. Both work well and keep time for the first 36 hours, then between 36h and 72h, both clocks run slow and never recover at the 72h synchronisation. I have logged the error to internet time as follows for the two clocks: Time passed Step move. error Sweep move. error 0h 0s 2s 11h -5s -36s 12h 0s 2s 35h 6s 0s 36h 0s 2s 60h -48s -69s 72h -50s -110s The behaviour on the sweep clock appears to be repeatable; this is the third time it has been reset; each time, it tracks GPS/internet time for the first 36 hours before losing synchronisation by a significant margin. I’d appreciate your views on what can be done to diagnose the problem. They both have new batteries measuring 1.5V, and no synchronisations have been missed during the 72 hours so far. (D. C., Tauranga, NZ) ● Geoff Graham responds: I don’t have a good explanation for this. The sudden errors do not make sense, especially considering that they happened similarly in two different movements. However, I can make some suggestions. First, it is important to note that the firmware accurately keeps track of the movement’s hands; it cannot suddenly skip or add pulses to the output stream. Nearly always, the reason that a clock runs slow is because the movement is not responding to the 106 Silicon Chip pulse stream. That could be because of excessive friction, debris like plastic flakes caught in the gears etc. After publishing the article, we discovered that some sweep clocks require extra-wide pulses in the drive signal and without that, they will stall at some point. This might be the reason for your problem with the sweep movement. The V1.2 firmware released in January 2023 and incorporated into kits made since then adds options to deal with that. This still leaves the errors in the stepping clock. My first suggestion is to open the movement and ensure it is thoroughly clean. Secondly, let it run for longer to see if the errors are corrected. The first synchronisation occurs after 12 hours and the delay is increased by 24 hours on each sync until it is capped at five days. So the times between synchronisations are 12h, 36h, 50h, 74h, 98h etc. Letting it run longer might allow the firmware time to detect and correct the errors you observed (assuming the fault is not in the clock’s movement). I’m sorry that I cannot offer a definite fix. It seems that more experimenting and testing on your part will be required. Driving stepper motor for analog clock I want to build a clock driven by a stepper motor, say the 5V XC4458 stepper from Jaycar. The stepper would pulse a minute hand geared to the hour hand. I want to use your GPS Analog Clock project from September 2022 with the WiFi option (ESP8266 D1 Mini; described in November 2022). I want to drive it from a 12V DC supply regulated to 5V. I believe all the modules can be powered by 5V, so I can dispense with the MCP16251 DC/DC boost converter. The PIC and op amp can run from 5V. I could make an interface to the stepper drive board from the MCP6041 op amp’s output. Does that seem like a feasible project? (F. C., Maroubra, NSW) Australia's electronics magazine ● Geoff Graham responds: it does sound reasonable except for two factors. Firstly, the firmware generates pulses once a second, so a rewrite of the firmware would be required. The second is that the stepper motor would draw a lot of power, so it could not be battery-powered. If you do not require battery power, you could make a much simpler project with a Micromite or PicoMite getting the time from the ESP8266 D1 Mini and driving the stepper motor. It would probably need less than 50 lines of BASIC code. Troubleshooting Wide Range Ohmmeter Phil Prosser has helped me troubleshoot his Wide-Range Ohmmeter project (August & September 2022; siliconchip.au/Series/384). I have been making progress but it still isn’t working correctly yet. I have reflowed the solder joints for IC1, IC2 & IC4. The 2.5V rail is correct. The calibration sequence isn’t quite right concerning the Enter and Select switches. To start the calibration procedure, either switch works. The Select switch doesn’t change the value; it jumps to the next range. The Enter switch sort of changes the value; it jumps around a bit while Select and Enter together toggles the direction. There is no short between the switches. They trace out OK to the input pins of PIC. I don’t get the “Over Range check sense conn” message on power-up as per the article. It says “19.9166 Meg Ohm”. Following the fault-­ finding chart in the article, the current between the anode of diode D3 and pin 3 of IC3 measures 50mA regardless of open/short on the Sense terminals. That is the biggest clue so far. I’ve tried to trace through the relays back to D3 and everything looks OK. I’ve checked that all components are in the correct position/value. Currently, I get the following readings when measuring the calibration resistors: siliconchip.com.au Fast and reliable temperature measurement. Digital Thermometers We stock a GREAT RANGE of thermometers, at GREAT VALUE, for domestic or commercial applications. MEASURE TEMPERATURES IN HOT, HAZARDOUS OR HARD TO REACH PLACES HELPS YOU AVOID FOOD FROM SPOILING FRIDGE/FREEZER THERMOMETER • -50°C to 70°C range • Min and max alarm function QM7209 JUST 34 $ Non-Contact Thermometer 95 • -50°C to 500°C range • 12:1 distance to spot ratio • Built-in laser pointer • Max, min, & auto data hold QM7410 JUST 5995 $ WATCH OVER THE TEMPS IN DIFFERENT ROOMS SUITABLE FOR THE LAB, WORKSHOP OR IN THE FIELD WIRELESS IN/OUT THERMOMETER/HYGROMETER • -45°C to 65°C (Outdoor), 0°C to 60°C (Indoor) range • 1% to 99% relative humidity range • Connect up to 3 sensors XC0322 JUST 4695 $ • -50°C to 750°C range • Built-in temperature sensor • K-type thermocouple input QM1602 RECORD AND STUDY TEMPS OVER TIME TEMPERATURE & HUMIDITY DATA LOGGER • -40°C to 70°C temp / 0-100% relative humidity range • 32,000 sample memory • Records at prescribed intervals • Easy USB interface QP6013 Shop at Jaycar for: Thermometer with K-Type Thermocouple • Thermometers & Thermocouples • Non-contact Thermometers • Probe/Stem Thermometers ONLY 129 $ JUST 4995 $ Includes Thermocouple • Digital Multimeters with Temperature • Desktop Temperature/Hygrometers • Weather Stations Explore our wide range of temperature measurement products, in stock at over 110 stores and 130 resellers or on our website. jaycar.com.au/thermometers 1800 022 888 Prices correct at time of publication but are subject to change. Jaycar reserves the right to change prices if and when required. 27.4W: 0.0013W 2.94kW: 0.1592W 97.6kW: 716W 976kW: 1067.67W 10MW: 10MW (B. H., Craigmore, SA) ● Phil Prosser responds: I think something is wrong with the relay switching. Have you checked that the transistors are all the right parts? Are the 1N914 (or 1N4148) diodes in the right way around? Have you melted the corner of a relay by touching it with your iron? I did that once and was surprised by how little external damage killed the relay. A constant current source drives the sense lines if the meter is in the low ohms range. If the sense lines are open, the relay should switch up a range and eventually into the high ohms range. So the 50mA reading makes sense but not with an open circuit. Hence my determination is that one relay is stuck. Check which relays are being driven by looking for 2-3V across the base resistors and about 0.6V on the bases. Verify that the transistor is on; the others should be off. If you find a relay is being driven but not actuating, take a good look at the diode that’s in parallel with the coil. If it has gone short-circuit or is reversed, the relay won’t switch, no matter what the transistor is doing. Metal halide lamp driver wanted I am looking for a driver circuit for a 35W metal halide lamp used for special effects lighting. Ideally, I would 108 Silicon Chip like to drive the lamp directly from the mains rather than 12V. Is there a suitable project that can fit the application? I took a snapshot of the drive waveform for a working lamp with an oscilloscope; it looks like it is just a 50Hz 100V square wave (shown in the screengrab below). If the ICs are still available for the 12V Fluorescent Lamp Inverter (September 2002 issue; siliconchip.au/Article/4027) and it can be modified from this application, I could run it from a 12V laptop power supply or similar. (B. R., Eaglemont, Vic) ● A fluorescent lamp driver is not suitable for driving metal halide lamps as described in ST Application Note AN2747 (“250 W HID metal halide electronic ballast”) at siliconchip.au/ link/abmk You might be able to modify the Fluorescent Lamp Inverter to provide the higher starting voltage and the warm-up phase required. The warm-up phase could be implemented using the dimming feature of the fluorescent lamp driver. You could apply mains voltage at the bridge rectifier input instead from the secondary of step-up transformer T1, and not use the 12V to AC step-up part of the circuit. The LM6574 driver IC is available from Mouser (siliconchip.au/ link/abml). Preventing vehicle batteries from degrading I’m an avid reader of Silicon Chip and a frequent builder of your amazing projects! However, apart from a good understanding of physics, electricity Australia's electronics magazine and components, and skills to assemble projects, I sadly lack knowledge in electronic circuit design. My idea for a useful circuit may appeal to many of your readers. A large number of lead-acid batteries are regularly damaged and eventually destroyed by infrequent use or long periods of not being charged. Part of the problem is the not-insignificant parasitic drains of modern vehicle components, such as wireless door locks, burglar alarms, clocks, system management computers and others. While these are low-current devices, they are draining the batteries 24/7. The issue is relevant for vehicles not regularly stored in reach of float chargers; for example, camper vans, caravans, boats, seasonal agricultural machines, aircraft and vehicles in long-term car parks with owners away overseas. The latter caused me to think about the problem more deeply. The device I imagine will completely disconnect one pole of the battery at a specified battery-safe low voltage, eg, 10.5V for lead-acid chemistry. The starter cable could remain connected, given that it may require several hundred amps of current capacity and does not typically draw any current. This would leave only chemical self-discharge to reduce its voltage over a much longer term. There may already be such a device that I’m unaware of, or an adaptation of a BMS for other chemistries. In that case, I’d be happy to hear or read about it! I have fitted our small camper van with solar panels and a charge controller and store it in sunlight when not in use. However, I have had to replace relatively ‘young’ batteries over the years following Victorian winters when I have been away by other means than camping. Some of my farmer friends have reported the same frustration with costly battery life to me. Modern agrimachinery appears to suffer the same problem with lots of parasitic computer loads but seasonal use. (J. H., Bendigo, Vic) ● We think you have touched on many salient points. The usual solution to this problem is a trickle charger, either mains-powered or solar-­ powered. For a solar-powered system to maintain a battery, Oatley Electronics has a relatively inexpensive kit (IT159PK1) siliconchip.com.au that we reviewed in the July 2022 issue (siliconchip.au/Article/15386). As long as it is placed where it will get sunlight year-round, it should prevent battery damage through over-­ discharge. It is still available for $39 + P&P. Ignoring trickle chargers and turning to the idea of preventing parasitic drains, the simplest method is to use an isolating switch on the battery. This can be switched open when you need to stow the vehicle. There are various types, including types with a key. Jaycar sells several; see www.jaycar.com. au/search?text=battery+isolation We have published several automatic/electronic battery isolators over the years. However, as you point out, they could not be used to isolate the battery as the starter current (which can be over 250A in some cases!) would cause them to self-destruct. These include: • The Dual Battery Isolator which was conservatively rated at 100A (July 2019; siliconchip.au/ Article/11699) . • The Battery LifeSaver rated at 30A (September 2013; siliconchip.au/ Article/4360). • The Dual Battery LifeSaver rated at 2 × 5A (December 2020 issue; siliconchip.au/Article/14673). It should be noted that much of the vehicle electronics is left connected to the battery when the ignition is off so that any access codes and learned trims in the engine management and gearbox are kept, as well as any adjustable settings. Disconnecting power may require access codes to be re-entered, settings redone and trims relearned. Also, remember that even if you’re bypassing the starter and alternator, the total current draw in a modern car can be in the hundreds of amps, depending on whether you have electric power steering etc. So realistically, you would need an isolator rated to handle at least 100A. Additionally, any automatic battery disconnector will draw a current of its own that will contribute to battery discharge. Consider that even if the battery is totally isolated, it will still eventually degrade due to its self-discharge current. So regular charging will still be necessary. Admittedly, that will be required less frequently if it is just the self-discharge that needs to be compensated for. Trouble connecting to the Explore 100 console I have finally finished building the DAB+ Radio controlled by a Micromite Explore 100 module (January-March 2019; siliconchip.au/Series/330). It is working well except for the AM band. I noticed there is a software update for the radio firmware to fix that, but I am having trouble loading it. I set Tera Term to connect to COM3 as per Windows Device Manager. I left the baud rate at 9600, as Device Manager set it up as that. When I tried connecting, all I got was a flashing cursor. I tried pressing the Enter key. I also tried pressing the reset button on the Micromite and got a lot of garbage. I tried setting the baud rate to 38,400 but that didn’t help. I tried using a PICkit 3 to reprogram the PIC; that worked fine, but I still can’t connect to the serial terminal. Could it be a driver problem? The driver is pretty new, dated 13/04/2023, version 11.3.0.176. (E. B., Meadow Springs, WA) Silicon Chip as PDFs on USB ¯ A treasure trove of Silicon Chip magazines on a 32GB custom-made USB. ¯ Each USB is filled with a set of issues as PDFs – fully searchable and with a separate index – you just need a PDF viewer. ¯ 10% off your order (not including postage cost) if you are currently subscribed to the magazine. ¯ Receive an extra discount If you already own digital copies of the magazine (in the block you are ordering). The USB also comes with its own case EACH BLOCK OF ISSUES COSTS $100 OR PAY $500 FOR ALL SIX (+POSTAGE) NOVEMBER 1987 – DECEMBER 1994 JANUARY 1995 – DECEMBER 1999 JANUARY 2000 – DECEMBER 2004 JANUARY 2005 – DECEMBER 2009 JANUARY 2010 – DECEMBER 2014 JANUARY 2015 – DECEMBER 2019 WWW.SILICONCHIP.COM.AU/SHOP/DIGITAL_PDFS Ordering the USB also provides you with download access for the relevant PDFs, once your order has been processed siliconchip.com.au Australia's electronics magazine August 2023  109 ● This is likely a problem with the baud rate setting. We suggest you try all the standard baud rates as one is likely to work, eg, 115,200, 57,600, 38,400, and 19,200. The best way to test is to reset the board and see if you get legible text after changing the baud rate. Once you do, press CTRL+C to interrupt the program and get to the Micromite command prompt. Increasing Multi-spark CDI voltage I’m about to start building your Multi-Spark CDI for Performance Cars (December 2014 & January 2015 issues; siliconchip.au/Series/279) and have a question about the DC Converter output voltage. Would there be any negative consequences to the circuit if I wound the transformer to produce 400V? Most ignition coils seem to have a turns ratio of 100 and a maximum voltage of 45kV. Was the lower voltage used to protect the rest of the ignition system if retrofitted to a Kettering-style system? I will be using the CDI with a coil designed for electronic ignition and all new ignition components, including HT leads with extra thick insulation. (N. N. G., Berlin, Germany) ● There are two reasons why we did not have the voltage set for any more than 300V DC. The first is that the transformer (T1) would need to be more carefully wound so that the high voltage secondary winding has a greater clearance between the two ends. It would also require a greater clearance or creepage distance at the winding sides. Otherwise, the windings would be prone to arcing. The second reason is that the 1μF discharge capacitor would need to be rated for a higher voltage. The X2-class 275VAC rated capacitor specified, while very reliable when used at 300V DC, is not suited for 400V DC. As you also mention, higher voltages make the ignition more prone to crossfire and ignition coil internal breakdown. Note that a CDI system has a much faster voltage rise time that places more stress on the insulation of the high-voltage components, including the ignition coil, compared to the slower rise time of a conventional ignition system. You could change the circuit to operate at 400V DC instead of 300V DC but with due care as to winding T1 and the selection of the 1μF CDI discharge capacitor. The feedback resistance for IC1 would need to be changed to produce the higher voltage, eg, by changing the two 270kW resistors to 360kW each. The two 33kW 1W resistors in series with zener diode ZD2 that derive the supply for IC3 would also need to increase to 39kW 1W each, or a second 75V zener diode would need to be connected in series with ZD2. Ultra-LD Amplifiers have gain difference I built two Ultra-LD Mk.3 Amps (July-September 2011; siliconchip. au/Series/286) from Altronics kits (K5154). The amplifiers sound amazingly good. However, the gains are slightly different by about 1.5-2dB. Could someone advise me on how to adjust and match the gain of the amplifiers? I don’t really need a preamp as I am using it to drive the front speakers in my home theatre. The Yamaha receiver line outputs provide enough signal to drive these awesome amps. (D. S., via email) ● It’s strange that the gain differs so much between channels. The gain is set by the ratios of the 12kW and 510W resistors, which should be 1% tolerance parts. The worst-case pairings with 1% resistors are 11.88kW/515W and 12.12kW/505W, which give gain figures of 22.9 times (27.2dB) and 24 times (27.6dB), respectively. So the channels should be within 0.4dB of each other in the worst case. How are you measuring the differences in gain? Have you tried feeding an identical signal to both amps (eg, using a Y-cable) to verify it isn’t the signal source that’s causing the difference? It would be worth measuring those gain-setting resistors on both modules to ensure they are within their specifications (ie, within 1% of nominal) and checking the 1000µF capacitors that are in series with those resistors. To solve this imbalance, increasing the gain in one channel is safer than decreasing the other. You can add a bit of gain to the lower output channel by soldering a resistor across the sole 510W resistor. A 2.7kW resistor added across it should increase the gain by 1.5dB. Reducing that to 2.2kW will make it closer to +1.8dB. Advice on making durable front panels I have been building the Programmable Ignition project by John Clarke from March-June 2007 (siliconchip. au/Series/56). I have all the required parts. My query is regarding the front panel for the related Hand Controller. continued on page 112 Raspberry Pi Pico W BackPack The new Raspberry Pi Pico W provides WiFi functionality, adding to the long list of features. This easy-to-build device includes a 3.5-inch touchscreen LCD and is programmable in BASIC, C or MicroPython, making it a good general-purpose controller. This kit comes with everything needed to build a Pico W BackPack module, including components for the optional microSD card, IR receiver and stereo audio output. $85 + Postage ∎ Complete Kit (SC6625) siliconchip.com.au/Shop/20/6625 The circuit and assembly instructions were published in the January 2023 issue: siliconchip.au/Article/15616 110 Silicon Chip Australia's electronics magazine siliconchip.com.au MARKET CENTRE Advertise your product or services here in Silicon Chip KIT ASSEMBLY & REPAIR FOR SALE FOR SALE DAVE THOMPSON (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, New Zealand, but service available Australia/NZ wide. Email dave<at>davethompson.co.nz LEDsales Lazer Security KEITH RIPPON KIT ASSEMBLY & REPAIR: * Australia & New Zealand; * Small production runs. Phone Keith: 0409 662 794 keith.rippon<at>gmail.com LEDs and accessories for the DIY enthusiast LEDs, BRAND NAME AND GENERIC LEDs. Heatsinks, LED drivers, power supplies, LED ribbon, kits, components, hardware – www.ledsales.com.au VISIT THE NEW TRONIXLABS parts clearance store for real savings on new parts at clearance prices, with flat rate express delivery Australia-wide – go to https://tronixlabs.com For Quality That Counts... QUALITY COMPONENTS + MORE New items are added monthly, some stock is clearing at great prices, check out the freebies – go to lazer.com.au ASSORTED BOOKS FOR $5 EACH Electronics and other related subjects – condition varies. Some of the books may have been sold. See photos (recently updated): siliconchip.au/link/abl3 Email for a quote (bulk discount available), state the number directly below the photo when referring to a book: silicon<at>siliconchip.com.au Issues Getting Dog-Eared? 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 Protect your Silicon Chip copies using our Australian-made Binders. Order online from www.siliconchip.com.au/Shop/4 See website for overseas prices or call (02) 9939 3295. REAL VALUE A T $21.50* PLUS P&P ADVERTISING IN MARKET CENTRE Classified Ad Rates: $32.00 for up to 20 words (punctuation not charged) plus $1.20 for each additional word. Display ads in Market Centre (minimum 2cm deep, maximum 10cm deep): $82.50 per column centimetre per insertion. All prices include GST. Closing date: 5 weeks prior to month of sale. To book, email the text to silicon<at>siliconchip.com.au and include your name, address & credit card details, or phone (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 2023  111 Is there a feasible way for me to achieve a robust, hard-wearing result? (S. M., Adelaide, SA) ● We have some information on making front panel (and other) labels on our website: siliconchip.au/Help/ FrontPanels In summary, you have a few options. Because the Hand Controller lid is clear, you could print the label out onto stiff photo paper and place it on the underside of the lid so that it can be seen through the lid. Cut the switch holes out with a craft knife. It may need to be held in place with double-sided tape or a smear of clear non-acid cure silicone sealant (roof and gutter type) between the inside of the lid and the top of the paper. Another method is to print as a mirror image onto overhead projector film using a type suitable for your printer (laser or inkjet). These are clear and, Advertising Index Altronics.................................25-28 Dave Thompson........................ 111 Digi-Key Electronics...................... 3 Emona Instruments.................. IBC Hare & Forbes..........................OBC Jaycar................... IFC, 9, 12-13, 35, ................................. 79, 89, 93, 107 Keith Rippon Kit Assembly....... 111 Lazer Security........................... 111 LD Electronics........................... 111 LEDsales................................... 111 Microchip Technology.................. 7 Mouser Electronics....................... 4 SC Pico W BackPack................ 110 Silicon Chip PDFs on USB....... 109 Silicon Chip Shop............ 104-105 Silicon Chip Subscriptions........ 29 The Loudspeaker Kit.com............ 6 Tronixlabs.................................. 111 Wagner Electronics..................... 85 Next Issue: the September 2023 issue is due on sale in newsagents by Monday, August 28th. Expect postal delivery of subscription copies in Australia between August 25th and September 13th. 112 Silicon Chip with the reverse image, the printed side is placed face down on the panel and adhered using non-acid-cure silicone sealant. Squeegee the film flat onto the lid but don’t remove too much sealant, and ensure there is an even coverage over the entire film. When cured, cut the switch holes out with a craft knife. Since the Hand Controller lid is clear, coloured silicone such as grey should be used to provide contrast to the printed label. Alternatively, print the front panel artwork (but not as a mirror image) onto an A4-sized Avery “Heavy Duty White Polyester – Inkjet” sticky label that is suitable for inkjet printers or a “Datapol” sticky label for laser printers. Cut out the holes and display opening with a sharp craft knife. These labels are available from: • www.blanklabels.com.au • averyproducts.com.au The first of those also has instructions and interesting information. For Avery labels, visit siliconchip. au/link/ably For Datapol labels, visit siliconchip. com.au/l/aabx Avery also has “Heavy Duty White Polyester – Laser” labels. We haven’t tried them, but we think they might be even better than the above, and they are available from Officeworks for both inkjet (siliconchip.au/link/ ablz) and laser printers (siliconchip. au/link/abm0). Help to identify an old EA project I want to get some information on an old project, possibly from Electronics Australia. It is a load-controlled mains switching box. Unfortunately, I have lost the information about it over the years. A load is connected to a ‘master’ mains socket, and the master load current operates a relay, which then enables several ‘slave’ mains outlets. On the top side, there is a 10W 10kW resistor, two 1W 82kW resistors, what looks like a bridge rectifier using discrete 1N5xxx diodes, a couple of smaller diodes, a couple of half-watt resistors, a 47μF 63V capacitor and a couple of small-signal transistors. On the bottom side of the board, all I can make out is “79”; the first part of the board part number was cut off when the relay was mounted on the board. Australia's electronics magazine Can you find any information about this project? I would like to try to increase its switching-on sensitivity. Keep up the good work with Silicon Chip. I started reading RTV&H in high school and am now semi-retired! I still buy the magazine each month. I have seen a lot of changes over the intervening years. (G. M., North Epping, NSW) ● EA published several mains slave switches, eg, in the January 1990 and January 1992 issues but none that match your description. For example, none include a 10kW 10W resistor. Despite an exhaustive search of the Silicon Chip, EA & ETI indexes and archives, we haven’t found an article on the device you described. We could have missed it, or it could be from another source. We assume a bridge rectifier is used to conduct current flow for the master appliance supply, and the voltage across it (about 1.2VAC) is filtered with a resistor and capacitor to provide a base drive to a transistor. We assume that drives another transistor for more current gain to drive the relay. In that case, the sensitivity can’t easily be increased. We suspect the bridge rectifier diodes are 1N5404 500V 3A types, and the 10W resistor is used to reduce the voltage applied to the relay from the mains, possibly via a 1N4004 (1A) diode so it is supplied with DC. Vintage Radio query on HMV Consort I remember a refurbishment of an HMV “Consort” in the Vintage Radio section. Can you please point me to the article? My neighbour wants his little portable repaired if possible. As far as I can see, apart from restringing the dial, it’s just a broken ferrite rod antenna. I love your articles; keep up the good work. (D. H., Greenwood, WA) ● We don’t have any record of publishing a Vintage Radio article on an HMV “Consort”. We have published around a dozen articles on various HMV radios; you can find them by putting “HMV” in the “Name” field and clicking “Search” on the following web page: siliconchip.au/Articles/ ContentsSearch You may be thinking of Radio Waves magazine, October 2011, which had an article on the HMV Consort by Ian Malcolm. SC siliconchip.com.au “Rigol Offer Australia’s Best Value Test Instruments” Oscilloscopes NEW 200MHz $649! New Product! 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