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JULY 2021 ISSN 1030-2662 07 9 771030 266001 The VERY BEST DIY Projects! $995* NZ $1290 INC GST INC GST 26 20A DC Motor Speed Controller 36 USB Power Delivery: how it works 46 Level Crossing for Model Railways 64 FM/AM/SW Digital Radio using Silicon Labs ICs Mars Mission Perseverance & Ingenuity siliconchip.com.au Australia’s electronics magazine July 2021  1 Build your own IoT Smart Wireless Switch Take your first step into DIY home automation. You will be able to view and control your appliances from the convenience of your phone or tablet over your home Wi-Fi network. Turn appliances on or off, or even modify the provided source code to create your own 'Internet of Things (IoT)' automation innovations. Phone not included. SKILL LEVEL: Intermediate For step-by-step instructions scan the QR code. CLUB OFFER BUNDLE DEAL 4495 $ www.jaycar.com.au/iot-wireless-switch See other projects at SAVE 25% www.jaycar.com.au/arduino 240V Soldering Irons Stainless steel barrel. Impact resistant handle. Electrically safety approved. 25W TS1465 $14.95 40W TS1475 $19.95 KIT VALUED AT $63.80 Electronic Circuit Board Cleaner FROM 1495 $ DON’T FORGET YOUR SOLDER! 15g Solder NS3008 $2.25 Dissolves flux residues & grime leaving the track work and board clean. 175g spray can. NA1008 1150 $ 100 $ gift card Awesome projects by On Sale 24 June to 23 July, 2021 ONLY ONLY 1795 $ Solder Flux Paste Provide superior fluxing and reduce solder waste. 56g tub. NS3070 Got a great project or kit idea? If we produce or publish your electronics, Arduino or Pi project, we’ll give you a complimentary $100 gift card. Upload your idea at projects.jaycar.com Light Duty Hook-up Wire Pack ONLY 3995 $ Quality 13 x 0.12mm tinned hook-up wire on plastic spools. 8 rolls of different colour. 25m each roll. WH3009 Looking for your next build? Silicon Chip projects: jaycar.com.au/c/silicon-chip-kits Kit back catalogue: jaycar.com.au/kitbackcatalogue 1800 022 888 www.jaycar.com.au Shop online and enjoy 1 hour click & collect or free delivery on orders over $99* Exclusions apply - see website for full T&Cs. * Contents Vol.34, No.7 July 2021 SILICON CHIP www.siliconchip.com.au Features & Reviews 12 The 2020 mission to Mars On July 30th 2020, the Perseverance rover and Ingenuity helicopter were launched into space. They arrived at Mars on February 18th 2021 to search for evidence of past life and find signs of habitable areas – by Dr David Maddison 36 How USB Power Delivery (USB-PD) works With the introduction of the Type-C connector came a new power delivery specification called USB-PD. It allows 0.5-100W of power (20V at 5A maximum) to be delivered. This article describes how it works – by Andrew Levido 42 El Cheapo Modules: USB-PD chargers A quick look at three different USB-PD power sources, which includes the Comsol COWCC30WH, XY-PDS100 and Belkin F7U060AU – by Jim Rowe NASA’s latest (and current) robotic visitors to Mars are the nuclearpowered Perseverance rover and its companion, the Ingenuity helicopter – Page 12 73 Review: Tecsun PL-990 radio receiver The Tecsun PL-990 is a high-performance AM, FM, shortwave (SW) and longwave (LW) portable radio all-in-one. The only downside is that it might be Tecsun’s last high-end portable – by Ross Tester Constructional Projects 26 20A DC Motor Speed Controller This small speed controller can drive motors rated up to 24V DC and 20A, with adjustable soft-start time, variable PWM frequency and minimum duty cycle adjustments, along with many more features – by John Clarke 46 Model Railway Level Crossing Moving barriers, flashing lights and a bell sound recorded from a real level crossing make this a realistic part of a model railway layout – by Les Kerr Our 20A DC Motor Speed Controller uses pulse width modulation (PWM) to drive motors rated from nearly 0 to 24V at 0-100% duty cycle – Page 26 64 Silicon Labs-based FM/AM/SW Digital Radio Single-chip technologies, like the Si4730 and Si4732 from Silicon Labs, make it much easier to build a capable digital radio which receives FM, AM and SW signals with just a handful of components – by Charles Kosina 76 Advanced GPS Computer – Part 2 The second, and final article, has the construction details of the Advanced GPS Computer along with how to use it and, for those that are interested, how the software works – by Tim Blythman Your Favourite Columns USB 3.2 is the first standard to officially allow power sources and sinks to negotiate the supplied voltage and current. This powerful feature is named USB Power Delivery – Page 36 61 Circuit Notebook (1) Coded door buzzer (2) Adding shuffle to a low-cost MP3 player module (3) DIY pulse oximeter 91 Serviceman’s Log I’ve repaired planes before, but never ‘tanks’ – by Dave Thompson 98 Vintage Jukebox The Rowe AMI JAL-200 jukebox – by Jim Greig Everything Else 2 Editorial Viewpoint 4 Mailbag – Your Feedback 104 Silicon Chip Online Shop siliconchip.com.au 106 Product Showcase 107 Ask Silicon Chip 111 Market Centre 112 Noteselectronics and Errata Australia’s magazine 112 Advertising Index This new FM/AM/SW Radio is smaller and uses fewer components than the previous BK1198-based model. It can use the Si4730 IC for AM & FM reception; or the Si4732 which also includes SW reception – Page 64 July 2021  1 Cover image: https://mars.nasa.gov/ resources/25757/curiositys-selfie-at-mont-mercou/ 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. Nicolas Hannekum, Dip. Elec. Tech. Technical Contributor Duraid Madina, B.Sc, M.Sc, PhD Reader Services Rhonda Blythman, BSc, LLB, GDLP Advertising Enquiries Glyn Smith Phone (02) 9939 3295 Mobile 0431 792 293 glyn<at>siliconchip.com.au Regular Contributors Dave Thompson David Maddison B.App.Sc. (Hons 1), PhD, Grad.Dip.Entr.Innov. Geoff Graham Associate Professor Graham Parslow Ian Batty Cartoonist Brendan Akhurst Founding Editor (retired) Leo Simpson, B.Bus., FAICD Staff (retired) Ross Tester Ann Morris Greg Swain, B. Sc. (Hons.) 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): 12 issues (1 year): $105, post paid 24 issues (2 years): $202, post paid For overseas rates, see our website or email silicon<at>siliconchip.com.au Recommended & maximum price only. Editorial office: Unit 1 (up ramp), 234 Harbord Rd, Brookvale, NSW 2100. Postal address: PO Box 139, Collaroy Beach, NSW 2097. Phone (02) 9939 3295. ISSN 1030-2662 Editorial Viewpoint Software: too many bugs, too many updates I can’t be the only person who is sick and tired of the barrage of constant software updates. Between Windows updates, Android updates, Adobe updates, Mozilla updates, App updates, and all the other software packages I use, I spend way too much time dealing with them every day. With some software packages I use only intermittently, they bother me about updating virtually every time I open up a file! And that’s the worst time to do it; I’d much rather they ask me whether I want to update when closing the software than opening it. I’m opening it because I have a task to complete, and I don’t want to stop that task to install another *$(!&#<at> update! It wouldn’t be so bad if these updates fixed bugs, but so often, not only do they fix nothing, but they introduce new bugs. Windows updates are the worst. Some of our staff suffered for weeks from constant ‘blue screens’ and reboots when printing files caused by a Windows update that initially they didn’t even realise had been installed. It cost us a lot of lost productivity until one smart guy figured it out and managed to uninstall that update on the affected machines (one of which was brand new; we thought it might be defective). Microsoft apparently knew about this bug and quickly released a patch to fix it, but the fix didn’t work! I hate to be negative and sound like I’m complaining, but this situation is just ridiculous. One of my pet peeves is how software companies – including the largest, richest ones in the world – prioritise adding features to their software rather than fixing bugs. This sometimes results in serious bugs that cause frequent crashes or otherwise break the software persisting for years, while they are busy adding useless new doo-dads that we don’t need. They are also far more interested in adding bells and whistles than addressing severe performance problems, making the software virtually unusable. For example, I have some software that can take literally hours to perform certain functions, depending on the complexity of the files I am working with. I have developed workarounds to accomplish these tasks in a reasonable timeframe, such as manually splitting the job into smaller chunks, then reassembling it later. I shouldn’t have to do that. I believe these operations could be completed in seconds (or faster) if the algorithms the software used were implemented in an even vaguely intelligent manner. I don’t know the solution to this, but I believe whether through user pressure, legislation or otherwise, the behaviour of software companies has to change. If you bought a car and it broke down several times a day, frequently slowed down to unusable speeds and needed to be brought back to the dealer for modifications every week to keep it roadworthy, you would ask for your money back. Yet we pay hundreds or thousands of dollars for a piece of software and then accept that it behaves in the same manner. That is totally unreasonable. Perhaps the open-source software movement will save us from this life of misery. In some areas, there are already excellent free pieces of software that provide most functions of their commercial equivalents, and they are often less buggy. If the commercial vendors don’t get their collective acts together, they might find themselves losing a lot of business to those alternatives. Printing and Distribution: by Nicholas Vinen 24-26 Lilian Fowler Pl, Marrickville 2204 2 Silicon Chip Australia’s electronics magazine siliconchip.com.au siliconchip.com.au Australia’s electronics magazine July 2021  3 MAILBAG your feedback Letters and emails should contain complete name, address and daytime phone number. Letters to the Editor are submitted on the condition that Silicon Chip Publications Pty Ltd may edit and has the right to reproduce in electronic form and communicate these letters. This also applies to submissions to “Ask Silicon Chip”, “Circuit Notebook” and “Serviceman”. Cleaning silver with electricity By harnessing the power of electrons, silver cleaning can be quick, easy and efficient. The most popular way to clean tarnished silver and silver-plated objects is using a paste containing ammonia and a mild abrasive. But it gradually removes the silver, which is particularly bad for silver-plated items. Another method uses acidified thiourea, which tends to leave a yellowish residue. Alternatively, the silver object can be placed in direct contact with an aluminium pot or a sheet of aluminium foil, and immersed in a hot solution of sodium bicarbonate, setting up an electrolytic cell. While this method works quite well, it is fairly slow and works best with small objects. This method can be sped up enormously and made much more efficient by the simple application of an electric current, as explained in the video at https://youtu.be/57iwtmT4LNQ Tarnish is silver sulphide, generated over time by hydrogen sulphide in the air, or perhaps from contact with egg yolks. The reaction is: 4Ag + 2H2S + O2 → 2Ag2S + 2H2O The reaction can be reversed by electrons, with a reduction potential of -0.69V. In a mildly alkaline solution, the sulphide remains ionised and soluble in water: Ag2S + 2e− → 2Ag + S2− The reduction of aluminium ions involves a potential of -1.66V: Al3+ + 3e− → Al This reaction is also reversible under certain conditions. When these metals are in contact with each other in a mildly alkaline solution, an electrolytic cell is set up. The difference in reduction potential facilitates oxidation of aluminium and liberation of electrons to silver sulphide, forcing its reduction to metallic silver. The sulphide ions travel to the 4 Silicon Chip aluminium, which is converted into aluminium sulphide. The reaction can be greatly sped up with the help of a 6V battery. As before, the metals are placed in a solution of hot sodium bicarbonate and table salt, but the aluminium foil and the silver are not in contact with each other. The silver is connected to the negative terminal, and the aluminium is connected to the positive. The battery facilitates the movement of electrons out of the aluminium and into the silver. The result is dramatic. Within just a few seconds, the blackened silver turns shiny. The beauty of this method is that the silver sulphide is converted back to metallic silver and redeposited on the item. Since silver ions are positively charged, they can’t go anywhere else, and there is no risk of damage to the silver. But, beware – if you get the polarity mixed up, your precious ancestral silver will be rapidly stripped! The practical procedure is very simple. Fill a non-metallic bucket or dish with very hot tap water. Add a tablespoon of salt and a tablespoon of sodium bicarbonate (baking soda) and stir to dissolve. Place a sheet of aluminium foil overhanging the side and connect it to the battery’s positive terminal. Then connect the silver item to the battery’s negative terminal and dunk it in the liquid – keep the connection point dry and above the liquid. Fizzing will start, and within seconds, the tarnish will disappear, and the silver will be restored. When you are satisfied with the result, remove the silver item and invert it so that the half that was outside the liquid is now immersed. Then attach the negative end of the battery to the top of the silver item above the liquid. The remaining part will be cleaned in seconds. Australia’s electronics magazine Remove the item and give it a gentle rubdown with a damp cloth. Rinse it thoroughly with tap water to make sure that there is no residual salt. That’s all there is to it. Silver cleaning need no longer be drudgery! Jim Goding, Princes Hill, Vic. Pong in a picture frame Congratulations to Dr Hugo Holden on his Silicon Chip article on Arcade Mini Pong (June 2021; siliconchip. com.au/Article/14884) and on a neat board design. It’s a very nice and compact layout – at first glance, I thought he had switched to SMD chips to make it that small. Come to think of it, one could do that to take this even further. It would enable a discrete Pong PCB somewhere around the size of a postcard. With Chinese manufacturers like JLCPCB offering very affordable SMD assembly in small lots, a batch of pocket-sized Pong boards would be quite feasible. Hugo Holden’s circuit analysis has been invaluable for me when I got started with my “framed Pong” project. It took me a while to get hold of an original Pong board, and I started my upscaler FPGA development before I had an actual board, based on his documentation. The detailed analysis also gave me the confidence to buy a non-working Pong board, since I had all the information needed to fix it. Thank you very much for sharing your knowledge! I wrote up my project at www. e-basteln.de/arcade/pong/pong/ Jürgen Müller, Hamburg, Germany. DAC chip has a fault in one channel I built the USB SuperCodec by Phil Prosser published in the August to October 2020 issues (siliconchip.com. au/Series/349), and while it generally worked, I found that the performance siliconchip.com.au of one channel was much worse than the other, with a much higher noise floor and a distortion figure 20-30dB higher. With further analysis, I discovered that it was one DAC channel that was not up to scratch. To investigate, I disconnected the four 240W resistors from pins 19, 20, 23 & 24 of IC9 to the op amps and swapped the channels over. The high distortion remained with the same DAC channel, ruling out the op amps or associated components as the culprits. So it looked like I had a faulty DAC chip. Not having the tools or skills to remove the SMD, I sent the board over to Phil Prosser, who graciously offered to swap the chip for a new one. That fixed it. Phil pointed out that a static discharge on one of the output pins could have damaged the faulty channel. Thanks to Phil for fixing it. Stephen Gordon, Thurgoona, NSW. DAB+ radio updates On May 18th, the ABC/SBS digital radio signal quality was adjusted. ABC Classic has been increased from 80kbit/s to 120kbit/s. After all the initial sound quality complaints, it will be interesting to see if anyone notices. ABC Jazz has been increased slightly to 88kbit/s, which is not likely to make a noticeable difference. The losers are ABC country, triple j and triple j Unearthed, reduced from 80kbit/s to 72kbit/s. This is interesting because triple j’s younger audience should have better hearing! ABC Kids Listen has also been reduced from 72 to 64kbit/s. The ABC local radio for each capital city is transmitted in 64kbit/s stereo, despite their AM transmitter radiating in mono except for Darwin, which is in FM stereo. SBS is unchanged, meaning that Chill and Pop Asia are still 72kbit/s stereo. All these channels use HE-AAC V2 compression. There is now an even more efficient compression called xHE AAC, but current DAB+ receivers cannot handle it yet. A Government DAB+ transmitter carries 18 programs. The commercial/ community DAB+ transmitters are carrying up to 32 programs each. There is an opportunity for regional areas to roll out DRM+ using the vacant analog TV channels 0-2, that can cover 6 Silicon Chip a much larger area than DAB+, which uses higher-frequency channels, increasing line-of-sight losses by 12 times. This could replace many AM and FM broadcasts. One DRM+ transmitter can carry the pair of programs from commercial broadcasters, and there is now a six-channel modulator that can transmit the 18 ABC/SBS programs using a single antenna. 2.8 million DAB+ receivers have been sold to date in Australia, and 77% of new cars have DAB+ receivers. Alan Hughes, Hamersley, WA. Secondary circuit breaker recommended with variacs Dr Hugo Holden’s Variac-Based Mains Regulator article (May 2021; siliconchip.com.au/Article/14856) is a great idea. I’ve had a commercial version protecting my small collection of vintage electronic equipment for 15 years, and it has been invaluable. We live a long way up a country road, where electricity is supplied by the proverbial “thin piece of wet string”, meaning that the mains voltage varies widely (far outside the nominal statutory limits) depending on farm loads, domestic cooking times and so on. Modern appliances with switchmode power supplies take it all in their stride, but it is a different story for the old-time stuff. As just one familiar example, until the advent of LED lamps, globe life in our home was very short indeed! However, I have a recommendation for anyone who decides to build one. If the variac of choice does not already have one as an OEM fitting (they usually don’t, in my experience), I suggest a thermal overload should be inserted in the secondary between the variac and the outlet socket, rated at the nameplate current of the variac. It is very easy to damage a variac by inadvertently overloading it, and a simple thermal circuit breaker or overload will prevent much heartache. They are readily available, small in size, moderately priced, and do a better Australia’s electronics magazine job than a secondary fuse because they will trip on small sustained overloads, which can damage the carbon brush. A photo is shown below of a typical thermal overload breaker, stocked by a reputable NZ supplier (mytools.co.nz). John Reid, Tauranga, New Zealand. Eliminating transformers in the IMSC I was interested in reading the recent advice you gave to a correspondent who wanted to run the Silicon Chip Induction Motor Speed Controller (IMSC) from 115V AC (April 2021, Ask Silicon Chip, p110). I have built a couple of them to run my pool filter and bench drill (both from 230V), and they work very well. I have made some modifications to the circuit for improved performance that would also enable 115V AC operation. It does require some repackaging of the unit and is a project for the experienced constructor, but the results are beneficial. I replaced both the transformerbased high-side and low-side 15V and 12V DC power supplies entirely with a couple of 12V 1A switchmode supplies from eBay (intended for the LED Christmas lights market). Many sellers have them. These supplies are enclosed, small in size and have a wide input AC voltage range, operating from 90V AC to over 240V AC. They allow the unit as a whole to run from 115V AC since the high voltage part of the circuit will be unaffected, as noted in your advice. However, as you mention, the low voltage protection circuitry will require modification. I could have used a 5V DC switchmode supply for the cold side, but chose 12V to standardise on one DC supply type. This means I had to add a small flag heatsink to REG1. I changed the output voltage of the high-side supply to the recommended 15V by replacing just one resistor in the switchmode supply. By coincidence, I saw later (after I had traced out the circuit) that Oatley Electronics had posted the procedure to change the output voltage of this generic power supply on its website. Notably, instead of powering the switchmode supplies directly from 230V AC, I used the mains rectified 325V DC bus that powers the 3-phase VFD chip. The same AC input terminals to the switchmode can be used, and they are polarity independent. siliconchip.com.au Ready for Tomorrow Over new brands * added PROCESS & ANALYTICAL INSTRUMENTS pi 3g p .pi3g.com Inventory increased by 25% SBC +64% Semiconductors +6% Passives +12% EMECH +202% Interconnect +16% Test and Tools +18% Contact us now Phone: 1300 361 005 Sales: au-sales<at>element14.com Quotes: au-quotes<at>element14.com au.element14.com/ready4tomorrow *from July 2019 POWER SUPPLIES PTY LTD ELECTRONICS SPECIALISTS TO DEFENCE AVIATION MINING MEDICAL RAIL INDUSTRIAL Our Core Ser vices: Electronic DLM Workshop Repair NATA ISO17025 Calibration 37 Years Repair Specialisation Power Supply Repair to 50KVA Convenient Local Support SWITCHMODE POWER SUPPLIES Pty Ltd ABN 54 003 958 030 Unit 1 /37 Leighton Place Hornsby NSW 2077 (PO Box 606 Hornsby NSW 1630) Tel: 02 9476 0300 Email: service<at>switchmode.com.au Website: www.switchmode.com.au 8 Silicon Chip This modification has significant advantages for me. Since the switchmode supplies operate down to below 100V, when power is switched off to the unit, the control circuitry remains powered along with the VFD chip, so the unit will continue to drive the load until the DC bus drops below 100V, or until the undervoltage protection kicks in (I don’t know which happens first). When powering a 1500W pool pump, this process takes less than a second. Even when the motor stops drawing its load current, the switchmode supplies continue to discharge the DC power supply capacitors until the DC rail is well below 100V. This means that the load resistors across the high voltage caps for safety are not required, so a major source of heating in the enclosure is eliminated. I was surprised to note another benefit. Builders of the IMSC will have noticed that when the power to the original unit is disconnected, the motor being driven stops completely with a jerk. Another reader reported this phenomenon some time ago and asked a question as to why this happens. The answer proposed that the integral protection diodes in the VFD chip were shorting the motor and acting like a dynamic brake. I haven’t tested this or other theories (I don’t have the HV test equipment or the courage) but, when the switchmode DC power supplies are introduced, this effect disappears, and the motor runs down smoothly. I think the IMSC is one of the most useful projects presented by Silicon Chip. An industrial electronics-scale project was a welcome addition to the project stable. It’s a shame that packaged kits are no longer available for this and, for that matter, most Silicon Chip construction projects – an unfortunate sign of these ‘maker’ times. David Hainsworth, Westlake, Qld. More on software for 3D printers Thanks for your advice on software for 3D printers (Ask Silicon Chip, June 2021, p108). I tried OpenSCAD (https://openscad.org/) initially, and that worked so well that I didn’t explore alternatives. It is easy to use, with a very good Wiki-style user manual. It is one of few software products that didn’t provoke me to put fists through computer screens. I noticed three quirks, but these are more amusing than annoying. It is a programming language, not an interactive pointand-click tool. Although that might seem odd in modern times, it leaves a record of what I’ve done and allows me to leave comments for myself. So if I don’t get my clever gadget perfect the first time, which I didn’t, I can read what I’ve done and fix it. It resembles languages like LISP more than procedural languages like BASIC or C, and everything felt back-tofront for a while. A bit like the German language it is, with verbs at the end of the sentences. That encouraged me to define my gadget using modules so that each module, Module N, had a pattern like: Use Module N-1 Add these bits Remove these other bits Once I got the hang of it, I produced modules that were quite pleasing and reliable. Although its documentation mentions variables, it also warns that they aren’t Australia’s electronics magazine siliconchip.com.au Our capabilities CNC Machining UV Colour Printing Enclosure Customisation Cable Assembly *** Box Build *** System Assembly Ampec Technologies Pty Ltd Australia’s electronics magazine siliconchip.com.au Tel: (02) 8741 5000 Email: sales<at>ampec.com.au Web: www.ampec.com.au FEBRUARY 2021 37 variables, but more like constants. For a proper programming language, this would create huge problems, but for doing what OpenSCAD does, it is no worse than a mildly irritating curiosity. I sent my clever design to KAD3D, and they turned it into a gadget that looks like the gadget I drew. Keith Anderson, Kingston, Tas. Historical articles enjoyed First off, let me thank you for the effort that you have put into the magazine over the years. Good work! Your article on the humble three-pin Aussie plug and socket was very interesting, and someone had done a lot of research into it; a great read (September 2020; www.siliconchip. com.au/Article/14573). Same with the articles on the VCR and its not so humble beginnings (March-June 2021; siliconchip.com.au/ Series/359). Coming from the electronics service industry, now retired and living in Tasmania, that article series brought back a whole lot of memories from a bygone era, including my studies at the local TAFE. Would it be possible to publish an article on the Compact Disc, DVDs, LaserDisc etc and the problems and formats that this medium provides? I find that type of article interesting and a good read. I re-read one of your articles from May 2019 (p104) on The History of Stromberg Carlson, and Admiral Television. This was a blast from the past. My family had one of these Admiral televisions (Imperial 800), and I can still remember the set being delivered around 1958/9. I was just a little kid at the time. This set was still going up until my parents purchased a colour television; whatever happened to that set, I do not know! I remember that when Channel 0 started transmission (later to become Channel 10), these and a lot of other sets needed the “0” biscuit modified to receive the new channel. The other time the set was repaired was when the flyback transformer failed. That, the horizontal output valve (6DQ6) and damper diode (6AX4) were all replaced during a house call. When I started working, I was lucky enough to land an apprenticeship as a radio and television trainee. I had not long turned 15 at the time, and I worked in the television reconditioning section. Many of these Admiral TVs were traded in at the time, and a lot were passed over as being too hard to work on due to the “new” printed circuit boards they used. I think that was before solder wick and solder suckers. The standard iron at the time was the old scope 300W iron, with no temperature control, and using one on printed boards was a real learning curve. Too much heat and the copper track would lift off the board. One soon learned. Television techs of that era enjoyed point-to-point wiring, and the ease with which those sets could be repaired. How soon that was to pass! I had a soft spot for our own Admiral set and soon took to several of the Admiral sets that were traded in. One Admiral set I remember also had a radiogram in the bottom of the cabinet. This pulled out like a drawer in a cupboard. I remember that the radiogram had push-pull output valves (possibly 6AQ6s) in the audio output stage. Stephen Gorin, Mildura, Vic. SC 10 Silicon Chip Australia’s electronics magazine siliconchip.com.au The Mars 2020 mission: Perseverance & Ingenuity Source: https://mars.nasa.gov/resources/25640/mastcam-zs-first-360-degree-panorama/ “ A re we alone? We came here to look for signs of life, and to collect samples of Mars for study on Earth. To those who follow, we wish a safe journey and the joy of discovery.” These words are written on the Perseverance rover as a message for future human explorers, or other intelligent lifeforms that might find the machine in the future. The Mars 2020 mission involved landing the Perseverance rover vehicle and the Ingenuity helicopter on Mars. Planning for the mission started in 2012, and the Atlas V rocket launched Fig.1: the Mars 2020 launch on an Atlas V rocket at 11:50am UTC on July 30th, 2020. 12 Silicon Chip on July 30th 2020 (see Fig.1). Touchdown occurred on February 18th 2021. The mission has a strong astrobiological emphasis, looking for evidence of past or present conditions suitable for lifeforms on Mars, or the actual lifeforms themselves. The landing is in an area thought to have once had conditions suited to life. Great care was taken to ensure no lifeforms from Earth were accidentally transferred to Mars. The lander will also collect and cache samples for a later Earth return mission, planned for 2031, for further analysis. It will also demonstrate technologies for future robotic missions (such as the helicopter), and future manned exploration such as oxygen production from the CO2 atmosphere of Mars. Perseverance is the fifth NASA rover to land on Mars after Sojourner (1997), Opportunity (2004), Spirit (2004) and Curiosity (2012). The first three were solar-powered and no longer function, while Curiosity is nuclear-powered via a radioisotope thermoelectric generator (RTG). Curiosity, which landed on August 6th 2012, is still operational, having travelled more than 25km so far. Perseverance is based on Curiosity Australia’s electronics magazine and is also powered by an RTG. The spaceflight and landing Launch dates and times are chosen carefully to fulfil numerous requirements such as: • Earth and Mars being in suitable locations within their orbits to minimise travel time. • an existing Mars orbiter be over the proposed landing site to relay data to Earth during the Mars entry and landing. • suitable weather conditions at the launch site. There were seventeen days over which the launch could have occurred, with available launch windows on each day from 30 minutes to two hours long (see siliconchip.com.au/link/ab8f for details). After launch (Fig.2), the next phase was interplanetary cruise (Fig.3), which started as soon as the spacecraft separated from the launch vehicle. During this time, checks were run on various spacecraft systems and several trajectory correction manoeuvres were made, especially on the final approach to Mars. The final phase was the entry, descent and landing (EDL) – see Fig.4. Ten minutes before this happened, siliconchip.com.au Mars is currently the only planet we know of occupied only by robots. This article is about NASA’s latest robotic visitors to Mars, the nuclear-powered Perseverance rover and the groundbreaking Ingenuity helicopter. Shown in the background is Perseverance’s first 360° panorama, taken by the Mastcam-Z instrument. This panorama was stitched together from 142 individual images. The rover looks distorted because of the 360° view. By Dr David Maddison the cruise stage was jettisoned. EDL began when the spacecraft, protected by an “aeroshell” heat shield, entered the top of the Martian atmosphere at 19,500km/h. During entry, small thrusters on the aeroshell were used to manoeuvre the spacecraft to its target landing location. Peak heating occurred 80 seconds into the entry, with parts of the craft reaching about 1300°C. Four minutes after entry, a parachute was deployed. The parachute is 21.5m in diameter and deployed at an altitude of 9-13km and a speed of 1512km/h. Twenty seconds after parachute deployment, the heat shield separated from the underside of the spacecraft. Another 30 seconds after that, the radar and Lander Vision System were activated at an altitude of about 7-8km. At 4km and 6m30s, the Terrain Relative Navigation (TRN) system, using inputs from the Lander Vision System (LVS), had determined the spacecraft position and the desired landing target. More on the TRN and LVS later. This was followed by back-shell and parachute separation at 6m50s, at an altitude of 2.1km and speed of 320km/h, followed by a powered descent. The descent vehicle, with the rover attached, used manoeuvring siliconchip.com.au Fig.2: the launch profile for Mars 2020 - SRB stands for solid rocket booster and PLF for payload fairing. These events occupy the first two hours; from launch to separation was just under one hour. Fig.3: the route to Mars. TCM stands for trajectory correction manoeuvre. Some of these TCMs were cancelled due to the high level of navigational accuracy achieved. Australia’s electronics magazine July 2021  13 Fig.4: the Mars 2020 entry, descent and landing sequence. thrusters to fly the vehicle to the landing target. The next phase of the landing was rover separation from the descent stage for the Sky Crane manoeuvre at an altitude of 21m. The powered descent stage becomes the Sky Crane, which uses its thrusters to remain stationary and lowers the rover on cables (Figs.5 & 6). As soon as the rover touchdown was confirmed, the Sky Crane flew away to a safe distance and landed about 700m away from the rover. The Sky Crane concept was used because the rover was too heavy to permit an airbag type of landing, as used for some past Mars missions. A retrorocket landing, as used for Viking 1 and 2, was deemed unsuitable as the rockets would have thrown up debris that could have affected the rover’s sensors. Note that the entire landing sequence was autonomous; due to speed-of-light limitations, the radio delay at the time of landing was over 11 minutes. Seven minutes after first atmospheric entry, the rover and its payload Ingenuity were safely on the surface. This period of seven minutes is known as “The Seven Minutes of Terror” because so many things can go wrong, and nobody on Earth knows what has happened until it is all over. There is a video of the landing with imagery looking down from the descent vehicle and up from the rover, titled “Perseverance Rover’s Descent and Touchdown on Mars (Official NASA Video)”, viewable at https:// youtu.be/4czjS9h4Fpg 14 Silicon Chip For a commentary on that video, see the video titled “Landing On Mars Like You’ve Never Seen It Before” at https://youtu.be/mfgzTfw_J6o Fig.5: a rendering of the final landing stage, with the rover being lowered beneath the Sky Crane. A hidden message Embedded on Perseverance’s parachute was a binary code that stated “Dare Mighty Things”, which is both a quote from a speech from President Roosevelt and the motto of the NASA JPL Laboratory (see Fig.7). The GPS coordinates for the California JPL Laboratory are also on it. Navigating from Earth to Mars For most of its journey, Mars 2020 received navigational signals from Earth. Remarkably, the spacecraft entered the Martian atmosphere within 200m of the desired entry point. This high level of accuracy made two planned correction manoeuvres unnecessary (see siliconchip.com.au/ link/ab8m). This was achieved partly by knowing the spacecraft thruster exhaust velocity exactly, to within millimetres per second. Even thermal radiation and solar radiation pressure, which were incredibly insignificant forces (about one-billionth of the force of gravity on Earth) had to be taken into account, or the spacecraft could deviate up to 3.7km in the final ten days. Importantly, antennas in NASA’s Deep Space Network, some of which are in Australia, were used to determine the spacecraft’s exact position. The location of these antennas on the Earth’s surface had to be known precisely, because an antenna location Australia’s electronics magazine Fig.6: an actual image of the Perseverance rover being lowered to the ground by the Sky Crane, as seen from the descent stage. Fig.7: a photograph of the descent stage’s parachute, showing the decoded binary message. siliconchip.com.au Fig.8: how spacecraftquasar delta differential one-way ranging works. The angle between the spacecraft and quasar should be less than 10° for good accuracy. error of 5cm would result in a 500m error over the 150 million kilometres to Mars. Also, the speed of rotation of the Earth had to be known within 0.2m/s, and the exact location of Mars, as determined by Mars Global Surveyor and Mars Odyssey, had to be known within about 800m or less. Navigators even had to take into account the wobble of the Earth and how solar plasma affected the speed of navigational radio signals from Earth. Additionally, a technique known as spacecraft-quasar delta differential one-way range or DDOR (pronounced “delta door”) was used to help locate the spacecraft (see Fig.8). A location in space can, in principle, be determined by trigonometry. That is, using the distance between it and two antennas, the angle between the antennas and the spacecraft and the baseline between the antennas. But inaccuracies are introduced due to variations in the speed of light/radio waves in the atmosphere and solar plasma, and clock instabilities in the ground station. An additional radio source is used to compensate for these variations, which comes from the same approximate direction as the spacecraft. The radio source used is that from quasars, which result from gases falling into supermassive black holes at the centre of some galaxies. Since radio signals from both the spacecraft and quasar follow the same path, the radio delay time from atmospheric effects and clock variations can be determined and compensated for. The spacecraft’s location is compared to previously-established maps with the planets in the positions as they appear during the spacecraft’s journey. Taking into account the gravitational 1 2 1 2 3 3 0 effects of nearby moons and planets, signals are sent to the spacecraft to fire thrusters to correct the course. Once close to Mars, Earth-based navigation can no longer be used due to the 11+ minute radio signal delay (the exact delay varies depending upon the relative position of Mars and Earth). It was desired to land within 40m of the target area; the final landing position was determined visually with reference to ground features, just like the Apollo astronauts did. But in the case of Mars 2020, it had to be done by computer alone. Terrain images previously acquired by Mars-orbiting spacecraft were stored in the spacecraft computers. The lander’s radar and visual landing (Lander Vision System, LVS) took over at an altitude of 4.2km. The Lander Vision System is the camera and computer system used to provide data for Terrain-Relative Navigation. Starting at an altitude of 4200m, the LVS has to process live visual imagery and compare it with stored visual imagery, taking an initial navigational position error that could be as much as 3.2km before entry (but it turned out to be 200m). It determined the precise spacecraft location with reference to that stored imagery, reducing the position error to a desired 40m or less for landing, all within 10 seconds. For details on the LVS, see siliconchip.com.au/link/ab8g Using the position established by the LVS, the Guidance, Navigation and Control (GNC) system selected a suitable landing position that was reachable with the available fuel for the eight thrusters on the descent vehicle (see Fig.9). Fig.9: matches between the stored navigational map and a simulated descent image from the spacecraft, as used in Terrain-Relative Navigation. Note how the matches are made despite the different orientations and resolutions of the two images. 4 4 siliconchip.com.au Australia’s electronics magazine July 2021  15 Fig.10: safe landing areas from the Safe Targets Map, within and near the target landing zone that avoid hazardous terrain and unfavourable slopes. The thrusters on the descent vehicle ignited at an altitude of 2100m. To manoeuvre to the selected landing site, it could alter the landing position of the rover by up to 600m. There is a Safe Targets Map covering a 20km x 20km area, and each pixel in the map is assigned a landing risk level and information on whether that area has a favourable slope or not (see Fig.10). The objective of the GNC system was to fly to the most favourable target that was reachable. For further details of the GNC, see the PDF at siliconchip. com.au/link/ab8h Mars 2020 is regarded as the most accurately navigated space mission ever. Jezero crater Jezero crater was chosen as the landing site for Perseverance because it was once thought to be filled with water, and thus a possible location for life in the past. There is also evidence of two ancient river deltas (see Figs.11 & 12). It is possible that deposits washed down by the river would also contain evidence of ancient life. Apart from the ancient river deltas, it was determined that there must be extensive sedimentation, perhaps up to 1km thick, because the crater is much shallower than expected. There are also clay minerals present and cracking of the surface, both suggestive of the past presence of water. Fig.11: a geological survey map of part of the Jezero crater landing region, showing ancient river delta, dunes, shoreline, ash and other deposits. This map includes the Perseverance landing site and a possible exploration route (the yellow line). You can see an interactive and larger version of this map at https:// planetarymapping.wr.usgs.gov/interactive/sim3464 Source: Wikimedia user Hargitai. Parachute & Back Shell Descent Stage Heat shield Perseverance Fig.12: an image taken from the Mars Reconnaissance Orbiter of the Perseverance landing site, showing the lander plus various components jettisoned during landing. 16 Silicon Chip Australia’s electronics magazine The Perseverance rover The Perseverance rover (Figs.13-16) is an upgraded version of the previous Mars rover, Curiosity. The rover weighs 1025kg, which happens to be exactly the weight of an Australian spec Toyota Yaris, unladen. The rover is 3m long, 2.7m wide and 2.2m tall. The rover consists of an enclosed box called the Warm Electronics Box (WEB), in which sensitive electronics and other equipment is kept warm by surplus heat from the nuclear power source. Six wheels are attached to the WEB via a suspension system. On top of the WEB is an Equipment Deck, with the following accessories attached: • the camera mast • a primary 2.1m-long robotic arm • a secondary robotic arm to assist with sample storage • three telemetry antennas • the nuclear power source siliconchip.com.au Navcam Rear Hazcams SuperCam Navcam SHERLOC (WATSON) Mastcam-Z Front Hazcams PIXEL (Micro-Context Camera) Fig.14: a comparison of the wheels from the older Curiosity rover with Perseverance. The tread pattern enhances traction. Fig.13: the location of some of the cameras on the Perseverance rover. There are a total of 23 cameras – 9 for engineering, 7 for science, and 7 for entry, descent and landing. Note that the MEDA SkyCam is not shown. • various sensors for dust, wind, noise, air pressure and radiation • other cameras and miscellaneous items The Ingenuity helicopter was stored beneath the rover. Some key differences between Perseverance and Curiosity are: • Perseverance is heavier by 100kg+ • a larger robotic arm with a bigger turret • more cameras and new science instruments • it will collect rock samples and cache them for later collection by an Earth return mission • improved wheels • the software has greater autonomy Perseverance wheels, suspension and motors The Perseverance wheels are attached to the body by titanium tubing. The “rocker-bogie” suspension is designed so the rover can drive over rocks up to 40cm tall, or into depressions up to the size of the wheels. The six wheels are made of aluminium with titanium spokes and are 52.5cm in diameter. They have a reduced width, larger diameter and improved design compared to the Curiosity wheels, due to those wheels having sustained some damage in the previous mission (see Fig.14). A separate motor drives each wheel, and the front and rear sets of wheels can be steered, meaning the rover can perform a 360° turn on the spot. The rover can tilt as much as 45°, but for safety, the tilt angle is kept under 30°. The top speed of the rover is 0.152km/h (~4.2cm/s). For the science mission, no greater speed is necessary. The drive system uses less than 200W peak; 110W or less from the nuclear power source, plus auxiliary power from batteries when necessary. Mars Relay Network, which relays data from Perseverance, Curiosity and the InSight lander to the Deep Space Network (DSN). Perseverance antennas Perseverance is equipped with three antennas. These are a UHF antenna for about 400MHz, a high gain X-band and a low gain X-band antenna for communications in the 7GHz to 8GHz range. The UHF antenna is used to communicate with Mars orbiters which relay the message to Earth. Data can be transmitted from the rover to the orbiter at up to two megabits per second (2Mb/s). This is the main communication system. For redundancy, the X-band highgain antenna is steerable and can transmit data directly to Earth, and also receive data. The antenna is 30cm in diameter and can transmit or receive data to or from Earth at 160 or 500 bits per second, or faster from the DSN’s 34m antennas, or at 800 or 3000 bits per second with the DSN’s 70m antennas. Mars Relay Network Two Mars orbiting spacecraft, the Mars Reconnaissance Orbiter (MRO) and the Mars Atmospheric and Volatile EvolutioN (MAVEN), form the Fig.15: the locations of various instruments on Perseverance. ► Fig.16: a depiction of the Perseverance rover operating on Mars. siliconchip.com.au Australia’s electronics magazine July 2021  17 Fig.17: the layout of a RAD750 3U CompactPCI singleboard computer used on the Mars Curiosity rover and similar to the one used on Perseverance. The version used on Perseverance has more memory and a higher clock speed. Fig.18: the Mastcam-Z cameras before being mounted on the rover, with a pocket knife for scale. an earlier RAD6000 computer). The computer has 2GB of flash memory (about eight times as much as Spirit and Opportunity), 256MB of DRAM (dynamic random access memory) and 256KB of EEPROM (electrically erasable programmable read-only memory). There is a second copy of the main computer for backup, plus another one for image processing. The computer might be ‘old tech’, but it is super-reliable and has ample power for the job. A modern CPU with smaller feature sizes would be more prone to errors in the high-radiation environment in space and on Mars. The operating system used on Perseverance is VxWorks by Wind River Systems. It is designed for embedded systems, operates in real-time with minimal processing delays and supports the PowerPC architecture. Perseverance cameras The low gain X-band antenna is used to back up the X-band high gain antenna and communicate with the DSN. It is not steerable, so the data rate is much lower at 10 bits per second with the 34m DSN antennas and 30 bits per second with the 70m antennas. Perseverance microphones There have been three prior attempts to send microphones to Mars, but they all failed. Perseverance carries two microphones. One was a commercial off-the-shelf microphone to record the sounds of the entry, descent and landing. That one failed to work during entry, but it recorded the sounds of the nuclear power source cooling pump and other sounds during spaceflight and a system check. To listen to the spaceflight sounds, visit siliconchip.com.au/link/ab8i Since landing, it has functioned and has recorded other sounds. 18 Silicon Chip The other microphone is attached to the SuperCam Mast. It is used to make recordings on Mars and listen to the laser’s sounds interacting with rock specimens; the popping sounds giving off clues about rock density. To listen to some more sounds recorded by the rover, visit siliconchip.com. au/link/ab8j Perseverance computer Perseverance uses a PowerPC 750 chip which is radiation-hardened. It is the BAE RAD 750 processor and associated single-board computer (see Fig.17). This is essentially the same processor as used on the 1998 “Bondi blue” iMac G3, although the version with radiation-hardening costs over US$200,000 (that’s the 2002 price, but it is still in production and is used in over 100 spacecraft). It operates at up to 200MHz, ten times faster than those on Mars rovers Spirit and Opportunity (which used Australia’s electronics magazine Perseverance has a total of 23 cameras, as shown in Fig.13. This is an unprecedented number for any space mission. The cameras can be divided by purpose into three categories: entry, descent and landing; engineering cameras; and science cameras. An emphasis was placed on using commercially-available hardware when possible. For details of the cameras, see the PDF file at siliconchip. com.au/link/ab8k Entry, descent and landing cameras Seven cameras were used for entry, descent and landing: • three on the back shell looking up at the parachute • one on the descent stage looking down at the rover while the Sky Crane lowered it • another down-looking camera on the descent stage, used by the Lander Vision System (1024x1024 pixels) for use in Terrain Relative Navigation • one on the rover looking up to watch the Sky Crane manoeuvre • one on the rover looking down to watch the landing (with a microphone) Engineering cameras Nine engineering cameras are divided into three sub-categories: six hazard avoidance cameras (HazCams), two stereo navigation cameras siliconchip.com.au (Navcams) and one CacheCam. These are mounted in various locations. Each has a 5,120 x 3,840 pixel sensor (20MP). They use the same camera body but different lenses according to their task. The HazCams are mounted three at each end. They are used both for rover navigation and by engineers when directing the robotic arm. The two mast-mounted stereo Navcams are designed for autonomous rover navigation, without decisions being made by controllers on Earth. The CacheCam is for taking pictures of collected samples before they are placed inside sample tubes, sealed and deposited for later pickup by an Earth return mission. Science cameras There are seven science cameras, as follows: Mastcam-Z (Fig.18) comprises a pair of mast-mounted stereo zoom cameras that can rotate in all directions. It captures colour images and video at up to four frames per second at 1600 x 1200 pixels and can generate a 3D image. The zoom range is 28-100mm and the image sensor is a Kodak Truesense KAI-2020 CM interline transfer CCD. The resolution is about 1mm close to the rover and 3-4cm at 100m distance. It is equipped with several bandpass optical filters to help identify or distinguish various minerals, plus solar filters to image the sun. The main purposes of Mastcam-Z are to characterise the Martian landscape, observe atmospheric phenomena such as clouds and dust devils, assist in rover navigation, sample collection and sample caching. The SuperCam is a mast-mounted instrument that uses a laser to either reflect off or vaporise soil, rock and dust samples beyond the reach of the rover’s robotic arm, up to 12m away. One of two lasers is fired at a sample of interest, and then one or more of four spectrometers are used to determine the sample composition. The red laser is used to vaporise samples of interest up to 7m away, with three spectrometers determining the sample’s elemental composition. The green laser is directed at samples up to 12m away but does not vaporise them. The identities of minerals or organic compounds can be determined by analysing the reflected beam using spectrometers. siliconchip.com.au Fig.19: a plot of the relative number of counts at different energies to identify elements with the PIXL X-ray fluorescence instrument. The infrared spectrometer, one of the four spectrometers, can see out to the horizon. SuperCam also incorporates a high-resolution colour camera, a Remote Microscopic Imager (RMI) to take pictures of distant samples using a telescope and one of the two microphones, a Knowles Corp EK Series. SuperCam was a collaboration between the Los Alamos National Laboratory (LANL) and the IRAP Astrophysics and Planetology Research Institute (France), with a contribution from the University of Valladolid (Spain). PIXL (Planetary Instrument for X-ray Lithochemistry) is an X-ray fluorescence instrument for elemental chemical analysis mounted on the robot arm. In X-ray fluorescence, an X-ray beam is directed at a material of interest. The energy of the X-ray removes one or more electrons from an atom by ionisation, and other electrons in higher energy orbitals within the atom move down in energy level to replace the ionised electron. When an electron or electrons move to a lower energy orbital, they emit radiation of a wavelength equivalent to the energy difference. This wavelength is characteristic and unique for each element and can be used for identification. The instrument can look at structures in soil or rock at a sub-millimetre level with a 0.12mm beam width, and operates at high speed. It can detect the following chemical elements: Na, Mg, Al, Si, P, S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, As, Br, Rb, Sr, Y, and Zr. That includes most of the elements from atomic number 11 to 40. Australia’s electronics magazine PIXL uses a Micro Context Camera (MCC) to acquire images of the test areas – see Fig.19. The SHERLOC (Scanning Habitable Environments with Raman and Luminescence for Organics and Chemicals) Context imager is an ultraviolet Raman spectrometer that uses a UV laser to look at mineral samples at a fine scale, to detect organic compounds, including biosignatures (see Fig.20). It is mounted on the robot arm. The rover is equipped with small pieces of spacesuit material, which it tests for accuracy and to see how they degrade with time. SHERLOC has a monochrome camera for context, attached to the robotic arm. SHERLOC can image an area of 2.3cm x 1.5cm with the camera (the Advanced Context Imager, ACI) and performs spectroscopy on a 7mm x 7mm area. Also associated with SHERLOC is a “context imager” camera named WATSON (Wide Angle Topographic Sensor for Operations and eNgineering), which takes extreme close-up photographs of the sample areas tested by SHERLOC. Fig.20: the SHERLOC ultraviolet spectrometer engineering model. July 2021  19 Apart from working with SHERLOC, WATSON bridges the resolution gap between the very fine detail obtained from SHERLOC and the much larger scale from Mastcam-Z and SuperCam (see Fig.15). WATSON is attached to the robotic arm and is mainly concerned with details of rock textures, fine debris, dust and structures. MEDA (Mars Environmental Dynamics Analyzer; see later) has a SkyCam camera to take images of the Martian sky. Power source Fig.21: a photo of the rover upside-down, showing the MMRTG unit in the centre. It is surrounded by eight cooling fins; the curved panels on each side are heat exchangers connected to the core by yellow coolant tubes. Bimetal ring Seal weld cover Surface emissivity change Min-K insulation Isolation bellows T/E getter assembly Isolation liner assembly Heat distribution block Mica Cooling tube General purpose heat source Microtherm insulation Thermoelectric couple assembly New TE technology Microtherm insulation Module bar Power out receptacle Fig.22: a cutaway view of the Enhanced Multi-Mission Radioisotope Thermoelectric Generator, similar to the one on Perseverance. Navigating with the Deep Space Network (DSN) Spacecraft can navigate using the radio telescopes of the DSN. The distance from Earth is established when a precise time-coded radio signal is sent from the DSN and returned. The time taken is used to calculate the distance, while the dish antennas can determine the angular position of the spacecraft compared to Earth. More precise measurements can be made using two DSN telescopes at the same time. This gives the spacecraft distance to each telescope. The distance between each telescope is also known precisely, so triangulation can be used to calculate the distance. Further accuracy can be obtained using the signals from a star type known as a quasar, with a known position as a reference, as explained in the main text. What is a sol? A sol is a solar day on Mars. It is slightly longer than an Earth day at 24 hours, 39 minutes, 35 seconds. There are 668 sols in a Martian year (about 687 Earth days). 20 Silicon Chip Australia’s electronics magazine The rover uses a Multi-Mission Radioisotope Thermoelectric Generator (MMRTG) for electrical power – see Figs.21 & 22. It was designed by Teledyne Energy Systems and is based on the design previously used by Pioneer 10 (1972) and 11 (1973), Viking 1 (1975) and 2 (1975). It converts heat from radioactive decay directly into electricity using thermoelectric couples connected in series as thermopiles. The MMRTG produces about 110W at launch, but due to radioactive decay and degradation of the thermocouples, that reduces over time. The Perseverance rover has a design lifetime of three of our Earth years, but it is expected that the MMRTG will produce sufficient power for its design life of 14 years; it will likely last much longer than that. The RTGs on the Voyager spacecraft (described in the December 2018 issue; siliconchip.com.au/Article/11329) are still going 44 years after launch (since 1977). To meet brief periods of peak electrical demand, the MMRTG charges two Li-ion batteries which provide supplemental power. Excess heat is dissipated with a heat exchanger that uses trichlorofluoromethane (CFC-11) fluid. Some of this heat is used to keep the rover systems warm during interplanetary cruise and on Mars’ surface. The MMRTG is a cylinder 64cm in diameter and 66cm long, weighing 45kg. It uses 4.8kg of plutonium dioxide as fuel, containing the isotope Pu-238. The radioactive heat source is contained within multiple layers to remain safe and survive the worst possible launch accident. Perseverance instruments apart from cameras MEDA is an instrument located at siliconchip.com.au siliconchip.com.au ► Fig.23: the process by which MOXIE converts Martian CO2 to O2. C&DH stands for Command and Data Handling systems, RCE is Rover Compute Element, RPAM is Rover Power and Analog Assembly and RAMP is Rover Avionics Mounting Panel (or Plate according to some sources). ► various places on the robot body to analyse airborne Martian dust and also make weather measurements – see Fig.15. It measures wind speed and direction, temperature and humidity, quantity and size of dust particles, and radiation from the sun and space. The instrument was developed and provided by the Spanish Astrobiology Center at the Spanish National Research Council in Madrid. You can view the latest Martian weather report at https://mars.nasa.gov/mars2020/ weather/ to see whether you need an umbrella on your Martian vacation. MOXIE, the Mars OXygen In-situ resource utilization Experiment, is a device inside the rover which is designed to test the technology of turning carbon dioxide (CO2), the dominant gas in the atmosphere of Mars, into oxygen (O2) – see Figs.2325. This technology could be used on later manned missions to produce breathable oxygen for Martian explorers to breathe. It is a 1:200 scale model of a plant that might be used for a manned mission. Oxygen can also be used as one component of rocket propellant. The reaction of 2CO2 → O2 + 2CO is a solid-state electrolysis reaction conducted within a ceramic reaction cell at high pressure and temperature (800°C). The carbon monoxide, CO, produced from this reaction can be used as a low-grade fuel when oxidised with the O2. Alternatively, it can be combined with hydrogen (H2) from the electrolysis of water (H2O), believed to be present on Mars in numerous locations, to produce methane (CH4) via the reaction CO + 3H2 → CH4 + H2O. H2 is a high-grade rocket fuel when used with O2 as the oxidiser. CO2 can also be converted to CH4 (methane) by the reaction CO2 + 4H2 → CH4 + 2H2O. Producing oxygen for breathing and propulsion and methane for propulsion is important because the large quantities required would be unfeasible to bring from Earth. Nuclear power would be the power source for these reactions. R I M FA X ( R a d a r I m a g e r f o r Mars’ Subsurface Experiment) is a ground-penetrating radar to probe the ground beneath the rover, looking at subsurface geological features Fig.24: a top view of MOXIE. It is designed to operate at very low Martian atmospheric pressures, 1% or less than Earth’s at sea level. Fig.25: the MOXIE device being lowered into the belly of the rover. The rover is upside-down to give better access for the installation. The unit measures 24 x 24 x 31cm, weighs 15kg and consumes 300W. Australia’s electronics magazine July 2021  21 – see Fig.29. It operates at 150MHz to 1200MHz, has a vertical resolution of 15cm to 30cm and a penetration depth up to 10m, depending on conditions. It can detect water, ice or salty brines, important in the search for water, and will operate as the rover drives along. It was developed and built by the Norwegian Defence Research Establishment (FFI). Ingenuity helicopter Fig.26: the locations of various systems on the Ingenuity helicopter, see https://w.wiki/3LWt Fig.27: technicians preparing Ingenuity, the actual vehicle that went to Mars, for flight tests inside the NASA/JPL 25-foot Space Simulator. The gold tubes are a support structure, not part of the helicopter. The stainless steel Simulator chamber is 26m high with an 8.2m diameter, and can be pumped down to the vacuum of space, or in this case, it can be pressurised to be the same as the Martian atmosphere. The facility has been in use since 1961. Fig.28: a selfie taken by Perseverance, along with the Ingenuity helicopter it carried as payload on April 5th 2021. Note the rover tracks. 22 Silicon Chip Australia’s electronics magazine The Perseverance rover carried with it a small helicopter which was the first powered aircraft to fly on another planet (see Figs.26 & 27). It is a technology demonstrator to prove whether a helicopter can fly on Mars. Photographs from a helicopter would have about ten times the resolution of orbital images, and could assist with route planning and mapping on future missions. The helicopter could fly ahead of a rover as a scout (see Fig.28), or it could pick up samples and bring them back to a central point for analysis. It could go to places a rover could not reach, such as to take close-up images of the sides of cliffs. Note that while this is the first powered aircraft on another planet, it is not the first aircraft. In 1985, the Soviet Vega missions deployed two helium balloons (“aerobots”) on Venus. Ingenuity was planned to have a 30-day program of test flights. A typical flight lasts up to 90 seconds, and it can go as far as 300 metres from the “airstrip” and as high as 3-5 metres. Images are taken during the flight. The helicopter communicates with Earth via a datalink with the rover or Martian orbiters. Once the flight test program is complete, the rover will drive off, leaving the helicopter behind, and it is not planned to be used again. Flying a helicopter on Mars has many challenges. The atmospheric pressure is extremely low; about 1% of that on Earth. This is eased somewhat by the lower gravity on Mars, about 38% that of Earth. According to Bob Balaram, Chief Engineer of JPL Mars Helicopter, flying a helicopter near the surface of Mars is equivalent to flying one on Earth at an altitude of 30,000m. The highest altitude ever achieved on Earth by a helicopter was 12,954m on March 23rd, 2002 by Fred North in a Eurocopter AS350 B2 (view the video at www. fred-north.com/record). siliconchip.com.au siliconchip.com.au Leg assembly Upper sensor assembly ► To fly on Mars, the helicopter’s coaxial rotors have to spin at about 2400rpm, compared to about 500rpm of a full-size Earth-based helicopter. However, this is not as fast as the rotors on a small quadcopter, which can reach about 6000rpm. The helicopter weighs 1.8kg on Earth or 684g on Mars (comparable to a DJI Phantom 4 at 1.38kg on Earth). Ingenuity’s rotors have a diameter of 1.2m, weigh 35g each, and are made of foam-cored carbon fibre. Their tip speed is restricted to Mach 0.7, as there are lots of undesirable effects at higher tip speeds. The rotor size was dictated by the available accommodation space on the rover. A further detail for aviation buffs is that the cyclic and collective are on the lower rotor, with just a collective on the upper rotor. A solar panel charges a six-cell Li-ion battery to allow one 90-second flight per day. The power required for flight is 350W. At night, energy is also consumed to keep the battery and other electronics warm and functional despite outside temperatures of -18°C to -100°C. Two-thirds of the battery energy is used to keep the batteries and electronics warmed to a temperature of at least -15°C, with only one-third of the battery energy used for flight operations. The cells used are commercially available Sony units, US18650VTC4 Li-ion cells of nominal 2.1Ah capacity each (2.0Ah rated capacity), which anyone can buy off the shelf! Some sensors on the aircraft include: • a solar tracker • gyros • inertial measurement unit (IMU) • a visual navigation camera (to keep track of flight by feature comparison with previous video frames) • a 13-megapixel Sony colour camera for photography • tilt sensors • laser altimeter (Garmin LIDARLite v3) • hazard detectors The helicopter runs Linux with multiple processors. The main one is a Qualcomm Snapdragon 801 2.26GHz ARM processor with 2GB RAM and 32GB of flash memory for high-level functions; this was also used in some smartphones. Two Texas Instruments Hercules TMS570LC43x automotive safety microcontrollers at 300MHz with Fig.29: an example of what a RIMFAX subsurface image might look like showing sedimentary layers. Avionics boards Battery Lower sensor assembly Fig.30: the arrangement of the avionics ► boards and other items around the six-cell battery assembly. This way, the heat generated to keep the battery warm also keeps the other parts warm. 512KB RAM and 4MB flash are used for flight control – see Fig.31. They run in synchrony, and if an error is detected in one, the other takes over and the one with the error is power cycled to reset it. A MicroSemi ProASIC3L FPGA (field-programmable gate array) is the heart of the helicopter, providing functions not implemented in software due to resource limitations such as processing time or bandwidth. It provides high-level flight control, including: • attitude control • motor control • waypoint guidance • sensor I/O from the inertial measurement unit (IMU) • altimeter and inclinometer interface • current monitoring and temperature sensing • fault monitoring • system time management (eg, waking up the helicopter at a particular time) It does this using 25 separate serial interfaces. The FPGA functions are implemented using configurable logic gates rather than software. The FPGA and the battery management system are the only two systems on the machine powered at all times. Communications uses the lowpower Zigbee protocol (COTS 802.15.4) with 900MHz SiFLEX02 chipsets relaying data at up to 250kbps with a range of up to 1000m. The ‘copter was test flown in a large vacuum chamber at JPL, the “25-foot Space Simulator” pumped out and back-filled with a carbon dioxide atmosphere at Mars pressure. Lower gravity was simulated by partially supporting the craft on a fishing line connected to a constant-force linear motor to offset part of the weight. The helicopter cannot fly freely on Earth without this offset. The reason for using a coaxial helicopter design rather than a quadcopter design, as is commonly used for drones, is that the blades would have Fig.31: the layout of the avionics boards on Ingenuity. They are wrapped into five sides of a cube around the battery pack as shown in Fig.30. Australia’s electronics magazine July 2021  23 Fig.32: NASA’s proposed Kilopower concept, with four individual reactors (umbrella-like objects) of 10kW each, plus a nuclear-powered crewed vehicle. to be so large that the aircraft would not fit on the rover. Coaxial rotors are also an efficient arrangement for providing thrust, although they are mechanically more complex than a traditional helicopter arrangement using a tail rotor. The helicopter’s software, like the rover, can be remotely updated from Earth. During the first high-speed rotor spin test of Ingenuity on Mars, a problem was identified: it “did not transition from a pre-flight check-out mode to its flight mode as expected... The onboard logic did not recognize the flight control computers as healthy and functional, even though it was confirmed they were.” A software update was developed and validated, then sent via the DSN to a Mars orbiting satellite, transferred to Perseverance, then to Perseverance’s Helicopter Base Station (HBS). The HBS is a “dedicated controller in the rover which collects, stores, and configures data communications between the rover and the helicopter”. The software was then relayed to the helicopter. Ingenuity had its first successful flight on April 19th, 2021. It lasted 39.1 seconds. See the video titled “First Video of NASA’s Ingenuity Mars Helicopter in Flight, Includes Takeoff and Landing (High-Res)” at https://youtu. be/wMnOo2zcjXA For further details on the Ingenuity helicopter, see the PDF file at http:// siliconchip.com.au/link/ab8l Power sources for future Mars settlements This mission partly relates to gathering information in preparation for a human landing on Mars, including converting atmospheric CO2 to O2. So it is worth considering what power sources could be used for such a settlement. Solar energy is too weak on Mars for serious use (sunlight is about 40% as intense as on Earth). Large amounts of power would be needed for atmospheric processing and other functions; therefore, nuclear power would likely need to be used. NASA has developed the Kilopower concept for nuclear power on Mars (see Figs.32 & 33). It uses a Uranium-235 core and can run for 10 years without maintenance. It uses a Stirling engine to convert heat to mechanical force, to power a generator producing electricity. It also uses a titanium radiator to dispose of excess heat, beryllium as a neutron reflector and a boron carbide rod to control the reactor’s output or shut it down. For more information on the Mars 2020 mission visit: https://mars.nasa. SC gov/mars2020/ Stirling engines and balancers Titanium radiator Stirling converters Sodium heat pipes Lithium hydride shielding Sodium heat pipes Beryllium shield and uranium core Fig.33: a highly simplified diagram of the NASA Kilopower nuclear reactor. Some of the internal detail is shown on the right. A Stirling radioisotope generator is about four times more efficient than a radioisotope thermoelectric generator (RTG), as used on the Perseverance rover and Voyage spacecraft. 24 Silicon Chip Australia’s electronics magazine Beryllium oxide reflectors Reactor core Boron carbide control rod siliconchip.com.au Design, Develop, Manufacture with the latest Solutions! Powering New Technologies in Electronics and Hi-Tech Manufacturing Make new connections at Australia’s largest Electronics Expo. See, test and compare the latest technology, products and solutions to future proof your business SMCBA CONFERENCE The Electronics Design and Manufacturing Conference delivers the latest critical information for design and assembly. Industry experts will present the latest innovations and solutions at this year’s conference. Details at www.smcba.asn.au In Association with siliconchip.com.au Supporting Publication Australia’s electronics magazine Organised by July 2021  25 BY JOHN CLARKE 20A DC Motor Speed Controller This small but powerful speed controller has a 20A rating and is packed with features. It suits a wide range of applications, and is simple to build and use. Features include low-battery protection, soft starting and adjustable pulse frequency. It can handle DC motors that run from near 0V up to 30V. T here are a great many applications for DC motors where speed control is desired or necessary. Since DC motors can be run directly from batteries, they are used in golf carts, electric scooters, bikes and skateboards, remote-controlled cars and boats – the list goes on. In most of those applications, you need a way to control the speed of the motor. Going flat out all the time isn’t always a good idea! A speed controller like this one is the ideal solution. It can handle DC motors with a rated voltage of up to 24V (30V maximum) and continuous currents up to 20A. The controller is presented as a bare electronic module built on a PCB that can be installed within a standard UB3 plastic case if required. It includes heavy-duty terminals for the power supply and motor connections, plus additional terminals for the speed control potentiometer that mounts off the PCB. The motor driving components are mounted on substantial heatsinks for cooling. The adjustable features like soft-start rate and feedback gain are set using onboard multi-turn trimpots with voltage test points. An onboard LED indicates the speed setting, as 26 Silicon Chip well as faults like low battery or motor disconnection. Speed controller design While we have published many DC motor speed controllers in the past, this version has more features and better performance. The motor speed is controlled using Pulse Width Modulation (PWM). That means that the motor is driven by a series of on and off voltage pulses rather than a variable DC supply, making it more efficient. Speed control of the motor is done by varying the pulse width. The ratio of the pulse width to the interval between pulses is the duty cycle. A low duty cycle will only provide a voltage to the motor for a small portion of the time, and the motor runs slowly. As the on-pulse duration increases, this greater duty cycle makes the motor run faster until it reaches 100% duty cycle and is driven continuously. Oscilloscope traces Scope 1 & Scope 2 show how this PWM scheme works. In Scope 1, the top (yellow) trace is the gate drive signal for Mosfets Q1 and Q2. When it is high, the motor is powered. In this case, the duty cycle is very low at about 9.5%, so the motor runs slowly. The lower cyan trace is related to the motor current. This is Australia’s electronics magazine used to maintain motor speed with a variable load. Scope 2 has the same two traces, but this time the duty cycle is much higher, and the motor runs faster. The motor is loaded less than in Scope 1, so the current reading is lower despite the higher duty cycle. What’s new One of the problems with controlling DC motors using PWM is that the motor can make extra noise due to the motor windings and other mechanical parts vibrating at the PWM frequency. This can be alleviated to some extent by adjusting the PWM frequency to produce minimal noise. That noise tends to be reduced as the PWM frequency is increased, and is mostly eliminated at PWM frequencies above 20kHz (around the upper limit of human hearing). But increasing the frequency can cause problems too. It becomes harder to maintain the motor speed against a varying motor load using the traditional back-EMF feedback system. Very high PWM frequencies can also cause a loss of motor torque. These problems and solutions are described in more detail in the separate section entitled “PWM motor siliconchip.com.au driving pitfalls at higher frequencies”. This controller gives you the ability to adjust the PWM frequency beyond audibility while addressing the problems of limited low-speed motor torque and control at elevated frequencies. Other features that are incorporated include soft starting, low-voltage cutout, LED status indication and optional motor disconnected detection. These features are easy to set up and adjust via trimpot adjustments. Features Soft starting • • • • • • • • • • • This is where the motor is slowly increased in speed, up to the setting of the speed pot. Soft starting reduces the surge of current and rapid build-up of motor torque compared to applying power suddenly. The PWM duty cycle is ramped up over a longer period, so the motor starts more smoothly. The maximum soft-start period is two seconds for the full range from 0% duty to 100%. This period can be adjusted from between zero and two seconds in 255 steps. Soft starting can be initiated in several ways. It applies when the controller is initially powered up, or when the speed control is started from the fully off position, and finally, after returning to regular operation from low-voltage shutdown. • • • • • • • • • • DC motor PWM drive Can drive motors rated up to 24V and 20A DC Motor and controller supply voltage can be separate 16 PWM frequency choices Motor load feedback control & gain adjustment Adjustable soft-start rate Motor speed curve adjustment Under-voltage cut-out with LED indication & adjustable hysteresis Duty cycle LED indicator Optional motor disconnect detection Specifications Speed adjustment range: 0% to 100% duty cycle Motor supply: from near-zero to 30V maximum Controller supply: 10.5V to 30V maximum (5.5-26V with ZD1 linked out) Speed indication: LED1 brightness varies with PWM duty cycle PWM frequency: 16 steps from 30.6Hz to 32.4kHz (see Table 1) Soft-start rate: 0-2 seconds in 255 steps for 0% to 100% duty cycle Speed curve adjustment: minimum speed can be set to 0-33% duty cycle Under-voltage (UV) threshold: 0-30V in 29.6mV steps UV hysteresis: 0-5V in 29.6mV steps UV indication: LED1 flashes on for 65ms at 1Hz Motor disconnection detection: motor is shut down if monitored current drops to zero while driving motor; indicated with 2Hz/50% duty cycle LED flashing • Speed pot disconnection detection: indicated with a dimly illuminated LED Scope 1: a pulsewidth modulated (PWM) drive signal at a low duty cycle, about 9.5%. Current has little time to build during each pulse, so the motor runs slowly. Low-voltage detection The low-voltage detection feature is included to prevent over-discharging a battery supplying power to the motor. Most batteries, including lead-acid and lithium chemistry types, will be damaged if discharged beyond a certain voltage. This features switches off the motor drive at a pre-set threshold voltage. This is indicated with a 65ms flash of the indicator LED at 1Hz. The voltage must be below the threshold for more than ten seconds before the drive to the motor is switched off. This prevents any nuisance low-voltage trips that would otherwise switch off the controller due to a short-term voltage drop when the motor starts up. Once shut down, the voltage needs to rise above the low-voltage detection threshold by a certain amount before it will start up again. This hysteresis prevents constant switching on and off as the battery voltage recovers with the motor load removed, only to switch off again once the motor restarts. siliconchip.com.au Scope 2: another PWM drive signal, this time with a duty cycle of 35.5%. This is roughly equivalent to driving the motor at 1/3 of the supply voltage, so it will run faster but not nearly at full speed. Australia’s electronics magazine July 2021  27 Motor disconnection The optional motor disconnect detection prevents the motor from starting up if it is disconnected and then reconnected while the speed setting is above zero. When the motor is detected as disconnected, the speed potentiometer needs to be wound fully anticlockwise and the motor reconnected before it can run again. The disconnected state is indicated with the indication LED blinking at 2Hz. Separate supply voltage Another feature is the ability to separate the controller’s supply voltage from the supply to the motor. This means that the motor can be run from a much lower supply voltage than that required to operate the DC Motor Speed Controller. So while the DC Motor Speed Controller requires a supply of at least 10.5V to operate (up to 30V), the motor can be run using a separate supply from near 0V up to 30V. The 30V limit is sufficient to allow for just about any 24V battery; eg, a fully charged 12-cell lead-acid battery is around 29V. You can use the same supply for both the controller and the motor, provided the voltage is in the 10.5-30V range, and that voltage is suitable for the motor. Circuit details The full circuit for the DC Motor Controller is shown in Fig.1. It is based around an 8-bit PIC16F1459 microcontroller, IC1, which provides the PWM drive signal and monitors the battery voltage, motor current and the voltage from several trimpots and the speed potentiometer. IC1 also monitors rotary switch S1, which selects the PWM frequency. IC1 has two PWM outputs, and we use both. One is at pin 5 (PWM1) and the other at pin 8 (PWM2). These PWM outputs have different functions, but provide the same PWM frequency and duty cycle most of the time while the motor is being driven. The PWM1 output is used to drive Mosfets Q1 and Q2 via gate driver IC3. IC3 is an MCP1416, designed to provide a high-current drive with fast rise and fall times to the Mosfet gates. This ensures that they switch on and off quickly. Each Mosfet gate is isolated from the other using a 10W resistor. The resistors also prevent Mosfet switching oscillations at the gate threshold. 28 Silicon Chip These Mosfets are logic-level types that fully conduct with a gate voltage of 5V. Non-logic-level Mosfets typically require at least 10V for full conduction. The two Mosfets are connected in parallel, and so share the load (motor) current. Low-value resistors are placed between the source of each Mosfet and ground, with Q1’s source resistor being used to monitor the current. The source resistor on Q2, while not used for load current measurement, is still necessary. That’s so that the total on-resistance of Mosfet Q2 and its source resistor matches Q1 and its source resistor. Since the Mosfet on-resistance is typically 0.014W, the 0.01W source resistor for Q2 helps maintain even sharing of the load current between the two Mosfets. Without it, Q2 would carry about 2/3 of the load current and Q1 only 1/3. Diode D1 is included between the positive supply and the Mosfet drains to clamp the induced voltage spike when the motor’s drive is switched off. This diode is effectively connected across the motor terminals. It is a dual 10A schottky diode that can conduct 20A continuously when the diodes are connected in parallel. Paralleling the diodes ensures nearly equal current sharing. That is possible because the two diodes are on the same silicon die, and therefore have the same characteristics and operating temperature. The motor supply is connected to the GND and motor supply + terminals on screw connector CON1. This positive supply is fed to the motor via fuse F1, an automotive blade-type fuse with a rating selected to suit the motor. Three 470μF 35V low-ESR electrolytic capacitors bypass the motor supply after the fuse. These are to provide a high short-term peak current supply. Feedback control Many DC motor speed controllers monitor motor back-EMF (electromotive force) to determine when variations in the load might reduce the speed of the motor. This back-EMF is the voltage generated by the motor when the supply to it is switched off and the motor is still turning. The induced voltage reduces when the motor slows under load. Speed control is maintained by Australia’s electronics magazine increasing the PWM duty cycle to increase motor torque and speed when its speed drops. But we don’t use the back-EMF sensing method for reasons described under the section “PWM motor driving pitfalls at higher frequencies”. Instead, we monitor its current draw. When Mosfets Q1 & Q2 are conducting, the voltage across Q1’s 0.01W source resistor is proportional to the current being drawn by the motor. When the Mosfet is off, there is no voltage across this resistor. So we use a sample-and-hold circuit to capture the voltage while Q1 is conducting. Mosfet Q3 and the 100μF capacitor form the sample-and-hold buffer. The gate of Q3 is driven by the PWM2 output of IC1, which follows the PWM1 output. So when Q1 and Q2 are on, so is Q3, and the 100μF capacitor charges or discharges so that its voltage approaches that across the 0.01W current sense resistor. When Mosfets Q1 & Q2 switch off, so does Q3, isolating the 100μF capacitor from the 0.01W resistor to prevent it discharging during the off-time. The reason we use the separate PWM2 output to drive Q3 has to do with the case when the motor is off. In this case, the PWM1 output has a duty cycle of 0% (ie, it’s held low), but PWM2 is programmed to produce a 60μs pulse every 13.4s. This switches Q3 on momentarily, discharging the 100μF capacitor via the 0.01W resistor. This on-duration is extended if the capacitor needs to be discharged from a higher voltage, especially when the motor is turned off by reducing the speed control. Without this, the 100μF capacitor slowly charges via leakage current from amplifier IC2, causing the motor to start rather abruptly. IC2 is an instrumentation amplifier and provides amplification of the small voltage across the shunt for current measurement. Its gain can be adjusted from between 611, when trimpot VR6 is at minimum resistance, and about nine times when the trimpot is at its maximum of 50kW. This caters for the wide range of motors that could be used, ranging from those drawing less than 1A up to 20A. The output from IC2 is monitored by the AN9 analog input (pin 9) of microcontroller IC1, which uses its internal analog-to-digital converter (ADC) to convert the voltage from IC2 into a 10-bit digital value (0 to 1023). siliconchip.com.au Fig.1: microcontroller IC1 monitors the positions of speed pot VR1 and trimpots VR2-VR5 via five analog input pins. It also reads the position of BCD switch S1 (used to set the PWM frequency) using four digital inputs. A PWM waveform is produced at pin 5, which drives Mosfets Q1 & Q2 via driver IC3; those Mosfets switch current through the motor. The motor current is converted to a voltage using a 10mW shunt; this voltage is amplified by IC2 and measured at pin 9 of IC1. Speed control Potentiometer VR1 is the main speed control. The voltage at its wiper varies with its rotation, and is fed to analog input AN5 (pin 15) of IC1. This is converted to a 10-bit digital value, indirectly controlling the PWM duty cycle applied to the Mosfets. Motor load compensation is performed by increasing the duty cycle of the PWM signal depending on the motor load, based on the motor siliconchip.com.au current. The amount of feedback applied is adjusted by setting the gain for IC2, as described above. Supply voltage monitoring The motor supply voltage is monitored at analog input AN10 (pin 13) of IC1. The supply voltage is reduced to one-sixth (1/6) of its full value by a 10kW/2kW voltage divider. So for a 0-30V motor supply, the voltage at AN10 is in the range 0-5V. Australia’s electronics magazine This voltage is filtered using a 100nF capacitor to prevent noise from altering the result of the ADC conversion. Setting adjustments This voltage is compared with the under-voltage threshold setting voltage at the AN7 input, pin 7, set by trimpot VR4. This trimpot is connected across the 5V supply, allowing a voltage range adjustment from 0-5V. July 2021  29 PWM motor driving pitfalls at higher frequencies When using PWM to drive a DC motor, the average motor winding current varies depending upon the duty cycle. Since torque is proportional to the winding current, the motor speed can be easily controlled. In theory, the motor speed is not affected by the frequency; it is only the duty cycle that matters because that sets the average current through the motor windings. Higher PWM frequencies will result in less ripple in the motor current, but will not affect the average significantly. But there are cases where higher frequencies can affect the current at lower duty cycles, to the point that the motor will refuse to turn at all with lower duty cycles. There is much confusion over the reasons for this and what to do about it. We trawled the internet trying to find a good explanation of this phenomenon, and most of the information we came up with was misleading or incorrect. So we performed several experiments to find out for ourselves. The bottom line is this: if you are using a half-bridge or full-bridge to drive a DC motor, it will behave pretty much as theory predicts. The motor current varies almost exactly linearly with the PWM duty cycle, regardless of frequency. That is what you would expect if you model the motor as an inductance in series with a resistance. If the inductance is L and the series resistance is R, the motor winding impedance is then R + 2π × f × L. The current for a sinewave at any given frequency f is then V ÷ (R + 2π × f × L). A PWM signal comprises a DC component (the average level, V × duty cycle) plus AC components at the switching frequency f, and its squarewave harmonics at 3f, 5f, 7f etc. The exact mix of harmonics varies with the duty cycle. As the current decreases with 30 Silicon Chip increasing frequency, the winding inductance attenuates the AC components of the PWM signal. The motor windings act to smooth out these ripples, but the inductance has no effect on the direct current level; it is solely determined by the supply voltage, duty cycle and motor winding resistance. Our tests bear this out. But like many simpler designs, our motor speed controller does not use a half-bridge or full-bridge design and therefore does not produce a square wave across the motor windings. The motor’s positive terminal is connected to V+, and the negative end is periodically pulled down to 0V when Mosfets Q1 & Q2 switch on. Some of the time, we have V+ across the motor. But the rest of the time, when Mosfets Q1 & Q2 are off, the winding inductance and back-EMF pull the motor’s negative terminal above the positive terminal. The voltage is clamped by diode D1 to around 0.5V above the positive voltage. So there is a negative voltage across the motor when the Mosfets are off, rather than 0V, and a significant recirculating current flows through diode D1. This causes the motor winding current to decay significantly faster than in the half-bridge or full-bridge case described above. You can see this if you compare Scopes 3 & 4. These show the same unloaded DC motor being driven at the same PWM frequency (3.92kHz) and same duty cycle (10%) but with half-bridge drive in Scope 3 and single-ended drive in Scope 4. The yellow trace shows the applied voltage, while the green trace shows the current through the motor windings. The rate of current rise and peak current are similar between the two. But when the high-side Mosfets switch off and the low-side Mosfets switch on in Scope 3, you can see a exponential decay in the motor winding current. Australia’s electronics magazine The current flows throughout the whole cycle until it starts rising again on the next cycle. In Scope 4, with the current recirculating through the diode during the off-time, it decays exponentially (but faster), then linearly, reaching zero before the next cycle. Therefore, the average current is much lower, around half (a reading of 400mV vs 800mV), despite the duty cycle being the same. Scope 5 shows the same half-bridge drive scheme used in Scope 3, again with a 10% duty cycle, but at a much higher PWM frequency of 31.4kHz. The average current is only a little bit lower, reading about 750mV compared to around 800mV, due to the Mosfet ‘dead time’ being more significant at this higher switching frequency. Scope 6 shows the same singleended drive scheme as in Scope 4, but this time at 31.4kHz. The current disparity has increased further – the average winding current is now only 286mV. So the effect of the single-ended drive scheme on motor current is worse at higher frequencies. With the single-ended drive scheme, the average motor current for low duty cycles is less than expected, and this effect increases at higher frequencies. So it is a good idea to increase the minimum duty cycle at higher PWM frequencies to compensate, which is the reason for trimpot VR3 in this design. The magnitude of this effect can vary with the motor, too. Larger motors with a higher inductance will tend to suffer more from reduced current (and torque) at low duty cycles with higher PWM frequencies. In practice, the easiest way to compensate for this effect is to tune the minimum duty cycle setting (by adjusting VR3) until you get satisfactory speed control at the lower end of speed pot VR1’s range. If this cannot be achieved for a given motor, try a lower PWM frequency. siliconchip.com.au Scope 3: the voltage across the motor (yellow) and current (green) with a half-bridge at 10% duty cycle. The motor inductance limits the current rise and fall times. The current does not fall back to zero before the next pulse, despite the relatively low duty cycle; the winding inductance sustains it. Test point TP4 is included so the set threshold can be measured. To make setting up easier, the voltage at TP4 is one-tenth the undervoltage threshold. So if you want the under-voltage threshold to be 11.5V, set the voltage at TP4 to 1.15V. The voltage at the AN7 input is converted to a digital value and multiplied by 1.6666, so the scale matches the dividedby-six motor voltage. The motor supply has to drop below this threshold for 10 seconds before the drive to the motor is switched off. When this happens, LED1 flashes momentarily each second. Typically, a battery will recover a little when the motor drive is switched off; the battery voltage will rise once there is no load. To prevent the motor from switching on again due to this effect, we add hysteresis. The motor supply will need to go above the low voltage threshold plus the hysteresis voltage before the motor drive will be re-enabled. In practice, the battery needs to be charged before the motor can run again. This hysteresis is set using trimpot VR5 and can be monitored at TP5. The TP5 reading is the full hysteresis voltage (not 1/10th as it is with the threshold measurement at TP4). So if you want a 1V hysteresis, adjust VR5 until TP5 reads 1V. Scope 5: switching back to half-bridge driving but bumping up the frequency to 31.4kHz, you can see that the average current value is hardly affected. The current level averages higher during the off-time due to the shorter off period. siliconchip.com.au Scope 4: like Scope 3 but we have switched from a halfbridge driver to a single Mosfet with a recirculating diode, as used in this (and many other) Speed Controllers. This dramatically affects how the current tapers off at the end of each pulse, so the motor current is much lower with low duty cycles. The soft-start period adjustment is with VR2, measured at TP2. This voltage is monitored at the AN6 input, and sets the maximum rate at which the motor speed increases. The maximum time to reach 100% duty cycle from zero is two seconds, with 5V at TP2. A 2.5V setting will give a one-second soft-start period, and so on. VR3 is the speed curve adjustment trimpot, with corresponding test point TP3. This is monitored at the AN4 input of IC1, pin 16. This allows the speed pot to be used over its entire range when the PWM frequency is set relatively high, and can also compensate for the fact that motors can require Scope 6: the single-ended drive with the higher frequency suffers from the same rapid decay in current as shown in Scope 4, except this time the average current is even lower as it has less time to build during the shorter on-pulses. Australia’s electronics magazine July 2021  31 Power supply The DC Motor Speed Controller with speed control potentiometer VR1 attached for testing. a duty cycle well above 0% before they start spinning. As described in the separate panel labelled "PWM motor driving pitfalls at higher frequencies", in some cases, driving a motor with a high PWM frequency can mean that the motor will not start until the duty cycle is at 20%, or even higher. The curve adjustment sets the initial duty cycle when the speed potentiometer is rotated just clockwise from fully-anticlockwise. This adjustment removes the dead zone from the speed pot. The curve adjustment range is from almost zero to a 33% initial duty cycle. Whenever the curve setting is nonzero, the software within IC1 expands the speed control range so that the maximum duty cycle is still achieved when VR1 is fully clockwise. Operation at low frequencies can also be optimised using the curve adjustment, with jumper JP1 inserted to pull the normally-high RA5 digital input low (pin 2). Without the jumper inserted, the RA5 input is pulled high via an internal pull-up current. The curve adjustment when JP1 is inserted allows for better feedback control at very low duty cycles. The adjustment reduces the motor snap-on effect, where the feedback voltage suddenly rises with an increase of the PWM duty just off from zero. This adjustment sets a feedback offset value so that feedback is ignored below the specified speed setting. Trimpot VR3 is also used to enable or disable motor disconnection detection. This is done by splitting VR3’s range into two halves, 0-2.5V and 2.55V. From 0V to 2.5V, motor disconnection checking is disabled. Above 2.5V, motor disconnect detection is enabled 32 Silicon Chip and the curve adjustment is reversed, with fully clockwise giving the same effect as fully anti-clockwise. When the motor current feedback is below a set value for more than about 200ms, the motor is determined as being disconnected. In this case, the PWM duty cycle is set to zero and the LED flashes at 2Hz. The motor will only start again after it is reconnected, and the speed pot is firstly wound fully anti-clockwise. This prevents erratic operation due to loose wires etc. Motor disconnect detection is optional because, unless the motor is set up correctly when used at high frequencies, false disconnection events can cause nuisance shutdowns. This can occur if the curve is not adjusted correctly, with a sufficiently high duty cycle at the start of the speed pot rotation. PWM frequency options Switch S1 is used to select the frequency of the PWM drive for the motor. This is a 16-position rotary BCD (binary-coded decimal) switch. There are four switch terminals labelled 8, 4, 2 and 1 plus a common connection, which we have connected to ground. The other switch terminals connect to the RA1, RB6, RB7 and RB5 digital inputs of IC1, respectively. All of these pins except for RA1 are configured in IC1 to provide a pull-up current. The RA1 input does not have such an option, so an external 10kW pull-up resistor connects to 5V. These pull-ups hold the inputs high (at 5V) whenever the switch does not connect that terminal to ground. The 16 possible combinations are decoded in IC1, and the required PWM frequency is selected (see Table 1). Australia’s electronics magazine Power for the controller is connected via the CON1 terminals between GND and the controller supply positive input. The supply current passes through zener diode ZD1, and the input of regulator REG1 is bypassed with a 470nF capacitor. REG1 is a low-dropout automotive 5V regulator. It is capable of withstanding a reverse polarity voltage, so it provides the circuit with reversed-supply protection. The maximum recommended operating voltage at the input of REG1 is 26V. So for use at up to 30V, ZD1 drops the voltage at the input by around 4.7V. The dropout voltage for REG1 is typically 0.5V. That means it needs 5.5V at the input to ensure that the output is regulated. The addition of ZD1 means that the minimum recommended voltage for the controller is 5.5V + 4.7V = 10.2V. We round this up to 10.5V to be safe. Note that the controller and motor positive supply connections are separate, so the motor can be run at a different voltage if required. That means the motor supply could be outside the controller’s range, and the circuit will still work as long as an appropriate controller supply voltage is applied. The two supply inputs can also be tied together when the motor supply voltage is within the controller’s suitable range. Table 1: PWM frequency options BCD switch setting (S1) PWM frequency 0 30.6Hz 1 61.3Hz 2 122.5Hz 3 245Hz 4 367.6Hz 5 490Hz 6 980Hz 7 1.96kHz 8 2.97kHz 9 3.92kHz A 5.88kHz B 7.84kHz C 11.8kHz D 15.7kHz E 23.5kHz F 32.4kHz siliconchip.com.au Construction The DC Motor Speed Controller is built using a double-sided, platedthrough PCB coded 11006211, measuring 122 x 58mm. Fig.2 shows the assembly details. Start by installing the two 10W surface-mount resistors and the two 0.01W resistors, all near Q1 & Q2. Now fit IC3, the surface-mounting Mosfet gate driver. Take care when soldering this; you might need a magnifying glass and a separate work light. Solder pin 1 first and check that the remaining pins are aligned correctly before soldering the remainder. Zener diode ZD1 can now be installed, taking care with its orientation. Follow with the seven throughhole resistors. Table 2 shows the resistor colour codes, but you should also check each one using a digital multimeter (DMM) before mounting it. Once these parts are in place, install the socket for IC1. IC2 can be mounted using a socket, or you can solder it directly to the board. Make sure each is orientated correctly. Now is a good time to fit Mosfet Q3, the LED and the two-way header for jumper JP1. Make sure LED1’s longer lead (anode) goes into the hole at the left, marked with an “A”. You could mount a two-pin header there instead, or solder a twin-lead cable to the board so that the LED can be chassis-mounted. The polyester capacitors can then be inserted; it's easiest to install the electrolytic types after all the semiconductors. Follow with the trimpots, which are all multi-turn types. Orientate them with the adjustment screws positioned as shown. BCD switch S1 can now be installed, with the orientation dot at the lower right. The 3-way screw terminal block (CON2) is next on the list. Make sure it is correctly seated against the board and that its openings face outwards before soldering its pins. CON1, the 6-way screw terminal barrier block, can then go in. Note that Altronics state these are 15A rated; however, the Dinkle data for these DT-35B07W-XX terminals rates them at 20A, so they are suitable for this 20A controller. The fuse holder is next. You can fit a monolithic holder or two separate fuse holder clips. If using individual clips, it might be a good idea to insert a fuse before soldering to ensure they are lined up correctly. You can install PC stakes at test points TP1-TP5 and TP GND, or leave them off and probe the PCB pads directly with multimeter probes. Installing the semiconductors Regulator REG1 is mounted horizontally on the board. It is installed by first bending the leads to pass through their mounting holes. REG1’s tab is then secured to the PCB using an M3 x 6mm machine screw and nut, after which the leads are soldered. Mosfets Q1 & Q2 and schottky diode D1 are mounted vertically and fastened to separate small heatsinks. The three heatsinks must be installed first, by soldering their locating pins to the relevant PCB pads. Make sure that the heatsinks are properly seated against the PCB before soldering them in place. Then slide Q1 & Q2 into their mounting holes and, using silicone washers and insulating bushes (see Fig.3) to isolate each from the heatsink, fasten them using M3 x 10mm machine screws into the tapped holes on the heatsinks. Tighten the screws firmly, then solder their leads. Diode D1 is mounted similarly. Now install the leftover electrolytic capacitors, taking care to orient them correctly. Finally, use your multimeter to confirm that the metal tabs of D1, Q1 and Q2s are isolated from their heatsinks. Testing Before inserting IC1 into its socket, check the regulator operation by applying 10.5-30V between the 0V and the controller positive supply terminals on CON1. Table 2: resistor colour codes Fig.2: the Speed Controller PCB is relatively compact and uses just five SMD parts: four resistors and Mosfet driver IC3. Mosfets Q1 & Q2 and diode D1 attach to PCB-mounting heatsinks for cooling. During assembly, watch the polarity of the three ICs, diode ZD1, the electrolytic capacitors and BCD switch S1. siliconchip.com.au Australia’s electronics magazine July 2021  33 The disadvantage of back EMF based speed feedback Typically, a DC motor acts as a generator when the power is switched off. When using PWM drive, this generated voltage or back EMF (Electromotive Force) occurs repetitively when the driving Mosfets are switched off. But the induced voltage is not developed immediately after switch-off; it does not happen until the stored charge in the inductance of the motor windings dissipates. In many speed controllers, the back EMF voltage is used to stabilise the speed with varying load. As the motor is loaded, the speed and back EMF reduce, and this change is used to provide feedback that increases the PWM duty cycle to maintain speed under load. However, with higher PWM frequencies, the back EMF voltage appears much later in the PWM cycle; sometimes, it is not developed until after the Mosfets are switched on again, so it is impossible to sense the back EMF. Compare scope grabs Scope 7 & Scope 8. They are the same except that the PWM frequency is just under 3kHz in Scope 7 and nearly 12kHz in Scope 8. You can see the back EMF ‘shelf’ appear about 80μs after switch-off in Scope 7, but it is barely visible in Scope 8 and would not be present at all with a higher switching frequency. The lack of back-EMF at high PWM frequencies means that we need to use a different way of detecting motor load. The easiest alternative is to measure the motor current. We only do this while the motor is driven by amplifying the voltage across a low-value shunt resistor in series with the motor. Using feedback control based on measuring current, the PWM duty cycle can be increased whenever the motor is loaded. This tends to overcome the shortcomings of low torque at high frequencies and lower duty cycles, to some extent at least. Scope 7: with a PWM frequency just under 3kHz, there is sufficient time for back-EMF sensing. The motor voltage shoots up immediately after the Mosfets switch off, then falls back to a lower plateau once the magnetic field has decayed and back-EMF starts to become dominant. Scope 8: with a PWM frequency of nearly 12kHz, the back-EMF voltage is barely visible just before the start of the next pulse. It would be impractical to sample the backEMF voltage at this frequency for this motor, and impossible at higher frequencies. 34 Silicon Chip Australia’s electronics magazine Measure the voltage between REG1’s metal tab and its right-most lead. You should get a reading close to 5V (4.75 to 5.25V). If not, check that the input voltage at the left lead of REG1 is at least 5.5V. If this reading is correct, switch off the power and install IC1, making sure it is oriented correctly, and none of its leads fold under the body. If you used a socket for IC2, plug it in now. At this stage, it is a good idea to wire potentiometer VR1 to CON2. You will also need to insert the fuse to continue testing. The fuse should be rated to suit the motor; if it is a 1A rated motor, install a 1A fuse; for a 20A motor, use a 20A fuse etc. Next, wind the curve adjustment trimpot VR3 fully anti-clockwise. You can find this position by winding at least 20 turns anti-clockwise or until a faint clicking sound is heard. When the circuit is powered, the voltage reading between TP3 and GND should be very close to 0V. Low-voltage cut-out testing When power is applied, the LED will flash at 1Hz because there is no power connected to the motor supply. Trimpot VR4 sets the low-voltage cut-out. With a multimeter connected between TP4 and TP GND, adjust VR4 for one-tenth of the desired low cutout voltage. So for a low voltage cutout at 11.5V (a safe level for most 12V lead-acid batteries), adjust TP4 until you get a reading of 1.15V. Adjusting the hysteresis is similar, using trimpot VR5 and measuring at TP5. The hysteresis is the voltage measured at TP5 (not 1/10th as before). So for a 1V hysteresis, set TP5 to 1V. Hysteresis can be set for up to 5V, but 1V is a reasonable starting point. With the recommended 11.5V cut-out voltage, that means the battery voltage needs to rise above 12.5V (about half-charge) before operation resumes. If you have an adjustable power supply, the low-battery cut-out can be tested. Connect this supply between the motor supply positive and 0V, and rotate VR1 fully clockwise. The LED will light up when the supply voltage is in the operating range and flash when a low voltage is detected. Set the supply to more than the low voltage cut-out setting plus the hysteresis setting, so the low-voltage cut-out will not initially activate. Then reduce the voltage to the cut-out voltage. Note siliconchip.com.au that the low-voltage protection will take about 10s to occur once the supply is below the threshold. LED1 should then flash at 1Hz. Slowly increase the supply to just over the threshold plus the hysteresis setting value (12.5V in our example), and LED1 should light fully. If necessary, adjust VR4 & VR5 to get it to cut out and in at precisely the voltages you require. Soft-start setting Adjust VR2 for the required softstart rate. Typically, 5V at TP2 is suitable giving a maximum two-second soft-start period. You can reduce this for faster starting, or disable soft starting with 0V measured at TP2. Curve adjustments VR3 sets the curve adjustment. This is off when VR3 is wound fully anti-clockwise, with 0V at TP3. Rotating VR3 clockwise will increase the curve adjustment. For settings above 2.5V, see the optional motor disconnection detection section below. As mentioned earlier, the curve setting provides high-frequency operation improvements when JP1 is out of circuit or low-frequency operation improvements with JP1 inserted. With JP1 out, VR3 increases the minimum duty cycle for low settings of VR1. To make the adjustment, rotate speed potentiometer VR1 slightly clockwise from fully anticlockwise, giving a reading of just over 20mV at TP1. Then adjust VR3 clockwise until the motor just starts to run. Adjust the gain control (VR6) for best motor control for maintaining motor speed under load. Clockwise will give more gain, and anti-clockwise will set a lower gain. Setting the gain too high can cause the motor speed to become unstable. Set the PWM frequency to a value that you find best for the motor. This will be a compromise between motor control performance and the amount of PWM noise made by the motor. Very low frequencies can cause the motor to run coarsely. Very high frequencies will improve smoothness, but can reduce torque at lower settings unless the feedback control is adjusted to give better performance under load. Adjust the response trim pot, VR3, to give the best speed control range for VR1. When the PWM frequency is low, you might find that the motor speed siliconchip.com.au Parts List – 20A DC Motor Speed Controller 1 double-sided, plated-through PCB coded 11006211, 122 x 58mm 1 UB3 Jiffy box (optional) [Jaycar HB6013, HB6023, Altronics H0203] 1 6-way 20A* PCB mount barrier screw terminals, 8.25mm pitch (CON1) [Altronics P2106] 1 3-way screw terminal with 5.08mm spacing (CON2) 1 10kW linear potentiometer (VR1) 1 knob to suit VR1 1 two-pin header, 2.54mm pitch, plus shorting block/jumper (JP1) 3 TO-220 silicone insulating washers and bushes 1 20-pin DIL IC socket for IC1 1 8-pin DIL IC socket for IC2 (optional) 3 TO-220 PCB-mounting heatsinks [Jaycar HH8516, Altronics H0650] 1 4-bit BCD switch (S1) [Jaycar SR1220, Altronics S3001A] 1 20A blade fuse holder (F1) [Altronics S6040] 1 blade fuse to suit motor (up to 20A) 4 M3 x 10mm panhead machine screws 1 M3 nut 4 6.3mm-long M3-tapped standoffs and 8 M3 x 6mm screws (optional; for mounting the board) 6 PC stakes (optional) * Dinkle specifies these as 20A-rated; Altronics state 15A Semiconductors 1 PIC16F1459-I/P microcontroller, DIP-20, programmed with 1100621A.hex (IC1) 1 AD627ANZ instrumentation amplifier, DIP-8 (IC2) [element14, RS] 1 MCP1416T-E/OT Mosfet driver, SOT-23-5 (IC3) [RS Components 668-4216] 1 LM2940CT-5.0 regulator, TO-220 (REG1) [Jaycar ZV1560, Altronics Z0592] 2 STP60NF06 N-channel Mosfets, TO-220 (Q1,Q2) [Jaycar ZT2450] 1 2N7000 N-channel small signal Mosfet, TO-92 (Q3) [Jaycar ZT2400, Altronics Z1555] 1 3mm high-brightness LED (LED1) 1 4.7V 1W zener diode (ZD1) 1 MBR20100 dual 10A schottky diode, TO-220 (D1) [Jaycar ZR1039] Capacitors 3 470μF 35V low-ESR electrolytic 1 470nF 63V MKT polyester 2 100μF 16V electrolytic 9 100nF 63V MKT polyester Resistors (all 1/4W, 1% metal film axial unless otherwise stated) 1 100kW 3 10kW 1 2kW 1 1kW 1 330W 2 10W M3216/1206 surface mount 2 0.01W M6432/2512 3W surface mount [RS Components Cat 188-0753, Vishay WFMA25120100FEA or equivalent] 4 10kW top adjust multiturn trimpots (3296W style) (VR2-VR5) 1 50kW top adjust multiturn trimpot (3296W style) (VR6) can increase sharply when winding VR1 up from zero, especially when there is high feedback gain. Adjusting the response using VR3 with JP1 inserted can reduce this snap-on effect. Start from 0V (at TP3) and adjust VR3 until the motor runs well at low duty cycles, without the snap-on effect. Motor disconnection detection If you want this option, the curve adjustment trimpot (VR3) is set in the opposite manner. There is no curve adjustment when VR3 is fully clockwise (5V at TP3), and the curve adjustment increases as VR3 is wound further anti-clockwise. It is usable down to 2.5V at TP3. SC Australia’s electronics magazine Fig.3: this side view shows the detail of how the TO-220 package devices are mounted to the heatsinks. The hole in the heatsink is pre-tapped. The heatsinks are connected to ground via the PCB and mounting pins, so you need the insulating washers and bushes. July 2021  35 How USB-C Power Delivery Works By Andrew Levido 4.5W 7.5W 15W 36W 60W 100W USB has come a long way from when it was introduced in the mid-1990s. The widespread adoption of USB 3.2 introduced the Type-C connector, plus a new Power Delivery (PD) capability that allows up to 100W (20V <at> 5A) to be delivered. It is quite a bit more complicated than previous USB power schemes, but well worth a look. O ur article in the June issue on the “USB Explosion!” described the USB Type-C (USB-C) connector in a fair bit of detail and touched on the new USB Power Delivery mechanism (siliconchip.com.au/Article/14883). However, there’s quite a bit more to say on both topics, so this follow-up article will fill in the gaps. We also have an article starting on page 42 which describes some lowcost USB Power Delivery (PD) compliant power sources. Next month, there will be a follow-up article that discusses ways to negotiate and monitor the voltage and current supplied by a USB-PD source. But first, read below to get an idea of why you would want to use those devices. As described in the May article, the USB 3.2 standard is the first that officially allows power sources and sinks (and the cable!) to negotiate the voltage and current supplied. But before we get into the details for how all this works, we need to get a few terms straight. Things have gotten more complicated since the days when there were only two possible things you could plug a USB cable into: a host, which sourced power and controlled communication, and a device, which consumed power and responded to host communication. Now USB ports can have three possible data roles and three possible power roles. Data roles include: • Downstream-facing ports (DFPs) – typically a host or hub 36 Silicon Chip • Upstream-facing ports (UFPs) – typically a device • Dual-role ports (DRPs), which can switch between device and host roles USB-C ports also have a power role: • Source role, supplying power • Sink role, consuming power • Dual-role power port Dual-role power ports can switch between source and sink roles. A good example of this is the USB-C port on a laptop, which can be a sink when connected to a power brick (or a monitor which can supply power) to power or charge the device, or a source when connected to a peripheral such as a USB hard disk. On attach, DFPs are source ports and UFPs are sink ports; however, this can be changed later by mutual agreement. The USB-C connector USB 3.2 introduced the new Type-C connector, which is used on both ends of a USB-C cable. This connector can be inserted either way around, and the connectors can optionally contain electronics that allows the system to identify specific cable capabilities. The USB-C connection includes a dedicated Configuration Channel (CC), used to detect cable attachment, plug orientation, cable capability, and to negotiate ‘Power Contracts’ between source and sink. In addition, USB-C has two super speed full-duplex differential channels for high-speed data communication, and two sideband use lines. We will focus on the CC for this discussion. The two rows of contacts in the receptacle are shown in the middle of Fig.1, with the two possible plug orientations (un-flipped and flipped) shown above and below respectively. The GND and VBUS pins are Fig.1: the pin assignment of the USB Type-C receptacle is shown in the centre. Above and below are two possible plug orientations. The CC1 and CC2 pins on the receptacle connect to the CC and VCON pins on the plug; it can tell which way the plug is inserted by monitoring which of CC1 or CC2 connect to CC. Australia’s electronics magazine siliconchip.com.au Fig.2: on attach, the source pulls up CC1 and CC2 via Rp, and the sink pulls them down via Rd. There is only one CC line in the cable, so both the source and sink can detect whether or not the plug is flipped at their end. An active cable pulls the VCON pin down via Ra to signal its presence. Passive cables leave VCON open. symmetrical, so these pins connect correctly regardless of the plug orientation. The classic USB D+ and D- also work correctly, as the two D+ pins and the two D- pins on the receptacle are connected together internally. The two super-speed twisted pairs will be swapped depending on the plug orientation, so the device must use a high-speed mux to un-swap these if the plug is flipped. Similarly, the sideband use (SBU) pins are swapped, and must be sorted out depending on the plug orientation. The pins we are interested in for Power Delivery are the two Configuration Channel (CC) pins on the receptacle, and the CC and VCON pins on the plug. These allow the ports at each end of the cable to work out the plug orientation, detect attachment, and determine the other end’s capabilities. Detecting attachment and cable orientation Refer now to Fig.2. When two USB Type-C ports are connected, the DFP will default to a source and pull the two CC lines high with resistors Rp, and the sink end will pull the CC lines down via resistors Rd. The source detects attachment when one of the two CC pins is pulled low by Rd, and the sink detects attachment when one of its CC pins is pulled high by Rp. On attachment, the source voltage defaults to 5V for compatibility and safety. The sink can determine what current the source can provide at 5V by measuring Rp’s value (or, more accurately, the current sourced). Table 1 shows how this works (overleaf). The source and sink can determine the plug orientation by noting whether their CC1 or CC2 pin is pulled up by Rp or down by Rd. Electronically marked cable assembly (EMCA) The connectors on a USB Type-C cable can optionally contain a microchip, allowing the cable to report its capabilities to the source and sink devices. For example, a standard USB Type-C cable can support power delivery at up to 3A. To take advantage of the maximum 5A capability, you need to use an active cable that can tell the source that it is rated to that level. The source will not allow the sink to draw more than 3A if the cable does not report that it can handle it. On attach, a cable indicates it is electronically marked by pulling the VCON pin down via resistor Ra, which is between 800W and 1.2kW. Nonmarked cables leave VCON open. If a Marked cable is detected, the source device is responsible for supplying a voltage at the appropriate CC pin to VCON to power the microchip in the cable, as shown in Fig.3. Other modes Type-C connectors support additional modes that use the sideband use (SBU) channels. These are the audio accessory mode (for headphones, for example) and a debug accessory mode, where the SBU channels can be used for transmitting debugging signals. Table 2 summarises the various combinations of pull-up and pulldown on the CC pins and what they signify. Power Delivery When attached, a USB Power Delivery source is configured to supply 5V for compatibility with legacy devices. It will be capable of supplying up to 1.5A for a maximum power of 7W, or 3A/15W, depending on Rp’s value as described above. If this is all the sink requires, it does not need to do Fig.3: if the source detects an active cable, it switches a power supply on to the VCON pin to power up the microchip in the connector. The cable must be capable of being powered from either end, as a USB Type-C cable can be connected either way around. siliconchip.com.au Australia’s electronics magazine July 2021  37 Fig.4: the power rating of a USB Power Delivery source generally indicates the range of voltages it can provide. This is not always the case (I’m looking at you, Apple), so it pays to check before buying. anything more. This is known as an implicit contract. If the sink requires more power or a higher voltage, it can request more by negotiating an explicit contract over the Configuration Channel. Before we get into details of how this is done, we should look at the voltages and currents typical USB Type-C sources can supply. Fig.4 shows that USB Power Delivery sources are generally rated by the power they can source. Up to 15W, they typically only supply 5V. Those rated above 15W generally supply 5V or 9V; those rated above 27W should offer 5V, 9V and 12V, while those above 36W should offer 5V, 9V, 12V and 15V. Those rated above 45W add 20V to the list. Note that while this is generally the case, some vendors have gone their own way and offer some oddball combinations. Negotiating a Power Contract Fig.5: the “start-of-packet” (SOP) header indicates whether the message is intended for the UFP, or a particular connector of an active cable. These are confusingly called SOP, SOP’ and SOP” packets respectively. Fig.6: a successful power contract negotiation starts with the source advertising its capabilities. The sink then requests one of these capabilities. If the request is accepted, the source sends an “Accept” message, changes its output, and then sends a “PS_RDY” message. All messages are acknowledged with a “GoodCRC” message if they are received correctly. 38 Silicon Chip Australia’s electronics magazine Data across the Configuration Channel is encoded into 32-bit packets using bi-phase mark coding (BMC) at 300 kilobaud, with CRC error correction. Communication is initiated by the DFP (usually a source). Messages start with a ‘start-ofpacket’ (SOP) packet, which describes where the message is intended to go. Confusingly, these are designated SOP, SOP’ and SOP’’ packets. As shown in Fig.5, messages headed by SOP packets are intended for the UFP; those with SOP’ packets are intended for the connector at the source end of an electronically marked cable (ie, that receiving VCON); and those with SOP” packets are for the connector at the sink end of the cable. It is important to keep in mind that, while the SOP signalling means the Configuration Channel uses a multidrop protocol, overall USB remains a point-to-point connection. The D+, D− signalling is unchanged from previous generations of USB, and the superspeed channels also operate point-topoint. You can still only connect one DFP to one UFP, and have one source and one sink in a given connection. The basic process for negotiating an explicit Power Contract is shown in Fig.6. Until an explicit Contract has been negotiated, the source will periodically send a “Source_Cap” message to advertise its voltage and current capacity. If this is received siliconchip.com.au successfully by the sink, it will respond with a “GoodCRC” message. The “Source_Cap” message includes a list of the possible voltages and maximum currents it can source. The sink may then request the source provide a specific voltage identified in one of the source capabilities, and specify the maximum current required (up to the advertised capacity) by sending a ‘Request’ message to the source. This is also acknowledged by the source with a “GoodCRC” message. The source will analyse the request and determine if it can accommodate it. If it can, it sends an ‘Accept’ message to the sink. Assuming it received a “GoodCRC” message acknowledging receipt by the sink, the source will change its output to the agreed level and send “PS_RDY” message to the sink. If that message is acknowledged, then the Contract is considered complete. Fig.7 shows a screen capture of this process, using a Total Phase USB Power Delivery analyser. At the top of the screen are the messages passing between the source and sink as Table 1: RP values and source current vs current capability Maximum source current Rp (pulled to 5V) Rp (pulled to 3.3V) Current sourced Default (0.5A or 0.9A) 56kW 36kW 80µA 1.5A 22kW 12kW 180µA 3.0A 10kW 4.7kW 330µA Table 2: decoding CC1 & CC2 states (from the source perspective) CC1 CC2 Attach? Active Cable? Flipped? open open no – – Rd open yes no no open Rd yes no yes open Ra no yes no Ra open no yes yes Rd Ra yes yes no Ra Rd yes yes yes Rd Rd debug accessory mode Ra Ra audio adaptor mode a contract is negotiated. The bottom half of the screen shows an expansion of the highlighted “Source_Cap” message. You can see that this particular source (a 45W Targus unit labelled APA95AU) can supply 5V, 9V, 12V, 15V and 20V, as described in the five “Power Objects” contained in the “Source_Cap” Message. Fig.7: the upper half of this screenshot shows the messages exchanged between the source and the sink during the successful negotiation of a 20V contract. The lower half shows the details of the highlighted “Source_Cap” message. In this case, there are five Power Description Objects, corresponding with the five voltage levels this source supports. siliconchip.com.au Australia’s electronics magazine July 2021  39 Fig.8: the same transaction as shown in Fig.7, but in this case, the lower panel shows the details of the Request message sent by the sink. It requests ‘Position 5’, corresponding to the 20V Power Description Object in the “Source_Cap” message. Fig.9: this capture shows a transition between a 5V contract and a 9V contract. The sink executes a “Soft Reset” message to force the source to re-advertise its capabilities so a new transaction can occur. The source continues to honour the existing contract until a new one is agreed upon. 40 Silicon Chip Australia’s electronics magazine siliconchip.com.au Fig.10: this transaction shows what happens on attach if an electronically marked cable is detected. The source first queries the cable with a “DiscIdentity” message. The lower panel shows the cable’s response. We can see, among other things, that this is an Apple cable and it can handle up to 5A. Fig.8 shows precisely the same negotiation, but highlights the sink’s Request message in response to the “Source_Cap” message. In this case, the sink requests 20V by asking for “Position 5”, corresponding to the fifth Power Object in the “Source_Cap” message. It also requests an operating current of 1A and a peak current of 2.25A, the maximum available at that voltage. Renegotiation If the sink wishes to negotiate a new Contract with the source, it can send a ‘Soft Reset’ message, which will result in the sink re-sending the “Source_Cap” messages. The sink can then request a different Contract. The current Contract remains in force until a new one is successfully negotiated. Fig.9 shows this in action. In this case, the sink requests a change from 5V to 9V. The bottom half of the screen capture shows the VBUS change corresponding with the “PS_RDY” message, just before the 13.4 second mark. siliconchip.com.au All of the transactions shown so far have involved a passive cable, so no SOP’ or SOP” packets were issued. Fig.10 shows the messaging after attach when an active cable is used. Initially, the source sends a “DiscIdentity” packet to the cable, which responds with a similarly labelled message containing details about the cable. This response is expanded in the bottom half of the screen. In the bottom row, you can see the cable is reporting its latency and indicates that it has a 5A capacity. Practical considerations If you want to build a project using USB Type-C power, you have a few options. By far, the simplest is to live with just 5V; ie, do nothing and accept the implicit 5V contract. This is identical to powering your device from a USB Type-B connector such as Mini-B or Micro-B. If you want to negotiate an explicit contract, you can use one of the offthe-shelf chips which provide various Australia’s electronics magazine degrees of integration. Assuming you are building a sink-only device, a good option I have used is the ST Microelectronics STUSB4500. This can be used as a standalone controller (once programmed, if the default does not suit you), or it can be used with a microcontroller, to give you full control over the negotiation process. I used this chip to build a simple power supply. This uses a linear regulator for low noise, and manages its input voltage via USB Power Delivery to minimise internal power dissipation. References • “STUSB4500 – Standalone USB PD Controller for Power Sinking Devices – STMicroelectronics” – siliconchip. com.au/link/ab73 • Microchip “AN1953 Introduction to USB Type-C” – siliconchip.com. au/link/ab74 • Texas Instruments “USB PD Power Negotiations,” 2016, 21 – siliconchip. com.au/link/ab75 SC July 2021  41 Using Cheap Asian Electronic Modules By Jim Rowe USB Power Delivery Chargers Left-to-right: the Comsol COWCC30WH, XY-PDS100 & Belkin F7U060AU This article describes some low-cost modules that have appeared recently to take advantage of the dramatic growth in USB capability, especially in the area of power delivery (PD). This assortment includes PD chargers, cables and cable adaptors, while a follow-up article will look at ‘trigger’ or ‘decoy’ modules, used to configure the chargers, plus USB-PD testers. As mentioned in my recent article on the ‘USB Explosion!’ (June 2021; siliconchip.com.au/Series/367), one of the application areas of USB which has grown dramatically of late is the delivery of DC power. When USB first appeared in the late 1990s, it could provide just 5V of power at up to 100mA for a ‘low power’ device, or up to 500mA for a ‘high power’ device like a USB hard disk drive. But as the data transfer capabilities of USB were expanded via USB 2.0, USB 3.0 and finally USB-C, the power delivery capabilities were expanded as well. For an in-depth discussion of how USB PD works, see the article on that topic starting on page 36 of this issue. We’ll give a quick summary here, before moving on to describe the modules. USB 3.0 kept the 5V supply voltage but raised the ‘high-power’ current level to 900mA, allowing a downstream device to receive up to 4.5W (rather than just 2.5W). When the USB-PD (Power Delivery) specification was finalised in 2012, 42 Silicon Chip a device could receive 5V at up to 1.5A or 7.5W of power via a standard Type-A to Type-B USB cable. The smaller USB-C 24-pin connectors appeared in 2014, and when the USB-PD specification was further revised in 2014, 2016 and 2017, they increased the power delivery voltage and current levels as well. Now devices can request power at either 5V, 9V, 12V, 15V or 20V, and can draw up to 5A – corresponding to 100W with a 20V supply. And since the USB-PD 3.0 revision of 2017, devices can also take advantage of the programmable power supply (PPS) protocol, which allows variation of the supply voltage in 20mV steps. This expands the possible USB-PD applications dramatically, and that’s why we’re seeing so many low-cost modules designed to take advantage of this increased flexibility. How USB-PD works As mentioned earlier, this is described in detail on page 36. But there are some points that we can add here, and we will also summarise the basics of USB-PD negotiation. Fig.1: the USB-PD system consists of five elements: a primary DC power source, a USB-PD ‘manager’ with a downstream facing port (DFP), a USB-C cable, a trigger circuit fitted with an upstream facing port (UFP) and finally, the power ‘sink’. The USB-PD manager element could be combined with the primary DC source, and the trigger circuit may also be combined with the sink. Australia’s electronics magazine siliconchip.com.au Essentially, USB-PD is made possible by some of the extra contact pins in a USB-C connector. Specifically, the CC1 (A5) and CC2 (B5) pins, which are designated the Configuration Channel (CC) pins. The notional arrangement is shown in Fig.1. Initially, a USB-PD capable power supply sets its VBUS output voltage to 5V. It also ties each of the CC pins of its output (downstream) USB-C connector to a logic high level via a pull-up resistor Rp, with the value of Rp chosen according to the supply’s current capacity. Devices designed to receive their power from the USB-C connector are fitted with a pull-down resistor Rd connected between one of the CC pins and ground. The value of Rd is chosen to indicate the current level wanted by the device. As a result, when a cable from the device is plugged into the USB-C connector, the voltage drop on one of the CC lines indicates to the host that: • A load or ‘sink’ device has been connected. • The orientation of the USB-C plug in the connector. • The current available from the host supply. There is then an exchange of data packets between the supply and the load/sink via the CC line, using DC-coupled BMC (Biphase Mark Code) or Differential Manchester encoding. This allows the load device to indicate the supply voltage it wants, and then the supply to change its output to the requested level if it can do so. As mentioned above, if the supply supports the PPS protocol, the voltage can be adjusted in 20mV increments. This negotiation can only occur if the load device is connected to the supply via a USB-C connector and matching cable. It won’t work if a Type-A Using USB-PD for fast charging Even before the USB-PD specification was released in 2012, various firms associated with the burgeoning mobile phone market worked out ways to use USB sockets for fast-charging mobile phone batteries. Examples are Qualcomm, which had developed its Quick Charge (QC) protocol, Motorola with its TurboPower protocol and Huawei with its SuperCharge (SC) protocol. Perhaps because of the widespread application of these protocols, the various revisions of USB-PD gradually USB connector is used, because this lacks any CC pins or cable lines. The initial USB-PD Rev.1 specification of 2012 allowed a device connected to a host/power supply via USB 2.0/3.0 Type-A and Type-B connectors to negotiate a higher voltage than 5V (eg, 12V or 20V) using a binary FSK signal on the VBUS line. But this approach was deprecated when USB-PD Rev.2.0 was released in 2014. So most USB-PD power supplies can only deliver 5V (or perhaps 12V) via their USB Type-A downstream port or ports. Note that the USB-PD negotiation protocol allows for power to be transferred in either direction – from host to device or vice-versa. For example, a laptop or tablet PC can get its battery recharged quickly from a USB-PD power pack/charger by requesting that the charging be done at 9V, 15V or 20V instead of 5V. The XY-PDS100 quick charger This first module is a ‘fast charger’ that can be configured to give a range embodied them. As a result, when the USB-PD revision 3.0 was released in 2017, including PPS (Programmable Power Supply), it essentially incorporated just about all of the earlier fast charging protocols. So that’s why the specifications of most of the USB-PD trigger modules and fast chargers will claim compatibility with a list of protocols such as PD 2.0, PD 3.0, Qualcomm QC3.0 and QC4+, Huawei SCP/FCP, Apple 2.4A, Samsung AFC, MediaTek PE2.0 and PE3.0, Oppo’s VOOC and so on. of output voltages and currents using the standard USB-PD protocol. The XY-PDS100 comes in an extruded aluminium case measuring 53 x 46 x 21mm. It is available from several internet suppliers, including Banggood, which at the time of writing has it for US$13.10 plus US$3.30 for shipping. As shown in the photos, the output end of the XY-PDS100 has a USB Type-A socket and a USB-C socket, plus a 3-digit 7-segment LED display (with 6.5mm-high digits) and three indicator LEDs. One lights when the output voltage is displayed, one when it’s showing the current being drawn from the USB-C socket, and the third when showing the current drawn from the Type-A socket. At the ‘input’ end, there are two sockets. One is a small concentric DC socket designed to accept 12-28V DC from a mains power supply, and the other a USB-C socket marked “Input-PD”. On the underside of the case, the latter input has the legend “PD Recommended 87W”, but it seems The XY-PDS100 is shown at left connected to an XY-WPDT trigger unit. This trigger unit helps to set the provided charging profile for the input device by outputting a fixed voltage. At lower right is the rear of the XYPDS100; both these photos are shown at approximately life size. siliconchip.com.au Australia’s electronics magazine July 2021  43 Take care when buying USB-C cables and adaptors Although you will find many low-cost USB-C cables from vendors on the internet, you need to be careful when buying many of them. For example, quite a few of the low-cost cables are really only suitable for providing power and battery charging, not transferring data, and especially not highspeed data transfer. Apart from the lines involved in power transfer (including the configuration channel lines), they might not have any of the data transfer lines, except perhaps those for USB 2.0 (D+ and D−). This applies particularly for cables fitted with a Type-A plug at one end to be simply an alternative DC input. Essentially, what the XY-PDS100 does is convert a no-frills power supply with an output of 12-28V DC into a ‘smart’ USB-PD battery charger or power source, which can respond to the negotiation from a trigger unit to provide one of the standard charging voltage and current profiles. So it’s basically a programmable switch-mode step-down DC-to-DC converter, which can provide up to 100W of power at voltages between 5V and 20V from the USB-C output, or up to 36W of power at voltages between 5V and 12V from the USB Type-A output. And it even includes a three-digit LED readout displaying the current output voltage and current. Not bad for a very compact little unit that costs less than $25. Because the XY-PDS100 is a stepdown converter, it needs to have a DC input voltage at least 2V higher than the highest output voltage that could be requested. So if you only want a maximum of 12V for charging via the Type-A output, an input voltage of 14-15V would be fine. But for the full range of voltages required for USB-PD fast charging, the input voltage will need to be at least 22-23V. I was quite happy with the measured performance of the XY-PDS100. It seems quite compatible with the PD 3.0 protocols, and also with the PPS ‘vernier adjustment’ protocol. While the XY-PDS100 is a ‘USB-PD Manager’ module, needing an external DC supply, the remaining devices we’re going to look at combine both 44 Silicon Chip and a USB-C plug at the other. In fact, the presence of a Type-A plug is a strong indication that a cable is not suitable for high-speed data transfer, and quite possibly only for power transfer and charging. And the power transfer/charging will only be possible at 5V, since negotiation of a higher supply voltage probably won’t be possible. This also applies to the many nominal USB-C adaptors. If these have a USB Type-A plug or socket at one end, that means they are probably only suitable for use in power transfer and charging, although they might be OK for low-speed and full-speed USB functions, forming a complete USB-PD power source. I had some difficulty obtaining them, though. I ordered a couple of interesting units from a Chinese supplier, but they didn’t arrive, and I eventually discovered that they were out of stock. I had to get them from local suppliers instead, which turned up in a couple of working days, but they cost significantly more than the units I had ordered from China. The first one is... The Belkin F7U060AU 27W power adaptor This unit cost $39.95 from JB Hi-Fi (www.jbhifi.com.au). It measures just 51 x 60 x 31mm and weighs 50g. The unit is pictured in the rightmost photo at the start of this article; it has a two-pin mains plug on one end and a USB-C socket on the other end. That’s it – it’s just an elongated version of the familiar USB plugpack. The inscription on the plug end advises that it was designed in California and assembled in China. When I tried it out with a couple of different trigger units, I found that although it would register as a PD 3.0 device, it would only provide a choice of three output voltages: 5V, 9V or 12V. The two lower voltage settings can provide up to 3A of current, while the 12V setting can provide up to 2.25A. So the power rating of 27W only applies when the unit provides 9V or 12V; when it’s providing 5V, it is really a 15W source. Of course, this would Australia’s electronics magazine data transfer via the D+ and D– lines, assuming those wires are even fitted. Even if a low-cost cable has USB-C connectors at both ends, that is no guarantee that it is suitable for really high-speed data transfer. This makes it a bit risky buying these cables via the internet, because you can’t test them before you buy them. In fact, if you see one of these cables for less than $15, you can probably assume it’s only suitable for power transfer and battery charging. USB-C cables capable of being used for really high-speed data transfer are likely to cost significantly more than that. be fine if you only wanted up to 12V and 15-27W. The Comsol COWCC30WH 30W wall charger This unit cost $39.88 from Officeworks (www.officeworks.com.au/ shop/). It measures 44 x 64 x 40mm, and weighs 80g. As you can see from the leftmost photo at the start of this article, it’s very similar to the Belkin unit, with a two-pin mains plug at one end and a USB-C socket at the other end. The inscription on its plug end simply says “Made in China”. When I checked this unit with a couple of different trigger units, it only registered as a PD 2.0 device, but could provide any of the full five output voltages: 5V, 9V, 12V, 15V or 20V. As with the Belkin unit, it could provide up to 3A at 5V or 9V, but at 12V, it could provide up to 2.5A. Then at 15V, it could provide up to 2A, while at 20V, it could provide up to 1.5A. So it’s only a 30W power source for three of the five selectable voltages. Considering that its price is virtually the same as the Belkin unit, the fact that it provides a choice of the full five PD voltages, and with a nearly consistent power capability of 30W, makes it better value for money. The range of voltages and currents available from this type of charger means that it could power a wide range of devices, including those you might build yourself. If each of those devices contains circuitry to negotiate the current and voltage required, that means you could siliconchip.com.au have a small selection of power supplies to power a wide range of devices. So, in essence, these chargers could be the new ‘multi-voltage plugpack’ we all use in future. The ALOGIC WCG1X65-ANZ 65W wall charger The third USB-PD wall charger I bought is the ALOGIC WCG1X65, which again is very similar in size to the Belkin and Comsol units. It’s slightly smaller, measuring 55 x 60 x 35mm, and weighs close to 95g. This unit also came from JB Hi-Fi, at a cost of $74 plus delivery, but it is also available from TechBuy (www. techbuy.com.au), another local supplier, for $72.70 plus delivery. While it is almost twice the price of the other wall chargers, it boasts over twice the power capability at 65W. It comes with a 2m-long USB-C charging cable and a tiny (90 x 110mm) fourpage quick start guide. It also features a white LED power indicator, just below the USB-C output socket. When I checked this unit with the same trigger units as before, it registered as a PD 3.0 device and could easily be programmed to give any of the five standard PD voltages: 5V, 9V, 12V, 15V or 20V. And it can provide up to 3A at any of the four lower voltages, or up to 3.25A at 20V, which is pretty impressive considering its compact size and weight. The makers claim that this is a result of using “the latest GaN charging technology”. Presumably, they are taking advantage of the ability of transistors and diodes using gallium nitride (GaN) substrates to operate at much higher voltages and with higher efficiency. So if you need a USB-PD wall charger capable of supplying up to 65W of power at any of the five PD 3.0 voltage levels, the ALOGIC WCG1X65-ANZ would be the best choice despite its significantly higher cost. Note that one of the devices that I tried and failed to source from China was the Bakeey HC-652CA 65W wall charger, which would probably also be a good choice, if and when it becomes SC available. USB-C breakout boards Because of the possible problems associated with USB-C cables, you might be interested in the low-cost ‘breakout’ module or test board shown in the photo below. It is available from internet suppliers like Banggood for only US$2.10 for a single, US$4.80 for a pack of five or US$9.00 for a pack of ten (all plus shipping, of US$3.30 in each case). This module’s PCB measures only 25 x 40mm and has a USB-C socket mounted at the centre of one of the 40mm sides. All 24 of the socket’s connections are brought out to two rows of 12 solder pads at the opposite edge of the PCB, with one row (A1-12) on the top and the other (B1-12) underneath. The socket’s metal frame is also brought out to a further “G” pad on each side of the PCB. A pair of these ‘breakout’ boards make it easy to test all of the lines and connections in a USB-C cable. I bought a pack of five, but wasn’t too impressed with the soldering for the 24 very closely spaced pins of the sockets; one of them seemed to have a dry joint or two. Since it would not be easy to repair these joints manually because of the very close spacing (about 0.5mm), I decided that the board concerned was throw-away material. So be warned! In the following article, we’ll be taking a look at some of the low-cost USB PD ‘trigger’ modules that can be used to set the output voltage and current of USB power supplies, like the ones described here. Useful links USB-C: https://w.wiki/nto USB-PD: https://w.wiki/34dT siliconchip.com.au/link/ab7l Quick Charge: https://w.wiki/34dU Gallium nitride: https://w.wiki/34dV siliconchip.com.au The ALOGIC WCG1X65-ANZ 65W wall charger, shown enlarged for clarity. It registers as a PD 3.0 compliant device, and therefore can provide the standard voltages of 5V, 9V, 12V, 15V & 20V at 3A (or 3.25A for 20V). As the output power increases, these chargers can become quite costly. Australia’s electronics magazine July 2021  45 Model Railway Level Crossing BY LES KERR This scale model Level Crossing has realistic moving barriers, flashing lights and a bell sound recorded from a real level crossing. It can be triggered automatically when a model train approaches. It’s controlled by a couple of low-cost PIC microcontrollers and can be built for a modest sum, assuming you have some basic model-making and electronic assembly skills. D uring the COVID-19 lockdown, I decided to build a model railway layout in OO gauge. As time went on, I added buildings, a tunnel, a bridge, a pond, and many other items, including a level crossing. This level crossing can be triggered manually, or automatically when the train passes by; it includes arms that automatically lower and raise, flashing lights and a realistic bell sound (video at siliconchip.com. au/Videos/Level+Crossing). This article describes how you can build your own level crossing just like mine. OO scale is 4mm:1ft which works out to 1:76.2. I applied this scaling to images of signs taken from fullsized crossings. For other items like the red flashing lights, servos, barrier, and posts, I used slightly bigger parts than the scaled-down real-life items. The bell sounds were recorded from an actual crossing. The Level Crossing project involves building two boxes with posts that sit on either side of the railway tracks 46 Silicon Chip where a road meets them. When the train approaches, they drop their arms to block vehicles from crossing the tracks while simultaneously flashing their lights and sounding alarm bells. Once the train has passed, the lights and bells turn off, and the arms lift up again. Initially, the arms/gates opened and closed at a speed determined by the servo motor manufacturer. This speed was excessive compared with the reallife version, so I developed a circuit to move the arms in small steps, with a delay between each. The easiest way to do this was to use an inexpensive microcontroller programmed to produce the correct number of steps, with a delay between each, covering the angle that the arm needs to move through. There are four red LEDs on each post: two facing each way, and they flash alternately in pairs (with the LEDs connected back-to-back illuminated together). Due to the alternate flashing, Australia’s electronics magazine normally you would need three wires to connect them up – one to each LED and one common to both. But the hollow post is so small that it is only possible to fit one wire up the centre; using the brass post itself as a conductor gives just two wires. The way around this is to put the pairs of LEDs to be illuminated together in series, then connect those pairs in inverse parallel. This way, if a current is applied across the set of four LEDs in one direction, two are illuminated, and if the current flow direction is reversed, the other two are illuminated. The only problem with this is that you need a ‘full bridge’ type driving arrangement that can drive one end of the LEDs high while it drives the other low, or vice versa, to illuminate all the LEDs. Luckily, this is easily achieved with a pair of microcontroller digital output pins. Circuit description Refer now to Fig.1, the Level siliconchip.com.au Fig.1: circuit diagram for the Level Crossing Controller. This project uses two PIC12F617 ICs, this saves on extra components as a 555 timer and some transistors would be needed instead to flash the LEDs. Crossing circuit diagram. It is based mainly around two PIC12F617 8-pin, 8-bit microcontrollers. When the start switch (S1) is closed, digital input GP2 on IC1 (pin 5) is taken high. The resistor and capacitor help to debounce the switch contacts. In response, IC1 brings its GP4 digital output high (pin 3), switching on Mosfet Q1, which applies 5V to the recording/playback chip (IC3) with the bell sound recorded on it. IC3 is wired in the continuous mode by connecting pin 2 to pin 13, which results in the bell crossing sound being produced constantly from the connected 8W speaker. The sound continues until Q1’s gate is brought low by microcontroller IC1, switching it and the playback module off. I was going to use a 555 timer to flash the LEDs, but the two-wire requirement meant that I would have to add extra transistors. An inexpensive microprocessor fits the needs perfectly, hence IC2. It probably would siliconchip.com.au have been possible to build this function into IC1, but that would make the timing tricky as IC1 also has to generate servo pulses with accurate timing. A separate chip makes that easy. At the same time as GP4 goes high, IC1 also brings its digital output GP1 high, which indicates to IC2 to start flashing the LEDs alternately. IC2’s digital pins GP4 and GP5 are configured as outputs. Initially, GP4 is taken low and GP5 high, resulting in two of the LEDs on pole one and two on pole two glowing red. Half a second later, GP4 goes high and GP5 low, causing the LEDs that were lit to extinguish and the other LEDs to light. This sequence is repeated until the start switch opens and IC2’s pin 6 input (GP1) goes low again. Shortly after the lights and bells are triggered, IC1’s GP0 digital output produces a series of pulses that go to the servos, causing them to move the arms slowly down until the servo arm is horizontal. It remains down until a Australia’s electronics magazine couple of seconds after the start switch opens (at which point the flashing lights & bells cease), resulting in the arms moving up slowly to their full upright position. Switch options The original design uses a toggle switch for S1, with the Level Crossing operated manually. The operator simply switches it on when the train approaches the crossing and switches it off after the train has passed through. However, some constructors may desire automatic operation. This can be achieved by gluing a strong magnet somewhere on the train floor, then positioning two reed switches at strategic points underneath the track. They must be positioned so that the magnet passes over one before the train reaches the level crossing, and the other after it has finished passing through. Ideally, the magnet should be underneath the train so that it passes as July 2021  47 Fig.2: a 1:1 scale diagram of the mechanical construction details for the unit. Note that the servomotors have their mounting arms removed so that they can be mounted sideways. Fig.3: the label artwork for the various parts of the Railway Level Crossing. This is shown at actual size and can be downloaded from siliconchip.com. au/Shop/11/5855 close to the tracks as possible without actually hitting them. However, with a strong enough magnet, you might get away with fitting it inside one of the carriages. Be careful not to place the magnets right next to the reed switches, as this could demagnetise the switches, making them useless. An alternative version of the firmware for IC1 (ending in B) changes the function of pin 5 on IC1 to toggle the Level Crossing on and off each time that pin transitions from a low to a high level. Therefore, wiring both reed switches across the S1 terminals will provide the required behaviour. If you have more than one set of tracks going through the level crossing (eg, trains going in both directions), you could wire more than two reed switches in parallel. However, note that odd things will happen if you have trains passing through the crossing in both directions at once. If you want to support that case properly, you will need to develop a 48 Silicon Chip small external circuit that handles the logic to trigger this circuit, and you’ll probably want to stick with the A firmware in that case. The logic could consist of two S/R flip-flops with their outputs wired through an OR gate, going into pin 5 of IC1. Note that the B firmware could also be used with a momentary pushbutton type switch wired across S1, to allow the operator to manually toggle it on and off if desired. Construction There are two main parts to the construction: the electronic assembly, which is pretty straightforward, and the fabrication of the boxes, poles, arms and other pieces that make up the level crossing, which generally will take longer. As it is most of the work, we’ll start with the mechanical assembly. The mechanical parts drawing (Fig.2) shows the dimensions and quantity of the parts to build the crossing. I will go through each piece and Australia’s electronics magazine describe how I made them. Mounting post This was made from a length of hollow square brass 3/32-inch (about 2.4mm) extrusion. Mine was made by KS metals, which most model shops stock. You have to drill a 1.5mm hole 48mm from the bottom as the exit hole for the LED power wire. Using a small round file, clean up the hole and the ends so that all burrs are removed that might cut the insulation on the wire. Backing plates There are six of these, all made from 0.5mm brass sheet, also from KS metal. You will need two of each of the rail crossing backing plates, track backing plates and stop backing plates. Using a small saw, cut out the required size and then use a file to round the edges and remove any burrs. Barrier You will need two; I made them from 1/16in (1.6mm) blank PCB scraps. You siliconchip.com.au An example of what the finished barrier and railway crossing sign looks like. can draw up the shape on the PCB or trace the shape from the label. Drill the 7mm hole and cut the barrier from the PCB using a saw and file. the arm before and after modification – you need two, one for each barrier. The barrier is glued to this part of the assembly, as described later. LED holder LED assembly I turned these up on a lathe by bolting eight square pieces of 0.5mm-thick brass together on a mandrel, each with a 3mm hole in the centre. Alternatively, buy some brass washers with a 3mm centre hole (the LED diameter) and an outside diameter of about 6mm (not critical). If the inner hole is slightly larger than 3mm, you can hold the LED in place using glue. The washers should be painted matte black. Make two LED assemblies, as shown in Fig.2. Use pliers to bend the leads so that you put limited stress on the LED connections. Cut the leads to size and solder them together. The anodes of the LEDs are marked with “A” on the drawing. At this stage, don’t solder it to the post. Post mount This is an optional part that adds a bit more realism. Because the base of my model railway was made of polyurethane, I had to insert a metal plate under the rails to which the crossing parts were mounted. I drilled a 6mm hole in the plate and held the post mount in place with Loctite. It’s a simple turning job to make the part out of aluminium round. Servo arm The miniature servo is supplied with a servo arm that has to be cut to size. The mechanical drawing shows siliconchip.com.au Servos So that the servomotors can be mounted on their sides, it is necessary to remove the mounting arms. Use a hacksaw to cut them to the size shown on the drawing. Sign labels Fig.3 shows the three sign labels and the covering for the barrier. To make these, download the 1:1 scale label drawing as a PDF from siliconchip. com.au/Shop/11/5855 and print it on a colour printer using 80gsm paper. Print the drawing and measure the 100mm line. Let’s say it measures 99mm. This gives a calibration factor of 100/99 = 1.01 or 101%. So if you print the file again at 101% scale, the 100mm line should measure 100mm. Australia’s electronics magazine Fig.4: the overlay diagram for the Level Crossing. Note the resistors are mounted vertically. Mechanical parts assembly The first step is to push the black LED holders over the LEDs. Next, with the mounting hole at the rear of the post, clean a 2mm strip on the front with a centre 50.25mm from the bottom and tin that strip with solder. Place the LED assembly over the post, as shown in the drawing. Using a soldering iron, attach it to the post. Select about 100mm of thin wire with high-temperature insulation and slide it into the hollow post at the bottom until it exits out at the 1.5mm hole, 48mm up. Strip off about 2mm of insulation and solder it to the LED assembly as shown in the upper left photo. The three backing plates are then glued to the post as shown, using Loctite GO 2. Leave it for 24 hours for the glue to set. Using heatshrink tubing and masking tape, cover the LEDs and then spray the assembly with aluminiumcoloured paint. When dry, remove the heatshrink tubing and masking tape and attach the three labels to their respective backing plates. The final task is to connect the second power lead to the post on the two post assemblies. This is done after they are assembled on the crossing, as any solder on the post would stop it from going into its mounting hole. July 2021  49 Fig.5: the wiring diagram for the project. For triggering the device, we recommend using a reed switch for S1 which is hidden under the tracks, so that it can be triggered by a magnet on the locomotive. Again, clean and tin a 2mm section at the bottom end of the post and attach a wire to it. I will leave the design of the road across the track up to you, as the sizes will depend on your particular railroad layout. Mine consisted of timber wedges painted matte black. Electronic assembly The heart of the level crossing circuit is built on a single-sided PCB coded 09108211 which measures 48 x 43mm. The PCB overlay diagram, Fig.4, can be used as a guide during construction. Start by fitting the PCB pins, then the IC sockets. We used IC sockets for the microprocessors and the recording ICs in case we ever wanted to reprogram or change the sound. Take care to orientate them correctly. Now add the resistors, which are mounted vertically, followed by the capacitors. Check that the 100µF capacitor is the right way round. Next, add the 2N7000 Mosfet Q1, orientated as shown. The wiring diagram (Fig.5) shows how to connect the two post assemblies, the loudspeaker, the trigger switch and the two servomotors. Rather than using a pushbutton switch as shown, we expect most constructors will use a reed switch hidden under a section of the track, with a magnet on the model locomotive to trigger it before the loco reaches the crossing. Finally, connect the positive of the 5V power pack to the +5V point on the board and the negative to 0V. Check that all the connections are correct and that there are no dry joints or solder bridges. At this stage, don’t plug in the PIC controllers, IC1 and IC2. There is no provision for programming either of the microcontrollers in-circuit, so you will either need to purchase preprogrammed micros, or program them yourself using an external programmer before plugging them in. You can download the HEX files from the Silicon Chip website; the one ending in A or B is for IC1 (depending on the type of switch used) and C for IC2. Recording the bell sound Here is an example of the completed project fitted onto a model railway track. 50 Silicon Chip Australia’s electronics magazine The download package on our website also includes a WAV audio file of the bell sounds, which you need to transfer to IC3. This is supplied as part of a module that is capable of recording by itself (see the photo overleaf). The simplest way to transfer the bell siliconchip.com.au sounds from a computer to the chip is to place the module’s microphone close to your computer speakers. First, though, the module needs a power source. Connect a 5V supply to its power input terminal block. With the green terminal block on the left, make sure that the two slide switches marked FT and repeat are switched to the left-hand side. It’s also a good idea to temporarily connect the 8W speaker to this module so that you will be able to hear and check what you have recorded. Hold the module so that its electret microphone is about 100mm from the computer loudspeaker. Play the downloaded WAV file at the maximum reasonable volume, and after it starts, hold down the REC button until LED D1 goes out (after the maximum recording time of about 10 seconds). Slide the repeat switch to the right and momentarily press the PLAYE button. This should verify that you now have a continuous recording of the level crossing bell sound on the chip. Testing the electronic assembly Plug the 5V power pack into the mains and, using a voltmeter, check that you have 5V between pins 1 and 8 on IC1’s socket. Switch off the power supply, remove the ISD1820P IC from the recording and playback module and insert it into level crossing PCB, orientated as shown in Fig.4. Do the same for the PIC microprocessors, making sure that you don’t get them mixed up. Switch the power on, close the start switch and you should see the red LEDs flashing alternately and hear the level crossing bell sound from the speaker. Half a second later, the servomotors should move slowly clockwise about 70°. On opening the switch, the servomotors should slowly move back, the flashing lights should extinguish, and the bell sound should stop. Parts List – Level Crossing Controller 1 control PCB assembly (see below) 1 5V DC supply (eg, USB charger with USB cable) 1 SPST toggle switch (S1) OR 1 momentary pushbutton switch (S1) OR 2 reed switches plus a magnet (S1; see text) 8 3mm high-intensity red LEDs with diffused lenses (LED1-LED8) 2 1.6kg.cm 9g micro servos [eg, Core Electronics SER0006] 1 8W speaker [eg, Jaycar AS3006] 1 ISD1820P-based audio recording/playback module [eg, Jaycar XC4605] 1 set of printed labels (see Fig.3) various lengths and colours of light-duty hookup wire various mechanical parts (see Fig.2) Control PCB parts 1 single-sided PCB coded 09108211, 48 x 43mm 2 8-pin DIL IC sockets (for IC1 & IC2) 1 14-pin DIL IC socket (for IC3) 1 PIC12F617-I/P 8-bit microcontroller programmed with 0910821A.HEX (for toggle switch) OR 0910821B.HEX (for momentary or reed switches) (IC1) 1 PIC12F617-I/P 8-bit microcontroller programmed with 0910821C.HEX (IC2) 1 ISD1820P audio recording/playback IC with bell sound recorded (IC3) (from module listed above) 1 2N7000 small-signal N-channel Mosfet (Q1) 1 100μF 16V electrolytic capacitor 2 100nF 63V MKT or 50V ceramic capacitors 16 1mm PCB pins Resistors (all 1/4W 1% axial metal film) 1 1MW 2 4.7kW 1 100kW 2 330W 1 10kW 1 220W and attach the servo arm to the servomotor. Glue the barrier onto the servo arm so that it is horizontal and let it dry. Do the same for the other servomotor. Open and close the switch to check that the barriers operate, as in the video. To hide the servomotors, I made boxes out of folded card and painted them silver. Fig.6 is the cutting diagram for this box, and it is also available as a PDF download. Print the 1:1 scale drawing on 80gsm paper, cut out the outline, fold it up into a box and use super glue to hold it together. In this operation, be very careful not to get super glue on your fingers – unsticking them can be painful! Use tweezers to hold the surfaces together when the glue is setting. Paint the box silver, cut out the hole for the servomotor and fit the box. Repeat for the other servomotor. Final fitting Glue the barrier covering labels to each side of each barrier and trim any excess overhang. Mount the servomotors side-on, as shown in the adjacent photo. Apply power and close the start switch. The servomotors will move down to the barrier closed position. Slide the barrier over the modified servo arm bush as shown in the photo, siliconchip.com.au Fig.6: this box was designed to hide the servomotors when displayed on the track. You can print this diagram on a suitable material, fold it and then paint it if you want. Australia’s electronics magazine July 2021  51 A more complicated approach to recording the bell sounds I designed the circuit shown in Fig.7 to provide a more elegant way of recording the bell sounds from a computer onto the ISD1820P chip. In the end, while it is a better solution, the effort and expense of building this circuit are not worthwhile for a one-off recording. The speaker/microphone method described in the text provides decent results with minimal effort. Regardless, I am presenting the circuit here for those interested. Audio from the computer’s output jack is adjusted in level using VR1, then AC-coupled to two op amps, IC2a & IC2b. These convert the single-ended computer audio into a balanced signal, ideal for feeding to the ISD1820P’s balanced microphone inputs at pins 4 & 5. The components at the top of the circuit detect when audio playback begins on the computer and automatically triggers recording on the ISD1820P (IC4), so that you don’t have to try to press both buttons simultaneously to get the best results. The ISD1820P is often sold as a module similar to this. This model in particular is sold by Jaycar (www.jaycar. com.au/p/XC4605). But there are a wide variety of alternatives available online that will also work. Note that they might have different arrangements for feeding in power, jumpers instead of switches and other minor variations. IC1a amplifies the audio signal by around 83 times and then feeds a diode charge pump (D1 and the 1μF capacitor). This capacitor quickly charges as soon as a signal comes from the computer. The other half of the dual op amp, IC1b, is connected as a comparator, pulling the GP2 digital input of IC3 (pin 5) low as soon as the charge on that 1μF capacitor exceeds about 3.3V. This also lights LED1. When 8-bit PIC microcontroller IC3 detects that its pin 5 has gone low, it generates a pulse from its GP1 digital output (pin 6) to trigger recording mode on IC4. This has an appropriate length to record the whole bell sound sequence. So IC3 is acting as a pulse SC stretcher. Fig.7: a circuit I designed to record sound to the ISD1820P module directly from a computer’s audio output jack. 52 Silicon Chip Australia’s electronics magazine siliconchip.com.au E V A S with ay ar d y r Eve at Jayc Gre alue V 1 ale On S July, 202 3 2 o ne t u 24 J Intelligent 15A Battery Charger Ideal for cars, motorcycles, boats and caravans with battery capacities between 20-200Ah. 6V/12V/24V. 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If we produce or publish your electronics, arduino or pi project, we'll give you a complementary $100 gift card. projects.jaycar.com 1800 022 888 www.jaycar.com.au Over 100 stores & 130 resellers nationwide HEAD OFFICE 320 Victoria Road, Rydalmere NSW 2116 Ph: (02) 8832 3100 Fax: (02) 8832 3169 ONLINE ORDERS www.jaycar.com.au techstore<at>jaycar.com.au Arrival dates of new products in this flyer confirmed at the time of print. Call your local store to check stock. Occasionally discontinued items advertised on a special / lower price in this flyer have limited to nil stock in certain stores, including Jaycar Authorised Resellers, and cannot be ordered or transferred. Savings off Original RRP. Prices and special offers are valid from 24.06.2021 - 23.07.2021. 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. Coded door buzzer Last year, our building was equipped with an RFID-based door entry system. One day, my brother lost his RFID key tag. On another occasion, my father left his key tag in his office etc. Their only way in is to use the pushbutton doorbell, but that only works if someone is present in our apartment. That raised the following idea: why not add some “intelligence” to the doorbell using a low-cost microcontroller? One could then use a simple code (eg, a mixture of short and long doorbell presses, like Morse code) to open the main building door. I opened our Videx audio handset and inside found a 12V AC powered buzzer. The buzzer signal is present only when the buzzer is activated, so Circuit Ideas Wanted siliconchip.com.au I designed a circuit powered by this voltage, and it also uses it to determine the sequence of button presses. The beauty of this is that it consumes no power in the idle state. The buzzer signal is rectified using diode bridge D1-D4, then peak-held to approximately 16.4V DC by D6 and the 2.2μF capacitor. The voltage across this capacitor is divided by two resistors to produce a ~5V DC signal. At the same time, the rectified voltage is fed to a 220μF bulk capacitor via diode D5. The charge in this capacitor provides power both for relay RLY1 and 5V regulator REG1, which powers microcontroller IC1. The 5V signal corresponding to the sequence of pulses from the buzzer goes to digital input pin 1 of IC1 (RA0). The microcontroller then decodes this and compares it to the “secret” code stored in its EEPROM. If it matches, it brings digital output pin 3 (RA1) high for a few milliseconds, switching on Q1, which activates relay RLY1 to unlock the door by simulating a press of the door open button. The 12V reed relay I used has a coil resistance of 1kW, so it consumes about 12mA when energised. To avoid the 220μF capacitor discharging too quickly before the door can be opened, I added a 180W series resistor. This takes advantage of the fact that the holding current of any relay is typically 20-50% less than the initial pull-in current. Benabadji Mohammed Salim, Oran, Algeria. ($100) Got an interesting original circuit that you have cleverly devised? We will pay good money to feature it in Circuit Notebook. We can pay you by electronic funds transfer, cheque or direct to your PayPal account. Or you can use the funds to purchase anything from the SILICON CHIP Online Store, including PCBs and components, back issues, subscriptions or whatever. Email your circuit and descriptive text to editor<at>siliconchip.com.au Australia’s electronics magazine July 2021  61 Adding shuffle feature to low-cost MP3 player module I had a few friends over during Christmas, and to provide background music, I had my stereo amplifier connected to a CD player. After a while, I got sick and tired of getting up to put on a new CD. I decided that I wanted a way to play at least 10 CDs worth of music with reasonable quality so that each track was randomly played. I came across the Jaycar XC3748 MP3 audio module at $14.95, which plays audio files on a TF/SD card. It also has a serial communication interface (UART) that can be used to control which music tracks are played and in what order, plus six pushbuttons to control the basic functions like play, pause, previous, next track and level adjustment. There is also a USB interface to enable you to add music files from your computer. Its headphone jack provides a stereo output at the right level to directly connect it to an amplifier. It uses the YX5200-24SS processor, which provides reasonable music playback quality and, at 77 x 33 x 8mm, it can be mounted in a small utility box. Looking at the data sheet, I found that if you sent the serial code “7E FF 62 Silicon Chip 06 18 00 00 00 FE E3 EF” (hexadecimal) at 9600 baud, the module would play the tracks in a random order, as I wanted. All I needed was a simple microcontroller circuit to generate the code. The accompanying circuit diagram shows what I came up with. The unit is powered from a standard 12V or 9V DC power pack. This feeds linear regulator REG1 to produce 5V DC for the Jaycar module and the microcontroller. To start playing music in a random order, the Random start button must be pressed, taking input pin 5 (GP2) of the PIC12F617 micro high. The 100nF capacitor across the switch eliminates contact bounce. This positive level causes the random playback code listed above to be sent to the Jaycar module’s RX input. If you look at the data sheet for the module, you will see many other commands that can be sent. For example, you could ask it to play a particular track. If you are into coding, this would be a simple modification. After converting my CDs to MP3 format and copying them onto a FAT32 card, which I inserted into the module’s socket, I mounted the playback Australia’s electronics magazine module and my circuit in a small plastic utility box. I fitted three pushbuttons to the top of the box: random start, next track and previous track, plus an on/off toggle switch and a power indicator LED. On the side, I added a socket for the 12V power input and a hole for the jack plug lead connecting it to the stereo amplifier. On the side next to the USB socket, I cut a rectangular hole so that a USB cable can be plugged into the Jaycar board. This enables you to add or erase music files from the micro SD card without having to open up the box. The next track and previous track switches on the utility box are wired in parallel with the associated switch on the Jaycar board. These switches can also be used to adjust the volume. Holding down the previous button reduces the volume, while holding down the next track button increases it. Note that the random play button always cases the first track to be played. If that annoys you, jump to the next track by pressing the next button. Les Kerr, Ashby, NSW. ($80) siliconchip.com.au DIY pulse oximeter Lately, our electronic markets have been flooded with pulse oximeter probes based on the MAX30100 IC for as low as INR250 (about $2) apiece, such as the RCWL-0530. I purchased a few from a local supplier, but I found that the readings were awfully wrong! After reading the MAX30100 data sheet and doing some internet research, I discovered that these lowcost oximeters have two main problems: poor regulation of the 1.8V supply and incorrect I2C pull-up resistor values. The MAX30100 is an I2C infrared measuring device. Ideally, the board should supply 3.3V for the infrared LED driver and 1.8V for the control & measurement circuitry. The I2C and interrupter pins need to be pulled up to 3.3V via 4.7kW resistors, but many implementations only pull them up to the 1.8V rail. In this case, they will not work with the I2C bus of an Arduino or ESP32 micro. The MAX30100 has a temperature sensor for oxygen reading correction, but it cannot be read separately, and the sensor has a power-down sleep state which is generally not used. I don’t know why. Check the voltage on either side of the 3-pin (SOT-23) regulator with a voltmeter. You should get readings of 3.3V and 1.8V. So far, so good. But the three 4.7kW resistors are connected to the SCL, SDA & INT pins from the +1.8V rail. This prevents us from siliconchip.com.au getting the correct measurements for this device, even though the software shows success. The adjacent image shows where you can cut the track and run a short length of small-diameter solid-core insulated wire to fix this (see github. com/oxullo/Arduino-MAX30100/ issues/51). We can now connect it to the ESP32 microcontroller module, as shown in the circuit diagram. I have added a DS18B20 temperature sensor since, as mentioned above, we can’t query the temperature sensor on the oximeter module. The resulting probe measures the oxygen level and temperature from a finger and uploads it to ‘the cloud’ at www.thingspeak.com The ESP32 has been programmed to support multiple WiFi SSID and password combinations. It will connect to whichever is available at that moment. The LED at GPIO12 will blink briefly to indicate that the data has been uploaded to the cloud server. After uploading the data, the micro goes into deep sleep mode for 20 seconds, then it wakes up and repeats the process. During sleep mode, the IR led of the MAX30100 sensor switches off and the total power consumption goes down to 4.2mA. During measurement, the current is 160mA. One 26650 3.7V Li-ion cell of around 3000mAh can sustain this for weeks non-stop. When attaching the sensor to a Australia’s electronics magazine On this RCWL-0530 module, the track marked in yellow must be cut, and then solder a piece of wire between the two locations marked in red. This connects the I2C pull-ups to the correct 3.3V rather than 1.8V supply. finger, ensure that the area which makes contact is clean and without oil, ink or grease. It’s better to clean it with alcohol beforehand. If the body contact is not perfect, the device will hang. To solve that, the micro will restart after 25 seconds. It will also restart if it is unable to upload data. The Arduino sketch to load onto the ESP32 is available for download from siliconchip.com.au/Shop/6/5860 You will need to open a free account at www.thingspeak.com and modify the API key in the software to match the one you are supplied with before it will upload data. Sample data is visible on my Thingspeak channel at www.thingspeak. com/channels/1203838 Bera Somnath, Vindhyanagar, India. ($100) July 2021  63 Single-Chip Silicon Labs FM/AM/SW Digital Radio Receiver By Charles Kosina The ultimate in FM/AM radio reception technology is the single-chip solution. All you have to do is connect some antennas to pins on an IC, send it some serial commands, and stereo audio comes out the other end. As a result, these Silicon Labs chips make building a capable radio receiver a doddle. It’s straightforward to set up and use, fits in a compact case and runs from a simple AC plugpack. I was fairly pleased with my AM/ FM/SW Receiver design from the January 2021 issue (siliconchip.com. au/Article/14704), at least in terms of how easy it is to build, ease of use, and coverage of multiple radio bands. But I still felt that its overall performance left a little to be desired. I was also not happy that I didn’t have enough information for full digital control of the BK1198 radio chip. While that radio design was relatively straightforward as radios go, it would have been a lot simpler if I could have gotten the digital control working. In the last few years, several new chips have appeared that greatly ease radio receiver design. Many of these are from Silicon Labs; there are about 34 varieties of chips in the Si473x family, and you can download the main data sheet from siliconchip.com.au/ link/ab7y They have a similar architecture to the BK1198 chip I used for the January 2021 design. One major advantage of the Silicon Labs chips is the documentation; whereas information on the BK1198 is sparse, to say the least, the application note for the SiLabs chips 64 Silicon Chip runs to 321 pages! (See siliconchip. com.au/link/ab7z). The board that I have laid out is suitable for a prebuilt module with the Si4730 chip, or a standalone Si4732 chip. Both are available on AliExpress at quite low prices. The Si4730 only handles the standard AM and FM bands, whereas the Si4732 can be programmed to cover longwave and shortwave. Both can decode FM stereo. The specifications give the following bands: Worldwide FM band support: 64– 108MHz Worldwide AM band support: 520– 1710kHz SW band support (Si4734/32/35): 2.3–26.1MHz LW band support (Si4734/32/35): 153–279kHz But what about the gaps between the Fig.1: the radio’s sensitivity across a widened AM band, from 153kHz to 1.7MHz. Except for a dip around 445-455kHz (typical intermediate frequencies), the result is pretty flat. Across the standard AM broadcast band of 550-1720kHz, there is only about 4dB variation. Australia’s electronics magazine siliconchip.com.au These two photos show that the topside of the PCB for the Si4730-based version (top) of this project is barely different from the Si4732 version (bottom). Ignore the additional screws/nuts as those are just for mounting the screen. bands? I decided to experiment and set frequencies in these gaps. And what a surprise; with the Si4732 chip, I could select any frequency from 153kHz up to 30MHz by sending the appropriate code to the chip. No gaps! Whether there is anything of interest in the gaps is another matter. As a result, I have the AM band programmed from 153kHz to 1730kHz, and the SW band from 2MHz to 30MHz. Performance On the FM band, a short piece of wire inside the box will bring in most of the Melbourne stations with a good SNR. With an outdoor long wire antenna connected directly to the AM antenna input, I could get many stations with an SNR of 25dB or better without any ferrite rod. This way, there is not a single inductor required in the circuit! Using a ferrite rod, the weaker Fig.2: a similar ‘frequency response’ plot for the SW range from 2MHz to 22.3MHz. siliconchip.com.au Australia’s electronics magazine stations came through, but there was a lot of hash caused by all the electronics in my lab. I made a plot of sensitivity on the AM band from 153kHz to 1700kHz, shown in Fig.1. Note the sharp dip at 450kHz. I have no idea why this is, but it is near the intermediate frequency of most superhet receivers, so it is of no consequence. On shortwave, the sensitivity is comparable to the AM band (see Fig.2). This is not brilliant, but adequate. There were a few ‘birdies’ on some frequencies, eg, 8MHz, 14MHz and 16MHz, which made SNR measurement difficult. Above 22MHz, the SNR display did not seem to give sensible readings, although performance up to 30MHz seemed the same as at 20MHz. The audio drive capability of the SiLabs chips is not stated in the data sheets. I determined experimentally that the minimum load resistance on the headphone output is 1.6kW. Any less and clipping will occur. The maximum output with this load is 250mV peak-to-peak or about 88mV RMS for a sinewave, giving less than 1mW. It still works with low impedance headphones, although at maximum volume, there will be some distortion. Sennheiser 60W headphones gave an acceptable listening level in a quiet environment. Panasonic noise-reducing headphones with a 330W input resistance (with the noise reduction turned on) gave a considerably higher sound level. Feeding the signal into external amplified speakers gave good-quality sound. Because of this weak output, I have added an op amp buffer that provides drive capability for low impedance headphones, while also providing enough voltage swing for insensitive high-impedance ‘phones. This is also useful if you’re feeding the audio to a preamp or amplifier, as the signal is closer to ‘line level’. When the tuning knob is rotated, each pulse from the shaft encoder sends out six bytes via I2C and then receives seven bytes of status. This takes a significant time, so if you spin the tuning knob too rapidly, the encoder pulses are missed, and you only get a small frequency change. Just slow down the rotation. Circuit description The full schematic is shown in Fig.3. The Si4730 module includes July 2021  65 The Si4732 version differs due to the installation of two 22pF capacitors, a crystal (X2) and the chip itself on the underside of the PCB. the 32.768kHz crystal and associated capacitors. The FM antenna is connected to the module’s FM input via a 1nF capacitor, while the AM band requires a ferrite rod, typically 400μH. An optional 10nF capacitor joins the two antenna inputs, allowing a single length of wire to provide both FM and AM reception in metropolitan areas. The SEN line is tied high internally on the Si4730 module. The audio output is coupled to header CON4. The drive strength from the radio chip itself is just adequate to drive 60W headphones; as hinted above, depending on the ‘phones, the volume level can be a bit low, and distortion can be higher than we’d like. The dual op amp (IC3) in the final version is not present in the prototypes shown. This gives a voltage gain of 4 and low-impedance output, enough to drive just about any headphones or earphones to a decent volume level (even insensitive types), and possibly even very efficient unpowered speakers. Alternatively, an external audio amplifier such as computer speakers can be used, with or without the op amp. If you don’t need the op amp, you can simply bridge pin pairs 1/3 and 5/7, to feed the radio chip’s output to CON4. CON4 also has +5V and GND pins. This supply might be used for a small amplifier module mounted in the same case, to drive 8W speakers. I don’t recommend Class-D amplifiers as they could generate hash which will interfere with radio reception, much the same as a switching regulator. Control is via a standard I2C serial bus and a reset line. I have specified a 32KB ATmega328P chip in a DIL package, although I used the 16KB 66 Silicon Chip ATMega168 in my prototype; the program only occupies 68% of its 16KB of flash, and I have heaps of these chips left over from a previous project. Besides the flash size, they are essentially identical. The display is a standard 16x2 alphanumeric LCD module. There is provision for an external crystal for the ATmega chip, but I found the internal 8MHz RC oscillator quite adequate. The processor runs from 5V, whereas the SiLabs chip requires 3.3V. This is not a problem for the I2C interface, as the output is open-drain, and the 15kW pull-up resistors go to 3.3V. There are also two 1kW series current-limiting resistors between the I2C outputs of the micro and the radio module’s inputs as a precaution against incorrect programming of the I2C pins. The typical value of an I2C pull-up resistor is 4.7kW, but the SCL and SDA pins on the SiLabs chip have limited drive capabilities. Operation with 4.7kW pull-ups could be marginal, especially given the 1kW series protection resistors. Hence the use of 15kW pull-ups; lower values would give a marginal low voltage with either pin when pulled externally low, via those 1kW resistors. I have not found any problems with these higher-value pull-up resistors (eg, sensitivity to EMI). Tuning is by a standard shaft encoder with a pushbutton switch (RE1). The switch cycles through different step sizes on the bands. The external band switch, S3, toggles between AM and FM modes. I used an ON-OFF-ON type switch to provide for three bands. This gives three different voltages which can be read by the analog-to-digital converter Australia’s electronics magazine (ADC) input on the ATmega, PC3 (pin 26). If the Si4730 module is used, there is no SW band, so you should use a two-position switch instead. Another ADC input, PC0 (pin 23), monitors the voltage at the wiper of potentiometer VR2 which sets the volume. The reading is scaled and sent via the I2C lines to control the volume of the SiLabs chip. A third ADC input at PC1 (pin 24) reads the position of potentiometer VR3; the reading is scaled and sent to the SiLabs chip to adjust the bandwidth on the AM band. I could have used a multiple position switch, but this is a simpler and cheaper option. The bandwidths that can be selected are 1.0, 1.8, 2.0, 2.5, 3.0, 4.0 and 6.0kHz. The potentiometer that I have used has a centre detent which gives a 2.5kHz bandwidth, but this is optional. There is no bandwidth option for FM. Using the Si4732 chip For those who wish to include SW or LW bands, you can use the Si4732 chip instead of the Si4730 module. This comes in the SOIC SMD package, which is not difficult to solder. There are only slight changes to the circuit, as shown in Fig.4. The SENB pin goes to ground on the Si4732, which gives it a different I2C address to the Si4730. It requires an additional crystal and three capacitors. The Si4730 module I2C addresses are C6 hex for writing, and C7 for reading. With the Si4732 chip, the corresponding addresses are 22 and 23 hex. Don’t load both the Si4730 module and Si4732 chip. Although they have different I2C addresses, the loading on the RF inputs is such that it severely degrades sensitivity. You will note that the I2C bus is made externally accessible via CON8, together with the +5V supply. This could be useful in future for expansion, or as a debugging aid. The power supply may be 9V AC or 9-12V DC via CON1. If a DC supply is used, it must not be a switching type, as they can create a lot of hash which can wipe out the AM band. A 7805 regulator supplies the ATmega chip and the LCD module, while a small TO-92 linear regulator provides 3.3V for the SiLabs chip. Debugging interface Mosfets Q1 and Q2 provide a serial debugging interface. This was siliconchip.com.au Fig.3: there isn’t a lot to the radio circuit thanks to the Si4730 radio module. The antennas at left are simply coupled to the module using capacitors, while the audio outputs on the right-hand side feed into a pair of op amp buffer/gain stages, which are better at driving headphones than the module by itself. IC2 controls the radio over an I2C serial bus while monitoring user input via rotary encoder RE1, and displaying tuning and signal strength information on a two-line LCD. siliconchip.com.au Australia’s electronics magazine July 2021  67 ► Fig.4(a): if you want SW ► reception, all you have to do is leave off the Si4730 module (MOD1) and instead fit IC1, its 100nF supply bypass capacitor, crystal X2 and its two 22pF load capacitors. All the other components shown here were in the original circuit (Fig.3) and are only duplicated to clarify how IC1 is connected to the rest of the circuit. Fig.4(b): how the panel-mount jack socket is wired to CON4. Check your socket’s pinout to determine the tip (T), ring (R) & sleeve (S) connections. invaluable for debugging purposes, but not required if you just want to use the radio. It is set up for 38,400bps, eight data bits, one stop bit and no parity. Microcontroller IC2 is programmed via the standard 6-pin header, CON9. A pushbutton switch is provided to reset IC2. Component Selection While I try to make sure that components can be sourced locally, it is not always possible. In this case, several major components have to be sourced from overseas suppliers. There are a few suppliers of the Si4730-V2.0 module on AliExpress that sell it for about $5. Make sure it’s the version with six connections on each side. There are some with only five connections on each side that will not fit. As with most orders from China, be prepared for a fairly long delivery time. The Si4732 chip is manufactured in the SOIC-16 package. It is available in lots of five on AliExpress, for a total of about $14, so you will have spares. It’s also available from Digi-Key and Mouser with a somewhat higher price, but the good news is that you can order it along with other parts (about $60 worth) for free express delivery. Apart from the 1000μF electrolytic and the 2W resistor, all other resistors and capacitors are either 1206 or 0805 (imperial) size SMDs, and there are no fine-lead-pitch devices to worry about. Figs.5 & 6: most of the components mount on the top side of the PCB; apart from a few SMDs, the only parts on the bottom are the two pots, the rotary encoder and crystal X2 (if IC1 is fitted). It’s best to fit all the SMDs on the underside, then the SMDs on the top, then the through-hole parts on the top, then the underside. Ensure the polarised parts like the radio module, all the ICs, the aluminium and tantalum electrolytic capacitors, bridge rectifier BR1, diode D1 and trimpot VR1 are orientated as shown. Errata: if using the specified part, REG2 should be mounted upside down relative to the overlay. Otherwise you can mount it on the underside of the PCB, making sure not to have it foul the front panel. This is due to the input and output pins being swapped on the PCB footprint. 68 Silicon Chip Australia’s electronics magazine siliconchip.com.au There are various colours of backlighting for the LCD module. We much prefer the white-on-blue version to the old-fashioned yellow/green version. This type is available from several Australian suppliers on eBay. But if you don’t mind waiting, the LCD module can cost as little as about $2.50 from Chinese suppliers. As we’re using the parallel interface, you won’t need the I2C serial interface board supplied with some of them. The LCD is mounted off the main PCB by standoffs, and connected using the supplied standard header plugging into a low-profile PCB-mounting socket strip. The LCD height above the board means that the two potentiometers and rotary encoder need 25-30mm long shafts. The parts list shows suggested components. Construction A word of caution. The crystal on the tiny ‘4730 module is not firmly attached and can be easily bent to one side and damage the board. I can vouch for that from experience! I recommend a spot of superglue to attach it firmly to the board. In any case, order two of these modules to be on the safe side. The circuit board (coded CSE210301C) is double-sided with components on both sides. It measures 123 x 49.5mm. Both versions use the same PCB; either you mount the Si4730 module on one side, or the Si4732 chip on the other. Refer to overlay diagrams Figs.5 & 6, and ensure that you either fit the module as shown in Fig.5, or the components in the red oval in Fig.6; not both. Start by mounting the 16-pin chip. This is the SOIC-16 type with pins spaced widely enough that they can be soldered individually using a finetip iron. First, apply some flux paste to the pads to reduce the risk of bridging between pins. If bridges do form during soldering, use more flux paste and some solder wick to remove it. Next, fit the SMD capacitors on the underside of the board. Note the two 22pF capacitors (values in parentheses) are only needed if you wish to use a crystal oscillator for the ATmega168/ ATmega328 chip. It is not necessary, so we suggest you leave them off. The other side of the board has the majority of components. Install the remaining surface-mount components next. If you are using the Si4730 module, make sure that it is positioned accurately. It needs a fair amount of solder to flow into the ‘half holes’ on either side (see the photo on page 65). Ensure that the 10μF & 100μF tantalum capacitors are placed with the This is how I wired up the prototype Si4730-based radio. siliconchip.com.au Australia’s electronics magazine correct polarity. The striped end is positive, so face the striped ends towards the “+” symbols on the PCB. Then add the through-hole components, possibly including the optional 8MHz crystal. There is also provision for an SMA socket, CON6, that I did not bother using. This is an alternative input for the AM, LW and SW bands. I prefer the LCD module to be removable; hence, I plugged it into a socket strip. The matching headers are not that easy to find, but the parts list mentions suppliers. The LCD is then attached using 9mm untapped spacers (Jaycar HP0862 or Altronics H21362) and M2.5 x 15mm screws and nuts. The last components to attach are the two potentiometers (VR2 & VR3) and rotary encoder RE1 on the LCD side. Finally, give the board a good wash on both sides with circuit board cleaner. Preparing the enclosure I encased the radio prototypes in the Hammond RP1175C box, which has a clear lid. This avoids having to make a rectangular cutout for the LCD, so you can drill all the holes. The only places I found selling it were Mouser and DigiKey. You could use a larger case that’s locally available, but that would make the radio a bit less convenient to use. You can place the power input connector, headphone jack and BNC antenna connector on any convenient surface. I chose the righthand side of the box. The headphone jack presents something of a problem. The case thickness is too much for easily obtainable 3.5mm stereo jacks. The simplest solution is to use a 6.35mm jack, and if necessary, a 3.5mm adaptor like the Jaycar PA3590. The drilling details are shown in Fig.7; use this as an initial template to locate the circuit board mounting holes (D) and the toggle switch holes (B). As accuracy is required, the blank circuit board can then be used as a template for drilling the mounting holes. Use a countersinking tool so that the screw heads will be flush with the front panel. You will note that there is a small hole in the centre of the encoder and two potentiometers. Once the four mounting holes (D) are drilled, attach the board to the panel with 3mm screws and drill 1mm holes through the centre of the two July 2021  69 Fig.7: if you use a box with a clear lid, then you only have to drill round holes, as shown here. You can stick masking tape on your panel, measure and mark the hole dimensions, or simply copy/print this diagram, cut it out and use it as a template. For the neatest result, countersink the holes marked D on the outside of the panel. potentiometers and encoder positions, to accurately mark the centres of the 8mm holes (A). I printed the 139 x 76mm front panel label on heavy photographic paper, and it fits neatly in the slot on the transparent panel. Fig.8 is the panel label for the Si4730 module-based version, while Fig.9 shows the label for the Si4732-based version. The only difference is in the labelling for the band change switch, adding the SW option for the Si4732 chip. You can also download these labels from the Silicon Chip website and print them out. Use a sharp blade to cut out the slot for the LCD and the five holes for potentiometers, encoder and switches, then cut out the panel and slot it into the inside of the clear lid. It should be a neat fit. Attach the circuit board to the back of the front panel using 12mm-long M3 countersunk head screws at the front and M3 x 6mm screws at the back. 18mm-long spacers are needed, which can be made from a 12mm threaded spacer plus an untapped 6mm spacer stacked. There might be other combinations of spacers to give the required 18mm. The potentiometer and encoder shafts are 6mm in diameter. Be careful if you are using metric knobs, as some might not be suitable for the shafts. Choose the types with a grub screw as these will fit a wide variety of shaft types. There remains the internal wiring to the various switches and connectors on the enclosure. This is relatively straightforward, and shown in the photographs (refer to Figs.3-6). Programming the micro Similarly, an example of the wiring for the Si4732 version of this project. 70 Silicon Chip Australia’s electronics magazine I wrote the control software using BASCOM, a BASIC compiler for AVR micros. Having the application and programming notes provided by SiLabs made the code fairly straightforward. Both the .BAS source code and .HEX firmware file are available for download from the Silicon Chip website. Note that you might need a paid version of BASCOM to compile the .BAS file. The program header on the board is designed for an AVRISP Mk2 programmer. This can be used in conjunction with the free Atmel (now Microchip) Studio program available for download from www.microchip.com Control of the SiLabs chip is via I2C serial commands, and believe me there are heaps of them. There are all sorts of features, such as scanning, that could be incorporated into the design, but siliconchip.com.au Parts List – Silicon Labs AM/FM/SW Radio 1 double-sided PCB coded CSE210301C, 123 x 49.5mm 1 9V AC plugpack with 2.1/2.5mm ID barrel plug 1 plastic box with clear lid [eg, Altronics H0326, Hammond RP1175C: Digi-Key; Mouser] 1 panel label, to suit version being built 1 16x2 alphanumeric LCD module with blue backlight (LCD1) 1 28-pin narrow DIL IC socket 3 2-pin polarised headers with matching plugs and pins (CON1-3) [Jaycar HM3412/02, Altronics P5492/72 + 2x P5470A] 1 5-pin polarised header with matching plugs and pins (CON4) [Jaycar HM3415/05, Altronics P5495/75 + 5x P5470A] 2 3-pin polarised headers with matching plugs and pins (CON5,CON7) [Jaycar HM3413/03, Altronics P5493/73 + 3x P5470A] 1 4-pin polarised headers with matching plugs and pins (CON8; optional) [Jaycar HM3414/04, Altronics P5494/74] 1 panel-mount BNC socket [Jaycar PS0658, Altronics P0516A] 1 PCB-mount DC barrel socket, 2.1/2.5mm ID, to suit plugpack [eg, Jaycar PS0522/4, Altronics P0620/1A] 1 panel-mount stereo 6.35mm jack socket [eg, Jaycar PS0182, Altronics P0065] 1 16-pin low-profile machine pin header strip with matching socket strip (for LCD) * 1 10kW multi-turn trimpot (VR1) 2 10kW 9mm vertical potentiometers with D-shafts (VR2,VR3) [eg, Bourns PTV09A-4030F-B103-ND; or use Altronics R1946 with a fluted shaft] 1 vertical rotary encoder with D-shaft and integrated pushbutton switch (RE1) [eg, Bourns PEC11R-4225F-S0024] 3 small or medium-size knobs to suit VR2, VR3 & RE1 1 PCB-mounting small tactile pushbutton switch (S1) [eg, Jaycar SP0601 or Altronics S1120] 1 SPDT miniature toggle switch with solder tags (S2) [eg, Jaycar ST0335] 1 400μH ferrite rod antenna (L1) [eg, Jaycar LF1020] 4 9mm untapped spacers (for LCD mounting) [Jaycar HP0862, Altronics H1362] 4 9-10mm-long M3 panhead machine screws and nuts (for REG1) 4 12mm-long M3 countersunk head machine screws 4 6mm-long M3 panhead machine screws 4 12mm-long M3 tapped spacers 4 6mm-long untapped spacers, 3.25mm inner diameter 4 15mm-long M2.5 panhead machine screws and nuts (for LCD mounting) various lengths of medium-duty hookup wire various short lengths of heatshrink tubing to suit wire size * some options include Semtronics SBU400Z (header) + MH1S19-140 (socket), Mouser 200-BBL116GF (header) + Mouser 200-SL116T10 (socket), element14 1667454 (header) + Jaycar PI6470 (socket) or Altronics P5400 (socket) Semiconductors 1 ATmega168 or ATmega328 8-bit microcontroller programmed with CSE210301.HEX (IC2) 1 5V rail-to-rail op amp, SOIC-8 (IC3) [eg, LME49721, available from Digi-Key, Mouser, eBay, AliExpress] 1 7805 5V 1A linear regulator, TO-220 (REG1) 1 LM2936-3.3 3.3V low-dropout linear regulator, TO-92 (REG2) 2 2N7002 small-signal N-channel Mosfets, SMD SOT-23 package (Q1,Q2) 1 DB104 bridge rectifier (BR1) [Jaycar ZR1308] 1 LL4148 small signal diode, SMD DO-80 MELF (D1) [Jaycar ZR1103] Capacitors (all SMD M2012/0805 size unless otherwise stated) 1 1000μF 16V through-hole radial electrolytic 2 100μF 6V SMD tantalum, SMA size 3 10μF 6V SMD tantalum, SMA size 2 470nF 50V X7R ceramic 3 220nF 50V X7R ceramic 5 100nF 50V X7R ceramic 5 10nF 50V X7R ceramic 1 1nF 50V X7R ceramic 2 100pF 50V C0G/NP0 ceramic 1 47pF 50V C0G/NP0 ceramic Resistors (all 1% SMD M3216/1206 size unless otherwise stated) 4 100kW 2 33kW 2 22kW 7 15kW 3 1kW 1 100W 5% 2W axial Additional parts for the Si4732-based version 1 Si4732 IC, SOIC-16 (IC1) [AliExpress, eBay] 1 on-off-on (centre off) miniature toggle switch with solder tags (S3) [eg, Jaycar ST0336] 1 32,768Hz watch crystal (X2) 1 100nF 50V X7R ceramic capacitor, SMD M2012/0805 size 2 22pF 50V C0G/NP0 ceramic capacitors, SMD M2012/0805 size Additional parts for Si4730 module-based version 1 Si4730 module, surface-mounting, with six pads on either side (MOD1) [AliExpress, eBay] 1 SPDT miniature toggle switch with solder tags (S3) [eg, Jaycar ST0335] Optional parts 1 vertical SMA socket (CON6) (external AM antenna input) 1 2x3 pin header (CON9) (for in-circuit programming of IC2) 1 8MHz crystal (X1) (see text) 2 22pF 50V C0G/NP0 ceramic capacitors, SMD M2012/0805 size siliconchip.com.au Australia’s electronics magazine July 2021  71 Figs.8 & 9: these panel labels are also available to download from the Silicon Chip website, so you can print them, cut them out and attach them to the inside (or outside) of the box lid. I decided to “keep it simple, stupid” (KISS). Others might wish to expand on what I have done. As mentioned above, the pushbutton switch integrated into the tuning encoder toggles through steps to allow fine selection or quick tuning across the band. On the AM band, the step is 1kHz, 9kHz or 100kHz. The FM band is 87MHz to 108MHz and has a step of 100kHz or 1MHz. On the SW band (if used), the step is 1kHz, 10kHz, 100kHz or 1MHz. About half a second after a frequency is selected, it and the step size are stored in EEPROM. This means that on the next power-up, the EEPROM values are read and that frequency selected. The top line of the 16 x 2 LCD shows the frequency, and on the AM and SW 72 Silicon Chip bands, it also shows the bandwidth. The second line shows the step size and the signal-to-noise ratio (SNR). The Si chip is sampled once a second to update the SNR figure. However, the Si4730 module does not give SNR readings on the FM band. Weaker signals give mono rather than stereo output as expected. Initial setup I did not want to have a separate control program for the Si4730 and Si4732 chips, so the chip type is automatically identified on power up. You don’t need to do anything. When I built a second unit, I discovered that the tuning was backwards. Clockwise decreased the frequency! It appears that shaft encoders differ. So I came up with a method to select Australia’s electronics magazine the correct tuning direction using the existing radio interface. If you find that your encoder action is reversed, use the following steps: 1. Turn the Bandwidth knob fully clockwise. 2. Tune the AM band to 500kHz. The display will show “Toggle Direction” on the top line, and “Direction 1” or “Direction 2” on the lower line. You don’t need to press the button, as it automatically selects the alternative direction when you access this display. 3. Tune to another frequency and make sure the tuning direction is correct. This setup only needs to be done once, as the parameters are stored in EEPROM & restored on power-up. SC siliconchip.com.au A first look at the “last” Tecsun radio receiver? Tecsun’s PL-990: SW/SSB, AM, FM, and LW Synthesised DSP Powerhouse T ecsun Radios Australia recently submitted the latest iteration of Tecsun’s “flagship”, the PL-990 multiband portable for review. It is a most worthy successor to the PL-880 which has received many excellent reviews since its introduction almost a decade ago, and which we looked at in the December 2014 issue (siliconchip.com.au/Article/8203). We have noted some comment on the net that the PL-990 will be the last high performance multiband portable that Tecsun engineers will produce. Indeed, this is even alluded to on Tecsun Radios Australia’s own website. by Ross Why? We cannot find any explanation. siliconchip.com.au Is it because they believe they have extracted every last ounce of performance of this type of design with the PL-990? Looking at the specs and spending some time “hands on” you could easily be led to believe this is the case. There are other indicators that Tecsun have produced something pretty significant when it receives very favourable technical comparison reviews when put up against some of the world’s best brands. But when you compare them dollar for dollar, the Tecsun doesn’t just win, it wins hands down! But we’re getting ahead of ourselves – and Tester the only way that you would really be able to Australia’s electronics magazine July 2021  73 Tecsun-PL990 Specifications Frequency range and tuning step: Long wave (LW): 100-519kHz 9kHz steps (1kHz fine tuning) Medium wave (MW): 520-1710kHz 10kHz steps (1kHz fine tuning)         or   522-1620kHz 9kHz steps (1kHz fine tuning) Short wave (SW): 1711-29999kHz 5kHz steps (1kHz fine tuning) FM: Selectable – 64-108Mhz, 76-108MHz, 87-108MHz, 87.5-108MHz, FM tuning step 100kHz/10kHz Intermediate frequency: AM first IF, 55.845MHz, second IF 10.7MHz, third IF (DSP) 45kHz FM 128kHz Sensitivity/Selectivity: LW MW SW FM: 3mV/m 1mV/m <20µV <3µV 40dB 40dB 45dB 60dB Audio format: Supports 16bit / 44.1kHz WAV, FLAC, APE, WMA, and MP3 formats MicroSD (TF) Card up to 128G (not included) Can also pair to mobile phone (Bluetooth) Speaker: 4, 3W Power: Internal:      External: 3.7V (18650 rechargeable lithium battery) DC power supply: USB 5V current >1A judge for yourself would be to do your own A:B comparison. For many, that won’t be easy, so let’s see if we can help you out somewhat. The PL-990 It’s described as a “high performance shortwave radio”. Talk about damning with faint praise – it is so much more than that. For a start, it covers much more than shortwave, though that covers from 1711-29999kHz in 5kHz steps and fine tuning steps of 1kHz. Even with shortwave radio broadcasts not the force or quantity they once were (witness Radio Australia!) if it’s on the shortwave bands, the PL-990 will give you the best chance of finding it. Looking at the AM band, it covers 522 to 1620kHz in 1kHz fine tuning steps when set to the standard Australian 9kHz channel spacing. If you change it to 10kHz spacing (which is just a couple of button presses) that upper limit increases to 1720kHz. If you’re more into FM broadcasts, you’ve got a much greater range than the “normal” 88-108MHz. You can switch the lower limit to 64MHz, 76MHz, 87MHz or 87.5MHz, with a selectable tuning step of 100kHz or 10kHz. Admittedly, there’s not a great deal of interest below our 88-108MHz band – it’s mainly allocated to fixed and mobile radio, especially business and industry. But a lot of listeners get a kick out of . . . listening! And we believe some footy enthusiasts like to eavesdrop on the referee’s two way radio comms in this band. And for the masochists out there (oooh – wait for the screams!) it also covers the long wave (LW) band of 100519kHz, in 9kHz steps or 1kHz fine tuning steps. Especially 74 Silicon Chip here in Australia, there’s not a great deal to listen to down there – but you could have fun trying. OK, there are a few aircraft nav beacons “down there” and even an amateur radio allocation for CW enthusiasts. As you can see, it really does cover a huge slice of the electromagnetic spectrum. But wait, there’s more! If you find there really is nothing worth listening to, you can always listen to your favourite music saved to a micro SD (TF) card – up to 128GB – in 16-bit/44.1kHz WAV, FLAC, APE, WMA or MP3 formats. You can also plug the PL-990’s digital audio input socket into your computer via a USB-C lead (not included) and play music stored on your PC. Audio quality And that brings us to another of the PL-990’s strong points: its audio quality. Read any review or comparison and that’s one thing that’s always commented on: it just sounds great – much better than you might expect an off-air signal (or even recorded music) to sound. It’s hard to be objective about this – but subjectively, we were impressed. It doesn’t sound anything like your typical portable radio – the Tecsun engineers have really excelled themselves here! The audio amplifier is coupled to a wide-range speaker. It’s not stereo (why would you bother listening to mono radio?) but the combination works very well. If you DO want stereo sound, say from your micro SD card or perhaps FM stereo broadcasts, you have the choice of stereo headphones or line out for an external amplifier. Size All this is packed into 198 x 120 x 38mm – much smaller than most competitors. There’s nothing remarkable about the case – it’s functional and puts all the controls at your fingertips. Information is imparted by means of a relatively large (65 x 25mm) LCD readout. Weight, by the way, is about 620g. It’s powered by a single 18650 Tecsun-branded li-ion cell. Like all li-ions, it’s rated at 3.7V and this one is rated at 2000mAh. We’re delighted to see it’s not one of those ten thousand mAh cells you find on ebay and the like! (You know the ones – they don’t exist...) Price As you might expect, a premium product like the PL-990 doesn’t come cheap. It retails for $550, and that includes the radio itself, a faux leather carry pouch, 18650 battery, 230V “USB” charger and lead (of course, you can use the lead to charge it from your PC, car USB supply, etc etc), a long-wire “wind up” antenna and a pair of stereo ear buds. Naturally, instructions are also included but it’s just as easy to download a copy from the Tecsun Radios Australia website (www.tecsunradios.com.au) – that way you can search for what you want. For those who want to protect their investment, a deluxe version is available which includes the hard clamshell case shown opposite – this fits the radio inside its carry pouch. Performance The PL-990 has been receiving high praise for its SSB performance. When resolving SSB signals, especially those way down in the mud, it’s very important that the radio is Australia’s electronics magazine siliconchip.com.au Two versions of the PL-990 are available from Tecsun Radios Australia: the radio itself, a rechargeable 18650 lithium battery with charger/supply and USB charging cable, a wind-up external antenna and a stereo earbud set. This retails for $550. For those who want to protect their investment, the deluxe version includes all the above plus includes the hard clamshell case shown here for $635. able to not only receive, but allow you to understand what is being received! On the PL-990, the noise floor is very low and the SSB is very stable. Along with the choice of direct entry (pushbutton) or rotary tuning, the radio has a fine tuning control to assist you in resolving SSB (upper or lower sidebands). DSP (digital signal processing) of course is responsible for a lot of the performance. It does things the old analog circuitry didn’t have a chance of handling. FM performance is also very good, especially with that fine audio quality we mentioned earlier. AM, similarly, is right up there. Sensitivity on the FM setting is quoted as <3µV, while MW (AM broadcast) is 1mV/m. Unfortunately, even with its widest tuning range set, the PL-990 cannot get as far as the 6m or 2m amateur bands. LW is problematic: finding a signal worth listening to (especially in this part of the world) is not real easy – we’re not real sure why long wave is included in many radios these days! Longwave sensitivity is 3mV/m. As we mentioned earlier, shortwave (SW) signals are also much more sparse than they were a couple of decades ago. There are amateur operators, of course (the PL-990 can tune into all amateur bands between 160m and 10m), and despite the comments above, there are still many countries (did someone mention China) pumping out signals on the shortwave bands. You should find some signals around the 16m, 31m and 49m bands, although broadcasts can occasionally be heard in the 22m, 19m and 41m bands. Shortwave band sensitivity is 45dB. Selectivity is quoted as >40dB on the medium wave and long wave bands, >45dB on shortwave and >60dB on FM. We haven’t mentioned the PL-990’s IFs. It is a triple conversion receiver, with IFs at 55.845MHz, 10.7MHz and the third IF (DSP) at 45kHz. The FM IF is 128kHz. Undocumented features The PL-990 instruction manual is very comprehensive in the steps required to achieve a myriad of functions. But the radio has several features which are not documented in the instruction manual. Some of these, such siliconchip.com.au as the ability to turn dynamic noise reduction on and off, ability to change the muting threshold, ability to change the FM de-emphasis and even the ability to adjust the line output level to suit your amplifier, are detailed on www. tecsunradios.com.au We’ve seen other references to the same things on the net and we’re sure as more and more users discover more and more features, they’ll be promulgated in the usual ways. Conclusion We started out by saying this is a very worthy successor to the popular PL-880 receiver. Apart from the noticeable improvements, such as better stability on SSB, better synchronous detection, (arguably!) better audio quality (though this was/is one of the PL-880’s strong points), the PL-990 just seems to do everything a little better (yes, that’s subjective but that’s the way we see it). Add to that little things like switchable antennas (the external antenna socket, so essential for “proper” listening, now works on long wave, medium wave and short wave). Of course, it has the features you’d expect in a good receiver – a clock with twin timers and alarms (never miss that transmission you wanted to listen to! We’re pretty impressed by this radio. If you own an earlier model it might be time to update to this, the latest . . . and possibly the last! A bonus! For Australian and New Zealand customers, whichever version you order, Tecsun Radios Australia will also include a stylish Tecsun polo shirt to show your jealous friends you’re part of the “in” crowd – those who own a Tecsun! (limited sizes available) Contact: Tecsun Radios Australia Address: 24/9 Powells Road, Brookvale, NSW 2100 Web: www.tecsunradios.com.au SC Australia’s electronics magazine July 2021  75 Advanced GPS Computer part two – construction and use Our new GPS Computer has many more features than the last two, and combines all their best features. Now that we have finished describing how it works, let’s move onto the construction and usage instructions. We’ll also delve into how the software works, for those who are interested. by Tim Blythman W e have a lot to cover in this article; after describing the assembly of the custom board, putting it all together and fitting it into its case, we also need to explain how to use its many features. Since the software is quite complicated and we had to solve some interesting problems to make it work, we also have a separate panel explaining some of the code’s trickier details, including the CFUNCTIONs that do most of the hard work. You can read that one if you are interested, or skip it if you aren’t. So without further ado, let’s move on to putting the Advanced GPS Computer together. Construction You will need to build the Micromite V3 BackPack 76 Silicon Chip module with a 3.5in LCD touchscreen. Its construction was detailed in the August 2019 issue (siliconchip.com. au/Article/11764) If you haven’t already done so, you will need to fit the DS3231 RTC IC and its accompanying passive components to the V3 BackPack (see photos overleaf). This is a surface-mounting part, so the usual cohort of SMD gear will be required. There are also a few SMDs on the GPS Computer PCB. A fine-tipped temperature-adjustable soldering iron is highly recommended, along with fine solder wire, flux paste, tweezers, a magnifier and solder-removal wicking braid. The flux releases smoke when soldering, so good ventilation and/or fume extraction is needed. Australia’s electronics magazine siliconchip.com.au One tile which we are sure will be popular is a simple, clear, large, easy-to-read speed readout. The units can be changed between many common road, nautical and aeronautical options. There’s even enough room left over to add a handful of other tiles below this. Start by applying flux to the pads for the DS3231, then carefully tack one lead in place, ensuring that its pin 1 matches the dot marked on the PCB. If necessary, adjust its position to centre the chip on its pads and ensure it is sitting flat on the PCB, then solder the remaining pins. Remove any bridges between pins by applying extra flux and then pushing the braid against the bridge with the iron. Allow it to draw up the excess solder before carefully pulling it away. Fit its bypass capacitor next, followed by the two resistors, and trim their leads short. When fitting header socket CON9, ensure it is fitted on the PCB’s underside and soldered from the top. Check that it is square and vertical so it will mate properly with the matching socket on the board underneath. You might like to leave this for later, and line up all the headers at the same time by sandwiching them between the two PCBs for alignment. This will guarantee that the headers will match. Also make sure to fit female headers to the underside of the V3 BackPack for the standard Micromite I/O pin connections. any bridges, as described above for the DS3231 on the V3 BackPack PCB. Once the surface-mounted parts are fitted, clean the PCB with a flux cleaner and allow it to dry before continuing. Through-hole parts Continue by fitting the fixed resistors. The values are marked on the PCB silkscreen; check each batch with a multimeter to confirm their values. After soldering, trim the leads close to the PCB so it will fit in the enclosure later. GPS Computer PCB assembly Refer to the PCB photos and overlay diagram, Fig.2, during construction to assist with component placement and orientation. Start with the surface-mounted components on the GPS Computer PCB. This includes Q1, Q2, IC3 and IC4. Apply flux to the pads and rest the parts in place. Take care not to mix up Q1 and Q2. Q1, Q2 and IC4 should only fit one way, but you’ll need to check IC3’s orientation. Its pin 1 should be towards the centre of the PCB. Tack one lead of each component and check the remaining pins are flat and square within their pads, adjusting if necessary. Then solder the remaining pins and remove siliconchip.com.au Australia's Australia’s electronics magazine The Advanced GPS computer PCB fits to the rear of a stack consisting of a Micromite V3 BackPack and a 3.5in LCD. A tactile switch can be mounted to the rear at the pads labelled SW2 (S2) to allow operation from the rear of a UB3 Jiffy Box. An integrated Li-ion battery and holder fit into a cutout within the rear PCB. July uly 2021  77 2021  77 Fig.2: the GPS Computer add-on board has four SMDs plus quite a few through-hole components. Of the surface-mounted devices, only IC4 has pins that are relatively close together, but there are only six of them. Ensure IC3 & IC4 are fitted with the correct orientation, then solder Q1 & Q2 and move onto the through-hole parts. The large rectangular cut-out is sized to fit a standard Li-ion rechargeable battery, either soldered directly to the board or in a holder. The TX wire of the GPS module should go to the RX pin on the PCB. 220mF Fit the two diodes next. The larger 1N5819 type (D1) is near CON2, while the smaller 1N4148 is near CON4. Observe their polarity and match the cathode bands to the PCB silkscreen. IC1 and IC2 go near the middle of the PCB, with their pin 1 markings facing away from the other. Carefully bend the leads so that the pins will slot into the PCB. Tack one lead in place and confirm the parts are flat before soldering the remainder. Fit CON1 and CON2 next. We found that these needed to be pressed quite firmly to snap into place, but this means that you can confirm their position before soldering. VR1 is next, ensuring that its wiper goes to the topmost pin and that it sits flat against the PCB. The 220µF electrolytic capacitor is mounted on its side, so install it next, right near VR1. Check that the negative-striped lead is closest to CON1. It’s easiest to bend the leads 90° before soldering it in place. There are six 1µF ceramic capacitors; four near IC1 and two near IC2. Their values are marked on the PCB. Follow with the two 4.7µF ceramic caps near IC4. None of these are polarised. Then mount the four 100nF MKT capacitors, then the solitary 10nF capacitor. Again, none are polarised. We’ll leave off some parts for now, including JP1, JP2, LDR1, LED1, the battery holder and tactile switch, so that we can align them correctly as part of the mechanical assembly after the headers are fitted. Headers and mechanical assembly Space in the UB3 Jiffy Box is tight, especially if you will be fitting the speaker and GPS module internally. Thus, we mount header sockets on the Micromite board and then solder individual male pins to the GPS Computer PCB, to save 2mm in height. We’ve made a custom front panel for this project (rather than reusing the existing 3.5in BackPack laser-cut panel) for two reasons. Firstly, it needs holes for the LDR and LED. Secondly, we have reverted to a design that sits ‘on top’ of the UB3 Jiffy Box, rather than slotting into the top cavity. This gains us another 3mm of usable space inside. This also allows us to add another hole above VR1 to enable adjustments to be made after the unit is fully assembled. The battery holder, LDR1 and LED1 all need to be fitted carefully to ensure they align neatly within the enclosure; that’s why we’ve left them until now. The battery holder needs to clear both the BackPack PCB and the case. There’s a bit of wiggle room, but it’s easier to judge when all the parts are present. As a rough guide, the battery holder’s centre axis should be in line with the PCB. Similarly, the LDR and LED are fitted to be near-flush with the top of the enclosure, and this is another thing that’s easier to do with everything present. It’s also easier to check and judge the holes that need to be made in the enclosure now. Everything is effectively fitted to the back of the front panel, which is then installed into the enclosure. So start with the front panel, with the matte side facing out. The LCD module fits with its 14-way header at the opposite end to the LDR and LED openings. Note from our photos how the silver connections at the The V3 BackPack should look like this when fitted with the DS3231 RTC IC and its associated passives. The 5V USB power jumper is required too, as seen in the lower left corner. Also note the two pin header (CON9) soldered to the underside of the BackPack PCB. 78 Silicon Chip Australia’s electronics magazine siliconchip.com.au When constructing the PCB, note that the Micromite and GPS headers are individual pins that are installed without their plastic shrouds by fitting them into their matching headers before soldering. The LED and LDR (shown with yellow heatshrink on their leads) are installed last to ensure they align with the front panel; SW2 with the back panel. touch panel’s edge align with the front panel. The LCD module is mounted using four 12mm M3 machine screws, and is stood off the front panel with M3 Nylon washers, which provide space for the soldered ends of the LCD module headers. Secure the LCD module to the front panel with four 12mm tapped spacers. If you haven’t fitted the header sockets to the underside of the Micromite V3 BackPack already, then do this now. You can use the GPS Computer PCB as a jig by slotting (but not soldering) the corresponding headers in place, to align the female headers squarely with their PCB. Now slot the Micromite V3 BackPack onto the LCD module, using its 14-way header. Then secure the GPS Computer PCB to the BackPack using 15mm machine screws threaded through the GPS Computer PCB, through the shorter spacers and BackPack into the previously installed tapped spacers. Check that the pads on the GPS Computer PCB line up with the sockets on the BackPack. Then remove the pins from their plastic spacers (eg, pull them out with pliers) and slot them into the headers through these pads. There are 24 in total; one 18-way, one four-way and one two-way. Ensure they are down firmly and level before soldering. When all are soldered, trim their ends. Fit the LED and LDR next. Align each component with its front panel hole and the GPS Computer PCB pads. A piece of masking tape over the holes in the front panel is a simple way to hold the parts flush against it. The LDR is not polarised, so can be fitted either way, but the LED orientation will matter. Set a DMM to diode test mode and connect its probes to the LED leads so that it lights up red. Failing that, use a 5V supply and a 470Ω current-limiting resistor. The lead to the red DMM probe (+) or positive supply lead is then inserted into the LED hole on the PCB nearest CON2. Slip small diameter heatshrink tubing over the LDR and LED leads to prevent them from contacting anything if something comes loose. Before fitting the battery, check that the charging circuit is working correctly. Apply power to the USB socket on the BackPack PCB; the voltage at the battery terminals should settle around 4.3V. The LED should also briefly light up green (perhaps after showing red), indicating that the charge IC has reached its ‘full’ voltage. If it is showing red, try reversing the LED. If it is near 5V, then there might be a fault which is connecting USB power directly to the battery. Do not connect the battery if this is the case! Fix the problem before proceeding, as such a fault could damage the battery or cause a fire. Disconnect USB power and unplug the GPS Computer PCB. Connecting the battery If you have a battery with tabs, you should take great care not to bridge any parts to the battery except the terminal you are working on. Beware that your iron may be Earthed and there may be a path for current through it if it touches anything else. And of course, double-check the polarity! We have fitted the V3 BackPack with female headers (like the RCL Substitution Box from June & July 2020). This allows shortened male headers to be installed on the GPS Computer PCB, making the final assembly more compact, to better fit into the box. siliconchip.com.au Australia’s electronics magazine July 2021  79 Fitting a holder is preferred, as we don’t have to worry about working with the live battery, and can pop it out before working on anything. It will also be much easier to change in future should it fail. Note from our photos that the battery faces outwards, allowing it to be changed if needed. In the unlikely event of it falling out, it will be held against the plastic enclosure rather than being thrust against the sharp edges of the BackPack PCB. Bend the leads so that the battery holder can be fitted to the PCB, then slot the leads into their pads. Then reattach the GPS Computer PCB to the BackPack to check locations and clearance. You might even like to use a plastic spacer to provide positive separation. Check the polarity, then use a generous amount of solder to secure the battery holder. When finished, remove the GPS Computer PCB. You can now fit JP1 and JP2, using a similar technique to the other headers, removing the pins from the plastic housing to reduce their height. If you have a spare fourway header socket, this can be used to secure and align the pins as they are soldered. Alternatively, if you intend to have a permanent setting for JP1 and JP2, these can be replaced with small wire loops soldered directly to the PCB pads. Press the PCBs together to check that JP1 and JP2 do not foul the BackPack PCB. Then fit the battery and reattach the PCB to the stack. Now is a good time to trim the short lead stubs at the back of the GPS Computer PCB. Installing the GPS module As we noted last month, we found that the POWER LED on the VK2828 GPS module drew about 2mA, even with the ENABLE pin taken low. Removing the LED brought this down to 40µA, so we suggest you do the same before fitting it. Next, solder the GPS module and speaker to their terminals. Note there are only four connections needed. Since the VK2828 modules have two spare leads, these can be terminated to either of the spare pads on GPS1 to stop them from floating around. We attached the GPS module and speaker to the PCB’s rear using double-sided tape during testing. Once everything is working, they can be secured with neutral-cure silicone sealant. We wouldn’t use hot-melt glue as it could loosen if the unit is inside a hot vehicle parked out in the sun. The assembly should slot into the UB3 case comfortably. If not, check your clearances before proceeding. Case cutting Fig.3: you can either cut holes in the lid supplied with the Jiffy box, or replace it with one of our laser-cut panels with all the holes neatly pre-made. That just leaves three holes in the sides of the box (two round holes for the 3.5mm jack sockets and a rectangular one for USB) plus a 4mm hole in the rear of the case to access the tactile power-on switch. Or you can fit a chassis-mounting switch instead. 80 Silicon Chip There are four holes to cut in the case; refer to the cutting diagram, Fig.3. It’s a good idea to check this against your assembled board, to ensure that everything is aligned and any minor variations in construction are accounted for. The 3.5mm sockets are set behind the panels to prevent the PCBs from catching on the case. Thus, you might need to enlarge these holes if you have bulky 3.5mm leads. This is easily done with a larger or stepped drill bit, or a tapered reamer. To create the square hole for the USB lead, we suggest drilling a 10mm hole within the outline. Then open out the corners with a needle file or similar. You can use a pencil to draw guidelines on the enclosure before cutting. A simple wipe with a finger is enough to remove pencil marks. Australia’s electronics magazine siliconchip.com.au Code in depth Since we have had so many requests for tweaks and updates to the Boat Computer, we will provide a bit more background on the inner workings. We are pretty much at the limits of what MMBasic can store in the Micromite’s flash memory, so some things have been done in terse and non-obvious ways to save flash memory. The following is quite in-depth. It isn’t critical to understand it; you certainly won’t need it to operate the GPS Computer with its default programming, but rather if you’re interested in making changes to the code. As with many Micromite projects, the colour scheme is set by several CONST values near the start of the program. Altering these is one of the simplest ways to personalise the GPS Computer. The chime sound heard alongside messages is defined just after the splash screen is displayed and is held in the BELL variable. Although declared as an integer type to allocate memory, it is processed as an array of bytes. It is created by a formula which generates a decaying sine wave which goes for 8000 samples, or one second. Changing this formula is the easiest way to customise this sound. The click sound (when buttons are pressed) and voice warning are stored in flash memory as part of the library file. The tile feature works through the TILE function, which calls individual functions based on each tile type. These specific functions can draw the tile graphics (using the coordinates they are set to), report their width or height (so the COMPOSE page can display them), or react to a button press. Creating new tiles will require other tiles to be replaced. The tile name is stored in the T_TYPE string array. Many tiles depend on other functions that return strings representing numerical values adjusted for and suffixed with the currently selected units. Any time the Micromite is not busy, it calls the IDLE subroutine, which attends to background tasks such as receiving and processing GPS data. It behaves like MMBasic’s PAUSE, but does other activities and can return control to the main program if a touch is detected on the touch panel. It also periodically updates the top right of the display, and adjusts the volume and backlight as needed. The number of pages, tiles and POIs are limited by the amount of available VAR SAVE flash memory; for the Micromite, this is 2kB. If you wish to adjust the balance of these items, the PG_CNT, ITEM_COUNT and POI_COUNT constants can be changed. We have already pushed these number to their limits, so increasing any one will require another to be decreased. Note that the MAIN MENU page only has room for up to six pages, so any more than this will not be accessible through the existing interface. as the API (application programming interface) numbers paired with named constants. For example, function 0 (CONST AUDIO_INIT) starts the timer interrupt in preparation for other functions. If you are using the LPC samples, then the CFUNCTION needs to know the location for some constant parameters. These can be set by pointing them to one of the data CFUNCTIONs noted earlier using API function 11, thus: Library and CFUNCTIONs When API number 49 (GPS_PARSE) is executed and finds a valid sentence, it reports the matching parser’s API number and copies the sentence elements (which are simply separated by commas) into the remaining array elements. Since certain items are always found at certain sentence locations, the appropriate array elements always contain the necessary data. Note that the string array dimensions and lengths are hard-coded into the CFUNCTION and must match. Once the elements are copied, the array elements containing latitude and longitude can be decoded into degrees, minutes and fractional minutes by using API numbers 61, 62 and 63, respectively. These return integers as there is much more overhead required for CFUNCTIONs to work with floating point numbers. The ILI9488 display driver is not new, and is based on code by Peter Mather at the Back Shed Forum (an excellent resource for Micromite related discussion). See www.thebackshed.com/forum/ ViewTopic.php?TID=11419 Apart from the GPS and audio CFUNCTION, we’ve also incorporated some CFUNCTIONs as wrappers for data to be stored in flash. These aren’t actual executable code, but can be stored compactly without the overhead of MMBasic. The COMBINED CFUNCTION incorporates the audio and GPS features that we use in this project. Each sub-function is invoked by calling the COMBINED function with a different first parameter. These parameters are listed near the start of the MMBasic code siliconchip.com.au JUNK=COMBINED(LPC_SET_CONST_PTR, PEEK(CFUNADDR LPC_CONST)) With this done, we can play audio samples. API function 4 (AUDIO_GET_STATE) reports the current state to avoid interrupting playback in progress. API function 1 (AUDIO_SET_PTR) sets the PCM data pointer, while API function 2 (AUDIO_PLAY) starts playback, like this: IF COMBINED(AUDIO_GET_STATE)=0 THEN JUNK=COMBINED(AUDIO_SET_PTR, PEEK(CFUNADDR CLICK)) JUNK=COMBINED(AUDIO_PLAY) ENDIF Replacing API function 2 with API function 6 (AUDIO_LOOP) will cause the sample to loop, while API function 7 (AUDIO_END_ LOOP) will cause a looping sample to revert to non-looped playback. This means that it will complete the current cycle instead of being cut off abruptly. We’ve written a small program in C which can convert WAV files into MMBasic CFUNCTION data; this is in the software collection as sample.c, compiled for Windows as sample.exe. Playback of LPC data works similarly, using API functions 8 (AUDIO_LPC_PTR) and 9 (AUDIO_LPC_START) respectively. We’ve included a spreadsheet document which can translate Arduino LPC sample definitions into CFUNCTION data. GPS decoding works similarly. API number 48 (GPS_SET) sets a pointer to a string variable which is filled with data from the GPS module by the MMBasic code. The MMBasic string variable format consists of one byte indicating the length, followed by up to 255 data bytes containing the string contents, eg: JUNK=COMBINED(GPS_SET, PEEK(VARADDR GPS_DATA)) API numbers 50-55 (GPS_PARSER0 – GPS_PARSER5) set pointers to string arrays. The first element of each array is filled with the sentence signature that is scanned for: GPRMC_PARSE(0)=“$GPRMC” Australia's Australia’s electronics magazine July uly 2021  81 2021  81 Here’s a side view to show how tightly everything is packed into the stack of PCBs, allowing room for a GPS module and speaker inside the UB3 Jiffy Box. The diagram also shows the location for a hole if you have a PCB-mounted tactile switch fitted to the S2 pads. A button with its actuator top 12mm above the PCB will sit just behind the panel (requiring a pen or similar to operate), while one that is around 15mm will sit just proud of the enclosure and be more accessible. So you should choose a height that suits how accessible you want the switch to be. Alternatively, any momentary switch can be run back to the terminals marked S1. This will allow you to fit a panel-mount pushbutton to the side or top of the case if the back is not suitable. We haven’t included any speaker vent holes; these will depend on your speaker’s size and location. Programming the chips There are a few ways to program the microcontrollers for this project. Screen1: on power-up, and whenever the EXIT button is pressed, the GPS Computer displays the MAIN MENU screen. Four custom pages are accessible through the buttons at left, while the buttons at right provide options to change settings and customise pages. 82 Silicon Chip If you have ordered from the SILICON CHIP ONLINE SHOP, then the micros will already be programmed, and you should jump ahead to the setup section. You can use the in-circuit serial programming (ICSP) interface to upload a HEX file (using either the Microbridge or an external programmer such as a PICkit 4), but remember to detach the GPS Computer PCB so that its connections do not cause a conflict. Use your programmer’s instructions to upload the HEX file, which you can find on the SILICON CHIP website. If you have a V3 BackPack that is already running MMBasic, you don’t need to worry about ICSP programming. We usually use MMEdit to work with BASIC files, but the process is much the same if you use TeraTerm instead. We’ve used MMBasic version 5.5.3, and we recommend you do the same, especially if you are installing MMBasic from scratch. We have not tested our code with other versions. Load the GPS Computer Library.bas file into the Micromite. Then, via the terminal, run the commands: LIBRARY SAVE CPU RESTART The Micromite will reset and load the ILI9488 display driver. Now you can run: OPTION TOUCH 7, 15 GUI CALIBRATE These commands are noted in the comments at the start of the library file. You can test the touch and LCD with these commands: GUI TEST LCDPANEL GUI TEST TOUCH Screen2: this page allows some troubleshooting of the GPS Computer. The satellite count is a good indicator of any problems the GPS module might have; we typically saw 1112 satellites using a VK2828 GPS module. Australia’s electronics magazine siliconchip.com.au Next, load the main GPS Computer.bas file and run it. If you have trouble with the GPS Computer.bas file, try the crunched version (with a ‘c’ suffix). This has had all the extraneous whitespace and comments removed. We found that our program was so large that even the ‘crunch on load’ option does not remove enough whitespace; it appears to leave some behind to maintain line numbering. This will get the Micromite to the same state as if it were programmed with an ICSP programmer and HEX file. Reassemble the stack if it is not complete, and supply power via the USB socket. A splash screen will appear for a few seconds, after which the MAIN MENU page (Screen1) should be displayed. If not, you might need to run the MMBasic program from the prompt, using a serial terminal program at 38,400 baud. Pre-programmed micros should not need this. While the splash screen is displayed, the Micromite is busy generating audio data for later playback. It requires less flash memory to generate these into RAM than to hard-code them, so we put up with the brief delay while this happens. Since the flash memory is quite full, but barely half the RAM is used, this is to our advantage. All screens will display the information seen at top right. You can quickly check the time, GPS status (a red or green G) and battery state at a glance. The time can be set to 12-hour or 24-hour format; the 24-hour format shows seconds as it does not need room to show the AM/PM indicator. At first start, the red “G” will be displayed until the GPS receiver is outputting valid data, which could take 15 minutes for the first time, even under good conditions. The battery icon should show a green charging symbol when connected to USB power. Pressing any button will trigger a short click to let you know that the button press has been detected, while a short chime accompanies messages and errors. The volume of these can be adjusted using VR1. The RAW DATA page (Screen2) can help with checking the GPS state. Check the satellite count; if you aren’t seeing at least four satellites after 15 minutes, and you have good visibility of the sky, there might be a problem with the GPS module. Zero satellites may mean that the GPS module is not receiving signals at all. The EXIT button will always return to the MAIN MENU. The SETTINGS page sets most user preferences such as units and GPS Computer behaviour. The five top items down the left-hand side (Screen3) are the settings for display units; pressing each button cycles between three and six options. These include three styles for latitude and longitude, including degrees, minutes and seconds, decimal degrees and the decimal minutes mode which GPS modules use. The latitude and longitude sign can be displayed as N/S or E/W, negative sign only (with implied positive sign) or explicit positive and negative signs. Both horizontal distance and vertical distance units can be set independently. The choices are metres, feet, kilometres, miles, nautical miles or flight level. Flight level is measured as multiples of 100ft and is often used for altitude in aviation. Speed offers the choice of metres per second (m/s), kilometres per hour (km/h), miles per hour (mph) or knots (equal to nautical miles [NM] per hour). None of these options are stored permanently until the SAVE button is pressed. This reduces wear on flash memory, and allows you to test settings before committing to them. The bottom item at left is for adjusting some numerical values. The ← button cycles between time zone, backlight high, backlight low, speed high, speed low, volume high and volume low. You can adjust each value with the + and – buttons. A short press increments or decrements each value by a small amount, while holding the button down allows it to change quickly. The time zone changes by 15-minute increments; see Table 2 for some handy timezone offsets. The backlight high and low settings set the brightness in high and low light conditions, respectively; the GPS Computer interpolates between these. Set the high level to be Screen3: we have crammed a lot onto this screen to cater to most users’ preferences. The SAVE button is needed to save any parameters to flash memory (to be saved through power-down), including POIs and custom page layouts. Screen4: the POI (point of interest) EDITOR allows the current coordinates to be quickly saved with the ADD HERE button. Any POI can be activated by scrolling up or down and then pressing the SET button at right. Setup and basic use siliconchip.com.au Australia’s electronics magazine July 2021  83 Table 2: Time zone offsets for Australia and New Zealand. comfortable in daylight, and the low level to be comfortable at night (or when the sensor is covered). When the GPS Computer displays a green “G” icon, pressing the TIME button will save the current GPS time to the RTC. If you get an error message, it might be that the RTC IC is not connected or not working correctly. The 12HR or 24HR button toggles how the time is displayed; the style shown on the button is currently active. The button marked “S<” or “S-” indicates whether the synthesised audio output is activated; again, the button shows the current state. Battery sensing Similarly, the high-speed setting corresponds to the speed at which the high volume setting is used, and the low-speed setting to low volume. Note that the displayed units will match the currently selected units. Internally, all speeds are in m/s and converted as needed. See Fig.4 for a graphical explanation of this. We suggest leaving the low and high speeds around these values, then getting a passenger to adjust the volume levels to be comfortable when travelling around the low and high speeds. This is because there won’t be much road or engine noise below 30km/h, and not much change above 80km/h. If you find this isn’t the case, then you can try tweaking these values too. Remember that both brightness and volume are programmed to ramp quite slowly (around 10% per second), so give the unit time to respond to significant changes. The RTC always keeps track of coordinated universal time (UTC), and the local time to display is calculated from that, based on current time zone and daylight savings settings. Turning daylight saving mode on and off is done by pressing the DST button. A “+” indicates that daylight savings is in effect and one hour is added to the current offset; a “–” means no adjustment from the set time zone. In practice, if you live in a state which uses DST, you should only need to adjust the time twice a year by merely pressing the DST button to turn daylight savings on or off. The six buttons at top right of the SETTINGS page control battery behaviour. The HI voltage is the threshold below which it is assumed that USB power is not available, while the LO voltage sets the lower limit for battery operation, below which the unit will shut down. In use, the battery icon will be green above HI and yellow between HI and LO. A bar-graph showing rough stateof-charge and a percentage are shown in the yellow phase. Below LO, the TO timer starts counting, and this is shown in red next to a red battery icon. When the timer expires, the software takes pin 9 low, meaning that the unit will power off if running from battery power. Any time the voltage rises above LO, the timer will reset. The defaults of 3.8V for LO and 4.4V for HI mean that the GPS Computer should run for as long as practicable from a Li-ion battery. The MAIN MENU page also shows the state of pin 9 as POWER(1) or POWER(0). Pressing the button will toggle the pin state. You can use this to force the GPS Computer to shut down even if it has some remaining battery life. The MAIN PAGE also has a SLEEP button, which turns off the backlight and puts the Micromite into its lowest power mode. The GPS module is still fully powered, so should be able to maintain a satellite fix. This is handy for conditions where you wish to save power but also require the GPS Computer to start up again with minimum delay. Pressing the screen for around one second will cause the GPS Computer to leave sleep mode. The long press is needed as the Micromite can only test for touches once per second in its low-power sleep mode. Screen5: the ADD HERE button provides a default name based on the coordinates; You can alter it by pressing the cancel button and using the keyboard. You will be prompted to confirm the name before it is stored. Screen6: custom coordinates can be entered in either degrees/minutes/seconds or decimal degrees. They are confirmed in the currently selected display units for latitude and longitude before being displayed in the POI list. Speed-based volume control 84 Silicon Chip Australia’s electronics magazine siliconchip.com.au Points of Interest (POIs) The POI EDITOR feature (Screen4) is accessed from the POI button on the MAIN PAGE. Five POIs are displayed from a larger list, and the complete list can be accessed by pressing the scroll buttons at left. One POI is marked in green; this is the currently active POI and is activated by one of the SET buttons at right. The current POI is used in any of the screens that provide POI tracking. Each non-empty entry shows a custom name, an absolute compass heading toward the POI, as well as its latitude, longitude, altitude and distance away. Pressing the ADD HERE button creates a POI with the current GPS coordinates; a default name based on the latitude and longitude is offered, but can be altered by pressing CANCEL. The ADD POI button allows all this data to be entered manually, such as creating POIs from a map or GPS coordinates. Screen5 & Screen6 show the relevant entry displays. Latitude and longitude can be entered in either decimal or degrees/minutes/seconds format; the value is converted to the currently set units for confirmation. Both ADD buttons will always look for an empty slot, so there is little risk of overwriting an existing POI. The DELETE button needs to be used to clear a slot, and an error message is provided if there are none. Finally, the REFR button refreshes the display. This is necessary as the headings and distances do not automatically refresh. Fig.4: if you are using the speed-sensitive volume control feature, this is how it works. The volume is fixed from stationary up to the low-speed threshold, after which it rises until reaching the maximum volume setting at the high-speed threshold. The COMPOSE page (Screen7) shows why the GPS Computer is so much more flexible than the Boat Computer. With so many people asking for specific combinations of information to be displayed, it made sense to make this as versatile as possible. So we’ve designed 23 different ‘tiles’, each capable of displaying a small amount of information. There are four pages which can each be customised with up to six tiles each. The restriction here is mainly due to the limited amount of flash memory available to save variables. As for other settings, the page composition is not saved until the SAVE button is pressed on the settings page. So you can easily experiment with layouts without committing to them. The COMPOSE page shows an overview of each page, allowing it to be edited as needed. The NEXT and PREV buttons cycle between the pages. The page and item number is shown at the top of the page, with its title below. You can edit the title by pressing the TITLE button; this title is used on the MAIN PAGE. On each page, the currently selected tile is marked in yellow, the others in grey. Pressing inside the display area will move the selected tile, if it doesn’t conflict with anything else. To align a tile, you can hold your finger on the touch panel and move it slowly in the desired direction. It's not quite drag-and-drop, but it's fairly intuitive. Pressing CLEAR will delete the selected tile and ADD will bring up a menu of the available tiles (Screen8). The GPS Computer will attempt to fit it in the current screen, and will report an error if it can’t. The algorithm does not try all possible locations, so you might have luck retrying if a tile doesn’t fit the first time. Pressing SEL<> cycles between the tiles on each page. Screen7: the COMPOSE page displays a mockup of the customisable pages, allowing the layout to be viewed before use. Note that each page also has an EXIT button at lower right. Screen8: there are 23 different tiles to choose from, so pretty much any combination of data can be displayed. A large speed display allows the GPS computer to be set up as a highly accurate speedometer. Composing your own displays siliconchip.com.au Australia’s electronics magazine July 2021  85 Tiles: a brief overview of each tile's features Sleep: Adds a button to put the GPS Computer into sleep mode, the same as the SLEEP button on the MAIN PAGE. Heading: Shows a dial with top fixed at north and an arrow indicating the current track (absolute bearing direction of travel, in degrees). School Time: A small banner that flashes and makes a warning announcement during school hours (internally set to 8:00-9:30am and 2:30-4:00pm) according to current local time. Compass: Shows a dial with the current track fixed at top and compass points rotating around to indicate the bearing. The track is also shown numerically inside the dial. Volume: A bar graph showing the current volume level; coloured green under 100%, yellow up to 200% and red above 200%. Each bar is around 8%. Small Speed: This text box displays the speed in text format using the current speed format and units. Current POI name: Displays the name of the currently selected POI. Latitude/Longitude/Bearing: Similarly, these tiles display GPS data such as latitude, longitude and altitude, also using the appropriate selected display format. POI heading: Shows direction to currently selected POI in text format. Large Speed: A text display of speed (using current units) which takes up most of the available screen. Average Speed: A digital average speed display. The button shows the time over which the average has been accumulated; pressing this button resets this. In other words, the average speed is measured from the time when the button was last pressed. Naturally, this doesn’t accumulate during sleep or shutdown. PAGE 1–PAGE 4: These add a shortcut button to the specified page. Their title will change if the page title changes. POI Compass/Distance to POI/Altitude difference to POI: Show the direction (in dial format)/horizontal distance/vertical distance to currently selected POI. POI Page/Settings Page: Shortcut buttons to the specified pages. Screen9: the larger 3.5in LCD and touch panel allows us to provide a full-sized keyboard to enter just about any ASCII character, except that the backtick is replaced by a degree symbol (not shown). 86 Silicon Chip Conclusion While we have gone into quite a bit of detail regarding how you can tweak the MMBasic code, we expect that many people will make good use of the COMPOSE feature to set up their own pages. We’re always interested to hear what people are doing with our projects, and no doubt our readers will think of SC something else to add. Screen10: a number of useful messages are provided when something interesting occurs. These are accompanied by a brief chime through the speaker to attract your attention. 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This compact digital storage oscilloscope and digital multimeter makes field testing easy, even when working in tight spaces or with equipment on site. Offers 2 channels with real time sampling of 125MSa/s per channel with waveform comparison tools and a full range of accessories. 10 SAVE 20% Specialises in low current, high 1mA resolution readings. Suits AC or DC use up to 80A. Cat III 600V. 2 year warranty. Includes test probes for other multimeter functions. Min reading 0.5A 62 $ Q 1070A Lockable Equipment Case With customisable foam inner and eggshell foam lid to keep equipment secure & safe. Ext. size: 495x365x128mm. SAVE 30% 55 $ Crimps and terminates 8P8C RJ45 pass thru (through wire) connectors in a single action. A great time saver for trades terminating UTP cabling. A handy 4” stainless steel bowl with magnetic base to keep screws from straying. Lockable Tool Field Case With tool pocket & perforated foam inner to keep equipment secure. Ext. size: 445x330x128mm. Mini Ratchet Driver Includes 7 driver bits stored inside the handle. 2 for $ 30 SAVE 24% T 5036A 15 compartments on one side, plus 10 removable containers on the other side. T 5021 T 5018A TOP VALUE! NEW! 68.95 $ T 1539 T 1574 ‘Pass Thru’ RJ Crimper T 4018 Magnetic Bowl Double Sided Parts Case NEW! 89 15.95 $ Price breakthrough for a True RMS multimeter! Packed with handy features like a 60MHz frequency counter, capacitance, non contact voltage detection, even a torch! Ideal for Anderson connectors $ T 2191A True RMS Accuracy 20 Range Multimeter High Resolution AC/DC Clamp Meter SAVE 25% $ 39 $ Q 0968 SAVE 20% 27 $ T 1522 Ratchet DC Lug Crimper Super Fast Wire Stripper Quick and easy crimping for Anderson SB50 connectors and other uninsulated lugs between 20AWG & 8AWG. Strips cable of insulation at the flick of the wrist. Our best selling cable stripper of all time! T 2748A 22.95 $ 5” Premium Cutters Tough chrome vanadium blades stay sharp for longer. Ideal for PCB assembly, cutting solid core wiring etc. T 2802 27.95 $ Chewed out a screw? No problem! This unique set of pliers features two serrated jaws, plus serrated circular opening on the front face for extracting screws up to 13mmØ. BUILD a bigger AV system. Opus One® 140W Soundbar Wireless Subwoofer SAVE $40 199 $ Our new premium finish soundbar offers rich, clear sound from it’s 6 high performance speaker drivers, plus a 8” subwoofer which can be placed anywhere in your lounge room thanks to wireless connectivity. Offers bluetooth audio streaming from your favourite devices, plus S/PDIF digital audio input for connection to your TV (cable included). C 5064 Demo in store! $90 299 SAVE Soundbar: 97 x 8 x 7.5cm, Subwoofer: 30 x 25 x 30cm $ Opus One® Bluetooth Bookshelf System C 5059 Similar spec to $600 systems with sound quality that’s just as good! Want top notch sound for your games, hi-fi listening or home theatre? These new active bookshelf speakers need no amplifier, just plug them in and connect via Bluetooth, digital S/PDIF or stereo RCA. Amazing sound for their price with a sleek oak grain finish - looks great with grilles on or off! Size: 146 x 164 x 240mm. Dynalink® F2 Pro Gaming Headset SAVE $50 189 $ A 4201 SAVE 27% 50 SAVE $20 C 9042 39 Multi-platform ready! Suits PC, Playstation, Xbox and Switch with included TRRS adaptor. Offers excellent comfort for long gaming sessions with RGB lighting effects (when USB is plugged in). 2m cable. Bluetooth® 2x50W Amplifier Stream audio directly from your device to your speakers in the study or entertaining area. 3.5mm and RCA inputs. Class D design. Internal headphone amplifier. Includes power supply, banana speaker plugs & 3.5mm to RCA cable. SAVE $30 $ D 0981 NEW! 69.95 $ A 1112 Experience wireless sound while you game. Also works with laptops! This tiny USB type C adaptor provides wireless audio streaming for two pairs of headphones for two player gaming on Switch, PS4 or watching media on PC & Mac. *Accessories for illustration purposes. SAVE 24% Great for caravans! 129 LED base light shows when your mic is on $ Great for gaming, YouTube and livestreaming. Quality omnidirectional mic insert. Mic gain and mute control knob with LED lighting. 1000’s sold. Clear & crisp sound! 45 $ $ USB Gooseneck Mic C 0392 SAVE $20 AE1101 12V/240V HD Set Top Box Add Bluetooth® audio to your favourite speakers! Want to get into recording podcasts, voice overs or making your own audio samples? This mini USB mixer connects directly to your PC or Mac and is powered directly from USB. Includes 3 band EQ and effects. A 2548 A 2809A This mini digital TV receiver features HDMI output for connection to any monitor. Runs off a 12V power source making it perfect for use in caravans etc. USB recording & playback. Includes plugpack, car adaptor & IR remote. Why buy new bluetooth speakers when you can add this module to existing speakers? Streams music direct from your phone! 2 x 25W RMS output. Bluetooth 4.1. Includes power supply. 4 Channel USB Mixer With Equaliser & FX 99 SAVE 24% A 1116 SAVE 25% SAVE $30 22 Instantly add wireless audio to any 3.5mm input - like your car, headphones or home amp. USB rechargeable battery provides 4 hrs listening. D 0984 $ 109 $ 15 $ Bluetooth 3.5mm Jack ® SAVE 28% 35 $ $ Entertainers Microphone • One of our all time best selling units • Superb vocal reproduction • Silent action on/off switch • Diecast body • Includes 6m XLR cable. With muting button D 0985 NEW! 75 $ D 0982 3.5mm Lapel Mic Ideal for audio recording on smartphones, laptops, vlogging cameras. 3.5mm TRRS or TRS connection. 2m lead. Condenser type. Electret Lapel Mic Need to record high quality audio for YouTube or live demos? This 6m electret mic offers excellent audio clarity and 3.5mm TRRS or 6.35mm TS connections. USB Conference Microphone Top quality audio for group communications or one-on-one meetings. USB C connection. Rugged diecast case with rubber feet for excellent isolation. Includes 2m USB cable. Buying for your business? Ask about our VIP-Trade discount accounts. MAKE your home smarter. Wi-Fi RGB Strip Lighting Kit X 3227* Answer the door when you’re not home! 75 .95 $ This kit includes 5m of RGB strip lighting, power supply, controller unit and IR remote control allowing you to create colourful lighting effects around your home. Controller features a music sensor input allowing the lighting to trigger to music being played in the room. Great for home entertaining. Works with Alexa and Google Assistant. 60 LEDs per metre. 139 $ Wi-Fi Video Doorbell with Tuya smartphone app control and 2 way audio. This stylish doorbell connects to your wi-fi and notifies your mobile phone when a person arrives at your doorstep. Great for telling the postie where to put packages. • Security camera mode • Motion detect notification • Includes power supply and indoor doorbell ringer unit. Music sensor can trigger lights to the beat! S 9455A 23.95 $ HOT PRICE! P 8149 Automate your appliances Switch any connected appliance on or off remotely from anywhere in the world. Set schedules, monitor and control via your using the Tuya Android/iOS app. Maximum 10A 2400W. Works with Google Home and Alexa What is Tuya® Smart Home? Tuya is a common application for thousands of products from the worlds leading Smart Home suppliers. It provides a single point of control for home security, lighting and appliance power allowing you to control everything you need from a the one smartphone app. The Tuya IoT platform powers over 250,000 home automation products across the globe! Tuya® Compatible Cameras. NEW! All Tuya cameras provide 1080p HD vision with audio and can be located anywhere you require camera coverage in your home. Camera measures just 10mm across S 9845A 89.95 Wi-Fi HD Camera Clock Wi-Fi Camera Module • Internal battery - set it up anywhere! • Day/night with IR • USB rechargeable • 100 mins motion activated recording time. • Ultra compact module can be built into custom enclosures • Completely wireless - set it up anywhere! • USB rechargeable • 100 mins motion activated recording time. Cable Free Wi-Fi Surveillance This handy 1080p camera can be installed just about anywhere indoors or out and has an in-built battery so you don’t need to run any cables! Offers 4-6 months of motion detect recording. When it’s flat, just take it off the wall & recharge via USB. Suits sheltered outdoor use. Also includes ball joint bracket. 199 $ S 9850 S 9844 Mini Wi-Fi Cube Camera S 9843B • Real alarm clock function • Two-way audio (mic & speaker) • Motion detect recording • USB or battery powered (S 4736 x 2 $18.50ea) *Note: We encourage this item be used responsibly for legitimate CCTV use. Outdoor Pan & Tilt Wi-Fi Camera S 9020 Provides extra coverage to your outdoor spaces with motorised pan (355°) and tilt (100°). Auto-tracks moving objects within the frame. Constructed from UV stabilised plastic with weatherproof rating to IP66. 2-way audio with mic and speaker. 30m IR night time coverage. Requires 5V 2A USB power supply. 139 $ Sale Ends July 31st 2021 Phone: 1300 797 007 Fax: 1300 789 777 Mail Orders: mailorder<at>altronics.com.au » Perth: 174 Roe St » Joondalup: 2/182 Winton Rd » Balcatta: 7/58 Erindale Rd » Cannington: 5/1326 Albany Hwy » Midland: 1/212 Gt Eastern Hwy » Myaree: 5A/116 N Lake Rd Outdoor Solar Powered Camera • IP66 rated for outdoor use • Two-way audio (mic & speaker) • Motion detect recording • 2MP 1080p HD sensor • Day/night operation with IR • Battery powered (included) with solar recharging - mounts anywhere! Indoor Pan & Tilt Wi-Fi Camera Makes a great baby or pet monitor, this camera features intelligent tracking of moving objects within the frame. 2-way audio with mic and speaker. 5m IR night time coverage. Requires 5V 1A USB power supply. Western Australia Build It Yourself Electronics Centres $ $ $ S 9846 199 169 89.95 $ HOT PRICE! 79.95 $ S 9017A Victoria 08 9428 2188 08 9428 2166 08 9428 2167 08 9428 2168 08 9428 2169 08 9428 2170 » Springvale: 891 Princes Hwy » Airport West: 5 Dromana Ave 03 9549 2188 03 9549 2121 New South Wales » Auburn: 15 Short St 02 8748 5388 Queensland » Virginia: 1870 Sandgate Rd 07 3441 2810 South Australia » Prospect: 316 Main Nth Rd 08 8164 3466 Please Note: Resellers have to pay the cost of freight & insurance. Therefore the range of stocked products & prices charged by individual resellers may vary from our catalogue. © Altronics 2021. E&OE. Prices stated herein are only valid until date shown or until stocks run out. Prices include GST and exclude freight and insurance. See latest catalogue for freight rates. *All smartphone devices pictured in this catalogue are for illustration purposes only. Not included with product. B 0091 Find a local reseller at: altronics.com.au/storelocations/dealers/ SERVICEMAN'S LOG I’ve repaired planes before, but never tanks Dave Thompson Some jobs require a great deal of patience and involve plenty of introspection. Did I do the right thing? When is the right time to call it quits? This is one such story, illustrating the pitfalls of my life as a serviceman. In the years that I have been The Serviceman, I have tried to keep this column from being too computerrepair centric, mainly because computers are quite boring to many of the service people who read this magazine. However (there’s always a however!), a repair I’ve had on the boil for almost a year now illustrates just how fickle the business can be, and how much we rely on others to do their jobs properly to have a successful outcome. I’d call this one a cautionary tale. It all started a long, long time ago in a galaxy far, far away (not really!) when a regular customer brought me a machine I was already very familiar with; a Dell Alienware M18X gaming laptop. The Alienware range of Dell laptop computers is well-known for their blistering performance. Therefore, they are a very sought-after machine within the gaming fraternity (and sometimes ‘power users’ too). As with any high-performance laptop, all this muscle doesn’t come cheap. My client bought his Alienware laptop in the USA when he was siliconchip.com.au travelling there some years ago. Even though it was ‘on special’ at the time, he still paid around $US6,000 for it, a staggering sum of money for a laptop at the time. It’s luggable, all right $US6,000 buys a lot of hardware, and this Dell is no exception. The computer boasted the likes of twin accelerated (and upgradeable) graphics cards, dual RAIDed hard drives and a high-definition 17-inch screen, a relative rarity at the time. To call this machine a ‘laptop’ is perhaps a bit disingenuous; it’s built like a tank. I certainly wouldn’t want to carry it around with me and plop it on my lap, given it weighs around 8kg. It is more of a ‘desktop replacement’ computer, intended to sit in one place most of the time, not be lugged around as one would a more ‘typical’ laptop. To give this some context, I took a standard Acer laptop with me on a trip to Europe a few years back, and by the third week of our travels, I was so sick of carrying it around I was seriously Australia’s electronics magazine Items Covered This Month • Servicing is often a tankless job • Pool pump filtration system • • failure Replacing shorted schottky diodes Fault-finding an audio level meter kit by ETI *Dave Thompson runs PC Anytime in Christchurch, NZ. Website: www.pcanytime.co.nz Email: dave<at>pcanytime.co.nz ready to drop it in a rubbish bin at Frankfurt airport. I can see the advantages of tablets! Even with a nice laptop bag, it was such a hassle to take everywhere with us. That’s even ignoring how much of a pain it was to take it through the customs checks in European airports, where customs officers seem to assume that every laptop is a disguised bomb. I almost ditched our laptop due to its weight and size, and in fact, I ended up leaving it in Croatia, where we spent most of our time over there, rather than lugging it back with us. That was an everyday laptop with a then-standard 15-inch screen; this Alienware thing I had in the workshop weighed at least three times as much, and the ‘bag’ that came with it looked (and felt) more like a shoulder-borne suitcase than a laptop bag. So, it’s a very large and well-appointed gaming laptop intended (I assume) to be sat on a desk and not moved unless absolutely necessary. I’ve worked on this machine before, mainly to rectify the odd software/ operating system glitch or similar small-fry stuff. Nothing too serious. July 2021  91 But then the owner brought it in one day last year with a problem; he’d lost video output, but just before that, the hard disks could no longer be ‘seen’ by the computer, and he was having that old chestnut “disk boot failure” message. A crash course in RAID While a common enough message with standard machines, the fact he had two hard drives in a RAID configuration made this a little more atypical, and not a good sign. RAID stands for either “redundant array of independent drives” or “redundant array of inexpensive disks”, depending on whom you ask. RAID is not just a fly spray; it is a range of configurations used by computer people to ‘gang up’ hard drives. A server machine, for example, might spread its data storage over several separate disks, or ‘mirror’ data over many disks, so not all their eggs are in one basket. 92 Silicon Chip The theory goes that if one hard disk fails (as they are wont to do), the others should still have a copy of the data and business can continue until the faulty drive is replaced (usually via a hot-swappable drive bay). The whole RAID thing is way beyond the scope of this column; needless to say, the way the twin hard disks in this machine were configured meant that data reads and writes were split between the two disks (known as striping), and this makes for excellent performance. The read speeds approach twice that of a single drive. Many gaming machines use this type of RAID configuration, but the biggest disadvantage is that if one drive fails, everything screeches to a halt, and all the data is gone (unless it has been backed up which is, of course, always a good idea). I feared the worst when the guy brought the machine in. My first assumption was that one of the drives had failed and all we’d have to do is Australia’s electronics magazine kiss his data goodbye, provide a new drive and reinstall Windows and his software and games on a rebuilt RAID. But no, there was something else afoot. A regrettable decision It turned out that he’d taken the machine to another repair guy first. This often happens with servicemen, and there is nothing much we can do about it. Customers can take their devices anywhere they want, and while it might sting a bit, such is the life of a serviceman. I’ve moved from several different parts of town over the years, sometimes due to the quakes and sometimes just because we moved house. While some customers will follow me, some will not, and I understand completely. I certainly don’t begrudge people’s decisions to go somewhere else; they might not be happy with my work, or, like in this case, they might live a fair way out of town. While once my workshop was a lot closer to him, it is now siliconchip.com.au much further away. He ended up taking this machine to a more local guy rather than trudge all the way across the city. The problem is that the local guy mustn’t have been very careful because as he pulled the hard drive assembly (consisting of the two hard drives) from the motherboard, he tore the flexible PCB ‘strap’ that connected the twin drives to the computer. Not only did the strap tear, leaving part of it behind still trapped in the socket, but he’d also yanked on the connector on the motherboard, which looked to have come unseated, damaging the tracks and rendering the board basically useless. He’d simply put it all back together (there is an easily-removed and replaced cover that exposes all this stuff) and given it back to my guy claiming it was ‘dead’. He brought it to me for a second opinion and, after my diagnosis, was more than a little miffed at being charged $150 by this siliconchip.com.au other guy essentially to wreck his machine. I said I’d see what I could do. It turns out that I couldn’t do much. Spares for these ultra-performance laptops are not readily available, especially those of this age. Dell couldn’t help, so it was down to me searching the second-hand market for parts. Sourcing new parts The first challenge was finding a suitable hard drive connector. As it turned out, AliExpress had plenty of vendors selling the part, and even though it was pretty expensive ($US65), I promptly ordered one while I got on with the rest of it. The vendor I bought it from had several other Alienware parts listed, so I bookmarked that page just in case. The part arrived six weeks later, but it was the wrong one. They’d sent me one for a three hard disk array; while I initially thought perhaps I’d be able to use two of the connectors, the connection to the motherboard was very different. Australia’s electronics magazine This is the most frustrating thing about buying from China; if they sent the part shown in the product picture and the specs below it (which we all tend to buy from), it would be fine. As it was, this part was useless. After the usual to and fro dealing with the vendor, they sent another one, the right part this time. In the meantime, I was trying to remedy the broken socket on the board. This is one of those PCB-mounted sockets with a flip-down ‘bar’ that, when toggled to the top, locks the flexible connector in once it is fully seated. The other guy had simply pulled the strap out, breaking the connector, tearing the flexible strap and, by the looks of it, lifting some PCB tracks. This wouldn’t be easy to fix. While the sockets are available from the usual suspects, I had no means of repairing something like this. I didn’t know how deep the damage went, and I could spend hours trying to resolve this for no good outcome. I bit the July 2021  93 Helping to put you in Control ECO PID Temperature Control Unit RS485 ECO PID from Emko Elektronik is a compact sized PID Temperature Controller with auto tuning PID 230 VAC powered. Input accepts thermocouples J, K,R,S, T and Pt100 sensors. Pulse and 2 Relay outputs. Modbus RTU RS485 communications. SKU: EEC-022 Price: $104.45 ea Mini Temperature and Humidity Sensor Panel mount Temperature (-20 to 80degc) and Humidity (0 to 100% non condensing) sensor, linear 0 to 10V output. Cable length 3 meters. SKU: EES-001V Price: $164.95 ea ESM-3723 Temperature and RH Controller 230 VAC Panel mount temperature & relative humidity controller with sensor probe on 3 metres of cable. It can be configured as a PID controller or ON-OFF controller. 230 VAC powered. Includes ProNem Mini PMI-P sensor. SKU: EEC-101 Price: $619.95 ea PTC Digital ON/OFF Temp Controller DIN rail mount thermostat with included PTC sensor on 1.5m m lead. Configurable for a huge range of heating and cooling applications. 230 VAC powered. SKU: EEC-010 Price: $98.95 ea Ursalink 4G SMS Controller The UC1414 has 2 digit inputs and 2 relay outputs. SMS messages can be sent to up to 6 phone numbers on change of state of an input and the operation of the relays can be controlled by sending SMS messages from your mobile phone. SKU: ULC-005 Price: $228.76 ea 20% off! 4 Digit Large 100mm Display Accepts 4~20mA, 0~10Vdc, is visible 50m away with configurable engineering units. 10cm High digits. Alarm relay and 230VAC Powered with full IP65 protection SKU: FMI-100 Price: $1099.95 ea Touchscreen Room Controller SRI-70-BAC Touchscreen Room Controller are attractive flush mounted BACnet MS/TP controllers with a large colour intuitive 3.5” touchscreen for viewing the system status and modifying the settings. SKU: SXS-240 Price: $306.90 ea For Wholesale prices Contact Ocean Controls Ph: (03) 9708 2390 oceancontrols.com.au Prices are subjected to change without notice. 94 Silicon Chip bullet and told my client that he needed another motherboard if this thing was going to run again. He was actually fine with this, and asked if we could take the opportunity to upgrade the video cards for better performance. I checked with the vendor I’d been dealing with, and he’d listed a couple of uprated graphics cards. Not cheap at several hundred bucks each, but the client agreed, so I ordered them along with a used motherboard. The spending on this job was getting huge, so I hoped what we got from overseas would be fit for purpose. I also requested a progress payment, something I very rarely do. But as the bill for parts was already nearing a grand, I thought it prudent. The bottom line was that my client loved this special machine and wanted it to work again; as a serviceman, this is always my goal as well. All we could do now was wait for the parts to arrive. Given that the pandemic had just started and flights were on and off, it took several months for the parts to arrive. When they did, it was the video cards first, then eventually the motherboard turned up. Many vendors post a video of the parts working on the test bench, possibly to ensure there was no comeback if something didn’t work. In this case, the vendor didn’t show anything. I received the board, well-packaged, and assembled the machine. Not a good sign When I fired it up, I had no video, which was the client’s original problem when he took it to the other guy. No matter what I tried, I couldn’t get any video output. The built-in HDMI port had nothing, with or without the twin removable video cards installed. Something was off. As was typical, dealing with these guys in China was problematic. I’d spent many hundreds of dollars but couldn’t get a straight answer. The board looked to be faulty, and I arranged to send it back; a not inexpensive task. Another month or two went by waiting for them to receive the board. They did get it, which was a miracle, as I’ve sent several things back over the years and not one has arrived at the address provided by the vendor. I didn’t hold much hope for this shipment either. To be fair, it did arrive, and the vendor sent another motherboard, which took the usual two months to get here. My client was extremely patient, and hats off to him for being so understanding. My hands were tied; there is not much I can do in situations like this. Given the pandemic and the fact that the usual lines for parts are closed or delayed, we didn’t have many options. The new board duly arrived. Again, I reassembled the machine and installed the graphics cards and other bits and bobs. I left the top of the case off so that I could see what was going on. On power-up, there was a puff of smoke; it came from one of the video cards. My heart sank. Now I didn’t know whether the graphics cards were faulty or the motherboard. Perhaps the last one had been OK too? This was a chicken and egg situation. I’d need knowngood graphics cards to test the motherboard, or a knowngood board to test the graphics cards. As it stood, I didn’t know what was good and what wasn’t, and I’d possibly just toasted a $500 motherboard. The serviceman’s lot is not always easy, and in this case, things were turning from bad to worse. What do I do now? Australia’s electronics magazine siliconchip.com.au What I did was pull the plug. I’d gone about as far as I could with this job. It was just under 12 months that I’d had it in bits on the bench. I dreaded calling my client and telling him the news, but I had to anyway. It’s the way of the serviceman. Knowing when to pull the plug on a dead-end job is something we all have to learn. If we don’t know that point, we’ll end up wasting time and money on something that isn’t achievable. He was surprisingly OK with it and quite philosophical. He was aware of the ups and downs of buying from overseas, and I’d made it clear along the way that we were buying second-hand parts, and things might not work out. He’d purchased another machine in the meantime, so at least he was up and running. While he had a lot of sentimental affection for this old Alienware machine, he accepted that sometimes it just isn’t feasible to carry on. He was also happy to pay the costs of the hardware I’d purchased. I didn’t add anything to those costs, and donated my time (he was a loyal client). I just wrote off the rest as one of those things that happens to a serviceman now and then when a job turns sour. As a result of this long-time saga, I wound up with some of the hardware. Whether I can move it on or use it anywhere is in the hands of the computer Gods. I did transfer his data and photos to his new machine (again not charged for), and he was happy, even though his beloved Alienware laptop was dead. I was relieved that we’d found a middle path and that he had everything salvageable from the old machine. Whether I will see him again, I don’t know. I did my best, and if he wants to take his new machine elsewhere, so be it. I’m not in business to lose money or clients, but sometimes things just don’t work out, and external forces can make or break a job. Whatever happens, life goes on, and the next phone call could be a great job or a real challenge. That’s the life of a serviceman. Pool pump filtration system failure A. H. of Attwood, Vic, had a recent problem involving some rain and a lot of mud. The problem continued with the inability of his pool’s filtration system to cope, leaving him with a pool pump that needed a repair... While away on business, it rained what can only be described as mud at home. This rain-mud turned our pool into a murky red-brown colour. For reasons unknown to me at the time, the pool filtration system didn’t cope. Fast forward a few days, and when I had my first chance to look at the pool, it was now a most unpleasant red-browngreen colour, and the bottom couldn’t be seen. Obviously, something fairly serious had gone wrong with the filtration system. Checking revealed the Chromatalyser complaining that there was no water flow for it to carry out sampling for Chlorine/PH levels. This was strange, as the system is fully automatic, injecting acid as required as well as controlling a Chlorinator to adjust chlorine levels. Overriding the system and turning on the filtration pump revealed a distinct lack of motor noise and an “Err64” message. This pump is a 9-star energy efficient variable speed Hayward Tristar model SP3215VS and is an absolute beaut when it works. The pump operating manual revealed that “Err64” is apparently an “Internal Short Circuit Failure”. siliconchip.com.au Australia’s electronics magazine July 2021  95 This sounded pretty ominous, although Hayward’s cure for this fault was to turn it off and back on, which of course didn’t help. So I was now up that well-known creek without a suitable motive implement. A weather forecast of 30-40°C for the next few days, with the wife and kids insisting that they would need to use the pool, meant that I had to fix it immediately, if not sooner. So I was forced to shell out over 1500 Aussie dollarydoos for a replacement pump. With the new pump installed and running, the pool returned to normal crystal clear water within a day or so. With that crisis averted, my attention turned to the old pump turned doorstop. Hayward pumps are very serviceable and easy to fix, but the electric motors that drive the pumps are not. In fact, there is no parts breakdown for the motor assembly at all, just the pump section. My admittedly limited knowledge on variable-speed drives made me think that the power switching module, or similar, would most likely be the culprit. So I commenced ripping the control box that was mounted on top of the motor apart. This revealed a circuit board with many components on it, but no power switching module. Inspection revealed a few connectors going into the bowels of the motor, where another circuit board was located. While playing around with this top board, something went “pfzzzt”, and the motor was completely dead. No display, no “Err64”, nothing. This top board appears to be a power 96 Silicon Chip filter/power factor correction/high voltage DC supply/soft-start device. It magically creates over 300V DC which is sent to the lower board. A 12V DC supply rail is returned to the top board for power as well as some switching signals for the soft-start relay. So it was time to gain access to the motor internals. Unfortunately, the manufacturer of the motor had used those stupid headsnaps-off-when-correctly-torqued type of bolts, which meant that they couldn’t be undone. A hacksaw made short work of that, and the motor split apart to reveal its secrets. I checked the motor windings and found no problems, so my attention turned to the internal circuit board. I expected to see a spectacular mess, but no, the board was remarkably clean with no noticeable damage. Unbolting it from the housing and turning it over revealed a “Dual Inline Intelligent Power Module” (IGCM15F60GA). Sure enough, desoldering and resistance-checking this module revealed a short circuit between the “Motor V-Phase Output” pin and the “V-phase Low Side Emitter” pin. So it looked like my hunch was right. Further troubleshooting on the top board revealed a low resistance between Vcc and the S-GND pin on the power factor corrector SMD IC (L4981BD). This was dragging the 12V DC rail down and shutting down the whole pump. Removing this IC returned the pump to its original “Err64” condition. I had nothing to lose, so I placed an order for a new IC, power module and Australia’s electronics magazine some bolts. A week later, the parts arrived, were soldered into place and the motor roughly slapped together for testing. At power-on, I was rewarded with the sweet sound of a motor spinning up to 3000RPM. Success! I reassembled the whole kit and kaboodle after a careful inspection of all the pump seals etc. I checked it for faults with my PATS tester (all good!) and reinstalled it into the filtration system for testing, where it has now worked for three weeks with no faults. For a total cost of around 30 bucks, I now have a working spare pump. I will probably never need it, but Murphy’s Law dictates that if I sell it, the next day the operating pump will cark it, and I’ll have to come up with another $1500... Replacing shorted schottky diodes in equipment R. S. of Fig Tree Pocket, Qld, has a couple of servicing stories, one about parts he has found to fail frequently, and another about turning two dud devices into one good one... I am finding many failed 200V schottky rectifier diodes in equipment that I am repairing. Hopefully, the manufacturing process for these diodes has been improved since these ones were made. Samsung monitors can have a shorted MR5200 (5A, 200V) in the power supply. There are two of these diodes in parallel. Sometimes one will siliconchip.com.au short out, stopping the monitor from working. Ryobi battery chargers (BCL14181H) also have two MR5200 in parallel, and one can short out. These chargers can also have a shorted P-channel FET (which feeds the charging current into the battery pack). The Dyson charging plugpack (Salom Model 17350-05) can have a shorted MR2200 (2A, 200V). You can crack these plugpacks open in a vice. Strangely, these have three output connections: 0V, 16.75V and 24.35V. The other Dyson plug pack (Model 205720-05) has only two connections, 0V and 26.1V. Dyson DC35 motors are a brushless DC motor, with a permanent magnet rotor driven by coils on the stator, powered by two half-bridges. The rotor has only one bearing at the fan end. As there is no bearing at the motor end to centre the rotor in the stator, mechanical inaccuracy can cause the rotor to rub on the stator. The motor then just buzzes but does not turn. To get the plastic back off the motor, hold that part in a vice, and then grab the rest and pull. I found this worked better than trying to pry it off, which damages the plastic. The first motor I came across was rubbing, and it was difficult to centre. Sometimes it would work, and then it would not. The second motor had a fault on the drive board with one of the components sending up a wisp of smoke. So I took the drive board (which includes the stator) from the first motor, and put it in the second motor. The two large capacitors on the drive board have glue on their tops and must be pried loose. You only have to resolder the power connections. This was successful, resulting in one good motor. I noticed the second motor was better mechanically than the first, with larger mounting screws for the board, so the design may have been modified during production. The adjacent photo is the power supply board for a Dell U2414Mb monitor, showing yet another example of a shorted schottky diode fault. The 150V, 8A SB8150 used for D702 at left had failed; I replaced it with a 5A, 200V rated SR5200. Editor’s notes: 200V is at the high end for schottky diodes, which more commonly are rated for a PIV in the range of 20-100V. So perhaps they are siliconchip.com.au The power supply board for a Dell U2414Mb monitor which shows an example of a shorted schottky diode circled in yellow. pushing the process to its limits, resulting in more failures in service. As for the Dyson plugpack with two output voltages, perhaps this suits two different vacuum models with different battery voltages. Fault-finding an ETI LED audio level meter kit N. B. of Wollongong, NSW, ran into a problem putting together a kit when he had built several others of the same type successfully. The solution turned out to be simple, but hard to believe... Over the years, I have assembled several kits of the ETI Bargraph LED audio level meter. The kits cost about $33.00 and took about half an hour to assemble. They all worked well, except the most recent one which I assembled some years ago. It wouldn’t work, so I put it aside and forgot it till recently. I then needed an audio level meter for a project, so out it came. I checked and rechecked everything, and it all Australia’s electronics magazine seemed fine, but it still didn’t work. Signal was getting to the processing IC; all voltages were as expected. I had a spare processor, so I fitted it, expecting it to work. It still didn’t. I then did a diode check on the display bar with its 10 coloured rectangular LEDs, seven green and three red. They all checked out OK. Out of desperation, I decided to compare the LED bar assembly on the board with a new one which I had recently bought. The bar is a preassembled commercial unit. To my amazement, I discovered that the LEDs were all inserted in the escutcheon bar the wrong way around! I desoldered the whole thing and found that I could coax the LEDs out of the escutcheon bar with a pair of longnose pliers. I refitted them the right way around, resoldered the bar to the PCB and hey presto, it worked! I must confess that I felt a great victory in finding that fault. SC July 2021  97 The Rowe AMI JAL-200 Jukebox This JAL-200 was made in Australia by National Instruments around 1963. It is 1.45m tall, 680mm wide, 850mm deep and weighs 150kg. Its audio power output is 25W per channel, and it can play either side of any one of 100 7-inch, 45RPM records, for a total of 200 songs. By Jim Greig 98 Silicon Chip Australia’s electronics magazine T he first jukebox was made around 1890, and multiple selection devices originated around 1918. So there were over 40 years of development behind this unit. It is interesting to compare it to its competitor another 40 years later – a matchbox-sized MP3 player with thousands of songs, connecting to a powered speaker via Bluetooth. Like most pre-computer jukeboxes, the JAL 200 is a mechanical marvel. Designed to work almost full-time in dirty, hot bars with minimal problems, it is sturdy and designed to be easily maintained. It was functional when purchased, but had to be cleaned and all capacitors were replaced. Changes were also made to improve its long-term reliability: • The metal rectifier (copper oxide or selenium) for the 30V DC control circuits was replaced with silicon diodes. • Capacitors used as back-EMF suppressors were replaced with silicon diodes (as in later units). • I added two fuses that were shown in the circuits but not installed. It has functional units which convert a pushbutton selection to rotary movement, store the selections and play the records. Many of these are visible in Fig.1. The pushbutton unit is robust (think of the stuff spilt into it!) and divided into two, 10 numbers (1-9 plus 0) and 20 letters (A to V except for I and O), as needed for a 200 record selection. This jukebox supports remote wall boxes, small selection units that can be mounted near selected tables at the bar/restaurant/etc. Each button is connected to a short copper track segment on the search unit (Fig.2). The number side is shown; letters are on the reverse. When two buttons are pressed, the search motor (top left) rotates the plastic arm until the outer brush touches the energised number segment. A relay picks up to drop power to the search motor, and energise the number sprag relay. The arm stops at the selected number. It is stopped quickly and in the correct place by the sprag relay, which has a long arm that pulls against a notched wheel and stops the rotation when a siliconchip.com.au tag on the end of the arm drops into a notch (see Fig.3). The number sprag relay is then released, and the arm is rotated until the energised letter segment is detected. Rotation is again quickly and precisely stopped by the letter sprag relay. As shown in Fig.4, the letters are split between an inner (EVEN or right) and outer (ODD or left) ring, most likely to provide room for the 200 pins. Holes in the plate provide easy access to the screws underneath. This unit was built to be repaired. On the same search shaft is an arm with an electromagnetic “pin pusher” on each end. Slip rings on the inner tracks of the number PCB provide a path for a select pulse to the pin pusher solenoids. The pin pusher arm has an inner solenoid on one end and an outer one on the other; the appropriate one is energised to push a pin (see Fig.5). The terms outer/odd/left and inner/even/ right are used throughout the manual. When the pins are pushed, they are loosely held in position and serve as the memory. The positions are 1 (A-V), 2 (A-V) ... 0 (A-V) for the 200 selections. Fig.6 shows the stopper switch assembly above the pins. Belt Magazine Pickup arm and platter drive Scan control Transfer assembly Search unit Annunciator Scanning The pushbuttons are reset, ready for the next selection. The magazine motor is energised, causing the magazine containing the records to rotate. It is geared to the stopping switch assembly. This assembly rotates until a left (or right) stopping switch pawl meets a pin and is pushed slightly back, to activate the left (if a left pin is encountered) and stopping microswitches – see Fig.7. Popularity meter Fig.1: the belt, visible above, holds the records in the bottom half of the magazine in place. The amplifier is housed underneath these components, while the credit unit is at the back. Other visible parts are labelled. Fig.2: the search unit encodes the numbers and letters as a series of tracks with contacting wipers. It is essentially a mechanical form of digital decoder. ► ► Fig.3: the sprag wheel and sprag relays act to stop the rotation when the search unit has selected the record that is to be played. siliconchip.com.au Australia’s electronics magazine July 2021  99 Fig.4: the pins drop into holes arranged in two rows in this wheel, because they would have to be too small if they were in a single row. That complicates the mechanism somewhat. Power to the magazine motor is then dropped. Rotation is stopped precisely with a magazine detent switch, similar to the sprag relay. The selected record is now at the very top of the magazine, and the transfer motor is energised. The transfer process is powered from a shaft driven by the transfer motor. There are cams on the shaft, and they activate microswitches to: • Start the turntable motor • Reset the pin • Energise the toggle shifter solenoid if the “A” side is to play • Stop the transfer motor when the record is in place • Reverse the process after the record has played Gears from the shaft cause the transfer arm to grip the selected record and move it to the turntable (shown partway in Fig.8). Another set of gears positions the tonearm over the outer groove and lowers it onto the record (Fig.9). The gripper arm will rotate to play the “B” side if the left side microswitch does not energise the toggle shifter solenoid (at the bottom right). Record changer Fig.5: one of the ‘pin pusher’ solenoids used to cue a record to be played. Fig.6: the pin stopper switch assembly. US 45RPM records have a 1.5-inch (~3.8cm) centre hole, first implemented by RCA, possibly to get around existing patents and minimise wear on the small hole as a record is dropped from an automatic changer. This player has a centre that supports both and detects which size is used. A 33RPM record pushes the assembly down to activate a solenoid which raises the idler wheel, brushing a smaller diameter on the motor shaft to reduce the speed (see Fig.10). This feature is disabled on this jukebox, as all Australian records have the smaller centre. When the end of the track is reached, all records have a run-out groove that moves the tonearm rapidly towards the centre. When the tonearm reaches a selected distance from the centre, a magnet on it activates a reed relay that initiates the reverse transfer, shown in Fig.11. If no more records (pins) are selected, and the last record is played, it would be possible for the magazine to rotate continuously until the next selection is made. To prevent this, the scan control limits it to one revolution. The scan control is linked with a Bowden cable to the annunciator, which displays the current selection – see Fig.12. Sound system Fig.7: these microswitches are responsible for stopping magazine rotation when the selected record is reached, by detecting the pin sticking out. 100 Silicon Chip The JAL-200 has stereo midrange speakers on either side, with common low and high-frequency units at the front. The midrange speakers are 15 x 23cm oval types, which reproduce signals in the range of 250~12000Hz. The tweeter measures 10 x 15cm and handles 400~15000Hz, while the horn-loaded woofer, mounted in the back with the horn exiting at the lower front, is 30cm in diameter and rolls off at around 250Hz. The power amplifier is a stereo unit with push-pull 7868 valves giving around 25W music power per channel, at 1.5% distortion – see Fig.13. Octal 7591 equivalents are installed here. The output valves operate at a conservative 370V HT for a long service life, and it uses global negative feedback. It also includes a mute Australia’s electronics magazine siliconchip.com.au Fig.10: this mechanism detects whether the record is a 33RPM or 45RPM type, and adjusts the turntable speed accordingly. Fig.8: a record being lifted out of the magazine by the transfer arm, ready to drop onto the turntable. Fig.11: this reed relay is triggered by the tonearm when it approaches the record centre, indicating that playback is finished. Fig.9: this set of gears is responsible for driving the transfer arm and positioning the tonearm over the starting track of the record on the turntable. Fig.12: the annunciator wheels show the location of the currently playing record. Fig.13: the stereo 25W audio amplifier is based on 7868 valves in a push-pull configuration, with global feedback only (not ultralinear). ► This jukebox was manufactured with serial number 12412, and interestingly enough, badged by National Instruments. The JAL-200 was the first jukebox sold by AMI that incorporated their “Stereo Round” system, which was four loudspeakers arranged in a 3-way configuration. siliconchip.com.au Australia’s electronics magazine July 2021  101 Credit unit Fig.14: the preamp includes a magnetic cartridge amplifier and treble/bass presets for the installer to adjust. Fig.15: use of amplifier tone controls for acoustical compensation (from manufacturer) Sound level in room Room Acoustics Average – moderately absorbent Dead or soft, highly absorbent Live or hard non-absorbent Bass boost Low Treble range Mod/Max Bass boost Low Treble range Mod/Max Bass boost Mod Moderate Low Max Mod Mod/Max Max Lim Low Mod Max Max Max Max Mod High Treble range Lim Note: reduce treble range setting as required by record noise (scratch) conditions F-9660 Fig.16: the credit unit tracks how many song selections to give depending on the inserted coins. Its clever mechanical design means that the jukebox owner has quite a few options for how many selections are given for different coin values. function that shorts the input unless a record is playing. Note the massive power transformer, designed for continuous use. The amplifier uses a fixed-bias pentode output stage with no ultra-linear connections. The goal is maximum power delivery; ultimate fidelity is not required. The separate preamp (Fig.14) has a magnetic cartridge preamp, volume 102 Silicon Chip compression bass and treble filters that are pre-set for room conditions and a cathode-follower output feeding the volume control potentiometer, which connects to the power amplifier. The recommended settings are clearly laid out for the installer, as shown in Fig.15. There are more charts showing connections for external speakers and radiation patterns to assist in siting the unit. Australia’s electronics magazine The credit unit accepts valid coins and stores the value. The stored value is decremented for each play. The credit unit in this machine has mostly been removed, and it is set up so that no money is needed. Credit information is stored in the front credit wheel; a ratchet wheel moved by the credit solenoid. It rotates one tooth clockwise for each credit. Coins are mechanically sorted, and there is a coin switch for each value. The coin switches are connected to the credit circuit board. This is wired to advance the front credit wheel depending on the coin inserted. As with other rotational functions, the credit solenoid only advances the wheel; it is stopped at the correct value by the credit stop arm reaching a set position. The stop arm is engaged by a pawl as the wheel moves and drops back when it stops. For the largest value coin (20¢), a screw sets the number of teeth to advance (positions 2-9 in Fig.16). For the smallest value (5¢), the lower stop coil is activated to limit rotation to one tooth. In between (10¢), the second stop coil limits the rotation according to the position it has been fixed in (three possible options: 2-4). By adjusting the positions, combinations like one play for 10¢ and three for 20¢ can be set. The wheel is held in place with a spring-loaded detent ball, acting on a linked rear credit wheel. The rear credit wheel (with teeth in the reverse direction) is activated with the cancel solenoid and decrements credits when a selection is played. A cancel stop solenoid (one or two credits) and cancel stop screw (one, two or three credits) control the deduction with the cancel stop arm acting like the credit stop arm. On the same shaft are a series of wipers, making contact with circular traces on a PCB. The position of the wipers reflects the credit status, and the contacts present it to the rest of the machine. This powers the credit lights (five, 10, 20 or more), ensures there is sufficient credit for a selection and allows a selection to be played. Links (screws) on the credit circuit board set combinations like one standard play for 10¢, and one EP for 15¢. EP records are not confined to 33RPM, but are set with a premium pricing unit attached to the number bank of the selection switches. One to five groups siliconchip.com.au Fig.17: this ‘popularity meter’ pushes in the pin corresponding to a given record a little bit each time it is played. Thus, the pins sticking out further correspond to records that have been played more times. of 20 consecutive records in the magazine can be set as premium. Popularity meter The popularity meter has 200 long pins, each corresponding to one side of a record. They are stored on a small drum and pushed a small distance each time a selection is made (see Fig.17). Cabinet construction The cabinet is solid 19mm ply allaround, with plenty of screws. The mechanism is spring-mounted to reduce feedback and improve stability when the cabinet is bumped. The glass top lifts to provide access to the records and labels. The front panel can tilt forward some 20°, and for better access, it can be removed entirely after disconnecting a few plugs. Selections are printed onto small paper or cardboard rectangles and inserted into marked spaces (eg, A1) corresponding to the slots in the magazine. Serviceability & adjustment The whole machine is designed for service. There is a detailed 250-page manual with circuit diagrams, troubleshooting procedures, stepping though a cycle, parts lists and adjustment details. The pushbutton assembly is removable, and all parts are easily disassembled with basic tools. Most parts are still available, mostly from stripped machines. A few, such as the idler wheel for the turntable, are still made. With the top up, and front door siliconchip.com.au Fig.18: a fault was traced to a dry solder joint on the 100uF capacitor near R1. removed, there is good access to most areas. Adjustments will drift with usage, causing operational problems. The magazine must stop in the right position (top record precisely inline with the transfer arm) so the screws locating it can be backed off while it is moved to the correct position. Repairs This jukebox had developed a fault where it would not play a record. When a record was selected, the pin pusher arm would rotate to the correct place but not push a pin. The pushbuttons were not cleared, so a second selection could not be made. Testing with a multimeter showed a pulse to the pin pusher coil, but it was not energising the solenoid. Cleaning the various relay contacts in the path did not fix it. Machines of this era can have problems with poor spade lug connections, but they all checked out OK. The next step was to check the circuit (Fig.18) to follow the sequence of operations to energise a pin pusher solenoid (EVEN, ODD). The A-V and 1-0 switches are closed when the pushbuttons are pressed. The letter sprag relay S2 is not active, and R1 closes Australia’s electronics magazine when the coin mechanism is happy the selection is paid for. The search motor rotates until the number and letter segments are found. S2 then closes and drops the power to R1. The selected pin pusher is energised through S2 (ON) and R1 (ON), but R1 is now off. A 100μF capacitor across the coil of R1 keeps it closed for long enough for the pin pusher solenoid to push a pin, then it drops out. The power to the search motor is then dropped, and the latch solenoid activates to clear the push button selection. On closer inspection, the 100μF capacitor had one dry joint, left there years ago when I replaced the capacitors. Resoldering it fixed the problem. The search unit motor, visible in Fig.2, shows signs of overheating. That happens when a fault causes the search motor to run continuously. Later models include a thermal switch in contact with the windings to prevent this. This motor has now been rewound, and a thermal switch included. The diagrams have been taken from the Rowe AMI Service manual. More details on this jukebox can be found at Radiomuseum (siliconchip.com.au/ link/ab80). SC July 2021  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 139, COLLAROY, NSW 2097 (02) 9939 3295, +612 for international You can also pay by cheque/money order (Orders by mail only) or bank transfer. Make cheques payable to Silicon Chip. 7/21 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 24LC32A-I/SN ATmega328P ATmega328P-AUR ATtiny85V-10PU ATtiny816 PIC10F202-E/OT PIC12F1572-I/SN PIC12F617-I/P PIC12F675-I/P PIC12F675-I/SN PIC16F1455-I/P PIC16F1455-I/SL PIC16F1459-I/P PIC16F1705-I/P PIC16F88-E/P PIC16F88-I/P $15 MICROS Digital FX Unit (Apr21) ATSAML10E16A-AUT High-Current Battery Balancer (Mar21) RF Signal Generator (Jun19), Si473x FM/AM/SW Digital Radio (Jul21) PIC16F1459-I/SO Four-Channel DC Fan & Pump Controller (Dec18) RGB Stackable LED Christmas Star (Nov20) PIC32MM0256GPM028-I/SS Super Digital Sound Effects (Aug18) Shirt Pocket Audio Oscillator (Sep20) PIC32MX170F256D-501P/T 44-pin Micromite Mk2 (Aug14), 4DoF Simulation Seat (Sep19) ATtiny816 Development/Breakout Board (Jan19) PIC32MX170F256B-50I/SP Micromite LCD BackPack V1-V3 (Feb16 / May17 / Aug19) Touchscreen Voltage / Current Ref. (Oct16), Deluxe eFuse (Aug17) Ultrabrite LED Driver (with free TC6502P095VCT IC, Sep19) Micromite DDS for IF Alignment (Sep17), Tariff Clock (Jul18) LED Christmas Ornaments (Nov20; specify variant) GPS-Synched Frequency Reference (Nov18), Air Quality Monitor (Feb20) Car Radio Dimmer (Aug19), MiniHeart Heartbeat Simulator (Jan21) RCL Box (Jun20), Digital Lighting Controller Micromite Master (Nov20) Refined Full-Wave Universal Motor Speed Controller (Apr21) Advanced GPS Computer (Jun21) Model Railway Level Crossing (two required – $15/pair) (Jul21) PIC32MX170F256B-I/SO Battery Multi Logger (Feb21) Motor Speed Controller (Mar18), Heater Controller (Apr18) PIC32MX270F256B-50I/SP ASCII Video Terminal (Jul14), USB M&K Adaptor (Feb19) Useless Box IC3 (Dec18) PIC32MX795F512H-80I/PT Maximite (Mar11), miniMaximite (Nov11), Colour Maximite Tiny LED Xmas Tree (Nov19) (Sep12), Touchscreen Audio Recorder (Jun14) Microbridge (May17), USB Flexitimer (June18) $20 MICROS Digital Interface Module (Nov18), GPS Finesaver (Jun19) dsPIC33FJ64MC802-E/SP 1.5kW Induction Motor Speed Controller (Aug13) Digital Lighting Controller LED Slave (Dec20) dsPIC33FJ128GP306-I/PT CLASSiC DAC (Feb13) Ol’ Timer II (Jul20), Battery Multi Logger (Feb21) 5-Way LCD Panel Meter (Nov19), IR Remote Control Assistant (Jul20) dsPIC33FJ128GP802-I/SP Ultra-LD Preamp (Nov11), LED Musicolour (Oct12) Ultrasonic Cleaner (Sep20), Electronic Wind Chime (Feb21) PIC32MX470F512H-I/PT Stereo Echo/Reverb (Feb 14), Digital Effects Unit (Oct14) 20A DC Motor Speed Controller (Jul21) PIC32MX470F512H-120/PT Micromite Explore 64 (Aug 16), Micromite Plus (Nov16) Flexible Digital Lighting Controller Slave (Oct20) PIC32MX470F512L-120/PT Micromite Explore 100 (Sep16) Auto Headlight Controller (Oct13), Motor Speed Controller (Feb14) $30 MICROS Automotive Sensor Modifier (Dec16) PIC32MX695F512L-80I/PF Colour MaxiMite (Sep12) Remote-controlled Preamp with Tone Control (Mar19) PIC32MZ2048EFH064-I/PT DSP Crossover/Equaliser (May19), Low-Distortion DDS (Feb20) UHF Repeater (May19), Six Input Audio Selector (Sep19) DIY Reflow Oven Controller (Apr20) Universal Battery Charge Controller (Dec19) KITS, SPECIALISED COMPONENTS ETC MODEL RAILWAY LEVEL CROSSING $15.00 $5.00 (JUN 21) $75.00 $25.00 $3.00 - Micromite LCD BackPack V3 kit (SC5082) - VK2828U7G5LF GPS module (SC5135) - MCP4251-502E/P IC (SC5052) ARCADE PONG (CAT SC5834) (JUN 21) $12.50 Pair of Signetics-branded NE555Ns, for critical A9/B9 paddle ICs MINI ISOLATED SERIAL LINK COMPLETE KIT (CAT SC5750) (MAR 21) $10.00 All parts required to build the project including the PCB MINIHEART HEARTBEAT SIMULATOR (CAT SC5732) (JAN 21) All SMD parts, including IC2 – does not include PCB AM/FM/SW RADIO $5.00 (JAN 21) $2.50 $3.00 $7.50 - PCB-mount right-angle SMA socket (SC4918) - Pulse-type rotary encoder with integral pushbutton (SC5601) - 16x2 LCD module (does not use I2C module) (SC4198) LED CHRISTMAS ORNAMENTS (CAT SC5579) (NOV 20) Complete kit including micro but no coin cell (specify PCB shape & colour) RGB STACKABLE LED CHRISTMAS STAR (CAT SC5525) $14.00 (NOV 20) $38.50 Complete kit including PCB, micro, diffused RGB LEDs and other parts FLEXIBLE DIGITAL LIGHTING CONTROLLER PARTS MICROMITE LCD BACKPACK V3 KIT (CAT SC5082) (JUL 21) - Pair of programmed PIC12F617-I/Ps - ISD1820P-based audio recording and playback module ADVANCED GPS COMPUTER siliconchip.com.au/Shop/ (OCT 20) 4 x Si8751AB ICs, 8 x S1HB15N60E-GE3 Mosfets, switchmode converter module, 6N137 opto, high-voltage resistors and capacitors plus SMD LEDs. $100.00 D1 MINI LCD WIFI BACKPACK KIT (OCT 20) Complete kit including 3.5-inch touchscreen, PCB and ESP8266-based module COLOUR MAXIMITE 2 $70.00 (JUL 20) Short form kit: includes everything except the case, CPU module, power supply, optional parts and cables (Cat SC5478) $80.00 Short Form kit (with CPU module): includes the programmed Waveshare CPU modue and everything included in the short form kit above (Cat SC5508) $140.00 (AUG 19) Includes PCB, programmed micros, 3.5in touchscreen LCD, UB3 lid, mounting hardware, Mosfets for PWM backlight control and all other mandatory on-board parts $75.00 Separate/Optional Components: - 3.5-inch TFT LCD touchscreen (Cat SC5062) $30.00 - DHT22 temp/humidity sensor (Cat SC4150) $7.50 - BMP180 (Cat SC4343) OR BMP280 (Cat SC4595) temp/pressure sensor $5.00 - BME280 temperature/pressure/humidity sensor (Cat SC4608) $10.00 - DS3231 real-time clock SOIC-16 IC (Cat SC5103) $3.00 - 23LC1024 1MB RAM (SOIC-8) (Cat SC5104) $5.00 - AT25SF041 512KB flash (SOIC-8) (Cat SC5105) $1.50 - 10µF 16V X7R through-hole capacitor (Cat SC5106) $2.00 VARIOUS MODULES & PARTS - Si4732 radio IC (Si473x FM/AM/SW Radio, Jul21) $7.50 - EA2-5NU relay (PIC Programming Helper, Jun21) $3.00 - VK2828U7G5LF GPS module (Advanced GPS Computer, Jun21) $25.00 - MCP4251-502E/P (PIC Programming Helper, Jun21) $3.00 - Pair of NE555N timer ICs (Recreating Arcade Pong, Jun21) $12.50 - 2.8-inch touchscreen LCD module (Lab Supply, May21) $22.50 - Spin FV-1 (Digital FX Unit, Apr21) $40.00 - 15mW 3W SMD resistor (Battery Multi Logger / Arduino PSU, Feb21) $2.50 - DS3231(M) real-time clock SMD IC (Battery Multi Logger, Feb21) $3.00 - Pair of CSD18534 (Electronic Wind Chimes, Feb21) $6.00 - IPP80P03P4L04 (Dual Battery Lifesaver / Vintage Radio Supply, Dec20) $5.00 - 16x2 LCD module (Digital RF Power Meter, Aug20) $7.50 - WS2812 8x8 RGB LED matrix module (Ol’ Timer II, Jul20) $15.00 - MAX038 function generator IC (H-Field Transanalyser, May20) $25.00 - MC1496P double-balanced mixer (H-Field Transanalyser, May20) $2.50 - AD8495 thermocouple interface (DIY Reflow Oven Controller, Apr20) $10.00 - Si8751AB 2.5kV isolated Mosfet driver IC (Charge Controller, Dec19) $5.00 - I/O expander modules (Nov19): PCA9685 – $6.00 ¦ PCF8574 – $3.00 ¦ MCP23017 – $3.00 - SMD 1206 LEDs, packets of 10 unless stated otherwise (Xmas Ornaments, Nov20): yellow – $0.70 ¦ amber – $0.70 ¦ blue – $0.70 ¦ cyan – $1.00 ¦ pink (1 only) – $0.20 - ISD1820-based voice recorder / playback module (Junk Mail, Aug19) $4.00 - 23LCV1024-I/P SRAM & MCP73831T (UHF Repeater, May19) $11.50 - MCP1700 3.3V LDO regulator (suitable for USB M&K Adapator, Feb19) $1.50 *Prices valid for month of magazine issue only. All prices in Australian dollars and include GST where applicable. # P&P prices are within Australia. Overseas? Place an order on our website for a quote. PRINTED CIRCUIT BOARDS & CASE PIECES PRINTED CIRCUIT BOARD TO SUIT PROJECT USB FLEXITIMER TEMPERATURE SWITCH MK2 LiFePO4 UPS CONTROL SHIELD RASPBERRY PI TOUCHSCREEN ADAPTOR RECURRING EVENT REMINDER BRAINWAVE MONITOR (EEG) SUPER DIGITAL SOUND EFFECTS DOOR ALARM STEAM WHISTLE / DIESEL HORN DCC PROGRAMMER (INC. HEADERS) ↳ WITHOUT HEADERS OPTO-ISOLATED RELAY (INC. EXT. BOARDS) GPS-SYNCHED FREQUENCY REFERENCE LED CHRISTMAS TREE DIGITAL INTERFACE MODULE TINNITUS/INSOMNIA KILLER (JAYCAR VERSION) ↳ ALTRONICS VERSION HIGH-SENSITIVITY MAGNETOMETER USELESS BOX FOUR-CHANNEL DC FAN & PUMP CONTROLLER ATtiny816 DEVELOPMENT/BREAKOUT PCB ISOLATED SERIAL LINK DAB+/FM/AM RADIO ↳ CASE PIECES (CLEAR) REMOTE CONTROL DIMMER MAIN PCB ↳ MOUNTING PLATE ↳ EXTENSION PCB MOTION SENSING SWITCH (SMD) PCB USB MOUSE AND KEYBOARD ADAPTOR PCB LOW-NOISE STEREO PREAMP MAIN PCB ↳ INPUT SELECTOR PCB ↳ PUSHBUTTON PCB DIODE CURVE PLOTTER ↳ UB3 LID (MATTE BLACK) FLIP-DOT (SET OF ALL FOUR PCBs) ↳ COIL PCB ↳ PIXEL PCB (16 PIXELS) ↳ FRAME PCB (8 FRAMES) ↳ DRIVER PCB iCESTICK VGA ADAPTOR UHF DATA REPEATER AMPLIFIER BRIDGE ADAPTOR 3.5-INCH LCD ADAPTOR FOR ARDUINO DSP CROSSOVER (ALL PCBs – TWO DACs) ↳ ADC PCB ↳ DAC PCB ↳ CPU PCB ↳ PSU PCB ↳ CONTROL PCB ↳ LCD ADAPTOR STEERING WHEEL CONTROL IR ADAPTOR GPS SPEEDO/CLOCK/VOLUME CONTROL ↳ CASE PIECES (MATTE BLACK) RF SIGNAL GENERATOR RASPBERRY PI SPEECH SYNTHESIS/AUDIO BATTERY ISOLATOR CONTROL PCB ↳ MOSFET PCB (2oz) MICROMITE LCD BACKPACK V3 CAR RADIO DIMMER ADAPTOR PSEUDO-RANDOM NUMBER GENERATOR 4DoF SIMULATION SEAT CONTROLLER PCB ↳ HIGH-CURRENT H-BRIDGE MOTOR DRIVER MICROMITE EXPLORE-28 (4-LAYERS) SIX INPUT AUDIO SELECTOR MAIN PCB ↳ PUSHBUTTON PCB ULTRABRITE LED DRIVER HIGH RESOLUTION AUDIO MILLIVOLTMETER PRECISION AUDIO SIGNAL AMPLIFIER SUPER-9 FM RADIO PCB SET ↳ CASE PIECES & DIAL TINY LED XMAS TREE (GREEN/RED/WHITE) HIGH POWER LINEAR BENCH SUPPLY ↳ HEATSINK SPACER (BLACK) DATE JUN18 JUN18 JUN18 JUL18 JUL18 AUG18 AUG18 AUG18 SEP18 OCT18 OCT18 OCT18 NOV18 NOV18 NOV18 NOV18 NOV18 DEC18 DEC18 DEC18 JAN19 JAN19 JAN19 JAN19 FEB19 FEB19 FEB19 FEB19 FEB19 MAR19 MAR19 MAR19 MAR19 MAR19 APR19 APR19 APR19 APR19 APR19 APR19 MAY19 MAY19 MAY19 MAY19 MAY19 MAY19 MAY19 MAY19 MAY19 MAY19 JUN19 JUN19 JUN19 JUN19 JUL19 JUL19 JUL19 AUG19 AUG19 AUG19 SEP19 SEP19 SEP19 SEP19 SEP19 SEP19 OCT19 OCT19 NOV19 NOV19 NOV19 NOV19 NOV19 For a complete list, go to siliconchip.com.au/Shop/8 PCB CODE Price PRINTED CIRCUIT BOARD TO SUIT PROJECT 19106181 $7.50 DIGITAL PANEL METER / USB DISPLAY 05105181 $7.50 ↳ ACRYLIC BEZEL (BLACK) 11106181 $5.00 UNIVERSAL BATTERY CHARGE CONTROLLER 24108181 $5.00 BOOKSHELF SPEAKER PASSIVE CROSSOVER 19107181 $5.00 ↳ SUBWOOFER ACTIVE CROSSOVER 25107181 $10.00 ARDUINO DCC BASE STATION 01107181 $2.50 NUTUBE VALVE PREAMPLIFIER 03107181 $5.00 TUNEABLE HF PREAMPLIFIER 09106181 $5.00 4G REMOTE MONITORING STATION SC4716 $7.50 LOW-DISTORTION DDS (SET OF 5 BOARDS) 09107181 $5.00 NUTUBE GUITAR DISTORTION / OVERDRIVE PEDAL 10107181/2 $7.50 THERMAL REGULATOR INTERFACE SHIELD 04107181 $7.50 ↳ PELTIER DRIVER SHIELD 16107181 $5.00 DIY REFLOW OVEN CONTROLLER (SET OF 3 PCBS) 16107182 $2.50 7-BAND MONO EQUALISER 01110181 $5.00 ↳ STEREO EQUALISER 01110182 $5.00 REFERENCE SIGNAL DISTRIBUTOR 04101011 $12.50 H-FIELD TRANSANALYSER 08111181 $7.50 CAR ALTIMETER 05108181 $5.00 RCL BOX RESISTOR BOARD 24110181 $5.00 ↳ CAPACITOR / INDUCTOR BOARD 24107181 $5.00 ROADIES’ TEST GENERATOR SMD VERSION 06112181 $15.00 ↳ THROUGH-HOLE VERSION SC4849 $.00 COLOUR MAXIMITE 2 PCB (BLUE) 10111191 $10.00 ↳ FRONT & REAR PANELS (BLACK) 10111192 $10.00 OL’ TIMER II PCB (RED, BLUE OR BLACK) 10111193 $10.00 ↳ ACRYLIC CASE PIECES / SPACER (BLACK) 05102191 $2.50 IR REMOTE CONTROL ASSISTANT PCB (JAYCAR) 24311181 $5.00 ↳ ALTRONICS VERSION 01111119 $25.00 USB SUPERCODEC 01111112 $15.00 ↳ BALANCED ATTENUATOR 01111113 $5.00 SWITCHMODE 78XX REPLACEMENT 04112181 $7.50 WIDEBAND DIGITAL RF POWER METER SC4927 $5.00 ULTRASONIC CLEANER MAIN PCB SC4950 $17.50 ↳ FRONT PANEL 19111181 $5.00 NIGHT KEEPER LIGHTHOUSE 19111182 $5.00 SHIRT POCKET AUDIO OSCILLATOR 19111183 $5.00 ↳ 8-PIN ATtiny PROGRAMMING ADAPTOR 19111184 $5.00 D1 MINI LCD WIFI BACKPACK 02103191 $2.50 FLEXIBLE DIGITAL LIGHTING CONTROLLER SLAVE 15004191 $10.00 ↳ FRONT PANEL (BLACK) 01105191 $5.00 LED XMAS ORNAMENTS 24111181 $5.00 30 LED STACKABLE STAR SC5023 $40.00 ↳ RGB VERSION (BLACK) 01106191 $7.50 DIGITAL LIGHTING MICROMITE MASTER 01106192 $7.50 ↳ CP2102 ADAPTOR 01106193 $5.00 BATTERY VINTAGE RADIO POWER SUPPLY 01106194 $7.50 DUAL BATTERY LIFESAVER 01106195 $5.00 DIGITAL LIGHTING CONTROLLER LED SLAVE 01106196 $2.50 BK1198 AM/FM/SW RADIO 05105191 $5.00 MINIHEART HEARTBEAT SIMULATOR 01104191 $7.50 I’M BUSY GO AWAY (DOOR WARNING) SC4987 $10.00 BATTERY MULTI LOGGER 04106191 $15.00 ELECTRONIC WIND CHIMES 01106191 $5.00 ARDUINO 0-14V POWER SUPPLY SHIELD 05106191 $7.50 HIGH-CURRENT BATTERY BALANCER (4-LAYERS) 05106192 $10.00 MINI ISOLATED SERIAL LINK 07106191 $7.50 REFINED FULL-WAVE MOTOR SPEED CONTROLLER 05107191 $5.00 DIGITAL FX UNIT PCB (POTENTIOMETER-BASED) 16106191 $5.00 ↳ SWITCH-BASED 11109191 $7.50 ARDUINO MIDI SHIELD 11109192 $2.50 ↳ 8X8 TACTILE PUSHBUTTON SWITCH MATRIX 07108191 $5.00 HYBRID LAB POWER SUPPLY CONTROL PCB 01110191 $7.50 ↳ REGULATOR PCB 01110192 $5.00 VARIAC MAINS VOLTAGE REGULATION 16109191 $2.50 ADVANCED GPS COMPUTER 04108191 $10.00 PIC PROGRAMMING HELPER 8-PIN PCB 04107191 $5.00 ↳ 8/14/20-PIN PCB 06109181-5 $25.00 ARCADE MINI PONG SC5166 $25.00 NEW PCBs 16111191 $2.50 Si473x FM/AM/SW DIGITAL RADIO 18111181 $10.00 20A DC MOTOR SPEED CONTROLLER SC5168 MODELmagazine RAILWAY LEVEL CROSSING Australia’s$5.00 electronics DATE NOV19 NOV19 DEC19 JAN20 JAN20 JAN20 JAN20 JAN20 FEB20 FEB20 MAR20 MAR20 MAR20 APR20 APR20 APR20 APR20 MAY20 MAY20 JUN20 JUN20 JUN20 JUN20 JUL20 JUL20 JUL20 JUL20 JUL20 JUL20 AUG20 NOV20 AUG20 AUG20 SEP20 SEP20 SEP20 SEP20 SEP20 OCT20 OCT20 OCT20 NOV20 NOV20 NOV20 NOV20 NOV20 DEC20 DEC20 DEC20 JAN21 JAN21 JAN21 FEB21 FEB21 FEB21 MAR21 MAR21 APR21 APR21 APR21 APR21 APR21 MAY21 MAY21 MAY21 JUN21 JUN21 JUN21 JUN21 PCB CODE 18111182 SC5167 14107191 01101201 01101202 09207181 01112191 06110191 27111191 01106192-6 01102201 21109181 21109182 01106193/5/6 01104201 01104202 CSE200103 06102201 05105201 04104201 04104202 01005201 01005202 07107201 SC5500 19104201 SC5448 15005201 15005202 01106201 01106202 18105201 04106201 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 Price $2.50 $2.50 $10.00 $10.00 $7.50 $5.00 $10.00 $2.50 $5.00 $20.00 $7.50 $5.00 $5.00 $12.50 $7.50 $7.50 $7.50 $10.00 $5.00 $7.50 $7.50 $2.50 $5.00 $10.00 $10.00 $5.00 $7.50 $5.00 $5.00 $12.50 $7.50 $2.50 $5.00 $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 JUL21 JUL21 JUL21 CSE210301C $7.50 11006211 $7.50 09108211 $5.00 We also sell an A2 Reactance Wallchart, RTV&H DVD, Vintage Radio DVD plus various books at siliconchip.com.au/Shop/3 PRODUCT SHOWCASE ElectroneX to return in September After a one year break, Australia’s only dedicated trade event for the electronics industry will be held in Sydney in September. ElectroneX – The Electronics Design and Assembly Expo will be staged during 15-16 September at Rosehill Gardens Event Centre. In addition to featuring a wide range of electronic components, test and measurement products and other ancillary products and services, companies can also discuss their specific requirements with contract manufacturers that can design and produce turnkey solutions for particular applications. This is a must-see event for decision makers, managers, engineers and industry enthusiasts or those designing or manufacturing products that utilise electronics. The SMCBA Electronics Design & Manufacture Conference, held concurrently with the Expo, will feature a series of sessions on the latest hot topics and workshops over the two days. The full program can be viewed at www.smcba.asn.au Registration for the Expo is now open and all visitors are asked to pre-register to avoid queuing at the entrance. Visitors can register for free online at www.electronex.com.au Australasian Exhibitions and Events Pty Ltd Suite 11, Pier 35-263 Lorimer St Port Melbourne VIC 3207 Tel: (03) 9676 2133 mail: ngray<at>auexhibitions.com.au Web: www.auexhibitions.com.au Open Source USB Power Delivery software from Microchip USB Type-C with Power Delivery (PD) and open source software are two technologies leading the next wave of wired connectivity. Microchip’s new Power Delivery Software Framework (PSF) allows you to modify and own the IP in your USB-PD systems. By merging your code with Microchip’s fully functional PD stack, you have the flexibility to create different product offerings while choosing from a wide variety of Microchip SmartHubs, micros and standalone PD solutions for USB systems. Microchip’s PSF provides an open-source code base for power delivery and a comprehensive programming environment, removing the need for manufacturer dependence and making it easy for users to program micros and immediately modify PD code as their system evolves. Using this, customers can reduce time to market and overall bill of materials. Developers can also choose from an expanded family of Microchip controller options to host PD functionality, including the new UPD301B and Microchip Technology Inc. www.microchip.com UPD301C standalone PD controllers. The PD architecture’s open approach enables customers to easily add a USB-C/PD port to a wide range of embedded applications, while also allowing customers to reallocate unused pins or CPU memory to other system functions A range of Microchip SAM and PIC MCUs and dsPIC Digital Signal Controllers (DSCs) are supported. The PSF solution gives designers the option to run PD on existing Microchip microcontroller infrastructure by adding the UPD350 PD transceiver, or by integrating PD into more complex product offerings with proprietary system code. The PSF is supported by Microchip’s MPLAB X IDE development environment. The PSF evaluation board can be purchased from: www. microchip.com/DevelopmentTools/ ProductDetails/PartNO/EV65D44A Silicon Labs’ EFM32PG22 microcontrollers now available at Mouser Mouser Electronics is now stocking the new EFM32PG22 (PG22) microcontrollers from Silicon Labs. The new Series 2 Gecko microcontrollers are ideal for energy-efficient and space-constrained applications in consumer electronics, personal hygiene devices, Internet of Things (IoT), and industrial automation devices. 106 Silicon Chip The microcontroller incorporates a low-power ARM Cortex-M33 core running at up to 76.8MHz, plus up to 512KB of flash and 32KB of RAM. The devices consume just 26μA/MHz in Active Mode at 38.4MHz and as little as 0.95μA in DeepSleep mode with 8KB of RAM retention. The PG22 development kit includes four different environmental sensors Australia’s electronics magazine and stereo PDM microphones, providing an ideal platform for the development of energy-friendly electronic devices. To learn more, visit www. mouser.com/new/silicon-labs/siliconlabs-efm32pg22-mcus/ Mouser Electronics Inc. Phone: (852) 3756 4700 Web: www.mouser.com siliconchip.com.au 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 Lab Supply support for 3.5in touchscreen The front panel artwork on your website for the Programmable Hybrid Lab Supply with WiFi (May & June 2021; siliconchip.com.au/Series/364) is for the 2.8in screen, but I built the 3.5in version. Could you please post that version? (J. A., Townsville, Qld) • The parts list for the Lab Supply calls for a 2.8in touchscreen because that is what the project is designed around, both in terms of software and mounting. The 2.8in screen is also shown as the only option on the circuit diagram. The control board supports the 3.5in screen, but that option was not used in the Lab Supply design. We contacted the designer, Richard Palmer, and he kindly created a version of the firmware for the Lab Supply to suit the 3.5in touchscreen, along with revised front panel dimensions for mounting the larger screen. We have created new front panel artwork based on those dimensions and posted that, along with the new firmware, on our website for download (siliconchip. com.au/Shop/11/5857). Advanced GPS Comp. with V2 BackPack Is it possible to build the Advanced GPS Computer (June & July 2021; siliconchip.com.au/Series/366) using the Micromite BackPack V2 instead of V3? I know that it does not have an onboard real-time clock, but I can’t see the point in having time if the GPS won’t work because there is no signal. (P. C., Balgal Beach, Qld) • This project requires the use of the ILI9488-based 3.5in LCD touchscreen and will not work with the ILI9341based 2.8in, 2.4in and 2.2in displays without extensive software changes. However, the V2 BackPack can be fitted with a 3.5in screen, so the rest of this answer assumes that is the configuration you are asking about. The V2 BackPack connects the SPI MISO lines of the LCD screen and siliconchip.com.au touch controller together. These were separated on the V3 BackPack, as we found that the 3.5in touch controller was driving this line even when it was deactivated. This was resolved with the V3 BackPack by simply leaving pin 9 of the LCD header disconnected – compare Fig.1 on p32 of the August 2019 issue to Fig.1 on p85 of the May 2017 issue. One way around this is to remove pin 9 (marked SDO/MISO) from the header on the 3.5in LCD. The mounting holes on the V2 BackPack will also not suit the 3.5in display, so the ‘stack’ will not be mechanically sound. Assuming you didn’t care about the time feature, everything else in the software should work fine, although we haven’t tested it. The time is not automatically set from the GPS receiver, so you would have to trigger this manually every time the GPS Computer is powered up. Serial Monitor baud rate mismatch I recently finished building the Arduino-based Adjustable Power Supply (February 2021; siliconchip.com. au/Article/14741), but I have run into difficulties. Sometimes when I load the Arduino software, it shows the S, U and J values a couple of times but then reverts to a series of reverse question marks. What could cause this? (M. W., Preston West, Vic.) • Based on what we can see in the screen grab you have sent, you have the Serial Monitor set to 9600 baud, while the sketch runs at 115,200 baud. That would explain your problems. For some reason, the Serial Monitor can briefly display valid data even when at a different baud rate, so that’s why you might see some values briefly. Simpler solar panel tester wanted On receipt of the January 2021 issue, I was interested to see an article about Australia’s electronics magazine a device for testing 12V solar panels. A place we have in the mountains has no mains power, so we were early adopters of low-voltage solar panels, many of which are now over 20 years old. Although they are still working OK, they probably need a proper assessment of output (other than the obvious check of open-circuit voltage and short-circuit current). Would it be possible for you to design and publish a simple circuit to enable me to test 12V panels under an appropriate load? Something like resistors and switches in a box to use with my multimeter, or with suitable panel meters incorporated. I have both analog and digital panel meters in my box of bits. (L. I., Beaumaris, Vic) • We believe that the open-circuit and short-circuit tests are sufficient to check that the panels are still working reasonably well. The open-circuit voltage can be measured when the panel is cool and in full sunlight. For a 12V panel, the open-circuit voltage is usually around 20V or a volt or two more. The short-circuit current is measured by connecting a multimeter to measure current across the solar panel terminals. Measure the current in full sunlight with a cool panel. For a 200W panel, the short circuit current is typically around 12A. If you really want to, you could load the panel with a suitable resistance to set the panel at its maximum power point. It is typically at around 18V for a 12V panel. The load resistance needs to be able to dissipate the power from the panel. So with a 200W panel, the load will dissipate up to 200W. We pulled up the data for this type of panel, which gave figures of 18.2V and 10.99A, meaning that you need a resistance of V ÷ R = 1.656W rated at more than 200W. There is no easy universal resistor box that can test panels at their maximum power point. The load resistor value is quite low. The most practical way to test the panel’s maximum power is to temporarily connect it to July 2021  107 an MPPT charger that can handle its full power and use that to charge a flat battery and measure the power being pulled from the panel. Ideally, use a charger with a power readout, but if you can’t get one, you should be able to find a DC panel meter that will read out watts and connect it in series with the MPPT charger’s inputs. Such a device would likely be cheaper to buy than a circuit we could design to perform a similar test. LCD screen backlight troubleshooting I purchased your Mini WiFi LCD BackPack kit last year (October 2020; siliconchip.com.au/Article/14599). It appears that the 3.5in touchscreen is faulty, as the screen does not light up at all. 5V power is present on pin 1, but there is no sign of anything on the screen. Is there anything I can do to test it? The mini WiFi chip appears OK, with the blue light flashing and the weather demonstration program has been loaded successfully. (J. L., Tauranga, NZ) • We will replace the LCD module if it is faulty, but it is worth making some more checks first, as it needs more than just 5V at pin 1 to light up. Check that there is a good ground connection at pin 2, and pin 8 also needs to be at 5V for the backlight to activate. It should be safe to short pin 8 to 5V, eg, to pin 1 on the LCD connector (CON1). You could use a DMM in current measurement mode (amps range), holding the probes on pins 1 & 8. Also try inserting a shunt on JP2 in the position marked 5V, if you haven’t already. That should force the LCD backlight on as long as Mosfets Q1 & Q2 have been correctly fitted. But the shorting approach doesn’t rely on those Mosfets, so it’s probably a better way to test the LCD screen itself. If it still doesn’t light up, then chances are the screen is faulty. If it does, you likely have a software problem or a problem with Mosfets Q1 & Q2. Fostex drivers for Concreto speakers Thanks for your “Concreto” loudspeakers article in the June 2020 issue (siliconchip.com.au/Article/14463). I’ve been thinking of building them 108 Silicon Chip with the more expensive Fostex FE103en speakers, as per the article, for better low-frequency response, particularly as I might not get to making the subwoofers. I like the simplicity of one amplifier only and the reduced space requirements. Although Fostex’s higher specifications over Altronics’ C0626 seem marginal, it looks from the figures that the differences would be easily discernable to the listener. However, if I tackle the subs one day, the equalisation curves with the better drivers might not dovetail in quite as nicely as they appear to with the Altronics drivers (as published on your measured curves). So could you do a build with the higher-spec drivers for a review of audible differences, and publish a response plot to compare that to the ones with the Altronics drivers? Fostex’s successor to the FE103en is the FE103NV. It is promoted as having a new cone mix (mixed length Kenaf fibre pulp plus mineral ore as a secondary material) to “improve propagation speed and rigidity”. Also mentioned is reduced harmonic distortion in the midrange through the elimination of metallic eyelets, as used in the original design (these were causing poor diaphragm weight balance). The FE103NV unit price is currently $92, direct from Fostex. (S. O’N, Page, ACT) • We tested the Fostex FE103en against the Altronics C0626 in the “Tiny Tim” loaded horn loudspeaker (October 2013; siliconchip.com. au/Article/4995), and that article included response curves. We preferred the Altronics drivers in a backto-back audition with those enclosures. If you want to use the Fostex drivers, consider using the Tiny Tim design because it gives you the best bass available. However, it is significantly more complex and expensive to build. The goal was to produce excellent natural sound without an “artificial” subwoofer. The philosophy behind the design of the Concretos was to create a really low-budget system based on readilyavailable components that was super easy to build. The problem is that although the FE103en or FE103NV have exceptional sound qualities, we don’t think their lower fundamental resonance (at Australia’s electronics magazine a much higher cost) will be enough to substitute for the Jaycar 5-inch CW2192 woofers in the Concretos. That’s because they can handle heaps more low-frequency power from that subwoofer channel. Both of the 4-inch drivers above only tolerate small amounts of power (5-15W RMS) and are easily blown by harsh transients. We actually blew a couple in testing their power handling! The Jaycar 5-inch CW2192 subs recommended for the Concretos can handle 50W each, so you can really wind up the bass, especially if you use two! In answer to your question about subwoofer balance, the subwoofer amplifier we used for testing had an independent volume control, adjusted to give a relatively flat response. Bass balance can therefore be adjusted according to your music choices and preferences, and the type of subwoofer you use. Alphanumeric LCD compatibility problems I’m contemplating building the AM/ FM/CW RF Signal Generator (June & July 2019; siliconchip.com.au/ Series/336). The circuit diagram on pages 32 & 33 of the June 2019 issue shows the LCD module as having 16 pins. The one I have, Jaycar QP5516, has 14 pins in two rows. Where do pins 15 & 16 go on my LCD module? (P. S., Griffith, NSW) • The main difficulty regarding the LCD you plan to use does not relate to missing pins/pads 15 and 16 but rather the LCD module power supply pins. On that module, pin 1 is Vdd and pin 2 is GND. On the PCB, this is reversed, with pin 1 being GND and pin 2 being Vdd. If connected without modification, the LCD module will likely be destroyed. However, there is a simple solution. When connecting the LCD module to the PCB, first solder a 6x2 DIL header (yes, 6x2, not 7x2) to the PCB LCD pads 3-14, leaving pads 1 and 2 unconnected. It is then a simple matter of transposing pins 1 and 2 between the PCB and the LCD module using thin hook-up wire or wire wrapping wire. Regarding the LCD backlight, which is what pads 15 (anode) and 16 (cathode) are for on the PCB’s 16-pin SIL header, these need to be connected to the ‘A’ and ‘K’ pads respectively, on siliconchip.com.au the right-hand side of the LCD module. The PCB overlay (Fig.5 on page 75, July 2019) shows the location of the 16-pin SIL header (top left) and the ‘A’ and ‘K’ pads on the LCD module. Again, use hook-up wire to connect pad 15 on the PCB to the ‘A’ pad on the LCD and pin 16 on the PCB to the ‘K’ pad on the LCD. New 14-segment display module Jaycar has just released a new quad LED alphanumeric display module (the 14-segment type). Their stock code is XC3715; their website doesn’t have a data sheet for the module. Do you know where I can find one? I’m not sure if it is made by Kingbright, Vishay or someone else. How would I drive it from a PICAXE? (P. H., Gunnedah, NSW) • As far as we know, the Jaycar XC3715 is the same or a copy of the Adafruit module that uses the Holtek HT16K33 driver IC. See siliconchip. com.au/link/ab9b Data for the HT16K33 IC is available from siliconchip.com.au/link/ab9c That IC uses an I2C serial bus for communications. You can find a tutorial on interfacing with I2C devices with a PICAXE chip at siliconchip. com.au/link/ab9d Speed controller for an e-bike Can the High Power DC Motor Speed Control from the January 2017 issue (siliconchip.com.au/Article/10501) be used to regulate a 1000W or 1500W e-bike motor powered from a 48V Li-ion battery? Apart from using this kit to regulate via the throttle, is there a way (by changeover switch) to use the Hall effect output of the crank sensors (in pedelec mode) to give a proportional motor speed? (P. B., Cooloongup, WA) • Yes, you can use the DC Motor Speed Controller from January 2017 to control a 1500W 48V e-bike motor. If you want to have speed controlled by the Hall Effect sensor output, the signal frequency from this sensor needs to be converted to a 0-5V DC signal suitable for applying to the speed input of the controller, where the speed potentiometer wiper originally connected. Our Twin-engine Speed Match siliconchip.com.au Indicator board can be used to do this frequency to voltage conversion (November 2009; siliconchip.com.au/ Article/1622). This can be powered from the 12V supply of the DC motor controller. The signal from IC3b of the speed match indicator can be used as the DC voltage fed to the Speed Controller. IC2 (the second frequency-to-voltage converter) is not needed. Adjust VR1 for the required speed match of the motor to pedal speed. You might need to increase the capacitance value at the charge pump (pin 2 of IC1); the value depends on the frequency of the Hall Effect sensor signal at pedal speeds. If using a polarised electrolytic capacitor for a low Hall Effect signal frequency, the positive side goes to pin 2. Switching high direct current with a relay Have you published anything that would help me remotely switch my 12V 40A air compressor? Or an article discussing snubber design or practical implementations of a high current 12V relay feeding an inductive load? I built a simple remote-controlled relay that worked fine 20 times, then welded the 100A relay contacts. This was a test, as I couldn’t work out a suitable snubber or the required characteristics of a suppression diode. I want to build a reliable version, but it’s tough to find information on practical mechanical relay contact protection or solid-state relay protection. (J. R., Narrabundah, ACT) • The relay contacts should survive if the compressor has a diode connected across its supply input with the cathode to the positive terminal. The diode clamps the voltage spike that occurs when the compressor switches off. A high-current rectifier with a continuous rating of 50A or more should be suitable. You could use one diode in a bridge rectifier package. Battery Charge Controller acting up I have just finished building the Universal Battery Charge Controller (December 2019; siliconchip.com.au/ Article/12159). I am using an old 10A charger and have built the controller into the case, bringing the LEDs out the front. Australia’s electronics magazine It seems to be working, except the charge LED and float LED come on within seconds of each other, bypassing the absorption phase. This happens in both the default and adjust positions. When charged, the battery sits at 15V, toggling between 15.1V and 15.8V. I note that under limitations, section 2, that it says the battery voltage might be maintained at a different value, but this seems too high. The appropriate LEDs flash when storing settings and changing the charge LED mode, so it looks like the software is working fine. As I am charging 18Ah SLA batteries, I have the charge rate set to 50%, but the rest as per defaults. I am also thinking of bypassing S1 so that the controller boots up when the charger is turned on, allowing it to start up again after a power cut. This would be handy if I am away for the day or weekend. I assume the thermistor control of charging is via pin 9, and not dropping out the relay. (T. O. L., Ngāruawāhia, NZ) • 15.1-15.8V sounds like too high a charge voltage, so something is definitely wrong. Try adjusting the cutout (VR2) and float (VR3) potentiometers anti-clockwise until the required voltages are correct for the battery used. Note that jumper JP1 must be inserted to use the adjustable parameters rather than the default settings. If that doesn’t help, check the component values connected to pin 2 of IC1. The absorption phase will only run when JP2 is in position 2, and will not occur if the bulk charge takes less than one hour. Also, because your final charge voltage is too high, the absorption phase might not run as the absorption rate could already be below 3% of the bulk charge rate before the absorption phase begins. You could bypass S1, although this is risky as it will prevent the battery discharge protection (via the relay contacts) from working. GPS Clock Driver differs when moved I have built the GPS-synchronised Analog Clock Driver (February 2017; siliconchip.com.au/Article/10527), and it works perfectly. My clock was mounted in the base of a cake tin. Every so often, the GPS module would July 2021  109 exhibit a red light followed by a flashing green light. I assumed that the red light indicated that the PIC module had powered it up via REG1 and the flashing green was when it was transferring data from the satellite to IC1. Are my assumptions correct? Recently, I bought a small wallmounted pendulum clock and modified it to run off the clock driver. It ran for a couple of days, then stopped at 11:50, indicating that it had not received sufficient satellite signals. I changed JP1 to the 5V position, and it has been working satisfactorily for over a week now, with no hiccups. I have not seen the green light come on, but I don’t sit there all day watching. It must sneak them as the system keeps working. Would a thin 1mm plywood cover have much effect on a satellite signal? (F. T., Narrabeen, NSW) • There’s a red LED on the main board, but presumably, you are referring to the two LEDs on the VK2828 GPS module. According to the VK2828 data sheet at https://nettigo.pl/attachments/378, “red lights means the power is working normally” and “green light flashing means positioned”. So the red LED is the power indicator, and the green LED flashes when a valid GPS signal is detected and decoded, indicating a valid position fix (and time). As for the reasons for the different behaviour, most blocking materials will have some effect on the signal, but the impact of 1mm plywood should be minimal. GPS signal strength can vary throughout a structure, and orientation can have an effect. It’s interesting that the higher supply voltage is apparently helping. Many modules will run from 3.3V or 5V but rarely do they state whether there is any difference in performance; your experience suggests that there is, and 5V should be used when possible. Perhaps the higher voltage is providing more gain to the internal RF lownoise amplifier. Monitoring water pump operation I have a pressure pump for my domestic water supply. I want to monitor when the pump comes on, how long it runs for and log this information using an Arduino to an SD card (I 110 Silicon Chip have this bit running on my temperature monitoring project). How can I detect when the pump turns on and off without connecting something in series with the mains power supply? (J. M., Adelaide, SA) • Take a look at our Cyclic Pump Timer (September 2016; siliconchip. com.au/Article/10130). It used a current transformer to detect when the pump is running while safely isolating the mains supply from the rest of the device. The current transformer is a Talema AC1015, available from the Silicon Chip Online Shop (Cat SC3438). You need to pass the mains Active pump wire through the current transformer core. The circuitry to the left of T1 on page 34 (Fig.1) converts the transformer’s output to a voltage in the range of 0-5V. This is suitable for being fed to a microcontroller ADC input, including those of most Arduino boards. Alternatively, a Hall effect sensor may work when placed against the pump motor to detect the magnetic field when running. The UGN3503 (Jaycar Cat ZD1902) should be suitable. A method for AC voltage calibration I want to calibrate some digital multimeters, including their AC voltage ranges. I found an AC reference on the ‘net using the SWR300 IC made by Thaler Corporation for $38 plus shipping. Is there a less expensive way to do this? I also want to calibrate their frequency reading modes. I plan to build a device based on the March 2021 Circuit Notebook entry titled “Two quartz crystal oscillators using a flip-flop” (siliconchip.com.au/Article/14779) with a 10MHz crystal, although I will have to divide this down because some meters only go to 4MHz. (R. M., Melville, WA) • Another way of deriving an AC reference would be to use a lowdistortion sinewave oscillator and a precision RMS to DC converter (eg, one based on the LTC1966). The resulting DC voltage could be read using a calibrated multimeter. So the DC reading would show what the AC RMS voltage applied to the RMS-to-DC converter is. This can be set to the value required Australia’s electronics magazine using the level control on the oscillator. Then set the multimeter to read AC and check its calibration. The RMSto-DC converter is cheaper and more easily obtained than the SWR3000 AC reference. For calibrating the other multimeter ranges, see the Accurate Voltage/ Current/Resistance Reference in the August 2015 issue (siliconchip.com. au/Article/8801). Fixing blown Motor Speed Controller Many thanks for your continuing excellent publication (I have all but one issue). I have a problem with the 230V/10A Speed Controller for Universal Motors featured in the February/March 2014 issues (siliconchip.com.au/Series/195) bought as a kit. It has worked reliably over the past three years on my 2kW DeWalt Table Saw, but its variable speed control stopped working recently (and for no apparent reason). It turns out the IGBT transistor has shorted out between its collector & emitter, so it now operates at full-speed only. I replaced the IGBT with the recommended equivalent IGW40N120H3FKSA1, as per the note published in the September 2020 issue (p112). It worked again (with variable speed across the range) for the next six starts, but it failed with the same C-E short circuit problem on the seventh start. Thinking it might be a problem with the snubber circuit not clamping high voltage spikes across the device, I replaced the 10nF X2 capacitor and checked the three 100W resistors (= 33W) in series with it. I installed another new transistor, and had the same outcome again after about six starts. All parts seem to check out OK, and there are no dry joints, so I can’t see what else could be causing the problem. I am not sure what to do next. Any help would be much appreciated. (K. F., Beecroft, NSW) • It would be worthwhile to replace diode D1 as well as the IGBT, as the diode protects the IGBT against overvoltage. It could be that the diode was the first part to go faulty, and it has been destroying the IGBTs by not clamping the voltage properly. continued on page 112 siliconchip.com.au MARKET CENTRE Advertise your product or services here in Silicon Chip FOR SALE FOR SALE KIT ASSEMBLY & REPAIR LEDsales VINTAGE RADIO REPAIRS: electrical mechanical fitter with 36 years ex­ perience and extensive knowledge of valve and transistor radios. Professional and reliable repairs. All workmanship guaranteed. $17 inspection fee plus charges for parts and labour as required. Labour fees $38 p/h. Pensioner discounts available on application. Contact Alan, VK2FALW on 0425 122 415 or email bigalradioshack<at>gmail. com LEDs and accessories for the DIY enthusiast PMD WAY offers (almost) everything for the electronics enthusiast – with full warranty, technical support and free delivery worldwide. Visit pmdway.com to get started. SILICON CHIP ASSORTED BOOKS FOR $5 EACH Selling assorted books on electronics and other related subjects – condition varies. Some of the books may have already been sold, but most are still available. Bulk discount available; post or pickup. All books can be viewed at: siliconchip.com.au/link/aawx Email for a postage quote, quote the number directly below the photo when referring to a book: silicon<at>siliconchip.com.au LEDs, BRAND NAME AND GENERIC LEDs. Heatsinks, LED drivers, power supplies, LED ribbon, kits, components, hardware – www.ledsales.com.au TRONIXLABS PTY LTD would like to thank all of our customers for their support and feedback. For any enquiries or customer technical support, please email support<at>tronixlabs.com PCB PRODUCTION PCB MANUFACTURE: single to multi­ layer. Bare board tested. One-offs to any quantity. 48 hour service. Artwork design. Excellent prices. Check out our specials: www.ldelectronics.com.au DAVE THOMPSON (the Serviceman from S ilicon C hip ) is available to help you with kit assembly, project troubleshooting, general electronics and custom design work. No job too small. Based in Christchurch, NZ but service available Australia/NZ wide. Email dave<at>davethompson.co.nz KEITH RIPPON KIT ASSEMBLY & REPAIR: * Australia & New Zealand; * Small production runs. Phone Keith: 0409 662 794 keith.rippon<at>gmail.com ADVERTISING IN MARKET CENTRE Classified Ad Rates: $32.00 for up to 20 words (punctuation not charged) plus $1.20 for each additional word. Display ads in Market Centre (minimum 2cm deep, maximum 10cm deep): $82.50 per column centimetre per insertion. All prices include GST. Closing date: 5 weeks prior to month of sale. To book, email the text to silicon<at>siliconchip.com.au and include your name, address & credit card details, or phone Glyn (02) 9939 3295 or 0431 792 293. WARNING! Silicon Chip magazine regularly describes projects which employ a mains power supply or produce high voltage. All such projects should be considered dangerous or even lethal if not used safely. Readers are warned that high voltage wiring should be carried out according to the instructions in the articles. When working on these projects use extreme care to ensure that you do not accidentally come into contact with mains AC voltages or high voltage DC. If you are not confident about working with projects employing mains voltages or other high voltages, you are advised not to attempt work on them. Silicon Chip Publications Pty Ltd disclaims any liability for damages should anyone be killed or injured while working on a project or circuit described in any issue of Silicon Chip magazine. Devices or circuits described in Silicon Chip may be covered by patents. Silicon Chip disclaims any liability for the infringement of such patents by the manufacturing or selling of any such equipment. Silicon Chip also disclaims any liability for projects which are used in such a way as to infringe relevant government regulations and by-laws. Advertisers are warned that they are responsible for the content of all advertisements and that they must conform to the Competition & Consumer Act 2010 or as subsequently amended and to any governmental regulations which are applicable. siliconchip.com.au Australia’s electronics magazine July 2021  111 Also, gate driver IC3 could have been damaged when the IGBT failed by applying a high voltage to the drive pin via the gate. The series-connected thermistor could also have become faulty, so check or replace that. Suitable white LED for tachometer I have several machine tools, some with variable speed drives (up to 12,000rpm) for which a reasonably accurate tachometer would be very useful. I have a couple of cheap Hall effect tachos but find them rather limited. After looking through many designs, I selected your August 2008 design as a suitable basis for a built-in tachometer (siliconchip.com.au/ Series/52). I have all the parts required for construction except the PCB. I produced very mediocre results with toner transfer and failed completely with the paint ablation method using a 7W laser. I am now waiting for the delivery of photo-sensitive film, with which I hope to get satisfactory boards. I have been experimenting with cupric chloride etchant and have been very pleased with the results. I made the initial cupric chloride by direct solution of copper metal into hydrochloric acid with air bubbling (as widely referenced on the web) before realising that I could have started with readily available copper sulphate/hydrochloric acid and saved some work. I think a strobe could be useful, so I added it to the project. However, I find that the types specified (eg, Cree XR-C white) appear to be no longer available. Jaycar does list them but as a discontinued line. An internet search found many high-intensity LEDs, but I struggled to find any that seemed equivalent or suitable. Can you offer any suggestions? (D. F., Bentleigh, Vic) • We suggest that you use the 1W LED available from LEDsales (www. ledsales.com.au), which is listed as a replacement for the star or Cree LED specified: siliconchip.com.au/link/ ab9a SMS Controller is out of date I bought a kit to build the SMS controller project, described in two parts in your magazine in 2004 (October & November; siliconchip.com.au/ Series/100), but I never got it working. I want to have another crack at it and was wondering if it is still possible to purchase a copy of the articles. (D. W., Currumbin Valley, Qld) • You can purchase back issues through our website. Those two particular issues are available at the following links: siliconchip.com.au/ Shop/2/423 & siliconchip.com.au/ Shop/2/425 For those back-issues that are unavailable (eg, due to being sold out), you also have the option to purchase the digital version or an article scan. Having said that, we don’t think you would be able to get the SMS Controller working now since all GSM networks in Australia have been shut down. You would need to build something like our 4G Remote Monitoring Station instead (February 2020; siliconchip. com.au/Article/12335). SC Advertising Index AEE ElectroneX........................ 25 Altronics...............................87-90 Ampec Technologies................... 9 Dave Thompson...................... 111 Digi-Key Electronics.................... 3 element14................................... 7 Emona Instruments................. IBC Hare & Forbes....................... OBC Jaycar............................ IFC,53-60 Keith Rippon Kit Assembly...... 111 LD Electronics......................... 111 LEDsales................................. 111 Microchip Technology.................. 5 Mouser Electronics.................... 11 Ocean Controls......................... 94 PMD Way................................ 111 Silicon Chip Shop...........104-105 Switchmode Power Supplies....... 8 The Loudspeaker Kit.com......... 95 Tronixlabs................................ 111 Vintage Radio Repairs............ 111 Wagner Electronics................... 10 Notes & Errata Advanced GPS Computer, June 2021: in the parts list on p29, the catalog code given for the laser-cut lid was SC5083, but that is the original ‘inset’ lid to suit the 3.5in touchscreen. As mentioned in the article, a different lid is needed to give enough clearance inside the box. The correct catalog code is SC5856. Mini Arcade Pong, June 2021: if you can’t get the 7450 or 74LS50, you can use the 74LS51, which is more readily available. To use the 74LS51, pins 11 and 12 need to be tied high (they must be left open if using the 7450). You can do this by bridging them together and then running a short wire link to pin 14. Refined Full-Wave Motor Speed Controller, April 2021: we have created an alternative version of the PIC firmware, 1010221B. HEX. This works identically to the original (A) version, except that it won’t start the motor if the speed pot is not at zero when power is applied. You need to rotate the speed pot to zero and then back up to start the motor. This safety feature could be useful in some situations. USB Flexitimer, June 2018: in the circuit diagram (Fig.1) on page 26, LED2 and LED3 are swapped. LED2 (ON) connects to pin 5 of IC1 via a 3.3kW resistor, while LED3 (OFF) connects to pin 2 via another 3.3kW resistor. The August 2021 issue is due on sale in newsagents by Monday, July 26th. 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