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DECEMBER 2020 ISSN 1030-2662 12 The VERY BEST DIY Projects! 9 771030 266001 $995* NZ $1290 INC GST YUZXYUZ INC GST Automotive Electronics • • • • • Uses Li-ion or LiPo cells Little to no EMI generated Battery over-discharge protection Reversed cell protection 24-135V HT and 1.2-2.5V LT Self-made PCBs using a laser Battery-Powered Supply for Vintage Radios Dual Battery Lifesaver Volt/Amp Panel Meters siliconchip.com.au Australia’s electronics magazine protect your batteries from damage December 2020  1 low-cost ● miniature ● DC awesome projects by On sale 24 November 2020 to 26 December 2020 Our very own specialists have developed this fun and challenging Arduino® compatible project to keep you entertained this month with special prices exclusive to Club Members. BUILD YOUR OWN: “Game of Life” Wall Thermostat Looking for a conversation starter in your home? Build our ‘Game of Life’ wall thermostat using our new XC4390 addressable RGB LED light strip. The display uses bright vivid colours from the strip to show off the temperature and interesting patterns of “Conway’s game of life”. It will also add some colour to your home’s décor too. SKILL LEVEL: Intermediate TOOLS REQUIRED: Soldering, Side Cutters & Knife WHAT YOU NEED: 1 x 2m RGB LED Strip with 120 x Addressable RGB LEDs XC4390 $29.95 1 x Leonardo Tiny Development Board XC4431 $21.95 1 x Temperature and Humidity Sensor Module XC4520 $9.95 1 x Breadboard Jumper Kit WH3032 $4.50 4495 $ SEE PARTS & STEP-BY-STEP INSTRUCTIONS AT: www.jaycar.com.au/wall-thermostat See other projects at www.jaycar.com.au/arduino SAVE 30% KIT VALUED AT: $66.35 Frame not included. For decorative purposes only. 10-PCE JUMPER LEAD SET SMALL BREADBOARD LAYOUT PROTOTYPING BOARD ’t e n o D t Th ge tials r o F sen Es Transfer your breadboard design without having to rework it. Includes five holes on each side per row and power rails running the length of the board. • 25 rows / 400 holes HP9570 Each cable consists of a pin to alligator clip. Multicolour. 20cm long. WC6032 ONLY 4 $ 4-PCE MINI PICK & HOOK SET 95 Ideal for use on O-rings, springs, snap rings, washers, checking soldering joints, etc. Stainless steel heat treated points. ONLY TH1762 1595 $ 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 Shop the catalogue online! Free delivery on online orders over $99* Exclusions apply - see website for full T&Cs. * CLUB OFFER BUNDLE DEAL ONLY 995 $ ASSORTED LED PACK - PACK OF 100 Contains 3mm and 5mm LEDs of mixed colours. Even includes 10 x 5mm mounting hardware FREE! ONLY ZD1694 2495 $ Looking for other projects to do? See our full range of Silicon Chip projects at jaycar.com.au/c/silicon-chip-kits or our kit back catalogue at jaycar.com.au/kitbackcatalogue www.jaycar.com.au 1800 022 888 Contents Vol.33, No.12 December 2020 SILICON CHIP www.siliconchip.com.au Features & Reviews 12 Automotive Electronics, Part 1 Cars have improved drastically over the last few decades. Much of this improvement is due to the expansion and integration of electronics such as the engine control unit, infotainment, cruise control etc – by Dr David Maddison 36 Making PCBs with a Laser Engraver or Cutter PCB prototypes are pretty cheap to order online, apart from postage, but it’s a long wait if you only want one or two boards. Using a laser cutter can be an inexpensive way to etch your own boards – by Andrew Woodfield 48 A Closer Look at the RCWL-0516 3GHz Motion Module Leading on from the short introduction we did on this module in February 2018, we take a more detailed look about the operation of this device and what modifications you can make to it – by Allan Linton-Smith Cars are constantly becoming more advanced and complex due to the inclusion of electronic systems. Let’s take a look at the various electronic systems that are used today – Page 12 76 El Cheapo Modules: Mini Digital Volt/Amp Panel Meters A surprising number of low-cost miniature panel meters have come onto the market lately. They display voltage and current (and sometimes more), with this article focusing on the DC variants – by Jim Rowe Constructional Projects 26 Power Supply for Battery-Powered Vintage Radios For most vintage radios, A & B batteries are extremely difficult to obtain. This power supply lets you use common Li-ion or LiPo cells to provide the A & B supplies for battery valve sets with HT in the range of 24-135V and LT of 1.22.5V – by Ken Kranz & Nicholas Vinen 44 Dual Battery Lifesaver This simple project helps protect rechargeable batteries from being drained if a device is left switched on. It works with devices that run from a single battery, or two separate batteries like our Supply above – by Nicholas Vinen This Power Supply makes it easy to modernise your battery-powered vintage radio sets. It uses Li-ion or LiPo cells and supplies a wide-range of high tension (HT) and low tension (LT) voltages – Page 26 68 Balanced Input Attenuator for the USB SuperCodec Pt2 Following on from the description of how the Input Attenuator add-on for our USB SuperCodec works, here’s how to assemble and test it – by Phil Prosser 90 Flexible Digital Lighting Controller – part three In the next part of the series, we’ll show you how to use RGB LEDs with the Lighting Controller and in conjunction with mains lighting – by Tim Blythman Your Favourite Columns 61 Serviceman’s Log A brush with disaster – by Dave Thompson Here’s a low-cost and relatively simple way to make your own PCBs using a laser engraver or cutter – Page 36 85 Circuit Notebook (1) Automatic tyre inflator/deflator (2) ‘Infinite’ impedance AC source (3) Controlling model railway points with a servo 100 Vintage Radio 1928 RCA Radiola 60 superhet – by Dennis Jackson Everything Else 2 Editorial Viewpoint 4 Mailbag – Your Feedback 98 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 Our new Dual Battery Lifesaver can be used to protect two separate batteries from being drained by wayward devices – Page 44 December 2020  1 www.facebook.com/siliconchipmagazine 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 Art Director & Production Manager Ross Tester Reader Services Ann Morris 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 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 (12 issues): $105.00 per year, post paid, in Australia. 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. E-mail: silicon<at>siliconchip.com.au ISSN 1030-2662 Printing and Distribution: Editorial Viewpoint Saying goodbye to Adobe Flash We have been using Flash to deliver our online magazines since 2012. Back then, there weren’t many alternatives. Flash has been moving towards obsolete status since 2017, probably because Adobe got sick of patching security bugs in it. Flash has to be in the running for the buggiest software ever written! Adobe’s official line has been that the features of HTML5 (especially the newly introduced Canvas) could replace Flash’s functions, so it was no longer needed. While that’s probably true, it’s an oversimplification of the situation. If you have access to their (expensive) Flash software, you can load simple Flash animations and then export them to HTML, as long as you don’t mind the file size growing significantly. But that would never work with our online magazines. They’re too large; even if the conversion worked, the resulting HTML files would be over 100MB, which is not practical. Part of the reason that we used Flash in the first place is that, at the time, Adobe made it easy for us. InDesign could export a layout directly to a Flash file. We then just had to upload that straight to our website to get an exact on-screen representation with minimal fuss (and nice page-turning animations). It worked well – as long as you had the Flash plugin installed on your system. With the end of Flash looming, I investigated many other options. I went through at least a dozen possibilities, but found none of them to be satisfactory. Virtually all of them resulted in some pages of the magazines looking wrong (in some cases, many pages!). Early on we tried to use EPUB but found it lacking. Firstly, not all fonts would display correctly, and the page layouts just wouldn’t display correctly exported as fixed or reflowable layouts. We decided in the end to stick to a HTML5-based viewer. The main problem is that while the HTML5 Canvas element works exceptionally well for certain things, it can’t handle some of the effects that we use in the magazine, resulting in some pages loading incorrectly. To solve this, I had to go through every page of every magazine back to about 1995 (around 30,000 pages!) and identify the problematic ones. We then had to experiment with various approaches until we came up with several different ways to alter the content so that it looked the same, but would display correctly on the HTML5 Canvas. We are still ‘mopping up’ a few very minor problems, but overall our online magazines (approaching 400 in number) look very good. Our new HTML5-based online viewer has been deployed and is now the default. So you no longer need any plugins to view magazines on our website, as long as you have a modern web browser. The good news about the new viewer is that the HTML5 rendering has excellent (almost unbelievable) clarity. I am blown away with how good text and diagrams look on a 4K monitor. It’s usable on lower resolution monitors (eg, 1080p) but a 2560x1440 resolution is much better. As 4K displays are now becoming more mainstream, I expect more of our readers will be using them in future, with ideal results. The slightly bad news is that specific pages of the magazine can take a bit longer to load, especially on older computers with slower CPUs. But I think that is a worthwhile trade-off for the improved clarity. You can also download the PDF and view it on most desktop viewers. So please bear with us while we clean up any small remaining problems with the new system, and tweak it to improve usability on smaller devices like smartphones. It should be pretty well sorted by early next year. And if you haven’t looked at our online edition in a while, now might be a good time to revisit it. 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 December 2020  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”. Xmas projects & soldering SMDs It’s good to see another round of Xmas Ornaments from Tim Blythman (November 2020; siliconchip.com.au/ Article/14636). Tim has successfully introduced me to working with SMT devices with the tiny Xmas Tree last year (November 2019; siliconchip. com.au/Article/12086). I have found that soldering SMT devices is less difficult than some people imply. In particular, I found the reverse (or self-closing) tweezers much easier to use than a clothes peg which turned out to be much too big to conveniently handle tiny components. I use solder paste in a syringe which has a very fine nozzle, which allows a suitably small amount of paste to be applied to pads. The fine point soldering iron is adequate for the soldering, and I’ve only made one or two mistakes which were easily corrected. Thanks again, Tim, for some engaging projects that the grandkids have, and will, I hope, enjoy. Eric McAndrew, Capel. WA. Response: thanks for your feedback. Note that when melting solder paste with the tip of a soldering iron, the solder paste can splatter, causing solder balls to make their way to unwanted locations. Reflowing the solder paste with hot air is safer, as long as it is done carefully. Article on capacitors desired I second your reader’s request in the November issue regarding a guide to capacitor usage. While there are plenty of web pages covering aspects of this topic, I would really value such an article as I know I can trust what you publish and that it would be up to date. At the end of your response, to show how complicated this topic is, you list all the various issues that would need to be addressed. Surely that in4 Silicon Chip dicates how worthwhile such a guide would be. Kim Windsor, Melbourne, Vic. Response: we agree that it would make for a good article and plan to start working on it soon. Oscillator rotary encoder reversed I would like to thank Silicon Chip and Andrew Woodfield for the Pocket Audio Oscillator kit (September 2020; siliconchip.com.au/Article/14563), it works well, is easy to use and I love the readout. The supplied kit needed a few minor construction hacks and interpretations but nothing insurmountable. I built the kit following the layout of Fig.3 on page 46. But I noticed that the frequency decreases as the knob is turned clockwise. I assume that either the rotary encoder is sending the opposite command to the ones that were used in the prototypes, or that the 1.8kW and 3.9kW resistors in Fig.3 are swapped. I swapped those two resistors and the unit is operating correctly. I understand the reasons that the maximum frequency is 10kHz, but I would find it far more useful if it could get to 18kHz or maybe 25kHz, even with excessive distortion and a flaky readout. I can’t hear these frequencies; I am just trying to catch the distortion caused by them. I really appreciate the magazine as it has a nice mix of topics. You folks are making many people happy, stimulating a swag of future professionals, exposing theoretical types to a lot of real-world experiences etc. In other words, doing a bloody magnificent public service! One of my many pleasures/aims/desires in life is to gently work at making the world a better place. Thank you for your efforts in that direction. Well done! Before Silicon Chip, I read Australia’s electronics magazine Electronics Australia, and I was reading electronics magazines even before that – struth! Len Braithwaite, North Sydney, NSW. Response: we built our prototype with the resistors in the positions shown, and it worked correctly, so we have to assume that different batches of encoders can have the encoder pins swapped. That’s frustrating, especially since it’s almost impossible to tell until you’ve mounted the encoder, but luckily swapping those two resistors is all that’s required to fix it. Vintage Radio index at Radiomuseum We have put up an index on www. radiomuseum.org to help enthusiasts locate models mentioned in Silicon Chip Vintage Radio columns in our ‘museum’. You can find a link to the latest version of the index (as a PDF) at the bottom of this page: siliconchip. com.au/link/ab5o Gary Cowans, Australian Administrator for Rmorg, Woodvale, WA. Lack of DAB+ reception in tunnels Unless my memory is mistaken or technology has changed over the years, the lack of digital radio reception in Sydney tunnels is due to the way the system is set up. If the setup was purely a high-gain antenna feeding a highpower amp connected to leaky coax, then every AM and FM service that can be received outside the tunnel should be received inside the tunnel. However, this is not the case. You will find that only the mainstream Sydney broadcasts can be received in the tunnels. For example, I have no trouble receiving 2GO/MMM Central Coast 107.7FM or The EDGE 96.1FM in Sydney in general, but not in our tunnels. Way back in my Telstra days, about 20 years ago, I attended to a data service fault at one of the tunnel control siliconchip.com.au centres. In one of the rooms, there were racks of AM and FM receivers and corresponding transmitters. All radio reception in our tunnels has to have the ability to be interrupted for tunnel announcements and emergency information. The only way to do this is to bring each radio service back to audio with a receiver, feed that audio into the info switch and then back into individual transmitters for that corresponding station. When 2UW was multicasting on both AM and FM before it officially stopped its AM transmission, it took about four weeks to get the FM reception in our tunnels. Hence the lack of digital reception in our tunnels. I retuned my digital radio, and currently there are nearly 70 services spread across the three digital frequencies of 9A, 9B and 9C. I can see several problems with retransmitting these services in tunnels. Firstly, every tunnel will require at least another 70 individual receivers to bring each station back to audio to feed via the info switch. This is complicated by the fact that the bitrates for stations can vary from 32kbps (eg, The EDGE) up to 128kbps or more (2CH, 2GB). These individual audio streams would then have to be fed back into the appropriate transmitter in the correct slot set up to the right bitrate. This could add to the 10-or-so seconds delay already heard in DAB+ broadcasts, compared to the same content on AM or FM. Then there is what I think is the biggest problem, the constant reshuffling and changing of digital stations. In the early years, 2DAY only had one service, now it has six. What problem will this cause the arrangement of digital in the tunnels? I can’t imagine a simple solution. Simon Kareh Penshurst, NSW. Calculating series & parallel resistor values On page 108 of the October 2020 issue, there is a link to a suggested website for calculating series and parallel resistors. That site works OK, but you might find this one more useful: siliconchip.com.au/link/ab5r It has conversions and calculators for 24 types of data, including series and parallel resistors and capacitors. I won’t list the other items, but I’m sure 6 Silicon Chip they will be useful to many people. It also includes a section to request an additional calculator if needed. Bob Denton, Hastings, Vic. Experimenting with PV hot water I have seen a few articles in Silicon Chip over the years about using solar panels to generate power for an electric hot water system. This interested me, but it never seemed feasible. However, second-hand solar panels are now cheaply available on Facebook and Gumtree. Also, technology has improved to reduce the cost of necessary devices further. So, I have made up a system that is working well. It only uses two 250W panels, as it is just a project to see if it stacks up. It is still a work in progress, as I am presently manually switching the inverter on in the morning, and off in the afternoon. I am using an ESP32 to monitor the solar power, and this is currently powered from a mains plugpack. In the near future, I will be adding a DC-DC converter to power the ESP32, and automating the stop/start for the inverter depending on the available light. I am using a 60V, 2kW “power frequency inverter board” sourced from AliExpress for $50. This board produces a sinewave from the DC supply voltage, giving around 36V AC from 60V DC. This is then fed to a large, heavy transformer to step up the voltage for driving the 3.6kW element in my hot water system. The efficiency of the inverter/transformer arrangement is 80%. I connected a Variac into this system to find the optimal voltage to drive the hot water element. Rotating it allowed me to find the maximum power point (MPP). Above the MPP, the power from the panels decreases exponentially. Unfortunately, the MPP is not static, and changes with clouds, time of day etc. To avoid going past the MPP, I selected a transformer with an output voltage slightly less than the peak with the panels in direct sunlight. This compensates somewhat for the many cloudy days in Cairns, but means I am not extracting maximum power from the panels during excellent sunny periods. So it’s a bit of a compromise, but it works reasonably well. The ESP32 sends solar data to a Raspberry Pi, which uploads data to Australia’s electronics magazine PVOutput at pvoutput.org/intraday. jsp?id=30164&sid=79430 Now that the concept has been shown to be feasible, I plan to set up a bigger installation with eight solar panels driving our primary hot water system (which has a 2.4kW element). When it rains for a month in Cairns, the backup option is to have a threepin plug on the hot water system, so I can manually change it over to mains power. I estimate the total cost outlay for the bigger system will be recouped within 1-2 years if I build it using secondhand panels. Sid Lonsdale, Cairns, Qld. Micromite Plus capacitor problem I came across a problem with the Micromite Plus recently. When I upgraded to MMBasic 5.05.03, one of my MM+ boards would not run the DAB+ digital radio software. It crashed many times every second, rebooting with a “bus error”. My other Micromite crashed differently; it would throw “font #16” or “font #8” errors, despite neither of them being used by the BASIC program. Versions 5.05.01 and 5.05.02 both worked fine on the same hardware and with the same BASIC code. I had seen this sort of thing on a previous (old) PIC32 design I had built years ago, and it turned out to be the 10µF capacitor on the PIC32’s Vcap pin. Increasing the Vcap capacitance fixed the problem both then, and again now. I piggy-backed a 47µF tantalum capacitor onto the 10µF X5R on the micromite board, and the problems went away. I guess that 5.05.03 is ‘exercising’ the internal 1.8V rail a little harder than previous MMBasic versions exercised it. It may be that either that the 10µF value specified in the data sheet is marginal, or the capacitors supplied in the Silicon Chip Micromite kits are marginal or not as low in ESR as they are claimed to be. Either way, the fix is easy. Stefan Keller-Tuberg, Fadden, ACT. Response: we purchase brand-name 10µF X5R capacitors (eg, Samsung or Taiyo Yuden) from reputable distributors. Their ESR ratings are much lower than the maximum of 1W specified by Microchip; they should be in the range of 0.01-0.1W. So we suspect siliconchip.com.au Wide range of fully equipped products up to R&S Essentials Promotion FULL BENCH. HIGH VALUE. 50 % off Order now through 31 March 2021 Up to 50 % off our signature instrument bundles. Pre-configured for you. Distributors www.rapid-tech.com.au/ https://au.element14.com/b/rohde-schwarz siliconchip.com.au Australia’s electronics magazine December 2020  7 DEAD OR DYING BATTERIES IN YOUR EBIKE? Advancements in automotive electronics SEGWAY? MOBILity BUGGY? GOLF CART? ESCOOTER? Premier Batteries can recell and/or custom manufacture Lithium Ion batteries for Segways, Ebikes, Electric Golf Carts, Scooters and Mobility Buggies – often with increased capacity and range etc. Quality cells are used and batteries are Fully Guaranteed PREMIER BATTERIES High quality batteries for all professional applications SUPPLIERS OF QUALITY BATTERIES FOR OVER 30 YEARS email: info.premierbatteries.com.au Web: www.premierbatteries.com.au 8 Silicon Chip that your first suggestion, of the 10µF specification being marginal, is the correct one. Of course, nominally 10µF capacitors can have values of around 8-9µF, or even lower at elevated voltages and temperatures. Still, we thought that the person writing the specification for the PIC32 would have taken that into account. Regardless, it looks like we will have to switch to supplying 15µF or 22µF ceramic capacitors in future kits to solve this. I thoroughly enjoyed the article on OBD2 (September 2020; siliconchip. com.au/Article/14576). When I first came to Australia, fuel injection, engine management and electronic ignition systems were still in their infancy. It seemed at that time that Bosch had a monopoly on the various electronic modules used. I have no idea how many Bosch 024 ignition modules I fitted or how many complete distributors I fitted to various vehicles (especially the early Ford Falcon with centrepoint injection). I used to exchange one of those distributors pretty much every day. We overhauled the old unit in-house with new bushes and sensors, except where the shaft itself had worn. I became a dab hand at reinserting those distributors back into the engine and slotting them into the oil pump feed, which was a hex-headed drive deep in the bowels of the motor. That vehicle had a rudimentary diagnostic system which would flash a light plugged into a socket under the bonnet. You could then trace out the fault with a wiring diagram. We also saw a lot of imported vehicles with various methods of diagnostics, usually by shorting a particular pin to GND and watching the CEL (check engine lamp) on the dashboard. Subaru had a few harness connectors below the steering shaft and above the driver’s knees, and connecting two would start the CEL flashing. Then came the Holden VL Commodore with the Nissan engine. Oh, what a car, very fast and powerful but with a few problems. For example, the optical pickup in the distributor (crank angle sensor) had a plate with holes punched through it to send the crank position and RPM to the ECU. Those sensors gave a lot of trouble, Australia’s electronics magazine as did the mass airflow meter also fitted to this Commodore. That optical disc could also be inserted into the distributor the wrong way around, resulting in a misfire on the number four cylinder. I also saw several of these vehicles with the optical slots filed wider, which I was told elicited a bit more power from the engine. The onboard diagnostic system was activated by turning a very small variable resistor through a small aperture on the side of the ECU, with the ignition on but the engine not running. Considering the ECU is behind the left-hand kick panel, this meant lying down on the floor in front of the passenger seat to turn that resistor. There are also two LEDs inside that aperture, one red and one green. The red showed tens when flashing, and the green showed the ones. Two red flashes and two green flashed meant the code was 22. Those same LEDs would show the sweep of the voltage coming from the oxygen sensor when the engine was running and the sensor up to temperature. That ECU also had inbuilt testing; on the initial DTC readout, several codes would be sent. It would send a code for the throttle position sensor, cleared by opening and closing the throttle. Then we would see a gear position sensor fault, cleared by moving the gear selector from park through each position and then back to park. Next would be a start inhibit fault, cleared by just quickly flicking the ignition switch into the start position. Usually, the last inbuilt test code was for the air conditioning and again, cycling the A/C switch on then off would clear that code. Next came the actual trouble code(s). The company I worked for at that time spent a large sum of money on a diagnostic package which connected to various engine points: the ignition coil negative, an inductive sensor on the cylinder number one plug lead, a second on the ignition coil to distributor lead, a pair of leads to the battery terminals and one to the battery connection on the alternator. With the DFI system (direct fire ignition or wasted spark ignition) in the next-generation Commodore, our diagnostic package was updated with new software and a new sensor lead package to help find problems on a car with no distributor and with multipoint injection. siliconchip.com.au I fixed a great many ECUs in my time; most had burnt out transistors and components that had been destroyed because someone had tried to jump-start the car with the jumper cables the wrong way around. I also saw many transmission sensors and solenoids fail, especially when people used standard transmission fluid (DEX III) instead of the automatic transmission correct fluid (TQ95). Standard fluid has an additive which strips the layer of varnish from the coils in the solenoids, causing all kinds of problems; TQ95 does not have that additive. When I left that employer to start work in a whole new town, I discovered problems with the ECU used in the Mitsubishi Magna. The electros used in that ECU would leak or burst, and that area of the PCB would heat up, eventually burning a hole all the way through the PCB! It was an easy diagnosis; you could smell the burnt ECU as soon as you opened the car door. I would repair the PCBs where I could, but a great many had large holes and severe damage. These required a new ECU to be fitted. I made sure that the suspect electros were replaced with high-quality components before doing so. After that, ECUs started becoming more complicated. They handled not only engine management and transmission control, but also air conditioning and climate control. Then security was added, keyless entry, cruise control, anti-skid braking and SRS (supplementary restraint systems), ie, airbags and seat belt tensioners. Then we had a body control module; the list goes on and on until we reach today’s vehicles, with multiple computers controlling an entire library of systems including drive-by-wire and intelligent braking, intelligent cruise control, lane centring, blind spot warnings and self-parking. I imagine that in the years to come, manufacturers will master all the issues with self-driving cars, flying cars and myriad other science-fiction inventions. Dave Sargent, Maryborough, Qld. Preparing for disaster Silicon Chip is a fine magazine. I know what it’s like to edit a technical journal, having managed two so far. I have also been a technical writer in siliconchip.com.au charge of producing responses to requests for tender where risk management was a major factor. I have fitted Solar PV panels on my roof to learn about using El Sol for electric power. Your approach on backup power (January 2020; siliconchip.com. au/Article/12215) left me wondering if there were a better way to achieve your end. So, I went back to some of my writings on risk management, in particular, based on AS/NZS 4360. Here is a generalised risk management approach that can be applied to all manner of potential problems we face. 1. List every possible event that could lead to damage or loss. 2. Assess the consequence of each such event. 3. Estimate the probability of occurrence of each precipitating event. 4. Multiply the consequence by the probability for each precipitating event. List these in decreasing order. 5. Assess the cost of dealing with each event, whether attenuating or eliminating each precipitating event, or providing a work-around for the inevitable. 6. Put these mitigation costs against the products list from step 4. 7. Discuss the results of your analysis with others likely to be affected. 8. Make plans for agreed mitigations. If that seems very complicated, consider the following: 1. You might want to focus on just a few nasties such as loss of electricity, loss of gas pressure, water management problems (loss of potable water, sewerage or flood), transport disruption, damage to roads, land management issues (eg, erosion, landslide, tremors or earthquakes). 2. Calculate the consequences in monetary terms. Look to insurance firm valuations if unsure. 3. Energy providers can tell you the likelihood and duration of outages based on historical records. The Bureau of Meteorology can provide estimates of temperatures, rain, wind and wave movements. State governments can probably tell you the likelihood and duration of water management failures; they can also tell you the likelihood of unplanned events, such as road, rail and bridge disruptions. Local councils can advise on land management issues, such as anticipated subsidence, road resurfacing. Australia’s electronics magazine December 2020  9 even though we were sitting by the phone. We’ve since pur4. Wilfredo Pareto observed that 80% of the costs of dochased an office mobile phone, so we can redirect calls ing things were accounted for by around 20% of the inwhen necessary. puts. This has become known as the 80/20 rule. Your list We spent hours with NBN tech support to no avail. So of consequence-probability products will probably show we decided to try rebooting the Telstra-supplied NBN routthis effect; ie, the first few items in your list will account er, which was working fine for internet access at the time. for the majority of your potential woes. That fixed it. 5. For each of the items high on your list, identify several solutions to deal with each event. These might preComments on backup power and DCC vent the untoward event or provide a work-around because Thank you for both the January 2020 and the February the event is inevitable but unpredictable (eg, running the 2020 editions of Silicon Chip. As usual, they were worth fridge on a UPS in case of a possible power outage). Or you reading. might decide to take out insurance against it, or consider The January 2020 Editorial Viewpoint and the accompaputting up with the nuisance (eg, wear warmer clothes if nying article on emergency backup power raised the quesyour heater fails mid-winter). tion: is it economical to maintain emergency backup pow6. By listing the costs of your ‘solutions’ against the er? To decide, there are two basic questions. How much consequence-probability products, and running a cumupower is required, and for how long? lative total on the solutions, you get an idea of the size of For a refrigerator, the cheapest and most reliable method your problem(s). for short term backup is to maintain “freezer bricks” in their 7. Present the results of your analysis to your family. RAYMING TECHNOLOGY frozen state and for the long term, maintain a working petSome solutions may require the co-operation of neighbours engined generator. Batteries are simply not economical or local authorities. PCB Manufacturing and PCB rol Assembly Services for the occasional short term power failure. 8. How will you pay for your solutions? For instance, Fuyong Bao'an Shenzhen China For our ‘must-have’ electronic devices, a generator is some insurance firms offer incentives to prevent problems, 0086-0755-27348087 overkill except for extended power outages, and batteries such as by offering reduced premiums on home and conSales<at>raypcb.com become more viable. Regardless, our governments and the tents insurance if you install a burglar alarm, or a UPS for power suppliers will do their best to maintain power and your freezer. www.raypcb.com to restore it when it is lost. Brian Clarke, BE, MBA, PhD, CPEng, Fellow Eng I have been trying to develop a DCC interface, which Aust, IPEC Eng (Aust), Loftus, NSW. has taken most of my energy of late. The DCC standard is such a mad dog’s breakfast, and I had written quite a large NBN reliability not as good as POTS comment/complaint about it, but decided not to send it to I have been on NBN for 2½ years and still have problems you. It was more appropriate for a model railway magazine. from time to time. When first connected, I lost my landline I was hoping to get some tips for my system from the DCC number and had to have this number redirected to my mostation article in the January 2020 edition (siliconchip.com. bile until it was fixed. Even now, I lose my landline conau/Article/12220), but I was disappointed. However, the nection and have to switch off my modem for five minutes. project did introduce me to the BTN8962TA half-bridges When the Telephone Directory came out early last year, and they are impressive. If I didn’t have a large quantity after 25 years I was no longer listed because I had changed of N and P channel FETs, I would use them. to the NBN and had to apply to be relisted. If I had the I’ve found that I could not create a DCC station using chance to go back to the old reliable system, I would do a PIC microcontroller alone. I was forced to implement it in a flash. I think the NBN should be renamed to No a double-buffered counter using a few discrete logic ICs Bloody Network. to create the DCC waveform and use the PIC to control Richard Cannan, it. The reason was jitter in the polarity reversals of the Warilla, NSW. DCC waveform. The small PICs that I wanted to use have Comment: we had a day-long dropout of the phone sera double-buffered PWM duty register but not a doublevice at our office a few months after switching to the NBN. buffered period register. It was frustrating because customers could not reach us RAYMING TECHNOLOGY Fuyong Bao'an ,Shenzhen, China Tel: 0086-0755-27348087 email: sales<at>raypcb.com web: www.raypcb.com PCB Manufacturing and PCB Assembly Services 10 Silicon Chip Australia’s electronics magazine siliconchip.com.au Considering that the DCC standard allows for a large period variation of the “0” pulse but only a few microseconds for the “1” pulse, it was impossible to ensure that the necessary precision would be met using an interrupt service routine without a double-buffered period register. I then wondered about the Arduino that was used in your project. What did the programmers of DCC++ do? I checked the specifications of the ATmega328P, and found that the Timer1 module has a double-buffered period register. But there was no mention in the October 2018 project of the quality of the DCC waveform. I can only assume it was acceptable. The project did raise one big concern with me which I believe is also partly to blame for the susceptibility of IoT devices to hacking. That problem was the subject of the February 2020 Editorial Viewpoint. Unless a person is very familiar with a language and particularly with tricks and short-cuts, it is very easy to miss flaws in the routines. When using a library, how many programmers check the validity of its routines before using them? I doubt that there are very many, and I am sure that inexperienced programmers will use anything that is stated to do a task without question. George Ramsay, Holland Park, Qld. Comments: I believe I covered the reasons for choosing a battery backup system quite thoroughly in the article. Granted, I had a somewhat unusual reason for preferring batteries. If you have the space to operate a generator, don’t need automatic fail-over and are willing to do the maintenance to keep the fuel fresh, it is indeed the cheapest option for a given amount of power over a long period. But keep in mind that you can get much cheaper batteries than the one I bought. For example, Rockby is currently selling a 12V 110Ah AGM deep cycle battery for $291.50 (Cat 38698, pickup only). Add a 2kW modified sinewave inverter from Jaycar (Cat MI5024, $299) and a charger you probably already have, and you can keep a typical fridge/ freezer running for around 24 hours for less than $600. Granted, Jaycar’s Cat MG4508 2kW inverter generator will keep the same fridge/freezer and other appliances running for a lot longer for just $100 more. But I think both solutions deserve consideration. Regarding DCC, if you have precise waveform generation requirements, it pays to check the microcontroller data sheets carefully to choose the best one. Micros designed for motor control generally have much more sophisticated and precise PWM generators, and keep in mind that serial interfaces are often a good way to generate an accurately timed pulse train. Another factor to consider is that some of the better micros (eg, PIC32s) allow you to set interrupt priority levels. So you could have a timer interrupt generating a pulse train set to maximum priority. Communications interrupt handler like those for USB or serial can then be set up with a lower priority so that they won’t interrupt the critical timer ISRs. You are right that blindly using libraries can cause problems. We had many problems with some popular software I2C libraries, and when we had a look at what they were doing, it was pretty clear that the authors either hadn’t read the I2C standard or didn’t understand it! For good security, you either can’t rely on third-party communications libraries, or you need to audit them. 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Australia’s electronics magazine December 2020  11 Automo Electron Recent decades have seen dramatic improvements in the fuel efficiency, emissions and safety of cars, mostly bought about by electronic systems, along with improved structural design and materials. The number of parts involved in modern automotive electronics is mind-boggling, and the cost is becoming a significant proportion of the vehicle overall. 12 Silicon Chip Australia’s electronics magazine siliconchip.com.au otive nics Part 1– by Dr David Maddison Image courtesy: www.facebook/public/images/ 01-picture-library/ ChristophHammerschmidt/ 2016-03-16-delphi_automotive_ power_distribution.jpg Terminology V ehicle electronics can be separated into several categories including engine and transmission management, safety, driver assistance (eg, lane departure warnings and cruise control), chassis control (braking, stability and traction controls and four-wheel-drive systems), passenger comfort, navigation and entertainment. In this article, we will take a look at the history of these devices, how they are currently used and how they work. We have covered some aspects of these systems in past issues such as engine management (October & November 1993), anti-lock braking (November 1994), traction control (March 1996 & February 1999), adaptive cruise control (September 2005), cylinder deactivation (January 2009), airbags (November 2016), onboard diagnostics (February 2010) and advanced diagnostics (September 2020). We also recently described MEMS devices in detail, which are used as sensors for airbag activation and vehicle stability control. That was in the November 2020 issue (siliconchip.com. au/Article/14635), so we won’t look at those in too much extra detail. siliconchip.com.au Confusingly, ECU can stand for either Engine Control Unit or Electronic Control Unit, and ECM can stand for either Engine Control Module or Electronic Control Module. We will use Engine Control Unit (ECU) for the device that controls the engine and Electronic Control Module (ECM) for the many other devices distributed throughout a car that control various systems. An ECU that controls the transmission as well as the engine is known as a Powertrain Control Module (PCM). ECMs control particular subsystems on the vehicle, such as doors and windows, batteries, lights, steering, the sound system, navigation, stability control, braking etc. Individual manufacturers might also have their own unique names for these devices. A brief history of automotive electronics One of the motivations for electronic engine management was laws passed in California, USA that required cars from the 1966 model year to have reduced emissions of hydrocarbons and carbon monoxide. Early mechanical emission controls were inefficient and power-hungry. Controlling emissions became much easier and more efficient as electronics became more capable and cheaper. As time progressed, the laws became much more stringent and were also adopted worldwide. Vehicle emission controls were introduced into Australia in 1972 through ADR26, followed by ADR27 for gasoline vehicles and ADR30/00 for diesel vehicles in 1976. Australia’s electronics magazine December 2020  13 Fig.1 (above): the Bosch electronic controller for manual transmissions from 1965. It was way ahead of its time. Source: Bosch Media. Fig.2 (right): the main board of a Bosch D-Jetronic analog fuel injection system from around 1968. Source: https://members.rennlist.com/pbanders/ecu.htm Some selected milestones in ECU development can be summed up as follows. In the 1970s, it involved electronic control of carburettor mixtures, fuel injection and ignition timing. In the 1980s, more extensive fuel management was introduced due to the widespread introduction of fuel injection and closed-loop lambda control (air-fuel mixture setting). In the 1990s, ECUs started managing vehicle security functions, making theft much more difficult. ECUs were also introduced on diesel engines. In the 2000s, drive-by-wire throttle control and turbocharger control were introduced. Increasing numbers of sensors and controller functions were added. In the 2010s, almost all aspects of a car came under the management of the ECU or another computer system. All devices are connected by high-speed data buses, and many vehicles introduced driver assistance features. A more detailed history follows • 1965: Bosch developed an electronic control for manual transmissions, negating the need for the clutch to be depressed (see Fig.1). Several hundred of these systems were installed on the Glas 1700 car in 1965. The technology was regarded as way ahead of its time, but BMW acquired the Glas company, and they lost interest in it. • 1968: Volkswagen introduced electronically-controlled fuel injection (using the Bosch D-Jetronic system; Fig.2) on the VW Type 3. The controller was an analog device. See the video titled “Type3FISlideShow” at https://youtu. be/jIN1HZUrxL8 You can find quite a bit of documentation on the DJetronic system at siliconchip.com.au/link/ab4f and siliconchip.com.au/link/ab4g • 1969: Ford introduced the Sure-Track Braking System (anti-skid brakes) as an option on the Lincoln Continental Mark III and the Thunderbird. For more information on this, see siliconchip.com.au/link/ab4h • 1973: Chrysler introduced electronic engine control. The points in the distributor were replaced with a magnetic pickup coil, and the rotor with a reluctor (toothed wheel). Both were connected to an ECU (see Fig.4). The system was very basic but improved reliability due to the elimination of the points and rotor, provided better timing accuracy, a stronger spark and a higher RPM limit. The development of the internal combustion engine isn’t yet over. . . New engine technology such as Mazda’s SkyActiv-X, variable As an example of what is now possible, the Audi SQ7 has an valve timing, variable compression ratios and engines without electric supercharger as well as traditional turbochargers. camshafts would be impossiThe electric supercharger Passive turbocharger ble without computerised engine is used to eliminate turbo Active turbocharger management. lag and can spool up from Air recirculation valve (See the separate panel on camidle to 70,000rpm in oneIntake manifold collector Compressor activation valve less engines.) quarter of a second (while with swirl control If engine ‘accessories’ are powthe turbos are still spooling EPC bypass valve ered electrically rather than meup), after which it is disenchanically, they become easier gaged. Electric powered to control. It requires significant compressor (EPC) Electric accessories can also power, just as an engineimprove fuel economy as they driven supercharger does. have virtually no parasitic loss It is powered by a 3kW Charge air cooler Charge air X-shaped when switched off (just that of the alternator which charges a manifold alternator, which will be present re- Electric supercharger 470Wh 48V battery which gardless, although many vehicles (compressor) on the Audi SQ8. Charge air cooler powers, via a DC-DC conthese days disconnect the alterna- This device would not have been possible verter, a 7kW 12V electric without sophisticated engine management. tor much of the time too). motor on the supercharger. 14 Silicon Chip Australia’s electronics magazine siliconchip.com.au Fig.3: an Australian advertisement for the Chrysler Electronic Lean Burn system from Time magazine, November 1978. • 1973: Japan Electrical Control Systems Co Ltd, now JECS Corporation, formed as a joint venture between Robert Bosch GmbH (Germany), Nissan Motor Co (Japan) and Diesel Kiki Co Ltd (Japan; now named Zexel Corp). This gave Nissan access to Bosch electronic fuel injection systems, which were manufactured in Japan. The original systems they used were Bosch L-Jetronic with Japanese electronics, (usually) German sensors and fuel pumps and regulators made under license to Bosch by Denso. JECS produced 16-bit ECUs for the Nissan 300ZX from 1993 onward. • 1975: Ford USA introduced the EEC1 electronic engine control system. It used a Toshiba TLCS-12 12-bit purpose-designed microprocessor. The system had 2800 logic gates, 512 bits of RAM and 2kb of EPROM. The 12-bit processor arose from a requirement for a measurement resolution of 0.1% or better (8-bit resolution would give 0.39%, 12-bit resolution gives 0.024%). It appears that the system was experimental, as it wasn’t introduced into vehicles until 1978. • 1976: GM and Motorola teamed up to develop a custom CPU for engine management. This was incorporated in the Computer Command Control System or CCC for emissions control, released in 1981. You can view a PDF with details about CCC at siliconchip.com.au/link/ab4i • 1976-89: Chrysler USA introduced its Electronic Lean Burn system. In Australia, some models of the CL Valiant Fig.4: an early Chrysler (USA) electronic ignition system scheme from around 1973. Based on an image from fourforty.com. siliconchip.com.au Fig.5: the GM MISAR electronic ignition timing system from around 1977. Source: www.delcoremyhistory.com Australia’s electronics magazine December 2020  15 Fig.6: the GM Computer Command Control System (CCC), introduced in 1981. Fig.7: typical engine torque output (black) and power (blue) as a function of engine RPM at full throttle. Despite torque falling from its peak at Ntmax RPM, power continues to climb until Npmax RPM as power is the product of torque and RPM, and RPM is increasing faster than the torque is decreasing to that point. Source: x-engineer.org (including the Charger) had it, and it was widely advertised (see Fig.3). • 1977: Oldsmobile introduced MISAR (MIcroprocessor Sensing and Automatic Regulation), a microprocessorcontrolled ignition timing system on the Toronado model (see Fig.5). It comprises two LSIs with a total of 20,000 transistors. It improved fuel economy by one mile per US gallon and made the engine more responsive and smoother running. It also helped to meet emissions targets. • 1977: Motorola released the 35,000 transistor MC6801 microprocessor, and in 1978, GM became the main customer for this device as it was used in the TripMaster digital trip meter for the 1978 Cadillac Seville. • 1978: The Ford EEC-1 (Electronic Engine Control) was introduced into some US models. It controlled ignition timing, the EGR (exhaust gas recirculation) valve and the ‘smog pump’. These were the 1979 model year cars, mainly the LTD and Mercury Grand Marquis with the 351 Windsor V8 motors sold into the California market (which had stricter emission laws than elsewhere in the USA). Fig.8: power curves for one engine as a function of throttle position and RPM. This sort of data is incorporated into engine maps. Source: x-engineer.org 16 Silicon Chip • 1979: Ford USA introduced the EEC-2, which controlled an electronic carburettor with oxygen feedback and a fuel supply stepper motor, ignition timing, the EGR valve and the ‘smog pump’. It used the Intel 80A49H processor. • 1980: Ford USA introduced the EEC-3, with fuel injection control. • 1981: GM introduced CCC, which (as described above), started development in 1976 (see Fig.6). • 1983: the ZF 4HP22 EH automatic transmission was introduced in the BMW 745i. It had electronic control over the pressure regulator, torque converter lockup and shift valves (previous automatic transmissions used hydraulic control). Fig.9: petrol engine emissions of various combustion byproducts as a function of the air/fuel ratio. The ratios for best power and best fuel economy are shown in red and blue respectively, along with the ‘compromise’ target range (green) to give good torque, power, economy and emissions. Deviations from the ideal stoichiometric air-fuel ratio of 14.7 are permitted under certain circumstances such as acceleration, maximum power, best economy or start-up, among others. Source: Toyota Motor sales literature. Australia’s electronics magazine siliconchip.com.au Fig.10: a graph showing how torque, fuel consumption and pollutants change with ignition timing. TDC stands for “top dead centre”, the point at which a piston is at its upper limit of travel; advanced timing is where the spark occurs before TDC during the compression stroke while retarded timing is where it happens afterwards. Based on a graph from what-when-how.com • 1984: Ford USA introduced the EEC-4 with OBD-1 support. It used the Intel 8061 microprocessor. The EEC-4 is a favourite among Ford performance engine enthusiasts, and it can run nearly any engine. It apparently has engine control features just as advanced as modern controllers. Extensive documentation for modification is available, for example, see www.tiperformance.com.au/Reference/ eectch98.pdf (we do not endorse modification; modify ECUs at your own risk). This gives a good insight into how these devices work at a highly detailed level. • 1986: Carnegie Mellon University developed a selfdriving car, the Nav lab-1. See the video titled “NavLab 1 (1986): Carnegie Mellon” at https://youtu.be/ntIczNQKfjQ and www.ri.cmu.edu/robotics-groups/navlab/ • 1986: Chrysler introduced multiplexed wired communication modules. These provide weight, space and l l l Fig.11: an engine map or ‘fuel map’ showing manifold absolute pressure (MAP) as a percentage vs engine RPM, with each point in the table indicating the volumetric efficiency. This is the amount of air flowing into an engine compared to its theoretical maximum (it can exceed 100% in some circumstances). This tells the ECU how much fuel to inject for a particular MAP and RPM. Live ECU data is shown above. Source: Summit Racing Equipment. • • • • • cost saving as much less wire has to be used, since communications can be over a single wire rather than multiple wires. 1987: the standards for the CAN (controller area network) bus were introduced. 1991: the first car with a CAN bus goes on sale, the Mercedes Benz W140 series which included the 300 SD, CL 500, CL 600, S 320, S 420 and S 500 sedans. 1991: the CAN 2.0 bus specification was published by Bosch. 1991: a partnership was formed between Ford and Motorola to develop a PTEC (powertrain and transmission electronics controller) using a Motorola PowerPC chip. This replaced Ford’s EEC-IV in 1994, which used an Intel chip. 1993: the CAN bus physical layer and data link standards were published by the ISO. The physical layer standards are not part of CAN 2.0. Repairing your ECU or ECMs Fig.12: the output voltage of a typical narrowband lambda sensor as a function of air-fuel ratio. This is often referred to as an ‘S-curve’. Low voltages indicate rich operation while higher voltages indicate lean; stoichiometric operation is around 500mV. siliconchip.com.au Dealers or independent mechanics may be able to repair or replace your car’s electronic modules. But also, in Australia, several companies specialise in repairing these devices. You can find them by Googling “car module repair”. If you want to do it yourself, there are also numerous YouTube videos and other online resources on the topic. Here is an example of a US video that shows how to reprogram a used ‘junkyard’ module to give it the identity of your current car. See the video titled “Save Money Using a Junkyard Engine Control Module” at https://youtu.be/Hhk7Wg0i3KE The dealer said it was impossible and needed an extremely expensive replacement module! Such a technique may or may not work for you or any diagnostic tools or modules you have. Australia’s electronics magazine December 2020  17 EXHAUST GAS HIGH-PRESSURE SEAL OUTSIDE AIR SLITS – V + INTERIOR PLATINUM ELECTRODE HOUSING ZIRCONIA SENSOR SENSOR SHIELD EXTERIOR PLATINUM ELECTRODE EXHAUST MANIFOLD Fig.13: a narrowband lambda sensor is usually a solid-state electrochemical cell made with zirconia ceramic material. These are cheaper than wideband but only really tell the ECU whether the engine is running rich or lean. • 1994: Ford USA introduced EEC-5 with OBD-2. This is also a favourite among Ford engine modification enthusiasts. • 1996: OBD-II onboard diagnostics became mandatory for all cars and light trucks in the USA. • 2001: EOBD, the European equivalent of OBD-II, became mandatory for petrol cars in the EU. • 2003 Ford US introduced the EEC-6. • 2004: EOBD became mandatory for diesel vehicles in the EU. • 2009: Google started their self-driving car project. • 2012: Bosch published further extensions to CAN called CAN FD (flexible data rate). This provides a faster bit rate, but is compatible with CAN 2.0, so CAN FD devices can coexist on the same network as CAN 2.0 devices. • 2014: the first commercial self-driving vehicle, the Navya, was launched. See https://navya.tech/en/ • 2016: the Tesla “Autopilot 8.0” system was introduced. It is intended for driver assistance, not for self-driving which some people inappropriately use it for (perhaps confused by the name). From 2009 to the present, there have been many innovations on self-driving vehicles, but they are beyond the scope of this article. Fig.14: this is how the more expensive and complicated wide-band oxygen sensors work. They provide a useful output over a lambda range of about 0.7 to over 2.0. That corresponds to air/fuel ratios from 10:1 to over 30:1 for petrol (ie, with the stoichiometric ratio of 14.7:1 being a lambda of 1.0). This allows for much more precise tuning of engine conditions for a particular target lambda value. Combustion optimisation with the ECU The most fundamental role of the ECU is to control the amount of fuel injected into the engine to give the right airfuel ratio, and to control the timing and duration of the ignition spark in non-diesel engines. A crankshaft position sensor indicates the position of the pistons in the cylinders, so that the correct injection timing and spark timing can be determined. The effect of varying air-fuel ratio and ignition timing on various parameters is shown in the figures above. Beyond those fundamentals, many other parameters are taken into account by the ECU. These includes: • the amount of air inducted into the engine • the throttle position • intake air temperature and pressure • engine load • camshaft position (when variable valve timing is used) • engine temperature • exhaust oxygen content • air filter restriction • vehicle speed • current gear • engine knock (if any is detected) • and more. CAN bus LIN bus Fig.15: this shows how the LIN bus complements CAN bus. It is simpler, cheaper and suitable for non-critical, low data rate applications. Source: CSS Electronics. 18 Silicon Chip Fig.16: SafeSPI is an automotive serial protocol for safetycritical devices like airbag controllers. Source: Synopsys, Inc Australia’s electronics magazine siliconchip.com.au The camless engine Fig.17: some of the functions provided by Advanced Driver Assistance Systems (ADAS) by Servotech. It uses a variety of electronic control modules (ECMs) with embedded software and sensors such as radar, cameras, ultrasonic and lidar to control steering, engine, transmission and brake systems. Source: Servotech, Inc. The main objectives in running a street car engine are to optimise power, fuel economy and emissions. Unfortunately, all these objectives tend to conflict with each other. Fortunately, the ECU can adjust engine parameters hundreds or thousands of times per second to find the best compromise between these three goals, depending on what the driver is doing. The stoichiometric air-fuel ratio is the ratio where all the fuel and oxygen will be consumed during full combustion. For perfect “test” petrol, 14.7g of air is required to burn 1.0g of fuel. If there is more air than required then the mixture is “lean”, and if there is less, it is “rich”. But the ideal ratio varies with things like the exact blend of fuel used. Most cars with an ECU use an oxygen sensor that measures the oxygen and hydrocarbons in the exhaust, providing feedback to the ECU to optimise the air-fuel ratio. This is known as lambda control (see Figs.12-14). In reality, a stoichiometric ratio is avoided except under light loads because it burns too hot, and it carries an increased risk of premature detonation or knocking, which can cause engine damage. For acceleration and other high loads, a richer (cooler burning) ratio is used, but emissions of unburnt hydrocarbons increase as a result. Fuel-injected, ECU-controlled engines (nearly all of them today) can operate in ‘open-loop’ or ‘closed-loop’ mode. In closed-loop mode, the amount of fuel injected is determined by the amount of air entering the cylinders and feedback from the oxygen sensor(s). In open-loop mode, the amount of fuel injected is an ‘educated guess’ by the ECU based on numerous tables and calculations that were generated during the engine’s development. Open-loop might be used constantly on racing engines, where fuel economy and emissions are not so critical. Still, closed-loop mode is required for street cars at least some of the time, and represents a compromise between best fuel economy and minimal emissions. Nevertheless, open-loop mode is used on street cars in circumstances such as: siliconchip.com.au There are significant advantages for an internal combustion engine without a traditional camshaft, with the valves instead operated electromechanically or hydraulically. It would be more compact, lighter, have reduced rotating mass, reduced internal friction and possibly a much higher RPM limit. Such a motor could also be started with only a small starter motor, as it could be started on one cylinder initially, and it could also be run in either direction, possibly obviating the need for a reverse gear. ECU-operated electromechanical valves would mean complete and precise control over the combustion cycle, which is extremely difficult with mechanically-operated valves, even with variable valve timing or lift. That would lead to much-increased power, improved fuel economy and lower emissions. Such an engine could use a variety of fuels, run lean fuel ratios, have ‘free’ cylinder deactivation. It could even allow brief bursts of two-stroke operation or the “five-stroke” Miller or Atkinson cycles, or homogenous charge compression ignition (HCCI), where gasoline is ignited by compression, similarly to diesel. Such an engine could continuously cycle between all types of operational modes, depending on what is required for the circumstances. The principle is simple; making something sufficiently robust to work in an engine is not. These engines are under development by a variety of manufacturers such as Camcon Auto Ltd and FreeValve (www.freevalve.com – a company related to hypercar manufacturer Koenigsegg).See the video titled “Intelligent Valve Technology - Petrol engine, diesel efficiency” at https://youtu. be/XdEhg9JDuEw Camcon Auto Ltd’s iVT, intelligent Valve Technology concept (https://camcon-automotive.com/). Valves are operated via a digital signal from the ECU rather than mechanical means giving enormous flexibility in engine operation. Video: “Intelligent Valve Technology - Petrol engine, diesel efficiency” https://youtu.be/XdEhg9JDuEw • starting and warm-up (like a choke on older engines, where more fuel needs to be injected); • at higher loads and during acceleration (where fuel economy is less critical; similar to the accelerator pump on carburetted engines); • and during deceleration and engine braking, or when the engine speed is rapidly varying. When engine RPM and the throttle position are stable, such as at idle or constant speed driving, the engine will operate in closed-loop mode for maximum fuel economy and minimum emissions. Australia’s electronics magazine December 2020  19 In some cases, the engine will run lean, which reduces fuel consumption, but not too lean as that could lead to the creation of too many oxides of nitrogen. In open-loop mode, the ECU controls the engine according to an “engine map” stored in the ECU, which sets engine parameters according to engine load, RPM etc. It receives no direct feedback from the oxygen (lambda) sensor, although long-term averaged data from the lambda sensor may be used to adjust the maps. An engine map is produced by a series of dynamometer tests that measure the engine performance against a range of variables such as engine speed (RPM), load, throttle setting, ignition timing, air-fuel ratio and engine and ambient temperatures. Maps are generated for such combined variables as torque and power as a function of engine speed; fuel consumption as a function of torque; emissions of CO, HC and NOx as a function of air-fuel ratio; and torque, fuel consumption and Types of fuel injection • Dual injection is another variation. One version is like port or sequential injection but with two injectors per cylinder, possibly spraying on two intake valves (in a three- or four-valve-percylinder engine). One injector may be smaller than the other, to give finer control over the amount of fuel injected. • Another variation is a combination of port and direct injection, with two injectors per cylinder, one internal and one external (see below). Toyota introduced this system on the 2006 Lexus IS350 and called it D-4S. Both port injection (PI) and direct injection (DI) have advantages and disadvantages. As fuel is injected, cooling of the surrounding intake air-fuel charge occurs either in the port (PI) or cylinder (DI). PI is good for naturally aspirated (non-turbo or non-supercharged) engines as it cools the incoming charge, which increases its density and allows more charge to enter the combustion chamber. It’s also mechanically simpler to locate the injectors in the port (PI) rather than the combustion chamber (DI). With PI, there is also more time for fuel vapourisation to occur. A disadvantage of PI is sometimes the fuel condenses on the port walls, affecting the fuel ratio. With DI, there is less chance of premature detonation (knock) because the charge and cylinder wall surfaces are cooled during the compression stroke, just before ignition. DI also allows for a higher compression ratio due to the cooling effect and therefore, more power. DI also gives the possibility of stratified charge ignition (SCI), with multiple fuel injections timed over a single compression stroke. A DI system is more expensive, and also allows carbon deposits to accumulate on the back of the intake valves. In PI, the valves are cleaned naturally by the fuel vapour passing over them. Dual injection systems with both PI and DI can have the advantages of both the PI and DI systems. LOW TORQUE HIGH Fuel injection is vital for modern engine management, as it gives superior fuel delivery accuracy to carburation. Several different types of fuel injection are in use, as follows: • Single-point or throttle-body injection is the simplest type of fuel injection and replaces the carburettor with a throttle body and one or more injectors. This is the easiest system to retrofit to an existing carburetted engine. • Port or multiport injection is where fuel is injected outside each cylinder’s intake port, making for more accurate and customisable injection than single-point. No fuel can condense in the intake manifold, plus there is less delay in it reaching the cylinder. • In conventional multiport injection, fuel for all cylinders is dispensed at the same time, so fuel must remain in the intake port waiting for a valve to open. During this time, engine running conditions may have changed. • Sequential fuel injection addresses this by injecting fuel for each individual cylinder before its intake valve opens. • Direct injection takes the sequential concept further and injects fuel directly into the cylinder, bypassing intake valves and providing the most accurate fuel metering. A high-pressure fuel pump (HPFP) is required, often driven off a camshaft. The low-pressure in-tank fuel pump remains, with its role being to supply fuel to the HPFP. A dual port injection system with one injector discharging directly into the cylinder (as in direct injection) and the other injector discharging into the port. Video: “Why New Cars Are Using Both Direct & Port Fuel Injection” https://youtu.be/66C4YIiwRbM 20 Silicon Chip LOW RPM At lower RPM both direct and port injection may be used depending on the torque requirement, while at higher RPM, only direct injection is used. Australia’s electronics magazine HIGH siliconchip.com.au Open-source ECUs There are several open-source ECU projects, as follows: • SECU-3 (https://secu-3.org/en/), originally of Russian origin, is described as an “open source ignition and fuel injection control system”. A variety of prebuilt units or kit components can be purchased from the website. Fig.18: an example of an automotive night vision system on an Audi S8. From the video titled “Audi S8: Night Vision with pedestrian detection” at https://youtu.be/-38NlE4KWZ8 emissions as a function of spark timing at specific RPM. Many different types of fuel maps are possible, optimising for various requirements such as maximum power, economy or minimum emissions. Note that in the case of emissions, some can be treated outside of the engine in the catalytic converter (we’ll cover catalytic converters next month in more detail). The objective of the fuel map is to indicate to the ECU the amount of fuel to be injected to satisfy particular operating conditions. These operating conditions are generally engine speed and load, where the load is typically indicated by either throttle position or intake manifold pressure or both (see Figs.7-11). Most ECUs support a “limp home” mode in the event of ECU or sensor malfunction. It provides the bare minimum of functionality to get the engine running. In some GM vehicles, there is a “Calpac” chip that is used in case the ECU PROM data becomes unreadable, or there are sensor malfunctions. It is a resistor network that contains preset base values to provide typical values that should be given by various engine sensors, but which are not present or ignored in a limp-home situation. Sensors are ignored, and the engine operates much like earlier generations. Data buses Individual electronic modules in a vehicle need to communicate with each other, and several data buses have been developed for the purpose. Ethernet is not commonly used Fig.19: the Australian-made Haltech Elite 950 aftermarket ECU, suitable for basic four, six and eight-cylinder engines, including carburettor conversions. See the video “Elite 950 Explained” at https://youtu.be/hGuAneUd2_4 siliconchip.com.au • Speeduino (https://speeduino.com/home/) is an Australian Arduino Mega 2560 R3 based project. A variety of prebuilt modules and kit components can be purchased from their website. See the video titled “Making an insanely fast Speeduino ECU” at https://youtu.be/xgNpUEs6CWE • RusEFI (https://rusefi.com/) is an open-source project for race cars and off-road vehicles. It is not intended for emissioncontrolled vehicles or those with integrated safety systems. The website has a shop for purchasing related components. See the video “rusEfi open source standalone ECU runs M73 BMW v12 engine” at https://youtu.be/TGf8IMwRuIY • Rabbit ECU (https://mdac.com.au/rabbit-ecu-project/) is a low-cost Arduino-compatible DIY ECU which has been fitted to vehicles including a Commodore SS, Holden Astra and Holden Corsa. • OpenECU (www.pi-innovo.com/product/openecu/) is software that allows manufacturers to develop applications for ECMs. See the video “Pi Innovo OpenECU Demonstration” at https://youtu.be/SbsCdAC0l7E • RomRaider (https://romraider.com/) is an “open source tuning suite created for viewing, logging and tuning of modern Subaru Engine Control Units and some older BMW M3 (MS41/42/43) DME”. • DIYEFI.org (www.diyefi.org) is “a truly open source engine management system, one that you can build for the cost of the components alone”. • Kvaser offers some open source software to support their hardware, in addition to purchased software. See www. kvaser.com/support/open-source-software/ in automotive applications. There have been many, but here are some current automotive data bus protocols; we will not include those for aircraft. • CAN bus (Controller Area Network) is one of the most popular vehicular data buses and operates at 5V over shielded, twisted pair wires. The ISO 11898-2 standard is for high-speed CAN bus at 1Mbit/s or 5Mbit/s, while ISO 11898-3 or fault-tolerant CAN bus runs at 125kbit/s. There are other variations. It has a high fault tolerance in electrically noisy environments. It is complementary with LIN (see below). Incidentally, it is used in areas other than motor vehicles such as the Shimano DI2 gear shifter on bicycles, automated environments, prosthetic limbs, passenger lifts, medical equipment and model railroads. • FlexRay is faster, more reliable and more expensive than CAN bus and has safety-critical features plus data rates up to 10Mbit/s. It is used on some Audi, Bentley, BMW, Lamborghini, Mercedes Benz, Rolls Royce, Land Rover and Volvo vehicles. • OBD-II onboard diagnostics supports five different communications protocols via the standard Data Link Australia’s electronics magazine December 2020  21 Fig.20: the Haltech iC-7 Display Dash that connects to a Haltech ECU via CAN bus. It can also be connected to most vehicles via the OBD2 port, which also carries CAN. See the video: “iC-7 Display Dash | PRODUCT OVERVIEW” at https://youtu.be/IDqIIXl2z2Q Fig.21: the optional Haltech CAN keypad that integrates with a Haltech ECU. See the video “Haltech CAN Keypads | PRODUCT OVERVIEW” at https://youtu.be/CaT1kT3hW4g Connector (DLC) that all modern cars have. The protocols are: (a) SAE J1850 pulse width modulation at 41.6kbps, used mostly by Ford. (b) SAE J1850 variable pulse width at 10.4kbps, used mostly by GM. (c) ISO 9141-2 asynchronous serial at 10.4kbps, used chiefly by Chrysler, European and Asian vehicles. d) ISO 14230 Keyword Protocol 2000 asynchronous serial at 10.4kbps, also used by Chrysler, European and Asian vehicles. (e) ISO 15765 CAN bus (up to 1Mbps), mandatory in the USA after 2008 and possibly found on European cars after 2003. • LIN (Local Interconnect Network) is an inexpensive single-wire protocol for serial communications between devices in a vehicle. It is complementary with, but not a replacement for, CAN bus (see Fig.15). LIN is used for low data rate, non-critical applications in a vehicle such as controlling a sunroof, interior lighting, steering wheel cluster, climate control, seat adjustment and other motors etc. It supports data rates of 1-20kbits/s, uses 12V signalling and can serve as a gateway to a CAN bus. 22 Silicon Chip See the video titled “LIN Bus Explained - A Simple Intro (2020)” at https://youtu.be/TresvW4dxlc • MOST (media-oriented systems transfer) is a fibre-optic network used to integrate multimedia devices such as navigation systems, CD players, video screens, digital radios, mobile phones and in-car PCs. It saves the manufacturers of such devices having to develop custom interfaces for each vehicle. Up to 64 devices can share one bus, and adding a new device is as simple as plugging it in. It is used in preference to other automotive buses such as CAN because they are not fast enough to carry video. • SafeSPI (serial peripheral interface for automotive safety) is a protocol for the MEMS devices (described in our November issue), as used in active and passive safety system sensors. A SafeSPI safety system controller queries them – see Fig.16 and siliconchip.com.au/ link/ab4j (PDF). Programming ECUs and ECMs SAE J2534 is a PC-to-vehicle communications standard developed by the Society of Automotive Engineers to enable manufacturers and independent repairers (the “independent aftermarket”) to use standard tools to repair or modify vehicles by recalibrating, reflashing or installing updates to onboard electronics. This includes ECUs, TCMs, PCMs, throttle controllers and optionally other controllers. Can jump-starting damage an ECU? There is much discussion online about whether jumpstarting a car can damage the ECU. It seems that, as long as it is done correctly and with the right polarity, it is safe. However, we recommend you go by the advice of your car’s manufacturer. In some cases, such as with BMW, a new battery fitted to the vehicle needs “registration”. A scan tool is needed to reset the vehicle’s intelligent charging system and erase previous battery charging history. Failure to register may result in a fault indication and can also damage the new battery. Australia’s electronics magazine siliconchip.com.au Remapping or rechipping your ECU or TCU There are many aftermarket options to rechip or remap your ECU (and also automatic transmission TCU) with the claimed advantages of more power, torque or fuel economy, or better transmission change points. These things are certainly possible, but in most if not all cases it will void your powertrain warranty (even if any fault developed is seemingly unrelated to the ECU or TCU modifications). We have heard stories of $15,000 engine repair bills which were not covered by warranty because the owner had altered the ECU. So such modifications should be made with caution. It means that a repairer can use one device for programming a variety of different brands of vehicles. It is legally required in the USA for all vehicles produced since 2004, and each vehicle manufacturer must make their ECU reprogramming application software and calibrations available, for which they may charge a fee. It is also widely supported on vehicles outside the USA. OBD diagnostics (see our September 2020 article; siliconchip.com.au/Article/14576) are typically read using ELM327 or STN1110 interpreter ICs via a dongle and are read-only (except for clearing certain fault codes). But some top-end diagnostic scanners use J2534 and can write data as well, as was mentioned in that article. The requirement for non-dealer mechanics to be able to interface to the vehicle’s electronic systems relates to the “right to repair”. If your car is out of warranty, you are a motoring enthusiast and don’t mind the possibility of exceeding the manufacturer’s design specifications, and risking expensive repairs, you could consider modifying your engine and/or ECU. Just make sure that it continues to meet statutory requirements for emissions, noise etc. The legality of such modifications varies by state and territory; some are much stricter than others. So you need to do your research beforehand, or you could potentially be fined and forced to return the vehicle to its original condition. The open-source project OpenXC (http://openxcplatform.com/overview/) is “a combination of open source hardware and software that lets you extend your vehicle with custom applications and pluggable modules. It uses standard, well-known tools to open up a wealth of data from the vehicle to developers.” “… by installing a small hardware module to read and translate metrics from a car’s internal network, the data becomes accessible from most Android applications using the OpenXC library.” Another relevant open source project is Nobdy (Linux) at https://elinux.org/Nobdy Its goal is to “implement a featureful, stable middleware suite that provides an extensible and flexible interface to automotive sensor and actuator buses for the purpose of enabling car manufacturers, owners and developers the Fig.22: an example of an aftermarket EFI conversion kit, the Holley “Sniper” with an ECU built into the throttle body. There is a digital readout in the car. It is “self-tuning”, so no complicated programming is required, although it can be customised. siliconchip.com.au Australia’s electronics magazine December 2020  23 power to create new software that enhances the safety, economy and enjoyment of the driving experience.” Converting a legacy engine It is possible to convert a variety of legacy engines, such as in classic cars, to use more modern technologies. One of the simplest conversions is to replace the points in a Kettering ignition system with an electronic ignition system. This gives better reliability, better performance and there is no longer any need to adjust points or ignition timing. The points are replaced with an angular sensor that typically uses the Hall effect, with a rotating magnet on the distributor shaft, and a sensor where the points used to be mounted. A small computer monitors this sensor and switches the ignition coil to generate sparks at the appropriate time. SILICON CHIP and its predecessors have published several such projects over the years. A carburettor can also be replaced with an electronic throttle body that provides single-point fuel injection. This then injects a precise dose of fuel into the intake manifold. There are several aftermarket conversion kits available for a variety of engines. Some have the ECU built directly into the throttle body, to simplify wiring. They also typically require the addition of an oxygen sensor to the exhaust stream. Throttle position, air temperature and manifold absolute pressure (MAP) may also be monitored within the EFI conversion throttle body. Naturally, the more sensors are used, the more engine control there will be. There are carburettor conversion kits available from Holley (Fig.22), FiTech, MSD and Howell. More sophisticated kits such as from Edelbrock are also available to retrofit multipoint fuel injection onto certain engines, but are much more expensive. Haltech (www.haltech.com) is an Australian company with a worldwide reputation that makes a wide variety of aftermarket ECUs to suit many vehicles and applications. They also have a comprehensive YouTube channel (see Figs.19-21). MegaSquirt (http://megasquirt.info/) is another popular engine controller for the enthusiast or professional. It is said to be able to run every engine from a single piston lawnmower engine to an alcohol-fuelled dragster. They have a variety of products, including one which you put together yourself. Advanced driver assistance systems (ADAS) ADAS is designed to assist drivers in operating the vehicle. These systems include many sensors such as radar and lidar, whose data is combined in a process called sensor fusion to control steering, engine, transmission and brake systems (see Fig.17). There may be many individual electronic control modules providing distributed ADAS functions, but there is a trend toward having a centralised ADAS module as the ‘brain’ of the car. These systems include: • adaptive cruise control, to keep a constant distance to the vehicle in front regardless of their speed • anti-lock brakes (ABS) • automatic high-beam headlights or even glare-free “laser” high-beam systems • automatic parking • blind spot monitor or camera • collision avoidance system, which detects a rapidly approaching object and sounds an alarm or applies the brakes • crosswind stabilisation, which measures yaw rate, steering angle, etc to keep the vehicle on the desired path • cruise control • driver drowsiness detection (eg, by analysing the driver’s facial expression or steering inputs) • electronic stability control (ESC) • emergency brake assist (BAS), which detects panic braking and applies maximum braking effort • head-up display, to project vehicle information on the windscreen • hill descent control (helps to stabilise offroad vehicles during steep descents) • hill start assist, which holds the brakes on a hill until the accelerator is depressed • lane-centring system (also known as steering assist) • lane departure warning • night vision, to assist in avoiding obstacles such as pedestrians (Fig.18) • pedestrian protection system, which lifts the car bonnet when a pedestrian is struck • pre-crash system, which takes actions like pre-tensioning seatbelts prior to impact • rain sensor for automatic wiper activation and speed control • rear cross-traffic assistance, which detects traffic in a road being reversed into which the driver cannot see • reversing camera or 360° camera • satellite navigation • terrain response system (adjusts a four-wheel-drive system to suit terrain) • traction control (TC) • traffic sign recognition (eg, to warn if the speed limit is exceeded) • tyre pressure monitoring (TPMS) Next month An entry-level MegaSquirt product you put together yourself, but most of the MegaSquirt range is prebuilt. 24 Silicon Chip As we have run out of space in this issue, the followup article in the next issue will describe, in more detail, the most interesting and important types of ECMs found in modern vehicles. SC Australia’s electronics magazine siliconchip.com.au T HI S . . . O R T HI S : Every article in every issue of SILICON CHIP Can now be yours forever in Nov 1987 Dec 2019 digital (PDF) format! High-res printable PDFs* n * Some early articles may be scans n Fully searchable files - with index n Viewable on 99.9% of personal computers & tablets Software capable of reading PDFs required (freely available) Digital edition PDFs are supplied as five-year+ blocks, covering at least 60 issues. They’re copied onto quality metal USB flash drives (at least 32GB). Just order which block(s) you want! n n November 1987 - December 1994 January 2005 - December 2009 n n January 1995 - December 1999 January 2010 - December 2014 n n January 2000 - December 2004 January 2015 - December 2019 Each five-year block is priced at just $100, and yes, current subscribers receive the normal 10% discount. If you order the entire collection, the 6th block is FREE (ie, pay for five, the sixth is a bonus!). All PDFs are high resolution (some early editions excepted) and the USB Flash Drives are high quality metal USB3.0, so if you save the files to your PC hard disk, the USB Flash Drives can be used over and over! SUBSCRIPTIONS TO SILICON CHIP REMAIN THE SAME! Of course, so you won’t miss out on a current issue you can still subscribe to SILICON CHIP . . . and you’ll $ave money over the newsstand price. Your SILICON CHIP will be delivered every month right to your mail box . . . no waiting! n Subscribe to the printed edition n Subscribe to the digital edition n Subscribe to the combo printed/digital edition Want to know more? Full details at siliconchip.com.au/shop/digital_pdfs siliconchip.com.au Australia’s electronics magazine December 2020  25 Vintage Battery Radio Li-ion Power Supply by Ken Kranz and Nicholas Vinen Vintage Radio enthusiasts know that “A” and “B” batteries have been effectively unobtainable for some time. So what to do? Try this compact and easy-to-build module: using Li-ion or LiPo cells, it can generate both the A and B supplies for most battery valve sets and suits sets with a wide range of HT voltages. It generates virtually no EMI (which could interfere with radio reception). It also incorporates battery overdischarge protection and reversed battery/cell protection. I wanted a power supply to run a typical battery-powered vintage radio from a set of 18650 (or similar) Li-Ion rechargeable cells. I considered developing a switchmode design for decent efficiency, but RFI from switchmode supplies can interfere with radio reception. So I designed this ‘low-tech’ supply using a low-cost PCB-mounting transformer and a few transistors and passives instead. This circuit was designed to power 26 Silicon Chip my Aristocrat Tecnico 859 from four 18650 Li-ion cells, but it would suit a great many valve sets. It is often tuned to 3WV in Victoria’s Wimmera from my home in Adelaide, South Australia, with no power supply noise evident. The set requires 90V for the ‘B’ supply and 1.4V for the ‘A’ supply. One of these was also fitted to the 1937 Velco radio that I described in the August 2020 issue (siliconchip.com. au/Article/14544) but left off all the low-voltage cutout components as the Australia’s electronics magazine set now runs from a 6V DC plugpack. The filament supply is 2V <at> 700mA, so I attached the low tension (LT) regulator to the diecast aluminium enclosure the PCB is fitted into. The B+ for this radio is 135V. Most battery-powered radios need a B+ supply of 90-135V DC at up to about 12mA (<1.7W). So I chose a 5W PCBmounting mains transformer which I used backwards, with the 230V primary used as the secondary output winding. I determined that I would need a siliconchip.com.au Scope1: a scope grab showing the operation of the oscillator, with VR1 and VR2 at their midpoints. The yellow and green traces are the waveforms at the collectors of Q3 and Q4, while the blue and mauve traces are the gate voltages of Mosfets Q1 and Q2. The duty cycle is not quite 50%, hence the need for adjustability. Note how the Mosfet switch-on is gradual while switch-off is fast. transformer with either 6V + 6V or 9V + 9V secondaries (acting as the primary here, configured as a single centretapped 12V or 18V winding). You can’t just determine the transformer turns ratio by dividing the secondary voltage into the primary voltage. Consider the 230V to 6V + 6V transformer; the 6V AC output voltages are determined for a resistive load at full power. With 230V AC on the primary, the 6V windings’ open-circuit voltages measure 8.4V AC each. So the actual turns ratio is 230V ÷ 8.4V = 27.5. Therefore, 8.4V AC is the nominal input voltage when the low-voltage winding is used as the input; if only 90V output is required, it can be somewhat lower. The small transformer’s primary winding DC resistance is around 800Ω, and the low-voltage secondaries measure around 2.5Ω each (or 5.6Ω each for the 9+9V version). This also needs to be considered, as does the high leakage inductance. The relatively high secondary winding resistance (which is the primary in Scope2: here the blue and mauve traces are still the gate voltages of Q1 & Q2 while the yellow and green traces are their drain voltages (ie, the push-pull drive to transformer T1). The Mosfets operate as inverters with significant inductive spikes at switch off; high enough to cause ZD5 and ZD6 to conduct this application) means that the driving Mosfets don’t need any current limiting at switch-on. The peak current is limited by the transformer itself. Respecting the current ratings for the various windings, an output of up to about 2W is possible; more than enough for this application. The best operating frequency is often above the 50/60Hz recommended for the transformers. The final design provides some frequency adjustment, to let you set the optimal operating point. The B+ supply normally needs to be galvanically isolated from the filament supply as back-bias is often employed. Because of this, and the fact the B+ current remains constant, a simple series resistor and zener diode is used to regulate the B+ output. Remember that the 800Ω transformer winding can be used to dissipate some energy. Caution Depending on how you have configured it, this supply could generate voltages above the 60V DC which is considered the limit of safe ‘extra low volt- Features & specifications • Runs from two or four li-ion, LiPo or LiFePO4 batteries (typically two series cells for the HT generator and two parallel cells for LT) • HT output (B): 24-135V DC at up to 2W • LT output (A): 1.2-2.5V at up to 3A (with a heatsink) • Low-battery cut-out voltages: 0-10V (B), 0-4.5V (A) • Quiescent current when off: around 10µA (B) & 2µA (A) • HT operating current (B): around 300mA <at> 6.2V for 135V HT • LT operating current (A): 5-10mA plus what the radio draws • Other features: low EMI, indicator LED, provision for low-current SPST on/off switch, adjustable transformer drive frequency and duty cycle siliconchip.com.au Australia’s electronics magazine age’ operation. While 100V or so may not seem very high compared to mains voltages, it’s certainly high enough to give you a serious shock should you come in contact with the high tension (HT) side of the circuit. So you must work in such a way that you can’t come in contact with the Supply or the HT circuitry it is powering while power is applied. When probing or adjusting the Supply, always use tools with sufficiently high voltage ratings. Once it has been set up, it must be housed in such a way that users can’t come in contact with any of the HT circuitry, and all wiring should be properly insulated. If you are already working on valve sets, chances are you will already understand the danger and have safe practices. If you are a novice, seek assistance from a more experienced technician before building or working on this Supply. Circuit description While the circuit and board are designed to operate from one or two batteries, it’s far better to have two batteries: a lower-voltage battery for the A supply and a higher-voltage battery for the B-supply. This improves efficiency and reduces heat dissipation. My recommendation is that the higher-voltage battery should consist of two li-ion, LiPo or LiFePO4 cells in series, giving a nominal voltage of around 7.4V (or 6.6V for LiFePO4). You could use two sets of parallel cells if you wanted to, ie, a 2S2P configuration, although that isn’t really necessary. December 2020  27 q q l SC Ó BATTERY VINTAGE RADIO POWER SUPPLY The lower-voltage battery can be one of the same cells, or better, two in parallel. This will then have a nominal voltage of 3.7V or 3.3V, depending on the chemistry. Assuming that two batteries are used, the higher-voltage battery is connected to CON1 and the lower-voltage battery to CON2 (see Fig.1 above). Both connections have reverse-polarity protection in the form of series 1A PTC thermistors and reverse-connected 3A diodes, D1 & D2. Should either battery be connected with the wrong polarity, the associated diode will conduct and cause the PTC to go high-resistance. The radio would then not work, and presumably, this would lead you to discover and correct the problem before the battery discharged. Those PTCs also provide a measure of over-current protection, should something go wrong on the power supply board or in the radio. The B IN + supply from CON1 then 28 Silicon Chip goes through P-channel Mosfet switch Q5 and runs the high-voltage B-supply generator, while the A IN + supply from CON2 goes through a similar Mosfet switch, Q6, and onto the A-supply generator. These Mosfets provide the low-battery cut-out protection, which will be described later. If a single battery is used, CON2, PTC2, D2, D4 and Q6 are left off the board, and a wire link is soldered across LK1. The B IN + supply then goes through switch Q5 and onto both the A-supply and B-supply generators. More on this possibility later. High-voltage generator As well as the description below, the operation of this part of the circuit is depicted in oscilloscope grabs Scope1Scope5 overleaf. With Mosfet Q5 on, current flows through the 220Ω resistor to charge the 10µF bypass capacitor for the oscillator. The voltage across that capacitor, and Australia’s electronics magazine thus the oscillator supply, is clamped to around 5.6V by zener diode ZD1 for consistent operation. NPN transistors Q3 and Q4 form a basic oscillator, with trimpots VR1 and VR2 providing a small amount of both duty cycle and frequency adjustment. This allows you to tune the oscillator to get a 50% duty cycle for the most efficient driving of transformer T1, and to adjust the frequency to tweak the power delivery to suit your radio. The oscillation frequency is determined by the time constant of the resistances and capacitors connected to the bases of transistors Q3 & Q4. With VR1 & VR2 centred, R = 100kΩ and C = 100nF, so the approximate frequency is 1 ÷ (1.38 x R x C) = 72.5Hz. With VR1 & VR2 at the extremes, it can be varied from about 54Hz up to 96.5Hz. The duty cycle is adjusted by varying the resistance of one trimpot slightly compared to the other. siliconchip.com.au Fig.1: the left-hand section of the Power Supply circuit provides input protection and the low-battery cut-out function, while the middle section is the HT drive oscillator and LT regulator. The oscillator drives the step-up section at upper right, with T1 providing high voltage AC that’s rectified by BR1 and filtered by two electrolytic capacitors and a resistor to give relatively smooth HT DC. Drive for the gates of Mosfets Q1 and Q2 comes from the collectors of Q3 and Q4 via 5.6kΩ current-limiting resistors. These form RC low-pass filters with the Mosfet gate capacitances, and their values may be increased if switching noise is a problem. The 18V zeners protect the Mosfets from an excessive gate-source voltage which might be caused by back-EMF from the transformer coupling through the Mosfet parasitic capacitances. In practice, they rarely conduct. Q1 and Q2 drive the ‘primary’ of transformer T1 in push-pull fashion. The 9+9V windings are intended to be the transformer’s secondaries when it is operated from the mains, but here we are using it in the opposite manner. T1’s centre tap connects to the battery supply before the 220Ω resistor, so that the transformer has a low source impedance. It draws around 0.5A when delivering more than 2W at 100V. Note that Q1 & Q2 must be logicsiliconchip.com.au level Mosfets as they will typically receive a maximum gate-source voltage of around 5V. The output of T1 is rectified by BR1 to charge the first 100µF capacitor. The second 100µF capacitor forms a lowpass filter with the 100Ω resistor to reduce ripple, while zener diode ZD2 limits the voltage applied to the radio until its HT current draw comes up to normal. After that, it’s limited by the transformer and 100Ω series resistor. Note that high voltage zener diodes have quite high zener impedances, so for example, if ZD2 is a 75V diode, the B+ OUT voltage could easily exceed 85V at light loads. This is unlikely to damage any radio, and it will drop to a more normal level as the radio draws more current. ZD2 is just there to prevent wildly high HT voltages from being applied. Filament supply The filament supply is based around Australia’s electronics magazine adjustable linear regulator REG1. This is similar to the LM317 but can deliver more current; over 3A, rather than 1.5A. The LD1085 also has a lower dropout voltage than the LM317 at similar currents, although that isn’t important here. The A OUT voltage is adjusted using trimpot VR5, which forms a divider with the 110Ω resistor between the OUT and ADJ terminals. As there is a fixed voltage between OUT and ADJ, and a fixed resistance, that means that the current through VR5 is essentially constant. So by varying its resistance, we vary the voltage between ADJ and GND, and thus set a fixed output voltage. A typical 5-valve portable radio (eg, the Aristocrat Tecnico 859) with a valve compliment of 1T4, 1R5, 1T4, 1S5 and 3S4 will require 300mA at 1.4V for the filaments. So with a 3.7V battery, the regulator will dissipate (3.7 – 1.4) x 0.3 = 690mW so little heatsinking is required for REG1. The heatsinking of REG1 can be adjusted as required; some heatsinking was required for my Velco radio. You could use a flag heatsink, as we did on our prototype, or bolt the regulator to a piece of metal, such as the chassis. Note than some battery radios had the filaments connected in series. Those radios will need a filament supply of something like 7.5V <at> 50mA. This circuit would be suitable for such radios with a few tweaks. For example, the 110Ω resistor would have to increase to say 620Ω to give REG1 sufficient adjustment range, and the B+ battery would probably need to be three Li-ion, LiPo or LiFePO4 cells in series to give REG1 a sufficiently high input for regulation, even when the battery is almost flat. The resistors connected to pin 5 of IC1b would also need to change from 1MΩ/2.2MΩ to something like 3.3MΩ/1MΩ so that the low-battery cut-out adjustment range would suit that battery. Low-battery protection Mosfet switches Q5 (and Q6, if fitted) are used to provide low-battery protection. If either battery’s voltage drops below a critical level, Q5 and Q6 switch off, so the power supply and radio shut down. In this state, the circuit only draws about 10µA from the B-battery and about 2µA from the A-battery. December 2020  29 Scope3: the yellow trace is the drive voltage across T1’s primary (ignoring the centre tap), while the green trace is the voltage across the secondary. Note the different scales: 20V/div for the primary and 50V/div for the secondary. The secondary shows little overshoot and no ringing. Scope4: a close-up of the edge of the waveform in Scope3. Here you can clearly see the primary overshoot is limited to around 60V by ZD5 and ZD6, which each conduct for around 3-5µ µs per cycle, protecting Q1 and Q2 from excessive drain voltages (although they are avalanche rated, so would likely survive). Note the 100µ µs delay between the leading edges of the primary and secondary waveforms. Presumably, you would notice the radio has switched off and either recharge them or swap them for fresh cells. But if for some reason you forget and leave the radio switched on, it would be several months before this minimal current drain could damage the cells. That’s why this circuit was designed with a low quiescent current in mind. When power switch S1 is closed, current can flow from whichever battery has a higher voltage, through small signal diodes D3 & D4 and then switch S1, into the input of REG2. This is an ultra-low-quiescent-current, low-dropout 3.3V linear regulator. It powers micropower dual comparator IC1 and also serves as a voltage reference. A fraction of this 3.3V reference is fed to the two inverting inputs of the comparators, at pin 2 and 6 of IC1. The fraction that is applied to those pins depends on the rotation of trimpots VR3 and VR4. These set the low-battery cut-out voltages, and they can vary the voltage at those inputs over the full range of 0-3.3V. The actual battery voltages are applied to the non-inverting inputs, pins 3 and 5, after passing through fixed resistive dividers. While these two dividers use the same resistor values, they are in different orders. So around 1/3 of the Bbattery voltage is applied to pin 3 of IC1a, while about 2/3 of the A-battery voltage is applied to pin 5 of IC1b. In combination with the nominally 3.3V reference and trimpots VR3 and VR4, that means that you can set the switch-on voltage thresholds to anywhere from 0-10V for the B-battery, and 0-4.5V for the A-battery. Those ranges are slightly wider than necessary, to allow for variations in the exact regulator output voltage between samples. Hysteresis is provided by 10MΩ feedback resistors between the comparator outputs and non-inverting inputs. This has been arranged so that the hysteresis is a fixed percentage of the voltage. The source impedance for the non-inverting inputs is 687.5kΩ in both cases (1MΩ || 2.2MΩ), and this forms a divider with the 10MΩ feedback resistor. It gives a hysteresis percentage of 687.5kΩ ÷ 10MΩ = 6.875% So for low-battery cut-out voltages of 3.3V and 6.6V for the A and B batteries, that would give you switch-on voltages 6.875% higher, or 3.525V and 7.05V respectively. The resulting hysteresis voltages are around 0.23V for the Abattery and 0.45V for the B-battery. When both batteries are above their switch-on voltages, output pins 1 and 7 of IC1 are high, at 3.3V. Therefore, the base-emitter junctions of NPN transistors Q7 & Q8 are forward-biased and so both conduct, pulling the gates of Mosfets Q5 and/or Q6 low and lighting LED1. If either battery falls below its switch-off voltage, the corresponding transistor switches off and thus Q5 and Q6 switch off. The high base resistors for Q7 and Q8 (2.2MΩ) are chosen because if one battery voltage is low but the other is high, current will still flow from the corresponding comparator output and this will increase the current drawn from the higher voltage battery (usually the B-battery). The 2.2MΩ base resistors are the highest practical values to minimise this, and determine the minimum value for LED’s current-limiting resistor as 12kΩ. That means that LED1 has to be a high-brightness type. 30 Silicon Chip On/off switch If you don’t need a power switch on the supply, you can simply place a shorting block on CON3. CON3 is provided as a convenient way to switch power on and off, and you only need an SPST switch that hardly has to handle any current. But with S1 off, there will still be a small quiescent current drawn from the two batteries due to the resistive dividers which remain connected. This is around 1.5µA from the A-battery and 3µA from the B-battery. That should mean the batteries last for around a year with the radio switched off. If you need to reduce the battery drain when off, you will instead need to use a DPST or DPDT switch to cut the battery connections to CON1 and CON2. That switch will need to handle the full load current of at least 1A for each battery. Note that the batteries may still suffer from a small amount of self-discharge, so it’s still a good idea to check and charge them every six months or so. Selecting ZD2 Four 5W zener diode options are given in the parts list, to suit different radio requirements. Common radio B-battery Australia’s electronics magazine siliconchip.com.au Parts list – Battery Vintage Radio Power Supply Scope5: the yellow trace is again the transformer primary waveform while the green trace is the voltage across the first 100µ µF capacitor, and the blue waveform is the voltage across the HT output, with a 20mA load (94.5V into 4.7kΩ Ω or 1.9W). You can see that the ripple before the RC filter is very modest at 92mV RMS, and it’s even less after; just 16.7mV RMS. voltages are 22.5V, 45V, 67.5V and 90V. Choose the diode type with a voltage rating just slightly higher than your B-battery voltage. Our suggestions are 24V, 47V, 68V and 91V respectively. For a 135V HT, you can use a 130V or 150V zener. Once the radio has warmed up, you can adjust the transformer drive frequency to get a voltage close to the rated B-battery voltage. The 5W zener diode (ZD2) is mainly included to limit the supply voltage before the valve filaments reach full emission. Note that it isn’t uncommon for the voltage to still rise by 5-10V or more above nominal initially, due to the relatively high zener impedance of these parts (it’s higher for higher voltage zeners). This usually should not cause any problems for most radios, given that it should still be within about 10-15% of the nominal voltage and won’t usually happen continuously unless there is a radio fault. Choosing a transformer The 9V + 9V version (Myrra 44236) should suit most constructors. With a 9V DC input, it will deliver around 100V into a 5kΩ load (20mA), or around 100V into a 10kΩ load (10mA) at 7.5V DC. It’s only if you need more current than this, especially at the upper end of the voltage range (approaching 135V) that you might need to substitute the 6V + 6V transformer, which will give you a bit more HT power. As the battery discharged, I did find that the HT dropped a bit with my test sets during use with the 9V + 9V transformer. However, I didn’t notice any variation in performance as a result of this. PCB design All of the HT tracks and components on the PCB have been spaced apart by 2.54mm, which is enough spacing to suit mains voltages (350V+ DC peak). This isn’t strictly necessary, but it was possible without increasing the board size, so I did it. There is one component (ZD2) that carries HT that’s quite close to one edge of the board, so avoid putting that edge right up against anything conductive. You could add some neutral-cure silicone sealant around its leads and the solder joints on the underside if you wantsiliconchip.com.au 1 double-sided PCB coded 11111201, 125 x 54.5mm 1 Myrra 44236 9+9V PCB-mount transformer (T1) [element14 1214600, RS 173-9939] or 1 Myrra 44235 6+6V PCB-mount transformer (T1) [element14 1214599, RS 173-9923] (see text) 2 RHEF100 or RHEF100-2 1A PTC/polyswitches (PTC1&2) [element14 3296327, RS 657-1772] 4 2-way terminal blocks, 5.08mm pitch (CON1,2,4,5) 1 2-pin header or polarised header with jumper shunt (CON3) 1 SPST panel-mount switch (S1; optional) 4 tapped spacers (for mounting the PCB) to match screws below 8 M3 x 6mm panhead machine screws (for mounting the PCB) 1 flag heatsink with TO-220 insulating washer and bush (for REG1; optional) 1 M3 x 10mm panhead machine screw, nut and two washers (for mounting the flag heatsink) Semiconductors 1 MCP6542-E/P dual micropower comparator, DIP-8 (IC1) [element14, RS, Digi-Key, Mouser] 1 LD1085V 3A adjustable regulator, TO-220 (REG1) [element14, RS, Digi-Key, Mouser] 1 S-812C33AY-B2-U micropower low-dropout regulator, TO-92 (REG2) [Digi-Key, Mouser] 2 CSD18534KCS N-channel logic-level Mosfets, TO-220 (Q1,Q2) [SILICON CHIP ONLINE SHOP Cat SC4177 or element14, Digi-Key, Mouser] 4 BC547 100mA NPN transistors, TO-92 (Q3,Q4,Q7,Q8) 2 IPP80P03P4L04 P-channel logic-level Mosfets, TO-220 (Q5,Q6) [SILICON CHIP ONLINE SHOP Cat SC4318 or element14, RS, Digi-Key, Mouser] 1 high-brightness LED (LED1) 1 5.6V 1W zener diode (ZD1) [^ element14, 1 24V 5W zener diode (1N5359B) (ZD2) [^ ] or Digi-Key, 1 47V 5W zener diode (1N5368B) (ZD2) [^ ] or Mouser] 1 68V 5W zener diode (1N5373B) (ZD2) [^ ] or 1 91V 5W zener diode (1N5377B) (ZD2) [^ ] or 1 130V 5W zener diode (1N5381B) (ZD2) [^ ] (see text) 2 18V 1W zener diodes (ZD3,ZD4) 2 56V 1W zener diodes (1N4758) (ZD5,ZD6) [^ ] 1 W04M 1.5A bridge rectifier (BR1) 2 1N5404 400V 3A diodes (D1,D2) 2 1N4148 small signal diodes (D3,D4) Capacitors 2 220µF 16V low-ESR electrolytic 2 100µF 250V/400V electrolytic [eg, Panasonic EEUED2E101S] 2 10µF 50V electrolytic 2 1µF 50V multi-layer ceramic 2 100nF 63V MKT Resistors (all 1% metal film except where indicated) 2 10MΩ 4 2.2MΩ 2 1MΩ 1 100kΩ 2 75kΩ 1 12kΩ 2 5.6kΩ 2 1kΩ 1 220Ω 1 110Ω 1 100Ω 1W 5% 2 50kΩ mini horizontal trimpots (VR1,VR2) 2 1MΩ mini horizontal trimpots (VR3,VR4) [eg, element14 108244] 1 100Ω mini horizontal trimpots (VR5) [eg, element14 2859725] Australia’s electronics magazine December 2020  31 Fig.2: use this PCB overlay and wiring diagram as a guide to build the Supply and wire it up to the radio and batteries. Construction is straighforward; simply fit the components as shown here, starting with the lowest profile types and working your way up to the highest profile. Make sure that polarised components like the IC, diodes, Mosfets, regulators and electrolytic capacitors go in the right way around. ed extra insulation. But note that this part can get quite hot at times. For that reason, we’ve also increased the amount of copper on the PCB connecting to its leads on both sides; this helps to draw some extra heat away (although its 5W rating is already pretty generous). Construction The Battery Vintage Radio Power Supply is built on a double-sided PCB coded 11111201 which measures 125 x 54.5mm. It has been made as compact as possible, within reason, so you to fit it and the li-ion cells in the space that would have been occupied by the original batteries. Refer now to Fig.2, the PCB overlay diagram, which shows where all the parts go. My original design used mostly SMD components, with many of them mounted under transformer T1, and therefore managed to be a bit more compact than this one. But I think that a lot of Vintage enthusiasts would find it fiddly to build, hence this all-through-hole version, which still manages to be fairly compact. Start by fitting all the small resistors – leave the 1W resistor off, for now. While you can determine the value of a resistor by reading its colour bands (see colour code table opposite), it’s best to use a DMM set to measure ohms to verify this, as some colours can look like other colours under certain types of light. If you are using a single battery to power the Supply, bend one of the resistor lead off-cuts to form link LK1 and solder it to the board in place of the header shown in Fig.2; otherwise, leave LK1 off. As you read the following instructions, keep in mind that you will not be fitting the middle terminal block (CON2), PTC2, diodes D2 or D4, or Mosfet Q6. Mount the smallest diodes, D3 and D4, then all the 1W zener diodes, ZD1 & ZD3-ZD6. All of these must be orientated with their cathode stripes facing as shown in Fig.2. At this point, it’s a good idea to fit comparator IC1. Make sure its pin 1 notch and dot go towards the top of the board, as shown in Fig.2. I don’t recommend using a socket for reliability reasons, although you could if you wanted to. With that in place, mount the larger diodes D1 & D2, again watching the cathode stripe orientation. Then fit bridge rec32 Silicon Chip tifier BR1, ensuring that its longer positive lead goes to the pad marked “+” (its other leads should also have their functions printed on the top of the package). Push it all the way down before soldering and trimming its leads. Now fit switch header CON3. You can use a regular or polarised header, or just solder a couple of wires to the PCB. If you want the Supply to always be on, you can either place a shorting block on CON3 or solder a small wire link in its place. The next step is to fit small signal diodes Q3, Q4, Q7 and Q8. They are all the same type; ensure their flat faces face as shown in the overlay diagram, and bend their leads out gently to fit the pad patterns. Follow with small regulator REG2, which is in a similar package to those transistors, then install the four ceramic and MKT capacitors where shown. Now mount the five trimpots, making sure that you don’t get the three different types mixed up. VR1 and VR2 are 50kΩ (and may be marked 503), VR3 and VR4 are 1MΩ (may be marked 105) while VR5 is 100Ω (may be marked 100). The next step is to fit the smaller electrolytic capacitors, ensuring that their longer leads go to the pads marked with a “+” symbol on the PCB (the striped side of each can indicates the negative lead). Leave the high-voltage capacitors for later. Follow with the two PTCs, which are not polarised, and then the four terminal blocks. Make sure their wire entry holes face towards the outside of the module, and note that the three side-by-side blocks are spaced apart and so should not be dovetailed; mount them individually. Now fit the five TO-220 devices, which all mount vertically. Make sure you don’t get them mixed up (see Fig.2 and Fig.1 or the parts list), and also ensure that their metal tabs are orientated as shown. You may wish to bend the leads of REG1 slightly before fitting it so that its tab is flush with or beyond the edge of the PCB, to make it easier to mount a heatsink later. Follow by mounting the two remaining capacitors. There are pads for a 7.5mm-pitch standard radial capacitor or a 10mm-pitch snap-in capacitor. The former suits the 250V Panasonic capacitor mentioned in the parts list, while the 10mm pads should suit the Altronics Cat R5368 100µF 400V Australia’s electronics magazine siliconchip.com.au This photo of the assembled PC board is, like the diagram opposite, at 1:1 scale. Not shown here are the battery holders because these will depend on the batteries you use and the way they are set up. You need 7.4V on CON1 – easily achieved with a dual “18650” battery holder (two cells in series). For the 3.7V required for CON1, we used a pair of single battery holders connected in parallel, as can be seen in the photograph on page 30. capacitor. You might also be able to get Jaycar Cat RE6156 (100µF 400V) to fit with a bit of lead bending. Fitting the transformer The transformer has four leads on one side and two on the other, and these should be an exact fit for the PCB pads. I had to do quite a bit of ‘massaging’ of the leads to get them to go in, though, as they are such a precise fit. I found that tweezers are a good tool for this, as you can slip them in under the transformer and gently bend and coerce the leads until they all pop into their respective holes. Make sure the transformer is pushed down all the way onto the board before soldering and trimming its leads. The transformer will now make a nice steady base as you mount the 1W resistor and 5W zener diode (ZD2). While you could push these all the way down onto the board, it will aid in convective cooling if you space them off the board at least a few millimetres. I raised them by about 8mm above the top of the PCB on my prototype. Remember to choose ZD2 based on your radio’s HT voltage. You can now install LED1. How you do this depends on what your plans are with it. If you don’t need an external power-on LED indicator, you can simply push it right down (with its longer lead on the side marked “A”, opposite the flat on the lens) and solder it in place. Or you could bend it over at right-angles, facing away from the module. If you want it to be externally visible, it would be best to chassis-mount it using a bezel. You could then either solder flying leads from its leads to the PCB pads, or solder a 2-pin header (regular or polarised) onto the PCB and then solder leads to the LED with a plug or plugs at the other end. If your radio will drawing more than about 500mA from CON5, especially if there is a big difference between its LT voltage and the battery supply, fit a flag heatsink to REG1. I used an insulating washer and insulation bush mainly to ensure good contact between the heatsink and regulator, but it’s also a good idea in case the heatsink could short to a metal case, the chassis or anything else. You will definitely need to insulate the tab from the case or chassis (using insulating washer and bush) if you are mounting it directly to the case/chassis for cooling. That just leaves the four tapped spacers, which you can attach to the provided holes on the board, for mounting the module to your radio case (or wherever you plan to use it). Testing and adjustment It’s best to test and adjust the Supply using a variable DC bench supply; ideally one with current limiting. You’ll also need a DMM at the ready, set to a high volts range. As the board can generate some hazardous voltages, make sure that it is in a location where it can’t short against anything and where you can probe it without any risk of coming in contact with the board. Start by centring trimpots VR1 and VR2, setting VR3 Resistor Colour Codes Qty.              2 4 2 1 2 1 2 2 1 1 1 Value     4-Band Code (1%) 5-Band Code (1%) 10MΩ 2.2MΩ 1MΩ 100kΩ 75kΩ 12kΩ 5.6kΩ 1kΩ 220Ω 110Ω 100Ω siliconchip.com.au brown black blue brown brown black black green brown red red green brown red red black yellow brown brown black green brown brown black black yellow brown brown black yellow brown brown black black orange brown violet green orange brown violet green black red brown brown red orange brown brown red black red brown green blue red brown green blue black brown brown brown black red brown brown black black brown brown red red brown brown red red black black brown brown brown brown brown brown brown black black brown brown black brown gold (1W/5%) Australia’s electronics magazine Minimising EMI radiation While this circuit has low EMI, component variations could mean that yours radiates enough to affect radio reception. If so, try increasing the values of the two 5.6kΩ resistors. These slow the switch-off of Mosfets Q1 & Q2, reducing the spikes at the transformer primaries. These should ideally be below the 56V conduction threshold of zener diodes ZD3 & ZD4. Test the supply with your radio tuned off-station. If you hear hash, try increasing the 5.6kΩ resistors to 15-22kΩ or possibly higher. If you have a scope, check the waveforms at the cathodes of ZD5 and ZD6 to see that the spikes have been reduced or just test it again with the radio. December 2020  33 and VR4 at maximum and VR5 to its minimum. If you’ve built the two-battery version, bridge the positive inputs together (you don’t need to bridge the negative terminals as they are connected on the PCB). Set your bench supply to around 4V and the current limit to a low value, then switch it off and wire up either input (CON1 or CON2) to the supply. Switch the supply on and watch LED1. It should not light yet, and the current drawn from the supply should be low (under 1mA). If it’s significantly higher than that, you could have a board fault, so switch off and check for short circuits and incorrectly located or orientated components. If all is well, increase the current limit to around 1A and wind the voltage up to about 8V, then rotate VR3 anti-clockwise until LED1 lights up. The circuit has now powered up, so check the voltage across the CON4 output. It should be slightly higher than the voltage rating of zener diode ZD2. You may notice ZD2 and/or the 100Ω resistor getting warm. Also check the output voltage at CON5. It should be around 1.2V. Check that you can vary it by adjusting trimpot VR5. You might as well set it to your desired voltage while you’re at it. Now rotate VR3 and VR4 fully anti-clockwise, set the supply voltage to your desired A-battery (li-ion) cutout voltage, then rotate VR4 clockwise slowly until LED1 switches off. Then increase the supply voltage to your desired B-battery cut-out voltage; LED1 should switch back on. Rotate VR3 slowly clockwise until the unit switches off. You have now set both battery cut-out thresholds. To set the ideal operating frequency, you will need to connect your actual radio to the outputs (after powering the supply down). Power it back on and wind the supply voltage back up to your nominal battery voltage (around 7.4V for two li-ion or LiPo cells in series). Switch the radio on and after it has warmed up, make sure it is working normally. Then adjust VR1 and VR2 in lockstep (eg, making small changes in one, then the other) while monitoring the HT voltage. Adjust until you achieve the specified voltage, or as close to it as you can get. Once you have done that, if you have a scope, you can adjust for 50% duty cycle in the transformer drive. Power down the circuit and connect the scope up to the ends of the 5.6kΩ resistors closest to Mosfets Q1 & Q2 and connect the scope’s ground to circuit ground (eg, the anode of D1 or D2). Power it back on and adjust VR1 and VR2 by small amounts in opposite directions until you achieve pulse widths on both channels that measure the same. You may need to re-tweak the frequency/HT voltage after doing that. You should eventually arrive at settings for VR1 and VR2 that satisfy both conditions. It’s then just a matter of mounting the Supply module and its batteries to your radio case or to a piece of timber you will install in the case. Or if it won’t fit inside the radio, you could mount it in some sort of Jiffy box and wire it up to the set. If doing that, make sure both the module and the wiring are properly SC insulated! You asked for it . . . WE’ve DELIVERED! Over 265 Articles from April ’97 right up to date! The Vintage Radio Collection from the pages of SILICON CHIP “Vintage Radio” is one of the most popular columns which appears every month in Australia’s most-read and authoritative electronics magazine, SILICON CHIP. Over the years many readers have asked us if there was a single source for all “Vintage Radio” articles so a particular set or sets they have managed to get hold of could be referenced. Until now, that was not possible. But now it is! We’ve put together a DVD# containing every “Vintage Radio” column for more than 20 years – from April 1997 right through to December 2018 – and included an easy-to-read index so you can nd the one you’re looking for. They’re all provided in PDF format so the quality is even better than in the magazine (you can actually read many dials!). And there’s much more than radios – there’s articles on vintage TVs, ampliers... all from a bygone era! Physical DVD: In paper sleeve – $55 seen In deluxe case Asabove – $60 (Both including p&p) Downloaded copy – $50 #To view, requires Adobe Acrobat on your computer (free to download): https://get.adobe.com/reader/ Cannot be used with an audio DVD Player Exclusively available from SILICON CHIP: www.siliconchip.com.au/shop 34 Silicon Chip Australia’s electronics magazine siliconchip.com.au Some people are just IMPOSSI BLE to buy Christmas gifts for! You know the problem: you want to give a Christmas Gift that will really be appreciated . . . but what to give this Christmas? We make the impossible possible! Give them the Christmas Gift that KEEPS ON GIVING – month after month after month: DECEMBER 202 0 ISSN 1030266 2 The VE RY BEST DIY Pro jects! 12 9 771030 266001 $9 95 * NZ $ 90 12 YUZXYUZ INC GS T INC GST Aut m ot ve E leco t roni ics • • • • • Self-mad e PCBs using a laser Uses Li-ion or LiPo cells Little to no EMI generated Battery over -dis Reversed cell char ge prot ection protection 24-135V HT and 1.2-2.5V LT BatteryPowered for Vint age Radi Supply os Dual Batt ery Lifesav er Volt/Am p Pane l Meter s siliconchip.com .au pro tec t you r bat ter Australia’s elect ies fro m dam age ronics magazine low-cost December 2020 ● minia ture 1 ● DC A GIFT SUBSCRIPTION to SILICON CHIP For the technical person in your life, from beginner and student through to the advanced hobbyist, technician, engineer and even PhD, they will really appreciate getting their own copy of SILICON CHIP every month in the mail. They’re happy because they don’t have to queue at the newsagent each month. 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Don’t forget to include all details! include your contact info! to PO Box 139, Collaroy NSW 2097 CHRISTMAS IS ONLY 3 WEEKS AWAY! Make PCBs with Laser Engraver Making PCBs at home is an attractive option as you can go from a design to a board in less than an hour, thus reducing the time needed to go from a prototype to the final version. But most of the well-known methods are tricky and/or messy. This one is easy and reliable. You just need a laser engraver or cutter, which are surprisingly inexpensive! M aking your own PCBs is popular with many hobbyists. This has been fuelled in recent years by the widespread availability of low (or no) cost, easy-to-use PCB design software. While designing a PCB is now relatively easy, turning beautiful layouts on the screen into equally attractive, ready-to-use PCBs is a far more demanding challenge. Methods used by hobbyists range 36 Silicon Chip from hand-drawn PCBs using a spiritbased marker pen, photographic image methods using special photographic film or laser/ink-jet printed transparencies, UV light tables and photosensitive PCBs, schemes using domestic irons or heated roller laminators to heat-transfer laser printed artwork to bare PCB, and various CNC milling methods. Others with greater mechanical skills have modified an ink-jet or laser printer to print their layouts onto Australia’s electronics magazine blank PCB directly. Except for CNC milling, all of these methods also require chemical etching and subsequent cleaning, drilling and trimming to complete the PCB. Each approach has its advantages and disadvantages. Hand-drawing a PCB is only really suitable for the most basic designs, so we will only consider methods involving computer-aided design (CAD). These are summarised in the table opposite. siliconchip.com.au a Low-cost or Laser Cutter by Andrew Woodfield The photographic method usually involves printing a PCB layout onto transparent film with a laser printer. A blank PCB is covered by a photosensitive layer (or purchased complete with this photosensitive layer) and exposed to UV light passed through the layout artwork. The PCB is then developed to expose the copper to be etched, and the PCB etched in the usual manner. This method yields very high-quality PCBs. However, some of the chemicals and good light exposure equipment can be relatively costly. Larger PCBs may be difficult to make since these require an even light distribution across the layout film. The process is also fairly time-consuming. In recent years, the CNC method has become popular for PCB prototyping. A CNC milling machine with a V-shaped cutting tool cuts the layout onto a blank PCB. The process is fairly slow compared to other methods, and machine vibration and V-cutter wear can quickly lead to poor results. You need very flat blank PCBs, a flat milling bed and suitable clamps to get good results (see Fig.2). Plus it produces a lot of dust. Milled PCBs can also require considerable post-processing to produce adequate results. Tiny copper whiskers left by the V-cutters can be very time-consuming to locate. Recent improvements such as bedlevelling software and USB interfaces have made PCBs somewhat easier to make with this method, and the cost of small milling machines has reduced in recent years. Such CNC systems can give excellent results, and one significant advantage of this approach is the avoidance of chemicals in the production process. Other popular hobbyist methods include the heat transfer method or modified printers, both of which can give good results. However, the variability of domestic irons, temperatures and pressures can lead to mixed results for many (we’ve had many frustrating failures with this approach). Similarly, few have the time or ability to modify an ink-jet or laser printer to achieve the excellent results possible with direct printing to PCBs. In any case, many hobbyists have drifted away from making their own PCBs, the result of very low prices for small quantity ready-made PCBs from PCB manufacturers. The quality of the vast majority of these PCBs is very high. Method Equipment needed Setup Time & Cost Production Method Production Cost Post Production Photographic Pre-sensitised PCB, PCB developer, UV light box  Printing or exposure, spraying, developing, etching – Moderate Rinse clean, PCB drilling and trimming  Rinse clean, PCB drilling and trimming – Can be good with care Can be timeconsuming   Good Low (Noisy) Slow  Depends on etching chemicals  Heat transfer CNC milling Domestic iron or heat roller / laminator CNC milling machine with a flat bed and holding clips, cutting bits Moderate Low to moderate Printing, heat and pressure, chemical etching   CNC milling  High Modified printers Modified ink-jet or laser printer Commercial production    None Nil Laser engraver or cutter, spray paint  Laser Engraver siliconchip.com.au   Moderate (too difficult for many) Moderate Low to moderate  Moderate (V-cutters, mill bits, drill bits) Direct printing to PCB Low Chemical or hand clean, PCB drilling and trimming Third party  Nil  Low to moderate Paint, laser engraving, chemical etching  Low to moderate Quality & Resolution   High Good   Very good Chemical or hand clean, PCB drilling and trimming Australia’s electronics magazine  Good Environmental Impact Time to Make One PCB Depends on etching chemicals  OK  OK Vendordependent (Can be high) Depends on etching chemicals  OK   Slow (delivery)  OK December 2020  37 Fig.1: this is the sort of result that can easily be achieved using the laser engraving method. The only real defects that you could complain about here are the result of my lessthan-perfect drilling accuracy, which has nothing to do with the laser! The major disadvantages are the waiting time – anywhere from a few days to six weeks – and the potential for waste. If you only need one or two boards, the shipping costs can be much more than the cost of actually making the boards. And if design errors are subsequently discovered, you have to pay for another shipment and then wait all over again. Exploring other options In an effort to make reasonablequality prototype PCBs more quickly and easily, and to obtain better firsttime results from PCB vendors for larger quantities, I spent some time looking for a better solution. A laser engraver looked like a suit- Fig.2: milling a simple PCB with a hobby-level PC-controlled CNC mill. While this can undoubtedly produce usable results, without needing any chemicals, it’s a slow, noisy and dusty process and you need to do a lot of tweaking to set it up properly. Our attempts to do this in the past have been stymied by blank PCBs that were not perfectly flat. able candidate because these provide a very high degree of accuracy and reliably recreating an image transferred from a PC with little fuss. The problem was then how to use them with a blank copper-laminated PCB, as they are not really designed for working with metal. Laser cutters and engravers These come in a variety of sizes and powers. Chinese-made equipment dominates the low end of the market. The largest and most powerful types use glass-tube CO2-based laser cutters built into desktop fully enclosed cabinets with top-opening covers, fume extractor fans and hoses for water cooling. Fig.3: a highpower ‘K40’ cabinettype laser cutter. This is similar to the one we have at SILICON CHIP. Ours is bigger but also a bit more crudely constructed. One of the best things about these devices is how accurate they are, and how good the repeatability is. Once they are set up, they work very well indeed. 38 Silicon Chip Australia’s electronics magazine Laser power outputs claimed by vendors for these “K40-type” basic laser cutters range from 40W to over 100W (see Fig.3). The 40W lasers will cut through 6-8mm thick plywood, and they also work well with acrylic plastic sheets. These machines typically cost around $AU1000 including delivery, and often require another $200 or more spent for water pumps, vent pipes, repairs and additional items to make them safe and ready for use. More recently, solid-state laser engravers at much lower powers have appeared. Laser power ranges from 1W to 10W, and they are made in either a ‘square frame’ or ‘crane arm’ arrangement (see Figs.4 & 5). In this latter type, the stepper motor balances the weight of the laser at the far end of the arm. Both have a small controller board fitted to the outside edge of the frame or onto a vertical side panel. Both feature USB interfaces and are supplied complete with a small laptop-style power supply, Windowscompatible laser software, and, usually, a pair of safety glasses. A few sample scraps of thin plywood and acrylic for initial testing are also usually included. It was these latter inexpensive low power laser engravers that appeared to have the most potential for PCB prototyping. They offer a simple solution to optically ‘write’ the layout onto a blank PCB. Prices for engravers with 5W lasers are relatively attractive, at under $AU250 including delivery. This outsiliconchip.com.au Fig.4 (above): a low-cost ‘square-frame’ laser engraver. They typically use solid-state lasers in the range of 1-10W. 5W is a good figure to aim for if you want to make PCBs. Fig.5 (right): a low-cost ‘crane arm’ type laser engraver. It’s more compact and probably cheaper than the square-frame type, but may not offer quite the same speed or repeatability. put power was claimed to be suitable for cutting 1-2mm card or timber veneer. Of course, the larger and more expensive fully-enclosed laser cutters are also very suitable, and are more flexible devices. But if you only want it for making PCBs, it’s hard to justify that extra cost. Engraving copper with a laser Blank PCBs are made by bonding a thin copper layer onto one or both sides of a low-cost phenolic or highercost fibreglass panel. The most commonly used “1oz” (1 ounce) PCBs have a copper layer which is 1.4 mils (thousandths of an inch or thou) thick. In metric terms, that’s 36µm or 0.036mm. At first glance, it seems like it would be child’s play just to blast this ultrathin copper layer off the board using a laser. Unfortunately, the thermal and optical properties of the PCB’s copper layer make this impossible to achieve directly with sub-100W laser power outputs. Much of the laser energy is (dangerously) reflected and scattered by the bare copper. The energy that does heat the copper is efficiently dissipated by the thin copper layer on the PCB. Copper vapourisation is undoubtedly achievable with high-power 5kW and 10kW industrial lasers, but such equipment is well outside the price range of the average hobbyist. The solution to this is to employ a two-stage process. First, a layer is applied to the copper which can be accurately engraved by the inexpensive, low-power 5W laser. A subsequent standard chemical etching process can then remove the unwanted copper. A useful outcome of my effort was the ability to make PCBs during and after the COVID-19 lockdown, when siliconchip.com.au international PCB production stopped and shipping was halted. It turns out that a ‘suitable layer’ can consist of almost any type of spray paint. The cheaper the paint, it seems, the better the result. Of the various spray paints I have tried to date (six different brands), all were easy to apply and give good visual coverage of the copper. Usefully, as it turns out, the cheapest paint has the worst adhesion. Just one layer of paint is sufficient. When the paint layer is removed by the low-power laser, clean copper remains. In one set of tests, the paint was left to dry for the recommended minimum recoat time (one to two hours) and the laser still completely removed all residue. If, however, the painted PCB was left for several days, the paint bonded much better to the copper and this occasionally resulted in a residual layer which the laser did not remove. Tests also showed that darker paints gave better results than lighter colours. The low-power lasers very effectively removed colours such as black, dark grey, dark green and navy blue. White spray paint can be used, but the laser is noticeably less effective. Increased laser power or repeated engraving runs are required. Also, the level of reflected laser light increases significantly, which could potentially be dangerous. Incidentally, there was no practical difference found between gloss and matte paint. Once the laser hit them, the surface finish of both paint types was instantly removed. For completeness, standard plastic model enamel paints, the type that comes in tiny paint cans, were also tested. These were applied with a small modelling paintbrush. These paints appeared to have significantly better surface adhesion. Coupled with the variation in layer thickness Fig.6: a negative of my PCB layout, without any infill. By negative, I mean that the tracks are white and the blank space is black; the opposite of what you usually get when you export a PCB design from ECAD software. Fig.7: the same layout as Fig.6 but with infill. This ‘floods’ the unused area with copper, meaning that the laser and chemicals need to remove a lot less material from the blank PCB to give you a usable design. As a bonus, if you connect the infill area to ground, it might also perform better and radiate less EMI. Testing spray paint Australia’s electronics magazine December 2020  39 Fig.8: a blank PCB after I applied a single coat of cheap black spray paint. I leave them to dry for 1-2 hours before moving onto the laser etching stage. caused by a brush application, they were not as easy to use, although PCBs produced this way were (just) usable. Suggested procedure The following procedure was developed for use with a 5W laser engraver. It was operated on power levels between 60% with the cheapest paints and 80% for other paints; running this laser at full power (100%) appeared to ‘bake’ the paint onto the PCB. Using this 100% power level at higher writing speeds would also almost certainly give identical results to the 60% and 80% tests, as long as your engraver motors are reliable at these speeds. You will need to do some testing yourself for your paint and your laser to find the ideal settings. Laser power outputs as low as 2W will work, but may require repeated engraving passes. More expensive 7W, 10W and 15W solid-state laser modules are also likely to be successful, probably with much lower power settings. If you change the paint you use, these tests will almost certainly have to be repeated. Left-over PCB scraps are ideal for such tests. Here are the suggested steps for making the PCB: 1. Export the PCB layout in a suitable format from your PCB design software. 2. Prepare the blank PCB. 3. Load the layout into the laser engraver. 4. Check the layout is correct, ie, size/scale, inverted, mirrored. 5. Configure/check the laser engraver settings. 6. Place the blank PCB under the engraver and check the image borders. 7. Engrave the PCB. 40 Silicon Chip 8. Clean any residue from the PCB 9. Etch, drill, trim and clean the PCB. Now let’s expand on those steps. 1. Export the PCB layout When designing the layout, use the widest possible tracks, and set the diameter of all drilled holes to 20mil (0.5mm) or 25mil (0.635mm) diameter to act as centres for manual drilling later. These settings help to compensate for the limited beam focus of these cheap lasers, plus any undercutting during etching. Similarly, if possible, maximise the layer infill to retain most of the copper. My layout software calls this ‘automatic ground plane’ (or you could manually add a ground plane). This feature speeds up the laser engraving process and the subsequent etching, as less copper has to be removed and smaller amounts of the chemicals are consumed. The PCB layout must be exported as a negative and mirrored image. A negative image is necessary because the laser is turned on when the image is black and turned off when the image is clear or white. Most PCB design software exports an image assuming the coloured trace shows where the conducting copper will be left. Similarly, almost all PCB layout design software assumes you are looking down on the component side of the PCB. The mirror image is required because the laser engraver assumes the image it is burning is as seen from the solder side of the PCB. Figs.6 & 7 show what the required files look like. When infill is not used in the layout software, the result is like Fig.6. The black area to be removed by the laser is much greater than in Fig.7, where infill is used, so the result in Fig.7 is preferable. Most laser engravers can accept a wide variety of file types. JPG or BMP are usually the easiest to use. However, the laser engraver software does seem to ignore image dimensions and Fig.9: I downloaded the software for my laser engraver from the supplier’s website. It is very easy to use. Here, the PCB image to be engraved has been loaded, and initial settings can be confirmed or adjusted. Australia’s electronics magazine siliconchip.com.au scaling set in layout software so carefully check this just before engraving (see step 4). 2. Prepare the blank PCB Clean the PCB. Use a mildly abrasive white liquid kitchen surface cleaner and wash off any residue cleaner under the tap. The copper should be clean enough to etch immediately. Spray the copper side of the PCB with a single coat of your selected spray paint. All the copper should be covered evenly (see Fig.8). Allow to dry for the manufacturer’s minimum drying time; 1-2 hours is typical. 3. Load the layout into the laser engraver Manually locate the engraver’s laser in the correct location if necessary (see Step 6). Connect the USB cable to the computer and power up the engraver. Start the engraver software and load the image. An example screenshot for such software is shown in Fig.9. 4. Check the layout is correct Check (again) that the image shows the tracks as white against a black background, and the image is mirrored. Most laser engraver software also allows you to invert and mirror the image at this point. Check the image size reported in the laser engraver software matches what you are expecting. This may not match the edge-toedge PCB size used in the PCB layout program. If not, adjust the scaling. 5. Configure/check the laser engraver settings These will vary depending on the software supplied with the engraver. It will, almost certainly, allow configuration of the laser output power, the writing speed, the image resolution to be used for writing by the laser, and the time spent on each point. As a suggested starting configuration, the following are the author’s configuration: Mode: Line (or raster) mode This writes the image as a series of Laser safety Fig.10: checking placement of the surface to be engraved using the ‘range review’ mode. The visible laser dot races around the edges of the design, so you can verify that it’s the right size and it is correctly located on the PCB surface. ‘continuously-on’ lines rather than a sequence of laser ‘dots’ or ‘points’. Power: 80% Speed: 1000mm/minute Resolution: 10 dots/mm Engraving Time: 10ms These must be determined for your laser and your spray paint. Start with the default settings provided by the laser vendor or those shown here, which are for a 5W 410-480nm laser. To determine the best laser settings, I designed a small 30 x 30mm sample PCB layout for testing. I tested various power, speed and engraving time settings, one by one, to find the best result. In each case, the paint was applied to the bare PCB, and the laser engraver operated to engrave the layout. The result of each test was evaluated, the paint removed, and fresh paint applied for the next test. Mineral turpentine usually removes the paint quickly, with the occasional assistance of an abrasive stainless steel pad from the kitchen. I didn’t bother etching it until a satisfactory laser engraved result was obtained. So, if your engraved PCB from your first try with this method is not satisfactory, just scrub off the engraved paint, spray on a fresh coat, and have another try. This is a simple, quick and effective method without having to Lasers, especially those at the power levels discussed here, can be very dangerous. You must not look directly into the laser light at any time. Safety glasses with a suitable rating for the laser light MUST be worn during operation. I have seen some serious doubts expressed over the suitability of the safety glasses shipped with some of these laser engravers. Suitable safety glasses which meet accepted standards are available in most countries. While the price for these glasses may appear high, at around AU$150, they will prevent damage to your eyesight from accidental laser exposure. So they are worthwhile. siliconchip.com.au toss away a pile of poorly etched PCBs! 6. Checking the laser focus and borders If you are using an engraver which lacks an enclosure, now is the time to put on your laser safety glasses. Usually, the laser engraver will initialise with the loaded image centred at the current location of the laser. This is its location when the laser engraver’s power is turned on. Place the prepared blank PCB under the laser engraver. It is not necessary to fix the PCB in place but larger PCBs, say over 50mm in any dimension, may require the laser engraver to be firmly attached to the bench or table. This is an optical process and stepper motor vibration, if any, does not appear to move the PCB. However, your engraver may not be as obliging. Double-sided adhesive tape or pinboard tacks should be adequate in such cases. The laser module has a small latching pushbutton to start the laser in a ‘preview/low power’ mode. Turn on this low power switch. Check that the laser is correctly focused on the surface of the PCB. Then turn off the latching low power switch on the laser head. This step is essential. If you forget to do this, the laser will faithfully try to engrave your layout One possible supplier of such glasses in Australia is www.lasersafetyglasses.com.au Neither Silicon Chip nor the author have any association with this company. Each reader must confirm the suitability of any safety glasses purchased. Make sure they are suitable for the specific laser and the intended use. Otherwise, then you’re better off buying a fully enclosed laser engraver or cutter with a lid safety interlock switch, but those cost even more than the proper safety glasses. Australia’s electronics magazine December 2020  41 Fig.11: for your first few designs, or a particularly critical one, it’s a good idea to do a test print on cardboard to check for scaling accuracy, PCB dimensions and component clearances. Just make sure you run the laser at reduced power with cardboard; you aren’t trying to cut through it! during the next step with something like 1% of the normal laser power. That will not work very well. Next, check the layout is correctly located on the prepared PCB. Start the ‘Range Preview’ mode using the engraver software. The laser engraver will now show the boxed outline for the image it is about to write (see Fig.10). This outline is repeated continuously by the engraver, to allow manual adjustment of the PCB location. This is carried out at low power. Even so, wearing safety glasses is strongly recommended. Make sure all of the image falls in the correct location on the prepared PCB. Also, check (again!) that the image size is correct and in the right place. Stop the ‘Range Preview’ mode using the engraver software. It is sometimes useful to run a ‘test print’ to double-check the board dimensions before engraving a PCB. In this case, you can use a scrap of cardboard of similar thickness to the PCB and use a laser power setting of, say, 10%. This will burn the PCB layout onto the cardboard to allow final confirmation of measurements, component clearances and pad sizes before engraving the actual PCB. An example of this can be seen in Fig.11, a PCB for a VHF FM receiver. This was for a larger 120mm x 50mm board. 7. Engrave the PCB Start the laser engraving process using the vendor-supplied PC software. It usually has a large bright ‘Start’ icon on the screen for this purpose. You may wish to have a fan running during the engraving process to encourage good airflow around the laser engraver. The vapourised paint fumes are almost certainly harmful. This process is not one for the kitchen 42 Silicon Chip or bedroom – definitely head for the workshop or garage. Avoid looking into the laser light. It’s tempting to watch progress, but the laser light can cause significant damage to your eyesight. Protective glasses are vital, and even with these, avoidance is best. Be aware, too, that the very bright laser light can reflect off the etching paint and any walls and ceiling of the room being used. Reflected laser light may also be a hazard to those with sensitive skin. In any event, the engraver does not need any attention during the process. It will stop and turn off the laser when it is complete. A fan will often continue running on the laser module throughout and after the procedure. The vendors don’t mention this, but leaving it running for a minute afterwards to cool anything hot is probably a good idea. 8. Clean any residue from the PCB Once the process is complete, the software will turn off the laser and return it to the starting position. The power to the engraver can now be turned off. It’s now safe to pick up the board to see the result. You will likely see the surface covered with a clear outline of your layout submerged in a thin layer of fine grey or black dust (Fig.12). Lightly brush this dust off the surface of the PCB with a small 12mmwide paintbrush. Tapping the bristles directly downwards on the surface removes any ash-like powder from the surface. The PCB is now ready for etching (Fig.13). Note, though, that it’s possible that after brushing, there will be a faint near-transparent residual layer left after the laser etching. This only happened for me when using relatively expensive spray paint, when the paint was left to dry for several days, or when the laser power was too low, or the writing speed was too high. Using cheaper paint helps to avoid this problem, as do higher power levels or slower writing speeds. This thin layer can be hard to see. Careful continuity measurement across the layout of these exposed copper areas with an ohm-meter or a buzzer will show it to be a remarkably good etch-resist. Don’t use super-sharp pointed probes for this test; rounded ones are best. Just gently lay them on two separated engraved areas of the layout which are electrically connected. If your PCBs have this layer after engraving, and different settings fail to resolve it, don’t worry. It’s not difficult to remove. Bunch up a few paper tissues into a ball, and dampen these with a little mineral turpentine. Carefully, and lightly, wipe the surface of the PCB. One or two wipes is sufficient. Wait for the surface to dry and retest with your ohm-meter or buzzer. If Fig.12: you can just make out the slightly dusty engraved layout on the surface of this PCB. Australia’s electronics magazine siliconchip.com.au Fig.13: the layout is much more clear after carefully brushing the dust away. you are getting good conductivity, you are ready to proceed to etching. If not, try another careful wipe. The idea is to wipe off just this unwanted residual layer while leaving the etch-resistant painted layer unaffected. If you press too hard with the tissues or repeat it too many times, the paint may also be removed. Again, that’s not a huge problem. You just have to repeat the whole ‘clean-paint-engrave’ process. The PCB has not been damaged, and a new paint layer will allow you to have another try at the procedure. 9. Etch, drill, trim and clean the PCB The PCB can now be etched in the usual manner. I mix 20% hydrogen peroxide (H2O2) solution and 30% hydrochloric acid (HCl) solution in equal parts; just enough to cover the PCB. The etching usually takes one to two minutes. I use a small 12mm-wide foam pad brush with a timber handle to help wash the etchant across slower-to-etch areas. Other etchants can be used equally successfully and are arguably less dangerous. However, other etching chemicals may require heating (ammonium persulfate – (NH4)2S2O8) and/or take considerably longer (eg, ferric chloride – FeCl3). The paint appears equally impervious to any of these chemicals. Fig.14: the PCB after it has been chemically etched and the paint removed with mineral turpentine. sharp beam focus from these low-cost solid-state laser modules. The quality of these lasers varies, as you might expect. This method does support SMD layouts as well as a reasonable range of PCB sizes. The laser retains good focus and performance across the engraving span of the equipment purchased. The author has successfully produced over two dozen different PCBs over the past five months for a variety of projects with this method. It now takes about half a day, much of that time spent cleaning and painting the blank PCB, then waiting for it dry. The process of laser engraving, etching, cleaning, drilling and cutting to size averages about 1-2 hours per board depending on size and complexity. That time certainly beats the Results One of several PCBs made while this article was being prepared can be seen in Figs.1, 14 & 15. The resolution of the process is reasonably close to the best hobbyist or in-house photographic methods. It’s limited only by the ability to achieve a siliconchip.com.au Fig.15: the completed PCB, trimmed to size and drilled by hand. Australia’s electronics magazine delivery time for any of the low-cost PCB vendors. The process could be used to make double-sided PCBs, but I have not attempted that to date. There is no inherent reason why it should not be possible. Similarly, the procedure works with both fibreglass and very cheap phenolic PCBs. There was no sign of any temperature damage or heat marks on the phenolic material. The costs of this process are not as low as some other methods, such as the domestic iron thermal transfer approach. The cost of the laser engraver and safety glasses must be considered. But arguably, it will give more consistent results. The chemicals used are relatively cheap, but some can be difficult to obtain in some locations. You certainly can use this process to make your own boards for less than it would cost you to buy them (mainly because of delivery costs). Without a doubt, commercial manufacturers deliver excellent quality PCBs, but the wait is considerably longer. This laser-based approach also allows layout design errors to be identified quickly. Then, rather than throwing 5-10 commercial PCBs away, a single PCB is binned and another PCB is ready the next day. If you are looking for a better or faster solution for making prototype PCBs, you should try this method. It’s a very good cost-effective solution, and once you’ve figured out the parameters to use, it’s very straightforward to repeat. Just don’t forget those safety glasses! SC December 2020  43 Dual Battery Lifesaver by Nicholas Vinen This small board provides an easy way to protect rechargeable batteries from being completely drained if a device is accidentally left switched on. It can work with devices that run from a single battery, or two separate batteries. Both thresholds are fully adjustable, and it can handle several amps per battery, drawing just a few microamps when off. W hile working on the Battery Vintage Radio Power Supply article (starting on page 30 of this issue), Ken Kranz suggested that the low-battery cut-out section of the circuit could be useful on its own, and we had to agree with him. So we have produced a separate PCB which contains just that portion of the circuitry. It can be used with just about any device powered by 3.6-15V DC at up to 5A per output. Typically, it is configured so that both outputs are cut off if either falls below its individual voltage threshold. However, it can also be reconfigured only to cut the outputs off if both fall below the threshold, or you can build a slightly simpler version for use with a single battery. No heatsinking is necessary as the Mosfets used for switching have minimal dissipation, around 100mW at 5A. It has provision for an optional onboard power indicator LED, and also provides for an SPST (or similar) switch to disable the outputs, so that you can use a small, low-current switch as a power switch. We previously published a very small single-battery Lifesaver in the September 2013 issue (siliconchip.com.au/ Article/4360), which has been quite popular. Besides being small, its other advantage is that it can handle quite a bit of current; 20A or more. However, it used quite a few SMDs 44 Silicon Chip and was a bit tricky to build, tricky to set up and had a limited adjustment range once built. This version uses all through-hole parts and so is nice and easy to build, and not all that much bigger despite being able to handle two batteries. This one is also straightforward to set up, with a single trimpot allowing the cutout voltage to be adjusted over a wide range for each channel. Circuit description Mosfets Q1 (and Q2, if fitted) connect the supplies at CON1 and CON2 to the outputs at CON3 and CON4 when switched on. They are switched off, disconnecting the outputs, if either (or both) supply voltages are below defined thresholds. When switched off, either via the switch S1 Shown here mounted on four insulating pillars, the Dual Battery Lifesaver uses all through-hole components so is very easy to build. Australia’s electronics magazine or due to a low battery voltage, the circuit only draws about 10µA from the higher voltage battery and about 2µA from the other. Presumably, you would notice the device has switched off and either recharge the cells or swap them for fresh ones. But if for some reason you forget and leave the device switched on, it would be several months before this minimal current drain could damage the cells. That’s why this circuit was designed with a low quiescent current in mind. When power switch S1 is closed, current can flow from whichever battery has a higher voltage, through small signal diodes D1 & D2 and then switch S1, into the input of REG1. This is an ultra-low-quiescent-current, low-dropout 3.3V linear regulator. It powers micropower dual comparator IC1 and also serves as a voltage reference. A fraction of this 3.3V reference is fed to the two inverting inputs of the comparators, at pins 2 and 6 of IC1. The fraction that is applied to those pins depends on the rotation of trimpots VR1 and VR2. These set the low-battery cutout voltages, and they can vary the voltage at those inputs over the full range of 0-3.3V. The actual battery voltages are applied to the non-inverting inputs, pins 3 and 5, after passing through fixed resistive dividers. While these siliconchip.com.au               SC   DUAL BATTERY LIFESAVER Fig.1: the Battery Lifesaver is built around micropower comparator IC1 and micropower regulator REG1, which supplies IC1 and also acts as the voltage reference. IC1 compares fixed fractions of the battery voltage(s) with the voltages at the pot wipers, and if the battery voltages are high enough, it switches on transistors Q3 and Q4, which in turn switch on Mosfets Q1 and Q2. two dividers use the same resistor values, they are in different orders. So around 1/3 of the CON1 voltage is applied to pin 3 of IC1a, while about 2/3 of the CON2 voltage is applied to pin 5 of IC1b. In combination with the nominally 3.3V reference and trimpots VR1 and VR2, you can set the switch-on voltage thresholds to anywhere from 0-10V for the CON1 battery, and 0-4.5V for the CON2 battery. Those ranges suit Li-ion, LiPo or siliconchip.com.au LiFePO4 batteries with one or two cells in series, respectively. You can easily change these ranges by changing the dividing resistor values. We suggest that you try to keep the total resistance around 3.3MΩ; lower values will increase the quiescent current, and significantly different values will alter the hystersis percentage (as described below). Table 1 shows some possible combinations for other voltage ranges. Hysteresis is provided by 10MΩ Australia’s electronics magazine feedback resistors between the comparator outputs and non-inverting inputs. This has been arranged so that the hysteresis is a fixed percentage of the voltage. The source impedance for the noninverting inputs is 687.5kΩ in both cases (1MΩ||2.2MΩ). This forms a divider with the 10MΩ feedback resistor, giving a hysteresis percentage of 687.5kΩ ÷ 10MΩ = 6.875%. So for low-battery cut-out voltages of, say, 3.3V and 6.6V, that would give you switch-on voltages 6.875% higher, or 3.525V and 7.05V respectively. The resulting hysteresis voltages are around 0.23V and 0.45V. When both batteries are above their switch-on voltages, output pins 1 and 7 of IC1 are high, at 3.3V. Therefore, the base-emitter junctions of NPN transistors are forward-biased and so both conduct, pulling the gates of Mosfets Q1 and/or Q2 low and lighting LED1 (as long as LK1 is in the position shown). If either battery falls below its switch-off voltage, the corresponding transistor switches off and thus Q1 and Q2 switch off. The high base resistors for Q3 and Q4 (2.2MΩ) are chosen because if one battery voltage is low but the other is high, current will still flow from the corresponding comparator output and this will increase the current drawn from the higher voltage battery (usually the one connected to CON1). The 2.2MΩ base resistors are the highest practical values to minimise this, and determine the minimum value for LED’s current-limiting resistor as 12kΩ. That means that LED1 has to be a high-brightness type. If LK1 is moved to the alternative position and LK2 is fitted, rather than being connected collector-to-emitter, Q3 and Q4 are in parallel, collector-tocollector. In that case, if either battery voltage is above the defined threshold, the associated NPN transistor will pull the Mosfet gates low, and so both outputs will be connected to the inputs. On/off switch If you don’t need a power switch on the supply, you can simply place a shorting block on CON5. CON5 is provided as a convenient way to switch power on and off, and you only need an SPST switch that hardly has to handle any current. But with S1 off, there will still be a December 2020  45 • • • • • • Features & specifications Two input/output pairs Individual low-battery cut-out voltage settings Passes through 3.6-15V at up to 5A per output Both outputs switch off if either (or optionally both) voltage falls below its threshold Fixed 6.875% hysteresis Quiescent current when off: around 10µA from the higher voltage battery and 2µA from the other small quiescent current drawn from the two batteries due to the resistive dividers which remain connected. This is around 1µA for every 3.3V. That should mean the batteries last for around a year with the device switched off via S1. If you need to reduce the battery drain further when off, you will instead need to use a DPST or DPDT switch to cut the battery connections to CON1 and CON2. That switch will need to handle the full load current for each battery. Note that the batteries may still suffer from a small amount of selfdischarge, so it’s still a good idea to check and charge them every six months or so. Construction The Dual Battery Lifesaver is built on a double-sided PCB coded 11111202 which measures 70 x 32mm. Refer now to Fig.2, the PCB overlay diagram, which shows where all the parts go. As you read the following instructions, keep in mind that if you are using the device with a single battery, you can omit D1, D2, Q2, CON2, CON4, VR2 and some of the resistors – see Fig.3. You will need to add a couple of wire links, shown in red, which you might be able to make from com- ponent lead off-cuts. Start by fitting all the resistors. While you can determine the value of a resistor by reading its colour bands, it’s best to use a DMM set to measure ohms to verify this, as some colours can look like other colours under certain types of light. If you are happy with the 0-10V adjustment range for the battery connected to CON1 and 0-4.5V for CON2, use 2.2MΩ resistors for RU1 and RL2, and 1MΩ resistors for RL1 and RU2, as shown in Fig.1. Otherwise, refer to Table 1 to determine the best resistor values to use. With all the resistors in place, follow with the two small diodes, D1 & D2. These must be orientated with their cathode stripes facing as shown in Fig.2. Then fit comparator IC1. Make sure its pin 1 notch and dot go towards the top of the board, as shown. We don’t recommend that you use a socket for reliability reasons, although you could if you wanted to. Next, fit switch header CON5. You can use a regular or polarised header, or just solder a couple of wires to the PCB. If you want the supply always to be on, you can either place a shorting block on CON5 or solder a small wire link in its place. The next step is to fit small signal transistors Q3 and Q4. They are the same type; ensure their flat faces lie as shown in the overlay diagram, and bend their leads out gently to fit the pad patterns. Follow with regulator REG1, which is in a similar package to those transistors, then install the two ceramic capacitors where shown. Now mount the two trimpots, which are the same value. Follow with the four terminal blocks. Make sure that their wire entry holes face towards the outside of the module, and note that the side-by-side blocks are spaced apart and so should not be dovetailed; mount them individually. Next, fit the two TO-220 devices, which mount vertically. Ensure that their metal tabs are orientated as shown. You could crank their leads so that their tabs are flush with the PCB edges, allowing heatsinks to be fitted later, but their dissipation should be low enough that heatsinks are not necessary. All that’s left is to solder the four-pin header shared by links LK1 and LK2 in place, followed by LED1. How you do this depends on what your plans are. If you don’t need an external power-on LED indicator, you can simply push it right down (with its longer lead on the side marked “A”, opposite the flat on the lens) and solder it in place. If you want it to be externally visible, depending on how you will be mounting the board, you may be able to mount it on long leads and have it project out the lid of the device. Or you could chassis-mount the LED using a bezel. You could then either solder flying leads from its leads to the PCB pads, or solder a 2-pin header (regular or polarised) onto the PCB Fig.2: the PCB has been kept as small as possible while still being easy to build, handling a decent amount of current and providing for easy wire attachment and mounting. Assembly is straightforward but make sure that the IC, terminal blocks, Mosfets, diodes and LED are correctly orientated. Use the component overlay above in conjunction with the same-size photo at right to assist you in component placement. Note that the values of RL1, RL2, RU1 and RU2 need to be chosen from the table overleaf. 46 Silicon Chip Australia’s electronics magazine siliconchip.com.au Fig.3: the same PCB can be fitted with fewer components if you only have one battery to protect, as shown here. Again, the two resistors shown in red need to be selected from the table at right. You will also need to add two wire links, shown in red. and then solder leads to the LED with a plug or plugs at the other end. Testing and adjustment It’s best to test and adjust the Dual Battery Lifesaver using a variable DC bench supply; ideally one with current limiting. The following instructions assume that you used the resistor values shown in Fig.1. If you changed them, you might need to alter the suggested voltages. Place one shorting block on CON5 and another across the middle two pins of LK1/LK2. Start by setting VR1 and VR2 at their maximum settings. If you’ve built the two-battery version, bridge the positive inputs together (you don’t need to bridge the negative terminals as they are connected on the PCB). Set your bench supply to around 4V and the current limit to a low value, then switch it off and wire up either input (CON1 or CON2) to the supply. Switch the supply on and watch LED1. It should not light yet, and the current drawn from the supply should be low (under 1mA). If it’s significantly higher than that, you could have a board fault, so switch off and check for short circuits and incorrectly located or orientated components. If all is well, wind the voltage up to about 8V, then rotate VR1 anti-clockwise until LED1 lights up. Then reduce the supply voltage slightly and check that LED1 switches off. Now rotate VR1 and VR2 fully anti-clockwise, set the supply voltage to your desired cut-out voltage for whichever of the two is lower, then rotate either VR1 or VR2 clockwise slowly until LED1 switches off. Then Parts list – Dual Battery Lifesaver 1 double-sided PCB coded 11111202, 70 x 32mm 4 2-way terminal blocks, 5.08mm pitch (CON1-CON4) 1 2-pin header or polarised header (CON5) 1 4-pin header (LK1,LK2) 3 shorting blocks/jumper shunts (CON5,LK1,LK2) 1 SPST panel-mount switch (S1; optional) 4 tapped spacers (for mounting the board) 8 M3 x 6mm panhead machine screws (for mounting the board) Semiconductors 1 MCP6542-E/P dual micropower comparator, DIP-8 (IC1) [element14, RS, Digi-Key, Mouser] 1 S-812C33AY-B2-U micropower low-dropout regulator, TO-92 (REG1) [Digi-Key, Mouser] 2 IPP80P03P4L04 P-channel logic-level Mosfets, TO-220 (Q1,Q2) [SILICON CHIP Online Shop Cat SC4318 or element14, RS, Digi-Key, Mouser] 2 BC547 100mA NPN transistors, TO-92 (Q3,Q4) 1 high-brightness LED (LED1) 2 1N4148 small signal diodes (D1,D2) Capacitors 2 1µF 50V multi-layer ceramic Resistors (all 1/4W 1% metal film, unless otherwise indicated) 2 10MW 4 2.2MW 2 1MW 1 100kW 1 12kW 2 1MW mini horizontal trimpots (VR1,VR2) [eg, element14 108244] siliconchip.com.au Australia’s electronics magazine Voltage range Upper resistor Lower resistor 0-4.5V 1.0M 2.2M 0-5.25V 1.2M 1.8M 0-6.3V 1.5M 1.5M 0-7.8V 1.8M 1.2M 0-10V 2.2M 1.0M 0-12.3V 2.4M 820k 0-15V 2.7M 680k Table 1 – suggested resistor pairs for various cut-out voltage ranges. increase the supply voltage to your other desired cut-out voltage; LED1 should switch back on. Rotate the other trimpot slowly clockwise until the unit switches off.Flasher has The old LM3909 LED been greathave but is getting You nowpretty set hard both battery to find . . . This new flasher is so cut-out thresholds. If you want both much more versatile: 0.1-10Hz flash rate . . . outputs to switch offDCwhenever daylight sensing . . . 0.8-3.3V supply . . . eitiny PCB (15 x 19mm) . . . suits SMDbelow and ther battery voltage drops the through-hole LEDs of any colour . . it’s ideal threshold you’ve set, the. unit is now for mounting inside toys, models, etc. complete. View article online at Ifsiliconchip.com.au/Article/10528 you only want it to switch off when both respecFulbatteries l kit availafall ble fbelow rom SILItheir CON CH IP tive limits, remove the jumper from ORDER NOW AT LK1/LK2 and insert two jumpers on www.siliconchip.com.au/shop SC the 4-pin header side-by-side. Micropower LED FLASHER Micropower LED FLASHER 0.8-3.3VDC 1-50mA supply Suits variety of LED types See SILICON CHIP January 2017 The old LM3909 LED Flasher has been great but is getting pretty hard to find . . . This new flasher is so much more versatile! 0.1-10Hz flash rate . . . daylight sensing . . . tiny PCB (15 x 19mm) . . . suits SMD and through-hole LEDs of any colour . . . it’s ideal for mounting inside toys, models, etc. View article online at siliconchip.com.au/Article/10528 IN B SA pT mod wit It’s bui fan you PCB ava ww IN R B ST ST A mo mo tra wi It’s wi you mo /re and Fea wh soc vol View Full kit available from SILICON CHIP ORDER NOW AT www.siliconchip.com.au/shop December 2020  47 ww A LOOK AT THE RCWL-0516 3GHz MOTION MODULE by Allan Linton-Smith A radar for $2? Yes, indeed. You may recall our description of this little ‘El Cheapo’ module in the February 2018 issue. It’s intended to be a motion detector, like a PIR sensor but with radio waves instead of infrared. Here we take a deeper dive into its operation and describe a few modifications you can make to change its behaviour. T hese modules are so cheap that you might as well buy a few to experiment with. You can turn on lights automatically, make burglar alarms, detect the movement of animals… if something moves, you can detect it with this little beauty! It can detect movement behind thin walls. It’s hard to believe that you can buy a tiny radar module so small and cheap that can detect movement within a seven-metre radius and operate a relay in response. One of the major differences between radar and passive infrared (PIR) detectors is that this radar module will detect the movement of any object larger than about 10cm2. In contrast, an IR detector will generally only detect movement of an animal or human, or perhaps lightning activity. The module As mentioned above, we described its operation in the February 2018 issue, starting on page 44 (www. siliconchip.com.au/Article/10966). We’ve reproduced the circuit here, as we will discuss its operation in more detail; it’s shown in Fig.1. Now we will unravel its secrets and show you some additional tricks! The module itself is about the size of a postage stamp at 17 x 36mm (and, 48 Silicon Chip The Elecrow RCWL-0516 Motion Detector, shown here close to life size, is available online from a variety of sources from just $AU1.65 including postage! unbelievably, not that much more expensive!). It operates from 4.5-24V DC with a quiescent current of 2.6mA. It has five terminals (CON1) for connection to a power supply, an output to trigger a relay, a 3.3V output and a terminal for the connection of a lightdependent resistor (LDR). The LDR can be used to disable its operation depending on the ambient light level. This was explained in more detail in the 2018 article. A small modification will allow you to send audio-level signals to an amplifier/oscilloscope/data logger for analysis. It can also be adjusted for sensitivity and on-time by adding two extra components. With a simple modification, you can even view the motions of moving objects on an oscilloscope or plot them on a data logger. Or listen to them via a frequency multiplier. The circuit Referring to Fig.1, note that there Australia’s electronics magazine are a few different versions of this module floating around, and the one we’re describing here has some slight implementation differences compared to the one described earlier. But they function in pretty much the same way. The differences are shown in green and with dotted lines on Fig.1. NPN transistor Q1 is the heart of the radar module and acts as a 3GHz oscillator, receiver and mixer. The PCB track antenna transmits and receives the signals. If a moving body comes within range, the reflected signal frequency changes due to Doppler shift (by a factor related to the body’s approach speed) and this is mixed with the transmitted signal, resulting in sum and difference products. These cause a voltage variation across Q1’s emitter resistor, sufficient to trigger a positive pulse at pin 2 of U1, which goes to the OUT terminal of CON1. Capacitors shown in red represent the parasitic capacitances of Q1 and are necessary for the correct performance of the oscillator. One of the innovative features of this radar circuit is that Q1, a 3GHz wideband transistor, acts as a multipurpose component. On my module, it is marked as siliconchip.com.au 100 4.7k 100nF 3x 100nF C CB B 1pF 2.2k Q1 MMBR941 (BFR620) E (BFR1 8 3) C 0.4pF C BE +3.3V +3.3V C CB, C BE AND C CE ARE INTERNAL TO Q1 10nF 1M C CE 12 0.2pF 13 16 22k (33k) INDUCTOR/ ANTENNA FORMED BY S-SHAPED PCB TRACK 22 F R–GN* 10nF VALUES IN GREEN ARE ALTERNATIVES 22k (18k) FOUND ON SOME MODULES SC 220 (2.0k) 33pF 56k A 22 F Vdd 2OUT RR2 2IN– RC2 1OUT RR1 RC1 1M 15 1.0k 33pF 1nF 22 F 100nF 1IN– VO VC IB 1IN+ 6 1M 1M 5 3 10k 10nF CON1 4 +3.3V OUT 1 10nF U1 RCWL-9196 VIN 14 R–CDS* 11 1 C–TM* (1.0k) 100 2 2 8 OUT 4 9 OUT 1M 1 0 0nF VIN 5 U2 7 133-1 10 Vss 7 GND 3 CDS IN GND 1 0 0nF  CDS* 2020 * OPTIONAL Fig.1: the complete circuit of the RCWL-0516 microwave radar motion sensor module. The track inductor forms the antenna for both transmission and reception of microwave signals and has a range of approximately 7m. “1N2”, and its origin is China. It is an oscillator, transmitter, receiver, amplifier and mixer, and also provides capacitances necessary for the oscillator and feedback. This transistor’s base is held at approximately 1V by the three resistors connected between its collector, base and ground. The 3.3V supply is decoupled by three 100nF capacitors at its collector and one across the base divider, which forms an RC low-pass filter in combination with the 100resistor. The oscillator circuit operates at close to 3GHz, set by the resonance of Q1’s collector-emitter capacitance (about 0.2pF) and the antenna inductance (0.014µH). The capacitance of the transistor is given by the manufacturer’s data sheet. Simulation confirms that this configuration will oscillate at 3.007GHz with a Q of 1.1 – see Fig.2. Performance We measured -23.51dBm or 4.5µW (microwatts) at 3.010GHz continuous- ly transmitted output power. This was measured with a 3GHz antenna connected to a spectrum analyser, with the module very close to the antenna (see Fig.3). While this seems like a small amount of transmitted power, it is strong enough for an effective range of 7m under normal conditions. The good news is that it is not strong enough to cause any interference with other devices. It does not even seem to interfere with identical radar modules, although the oscillators vary quite a bit due to variations in the transistor performance and component tolerances. The fact that the detector is only activated by the differences between the transmitted and received signals means that the oscillator does not have to be drift-free. This makes the module much cheaper compared to a device with a PLL or YTO (Yttrium-iron-garnet Tuned Oscillator. Antenna Fig.2: a simulation of the module’s oscillator. The predicted frequency of 3.007GHz is very close to the measured frequency. The frequency varies due to temperature, supply voltage and other variables. But only the frequency shift due to motion matters, so that doesn’t affect its operation. siliconchip.com.au Australia’s electronics magazine The antenna is actually a snakeshaped curved trace on the circuit board which has been tweaked using a series of tiny holes. The antenna is therefore multitasked as a transmitter, receiver and inductor. There is also some capacitance designed into the PCB by way of overlap with tracks on the underside and a small circle which acts as receiving antenna. The transmitter is actually a Colpitts December 2020  49 Fig.3: we measured a continuously radiated power of -23.51dBm at 3.010GHz, which equates to around 4.5 microwatts. The peak ‘dances’ around the centre frequency when moving objects are nearby. oscillator with feedback tapped between the 0.4pF and 1pF parasitic capacitors of Q1. These capacitors are the internal capacitance of the transistor CCB and CBE respectively, and are shown in red on the circuit diagram. A small amount of stray capacitance on the PCB from the three overlapping tracks has a small effect on these values. It has also been suggested that the circular pad on the underside of the module is also part of the LC oscillator and is “inserted” between the base and collector. Still, judging from its size, it is primarily intended as a receiving antenna, to assist with the efficiency of the overall package. The selection of the transistor is important both in terms of its highfrequency cut-off and its internal capacitance. When there are no moving objects in its range, Q1 oscillates in a steadystate with a 1.0V bias on its base. It draws a relatively constant current, Fig.4: the signal at pin 12 of U1, ie, Q1’s emitter voltage after the low-pass filter. We waved a broom around two metres from the radar module behind a thick shield, triggering the module. which provides a constant voltage of approximately 0.4V across its emitter resistor. Once an object moves within its range, the reflected signal is picked up by the antenna and mixed by Q1. This creates a fluctuation in the mixed signal amplitude and a corresponding voltage fluctuation across the emitter resistor, which increases to about 0.8V peak. This is shown in Fig.4. This voltage is fed to pin 14 (1IN+) via an RC low-pass filter with a -3dB point of around 159kHz, to remove the 3GHz carrier. Note that there is a bit of a delay between the movement and the output being triggered, probably due to onboard filtering to prevent EMI and other brief transients from triggering the unit. This delay amounts to about one second. Output pin 2 remains high for around three to five seconds (or until movement stops). The signal at the OUT terminal of CON1 can be used to power LED(s), trigger a relay (via a relay driver ar- rangement) or into a digital input on an Arduino, Micromite, Raspberry Pi etc. The chip, U1, is marked RCWL9196 which is almost identical to a BISS0001. This is a commonly used IC for passive infrared (PIR) detectors. It’s a CMOS bi-directional level detector with excellent noise immunity and was originally designed to trigger alarms from IR detectors. It features power-up disable, output pulse control logic and selectable retriggerable/non-retriggerable modes. In this module, it is configured to activate for three seconds when it is triggered and then reset automatically (ie, it is set in re-triggerable mode). Component layout The component layout on the top of the module is shown in Fig.5; there are a few components on the underside also, primarily regulator U2 (a 7133-1 low-dropout linear regulator). U2 was not present on the original board from Elecrow that we described Fig.5: RF transistor Q1 is on top of the board, which supplies the outgoing signal via the snakelike antenna from its emitter. This antenna also receives reflected signals. 50 Silicon Chip Australia’s electronics magazine siliconchip.com.au REG1 7805 K D1 1N 4148 470kW 10kW 2 4.7mF 1.5mF 470kW A 3 15 8 1 IC1a 14 3 1MW K D2 1N 4148 PHASE COMPARATOR & VCO 22n F 100kW A I NP U T 100kW OUT 16 SIGin COMPin 6 7 C1a C1b IC2 4046 100kW 100kW VCO 4 out PCout VCOin R1 13 9 8 11 1MW INPUT BUFFER/ SCHMITT TRIGGER 100mF 16V 10kW IN K GND S2 +9-12V A 100mF 16V 100kW OUTPUT BUFFER/ SCHMITT TRIGGER 6 5 R2 12 D3 1N4004 220W 7 IC1b OUTPUT 1.5mF 4 100kW 1.8MW 100kW 1.5mF S1 Fig.6: a slightly modified version of the Circuit Notebook entry “Frequency multiplier for LF measurements” from the February 2004 issue (p71). It uses phaselocked-loop (PLL) IC2 and dual decade counter IC3 to multiply the frequency of the incoming signal by a factor of 10 or 100x, depending on the position of switch S1. x 100 100n F in 2018. Instead, the VIN pin of CON1 was wired to pin 8 of U1, the input to its internal 3.3V regulator. That board also had two 100-150nF bypass capacitors on that line, while this one has a similar pair of capacitors at regulator U2’s input and output. Also, Q1 was an MMBR941 on the previous board, rather than the BFR183 used on this one. Presumably, the three alternatives for transistor Q1 are all very similar or else the oscillator would not work correctly. There are a few other minor component value differences, but otherwise, the modules seem quite similar. U2 provides the +3.3V rail. The advantage of external regulator U2 is that it allows for more current to be drawn from the +3.3V output at CON1 by external circuitry. But it does limit the maximum supply to 24V rather than 28V. C-TM R-GN R-CDS siliconchip.com.au x 10 IC1: LF353, TL072 IC3: 4518 1N4148 16 CP1 10 9 IC3b CP0 15 8 MR O3 O2 O1 O0 14 13 12 11 1/ 10 CP1 2 A 1 CP0 7 MR O3 O2 O1 O0 6 5 4 3 IC3a 1N4004 A 1/10 If a lot of current was drawn from the 3.3V rail, U1 could overheat, so having it supplied by a separate device is probably a good idea. By the way, one of the few differences between the RCWL-9196 IC and the BISS0001 it is supposedly a clone of is that pin 8 has an entirely different function; here, it goes to the internal voltage regulator, whereas on the BISS0001 it is the reset and voltage reference input pin. K K Connecting it to an Arduino or Micromite We covered this in detail in our February 2018 article, but as it’s quite simple, we’ll go over it quickly again. Just connect GND and VIN on CON1 to GND and 5V on the micro board respectively. Then connect the OUT pin of CON1 to a digital input on the micro, such as D2 on an Arduino, ESP8266 or ESP32. Making modifications Connecting it to something else As we explained in our earlier article, an SMD resistor can be soldered to the pad marked “R-GN” to lessen the sensitivity, so that it only triggers at close proximity. A value of 1Mwill halve its sensitivity. There is also a pad marked “C-TM”; adding a capacitor here will lengthen the on-time at VO (pin 2); a 10nF capacitor will roughly double it. You could feed the output of this module to our Opto-Isolated Mains Relay (October 2018; siliconchip.com. au/Article/11267) to switch just any mains-powered device on when motion is detected. With some simple modifications, that same project could also be used to switch low-voltage DC at reasonably high currents. Alternatively, a simple transistor 3.3V GND OUT VIN CDS Fig.7: on the underside of the board there is a regulator (U2) as well as three locations for optional components: R-GN to adjust the gain, R-CDS for light sensing, and C-TM to increase the on-time. Australia’s electronics magazine December 2020  51 VCC 1N4 004 (NOT REQUIRED FOR LED) SUITABLE RELAY (OR LED) D PIN3 CON1 G S IRF540 etc can be added to the output of the module if you wish to operate a high powered LED or drive the coil of a relay, as shown above. The simplest way to do this is to use an N-channel Mosfet like the IRF540. Connect its gate to pin 3 of CON1 (OUT) and its source to pin 2 (GND). Its drain can then drive the negative terminal/cathode of the high-power LED or other low-voltage DC device, with the device’s positive terminal/ cathode connected to the 12V DC (or similar) supply. If the device is a relay, it’s also a good idea to connect a 1N4004 diode across its coil, with its anode to the Mosfet drain (negative) side. Listen to moving objects! One of the more interesting ideas for this module allows you to hear moving objects by using a frequency multiplier. The signal from pin 12 of U1 is an amplified version of the signal that was fed into pin 14. This then goes to the input of a frequency multiplier (circuit shown in Fig.6) and its output is connected to a small audio amplifier and an earpiece. For the audio amplifier, you could use our version of the popular Champ project (February 1994; siliconchip.com.au/Article/5303) or its more recent update, the Champion (January 2013; siliconchip.com.au/ Article/1301), which also incorporates a basic preamplifier. Each moving object has its own characteristic, so could possibly be of use for the vision-impaired, to help warn of fast-moving objects, vehicles or even stationary objects which can be detected by walking up to them. The frequency multiplying circuit uses a PLL and can be set to 10x or 100x. It requires an input of at least 0.8V RMS (2.25V peak-to-peak). Most of the signals from pin 12 of U1 are infrasonic; for example, when I was waving a broom, the resulting signal was around 3Hz. This cannot be heard directly, but when multiplied by a factor of 100, Useful links and videos: • www.codrey.com/electronic-circuits/ microwave-radar-motion-sensorswitch/ • www.rogerclark.net/investigatinga-rcwl-9196-rcwl-0516-radar-motiondetector-modules/ • https://youtu.be/rgVu9n_j9pM • https://youtu.be/9WiJJgIi3W0 • https://youtu.be/Hf19hc9PtcE it becomes a very audible (but weird) 300Hz signal. You can listen to some examples here: www.siliconchip.com.au/ Shop/6/5501 Summary This innovative little module is a very efficient design, uses just a few components to keep the cost and size to a bare minimum. You can have heaps of fun playing with this radar without having to spend much dosh, and it’s also very safe to experiment with. There are countless applications for this clever little module, examples of which can be found all over the web! SC LAST CHANCE FOR CHRISTMAS 2020! Want to have the brightest Christmas ever with our superb LED Decorations (see November issue)? Wow! We can’t believe just how popular our LED Christmas decorations have been! We’ve sold HUNDREDS of kits and they’re still racing out the door. But time is short: you’ll need to get in really quick to have these little beauties ready to brighten your Christmas – not just time for us to get them to you but time for you to build them! RED SLEIGH red rEINDEER red tree green tree white tree red cap red green sTockING sTockING red CANE WHITE STAR RED bauble YELLOW bauble GREEN BAUBLE BLUE BAUBLE ALL THE KITS ARE THE SAME PRICE: Just $14.00 each inc GST (plus P&P -- $10 per order). Buy one kit or buy lots for sensational displays! Simply order the kit for the decoration you want (easiest and quickest via www.siliconchip.com.au/xmas2020 www.siliconchip.com.au/xmas2020). The kit will include all non-optional parts: the pre-programmed PIC12F1572-I/SN for that decoration, the appropriate PCB, required resistors and a mix of twelve red, white and green LEDs (so you can choose the pattern you want) plus the button cell holder (but not the button cell). Or choose the giant RGB stackable LED Christmas Star . . . Also from the November 2020 issue, our giant (194 x 185mm) RGB LED Christmas Star will take pride of place on your tree (or anywhere Just $38.50 each inc GST else!) this Christmas (and for years to come). Kit includes PCB, (plus P&P – $10 per order) programmed micro, 30 RGB LEDs and all other non-optional parts. ORDER NOW AT WWW.SILICONCHIP.COM.AU/SHOP 52 Silicon Chip Australia’s electronics magazine siliconchip.com.au y r r e g m A akin s m istma $699 r h C Hardcore electronics by On Sale 24 November to 26 December, 2020 • IDEAL FOR FINE DETAIL COMPARED TO FILAMENT 3D PRINTERS • HIGHEST PRINT QUALITY BUY ALL THREE FOR MONO UV PHOTON SAVE $88.95 RESIN 3D PRINTER 3D printing with UV activated resin produces much smoother & detailed results than can be achieved with PLA or ABS. The removable top cover grants easy access to the print bed. • 6” 2K Monochrome LCD • 2.8" Touchscreen • Prints up to: 130(L) x 80(W) x 165(H)mm JUST TL4422 VALUED AT $787.95. DEAL INCLUDES: 1 x Resin 3D printer TL4422 1 x Curing & washing machine TL4424 1 x 500ml resin (choose from black, grey, clear, blue, and green. TL4425-TL4429) LEARN ELECTRONICS, SOLDERING & ARDUINO 249 $ JUST 995 $ 2-IN-1 WASH & CURE MACHINE MAKE YOUR OWN: CHRISTMAS TREE Get into the Christmas spirit with this tree shaped circuit board, coloured LEDs, and electronic components to make the tree produce amazing lighting effects when combined with an Arduino® UNO board (XC4410 $29.95 sold separately). Soldering required. • 90(H) x 50(W) x 12(D)mm (incl pins) XC3754 JUST 2995 $ Bring Santa and his reindeer to life with 126 multicolour flashing LEDs, with a clever circuit that creates the illusion of a flying reindeer while Santa’s hat flaps in the wind. Based on the Bipolar Junction Transistor, you'll see how they can be configured into an oscillator to make LEDs flash. Soldering required. • 145(L) x 80(H)mm XC3756 500ML RESIN Black TL4425 Grey TL4426 Clear TL4427 PCB Making, Engraving & Etching NOW FROM 595 ETCH RESISTANT PEN Hand draw a PCB pattern with the ink from this pen. When the blank board is etched the copper tracks will remain. JUST • Dries in seconds TM3002 695 $ $ RGB LED STRIP MODULE • Eight RGB LEDs controlled by a single Arduino® pin • Each channel has 256 brightness levels • Current draw 500mA per module max • 54mm long XC4380 JUST 9 $ 95 Free delivery on online orders over $99* Exclusions apply - see website for full T&Cs. * CLUB OFFER: $50 GIFT CARD 1349 $ Pure copper bonded to quality fibreglass base. 150 x 75mm Single Sided HP9514 $5.95 150 x 150mm Single Sided HP9512 $8.95 150 x 150mm Double Sided HP9515 $9.95 300 x 300mm Single Sided HP9510 $24.95 2995 EA JUST BLANK FIBREGLASS PCBs $ JUST 3995 $ • 3D print, engrave and laser cut with a single machine • Featured with 3.5" colour touch screen, heated build plate, easy swap & interchangeable modules and more • Includes easy to use software • Prints up to: 125(L) x 125(W) x 125(H)mm TL4400 See website for details. Engrave all your valuables for security or SAVE $5 insurance. • Suitable for glass, ceramics, metals and plastics • 2 x AAA batteries & case included • Replacement tip (TD2469 $6.95) sold separately TD2468 WAS $29.95 A flexible LED strip light with 120 (60 LEDs/m) addressable WS2812B RGB LEDs to create amazing lighting displays using your favourite microcontroller. JUST IP65 water resistant rating. 5V. • Flexible and waterproof As seen in Silicon Chip Magazine December, • 2m long 2020: Flexible Digital Lighting Controller Part 3 XC4390 Blue TL4428 Green TL4429 3D PRINTER/ CNC/LASER ETCHER 2495 $ RGB LED STRIP LIGHT Shop the catalogue online! Liquid resin makes for much higher resolution 3D models. It is the latest in 3D printing technology. Powerful UV light, compatible with most resin 3D printers. Comes with a sealed container and lid to store the washing liquid and re-use. • Rotatable curing platform • Touch button TL4424 MICRO ENGRAVER RIDING SANTA 499 $ JUST 50 $ PCB ETCHING KIT Complete with assortment of double-sided copper boards, etchant, working bath and tweezers. HG9990 WAS $29.95 NOW 2495 $ SAVE $5 RGB LED MATRIX DISPLAY • Full 8 x 8 matrix controlled through 32 pins • Flush edges for creating extended displays • 192 LEDs in 64 pixels. ZD1810 JUST 1995 $ www.jaycar.com.au 1800 022 888 think. possible. Your destination for... projects & DIY PROJECT: Gift Guessing Game Your ‘Christmas Gift’ Crystal Ball DIY kit. Assemble a magic-8-ball inspired bit of kit that will tell you what's under the tree when you shake it, detected by the triaxis tilt sensor and shown on the massive 1.3” OLED screen. A fun filled fortune-telling Christmas! SKILL LEVEL: Beginner WHAT YOU NEED: 1 x UNO R3 Development Board XC4410 $29.95 1 x 1.3" Monochrome OLED Display XC3728 $24.95 1 x Tri-Axis Digital Tilt Sensor XC3732 $9.95 1 x 150mm Plug to Socket Jumper Leads 40-pcs WC6028 $5.95 1 x 9V Battery Snap DC Cable PH9251 $5.45 1 x 9V Eclipse Battery SB2423 $4.50 4995 $ SAVE 35% SEE PARTS & STEP-BY-STEP INSTRUCTIONS AT: www.jaycar.com.au/gift-guessing-game See other projects at www.jaycar.com.au/arduino KIT VALUED AT: $80.75 BUILD YOUR OWN: 10" SCREEN RETRO ARCADE GAME CONSOLE Retro Pi Arcade Console PLAY 000'S OF CLASSIC RETRO GAMES! Let the games begin with these exciting retro arcade consoles. Simply install a Raspberry Pi 3B+ (XC9001 $89.95 sold separately), into the console, insert a Retropie installed micro SD card (XC9031 $24.95 sold separately), copy over some games and you are ready to play. • Includes a joystick and 6 buttons. • Built-in speaker XC9064 $249 See website for detailed install instructions. RETRO ARCADE GAME CONSOLE • Connects to your TV, monitor or projector with HDMI or VGA cable • 2 Player console XC9062 $169 BUNDLE WITH A RASPBERRY PI & RETROPIE ONLY BUNDLE WITH A RASPBERRY PI & RETROPIE ONLY 249 299 $ $ SAVE $34.90 SAVE $64.90 VALUED AT: $283.90 VALUED AT: $363.90 NOW NOW FROM 10 $ 14 50 $ SAVE 20% Electrolytic 1μF - 470μF - 55 Pieces RE6250 WAS $13.50 NOW $10.50 Greencap 0.001μF - 0.22μF - 60 Pieces RG5199 WAS $14.95 NOW $11.95 54 95 SAVE $7 CAPACITOR PACKS click & collect CLUB OFFER BUNDLE DEAL SOLDERLESS BREADBOARD WITH POWER SUPPLY Power from USB or 12V plugpack. Includes 64 mixed jumper wires of different length and colour. PB8819 WAS $21.95 Buy online & collect in store NOW 29 $ 95 SAVE $10 ULTIMATE RESISTOR PACK 1/4W 5% miniature sized carbon film. 1700pcs. RR2000 WAS $39.95 JUST 995 $ RETRO NES STYLE CONTROLLER SNES layout. Features A/B/X/Y buttons, start, select, and direction controls. Easily configurable, USB powered. XC4404 JUST 3995 $ RETRO NES CASE Includes access to all ports on your Raspberry Pi, additional USB ports, and a handy storage slot for your spare micro SD cards. XC4403 Product colour may change without prior notice NOW 2995 $ SAVE $10 LIGHT DUTY HOOK-UP WIRE PACK Quality 13 x 0.12mm tinned hook-up wire on plastic spools. • 25m on each roll WH3009 WAS $39.95 ON SALE 24.11.2020 - 26.12.2020 think. possible. Your destination for... Arduino® compatible boards, shields & modules SAVE 25 % SIMPLE › ADVANCED: Experimenter's Kits On selected Arduino® Compatible boards LEONARDO R3 DEVELOPMENT BOARD 21 21 95 $ 95 RGB LED SAVE $5 SAVE $8 RING ARDUINO COMPATIBLE NANO BOARD MODULE Small in size, but packs virtually all ® Add dazzling circular-shaped LED patterns to your next project or costume with this addressable RGB LED ring module. • 72mm in diameter and 24 x RGB LEDs with 256 brightness levels XC4385 WAS $17.95 SAVE $8 the features of the full Duinotech boards into a tiny DIP-style board that drops directly into your breadboard. • ATMega328P microcontroller XC4414 WAS $29.95 79 $ SAVE $20 37-PCE DELUXE MODULE PACKAGE SAMD21 WIRELESS DEVELOPMENT BOARD A compact Arduino® compatible board with 2.4GHz Wi-Fi communication. USB Type-C socket for power and programming. Includes provision for connecting and charging a NOW 3.5-4.2V Li-po battery (not included). • Atmel® SMART™ SAM D21 ARM Cortex-M0+ microcontroller SAVE $20 XC3812 WAS $69.95 4995 In the Trade? SAVE $10 ARDUINO® COMPATIBLE LEARNING KIT Kit includes wires, components, 400 point breadboard and instruction booklet to get you started. • Classic Arduino® UNO board • Light sensors, pushbuttons, LEDs and more! XC3900 WAS $79.95 See website for details. SAVE $20 1995 128 X 64 LCD DISPLAY MODULE 4 $ 95 STACKABLE HEADER SET The prefect accessory to the ProtoShields and vero type boards when connecting to your Arduino® compatible project. 1 x 10-pin, 2 x 8-pin, 1 x 6-pin, 1 x 2x3-pin (for ICSP). HM3208 JUST 29 $ SAVE $10 JUST Allows SMD IC's and other smaller pitch components to be used with standard 0.1" prototyping equipment. PI6530 NOW 4995 $ JUST 28 PIN SOIC/SOP TO DIP BREADBOARD ADAPTOR 6995 $ $ NOW $ NOW Includes commonly used sensors and modules for Duinotech and Arduino®: joystick, magnetic, temperature, IR, LED and more. Packaged in a clear plastic organiser. XC4288 WAS $99 2 SAVE $5 See website for details. Large display with cool white on blue graphics. Similar to the character LCD’s with inbuilt character ROM, but the flexibility to show graphics. • 8 bit, 4bit and serial interfaces available • 95(L) x 70(W)mm XC4617 WAS $29.95 95 3495 $ Kit includes all the essentials to get you started in the exciting world of Arduino® including an UNO board, jumper leads, resistors and more. XC3902 WAS $39.95 Provides an attractive colour display for your next project. • SSD1351 Chipset • 34(L) x 34(W) x 2(D)mm XC3726 WAS $69.95 NOW NOW ARDUINO® COMPATIBLE STARTER KIT 1.5" 128 X 128 OLED COLOUR DISPLAY MODULE $ 95 NOW NOW 12 $ NOW $ A programmable microcontroller board based on the ATmega32u4 with easy to use open source hardware. Use it to emulate a keyboard, mouse, joystick or any other type of input device. XC4430 WAS $29.95 ALSO AVAILABLE: Leonardo Tiny ATMEGA32U4 Board XC4431 WAS $21.95 NOW $15.95 SAVE $6 95 240 X 320 LCD COLOUR TOUCH SCREEN MODULE Large, colourful touch display shield which piggybacks straight onto your UNO or MEGA. microSD card slot. • Resistive touch interface • 77(L) x 52(W) x 19(H)mm XC4630 NOW JUST 99 $ SAVE $10 MEGA EXPERIMENTER'S KIT Contains an Arduino-compatible MEGA main board, a breadboard, jumper wires and a plethora of peripherals in a plastic organiser. XC4286 WAS $109 See website for details. JUST 595 $ EA 150MM JUMPER LEADS 40-pce of various colours for prototyping. Each flexible lead has pins to suit breadboards or PCB headers. Plug To Plug WC6024 Socket To Socket WC6026 Plug To Socket WC6028 JUST 695 $ ADHESIVE COPPER TAPE Adhesive backing. Solderable. Repair printed circuit boards. 5mm x 10m. NM2870 55 think. possible. Your destination for... er d l So ining trakits young maker projects ANY 3 KITS FOR 40 $ These kits are a great way for your kids and grand kids to start soldering and pick up some electronics on the way. They will also learn about how various components work including LEDs, transistors, integrated circuits and more. Each kit requires a CR2032 battery (SB2522 $3.25 sold separately). RRP $19.95 each SAVE $19.85 JUST 8995 1. Skull Badge 2. Owl Badge 3. Rocket Badge 4. Pirate Badge 5. Robot Badge 6. Electronic Dice Goot 15W 240V Soldering Iron TS1430 4 X 4 X 4 BLUE LED CUBE KIT Learn to solder in 3 dimensions by building a dazzling array of 64 ultrabright blue LEDs. Using the supplied template, you will arrange this 4 x 4 x 4 matrix into a work of art. Fifteen different psychedelic patterns are included, with instructions on how to create your own. • 65(W) x 88(H) x 65(D)mm KM1097 with Alternating Flashing LEDs with Touch Sensitive LEDs with Flashing LEDs with Flashing LED Eyes with Touch Sensitive LEDs & Buzzer with Flashing LEDs $4.50 sold separately) JUST 19 95 FROM 995 $ Soldering Iron Stands Economy TS1502 $9.95 Deluxe TS1507 $16.95 FROM 16 $ 95 Take your soldering skills to the next level then put it to good use by placing this traffic light onto the kids car or train sewvt. Based on the 4071 IC, you will see first hand how logic gates operate. XC3758 1mm Solder Wire 200g NS3010 $16.95 1kg NS3015 $74.95 1795 $ Solder Flux Paste 56g tub. NS3070 MAKEY MAKEY LEARNING KIT VALUED AT OVER $125 SPARKLE STITCH KIT Learn simple sewing and electronics and make spectacular light-up wearable technology. Kit includes everything you need to get started - felt cloth, needles, thimble, thread, glue gun, multimeter, electronic components, 62 page guide & more. KM1080 See website for details 79 $ WEARABLE ESP32 DEVELOPMENT BOARD Designed to be sewn onto fabric to create wearable electronic jewellery. Arduino® Compatible. 56mm dia. • Wi-Fi and Bluetooth® • Lightweight and thin design • Smartphone control Conductive thread (WW4100 $8.95) sold separately. XC3810 WAS $39.95 JUST NOW 29 $ 95 SAVE $10 COMPATIBLE Have fun using everyday WITH SCRATCH objects to create innovative projects e.g make a piano using bananas. Ages 8+. • Supplied with six coloured leads with alligator clips, USB cable and jumper wires to provide even more output. XC3750 WAS $49.95 NOW 3995 $ SAVE $10 STARTER KIT FOR MICRO:BIT INCLUDES MICRO-BIT BOARD An excellent introduction to electronic construction and coding, ideal gift for a young maker! Includes micro:Bit board & common electronics components such as resistors and servo motor, and all the necessary prototyping accessories plus 36-page instruction guide. • No soldering or prior programming knowledge is required. XC4322 WAS $99.95 NOW 8995 $ SAVE $10 Gift Ideas for the Young Maker NOW NOW 14 $ 16 95 $ SAVE $2 SAVE $3 MAKE YOUR OWN: CLOCK KIT Easy to assemble. No batteries required. 31 pieces. Ages 6+. KJ8996 WAS $16.95 56 95 click & collect SOLAR BUG KIT Easy snap together construction kit teaches about renewable energy. KJ9027 WAS $19.95 NOW 16 $ 95 SAVE $3 6-IN-1 SOLAR ROBOT KIT Build robots out of a can or water bottle. 6 robots to build. Ages 10+. KJ8939 WAS $19.95 Buy online & collect in store NOW 19 $ $ SAVE $5 SOLAR ROVER KIT Learn about science and solar. Easy snap together construction. Ages 8+. KJ9026 WAS $24.95 NOW 3995 95 SAVE $10 14-IN-1 SOLAR ROBOT EDUCATIONAL KIT Can be transformed up to 14 different functional robots. Ages 10+. KJ8966 WAS $49.95 ON SALE 24.11.2020 - 26.12.2020 02 15 TS JUST JUST 3D TRAFFIC LIGHTS KIT $ Requires Arduino® UNO Board KM1090 KM1092 KM1094 KM1096 KM1098 KM1099 1995 $ 9V Battery (SB2423 (XC4410 $29.95) sold separately 6 6 DIFFERENT KITS AVAILABLE: 3 $ 5 WEARABLE BADGES & ELECTRONIC DICE KITS think. possible. Your destination for... Imp me rove y dia o roo ur m advanced DIY projects IN-CEILING 2 WAY SPEAKERS Re-Create your Garden Excellent audio quality compared to traditional PA speakers. Combination of coaxial woofer with dome tweeter. Sold as a pair. 5.25" 30WRMS CS2451 WAS $69.95 NOW $54.95 SAVE $15 6.5" 40WRMS CS2453 WAS $84.95 NOW $69.95 SAVE $15 8" 50WRMS CS2455 WAS $99.95 NOW $74.95 SAVE $25 NOW 2495 $ SAVE $8 IP54 WEATHERPROOF OUTDOOR POWERBOARD ENCLOSURE Fits most 4-way powerboards, and will house plugpacks for Christmas lights and garden ornaments with ease. • Suitable Cable: 6.9mm - 10.5mm dia. HB6173 WAS $32.95 ALSO AVAILABLE: Mains Plug & Socket Enclosure HB6172 $9.95 35 SAVE $24.85 95 3-IN-1 STUD DETECTOR WITH LASER LEVEL NOW 199 SAVE $50 EXTENDABLE UNIVERSAL PROJECTOR CEILING BRACKET Aluminium projector ceiling mount. Fits for most projectors. • Max loading 10kgs • Rotation 360° • Height adjust: 240-310mm CW2857 WAS $59.95 NOW 3995 $ JUST JUST 1595 $5995 $ Select up to 12 different colours and 3 different light patterns. IP65 rated with a max depth of 2m. • Requires 3 x AAA batteries (SB2413 $3.25 sold separately) SL3933 $19.95 EA. SAVE $20 Car Maintenance & Upgrades RESPONSE COAX CAR SPEAKERS LED PROJECTION LIGHT Light up your home or garden producing dazzling light patterns. Extremely bright 4W RGB LED. Includes a garden stake, stand, NOW and wall-mounting kit. • Wave ripple effect • IP65 weatherproof housing SAVE $20 SL3403 WAS $49.95 2995 $ SOLAR POWERED WATER PUMPS Run your outdoor water feature, aquarium or garden pond without the need for wiring. Comes with its own solar panel, cable and pump. 0.9W ZM9200 WAS $54.95 NOW $44.95 SAVE $10 2.4W ZM9202 WAS $84.95 NOW $74.95 SAVE $10 NOW FROM $ SAVE $10 PR SAVE UP TO $25 $ input. Remote control included. RCA input. 6.5mm output. • 240V Mains powered • 285(W) x 275(D) x 90(H)mm AA0520 WAS $249 Laser levelling, layout and stud Ideal for any surface that needs to be locating on vertical and deadened e.g. car door or floor panels. horizontal surfaces. • 675(L) x 330(W) x 2.3(D)mm • 1 x 9V battery AX3680 included QP2288 RGB UNDERWATER LIGHT 4495 Provides crisp audio power with two channels at NOW FROM a powerful 120WRMS each. Dual line audio 54 $ HEAVY DUTY SOUND BARRIER DAMPING MATERIAL 3 FOR $ 240WRMS STEREO AMPLIFIER WITH REMOTE CONTROL CS2451 ZM9200 NOW 1995 $ SAVE $7 AUTOMOTIVE FUSE ASSORTMENT 120 standard size automotive blade fuses housed in a 6 compartment storage box. 20 x 5A, 10A, 15A, 20A, 25A & 30A fuses included. SF2142 WAS $26.95 REPLACEMENT GLOBES A range of 150 lumens ultrabright white LED replacement globes for car interior lights. Compatible with modern "CANBus" sytems. 120° wide beam. 12VDC. 3 sizes available. ZD0750-54 AUTOMOTIVE MULTI-FUNCTION CIRCUIT TESTER WITH LCD 5995 JUST 4995 $ SAVE $5 EA PR SAVE 15% Perfect for the workshop as an an engine analyser as well as basic DMM. Full dwell angle measurement and tacho. Max/data hold and bright backlit LCD. • Cat II 1000V / Cat III 600V • 2000 Display count • RPM x 10 QM1446 $ JUST NOW FROM 3295 $ AUTOMOTIVE DMM WITH DWELL AND TACHO Designed to test the electrical system of an automotive vehicle running on 12V or 24V. • Tests voltage and polarity of a circuit, continuity check and more NOW • LED indicator QM1494 WAS $64.95 1295 $ Titanium coated fibre woofers and silk dome tweeters for smooth high frequency response. 2 way. Sold as a pair. 4" 15WRMS CS2310 WAS $39.95 NOW $32.95 SAVE $7 5" 17WRMS CS2312 WAS $45.95 NOW $38.95 SAVE $7 6.5" 22WRMS CS2314 WAS $56.95 NOW $46.95 SAVE $10 6 x 9" 27WRMS CS2316 WAS $79.95 NOW $64.95 SAVE $15 Gift Ideas for the Advanced Maker NOW JUST 1795 $ JUST 2695 $ AUTOMOTIVE CRIMP TOOL CABLE TIE BOX WITH CONNECTORS Kit consists of: 100 pcs x 200mm, Cut and strip wire and crimp connectors. Comes with 80 popular connectors. TH1848 More ways to pay: 100 pcs x 150mm, 200 pcs x 100mm packed in a see thru flat storage case. 400 pieces. HP1216 2495 $ SAVE $10 HEATSHRINK TUBING TRADE PACK A box of six common sizes of glue lined pre-cut heatshrink. 60 pieces. WH5521 WAS $34.95 5-PCE STAINLESS STEEL TOOL SET Set of 5 x 115mm cutters & pliers. • Soft ergonomic grips. TH1812 WAS $34.95 NOW 2995 $ SAVE $5 57 think. possible. Your destination for the best rewards & perks. love jaycar? you're going to love our rewards! SHOP In store & online EARN POINTS For dollars spent 1 point = $1 GET REWARDS eCoupons for future shops in store + PERKS offers, event invitations, 200 points = $10 eCoupon account profile and more... 8 EXTERNAL ANTENNAS FOR IMPROVED WI-FI RANGE & SIGNAL STABILITY 25 CLUB OFFER CLUB OFFER % 1990 199 $ $ SAVE 35% OFF TV WALL BRACKETS* * CLUB OFFER SAVE $30 FLEXIBLE EL WIRE LIGHTING Add colourful lighting to your Christmas decorations, party, costumes, signage etc. Includes 2 x EL wire light, controller and splitter. See T&Cs for details. RRP $32.80 See T&Cs for details 4 LAN PORTS AC3000 TRI-BAND SMART WI-FI ROUTER Massive wireless speed of up to 3000Mbps. 10X faster than conventional Fast Ethernet. YN8396 RRP $229 CLUB OFFER SAVE CLUB OFFER SAVE CLUB OFFER SAVE CLUB OFFER SAVE PANEL MOUNT CIRCUIT BREAKERS 100W LARGE GLUE GUN LIGHTNING TO USB CABLE 7.5A 2-CORE TINNED DC 20% 25% 25% 25% Heavy duty. 60A, 120A & 200A available. SZ2081-85 RRP $44.95 CLUB $34.95 Mains powered. Supplied with 11mm dia. glue sticks. TH1999 RRP $19.95 CLUB $14.95 CLUB OFFER SAVE CLUB OFFER SAVE CLUB OFFER SAVE CLUB OFFER SAVE 12" WOOFER SPEAKER PROFESSIONAL CAT IV MULTIMETER PROBES 10A DOUBLE GPO POWER POINT WITH IN-BUILT RCD JB WELD STEELSTIK EPOXY PUTTY 20% Paper cone. 225WRMS. 8 Ohm. CW2199 RRP $89.95 CLUB $69.95 20% High grade. 120mm long. WT5338 RRP $24.95 CLUB $19.95 3m long Lightning cable. Suit iPod 5S & POWER CABLE more. WC7733 RRP $34.95 CLUB $24.95 Double insulated. 30m Roll. WH3053 RRP $39.95 CLUB $29.95 20% 2 x 10A GPO. Built-in RCD. PS4048 RRP $49.95 CLUB $39.95 15% Sets in 3-5 minutes. NA1519 RRP $17.95 CLUB $14.95 CLUB OFFER SAVE CLUB OFFER SAVE CLUB OFFER SAVE CLUB OFFER SAVE 6-PCE PRECISION TAMPERPROOF TORX SET 6-WAY BLADE FUSE BLOCKS 3-30VDC TESTER WITH VOLTAGE/POLARITY DISPLAY SEALED POLYCARBONATE ENCLOSURE - IP65 25% T7, T8, T9, T10, T15 and T20 drivers. TD2021 RRP $19.95 CLUB $14.95 20% Integrated "fuse blown" indicator LEDs. Screw or spade terminal connection. SZ2095-96 RRP $21.95 CLUB $16.95 25% Works on 6/12/24V systems. QP2216 RRP $19.95 CLUB $14.95 20% OFF EXCLUSIVE CLUB OFFER COMPONENT STORAGE CASES* *See T&Cs for details. 58 click & collect Buy online & collect in store 20% 171(W) x 121(D) x 55(H)mm. Clear lid. HB6248 RRP $24.95 CLUB $19.95 YOUR CLUB, YOUR PERKS KEEP UP TO DATE WITH THE LATEST OFFERS & WHAT'S ON! Visit jaycar.com.au/member-access ON SALE 24.11.2020 - 26.12.2020 think. possible. Your destination for... workbench essentials 1. LARGE RARE EARTH MAGNETS 4. SOLDER FUME EXTRACTOR • Remove dangerous solder fumes from the work area • Ball bearing high volume fan • ESD safe • Spare filter Pk5 (TS1581 $9.95 sold separately) TS1580 WAS $74.95 Exceptionally strong (SCARY!) • Made from NdFeB (Neodymium Iron Boron) • Nickel plated ONLY • Sold as a pair LM1652 PR 29 $ 95 • Durable A3 size cutting mat for protecting work benchtop • 3mm thick PVC • 450(W) x 300(H) x 3(D)mm HM8100 ONLY 5995 4 SAVE $15 • Digital control, large LED display • Built-in over-current & short circuit protection • Output current: 0-5A NOW • 270(L) x 120(W) x 185(H)mm MP3840 WAS $189 159 $ 12 95 SAVE $30 6. IP67 TRUE RMS AUTORANGING DMM WITH USB INTERFACE 3. 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Prices and special offers are valid from catalogue sale 24.11.2020 - 26.12.2020. SERVICEMAN'S LOG A brush with disaster Dave Thompson It’s that time of year again; the days are longer, the clocks have changed, and there’s more time to contemplate all those jobs I’ve been putting off doing over the winter. While the lure of the interweb, streaming services and reading back-issues of Silicon Chip magazine keeps me office-chair bound, duty calls – and it’s about time I answered! I have several yard projects lined up; not that I’m really into gardening and landscaping mind you, but they need doing, and there’s nobody else in the frame. So I’m the one who has to do them. You’d be forgiven for thinking there’s nothing electronic-servicemanworthy in this type of work, but you’d be wrong; power tools come under that umbrella! I’m into DIY as much as anyone else, and like most engineers and servicemen (and as elaborated upon previously), I like to use the best tools for the job. However, this can create problems, especially when the tools run into certain ‘minor’ problems, such as no longer working. I recently had to sand some timber in the garden. While most people wouldn’t care that the odd fence joint doesn’t match up, as a former furniture creator and hobbyist luthier, that type of thing annoys me greatly. In an effort to make it as tidy as it can be, I fired up my new-ish Bosch 1/3-sheet sander to straighten up some edges I had cut badly. To my surprise, it didn’t work very well. This was unusual, because it had performed admirably in the past, and I’d used it to do a small amount of work during a house renovation I completed a while back. But now, while it powered on, it seemed to labour terribly and there was a distinct electrical-type smell coming from it. You probably know the smell I’m talking about; it’s a type of ‘Eau de burnt insulation’ scent that indicates that something is not quite right. onto my workshop floor a while back while doing another job. I thought nothing of it at the time, and it worked fine afterwards; or so I remembered. I have dropped power tools before; they are built to be tough (frequent power tool users are generally not renowned for their elegance!), so I didn’t think much about it. Even though my tools are not designed for ‘commercial use’, they are Items Covered This Month • • • • The brush arcing investigation Fluke 77 DMM repair DAB radio screen repair A ‘simple’ SMPS repair *Dave Thompson runs PC Anytime in Christchurch, NZ. Website: www.pcanytime.co.nz Email: dave<at>pcanytime.co.nz Past mistakes come back to haunt me I then recalled dropping this sander siliconchip.com.au Australia’s electronics magazine December 2020  61 very well made, and rightly or wrongly, I’ve used most of my power tools in that role over the years. I am now starting to think that the fall mentioned above might have something to do with the current state of affairs. So anyway, I powered it down and made a quick visual inspection of the tool exterior. The problem is that there is not much to see from the outside. The sanding plate at the bottom seemed free enough to move, but something was really stressing the motor out, and I could see the commutator and brushes arcing like mad through the small plastic cooling vents/grilles on the side. The case around the motor also got unusually warm after just a minute’s use – a classic sign that something is not right. As I don’t have an X-ray machine, the only way to find out for sure what was going on was to open the sander up and take a good look at its guts. Fortunately, there were none of those terrible security fasteners in sight; however, the PK screws holding the two halves together were embedded very deeply down moulded plastic channels. To gain access, I needed a very long-reach and thin-shanked number 2 Philips screwdriver, which in a way is a security feature in itself. Not 62 Silicon Chip many people have such a long-reach driver available, but as I do (several in fact!), it was just a matter of removing the screws and separating the case. Tools not made to be serviced This is where things started going a bit wrong. The two sections of the case didn’t want to ‘let go’. They parted ways by about a centimetre, but would go no further. I couldn’t see what was holding it up either, as there is a lot crammed in there, and due to the narrow gap and limited viewing angle, not much was visible. Australia’s electronics magazine I reluctantly used a pry tool to try to coerce them apart gently. I don’t usually like using tools to separate cases; in my perfect world, they should just come apart when all the fasteners are removed. But in this case (hah), it was fighting me all the way, and I had to use quite a lot of mustard to lever it apart. Eventually, the upper part of the case came away, and I could see everything inside. The first thing I noticed was several bits of what looked like one of those Airfix plastic model kits after the parts had been snipped out of it. Also, I found a coil spring lying in the bottom of the case. I was a bit puzzled at first, but it didn’t take me long to figure out from whence the bits came. At the top end of the motor, near the commutator, is a rectangular grid made from injection-moulded plastic. This shaped part includes the brush housing, and this whole assembly is aligned and located into a corresponding moulded void in each half of the case by a small plastic tongue. This is designed to keep the motor assembly properly centred and the brushes aligned with it. These tongues had broken away on both sides, leaving each of the pieces half-stuck in their slots in the case. siliconchip.com.au Marvellous! This alone pretty much ruined the tool, as without the motor assembly correctly aligned, it just wasn’t going to work correctly. Then that familiar serviceman’s muck-up sinking feeling set in as I realised I’d done this damage while prying the case apart. Now I had to scramble to find a solution that would get this almost-new tool back up and running. While potentially show-stopping, this damage didn’t explain why the sander laboured in the first place, so I likely had two problems to solve. Excellent! As if I don’t have enough to do anyway…. Getting on with the job One of the bits lying in the bottom half of the cover was a small plastic pillar, about 1.2cm long and 3mm in diameter. It was smooth on one end and had obviously snapped off on the other. Looking at the remains of the plastic latticework brush housing assembly, I could see another similar but intact pillar holding one of the coil springs used for maintaining brush tension. I could also see where this pillar had broken off the other side of the brush housing, assisted by the tension of the spring. That must have happened in the original fall, and without spring tension keeping that brush in good contact with the commutator, the motor would run erratically, if at all. At least I’d discovered a possible reason for the initial running-rough problem; the good news is that I still had the plastic pillar, the brush coil spring and the various broken pieces of the brush plate assembly. This might be salvageable after all! Pondering plastic permutations The problem with plastics is that not all can be successfully glued together; at least, with the glues I have on hand. Some plastics are too oily, some overly porous and some just too weak once they have been broken from their original, moulded shape. The grids of this brush housing frame measure about 3mm across for the most part, while the plate itself is about 1.5mm thick; why they didn’t make the whole assembly from one solid piece of moulded plastic is a mystery. The saving of perhaps one gram of siliconchip.com.au weight and a cent or two in production costs would make no engineering sense, except perhaps if it were made this way for airflow/cooling purposes. My guess is that like most manufacturers, they wanted to minimise parts cost, maximise profits and build in some obsolescence along the way. By making the internal components so fragile they cannot withstand a drop from standard working height to a floor, or even survive the separation of the case for maintenance, then it makes some sense. I suppose this is also what separates the home/DIY tools from their hardier (and usually much more expensive) commercial cousins. But no amount of theorising would solve my problems. To get this back up and running, I’d have to repair that broken spring holder and the frame it all mounts to. If I had a 3D printer, I could probably sketch it out and print one up, but as I don’t know anything about 3D printing, I have no idea whether a piece I could print at home would be strong enough for the job anyway. I’m no expert, but as dad owned an injection moulding machine for many years, I got familiar with some of the more commonly-used plastics. By the look of it, this was some flavour of glass-filled Nylon. As is typical, there were no markings or part numbers on it, and I couldn’t locate a service manual for the sander either, so I had to guess. In my experience, this stuff usually glues OK with the likes of a good epoxy resin, and as that’s what I had in my glue drawer, that’s what I chose to use. (When all you have is a hammer, everything looks like a nail, and all that.) First, I had to disassemble the remains of the brush holder assembly from the commutator. That meant pulling the bearing off as well, and of course, it was pressed (and likely glued) on very tightly to the armature. It always amazes me how a small job can snowball into something requiring a workshop full of specialised tooling! Fortunately, I’ve been collecting tools for years, so I had what I needed; using an arbour press and various vices and mandrels, I first cracked the glue and then slowly eased the bearing from the shaft without any damage to the armature. If I didn’t have those tools, I’d likely be throwing this sander Australia’s electronics magazine December 2020  63 in the bin and writing off the purchase price of a new one. If anyone needs an excuse to buy more tools, look no further! Feel free to clip out that last paragraph and bring it with you next time you walk out of a hardware store with several hundred dollars in tools you hadn’t planned on purchasing. Anyway, once the brush assembly was free, I pieced it all back together on the bench, CSI: Christchurch style. I only had seven bits to assemble, so it wasn’t exactly rocket surgery, and fortunately, they had all snapped cleanly and fit back together quite nicely. Once I was happy with it, I put a few strips of two-inch (~50mm) masking tape down on my flat melamine workbench and mixed up a swag of longcure epoxy resin (the quicker-setting epoxies aren’t as strong). After painting the ends of each piece with glue, I press-fitted it all together. I held it all as tightly as I could with more masking tape, leaving the gaps clear, and then filled those gaps with what was left of the resin. I left it for two days before attempting to get it off the bench. By then, it was as set as it was going to get, so I removed the tape from the top, then carefully lifted the now-almost-solid brush housing off along with the masking-tape foundation. It came off relatively easily and was dead flat. After removing any remnants of tape, I prepared it for reassembly. One problem left to solve Except, I still had a broken brushspring pillar. The sander wasn’t going to work without that being resolved. The problem I had was that no amount of glue (that I had or could fit in the limited space) was going to be able to hold that spring pillar in place. I could try gluing it, but my experience told me that as soon as I tensioned the coil spring, the pillar would just pop off. I might be able to get it stuck onto the plate strongly enough with a decentsized blob of glue, but this would foul the operation of the spring, so I needed something more robust but which still allowed the spring to do its job. I ended up drilling a 2mm hole through the brush plate, precisely in the centre of where the pillar used to stand, and literally bolted in what looked like an old tape machine capstan screw from my parts box. The shaft height and diameter of the ‘screw’ 64 Silicon Chip was almost the same as the broken plastic one, and there was enough thread protruding underneath to fit a decent nut and washer. There is nothing directly below that part of the plate anyway, so I had plenty of room. I put the brush into the holder and slipped the spring onto the screw first before mounting it, and a dab of Loctite on the threads before tightening the nut up should ensure it doesn’t move in a hurry. I pondered whether I should do the same thing to the other pillar as well, but I’d tempted the servicing Gods well enough already. The first acid test was to reassemble the tool and hope everything fit into the case with the ‘mods’ I’d made. It was a bit finicky putting the brush plate back onto the armature and refitting the bearing with it in place, and I was very careful not to put any stress on anything lest it all come crashing down. It went together OK, though. I used an old trick (which no doubt everybody else uses too) to keep the brushes out of the way while I installed the commutator/armature assembly. I pulled the brushes out of their holders about halfway past the springs, then used the tension of the springs to hold them open while I slipped the commutator between them. Once in place, it’s then a simple matter of prodding the brushes inwards a little until the springs snap back behind them. With all that now in one piece, it was time to re-fit it back into one half of the case. This is where it could all come unglued (ha ha!). I was reasonably sure the brush plate would fit, because it was glued back together flat, but you never know until you try. I also knew that if I pushed the now re-glued locating tongues into position, I might not get a second chance at repositioning them. After a bit of give and take, I managed to get the assembly sitting flat into the case. Halfway there! Making sure everything was in the right place, I got the top half of the case and gently positioned it until I was reasonably sure it was in the right place. The next move would make or break the repair. After lining it up, I gradually applied pressure and finagled everything into place; the cable clamp boot, the wiring pushed into the channels, and the case perfectly aligned to the Australia’s electronics magazine bottom half. With a final push, it all went together. I installed the screws, held my breath and plugged it in. It powered up and with a bit of arcing (I’d probably put the brushes back in the wrong holders), it worked a treat. After an hour’s work, it is sanding as well as it ever did. Phew! The job was done! Editor’s note: power tools with brushless motors are becoming more common and are now available at reasonable prices. Besides avoiding this sort of problem (you can’t have a brush spring detach if you don’t have brushes!), they also seem to have better power, less noise and more battery life than their brushed counterparts. I am impressed, and recommend you take a look next time you are tool shopping. Fluke 77 digital multimeter repair J. R. of Tauranga, New Zealand, had to use a fair bit of creativity for this repair, as the replacement parts he needed were not available. We think his solution is ingenious... I’ve had a Series I Fluke 77 DMM since the early 1980s. It has given me excellent service over countless hours. Unfortunately, I managed to connect it across a 2kV supply, and it was no more. Buy another? Flukes are very expensive, and I can probably no longer justify a new one. Throw it out and replace it with a cheap clone? Perhaps the best option, but nostalgia has its place even in the minds of dispassionate, ruthless engineers. So I thought I would see if I could fix it. Fluke multimeters have input protection which many times prevents expensive damage when oopses like this happen. 80-series meters employ the same concept as the 70-series, as do some of the 20-series. The current circuits are properly fused, and the volt/ohm ranges are protected by a combination of series fusible resistors and either a pair of high voltage MOVs or, on early models, a spark gap which arcs over at around 1500V. In either case, the resulting highbut-limited current blows the fusible resistor and open-circuits the input before anything else happens. Mine has the spark gaps. Indeed, that is what had happened. Spark gap E1 had been destroyed, and resistor R1 was split along its length and measured open-circuit. siliconchip.com.au I had repaired another Fluke 77 multimeter with the same fault around 2013, and at the time, the special resistor and spark gap together cost NZ $69.00 from Fluke. So I while expected the fix would be worthwhile, I knew it wouldn’t be cheap. I quickly found out that the genuine resistor from the Fluke NZ repair agent would be over NZ $60 by itself, but the spark gaps were no longer available. A Google search confirmed this is a well-known problem, with lots of people asking where to get them and none showing up anywhere, even on eBay. It seems like when you blow up the protection, you now have to throw away the meter! I then thought about converting the input circuit to use the two MOVs that the later models use instead. However, I found from Fluke that the MOVs were NZ $55 each, so without any labour cost, a repair would be nearly NZ $200 once freight and packaging were added. Anyway, I couldn’t fit the MOVs without butchering the PCB. Even third-party MOVs on eBay ostensibly meeting the Fluke specification were also scarce and expensive. It is essential to use the correct fusible resistor for R1, because it limits the energy in a fault and then opens, so preventing real damage and perhaps even injury. Any old 2W resistor looks pretty much like the real thing, and I found quite a few sellers on eBay offering “Fluke R1 resistors” or “fusible resistors for Fluke” for a few dollars each. But on close examination, none of the resistors being offered seemed to be anything but ordinary 2W metalfilm resistors which the sellers could have been buying for a few cents. The manufacturers do not state the fusing characteristics of most resistors at all, and they are typically designed for 300V whereas the correct resistor has a short-time withstand of 1000V. Before giving up, I had one last look on Google and ran across a chap who repaired meters, and who seemed pretty authoritative. While he had no solution for the spark gaps or MOVs, he had done the homework and found that at the time of posting (2015), one type of resistor was still being made by TT/IR which was fusible and had the right short-term voltage rating. He stated that it had been used by Fluke in the past, although they had superseded it with an upgraded version, siliconchip.com.au An old Series I Fluke 77 DMM from the 1980s. The destroyed spark gap E1 and opencircuit resistor R1 adjacent. The input protection section of the Fluke multimeter circuit. Australia’s electronics magazine December 2020  65 New rectangular spark gaps were made using copper wire and polyester resin. The spark gaps removed from the moulds. A hobby mill was used to cut the 0.008in slits for the spark gaps. A new resistor was fitted for R1 and the spark gap placed as well. The spark gaps were tested with a high-potential (hi-pot) insulation tester. They were consistent and arced between 1550-1650V. 66 Silicon Chip Australia’s electronics magazine he could not locate it from third parties. I found the manufacturer’s specs and confirmed what he said. Even better, I found they were still available in 2020 from Mouser. So I had a source of safe resistors but no MOVs or spark gaps. The Fluke 77 has two spark gaps, but only one was damaged. I had a close look at the clean one and found the air gap to be just under 0.2mm (actually 0.007 inches, ie, 7 mils). I found a website which had a credible relationship between air gap length and strike voltage for small air gaps (and no it’s not 30kV/cm!) and tried a few sums. A gap of 0.007in predicted a voltage just a little under the 1500V specified by Fluke, so given things lined up, it looked as if there was probably nothing magic about the gap, meaning it might be worth trying to make one. I could buy a 0.008in (0.2mm) slitting saw. Using the website formula, I found that the arc voltage wasn’t very sensitive to the gap; the predicted voltage for a 0.008in gap was a bit over 1500V. So I ordered a saw and the Mouser resistors, which are TT/ IR SPH1001J 1kW 2W wirewound fusible types. I made the gaps out of copper wire and polyester (fibreglass) resin that I had in the shed. The new gaps are rectangular: 8mm wide, 4.5mm thick and 10mm high and more-or-less fit into the space occupied by the original oval commercial ones. I machined a few simple mould shapes into a polyethylene chopping board. I thought the resin would release easily from that plastic, but I sprayed the holes with Teflon garage door dry lubricant to make sure. I used Blu-tack to hold the wires in the right place and poured in the resin. Once set, I removed them from the moulds (easy) and eventually got rid of the Blu-tack (hard). I won’t use Blutack for this sort of job again. I then put them into the little hobby mill and cut the 0.008in slits. I found the gaps were a bit bigger than 0.008in – they were actually around 0.009in. This was probably due to run-out on the saw arbour, or the saw itself. But the web formula indicated they would still meet the spec. I then tested them with a hi-pot insulation tester. They were pretty consistent, arcing at between 1550V and 1650V. The hi-pot has current limiting, which I set to 20µA, so the gaps were siliconchip.com.au not damaged or altered by the test. Since Fluke’s specification for the original spark gaps is 1500V ±20% (1200-1800V), the home-made ones are satisfactory. I tested the remaining good original spark gap, and it arced over at 1500V. I then fitted a new resistor for R1 and one of the home-brew spark gaps and reassembled the meter. When compared with an HP bench voltmeter, the Fluke 77 is as good as ever. No, I don’t propose to deliberately test the over-voltage failure mode! All in, the exercise cost me about $70 NZ, of which FedEx got a fair chunk for shipping $5 worth of resistors from Mouser. The repair (apart from my labour) was therefore economic; nostalgia has its place it seems. I now have nine spare resistors and six extra spark gaps, a mould plate and a slitting saw in case I do it again to my meter or come across someone else who needs the same fix. Radio LCD screen repair G. McD., of Jindalee, Qld had some spare time over the Christmas break and decided to spend some of it repairing the faulty LCD screen on his wife’s radio. Here is what happened… My wife bought herself a brand new DGTECH BC76183 DAB/FM digital radio soon after digital radio became available to listeners in the Brisbane metropolitan area. It served her well on a daily basis until the LCD screen suddenly went blank. The idea of binning it and purchasing another had crossed our minds. But first, I decided to have a closer look at it to see if I could repair the screen as she was otherwise happy with the radio. Before pulling it apart, I ran some quick tests to try to narrow down the likely cause of the fault. I switched on the radio and sure enough, the sounds of ABC Jazz came through as impressively as it did when the radio was new. Then I reached for my torch and shone it directly at the screen. As if by magic, I could once again read the name of the station as well as details of the tune being broadcast. This indicated to me that there was nothing wrong with the LCD screen itself or the wiring connecting it to the PCB. The fault lay with the LCD backlighting. It was now time to explore the innards of the radio. After turning it off and unplugging the mains lead, I unsiliconchip.com.au did two screws on the back cover as well as the two marked screws hidden beneath rubber pads on the underside of the enclosure. The back cover could then be carefully prised open, after gently pushing the earphone socket clear with a small screwdriver. This exposed the inside of the radio, but the rear cover remained connected to the main body by the speaker wires. I unplugged this and three other wire harnesses from their sockets, allowing the two halves of the enclosure to be separated. I now had access to the PCB on which the LCD screen was mounted. But as is usually the case, I couldn’t get to it as the screen was on the underside of the board; I would need to remove the PCB. The PCB was held in place by four white plastic retaining clips which needed to be swung clear. Next, two of those that were marked needed to be unscrewed as they provided additional stability to the pushbutton arrangement. Then four screws on each corner of the PCB were removed and set aside. After pulling off the volume control knob, the PCB came clear and turning it upside-down exposed the LCD screen. I unclipped the white plastic cover that butted up to the right-hand side of the screen; this housed the LED that I suspected to be the problem. To verify this, I reconnected the four wire harnesses, plugged the power cord into the mains supply and turned the radio on. Once again, the radio came alive but the screen remained defiantly blank. I turned on my DMM, which had been set to read 20V DC, and probed the two leads of the unlit LED; I obtained a reading of 2.65V. Now that I had verified there was voltage across the LED, I assumed that the fault lay with the LED. Not having a spare white LED in my spares storage, I paid a quick visit to Jaycar and purchased the closest I could find to the original, Cat ZD0192 for $1.65 each. On arriving back at the workbench, I discovered that the replacement LED was longer than the original and wouldn’t fit into the space provided (the original LED was flat-topped and not domed as the one I had just bought). This was verified after I had removed the offending part, cleaned up the two through-holes with solder wick and tried the replacement for a fit. Australia’s electronics magazine So it was out with my trusty modeller’s knife, with which I began shaving away at the inside of the housing until there was just enough space for the replacement part to squeeze in. The new LED was soldered into place, the leads trimmed and the lid of the housing clipped back into place. All that was left for me to do then was to reassemble the radio, taking care not to crimp any of the wire looms during fitting, and run a “smoke test”. To my delight, the screen lit up immediately upon switching on, with everything operating as it should. My wife can now look forward to many happy years of service from this excellent radio. A ‘simple’ SMPS repair R. S. of Fig Tree Pocket, Qld, has a lot of experience repairing switchmode power supplies. This turned out to be one of his simpler repairs, although not necessarily the easiest to diagnose... I had a problem with a Bosch 30V 0.5A battery charging plugpack for a cordless vacuum cleaner. It stopped producing any output, so the vacuum cleaner battery was not charging. This charger uses an On Bright Electronics OB2358 IC in an 8-pin DIL package. This IC has an inbuilt 600V FET, which connects directly to the primary of the flyback transformer. The OB2358 was not starting up, and therefore not generating its own supply voltage, via an extra winding on the flyback transformer. For some reason, there is a surfacemount zener diode on the board from the feedback pin 3 of the OB2358 to ground pin 8. This was leaking enough current to hold pin 3 low and prevent the circuit working. Removing the zener diode got the plug pack working again. I cannot see any reason for the zener diode; it is not shown in the typical application circuit in the IC data sheet. Editor’s note: probably to protect the IC from damage if the feedback mechanism stops working for some reason or the output is externally pulled high. Luckily, this plugpack can be split open without damage. Usually, they are glued together so well that the case breaks when you try to open them. One other note: the feedback circuit on the low voltage side uses a 6-pin surface mount IC marked OD=28X instead of a TL431. Can anyone identify this part? SC December 2020  67 As described last month, this add-on board for the USB SuperCodec provides two balanced inputs with four attenuation options: 0dB, 10dB, 20dB and 40dB. It will fit in with the SuperCodec itself (in the same instrument case), resulting in a sleek all-in-one recording and measurement instrument. Now let’s get onto building it! Part 2: by Phil Prosser Balanced Input and Attenuator for the USB A ll of the components shown and described in the circuit last month fit on a single PCB which is quite quick and straightforward to build. The wiring to connect the two boards isn’t too difficult to make up either, consisting of one stereo shielded cable and one three-wire DC supply lead. The case end panels also need to be drilled differently than what was described for the original SuperCodec. The first step in assembly is to mount all the main components on the printed circuit board. Before assembling it, if you have an accurate resistance meter, you may wish to measure the 0.1% tolerance resistors and find the best matched sets amongst those you have purchased. However, that is optional. As long as they meet the specified tolerances, the performance of your unit should be close to that of our prototype; it might even exceed ours, if you’re lucky. PCB assembly We have made an effort to use only through-hole components for ease of construction and made the room for relay switching of the attenuators rather than a rotary wafer switch. Before starting construction, you will need to determine your desired input impedance. Review last month's article 68 Silicon Chip and then refer to the parts list to see which parts you will need for your selected option. The add-on board is coded 01106202 and measures 99.5 x 141.5mm. Refer to the overlay diagram, Fig.9, during construction. Start by loading the low-profile components: ferrite beads FB1-FB4 and all resistors. Make sure that the 0.1% types go in the specified locations. Tip: if you can match resistors between the ‘hot’ and ‘cold’ legs of each channel, you will get a useful improvement in common-mode rejection but this may not be possible depending on the resistors you purchase and the accuracy of your ohmmeter. If your ferrite beads are the loose types, feed resistor lead off-cuts through them. Keep them tight on the board, and it’s a good idea to use dobs of neutral cure silicone sealant or similar glue to stop them from moving and rattling. Next, mount all the zener diodes and the 1N4148 signal diodes. Be careful to orientate the diode cathode stripes as shown in Fig.9, as they don’t all face the same way. We have specified 3.9V zeners for ZD3 and ZD4, but any value from 3.3V to about 4.7V should work, as these just establish a protection voltage. Australia’s electronics magazine siliconchip.com.au Now install the electrolytic capacitors, which are also polarised; their longer leads must go into the pads marked with + symbols. The 10µF capacitors must be laid down flat as shown in the accompanying photograph, or selected as very low profile units. This is important, as we will be squeezing this board into the box with the USB interface, ADC and DAC. Next, fit the remaining capacitors (plastic film and ceramic). Remember to use 10µF plastic film capacitors for Because the board is a tight fit in the SuperCodec case, some electrolytics must be installed horizontally, as shown here. Indeed, in some cases, they lie horizontally spaced above other components. siliconchip.com.au the coupling caps if you’ve chosen resistors for a 10kΩ input impedance, or 1µF for a 100kΩ input impedance. These too must be laid over on their sides to clear components on the other board. After that, solder the six NE5532 ICs and eight relays. The IC and relay orientations are critical. All the relays are orientated with pin 1 away from the input connectors, while all the op amps have pin 1 toward the inputs. You can mount the ICs on sockets, but we prefer not to as the contacts can oxidise over time, leading to poor connections. If using sockets, solder them with the orientations shown, then straighten the IC pins and carefully push them fully into the sockets. Mount the connectors next, followed by the input select switch. The two right-angle polarised headers can be soldered from the top side, but it’s a good idea to solder the pins on the bottom too. Follow with the two 6.35mm TRS sockets. Make sure these are the specified low-profile types and that they are fitted snug to the board. Your add-on board should now be finished. The three boards are connected by several cables, which we will now describe. Australia’s electronics magazine December 2020  69                          10F                            10F  The output of the Balanced Input Attenuator board is connected to the USB Sound Card board by a 180mm length of shielded cable. To make this, cut a piece of figure8 shielded cable to 180mm, strip 18mm off the sheath at each end, twist the screen wires together and apply the 2.5mm diameter heatshrink to these. Then put the 5mm heatshrink over each coax line and shrink, as shown in the adjacent photograph. Crimp pins Silicon Chip   Making the internal cables 70          10F 10F Fig.9: use this PCB overlay diagram and the photo below as a guide during construction, to see where the components are mounted on the board. Watch the orientations of IC1-IC6, RLY1RLY8 and all the electrolytic capacitors and diodes. The other parts either only go in one way around, or it doesn’t matter. Make sure to trim all soldered leads close to the underside of the PCB to prevent them shorting against the case later. You may notice that diodes D5-D8 are missing from this photo – they were left off the prototype to verify that they had no effect on performance (they didn't!) but were added later. Constructors should fit all eight diodes (D1-D8) as shown on the component overlay above. on each end and insert them into the 4-way plug as shown opposite. The middle two pins are Earth while the outer two pins are for the signal wires. Preparing the SuperCodec board If you haven’t already built the USB Sound Card board, as per the series of articles in the last three issues, do that now. But note that there are two things you need to do slightly differently when building it: Australia’s electronics magazine siliconchip.com.au The output cable should be 180mm of twin screened coaxial cable. The middle two pins are the shields. 1) Do not mount the two 6x2-pin 2.0mm pitch header sockets on the back of the board for the MCHStreamer. We will instead be soldering pigtailed connectors to these locations, to allow us to mount the MCHStreamer above the USB Sound Card board. 2) When building that board, you need to make sure the voltage regulator that is not mounted on a heatsink is pushed right down onto the PCB, or it might foul the Balanced Input Attenuator board. Having completed that board (minus the MCHStreamer connectors), the next step is to solder a power cable to it, which will plug into the Balanced Input Attenuator board and power it. To do this, take 100mm lengths of red, green and black medium-duty hookup wire and attach them to crimp pins, then push these into the power header, as shown in the photograph below. Red (positive) is at the right-hand end, ground (green) in the middle and black (negative) at the left. Power cable and header for the attenuator board. Sleeve the whole cable in a heatshrink tubing sheath, with around 3cm of each wire protruding, then strip the insulation back by about 5mm on each wire and tin the ends. These bare ends are then soldered to component pads on the SuperCodec PCB. The photo below shows where they go. Check you have the wires in the right spots! The black wire goes to the end of the corner-most 10Ω resistor that is closest to the board edge; the red wire goes to the same end of the adjacent 10Ω resistor; the green to the end of the adjacent 5.6kΩ resistor that is furthest from the board edge. Once you’ve done this, double-check that the wires go into the appropriate positions on the plastic block at the other end; otherwise, there will be trouble when you plug it in later. sible to fit the Balanced Input Attenuator in the same case. Rather than plugging the MCHStreamer directly onto the SuperCodec board, is connects via two 12-way plugs that connect to the board via sets of 12 flying leads. The plugs with attached leads should have come with the MCHStreamer unit. To prepare them, measure and cut the pigtail wires to 50mm (5cm), as shown in the photo. The MCHStreamer is supplied with pre wired headers. Trim the leads to 50mm as shown. We need to keep these as short as practicable. Cut all the attached wires to this length and strip, twist and neatly tin 5mm at the ends. Note that while the plugs supplied have black wires on one side and red on the other, they will plug in either way around, and while there is a ground pin on one side, most of the pins carry signals. So it isn’t critical which way around you solder them. The best approach to soldering these to the sets of twelve pads on the PCB is to stand the connector vertically and looking from above, solder the inside row of wires to the outside row of holes in the PCB. We will be plugging this to the top of the MCH Streamer, which will swap the inside and outside rows of wires, as shown in the following photos. Connecting the MCHStreamer The next step is to connect the MCHStreamer to the SuperCodec board, but we are doing it differently than for the standalone USB SuperCodec. Otherwise, it is impos- When plugged into the headers the MCHStreamer ought to sit as shown above. A tight fit but without stressing parts. We need to solder the power cable to the main PCB as shown. Try to hook the wires around the resistor leads and keep things tidy! siliconchip.com.au With the two cables soldered in place, present the MCHStreamer to the pigtailed headers and fold them as shown in the photo. The result is somewhat tight, but does fit inside the box. At this stage, it’s worth checking both PCBs to make sure that you trimmed all component leads neatly. If you’ve left Australia’s electronics magazine December 2020  71 any long, they could interfere with, and possibly short out against the case once inserted into it. There is adequate room below the USB Sound Card to accommodate normal lead lengths; you should not have any problems provided you are tidy. Testing Before inserting everything in the case, it’s a good idea to make sure it’s all working. If you haven’t already tested the USB SuperCodec board in isolation, do it per the instructions in the third SuperCodec article. This will also involve installing the MCHStreamer drivers and getting it working on your computer. Power down the SuperCodec board and plug the power connector from the SuperCodec PCB into the three-pin header on the Balanced Input Attenuator board (CON3). Then use the length of shielded cable with plugs on either end you prepared earlier to connect the audio output of the Attenuator (CON4) to the audio input on the USB Sound Card (also CON4). For the outputs, make up a twin shielded cable with RCA chassis connectors on one end and a 4-pin polarised plug on the other, as per the final SuperCodec article (if you haven’t already). Plug this into CON5. Make sure the whole rig Fig.10: this shows the sizes and shape    of the front & rear panels (front panel at the bottom), and where to cut or drill holes in them. The 3mm hole below the 7.5mm hole only needs to go partway through the inside of the panel. The ventilation holes shown in red are optional, but do help to keep the internal components at a reasonable temperature in hotter environments, so are recommended. When soldering the MCHStreamer connector to the board, the red and black rows of wires need to cross over as shown. 72 Silicon Chip is resting on a non-conductive surface, and nothing can short to anything else before proceeding. Now would be a good time to check, using a continuity tester, that the +9V and -9V rails on the two boards are connected the right way around and not swapped. Check for 0V continuity between the boards at the same time. Then, with the MCHStreamer plugged into the USB sound card, plug in the 12V supply to power the whole assembly up. Assuming it passes the “smoke test”, verify that all the supply rail voltages are still correct. You would have tested these with the SuperCodec alone already, but a fault on the Balanced Input Attenuator board could cause them to be wrong now. Assuming they’re OK, check that the attenuator relays work; each time switch S1 is moved, it should generate a nice click from the relays. Then plug the whole device into your computer and repeat the output test that you carried out earlier. Check that the USB Sound Card generates a signal when you play sound or music. If this does not work, check that there are no faults on the Balanced Input Attenuator board and check the wiring thoroughly. We have not changed this part of the USB Sound Card, so it should still work fine. Now launch your recording or analysis software (Audacity will work for basic testing). Set the input attenuator to 0dB, apply an audio signal of no more than 1V RMS to Australia’s electronics magazine siliconchip.com.au Modifying your prebuilt SuperCodec Fig.11: if you drilled the ventilation holes on the rear panel, you should also drill some holes towards the front of the bottom panel, as shown here. These allow cool air to be drawn in via convection, which flows along and cools the two boards before exiting through the holes at the top of the rear panel. one of the balanced inputs (eg, using a test oscillator) and check that it is received undistorted in the correct channel (left or right). If you don’t have a test oscillator, you can rig up some cables to loop the USB Sound Card’s outputs back to the balanced inputs and play a test tone. If you do this, remember to set the output level no higher than -8dB to avoid overloading the inputs. If that checks out, switch to the -10dB setting and verify that the input level drops appropriately. If your test oscillator level can go higher, increase it to a maximum of 3V RMS and confirm that you get undistorted near-full-scale input signals. You can also check the -20dB and -40dB settings and verify that the input level drops appropriately, but the waveform shape remains undistorted. Drilling the front and rear panels As mentioned earlier, we are using the same case that was used for the basic USB Sound Card. However, because we’ve had to pack an extra board in, the boards mount to the front and rear panels differently. The revised drilling details are in Fig.10. You can copy/print this and use it as a template, or you can measure with a ruler and mark out the hole locations on the panels. If you have already drilled the panels for the basic USB Sound Card, it is not hard to cut and make new panels from an aluminium sheet of a suitable thickness. You can achieve a high-quality finish by sanding with 400 grit paper after making the holes, then spraying the panels with satin finish black paint. Cut and finish the metal panels as shown in Fig.10. The 3mm “hole” below the switch hole on the front panel (7.5mm in diameter) does not need to be drilled through; it is there to hold the locking pin on the switch. Note the series of holes on the rear panel shown in red; these are for venting hot air and help to lower the operating temperature of the internal components by around 5°C. These are necessary due to the extra internal dissipation siliconchip.com.au If you already built the SuperCodec USB Sound Card and have soldered the headers to the back of the PCB, it is possible to still add the Balanced Input Attenuator, but it’s tricky. Removing the two throughhole headers is not as simple as it sounds. We did it on our prototype, but note that this procedure is for advanced builders wishing for a little excitement! You will need a hot air gun set to about 290°C, a pair of pliers and a steady hand. Set the USB Sound Card on edge and grip the first 12-pin header with the pliers. Heat the solder side of this connector with the air gun, from a distance of about 10mm, and gently wriggle the connector with the pliers. Observe the solder connections and adjust your heating until you see some, then all pins moving in the PCB. At this point, gently pull the connector out while continuing to heat, ensuring that all pins are free to come out. Do not use force! Then use a solder sucker to clean the holes up, ready for the MCHStreamer connector wires. due to the Balanced Input Attenuator board. You could opt not to drill these if you are never going to operate the device at higher ambient temperatures (ie, if it will always be used in an air-conditioned room). But as they are on the rear panel, they are unobtrusive, and it’s generally better to keep the components as cool as possible. Similarly, we have prepared a bottom panel drilling diagram (Fig.11) which shows the location of some extra holes in that panel. Combined with the holes on the rear panel, these provide some convective cooling to drop that temperature. If you’re going to drill one set of holes, you should drill both, or they will not be effective. When finished, install the rubber foot on the front panel as shown in Fig.10 to ensure that the USB Sound Card is held snug against the rear panel. We cut the chamfer of the top of the foot to ensure that the rubber foot fully pushes the PCB back into the case. Then do a test assembly and make sure everything fits OK. Get used to the jiggling required to get things in. Final assembly Assembly is pretty straightforward. Slip the bottom panel off the case, and slide the USB Sound Card in the top slot with the components facing to the bottom panel. The MCHStreamer should already be plugged to the USB Sound Card. Attach the MCHStreamer to the rear panel using an M3 crinkle/star washer, TO-220 bush and fibre or plastic washer. The bush and insulating washer are to ensure that it is insulated from the rear panel, as described in the USB Sound Card article. Make sure the bezel is in place (omitted in photo). You can now put the four screws into the rear panel. Then mount the output connectors as described in the USB Sound Card article. Again, make sure they are insulated from the case. Attach the Earth screw and solder tags as described in the USB Sound Card article, and solder the 10nF capacitor between the Earth tag and ground of the output connector. Australia’s electronics magazine December 2020  73 Assembly is tight, but with the cable lengths recommended allows the balanced attenuator to slide out sufficient to allow the output and power connectors to be plugged in. Watch for the cables snagging on parts on the Codec main board though. The MCHStreamer is fixed to the rear panel using an insulating bush kit. Don't forget this! Plug the 18cm cable that goes between the USB Sound Card input and Balanced Attenuator output into CON4 on the SuperCodec board. Now slot the Balanced Attenuator into the bottom slot, with its components facing towards the USB Sound Card. As you slide it in, pull out the power cable and audio cable that run between the cards and plug them into the Balanced Input Attenuator power connector and output connector. You will need to jiggle things to make sure that the cables do not foul between the two boards. Trust us; it will fit! Ensuring that the rubber foot is stuck to the front panel as shown in the drawing (Fig.10), push the front panel bezel into place. You then need to slide the bottom panel on. After that, push the 6.35mm sockets and switch through the front panel and screw these tight with the provided mounting A view with the bottom panel off during assembly. Next comes the Balanced Attenuator and base plate. 74 Silicon Chip kits. You can now put the four screws into the front panel. At this point, you should be ready to go! Making some test leads If you’re primarily building the Balanced Input Attenuator so that you can make recordings from equipment with balanced outputs, chances are you already have suitable cables. You may need to purchase (or make) some XLR to TRS adaptor cables, to allow you to plug XLR equipment into the inputs. These are readily available and usually not too expensive; for example, Altronics Cat P0750. For audio equipment and distortion testing, though, you will probably want a set of cables with alligator clips on one end and TRS jacks on the other. This provides you with maximum flexibility to connect to the ends of various components in audio gear as needed. The process of building leads is open to your needs and imagination. We will show our approach, but this is by no means the only way. We used 90° “stereo” TRS 6.35mm jacks to get the cables out of the way of the attenuation switch. Strip 25mm off the ends of the balanced (twin-core shielded) cable. Also, strip First extend the Hot, Cold and Screen of the leads, then cover with two layers of heat-shrink to make a robust test lead. Australia’s electronics magazine siliconchip.com.au Test programs for your PC TIP (hot) RING (cold) SLEEVE [or BODY] (screen) Connnections to the 6.35mm stereo plug. We have used the "TRS" naming standard, although you will often see "TRB" used instead. It doesn't matter: the sleeve IS the body! 10mm off each of the inner conductors. Strip 10mm off each end of short lengths of red, green and black hookup wires, and twist and solder these to the balanced cable as shown. Then slip 20mm length of 3mm heatshrink over the solder joints and shrink them down. Now take two 40mm lengths of 6-8mm diameter heatshrink tubing and shrink these over the junction of the cables. We used thin cable; you may need to use larger diameter heatshrink here. Then take two 60mm lengths of tubing and put these over the top as a strain relief. This will give you a secure connection and minimise the likelihood of wire fatigue. The next step is to connect alligator clips of your preference to the red, black and green wires. Start by slipping the rubber covers over the wires first, so you don’t forget them! Then slip a 15mm length of 3mm heatshrink over the cable. Strip off an appropriate length of insulation; for the Jaycar clips, this is about 6mm. Solder and trim off any daggy bits, then crimp the metal strain relief tabs, right at the end of the clip, over the wire. For extra protection, slip the heatshrink down the wire and over the metal strain relief and shrink. Slide the covers over the clips, and these are done! The 6.35mm jacks are similar, just much larger. Don’t forget to slip the covers onto the cable first! Follow with 30mm of 3mm diameter heatshrink as a final cover for the cable (we used thin cable, you may need to use larger diameter tubing). We put some heatshrink over the alligator clip to cable transition to act as strain relief, then slid the rubber boot over the lead. siliconchip.com.au We have used AudioTester 3.0 for testing a lot of different audio gear. This is available as shareware, and a paid subscription is available. It is good but not perfect. You need to select the ASIO interface for playback and record, and also 192kHz for the sampling rate. You can download it from www.audiotester. de/download.htm One problem we’ve noted with AudioTester is that its THD+N readings seem off, especially with test signals well below or above 1kHz. We prefer to use it to measure THD only, and SNR only, then compute the THD+N reading as the RMS sum of the two figures. It appears to do a good job of computing THD, but you need to be careful to use a test signal that isn’t too far below the maximum that the device can accommodate. Otherwise, the resulting harmonics can be so low that they are unmeasurable or severely quantised, and you get an artificially low distortion reading. One alternative that we have used, but not as much, is ARTA. Many people seem to like this software. You can get it from www.artalabs.hr We stripped about 15mm of insulation off the cable, and applied about 8mm of 2mm heatshrink to the Earth screen. Check the connections for the solder lugs to the Tip, Ring and Sleeve. The tip is Hot (red), the ring is Cold (black) and the sleeve is ground (green). Solder these on. If you intend to use this for testing amplifiers, the connector and cable will see the full amplifier output voltage in some cases. Make sure that all connections are secure and that clearances of no less than 1mm are present and secure. Do not use these on mains voltage, in any circumstances! Final testing With the case all put together, power the unit back up, plug it back into your computer and verify that everything still works as before. If it doesn’t, you may have a short circuit somewhere, or forgot to plug something back in when you put it all in the case. If you are recording from a professional audio source, plug this in and set the attenuator level to 10dB, and you are all set. SC Our finished lead. Yes, when constructing the prototype we found we had run out of green clip covers – at least the lead is green! Australia’s electronics magazine December 2020  75 Using Cheap Asian Electronic Modules By Jim Rowe Mini Digital Volt/ Amp Panel Meters There are many low-cost digital panel meters available which can display voltage and current at the same time. Quite a few have popped up on the market in the last year or so. So let’s take a look at some of the more popular models, see what’s inside them and whether they’re easy to use. T here are a surprising number of these low-cost digital panel meters currently available. Many are quite similar to each other, but a few are noticeably different. This article will focus on a few of the more popular and useful models. We’ll be looking at the meters designed to measure DC parameters this month (ie, DC voltage and current), with a follow-up article to describe those which make AC measurements. The first one is the DSN-VC288 from the Chinese firm Geekcreit (we’ll be seeing more of their products in later articles). It is available in two versions: one with a 0-10A current range using an internal current shunt, and the other with a 0-50A current range using an external current shunt. Both versions have a 0-100V voltage range. The 10A version comes with two plug-in connection leads for around $5.50 plus delivery, while the 50A version comes with both the leads and an external 50A current shunt for around $8.50 plus delivery. The DSN-VC288 is quite small, at 48mm wide, 29mm tall and 22mm deep. Although some of the suppliers describe it as having a 0.56-inch dual LED display, that is misleading. 76 Silicon Chip The three-digit seven-segment displays used for both voltage (red) and current (blue) are each only 7mm or 0.28in high. Despite this, the displays are quite readable. The display ‘window’ is 35 x 18mm. Both versions of the DSN-VC288 can be powered from a supply voltage of 4-30V DC, usually drawing less than 20mA. So if they are to measure voltages in this range, they can be powered from the same voltage source. The only thing to bear in mind is that the DSN-VC288 can only measure voltages which are positive with respect to its negative rail. That also applies to current measurements. Inside the DSN-VC288 The circuit of the DSN-VC288 is shown in Fig.1. It’s all based on IC1, an STMicro STM8S103F3 8-bit microcontroller. This runs firmware which directs it to take voltage and current measurements every 300ms or so, then show them on volts display DS1 and current display DS2. Three-pin connector J3 at upper left is used for both the meter’s supply input (V+ and V-) and its voltage measurement input (Vin). The V+ supply input connects to the anode of diode D1 and then to the input of REG1, an Australia’s electronics magazine ME6203 LDO (low drop-out) regulator, which provides a regulated 3.3V supply for the rest of the circuit. On the other hand, the Vin input from J3 goes to the AN4/PD3 input (pin 20) of IC3 via a 270kW/8.2kW resistive voltage divider, together with VR1 (the voltage calibration trimpot) and a 100nF filter capacitor across the 8.2kW resistor. The meter’s ‘current’ input is via two-pin connector J4, at lower left. Here pin 1 (-) is connected straight to the meter’s negative rail, while pin 2 (+) connects to the non-inverting input of IC2b, via a low-pass filter formed by a 330W resistor and 100nF capacitor. IC2b is connected as a DC amplifier with an adjustable gain between 23 and 25 using trimpot VR2, to calibrate the current range. Resistor RS connected across the current input pins of J4, shown in red, is the internal current shunt. For the DSN-VC288 version with the 10A current range, RS is a 7.5mW (milliohm) resistor. In contrast, the DSNVC288 version with a 50A current range has no internal resistor RS, as the current shunt is external, with a value of 1.5mW. The only other thing to note about Fig.1 is that ‘connectors’ J1 and J2 are siliconchip.com.au Fig.1: circuit diagram for the DSN-VC288 digital panel meter. The internal current shunt RS is only fitted on the 0-10A current range version, the alternative model with a current range of 0-50A uses an external shunt instead. not physical connectors, but actually a row of test points in the case of J1, with the purpose of J2 unexplained. Presumably, J1 is also used to program IC1 at the factory. Using the DSN-VC288 It’s easy to put the DSN-VC288 module to use, as shown in Fig.2. The first two diagrams show the connections for the version with the internal 10A current shunt, with (A) showing the connections when the module has a separate power supply, and (B) showing the connections when it shares its power supply with the load. (B) can only be used when the load supply is below 30V. The other two diagrams show the connections for the DSN-VC288 version with an external 50A shunt. (C) shows the connections when the module has a separate power supply, while (D) shows the connections for a shared power supply. Again, it must be less than 30V. The two short (150mm) connectsiliconchip.com.au ing leads which come with the DSNVC288 are distinguished by both their size and their insulation. The wires attached to the 3-pin connector that plugs into J3 are thin, while the two wires attached to the larger 2-pin connector that plugs into J4 are thicker. But these four connection options are not the only way that the DSN- VC288 modules can be used. For example, if you want to measure lower currents than their nominal 10A or 50A, you can do that. Bear in mind that the current range of the DSN-VC288 is really just a 0-75mV voltage range, with the firmware scaling this range to show the current passing through the shunt. So you can get a lower current range The underside of the 50A current range version of the DSN-VC288 module. Australia’s electronics magazine December 2020  77 FIGURE 2 by changing the shunt resistor value. This is easier with the version using an external 50A shunt, but it’s also possible with the other version if you’re careful. For example, if you’d like to use the 50A version to measure currents between 0 and 50mA, replace the big 50A shunt with a 1.5W 0.1% resistor. The meter’s scaling will then simply provide current readings from 0-50mA instead of 0-50A. The same approach could be used to give the meter current ranges of 0-500mA or 0-5A, although the decimal point will be in the wrong position. If that doesn’t worry you greatly, the shunt values to use would be 150mW for 0-500mA, or 15mW for 0-5A. If you have the internal shunt version of the DSN-VC288, to change its current range, you’ll need to remove the internal 10A shunt. This is a stout U-shaped wire soldered to the meter’s PCB just to the right of J4, looking from the rear. This is what you need to desolder to change the meter’s current range. Since the internal 10A shunt has a resistance of 7.5mW (providing 75mV when 10A is flowing through it), the scaling firmware in this version will turn 75mV into a reading of “10.0”. So you can change its current range to 0-10mA by replacing the internal shunt with a 7.5W resistor (ideally with 0.1% tolerance). Or again, you could give it a range of 0-100mA by using a 750mW shunt, or a range of 0-1A by using a 75mW shunt. But in both cases, the decimal point will be in the wrong position. Testing I ordered a couple of 50A versions of the DSN-VC288 from Banggood and put them through their paces. Both worked exactly as claimed, with an operating current of 20mA, a voltage measurement accuracy within ±0.1% and a current measurement accuracy of ±1%. In both cases, the readings could The external 50A 75mV shunt is in the foreground, with a similar 100A shunt behind. 78 Silicon Chip Australia’s electronics magazine siliconchip.com.au The Current Shunt Story The stout U-shaped wire (circled in red) is what needs to be removed to change the meter’s current range. be made ‘spot on’ compared with my reference instruments using little trimpots VR1 and VR2. So bearing in mind that the DSNVC288 is very compact and has relatively small readouts, it is very practical and useful, as well as being great value for money! The PZEM-051 meter module The PZEM-051 is one of a range of measurement modules made in China by Ningbo Peacefair Electronic Technology, based in Ningbo City, Zhejiang Province. It’s available from various suppliers via online markets like AliExpress, eBay and Amazon for between $9.00 and $14.95 plus delivery, depending on whether you want the 50A version or the 100A version. There is also a very similar module with a 20A current range available from Banggood for $21.00 plus delivery, designated the PZEM-031 (siliconchip.com.au/link/ab5h). Also, Banggood has another version In the not-too-distant past, voltages and currents were measured using “moving needle” analog meters (ie, moving-iron and moving-coil meters). The current shunt was developed to allow these meters to measure currents that were higher than their basic sensitivity. For example, if a meter needed 1mA to give a full-scale reading (ie, 1mA FSD), it could be used to measure currents up to say 1A by connecting a low resistance ‘shunt’ across its terminals. The resistance was chosen so that it would carry 99.9% of the current, leaving just 0.1% to flow through the meter itself. This effectively converted the 0-1mA meter into a 0-1A meter. Similarly, the meter could be used to measure currents up to 10A by shunting it with an even lower value resistor which would carry 99.99% of the current, leaving just 0.01% to flow through the meter itself. The current shunt would conduct all of the current at 10A, except the 1mA needed for the meter to achieve full-scale deflection (FSD). The name “shunt” comes from railways, where a train is shunted onto a parallel section of track, just like how the current shunt parallels the pre-existing current path through the meter. Working out the required resistance of the current shunt was fairly easy, once you knew the resistance of the meter itself, and the fraction of the current which needed to be diverted past it. For example, if the shunt needed to take 999 times the meter current (999mA/1mA), it would need to have a resistance of only 1/999 that of the meter itself. So if the meter had a resistance of 100W, the shunt would need a resistance of 0.1001W or 100.1mW (100W ÷ 999). In the same way, to take 9999 times the meter current, the shunt would need to have a resistance of 10.001mW (100W ÷ 9999). So that was the purpose of current shunts back in the old ‘analog’ days. But things changed with the advent of digital meters. Since these essentially respond to voltage rather than current, the role of current shunts needed to change as well. Instead of just taking the major proportion of the current, they became a current-to-voltage converter. Their resistance value is chosen to cause minimal disturbance to the circuit in which the current is flowing, while still providing enough voltage drop to allow accurate measurement. And the voltage level chosen was 75mV (millivolts), so most modern digital meters are designed to have this full-scale voltage sensitivity on their current ranges. It is still relatively easy to work out the resistance value of a shunt for any particular current range. For example, if a meter needs a 0-10A current range, the shunt value required would be V/I or 7.5mW (0.075V ÷ 10A), according to Ohm’s famous law. Or if you wanted to give the same meter a 0-1A current range, you’d need a current shunt with a value of 75mW (0.075V ÷ 1A). So that’s the function of a current shunt nowadays – to provide a small but accurately measurable voltage drop when a particular current is flowing through it. Front and rear views of the PZEM-051 module. As shown by the label on the back, this meter has a voltage range of 6.5-100V DC and a current range from 0-50A or 0-100A depending on the external shunt used (see opposite). siliconchip.com.au Australia’s electronics magazine December 2020  79 serial EEPROM which is presumably used to store measurement and display settings. So the design of the PZEM051 is quite elegant. Trying it out An inside view of the PZEM-051 module. The main controller for this board is a Mixchips MXM11P62 (U3; lower middle) which is an 8-bit microcontroller. called the PZEM-015 (siliconchip. com.au/link/ab5g), with extra displays including a bar chart display and measurements of battery capacity and internal resistance. That one comes with a 50A-300A shunt and costs just over $18.00 plus delivery. The common PZEM-051 is somewhat larger than the DSN-VC288, at 90mm wide, 50mm high and 25mm deep. It has a display ‘window’ measuring 50 x 30mm, and the display is an LCD with blue LED backlighting. As you can see from the photo, it offers four-digit displays of both voltage and current, plus two additional four-digit displays: one for power (in either watts or kW) and the other for energy in either watt-hours (Wh) or kilowatt-hours (kWh). Other features include switching the display backlighting on or off, resetting the energy indication to zero, setting a voltage alarm level and configuring the PZEM-051 for use with either a 50A or 100A current shunt. These functions are changed using the small pushbutton just to the right of the display window, via various long and short button press combinations. The button is recessed slightly to prevent accidental presses, and can only be pressed intentionally using a small screwdriver or stylus. All of these settings are stored in non-volatile memory, and are retained even when the power is turned off. The operating voltage range of the PZEM-051 is 6.5-100V DC, and it can measure voltages within the same range. The current measurement range is either 0-49.99A or 0-99.99A, de80 Silicon Chip pending on the version and the current shunt. The power measurement range is 0-10kW, with a display format of 0-999.9W for levels below 1kW, or 1000-9999W otherwise. Similarly, the energy measurement range is from 0-9999Wh for levels below 10kWh, or 10-9999kWh for levels of 10kWh and above. I couldn’t find a circuit diagram for the PZEM-051, but once the 100A version I ordered from AliExpress arrived, I carefully opened its case to take a look inside. As you can see from the internal photo, there is not a great deal in it. At its heart, there’s a Mixchips MXM11P62 8-bit microcontroller (U3) with 14KB of one-time programmable ROM, 256 bytes of SRAM, an ADC with 24-bit resolution, 18 bidirectional I/O pins, three 8-bit timers and a UART. There’s also a Holtek HT1621B LCD interface chip (U2) which links the MCU to the four 4-digit displays on the LCD, and a K24C02 (U4) two-wire Using the PZEM-051 is just as easy as the DSN-VC288, as you can see from Fig.3. The two uppermost screw terminals need to be connected to the voltage/power source, while the two lower terminals are connected to the ends of the current shunt. The two inner terminals must be connected to the negative side of the power source and the current shunt, respectively. Note that the screw terminals are located at the rear of the PZEM-051, at the left-hand end. They’re shown at the front in Fig.3 purely for clarity. I measured the PZEM-051’s voltage readings as 0.16% high, while the current readings were just over 2% high. The latter may be due to the current shunt tolerance. There was a pleasant surprise when I measured the meter’s own current draw, which was just below 3mA with the backlight switched on, falling to around 1mA when it was switched off. Therefore, despite its extra functions, the PZEM-051 is much more energy-efficient than the DSN-VC288, due to the use of an LCD rather than LED screen. To summarise, then, the PZEM-051 multifunction DC measurement module can only be described as both extremely useful and decent value for money. Coming up As mentioned earlier, a future follow-up article will describe some of the newer AC-measurement meter SC modules. Fig.3: a simple example of how you can use the PZEM-051 meter to measure DC power, voltage, current and energy consumption. Australia’s electronics magazine siliconchip.com.au Build It Yourself Electronics Centres® SAVE $10 39.95 $ C 9034A HOT PRICE! 39.95 $ D 2038 Portable Summer Tunes Dynalink® BT5.0 Can Speaker 20 to cap off 20 ts e g d a g ‘n Gifts ear! your new y rt ta s k ic k & The outdoor entertainer! 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Western Australia Build It Yourself Electronics Centres Sale Ends December 31st 2020 Phone: 1300 797 007 Fax: 1300 789 777 Mail Orders: mailorder<at>altronics.com.au » Perth: 174 Roe St » Joondalup: 2/182 Winton Rd » Balcatta: 7/58 Erindale Rd » Cannington: 5/1326 Albany Hwy » Midland: 1/212 Gt Eastern Hwy » Myaree: 5A/116 N Lake Rd Victoria 08 9428 2188 08 9428 2166 08 9428 2167 08 9428 2168 08 9428 2169 08 9428 2170 » Springvale: 891 Princes Hwy » Airport West: 5 Dromana Ave 03 9549 2188 03 9549 2121 New South Wales » Auburn: 15 Short St 02 8748 5388 Queensland » Virginia: 1870 Sandgate Rd 07 3441 2810 South Australia » Prospect: 316 Main Nth Rd 08 8164 3466 Please Note: Resellers have to pay the cost of freight & insurance. Therefore the range of stocked products & prices charged by individual resellers may vary from our catalogue. © Altronics 2020. 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. B 0091 Find a local reseller at: altronics.com.au/storelocations/dealers/ CIRCUIT NOTEBOOK Interesting circuit ideas which we have checked but not built and tested. Contributions will be paid for at standard rates. All submissions should include full name, address & phone number. Automated tyre inflator/deflator ing winter, then as the ambient temperature increases going into summer, they can become overinflated, which could lead to the tyre popping in extreme cases or suffering excess wear. This circuit takes the guesswork out of the equation; rather than letting the air out, then re-inflating them to the correct pressure, it does it all for you. The main components are a microcontroller, 0-100PSI pressure sensor, solenoid driver, motor driver and LCD screen. Pushbuttons S1 & S2 are used to set the desired pressure, which is shown on the LCD screen. It then checks the tyre pressure and if it is higher than the set pressure, actuates the pressure release valve solenoid until the tyre pressure drops to the set pressure. Alternatively, if the tyre pressure is too low, the motor driver is activated to power up a 12V compressor which then raises the pressure until it reaches the set point. The motor is then switched off. The prototype was built on a Curiosity development board. ► The 0-100PSI pressure sensor is connected directly to the pipes near the hose connection point, although an onboard sensor can be used instead. ► siliconchip.com.au Australia’s electronics magazine ► I decided to build my own digital tyre inflator, mainly because pretty much all the affordable ones I found online could only increase the tyre pressure, not decrease it. Sometimes you just want to dial in a pressure value (in PSI, kilopascals or bar) and let the device do all the work for you. It runs off a 12V battery, so it could even be kept in your car and used on the road. Keep in mind that if you keep your tyres inflated to the right pressure dur- The final build uses a custom PCB design and a significant heatsink. This all mounts closely to the motor, pipes and valves. December 2020  85 In either case, when the tyre pressure reaches the target, the piezo buzzer sounds to let you know. In terms of the air plumbing (not shown), the following are all connected together via threaded pipes and joiners: the air hose, 12V compressor, pressure sensor and pressure release valve. Make sure all the pipes and connectors are gas-tight; use yellow Teflon tape on each set of screw threads. The air release valve is not shown on the circuit; it is a readily available type and connects to the terminal marked “VALVE” near the bottom. 86 Silicon Chip The output from the absolute pressure sensor at upper left is 0.5V at 0 PSI, 2.5V at 50PSI and 4.5V at 100PSI. This signal is reduced via a resistive divider to be within the 0-3.3V range that the PIC24 micro can handle, then filtered and buffered by IC3a, part of an MCP6004 quad rail-to-rail op amp. It is then fed into one of the PIC24’s analog input pins, AN6 (pin 25). The output from an optional second pressure sensor (eg, ambient) goes to AN7 (pin 24), while the output of an analog temperature sensor (IC4) is similarly fed to AN8 (pin 23). Australia’s electronics magazine This could be used to compensate the pressure setting for variations in ambient temperature, but you would need to change the software. Analog input AN9 (pin 26) is used to sense the battery voltage, for the under-voltage cutout to protect the battery. The air release valve is powered by Mosfet Q4, which is controlled via an opto-isolator for simplicity. It is driven from one output of MCP23S08 I/O expander IC2, as many of IC1’s pins are occupied driving the display. Similarly, the motor is driven by a parallel pair of high-current Mosfets siliconchip.com.au (Q2 & Q3), which are in turn driven by Mosfet Q1. It is controlled by another opto-isolator, this time driven from the RA0 output of IC1 (pin 2). There is no need to reverse the motor, so this part of the circuit acts as a switch. The I/O expander (IC2) also handles sensing when pushbuttons S1 and S2 are pressed, along with controlling the air release valve, piezo buzzer, some of the low-speed LCD signal lines plus indicator LED2. Circuit power comes from a 12V battery which must be able to supply a siliconchip.com.au substantial amount of current to drive the compressor motor. Power for the rest of the circuit goes via protective fuse F1 and reverse polarity protection diode D1, with the piezo and pressure relief valve running off that 12V rail (it’s also fed to IC3d for battery voltage sensing). The rest of the circuitry runs off 5V or 3.3V, derived from the 12V supply by low-dropout linear regulators REG1 & REG2. An in-circuit serial programming (ICSP) header is provided to allow microcontroller IC1 to be re-proAustralia’s electronics magazine grammed in-circuit, while the COM1 serial port header is provided for debugging purposes. The original prototype was built by hanging the various modules off a PIC24FJ256GA7 Curiosity development board from Microchip, while my final version uses a custom-designed PCB. The PIC24 firmware files (source code and HEX file) are available for download from siliconchip.com.au/ Shop/6/5637 Tom Croft, Sunnybank Hills, Qld. ($150) December 2020  87 “Infinite impedance” AC source The resonant circuit shown in the upper part of the adjacent diagram, when driven with a sinusoidal voltage, will deliver a constant amplitude alternating current into a wide range of resistive loads. The mathematical proof that this is the case is given in the PDF at www.siliconchip.com.au/ Shop/6/5350 The concept of a constant alternating current may seem like an oxymoron, but it is not. After all, a constant direct current source or sink is just a load-independent current. So why not a load-independent alternating current? The theory is not new, but I wanted to test it in reality. If you’re wondering what “infinite impedance” means, consider that a zero impedance has an unchanging voltage amplitude regardless of the load current. A circuit with infinite impedance is the opposite; it delivers an unchanging current amplitude, regardless of the voltages it needs to generate to do so. As the equations are a bit complicated, I thought it would be handy to visualise the multi variables in a graphical form, bypassing the heavy-duty mathematics. I used the GNUplot software to generate the graphics (available free from www.gnuplot.info/). These plots are also in the PDF linked above, in Appendix A. These plots can 88 Silicon Chip be used as a starting point for circuit design. I had 60nF capacitors and a 1.25mH inductor at hand. From the L/X graphic shown below, the point corresponding to these components gives an operating frequency of around 18kHz and an impedance of around 145W. Substituting these component values into the equations from the proof gives a frequency of 18.4kHz, and the impedance as 144W. To drive this resonant circuit, I used the Touchscreen DDS Signal Generator (April 2017; siliconchip.com.au/ Article/10616) and an LMC6482AIN op amp, as shown in the lower circuit. For measuring and monitoring the output, I used a True RMS auto-rang- Australia’s electronics magazine ing DMM and a two-channel digital storage oscilloscope. To prove that the load current of the resonant circuit is independent of the load resistance, I carried out three tests, with 50W, 100W and 200W load resistors. The PDF mentioned above has screengrabs showing these three test conditions. Each time the load resistor value was doubled, the output voltage also doubled, thus maintaining a constant output current. The amplitude of the output current can easily be controlled by adjusting the ratio of the op amp feedback resistors, R2:R1. A power op amp or audio amp could be used instead of an op amp, to allow for higher currents. siliconchip.com.au A simple control loop and added synchronous rectification could make this circuit useful for driving LEDs. Other applications await. Note that another way to achieve a similar result would be to use an op amp monitoring the voltage across a shunt in series with the load, and using negative feedback to provide the required drive voltage to match the shunt voltage to a reference sinewave. However, such a circuit may suffer from stability problems, necessitating added compensation components which would reduce its precision. Mauri Lampi, Glenroy, Vic. ($90) Controlling model railway points with a servo This controller was created to operate a set of points (or turnout) on a OO/ HO model train layout using a small 9g model servo (eg, Jaycar YM2758). For simplicity, each set of points has its own small microcontroller with just three inputs. Potentiometers VR1 and VR2 set the two positions, while switch S1 selects between them. It runs from a DC supply of at least 9V and 1A. This is reduced to 5V by 7805 regulator REG1, which is adequate to operate a 9g servo. Power for the microcontroller is decoupled by schottky diode D2 and a 220µF filter capacitor, to prevent motor current surges affecting its operation. The controller should be close to the servo and the points, due to the weak drive and to minimise power losses in the wires. So switch S1 may be several metres away, and thus its wiring is susceptible to interference. Circuit Ideas Wanted siliconchip.com.au The 1kW/100nF RC low-pass filter between S1 and the GP3 input of IC1 (pin 4) reduces the effects of EMI, and it is advisable to use twisted pair wires and/or grounded shielding to further reduce the chance of interference. Potentiometers VR1 and VR2 are wired across the micro's supply, and the wiper voltages are stabilised by 100nF capacitors which perform two functions. They reduce the effects of stray electric fields and also provide the low source impedance required by the micro's internal analog-to-digital converter (ADC). The servo signal has a 330W series resistor to protect IC1 from accidental shorts at CON1. A heartbeat LED, LED1, flashes to indicate when the circuit is operational. Setup is simple. With the power off, set VR1 & VR2 to their mid positions and the points also in their mid positions. Turn the power on and adjust one potentiometer to set the points to "ahead" or "turn". Then change the position of switch S1 and adjust the other potentiometer. The points are then operational, controlled by S1. Note that if the points are hard against either end position and the servo is trying to move the points more, the servo will be destroyed in little time. To prevent this, the mechanical link between the servo and the points should not be rigid. You can use an open-coil spring or provide a U-shaped loop so that there is some compression or extension of the link. The software was written in PICBASIC Pro. The Servo_Dual_Posn_ SC.BAS and Servo_Dual_Posn_ SC.HEX files are available from siliconchip.com.au/Shop/6/5638, along with a PDF of the PCB pattern. George Ramsay, Holland Park, Qld. ($80) 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 December 2020  89 Flexible D i g i ta l Lighting Controller Part three – Using it with RGB LEDs – by Tim Blythman Addressable LEDs are a simple and effective way to add coloured lights to all manner of displays. They make the perfect addition to our Digital Lighting Controller. In this final instalment, we’ll show you how to use them alone or in combination with mains-powered lights as part of our new system. W e noted early in this series that addressable LEDs are now a standard part of lighting displays. They’re easy to control and being low-voltage, are very safe. So it makes sense that you should be able to use them with the new Flexible Digital Lighting Controller. In January 2020, we described an 8x8 RGB LED matrix made from addressable LEDs (see siliconchip.com. au/Article/12228). These use the WS2812 addressable LED IC, which can be found in many other forms; last month, we reviewed some of Jaycar’s range of “wearables”, which includes their Cat KM1040 RGB LED Raft Pad, based on a compatible IC. They (and other retailers) can also 90 Silicon Chip supply the same (or similar) ICs on strips and/or reels. We’re going to use these handy modules and strips for our experiments. In this article, we’ll describe several different ways to integrate addressable LEDs into a lighting project based around our Digital Lighting Controller. The first option we’ll present is an alternative ‘slave’ unit which can control sets of these addressable LEDs. The slave unit already described can control up to four mains-powered lamps. Our LED slave can instead drive up to 64 addressable LED modules, using signals from the same master units we described last month. The two different slave units (fourchannel mains and 64-channel LED) are a great way to combine mains and Australia’s electronics magazine LED lamps with the excellent sequencing software that we produced for the original Digital Lighting Controller many years ago. We’ll also describe example software for Micromites and Arduinos which can directly drive addressable LEDs at the same time as controlling one or more mains-powered slave units. If you’re happy programming a Micromite or Arduino, you can modify our sample code and build a lighting display that does precisely what you want. Addressable LED slave unit Being able to control up to 64 mains lamps using our Digital Lighting Controller makes it easy to build an insiliconchip.com.au Here’s the LED Slave Unit driving a length of Jaycar’s XC4390 addressable LED strip for testing – and found that it not only worked well . . . it looked spectacular! It would look even better strung up outside, or wrapped around a Christmas tree! credible lighting display, but there is no doubt that the cost of doing so will add up very quickly. Our LED slave allows you to strike a compromise between expense and grandeur. One of these can control up to 64 LEDs, while each mains slave unit adds another four lamps. They can be mixed and matched in any combination within the 64 addresses that exist. The addresses can be set independently, so lamps can be set to some addresses and LEDs to others. You can even set some devices to the same address, to allow simple sequences to be more impressive by controlling both lamps and LEDs. Since the addressable LEDs tend to be smaller and produce much less light than mains-powered lamps, we’ve also come up with ways to have multiple LEDs in the same strip respond to a single address, so that you can conserve the 64 available addresses. There are various options when it comes to addressable RGB LEDs to control. We tested Jaycar’s XC4390 siliconchip.com.au addressable LED strip and found it worked well. These IP65-rated 2m strips are sealed in silicone and backed with 3M adhesive tape. Each strip has 120 LEDs (one every 17mm) and is terminated at both ends with a locking plug and socket. Each end of the strip also has a pair of wires for a separate power connection, which is handy when running longer strips. There is also a prewired plug with bare leads which we connected directly to the LED slave’s screw terminals. Although not marked, the connections are red to 5V, white to ground and green for data. We should also mention Altronics Cat X3223A, which is a 5m-long strip with 300 LEDs. While we have not tested this ourselves, we expect them to be fully compatible; you could even mix and match the two. Circuit details The LED slave circuit is shown in Fig.16, overleaf. You might recognise part of the circuit from the mains slave unit; it works in much the same fashion. Australia’s electronics magazine Opto-isolator OPTO1 receives the serial data via CON3, with CON4 available to daisy-chain the signal to another slave. CON3 and CON4 are wired in parallel and are interchangeable. A 220Ω resistor limits the current through OPTO1’s LED to a suitable level, while the diode limits its reverse bias voltage. Since there are no mains voltages involved in this circuit, OPTO1 might seem unnecessary, but it prevents the formation of ground loops, which might occur depending on how the unit is wired. It also allows circuits with different grounds to be connected without problems. OPTO1 has an open-collector output, so a 1kΩ pull-up resistor brings the output of the optoisolator to 5V when its internal transistor is off. The serial data from OPTO1 goes to the UART pin (pin 5) of IC1, a PIC16F1455 microcontroller. This decodes the serial data and produces data to drive LEDs on pin 2. This signal is fed through a 390Ω resistor and along with 5V power and ground, is made December 2020  91 l l l SC Ó DIGITAL LIGHTING CONTROLLER WS2812 SLAVE Fig.16: the circuit for the LED slave unit is quite simple, and much of it is borrowed from the mains slave described in the October issue. Virtually all of the work is done by PIC micro IC1, which receives the DMX-512-like serial data at its RC5 digital input, pin 5. It then produces a signal to drive one or more WS2812B RGB LEDs from its RA5 digital output at pin 2. available at screw terminal CON5. The resistor protects the micro and LEDs from excessive current flow under fault conditions. Power for the unit is supplied via CON1, a mini USB socket. JP1 and JP2 provide option settings. CON2 is an in-circuit serial programming (ICSP) header for IC1, in case that is required. VR1 is a 10kΩ trimpot which is used to control LED brightness, by varying the voltage applied to the analog input at pin 3 (AN3) of IC1. Indicator LED2 lights up when power is applied, while LED1 lights up when serial data is supplied. Operation The serial protocol used is explained in the previous articles in this series; it is similar to DMX-512 but uses a simpler and slower serial interface. Microcontroller IC1 decodes the serial data received at pin 5 and produces data suitable for driving ad92 Silicon Chip dressable LEDs at digital output pin 2. We used a PIC16F1705 in the mains slave, as it is slightly cheaper than the PIC16F1455 and we do not need the USB peripheral in the 16F1455. However, the PIC16F1455 also has a higher maximum clock speed (48MHz vs 32MHz). We need that for this design, to ensure that the serial data can be processed and the timing-critical LED data is produced with accurate timings. Jumper header JP2 provides the same address setting feature that the DIP switches provided in the mains slave unit. Unlike that one, the LED slave unit is not limited to controlling four lamps. So one LED slave unit set to address 0 can provide control of 64 LEDs. If the address is not set to 0, then the offset is applied and the addresses ‘wrap around’. For example, if the address is set to 16, the brightness of the first LED in the chain will be set Australia’s electronics magazine by the 16th data byte, the second LED by the 17th data byte, the 48th LED by the 64th data byte, the 49th LED by the first data byte etc. JP1 controls whether each data byte controls an entire RGB LED, or the individual colour channels (red, green and blue) within each LED. When JP1 is inserted, each LED receives identical data on each of the red, green and blue channels from the data at a single address. So the LEDs will light up white with adjustable brightness. When JP1 is out, each individual red, green or blue LED element is treated as a separate channel. Thus, you can control up to 21 individual RGB LEDs in this mode. Potentiometer VR1 is used to control the brightness, but also sets some other configurations. VR1’s wiper is divided into three roughly equal sections. Within each section, the position sets a global brightness value. You might siliconchip.com.au like to reduce the overall LED brightness either because these LEDs can be too bright, or to simply limit the current needed by the supply. Each of the three sections corresponds to a different LED configuration. At the ‘lowest’ (most anti-clockwise) section, each colour channel corresponds to one LED. In the middle section, each channel corresponds to four LEDs, and in the top section, one channel corresponds to 16 LEDs. This allows more LEDs to be controlled from fewer channels. A similar effect could be had by cutting and wiring LED strips so that they are fed data in parallel, but we think this is a much simpler approach. To keep the timing tight, each LED slave unit only produces data for 64 LEDs, so in four-LED mode, only 16 channels are used, and in 16 LED mode, four channels are used. JP1, JP2 and VR1 are continuously sampled during operation, so you can tweak the controls in real-time to get a feel for how the different modes work and look. You’ll also note that we’ve wired the USB D+/D- lines to the USB socket. The software doesn’t use these pins or the USB peripheral, so we figured that they might as well be connected, in case anyone wants to modify the software so that it does use the USB function. Software Although the brightness is set by an analog voltage from a potentiometer, the addressable LEDs use all digital data, so this conversion must be done in software. To avoid the (relatively slow) multiplication that would be needed to do this ‘live’, an array in flash memory stores a table of pre-calculated values for 16 brightness levels. This reduces the processing load on the micro. The 16 brightness levels are not linear, but are roughly logarithmic, which corresponds to the human perception of brightness. The LED data takes about 2ms to produce, during which time no serial data can be received, as the micro is too busy ensuring that the LED signal is timed accurately. So we only process every second ‘update’ from the master. With our Micromite master unit, this still means an update rate around 30Hz, which is fast enough to be unnoticeable. Eagle-eyed readers may have noted that there are no pull-up resistors on JP1 or JP2 and that the PIC16F1455 does not have internal pull-ups on PORTC (which is connected to JP1 & JP2). To simulate a weak pull-up, the pin is pulsed high very briefly (around 83ns). Stray capacitance keeps the pin high unless the jumper is in place, so the jumper state can still be sensed, and the circuit is simplified. Construction The LED slave unit is built on a small PCB which is sized to fit in a UB5 Jiffy box. It measures 79 x 45mm and is coded 16110205. Refer to the PCB overlay diagram, Fig.17, to see where the components go on the board. The USB socket is the only surfacemounted part and should be fitted first. Here, some flux paste, a fine-tipped soldering iron and a magnifying glass will come in handy. Some solder braid will help if you manage to bridge any pads. Apply flux to the pads and place the USB socket on the PCB. There are small holes in the PCB to locate it accurately. Add flux to the top of the pins as well. Now load the iron’s tip with a small amount of solder. You want to be able to touch the iron to the PCB pads and allow just the right amount to run off to form the joint; the flux will encourage this. If the USB socket is firmly against the PCB, you may only need to touch the PCB pad. If that doesn’t work, carefully bring the iron to meet the socket’s pin where it sits on the pad. A fine tip will help to prevent bridges. Then solder the four connected pins; the fifth is not needed. If you bridge any pins, finish soldering the remaining pins before attempting to remove the excess. If you are confident that the pins are lined up accurately, solder the larger side tabs to secure the part mechanically. If you have solder bridges to remove, apply some flux to the area and clean the iron’s tip. Place the braid against the solder and press gently with the iron. When the braid takes up the solder, carefully draw it away with the iron. Once you are happy, you can use a flux cleaner to remove any that is left on the PCB. Follow with the resistors, checking the values as you install them; there are six resistors with four different values. Then mount the three MKT capacitors, which are identical and not polarised. The solitary diode has its cathode facing to the right – solder it in place. CON2, JP1 and JP2 are simple pin headers. In each case, it is a good idea Fig.17: fit the parts to the LED slave PCB as shown in the component overlay above and the matching same-size photo at right. CON1 is the trickiest part to fit, so do that first. CON2 is optional if you have a pre-programmed microcontroller, and CON4 is not needed if you don’t wish to connect any downstream slave units. siliconchip.com.au Australia’s electronics magazine December 2020  93 Fig.18: connecting addressable LEDs to the LED slave is straightforward. This shows Jaycar LED Raft Pads (Cat KM1040), but other addressable LEDs will also work, such as Jaycar XC4390 or Altronics X3223A strips. to solder one pin and check that the header is straight and square before soldering the remainder. For JP1 and JP2, you can temporarily fit the jumper shunts to ensure that the pins stay aligned. CON2 is only needed if you wish to program IC1 in-circuit. When mounting IC1, ensure that its pin 1 orientation matches the PCB silkscreen and overlay diagram. You can solder it directly to the board (the more reliable method) or via a socket, which is useful if you want to reprogram it out of circuit. Solder two diagonally opposite pins, then check that the IC or socket is square and flat before soldering the rest. If you are using a socket, insert the programmed IC carefully, ensuring that no pins are bent underneath. OPTO1 can be socketed too, but it does not need to be. Use the same procedure as for IC1. VR1 will only fit one way, but you may need to bend the leads to fit it. Once it has clicked into place, solder all three leads. CON3 and CON4 are the RJ45 sockets. If you plan only to use one socket, then only one needs to be fitted. This will also save you cutting a hole in the case. In any case, snap the socket into place and solder one pin to secure it. Check that it is flat and parallel to the Parts list – Digital Lighting LED slave 1 double-sided PCB coded 16110205, 79 x 45mm 1 UB5 Jiffy box 4 12mm-long M3 tapped spacers 8 M3 x 6mm panhead machine screws 1 SMD mini USB Type-B socket (CON1) 1 5-way pin header (CON2; optional, for ICSP) 2 PCB-mount RJ45 sockets (CON3,CON4) [Altronics P1448] 1 3-way 5mm pitch screw terminal (CON5) 1 2-pin header (JP1) 1 4x2-pin header (JP2) 5 jumper shunts (JP1,JP2) 1 14-pin DIL IC socket (optional; for IC1) 4 self-adhesive rubber feet Semiconductors 1 PIC16F1455-I/P microcontroller programmed with 16110205.HEX, DIP-14 (IC1) 1 green 3mm LED (LED1) 1 red 3mm LED (LED2) 1 6N137 optoisolator, DIP-8 (OPTO1) 1 1N4148 signal diode (D1) Capacitors 3 100nF MKT Resistors (all 1/4W axial 1% metal film) 1 10kΩ (brown black black red brown or brown black orange brown) 3 1kΩ (brown black black brown brown or brown black red brown) 1 390Ω (orange white black black brown or orange white brown brown) 1 220Ω (red red black black brown or red red brown brown) 1 10kΩ mini horizontal trimpot (VR1) (code 103) 94 Silicon Chip Australia’s electronics magazine silkscreen markings before soldering the remaining pins. After those are finished, install CON5. The LEDs are mounted so that their lenses go through holes in the front panel. We’ve left them to last so that you can check the mounting arrangements before soldering them in place. Fit the LEDs so that the tops of their flanges sit around 10mm from the PCB. This ensures that the flanges clear the lid when fitted, and the LEDs don’t sit too proud. LED2 (on the left) is the power LED, which should be red. The serial data LED, (LED1) is on the right and should ideally be green. Both their cathodes are to the left, which means that their longer (anode) leads are to the right. Programming Use the MPLAB X IPE (a free download) to program IC1 if it is not programmed already. Connect a PICkit 3 or PICkit 4 programmer to CON2, select PIC16F1455 as the Device, then click Apply and Connect. You may need to select “Use Low Voltage Programming mode entry” and “Power Target Circuit from Tool” from the Power menu. LED2 will light up when power is applied through the tool. Browse for the HEX file, then press “Program” and check that it was successful. Testing Before completing the assembly, it’s a good idea to test the LED slave unit. Connect a USB power supply to CON1; the power LED should illuminate. Then connect any of the master units described in parts 1 or 2 to apply a signal to the LED slave unit. LED1 should light up when a signal is received. If all is well, connect some addressable RGB LEDs; Fig.18 shows how to connect Jaycar’s RGB Island Pads. Any compatible addressable LEDs should have similar pin markings. Check that the current draw of the connected LEDs will be within the capacity of the USB supply. The contacts on most mini-USB type sockets are rated up to around 1A; this puts a hard limit on what the LED slave unit can supply (besides what the supply can actually deliver). If you have control data coming into CON3 or CON4, you should see attached LEDs illuminate. If not, check siliconchip.com.au Fig.19: the LED slave fits neatly in a UB5 Jiffy box; make the holes as shown here. The wires for the LEDs are fed through the holes on the right-hand side, so you can adjust them to suit your wiring. Fig.20: this is the lid panel artwork, which can also double as a drilling template for the LED holes. that VR1 is not wound fully anticlockwise. Preparing the enclosure The PCB mounts in the base of a UB5 Jiffy box using four threaded spacers. The box we used had four small holes marked on the base already, so we based our design around these dimensions. If your case has similar markings, that will make construction easier. Drill four holes in the base according to Fig.19. Thread an M3 machine screw through the bottom of each hole and secure with a tapped M3 spacer from above. You might like to use Nylon machine screws so that their heads also form feet for the box. Alternatively, you could fit rubber feet (screw mounting or stick-on). siliconchip.com.au Cut the remaining holes in the sides of the base of the box as shown in Fig.19. The larger holes for the RJ45 sockets are at the top edge, so they can be started by carefully making vertical cuts with a hacksaw on either side. You might be able to snap the tabs out with wide-nosed pliers or by drilling some holes to weaken it. Then straighten up the holes with a file, carefully bringing them to the required dimensions. The hole for the USB socket is a bit trickier. Start with a pair of 4mm drilled holes, then bring the holes out to size with a small file (such as a needle file). Alternatively, a single 10mm round hole will do the job, although it won’t be as elegant. Also drill the lid as shown, to suit the LEDs. Alternatively, use the lid Australia’s electronics magazine artwork (Fig.20) as a template. Now slot the PCB into place to test it fits. Guide the USB socket into place and then rotate the PCB to bring the RJ45 sockets into their slots. Rest the lid on top and ensure that the LEDs go into their holes. Remove the PCB and make any necessary adjustments. You should also drill some holes to suit the LED wires. We used 3mm holes; this should be sufficient for most cases. Re-seat the PCB and screw it down onto the spacers with the remaining M3 machine screws. The wires for the RGB LEDs can be terminated by feeding them in through the holes and screwing them into CON5. Now print the lid artwork, cut out the holes and glue it to the lid. You can download this as a PDF from the December 2020  95 Screen1: our Arduino sample code uses Adafruit’s Neopixel library to control the addressable LEDs. It’s easily downloadable via the Library Manager, as shown here. SILICON CHIP website and print it in colour. Print it onto overhead projector film (in reverse so that it appears correctly when printed on the back) or laminate a paper copy to protect it. Use neutral cure silicone to secure it to the lid, being sure to squeeze out any bubbles. We h a v e m o r e i n f o r m a t i o n about making front panel labels at siliconchip.com.au/Help/FrontPanels Fit the lid onto the base and over the LEDs, and secure with the screws supplied with the Jiffy box. to the mains slave units, depending on how you want your display to look. Multiple chains of addressable LEDs can be connected to one of our LED slave units, although we haven’t tested how many you can parallel before the signal degrades. The current drawn by the LEDs will probably be the main constraint. This could be handy for waterfall type effects, where parallel chains of LEDs can connect to a common data source, allowing for stunning effects from even a single controller. For larger displays, you might have to consider connecting an alternate supply for 5V power. Remember that you can also drive LED strips in sets of four or 16 LEDs by adjusting VR1. You could also com- Usage With JP1 fitted, each LED becomes a single channel and produces white light (equal amounts of red, green and blue). If JP1 is not inserted then each colour becomes its own channel. This reduces the number of LEDs that can be addressed, but allows for more colour options. The colour order is red, green then blue. JP2 allows the slave address to be set. It operates identically to S1 on the mains slave. Of course, since this unit can address up to 64 LEDs, it should be considered more of an offset than an address, and the address may wrap around in some cases. You can set the LED slave unit to use the same address or different addresses 96 Silicon Chip Fig.21: using an Arduino to control both addressable LEDs and lamps via our slave units is easy. This shows the Uno, but you can also use a Mega board with identical wiring. Other boards may have different pin requirements for the serial data, but just about any Arduino can be made to work. Australia’s electronics magazine siliconchip.com.au bine this feature with multiple strips in parallel. example to write your own program. Arduino and Micromite You will need to have the Arduino IDE (integrated development environment) set up to program an Arduino board to control lights (download it from siliconchip.com.au/link/aatq). We’re using version 1.8.5 of the Arduino IDE; any version since 1.8.0 should work much the same. Wire up your Arduino board to the CP2102 Interface board and RGB LEDs as shown in Fig.21. Not shown is the RJ45 lead from the socket on the CP2102 Interface PCB to the Slave units. The data connection for the LEDs passes through a 390Ω resistor to protect the two halves of the circuit from voltage differences between independent power supplies. We’re using digital output D6 to produce the addressable LED data, but the library is configurable, so this can be changed as needed. Adafruit helped make addressable LEDs popular with their “Neopixel” range of products; they also produced a library to make them easy to work with. We’re using this library to drive our LEDs, as it doesn’t work only with Ne- You can also drive addressable LEDs from an Arduino or Micromite which is also acting as a master unit for our Flexible Digital Lighting Controller. This saves you having to build any LED slaves; the master can do all the work. This means that the addressable LEDs do not take up any of the 64 addresses, so you can have even bigger displays. In terms of hardware, we’re assuming you are using at least one slave unit (mains or LED type). You will also need one of the CP2102 Interface boards described in the October issue, to allow a Micromite or Arduino board to drive multiple slaves; otherwise, you’ll be limited to controlling 2-3 slave units. And you will, of course, need either an Arduino (we’re using the Uno) or Micromite LCD BackPack (the V3 is ideal). The examples contain some simple subroutines that produce interesting patterns on both the LEDs and mains lamps. You can try changing these by altering some of the parameters, or you might like to use our code as an Arduino opixels; it can drive any WS2812Bcompatible device. Install this library by searching for “Adafruit_NeoPixel” in the Arduino Library Manager or by downloading it directly from https://github.com/adafruit/Adafruit_NeoPixel Screen1 shows the correct library to install in the Library Manager. The library comes with example code that works with addressable LEDs, but we’ve also written a demo program that combines this with data for the slave units (allowing mainspowered lamps to be controlled too). It is part of the download package for this article. Extract the sketch, open it, select the correct serial port and board type. Press “Upload” and the LEDs and lamps should spring to life. Micromite We’ve put together a similar demo for use with a Micromite; we prototyped our version on a V3 BackPack, but any Micromite variant using the PIC32MX170F256B should work with our code. The wiring diagram is seen in Fig.22. And like the Arduino master, the pins are configurable, but in this case, we have chosen to use pin 9 for the LED data and pin 10 to drive the mains slaves. As with the Arduino example, if you need more current to drive LEDs than the USB port can provide, you will need to connect another power supply. There are no libraries to download, as these are embedded in our BASIC program as CFUNCTIONs. Open the BASIC program, send it to your Micromite (using MMEdit, TeraTerm or another terminal program) and run it. Once you have confirmed that it all works, you can modify our example to suit your requirements. Conclusion Fig.22: you can also drive RGB LEDs and/or mains lamps using any Micromite with a PIC32MX170F256B chip onboard – we tested our code using a V3 BackPack, as shown here. The pins used are reconfigurable in software. siliconchip.com.au Australia’s electronics magazine Our new Flexible Digital Lighting Controller gives you lots of options, both in terms of how you arrange the lights (using LEDs, mains-powered lighting or a mixture of both) and also how you control them, using a PC, Arduino or Micromite with your own control code, or using our sequencing software. We’re looking forward to seeing what incredible displays our readers will create, using this design as a starting point! SC December 2020  97 SILICON CHIP .com.au/shop ONLINESHOP HOW TO ORDER INTERNET (24/7) PAYPAL (24/7) eMAIL (24/7) MAIL (24/7) PHONE – (9-5:00 AET, Mon-Fri) siliconchip.com.au/Shop silicon<at>siliconchip.com.au silicon<at>siliconchip.com.au PO Box 139, COLLAROY, NSW 2097 (02) 9939 3295, +612 for international You can also pay by cheque/money order (Orders by mail only) or bank transfer. Make cheques payable to Silicon Chip. 12/20 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 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 PIC16F1507-I/P PIC16F1705-I/P PIC16F88-E/P PIC16F88-I/P $15 MICROS RF Signal Generator (Jun19) PIC16F1459-I/SO Four-Channel DC Fan & Pump Controller (Dec18) RGB Stackable LED Christmas Star (Nov20) PIC16F877A-I/P 6-Digit GPS Clock (May09), 16-bit Digital Pot (Jul10), Semtest (Feb12) Shirt Pocket Audio Oscillator (Sep20) PIC32MM0256GPM028-I/SS Super Digital Sound Effects (Aug18) ATtiny816 Development/Breakout Board (Jan19) PIC32MX170F256D-501P/T 44-pin Micromite Mk2 (Aug14), 4DoF Simulation Seat (Sep19) Ultrabrite LED Driver (with free TC6502P095VCT IC, Sep19) PIC32MX170F256B-50I/SP Micromite LCD BackPack V1-V3 (Feb16 / May17 / Aug19) GPS Boat Computer (Apr16), Micromite Super Clock (Jul16) LED Christmas Ornaments (Nov20; specify variant) Touchscreen Voltage / Current Ref. (Oct16), Deluxe eFuse (Aug17) Temperature Switch Mk2 (Jun18), Recurring Event Reminder (Jul18) Micromite DDS for IF Alignment (Sep17), Tariff Clock (Jul18) Door Alarm (Aug18), Steam Whistle (Sep18), White Noise (Sep18) GPS-Synched Frequency Reference (Nov18), Air Quality Monitor (Feb20) Trailing Edge Dimmer (Feb19), Steering Wheel to IR Adaptor (Jun19) RCL Box (Jun20), Digital Lighting Controller Micromite Master (Nov20) Car Radio Dimmer Adaptor (Aug19) PIC32MX270F256B-50I/SP ASCII Video Terminal (Jul14), USB M&K Adaptor (Feb19) Motor Speed Controller (Mar18), Heater Controller (Apr18) PIC32MX795F512H-80I/PT Maximite (Mar11), miniMaximite (Nov11), Colour Maximite Useless Box IC3 (Dec18) (Sep12), Touchscreen Audio Recorder (Jun14) Tiny LED Xmas Tree (Nov19) $20 MICROS Microbridge (May17), USB Flexitimer (June18) dsPIC33FJ64MC802-E/SP 1.5kW Induction Motor Speed Controller (Aug13) Digital Interface Module (Nov18), GPS Finesaver (Jun19) Digital Lighting Controller LED Slave (Dec20) dsPIC33FJ128GP306-I/PT CLASSiC DAC (Feb13) Ol’ Timer II (Jul20) dsPIC33FJ128GP802-I/SP Digital Audio Delay (Dec11), Quizzical (Oct11) Ultra-LD Preamp (Nov11), LED Musicolour (Oct12) 5-Way LCD Panel Meter (Nov19), IR Remote Control Assistant (Jul20) Ultrasonic Cleaner (Sep20) PIC32MX470F512H-I/PT Stereo Echo/Reverb (Feb 14), Digital Effects Unit (Oct14) Wideband Oxygen Sensor (Jun-Jul12) 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 LED CHRISTMAS ORNAMENTS (CAT SC5579) (NOV 20) RGB STACKABLE LED CHRISTMAS STAR (CAT SC5525) (NOV 20) FLEXIBLE DIGITAL LIGHTING CONTROLLER PARTS (OCT 20) D1 MINI LCD WIFI BACKPACK KIT (OCT 20) SHIRT POCKET AUDIO OSCILLATOR (SEP 20) SWITCHMODE 78XX KIT (CAT SC5553) (AUG 20) COLOUR MAXIMITE 2 (JUL 20) Complete kit including micro but no coin cell (specify PCB shape & colour) Complete kit including PCB, micro, diffused RGB LEDs and other parts $14.00 $38.50 4 x Si8751AB ICs, 8 x S1HB15N60E-GE3 Mosfets, switchmode converter module, 6N137 opto, high-voltage resistors and capacitors plus SMD LEDs. $100.00 Complete kit including 3.5-inch touchscreen, PCB and ESP8266-based module $70.00 Kit: including 3D-printed case, and everything else except the battery and wiring $40.00 - 64x32 pixel white OLED (0.49-inch/12.5mm diagonal) $10.00 - Pulse-type rotary encoder with integral pushbutton $3.00 Includes PCB and all onboard parts (3.3V, 5V, 8V, 9V, 12V & 15V versions) in stock now $12.50 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 MICROMITE LCD BACKPACK V3 KIT (CAT SC5082) (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 siliconchip.com.au/Shop/ ULTRASONIC CLEANER (SEP 20) 40kHz 50W ultrasonic transducer (Cat SC5629) ETD29 transformer components + three Mosfets (Q1-2,Q6) (Cat SC5632) $54.90 $35.00 VARIOUS MODULES & PARTS - Pair of CSD18534 (Vintage Radio Supply, Dec20) $6.00 - IPP80P03P4L04 (Dual Battery Lifesaver / Vintage Radio Supply, Dec20) $5.00 2 - 16x2 I C LCD (Digital RF Power Meter, Aug20) $7.50 - DS3231 real-time clock SMD IC (Ol’ Timer II, Jul20) $3.00 - 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 - LM4865MX amplifier & LF50CV regulator (Tinnitus/Insomnia Killer, Nov18) $10.00 - 2.8-inch touchscreen LCD module with SD card socket (Tide Clock, Jul18) $22.50 - ESP-01 WiFi Module (El Cheapo Modules, Apr18) $5.00 - WiFi Antennas with U.FL/IPX connectors (Water Tank Level Meter with WiFi, Feb18): 5dBi – $12.50 ¦ 2dBi (omnidirectional) – $10.00 - NRF24L01+PA+NA transceiver, SNA connector & antenna (El Cheapo, Jan18) $5.00 - WeMos D1 Arduino-compatible boards with WiFi (Sep17, Feb18): ThingSpeak data logger – $10.00 | D1 R2 with external antenna socket – $15.00 - ERA-2SM+ MMIC & ADCH-80A+ choke (6GHz+ Frequency Counter, Oct17) $15.00 - VS1053 Geeetech Arduino MP3 shield (Arduino Music Player, Jul17) $20.00 - 1nF 1% MKP (5mm) or ceramic capacitor (LC Meter, Jun18) $2.50 - MAX7219 red LED controller boards (El Cheapo Modules, Jun17): 8x8 SMD/DIP matrix display – $5.00 ¦ 8-digit 7-segment display – $7.50 - AD9833 DDS modules (Apr17): gain control (DDS Signal Generator) – $25.00 ¦ no gain control – $15.00 - CP2102 USB-UART bridge $5.00 - DS3231 real-time clock module with mounting hardware (El Cheapo, Oct16) $5.00 *Prices valid for month of magazine issue only. All prices in Australian dollars and include GST where applicable. # P&P prices are within Australia. Overseas? Place an order on our website for a quote. PRINTED CIRCUIT BOARDS & CASE PIECES For a complete list, go to siliconchip.com.au/Shop/8 PRINTED CIRCUIT BOARD TO SUIT PROJECT DATE PCB CODE Price PRINTED CIRCUIT BOARD TO SUIT PROJECT DATE PCB CODE Price 3-WAY ADJUSTABLE ACTIVE CROSSOVER ↳ FRONT/REAR PANELS ↳ CASE PIECES (BLACK) 6GHz+ TOUCHSCREEN FREQUENCY COUNTER ↳ CASE PIECES (CLEAR) KELVIN THE CRICKET SUPER-7 SUPERHET AM RADIO PCB ↳ CASE PIECES & DIAL THEREMIN PROPORTIONAL FAN SPEED CONTROLLER WATER TANK LEVEL METER (INC. HEADERS) 10-LED BARAGRAPH ↳ SIGNAL PROCESSING FULL-WAVE MOTOR SPEED CONTROLLER VINTAGE TV A/V MODULATOR AM RADIO TRANSMITTER HEATER CONTROLLER DELUXE FREQUENCY SWITCH USB PORT PROTECTOR 2 x 12V BATTERY BALANCER USB FLEXITIMER WIDE-RANGE LC METER (INC. HEADERS) ↳ WITHOUT HEADERS ↳ CASE PIECES (CLEAR) 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 SEP17 SEP17 SEP17 OCT17 OCT17 OCT17 DEC17 DEC17 JAN18 JAN18 FEB18 FEB18 FEB18 MAR18 MAR18 MAR18 APR18 MAY18 MAY18 MAY18 JUN18 JUN18 JUN18 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 01108171 01108172/3 SC4403 04110171 SC4444 08109171 06111171 SC4464 23112171 05111171 21110171 04101181 04101182 10102181 02104181 06101181 10104181 05104181 07105181 14106181 19106181 SC4618 04106181 SC4609 05105181 11106181 24108181 19107181 25107181 01107181 03107181 09106181 SC4716 09107181 10107181/2 04107181 16107181 16107182 01110181 01110182 04101011 08111181 05108181 24110181 24107181 06112181 SC4849 10111191 10111192 10111193 05102191 24311181 01111119 01111112 01111113 04112181 SC4927 SC4950 19111181 19111182 19111183 19111184 02103191 15004191 01105191 24111181 SC5023 01106191 01106192 01106193 01106194 01106195 01106196 $20.00 $20.00 $10.00 $10.00 $15.00 $10.00 $25.00 $25.00 $12.50 $2.50 $7.50 $7.50 $5.00 $10.00 $7.50 $7.50 $10.00 $7.50 $2.50 $2.50 $7.50 $7.50 $7.50 $7.50 $7.50 $5.00 $5.00 $5.00 $10.00 $2.50 $5.00 $5.00 $7.50 $5.00 $7.50 $7.50 $5.00 $2.50 $5.00 $5.00 $12.50 $7.50 $5.00 $5.00 $5.00 $15.00 $.00 $10.00 $10.00 $10.00 $2.50 $5.00 $25.00 $15.00 $5.00 $7.50 $5.00 $17.50 $5.00 $5.00 $5.00 $5.00 $2.50 $10.00 $5.00 $5.00 $40.00 $7.50 $7.50 $5.00 $7.50 $5.00 $2.50 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) DIGITAL PANEL METER / USB DISPLAY ↳ ACRYLIC BEZEL (BLACK) UNIVERSAL BATTERY CHARGE CONTROLLER BOOKSHELF SPEAKER PASSIVE CROSSOVER ↳ SUBWOOFER ACTIVE CROSSOVER ARDUINO DCC BASE STATION NUTUBE VALVE PREAMPLIFIER TUNEABLE HF PREAMPLIFIER 4G REMOTE MONITORING STATION LOW-DISTORTION DDS (SET OF 5 BOARDS) NUTUBE GUITAR DISTORTION / OVERDRIVE PEDAL THERMAL REGULATOR INTERFACE SHIELD ↳ PELTIER DRIVER SHIELD DIY REFLOW OVEN CONTROLLER (SET OF 3 PCBS) 7-BAND MONO EQUALISER ↳ STEREO EQUALISER REFERENCE SIGNAL DISTRIBUTOR H-FIELD TRANSANALYSER CAR ALTIMETER RCL BOX RESISTOR BOARD ↳ CAPACITOR / INDUCTOR BOARD ROADIES’ TEST GENERATOR SMD VERSION ↳ THROUGH-HOLE VERSION COLOUR MAXIMITE 2 PCB (BLUE) ↳ FRONT & REAR PANELS (BLACK) OL’ TIMER II PCB (RED, BLUE OR BLACK) ↳ ACRYLIC CASE PIECES / SPACER (BLACK) IR REMOTE CONTROL ASSISTANT PCB (JAYCAR) ↳ ALTRONICS VERSION USB SUPERCODEC SWITCHMODE 78XX REPLACEMENT WIDEBAND DIGITAL RF POWER METER ULTRASONIC CLEANER MAIN PCB ↳ FRONT PANEL NIGHT KEEPER LIGHTHOUSE SHIRT POCKET AUDIO OSCILLATOR ↳ 8-PIN ATtiny PROGRAMMING ADAPTOR D1 MINI LCD WIFI BACKPACK FLEXIBLE DIGITAL LIGHTING CONTROLLER SLAVE ↳ FRONT PANEL (BLACK) LED XMAS ORNAMENTS 30 LED STACKABLE STAR ↳ RGB VERSION (BLACK) SUPERCODEC BALANCED ATTENUATOR DIGITAL LIGHTING MICROMITE MASTER ↳ CP2102 ADAPTOR JUN19 JUN19 JUN19 JUN19 JUL19 JUL19 JUL19 AUG19 AUG19 AUG19 SEP19 SEP19 SEP19 SEP19 SEP19 SEP19 OCT19 OCT19 NOV19 NOV19 NOV19 NOV19 NOV19 NOV19 NOV19 DEC19 JAN20 JAN20 JAN20 JAN20 JAN20 FEB20 FEB20 MAR20 MAR20 MAR20 APR20 APR20 APR20 APR20 MAY20 MAY20 JUN20 JUN20 JUN20 JUN20 JUL20 JUL20 JUL20 JUL20 JUL20 JUL20 AUG20 AUG20 AUG20 SEP20 SEP20 SEP20 SEP20 SEP20 OCT20 OCT20 OCT20 NOV20 NOV20 NOV20 NOV20 NOV20 NOV20 05105191 01104191 SC4987 04106191 01106191 05106191 05106192 07106191 05107191 16106191 11109191 11109192 07108191 01110191 01110192 16109191 04108191 04107191 06109181-5 SC5166 16111191 18111181 SC5168 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 18105201 04106201 04105201 04105202 08110201 01110201 01110202 24106121 16110202 16110203 SEE P31 16109201 16109202 01106202 16110201 16110204 $5.00 $7.50 $10.00 $15.00 $5.00 $7.50 $10.00 $7.50 $5.00 $5.00 $7.50 $2.50 $5.00 $7.50 $5.00 $2.50 $10.00 $5.00 $25.00 $25.00 $2.50 $10.00 $5.00 $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 $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 $7.50 $5.00 $2.50 BATTERY VINTAGE RADIO POWER SUPPLY DUAL BATTERY LIFESAVER DIGITAL LIGHTING CONTROLLER LED SLAVE DEC20 DEC20 DEC20 11111201 11111202 16110205 $7.50 $2.50 $5.00 NEW PCBs We also sell an A2 Reactance Wallchart, RTV&H DVD, Vintage Radio DVD plus various books at siliconchip.com.au/Shop/3 Vintage Radio 1928 1928 RCA RCA Radiola Radiola 60 60 superhet superhet radio radio By Dennis Jackson Made during the end of the Roaring 20s, just before the Great Depression, this set by RCA was definitely a luxury item, as showcased by the detailed escutcheon and likely mahogany cabinet. It sold for US$147 and weighed over 20kg – at least they decided not to make it into a portable. Of late, my most prized radio items have come from the collections of friends, who have reason to downsize and have donated parts and sets they constructed as radio amateurs. I firmly believe that such treasures should be shared and brought out into the open, and that is why I wrote this article. Radio technology, electricity and electronics in general mushroomed from small beginnings due to the genius of a dedicated few. As a result, these fields became a significant influence on our lives. fication were added on the input side of the detector. Once that had been done, why not add a couple of stages of transformercoupled audio amplification to boost TRF development in the 1920s Generally speaking, in Australia, the 1920s was the era of the tuned radio frequency (TRF) wireless receiver, at least as far as the general public was concerned. Simple single-valve regenerative receivers, although efficient, had their drawbacks. So typically two stages of separately tuned RF ampli- 100 Silicon Chip the output? That would allow a moving iron, rocking-armature or diaphragmtype horn or cone speaker to be driven, for all to hear. The resulting audio usually left a bit to be desired, sounding rather like a person speaking through a long tube, but who cared? This was wonderful wireless. These early, uncomplicated TRFs were very well suited to athome construction. I recently finished restoring an elegant Planet Waldheim TRF console wireless manufactured during the early 1930s. It came in an elaborate timber cabinet with a lift-up lid to house an optional electric turntable and heavy magnetic pickup, to play the latest 78s. An inverted-tray type iron chassis replaced the usual breadboard. It has three pentode RF valves, a triode detector, two 2A3 triodes work► The RCA Radiola 60 with a Radiola 103 tapestry speaker mounted on top. Australia’s electronics magazine siliconchip.com.au ing in push-pull to drive the electromagnetic moving coil speaker and all three capacitor tuning gangs mounted axially on a single shaft. There’s also a separate AC power supply using an 80 rectifier, with its main antiquity being the use of large paper filter capacitors in place of the yet-to-be-developed electrolytics. I mention this to demonstrate the very rapid advancement in wireless technology which occurred during the twenties, a fascinating period. Wireless sets such as these were the final burst of glory for TRF receivers. Enter the Radiola 60 While I had an example of the first commercial superhet, the RCA AR-812 (described in the August 2019 issue; siliconchip.com.au/Article/11782) and an L2 Ultradyne Superhet from 1924-25, I was missing a superhet radio which represented the late 20s/ early 30s, a time of significant radio technology advancement. The Radiola 60 superheterodyne, sold from September 6th 1928 to September 1930 by the Radio Corporation of America (RCA), fired my imagination. This was the first Superhet to connect to the AC mains via the lighting circuits, making use of the then-new UY227 triodes with indirectly heated 2.5V cathodes. These were designed to avoid the AC hum problems caused by the slight heating and cooling between AC cycles when using directlyheated cathodes. My chances of acquiring such a set were very slim, but miracles do happen; an RCA Radiola 60 eventually became available on eBay for “local pickup only”, which posed a problem as it was in Sydney and I am down in Tassie. Luckily, my two teenage nieces were flatting in Sydney while studying, and they even had a car. That old thing was very heavy to carry up all of those stairs, but they did it for their Uncle Den, who will be forever thankful. The set eventually arrived by courier at our home in Hobart, after the nerve-racking process of last-minute bidding was successful. rounded feet of pressed wood fibre, typical of the 1920s. The separate power supply chassis originally housed three large rectangular cans, one containing four 0.5µF rice paper dielectric capacitors (then referred to as “condensers”), and three similar 2µF caps, plus the final HT filter choke/audio-blocking inductor. One adjacent can contains two series-connected filter input chokes for the HT+ supply. Three filter chokes in series may seem to be overkill, but the paper filter capacitors had pretty low values, so a high inductance was needed to achieve sufficient filtering. The third can originally contained the power transformer with its type 80 rectifier valve alongside. There was a problem with the power transformer overheating after ten minutes or so of use. Its enclosing can was missing, with the unsecured transformer being held in place only by its connecting wires. This may have been the reason the seller had insisted on local pick-up only. The seller had informed me of this problem, and he had assured me the transformer had been designed for our 240V (now officially 230V) mains. A small brass plate on the chassis verified this. RCA had produced mains-powered TRF radio receivers before the Radiola 60 Superhet; namely, the Radiola 17 and 18 in 1917, using a similar chassis and layout. Maybe the composition of the iron laminations had yet to be improved. Some power transformers used silicon steel laminations to reduce hysteresis losses, which otherwise could result in overheating and a loss of efficiency. There do appear to be common problems with the Radiola 60’s power transformer, according to various web forums. I also considered that its problems might have been due to shorted turns, aged and brittle inter-layer insulation and/or leaky paper-dielectric filter capacitors. Before switching on, I changed the twin-conductor power cord to a regulation three-wire type fed through a cord clamp and grommet, and also fitted a 0.75A fuse in the Active line. I bypassed the wafer on/off switch, as I considered that it could be unsafe by modern standards, especially considering that it was nearly a century old. I replaced most of the wire-wound resistors in the power supply; their phenolic cores were charred. I had a look, but I could find no obvious problems within the radio chassis itself. After plugging in the nicely-restored RCA Radiola 103 rocking-armature tapestry speaker (described below), which had been part of the deal, it took a full 90 seconds for the indirectly heated valve cathodes to reach The power supply chassis The internal electronics are contained in an attractive table-top lidded case, which had been refurbished by the previous owner. It boasts prominent pot metal escutcheons, and short siliconchip.com.au The power supply chassis is shown with the new power transformer (right), the defective one is shown below. The small transformer on top of that is a multi-tap from Jaycar with secondary removed and rewound to supply 2.5V. Australia’s electronics magazine December 2020  101 The RCA Radiola 60 was a simply designed and operated radio when compared to others of the time. It had single dial tuning (right), a single control for volume, a power supply integrated into its case and good reception. The only problem might lie in its non-linear tuning range (the frequency division over the MW band is non-linear over the 1-100 scale range). emission temperature. The set then performed well for some minutes, until there was a definite smell of hot tar, so I immediately switched it off. The type 80 rectifier valve draws a filament current of 2A at 5V. To lighten the load on the overheating power transformer, I removed the type 80 and substituted two 800V power diodes. This is a much more efficient arrangement, but has the drawback of causing the full 300V+ open-circuit voltage to be applied to the HT filter components for the minute or two it takes for the valves to conduct and draw the voltage down. This helped, but it did not entirely cure the overheating problem. My next move was to disconnect some leads and measure the resist- ance across the seven 0.5µF/2µF paper dielectric filter capacitors in the power supply cans. All were very leaky, having resistance values of just 100-500kW. So I left them in place but disconnected them, to preserve originality, and substituted 250V polyester types with the same values. I would have preferred to use caps with a higher voltage rating, but didn’t have any on hand. After fifteen minutes of use, the power transformer windings were still becoming reasonably warm to the touch, but as the set would be used only for demonstration purposes, it was probably good enough. Still, I was not happy. I once had wax dripping from a power transformer catch alight during a soak test. Above: the valve layout diagram for the Radiola 60. Left: the internal connections of the filtering, bypass & output condensors and choke of the power supply. 102 Silicon Chip Australia’s electronics magazine There was little hope of me finding a direct replacement, but an idea came to mind. Fixing the overheating transformer I decided that the simplest solution was to replace the original transformer with a modern version with 240V centre-tapped HT windings and 6.3V filament supplies, with the latter voltages reduced by dropping resistors to get 5V AC for the type 71A output valve filaments. I did some experimentation and found that 4.5W series resistors gave 4.5V AC at the filaments, which worked pretty well. The HT winding centre tap also proved suitable to derive the bias for the control grid network. To supply the 2V heaters of the remaining six valves, I decided to use one of those handy multi-tapped dualbobbin transformers available cheaply from electronics stores with a rewound secondary. I unwound the original secondaries to figure out the number of turns per volt, then wound three separate parallel coils of 1.25mm diameter enamelled copper, ten turns each, in the same direction and paralleled. The resulting output was 2.1V, matching the original transformer. I fitted this filament transformer into a small timber box together with a fuseholder in the mains Active lead. siliconchip.com.au Volume Control Tuning Dial R14 450W 450W C10 / C18 0.5µµF 0.5 R10 2kW 2kW 3rd IF C16 1µ 1µF 0kW 2nd IF R11 3kW 3kW R15 4 1st IF R12 40kW 40kW C15 2400pF C17 580-640pF Osc. Tracking C28 (1400kHz) / C27 (600kHz) L2 Mixer L1 RF L3 Local Osc. An oddity with this set was the requirement to remove the tuning capacitor before performing alignment, as the IF and neutralisation adjustment trimmers are under the tuner, along with needing a “dummy” UY-227 (one heater prong removed). This was probably done in standard RCA fashion to prevent meddling. I screwed it to the inside back of the case, opposite the power transformer. A 1.2kW 4W wirewound resistor immediately after the diode rectifiers and before the first input filter choke reduced the HT to around 185V DC, just above the recommended value. This should also give a measure of protection if a major fault occurs. This arrangement is now working reliably and giving surprising results. The B+ plate voltage is somewhat critical because this has some influence over the grid bias to the amplifying valves via the resistive network, of which the volume control is a part. To operate correctly, the anode bend Here is the type 60 IF transformer removed from its can. siliconchip.com.au detector must be biased at cutoff or distortion will occur. Testing the radio The Radiola power supply connects to the receiver via eleven screw terminals. Connecting it up and switching it on resulted in nary a sound from the speaker. I have become accustomed to these antics over the years, so anything which works on the first go frightens me! The set had worked previously; only the power supply had been tinkered with. So I resolved to check all supply voltages, while keeping in mind most of the circuit is floating above chassis, resulting in unusual readings. I have learned to take voltage readings from terminal seven, which goes to the HT centre tap on the power transformer, as this also provides the bias for the valve grids. The voltages seemed to be correct, with all HT readings being around the 170-185V DC mark. I spent a pleasant hour or two checking all valves for emission with a University valve tester. The Radiola 60 originally used all type 27 or UY227 valves in the RF sections; mine collected three type 56 substitute valves at some point. These are drop-in replacements; most tested in the 7080% range. One type 27 proved to have low emission, so I replaced it. Another later proved to be the cause of the Australia’s electronics magazine sound fading away after some minutes of operation. A check along the signal path with my Radio & Hobbies senior signal tracer (June 1954) soon isolated the fault to the area around the first IF, although all seemed in order after a further resistance and voltage check. It was now time to draw upon experience, remembering similar timewasting problems in other early sets due to socket contacts making unreliable contact with valve pins. A gentle wriggle sometimes reveals this problem, but not this time. After removing all the valves and carefully bending the brass contacts closer together, the set finally came slowly back to life, again taking 90 seconds to warm up and another 30 to reach full volume. My next job was to make a record of all working voltages, taken between terminal 7 (the HT centre tap) and the plates, cathodes and grids of all valves on the receiver chassis for future trouble-shooting reference. To better understand the circuit, I redrew the schematic larger using coloured pencils to mark out the various circuit operations and then matched this to the physical layout of the radio. Circuit description This circuit deviates from later Superhet designs by having two RF amplification stages in front of the mixer, or first detector as it was then known. December 2020  103 The Radiola 103 speaker is a rockingarmature type, which at the time were starting to fall behind electrodynamic models (below). This Magnavox R-3 14-inch horn speaker (1922) works well with the Radiola 60, but needs a 6V accumulator to energise its field coil. 104 Silicon Chip This is an autodyne type, suiting the single-purpose triode valves of the twenties and early thirties. This set also appears to use an anode bend detector (or plate detector, as it was known in the USA). The first RF valve is untuned, the aerial being connected directly to its grid. A 2kW resistor to chassis Earth provides a measure of grid bias. All signals from the aerial are amplified. RF transformer T1 is in the form of a tubular coil. It and a variable ganged capacitor tunes the secondary, coupling the selected station RF carrier from the plate of V1 into the grid of V2. A third smaller winding shown below T1 serves as part of a neutralising circuit, preventing parasitic oscillations due to the internal capacitances of V2. The amplified RF signal is coupled into V3 via a similar RF coil RF2, without neutralisation. V3 and T3 form the second detector (mixer), where the incoming RF is mixed with the local oscillator to result in the fixed intermediate frequency (IF) signal. In this set, the IF is 180kHz. The local oscillator is driven by a separate triode (V6), unlike newer sets which use a single purpose-designed pentode to drive the resonant oscillator ‘tank’ and also mix the signals. In this case, the oscillator is a modified Armstrong design. Feedback to keep the tuned circuit running is accomplished inductively via a tickler coil coupled to the valve plate. The first two sets of variable capacitors making up the tuning gang simultaneously tune the transformers feeding V2 and V3 to the station frequency, while the third set controls the oscillator frequency. An adjustable ‘padder’ capacitor, or capacitors, are in series with the oscillator tuning gang to reduce its effective capacitance, so that the local oscillator tracks 180kHz above the tuned station frequency. Following the mixer, there are three single-tuned intermediate stages of fixed RF selectivity and amplification, with the last also serving as an anode-bend detector, biased at or near cutoff by the voltage divider network between the power supply connecting terminals 6 and 7. Probably because indirectly heated output valves were then not readily available, a type 71A directly-heated Australia’s electronics magazine triode supplied from a separate 5V AC heater winding is used as an output valve. This could be a source of mains hum due to slight heating and cooling of the cathode over the mains AC cycles. To reduce this effect, the 5V AC heater circuit is centralized by two 8W resistors, which also form part of the C-negative grid bias circuit. Being at the end of the amplification chain, any induced hum would probably be well below that of the audio signal, minimising its effect. User controls Contrary to earlier wireless sets, controls are sparse on the front panel, mainly because single-point tuning is used and there is no need for filament rheostats. A wirewound volume control pot varies the bias to the grids of the amplifying valves via a resistive network. A simple wafer on/off switch completes the lineup of only three controls. High-value carbon track potentiometers which could be simply inserted into the audio line after the detector seem not to have been available then. Also lacking were electrolytic capacitors for the power supply, and purpose-designed valves for each section were not yet common. It is interesting to note that the grandfather of all valves, the type 80 dual-anode rectifier, was present in one of its forms; it is still used in guitar amplifiers to this day. Overall, I think set designers did an excellent job with what they had to work with. siliconchip.com.au This article would not be complete without a brief description of the Radiola 60’s matching 103 rocking-armature/balanced-armature loudspeaker. Similar speaker cone drivers were used in the model 100 drum type loudspeaker which came out with the first superhet, the AR-812 and the model 100A Mantel, which had a pot metal housing. The mechanism consists of a large horseshoe magnet, the poles of which are continued across to the centre to provide a small magnetic gap bridging both ends of a soft iron armature about 40mm long and 3mm square. This armature, which lays parallel to the arms of the magnet, is firmly pivoted in the middle, having only a minute amount of springy play. It is surrounded by two bobbins of fine wire, each with a 1000W impedance, firmly fixed to the frame at either side of the pivot point and with a small air gap in the centre to allow armature movement. The inner end of the armature is several millimetres longer and connects to a thin rod, transferring vibrations down to the apex of the speaker cone. My interpretation of the action is like two pairs of men sawing in unison at each end of a log pivoted in the middle, on a sawhorse. Both saws always move in opposite directions, but with varying velocity. Both bobbins need to be connected in the correct phase. The allowed movement is so small one must wonder how this mechanism can work at all, but it does, and it gives reasonably good reproduction. The RCA Radiola 60 also works very well with a movingcoil speaker and matching output transformer, plugged in directly. The 103 speaker frame is constructed from pressed and moulded wood fibre with a fabric bonnet covering the works at the back. Conclusion This is a wonderful piece of history. It still looks great, taking pride of place in our living room. When this became available, the public finally had a radio which had singlepoint tuning, making it very simple to operate. And could be heard all over the house. Unlike the RCA AR-812 of 1923 (the first superheterodyne set), there is no double spotting or heterodyne whistles when tuning. The set has a reasonable range and good volume and fidelity. It works well with the thennew moving coil speakers as well as the earlier rockingarmature types. Its price in its first year of sale was $147 US plus speaker; a bit less than half the cost of the AR-812. Last, but certainly not least, this was amongst the first radios to relieve its owners of the tedious and expensive routine of replacing batteries by being mains-powered. Previously, this feature was restricted mainly to AC-powered TRF types like the RCA Radiolas 17 and 18. The Radiola 60 has stood the test of time, and a few are still working in original condition after ninety years or so. I would say that the Radiola 60 was the most electronically advanced of all domestic radios when it first hit the market in September 1928. Although the superhet still had a way to go developmentwise, the Radiola 60 certainly set a precedent proving the supremacy of Edwin Armstrong’s concept, and lead the charge in replacing TRF sets as the standard. A good write-up on the Radiola 60 can be found at: siliconchip.com.au/link/ab4b SC siliconchip.com.au The circuit diagram for the Radiola 60; the power supply section is on the right-hand side of the terminal strip. Many of the capacitors, and some resistors, are unlabelled. This may have been because of the values varying during construction depending on testing by the workers. Every valve in this set except the rectifier is a UY-277 type with an indirectly heated cathode, reducing hum. No reflexing is used in this set. The RCA balanced armature loudspeaker Australia’s electronics magazine December 2020  105 PRODUCT SHOWCASE Digi-Key Electronics to distribute National Instruments test and measurement products Microchip’s new 47L64 serial EERAM Digi-Key Electronics announced it has expanded its product portfolio to include certain National Instruments (NI) software-connected test and measurement products. This initiative greatly expands Digi-Key’s overall offerings in automated testing. NI’s USB X Series Multifunction DAQ is now available through Digi-Key Electronics. Companies continue to face the challenge of getting quality products to market with shorter timelines. Engineers using Digi-Key’s global distribution channel and next day shipping have quick access to tools they can use to provide them with high quality, repeatable test and measurement data that will help them accelerate the verification and production of their products. The ease of set up and configuration offered by NI’s PC-based products frees up engineers’ time so they can focus on driving greater impact in development. The 47L64 is structured as a 64Kbit SRAM with EEPROM backup in each memory cell. The SRAM is organized as 8,192 x 8 bits and uses the I2C serial interface. The device can be treated by the user as a full symmetrical read/ write SRAM. The I2C bus uses two signal lines for communication: clock input (SCL) and data (SDA). Access to the device is controlled through a chip address and address pins, allowing up to four devices to share the same bus. Backup to EEPROM is handled by the device on any power disrupt, so the user can effectively view this device as an SRAM that never loses its data. For a quick overview of EERAM see https://youtu.be/17P2MGe4xSY and https://youtu.be/3Q5-hH_yjlw This device is now our largest I2C density EERAM. Our current EERAM families are 4Kb, 16Kb and 64Kb for I2C; and 64Kb, 256Kb, 512Kb and 1Mb for SPI. “Connecting engineers to the right tools when and how they need them accelerates productivity,” said Jim Ramsey, vice president of the Global Partner program at NI. “Offering our products through Digi-Key allows us to meet their customers where they are through the processes they’re accustomed to and gives us new avenues to equip more engineers with the tools they need.” “We’re very proud to be able to offer NI products to our customers,” said David Stein, vice president of global supplier management at Digi-Key. “NI’s automated test and measurement products will help our customers to advance their projects faster by helping them analyze the data from their systems in real time.” For more information about NI and to order from their product portfolio, including USB and PCI DAQ solutions, please visit Digi-Key’s website at www.digikey.com Digi-Key Electronics Thief River Falls Minnesota, USA Phone: 1800 285 719 Website: www.digikey.com Microchip Technology Inc. Unit 32, 41 Rawson Street Epping 2121 NSW Phone: (02) 9868 6733 Website: www.microchip.com Elecrow’s CrowPi2 all-in-one Raspberry Pi laptop CrowPi2 combines a Raspberry Pi and a range of common sensors. It’s useful for learning about STEAM education (STEM plus the arts) and using it as a portable laptop. The CrowPi2 is great for Raspberry Pi fans, educators, kids and laypersons alike! The CrowPi2 has an 11.6-inch 1920x1080 display, with stereo speakers and a 2MP camera with microphone. It runs off a 5V USB power supply and weighs only 1.3kg. It also comes with a removable wireless keyboard, giving you access to all the interior sensors for when you want to breadboard. CrowPi2 offers an all-in-one board with 22 sensors, such as a buzzer, RGB LED, relay and so on, which is very convenient for you to learn embed106 Silicon Chip ded electronics programming. It even has a built-in video and audio player. CrowPi2 integrates various programming languages such as Python, Scratch, Micro:bit, Arduino etc. Over 70 lessons in Scratch, Python, AI and Minecraft are provided. In addition, more than 30 extra projects and Python games are there for you to discover all the joys of Raspberry Pi. It’s based on the latest version of the Raspberry Pi 4, but is also compatible with the Raspberry Pi 3. Some of the projects possible with the CrowPi2 include: AI facial recognition, voice recognition, remotecontrolled car, fruit-based piano, simple video games etc. You can find more details at www. elecrow.com/crowpi2.html Australia’s electronics magazine Elecrow Limited West of F-building 8th floor, Fusen industry park, Gushu Hangcheng road, Bao’an Ave Shenzhen China Website: www.elecrow.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 Purpose of indentations in some mains plug pins I was very interested in the article on the development of the Australian three-pin plug and its history by John Hunter (September 2020; siliconchip. com.au/Article/14573). But something I have always wanted to know is why the pins on some plugs (especially the older ones) are indented and not just flat? By the way, I really enjoy your great mag. which turned up here in Germany right on time. It seems the post is now back to normal. (C. R., Tuebingen, Germany) • John Hunter replies: I used to think the indentations in some sockets were for pin retention. However, in the hundreds of ancient sockets I have examined, I haven’t found any evidence of that. All of them have the plain folded flat contacts; the same type still used today. Also, if such an arrangement did exist, it would be problematic with pins having straight sides, since the contact area would be reduced. As a general observation, that indented side pin shape began to be discontinued in the 1950s, first by HPM, then later by Clipsal. I haven’t found any similar arrangement in US-made sockets, which would mate with the holes in the ends of their plug pins. I did once see a vague reference that the holes were to keep the pins in position whilst the plug was moulded around it during manufacture. A few Australian (notably CMA) plugs also had these holes, so if there is some truth to it, perhaps the indented sides were for the same purpose. Odd electrical sockets on GPOs I just read the article on the History of Australian GPOs (September 2020; siliconchip.com.au/Article/14573) – what a fascinating article! He did not show a four-pin socket, but I have a photo of one that I took at siliconchip.com.au Lanacks Castle, Dunedin, NZ when I took a tour through it. It was in a small room behind a rope and was not in use. The Castle guides did not know anything about it, nor what the house voltage was at that time. The castle was built in about 1910, and most of it was imported, including the electrics. It is a GEC 230V 10A USA socket, but it might have come from England as most of the castle came from there. I have asked electrical inspectors from both England and New Zealand about it. I was an Inspector before I retired a few years ago. Can you help to identify it? (P. J., Auckland, NZ) • John Hunter responds: I am familiar with that socket and have one in my collection. It’s designed to take the normal US blade plug with two parallel pins, as well as the ‘tandem’ type plug. The tandem plug went out of fashion early on, to be replaced entirely by the common parallel blade type. It did reappear later, but with an Earth pin, and these days is used for 240V appliances in the USA. You can see the pin pattern at https://w.wiki/jsm want to build the Balanced Attenuator later). (O. A., Singapore) • Phil Prosser responds: you certainly should not be able to hear any hum. Check the voltage levels at the ADC inputs, at pins 17, 18, 29 and 20. These should all be close to 2.5V. Then follow the signals back through the buffer; check pins 1 of IC2a and IC4a. These should have a DC offset of 0V. Similarly, IC2b and IC4b pins 7 ought to have 0V DC offset. Are the 10µF capacitors on pins 3 and 5 of IC3 and IC5 in the right way around? Check all your solder joints carefully, since a bad (high-resistance) joint could explain your symptoms. That ADC is excellent. When you find the bug, you should have a super hifi ADC and the makings of an awesome piece of test kit. Editor’s note: O. A. traced the fault back to a bad solder joint on pin 3 of the ADC chip. Pressing on the chip affected the hum level, and reflowing that pin completely eliminated it. USB SuperCodec hum problem The Colour Maximite 2 is another great project (July-August 2020; siliconchip.com.au/Series/348). I managed to get it up and running after a brief problem with the VGA connector (no video output). I believe the connector holes are a little too large, so solder can wick in and wet the pin and via without forming a bridge, unless you use a lot more solder than usual. After fixing that, I found a couple more strange things. Firstly, when I plug in my Microsoft wireless keyboard, everything works OK except that the “<at>” and “:” characters were once transposed (don’t ask me how long it took to find this…), but on other sessions, remained good. Secondly, I have the latest version of Tera Term, but the connection is very “flaky”. It only connects about 1 in 10 attempts, sometimes displays graphics characters at start-up, and is prone to hang mid-sentence on occasions when After I finished building the USB SuperCodec (August-September 2020; siliconchip.com.au/Series/349), I tested the DAC section on my amplifier, and it works very very well. It’s crystal clear! I also tested the ADC. It works, but I have some hum in the background. I can adjust the input level to make it inaudible, but then when I feed it with the DAC output, I cannot hear the music (even if I set the volume to its maximum on the PC). The only way is to increase the input level, but then the hum and music are superimposed. I noticed that the +9V rail is +8.25V and the -9V rail is -8.2V. But since the DAC part works, I don’t think that’s the problem. I soldered the USB Streamer, but only the six pins that are needed (I Australia’s electronics magazine Colour Maximite 2 queries December 2020  107 entering commands (yet, the direct keyboard connection remains good). Another surprising thing – when I “Restore Setup…” in Tera Term, it never gets the saved serial port correct – I have to go back in and set the correct serial port. (I. T., Duncraig, WA) • The swapped characters (“<at>” and “:”) are probably caused by the keyboard being set to the wrong language in MMBasic. Try entering OPTION USBKEYBOARD US at the command prompt (this option is saved so it will be remembered on reboot). As for your connection problems, assuming you have checked all the solder joints, the other likely cause is that the PC or laptop does not have the grunt to supply the approximately 200mA required by the CMM2. This can be tested by using a high-capacity USB charger to power the CMM2; if everything works OK, that points to a power supply issue. Another possibility is that the USB cable is faulty. We have found that about ¾ of problems with the CMM2 can be traced to either a bad power supply or a faulty USB cable. ADF5355 DDS module output is noisy I have been testing the ADF5355 13.6GHz Touchscreen Frequency Generator (May 2020; siliconchip.com. au/Article/14437), and noted that the output signals are not as clean as those from other units (based on the ADF4351 and MAX2870). Some people online have attributed this behaviour to noisy and cheap voltage regulators used in the cheap ADF5355 boards. I have ordered a few daughter boards from Brian Flynn GM8BJF that use voltage regulators with significantly lower noise (ADM71503.3 and ADM7150-5.0). These are not cheap in small quantities (<1000 units). Did you also note that the ADF5355 board was also ‘noisy’, which the engineering chaps call “phase noise”? This was not mentioned in the May 2020 article. I looked at the output signals over the range of my spectrum analyser (3.2GHz) and noted that the ADF4351 (two versions available from BangGood – TFT/OLED) and the MAX2870 produced very clean signals. (S. G. E., Hackham West, Vic) • We did not measure the phase noise 108 Silicon Chip of that unit because, for hobbyists who need a sweep generator to test performance such as the frequency response of filters, cables etc, phase noise is not so important. We used a 5V lab supply to power our device, and did notice that the signal was somewhat noisy, but we were not too critical because we did not expect the world for $280! For your application where you need a pure signal at a fixed frequency, the changes you highlighted seem like a good way to improve the power supply and vastly reduced phase noise. We did check the unit’s harmonic distortion up to 20GHz, because this is one of the most essential factors to produce signals that do not cause interference in higher bands. We found the unit to be well within the specifications of the AD5355 with –33dBm distortion at 19.9538GHz. It seems like a lot of work to improve the module, but as long as a good 5V supply is used, it still gives a creditable performance. 2003; siliconchip.com.au/Series/293) says that its power supply can deliver a peak current of around 40mA at 265V DC. The 2016 valve supply has no details of its current delivery capabilities, can you tell me what it can deliver? I’m studying the design of boost converters and flyback converters so any help would be most appreciated concerning this topic. (J. H., Scotland, UK) • The January 2016 Stereo Valve Preamp states (p33, right-hand column) that the power supply is purposefully designed to operate at its current limit while supplying the anode current for the two 12AX7 twin triodes. If you calculate their current draw using Ohm’s Law and the values given on the circuit diagram, that is a total of around 4mA. It’s probably possible to modify the supply circuitry to deliver more than that, but as it was adequate for that particular design, we didn’t test it to see how much current it could deliver at 265V. Finding LCD for Reflow Oven Controller Identifying SMD TVS cathode I am getting together all of the parts to build the DIY Reflow Oven Controller (April-May 2020; siliconchip.com. au/Series/343). I am struggling to find an LCD screen based on the KS0108 controller (looking in the source code shows that the driver is for this chip). As far as I can see, Altronics do not have anything suitable, and Jaycar only has an ST7920-based board (XC4617). (S. G., Thurgoona, NSW) • Phil Prosser responds: I bought mine from eBay where they are prevalent and usually very cheap. A search for “KS0108 LCD” gives many results, mostly at 128x64 resolution. The choice of white on blue or black on green is up to you, but we find the blue ones have better contrast. I have not had any problems with them from that source – either they are not worth faking, or the fakes work well. In 2018, I bought two kits for your Mini 12V USB Regulator (“Install USB Charging Points In Your Car”, July 2015; siliconchip.com.au/Article/8676). I built one at the time but without success (I hadn’t mastered soldering very small SMDs). With COVID-19 shutting down New Zealand, I decided to give the second kit ago with some success, having gotten much better at soldering the very small SMDs (using solder paste and a hot air rework station). You’ve explained how to orientate the SMAJ15A and SK33A parts by identifying a stripe on one end of each these. I have had no trouble finding the stripe on the SK33A, however, even with a very strong light and magnification I can’t find one on the SMA15J. With the body of the part orientated so that it is taller than it is wide, I can read some text which says “BM” and then below it, “4LZEO”. Above the “BM” is what looks like a company logo. Is this enough information to figure out which way around it goes? (R. K., Auckland, NZ) • Unfortunately, there are multiple manufacturers of the SMAJ15A, and they use different marking schemes. So it helps to know who made the part to Switchmode power supplies for valves I built the power supply for the Stereo Valve Preamplifier (JanuaryFebruary 2016; siliconchip.com.au/ Series/295) on a small PCB to experiment with valve circuits. The Valve Preamp article (November Australia’s electronics magazine siliconchip.com.au figure this out. I checked our records to see which exact part we purchased for these kits, and it turns out it was Littelfuse. Here is their data sheet for that part: siliconchip.com.au/link/ab5p That shows that BM is the correct marking. 4LZEO is the date and batch code. With the writing orientated so that you can read it, the cathode is at the top. So, in other words, the Littelfuse logo marks the cathode. You can also check this with a DMM set on diode test mode. You should get a reading of 0.6-1.0V with the red probe to the anode (bottom) and the black probe to the cathode (top). Questions about Motor Speed Controller I see in the Notes & Errata published in the September 2020 issue that you have recommended a replacement for the obsolete IGBT used in the 230V 10A Universal Motor Speed Controller (February-March 2014; siliconchip. com.au/Series/195). However, unlike the original device, the replacement does not have an inbuilt reverse-polarity protection diode. Would that be a problem? Secondly, I am puzzled as to the reason for having the motor on the IGBT side of the bridge rectifier. No explanation for this is given in the article. If the motor were placed inline with the Active connection on the mains side of the bridge, the motor would see a more-or-less normal mains waveform, albeit PWM chopped. As you have it, the motor is effectively subject to rectified DC but with 100Hz ripple. I wonder if there may be some instances where that could cause problems. (D. S., East Melbourne, Vic) • The lack of a reverse diode within the IGBT between collector and emitter is not important in that motor controller since current does not flow in that direction in our circuit. There does need to be a diode between the positive supply and the IGBT’s collector to protect against over-voltage when the motor is switched off; hence, our inclusion of diode D1. The motor could be placed inline on the Active side of the bridge rectifier, with the collector of the IGBT connected to the positive rectifier output. But it would be very difficult and expensive to include over-voltage clamping to protect both the rectifier bridge and IGBT when the IGBT is switched off. siliconchip.com.au This protection would require two inverse-series-connected high-current zener diodes across the motor, or a similar clamping circuit that would be reliable. Since the motor controller is for universal motors that run on DC or AC, there is no problem running the motor with pulse-width modulated pulsating DC, as we have done. Running 250W Class-D amp from a car battery The local boys have had me build numerous Silicon Chip 250W ClassD amps (November-December 2013; siliconchip.com.au/Series/17) from Altronics K5181 kits for their cars. I have made it clear that they have to find power supplies to drive these amps to their full potential. After constant hounding by the natives, I have been looking at the constant voltage DC-DC converters available from Wish, AliExpress etc and am finding this very much out of my league. Can you find a converter which would suitable to power the 250W Class-D amp to its maximum or close to it, in a car? (J. C., Pialba, Qld) • We published a DC-DC Converter for the Class-D amplifier (May 2013; siliconchip.com.au/Article/3774), but it is not sufficient to get the full 250W from the amplifier. It will produce up to 125W into 4W on program material. You would need two converters for a stereo amplifier. For more power, our 600W DC-DC converter (October-November 1996; siliconchip.com.au/Series/152) could be used. Adjust its output voltage to ±55V by winding fewer turns on the transformer. This could power a stereo amplifier for 500W (250W per channel). We looked for suitable commercially-made DC-DC converters but couldn’t find any. Electronic control of induction motor speed I have built a device to give closedloop torque control of a 3-phase induction motor using your 1.5kW VSD (April & May 2012; siliconchip.com. au/Series/25) which I built from an Altronics kit (Cat K6032). It works well with manual torque control and PID control; however, I noticed that the motor speed would sometimes have some annoying chatter. Australia’s electronics magazine When driving the inverter and motor in open-loop mode with a steady voltage that I vary up or down, I discovered the motor speed steps neatly in 60RPM increments and chatters when the control voltage approaches inverter speed step thresholds. So basically, the inverter produces frequencies in 1Hz steps. The inverter internal speed set pot (VR1) also varies the inverter output in 1Hz steps. But when set to ramp up to a set speed via the inverter internal control, the motor spins up to the selected speed very smoothly! The specifications for the inverter state that its “speed control range” is 0.5-50 or 75Hz in 0.05Hz steps. It looks like the inverter is stepping in 0.05Hz steps when ramping between the discrete 1Hz settings, which isn’t what I was expecting. Can the inverter microcontroller be set up so its speed setting increments in 0.05Hz steps just like it does while ramping? (N. R., Glenroy, Vic) • Andrew Levido responds: the 1.5kW inverter was not designed to be controlled in this manner. While the frequency resolution is 0.05Hz, the ramp up or down between frequency setpoints will not commence unless the setpoint has moved 0.5Hz from the operating frequency. This is to avoid the ‘hunting’ that would otherwise occur if there was the slightest bit of noise on the analog input. I can see why this might look like 1Hz steps when trying to move in small frequency increments. The threshold is set in the software. This could be reduced to a threshold of 0.05Hz if the code was recompiled. This should work, but I have not tried it. Note that we have not released the source code because you need to know what you are doing to make any changes. SL32 NTC thermistor failure I’ve had the Induction Motor Speed Controller (April-May 2012; siliconchip.com.au/Series/25) operational for about a year now, but the SL32 10015 inrush current limiting thermistor has now failed. I noticed about six months ago that it had a crack in it, but I left it in place because the controller was working OK otherwise. It has obviously become very hot to December 2020  109 the point where it became an opencircuit crumbling mess. Have you had others report this problem? I’ve modified my charred PCB and mounted a new SL32 10015 offboard, in the airflow at the top of the box. Another modification I installed right from the start of the initial build is a full 12V supply to the muffin fan for maximum airflow. The new SL32 is running very hot like the original, even in its new, improved location. I expect it also will eventually fail. How would it be if I installed two MS32 5R020’s in series? That would still give 10W but spread the load (heat) between them. • We have heard of numerous failures of the SL32 devices in soft starters, but not in the IMSC. We’ve also heard reports of (expensive) commercial and industrial devices which use NTC thermistors for inrush current limiting failing during normal use, sometimes explosively. It seems that these parts can’t really handle the rapid thermal cycling, even though they are designed for this very job. We aren’t sure if it is a quality control problem at the factory, or perhaps that in some cases they are being pushed harder than intended (despite the device data sheet not giving any guidance on this matter). The SL32 10015 is rated at 15A continuous, so you would expect it to survive being part of a 10A motor controller. Your solution of the two MS32 5R020s in series should be a lot more robust. We suggest anyone building one of our SoftStarter projects for use with a large, bench-mounted power tool should do what you have done and use a larger number of lower-resistance NTC thermistors in series. Especially if it is going to experience frequent cycling. Using Soft Starter with large aircon Can I use your July 2012 Soft Starter for Power Tools (siliconchip.com.au/ Article/601) with a Panasonic 5kW split system air conditioner? It is no longer under warranty and therefore the sky’s the limit, so I am doing my research to convert it to run off-grid permanently from a dedicated inverter and bank of batteries/solar panels. 110 Silicon Chip I need to limit the inrush current the compressor draws, as to prevent the inverter going into trip mode under start-up conditions. It is rated to draw up to 5.5A continuously in cooling mode and 6.8A in heating mode, with peak currents of 14A and 17.5A respectively. During normal operation, the current I have measured is less than 5A. (B. A., Dee Why, NSW) • It might work, but we wouldn’t recommend it, at least not without a lot of testing first. It’s going to be hard on the thermistors since a compressor starts up under quite a lot of load, especially if it’s already hot. So they might fail pretty quickly (as described above, albeit in a different application). We suggest that if you do try it, use a larger bank of thermistors in series/ parallel or higher-rated thermistor(s). That would necessitate a larger box at the very least. We’re also concerned about possible compressor burnout if it doesn’t start properly, although the Soft Starter does bypass the thermistors with a relay after a short time, so the compressor should start eventually, even if it hard-starts. Still, we would want to monitor its operation very carefully for a while after installation. It’s also possible that the relay could have a short life if the compressor isn’t starting until the relay kicks in, or if the compressor is still drawing significant current by that time even if it has started. Varying Tempmaster Mk2 range I have just purchased a kit for your Tempmaster Electronic Thermostat Mk2 (February 2009; siliconchip.com. au/Article/1337) from Jaycar Electronics (Cat KC5476). I am hoping to use it to operate a cooling fan. When I opened the instructions, I found it has a range of 2-19°C, to suit fridges. I would like to change the operating range to about 15-35°C, although it would be good enough if I could just increase the upper limit to anything above 30°C. Is it possible to change any components to achieve this? Any help would be appreciated. (T. J., Adelaide, SA) • You can change the Tempmaster Mk.2 temperature range to 14-35°C by changing the 2.7kW and 3.3kW resistors in series with VR1 to 2.0kW and Australia’s electronics magazine 2.7kW respectively. Or you can get an even wider range of -5 to +40°C by using 1.2kW and 1.5kW value resistors. Coil for the High Energy Ignition System I have been searching the internet for weeks trying to find an appropriate high-energy ignition coil to use with your High-energy Ignition design (May 1988; siliconchip.com. au/Article/7739; built from a Jaycar KC5030 kit). I would appreciate it if you could recommend a high output ignition coil or coils to suit. I have been using the Prestolite points distributor in my 1962 Studebaker Hawk GT to run the ignition system for many years without a problem. I have owned the Stude since I was 21 years of age – 50 years ago! (R. B., via email) • We recommend you use a quality standard coil such as the NGK coil listed at siliconchip.com.au/link/ab5q The High-energy Ignition system is designed to work with a standard coil. So-called high-energy coils can cause arcing and misfiring if the distributor and ignition leads are not suited to the higher voltage and faster voltage rise time. Solar charger for 32V battery Several months ago, I purchased an MPPT solar controller via eBay. I am using three 20V solar panels to charge a 16-cell (32V) lead-acid storage battery. The unit has a range of desirable features including reverse current protection and continuous read-out of the panel and battery voltage, current, amp-hours delivered and battery state of charge. However, it does not seem to be a ‘smart’ battery charger, despite having an elaborate programming procedure. As a result, I conclude that the controller should not be left connected permanently between the panels and the battery, as the voltage can readily exceed 2.5V/cell (40V) in sunny weather. At that voltage, the charging current is around 3A. My method of manual regulation is to switch off the solar panels using a DC circuit breaker when the battery voltage reaches 40V. The battery remains connected to the MPPT controller. I recently noticed that there is a continued on page 112 siliconchip.com.au MARKET CENTRE Cash in your surplus gear. Advertise it here in SILICON CHIP KIT ASSEMBLY & REPAIR FOR SALE 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 GREAT VALUE PARTS and more are found in the Tronixlabs ebay store via tronixlabs.com.au – for enquiries or support please email support<at> tronixlabs.com 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 Silicon Chip Binders REAL VALUE AT $19.50 * PLUS P & LEDs, BRAND NAME and generic LEDs. Heatsinks, fans, LED drivers, power supplies, LED ribbon, kits, components, hardware, EL wire. www.ledsales.com.au ASSORTED BOOKS FOR $5 EACH Selling assorted books on electronics and other related subjects – condition varies. All books can be viewed at: siliconchip.com.au/link/aawx Email for a postage quote, quote photo numbers when referring to a book: silicon<at>siliconchip.com.au 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 P Keep your copies safe, secure and always available with these handy binders These binders will protect your copies of SILICON CHIP. They feature heavy-board covers, hold 12 issues & will look great on your bookshelf. 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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 December 2020  111 4mA current flowing back from the battery to the controller. Is that normal? Have you ever published an MPPT solar charger that would suit a 32V 200Ah battery being charged from three standard 20V solar panels? (R. W., Loxton, SA) • The amount of current drawn by a charger from the battery depends upon the circuit design. It is normal for there to be some current drawn by the controller (whether it is an MPPT charger or not). After all, the charge controller circuit needs power to operate, and that can only come from the battery when there is no solar power available. The 4mA drain is not huge compared to the overall battery capacity – it would take nearly 290 days to fully discharge your battery at that rate. However, the less the charger draws from the battery, the better. Unfortunately, we have not published an MPPT solar charger to suit a 32V lead-acid battery. That is a somewhat unusual voltage; 12V, 24V, 36V and 48V are more common. It’s close enough to 36V that a charger designed for a 36V lead-acid battery might work; as long as it’s adjusted. Modifying the 40A DC Motor Speed Controller I have a customer who is using a number of your March-April 2008 40A DC Motor Speed Controllers (siliconchip.com.au/Series/48) to vary the speed of trolling motors on their boat. They want to speed up the soft-start ramp or remove it. Currently, the soft start runs for about 10 seconds, but they need it to be under three seconds. I’ve had a brief look at the assembly code for it, but my knowledge of assembly is so rusty it would take months to dissect it. I did have a go at assembling the source code which is available for download from your website, but I got several errors regarding missing functions named float_ascii2 and float_ascii4. They don’t appear to be part of the standard library. I also found that I had to add these two lines at the top of the main .asm file, which got rid of several other errors: #define P16_MAP1 0 #define P16_MAP2 1 I know that you have since released a more modern speed controller which has the soft-start control they’re after, but they’ve already built these kits and have been using them for a little while. We didn’t make a kit of the updated one so it would still be a fair amount of running around for them to switch. (Tom Skevington, Kits Manager, Altronic Distributors) • The float_ascii2 and float_ascii4 functions were in another file which was not included in the ZIP download for that project. That has now been corrected. Thanks for the tip about the two added defines which are needed. The software has two variables in which values are stored to increase or decrease the PWM duty cycle, named pdeltah and pdeltal. These are loaded with +1 on lines 819-821 of the main ASM file to decrease the speed, or -1 on lines 824-827 to increase the speed. Since this gives a soft start time of around 10 seconds, changing the increments to +4 and -4 should give a ramp time of around 2.5 seconds. To achieve this, change line 819 to: movlw 0x04 movlw 0xFC and change line 824 to: This will also make the motor speed ramp more quickly in response to the rotation of the speed control pot, or changes in load (ie, feedback). SC Advertising Index Altronics...............................81-84 Ampec Technologies............. OBC Dave Thompson...................... 111 Digi-Key Electronics.................... 3 Emona Instruments................. IBC Jaycar............................ IFC,53-60 Keith Rippon Kit Assembly...... 111 LD Electronics......................... 111 LEDsales................................. 111 Microchip Technology.................. 5 Ocean Controls......................... 11 Premier Batteries........................ 8 RayMing PCB & Assembly........ 10 Rohde & Schwarz........................ 7 SC Vintage Radio DVD.............. 34 Silicon Chip Christmas Kits...... 52 Silicon Chip Online Shop....98-99 Silicon Chip PDFs on USB....... 25 Silicon Chip Subscriptions....... 35 The Loudspeaker Kit.com........... 9 Tronixlabs................................ 111 Vintage Radio Repairs............ 111 Wagner Electronics................... 63 Notes & Errata Digital Lighting Controller pt2, November 2020: on p101, the parts list correctly includes a 27W 1W resistor for the Micromite master unit but incorrectly lists it as 25W 1W for the CP2102 Adaptor module (it should also be 27W 1W). Tiny LED Christmas Ornaments, November 2020: the parts list incorrectly lists the Bauble PCB dimensions as 91 x 98mm when they should instead be 52.5 x 45.5mm. Also, the Cane PCB is incorrectly listed as 84 x 44mm when it should be 84 x 60mm. Two new 7-band Audio Equalisers, April 2020: in the first batch of stereo equaliser PCBs sold (code 01104202), the connection between the 220pF capacitor and 51kW resistor in the lower right-hand corner of the board went to the top of the resistor instead of the bottom (which was floating). This can be fixed by cutting the track between the two components and running a short wire from the bottom of the resistor to the nearest pad of the capacitor. PCBs sold from November onwards do not have this problem. The January 2021 issue is due on sale in newsagents by Thursday, December 31st. 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