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MARKET CENTRE Cash in your surplus gear. Advertise it here in SILICON CHIP Where do you get those HARD-TO-GET PARTS? Where possible, the SILICON CHIP On-Line Shop stocks hard-to-get project parts, along with PCBs, programmed micros, panels and all the other bits and pieces to enable you to complete your SILICON CHIP project. SILICON CHIP On-Line SHOP www.siliconchip.com.au/shop 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 Trouble buying old components? Need to re-spin an obsolete PCB? We do PCB layouts from files, drawings or samples. Contact Steve at sgobrien8<at>gmail. com or phone 0401 157 285. Get your old PCBs updated and keep production going! KIT ASSEMBLY & REPAIR KEITH RIPPON KIT ASSEMBLY & REPAIR: * Australia & New Zealand; * Small production runs. Phone Keith 0409 662 794. keith.rippon<at>gmail.com DAVE THOMPSON (the Serviceman from SILICON CHIP) is available to help you with kit assembly, project troubleshooting, general electronics and custom design work. No job too small. Based in Christchurch, NZ but service available Australia/NZ wide. Email dave<at>davethompson.co.nz FOR SALE LEDs, BRAND NAME and generic LEDs. Heatsinks, fans, LED drivers, power supplies, LED ribbon, kits, components, hardware, EL wire. www.ledsales.com.au tronixlabs.com.au – Australia’s best value for supported hobbyist electronics from Adafruit, SparkFun, Arduino, Freetronics, Raspberry Pi – along with kits, components and much more – with same-day shipping. 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 ADVERTISING IN MARKET CENTRE Classified Ad Rates: $32.00 for up to 20 words (punctuation not charged) plus $1.20 for each additional word. Display ads in Market Centre (minimum 2cm deep, maximum 10cm deep): $82.50 per column centimetre per insertion. All prices include GST. Closing date: 5 weeks prior to month of sale. To book, email the text to silicon<at>siliconchip.com.au and include your name, address & credit card details, or phone Glyn (02) 9939 3295 or 0431 792 293. isting ones, or use a separate 15-0-15V transformer. Testing optocoupler in MPPT Charger I built the Solar MPPT Charger & Lighting Controller from the February and March 2016 issues (siliconchip. com.au/Series/296) and tested it but the 4N28 optocoupler (OPTO1) does not seem to be working. I measured 4.8V at pins 1 and 2 and 12V at pin 5 siliconchip.com.au but 0V at pin 4 so suspect it is faulty. Can I use a 4N25 instead as I have a spare one? If so, would I need to change the circuit? (E. B., Bridgetown, WA) • A 4N25 can be used in this circuit without changes. However, based on the voltage measurements you have supplied, it does not seem that the 4N28 is faulty. If you measure 4.8V at both pins 1 and 2, that means there is no current flowing through the optocoupler LED Australia’s electronics magazine and thus you would expect a low voltage reading at pin 4. Check the soldering and parts placement on your unit before deciding if OPTO1 is at fault. Also, note that the optocoupler is only switched on when Q5 is on (via gate drive from RB5). In this case, pin 2 should be around 3.8V, ie, around 1V between pins 1 and 2. We suggest you re-check the voltages on the pins of OPTO1 when S1 is pressed. This switches on the optocoupler. SC August 2018  103