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Advertising Index Altronics.................................35-42 Control Devices........................... 51 Dave Thompson........................ 111 Digi-Key Electronics...................... 3 ElectroneX................................... 17 element14................................OBC Emona Instruments.................. IBC Hare & Forbes............................. 47 Icom Australia............................. 13 Jaycar.................IFC, 11, 15, 18-19, ................................... 93, 95, 97, 99 Keith Rippon Kit Assembly....... 111 Lazer Security........................... 111 LD Electronics........................... 111 LEACH PCB Assembly................ 55 LEDsales................................... 111 Mastercut Technologies............. 16 Microchip Technology............ 7, 71 Mouser Electronics....................... 4 Oatley Electronics..................... 111 Rohde & Schwarz.......................... 9 SC Raspberry Pi Pico W............. 46 Silicon Chip Shop............ 106-107 Silicon Chip Subscriptions........ 72 Silicon Chip Test Tweezers..... 109 The Loudspeaker Kit.com.......... 12 Tronixlabs.................................. 111 Wagner Electronics....................... 8 Errata and Next Issue _____________ Active Mains Soft Starter, February & March 2023: the right-hand column on page 71 of the March issue says to use red or black wire for Active. It should have said red or brown. Next Issue: the June 2023 issue is due on sale in newsagents by Monday, May 29th. Expect postal delivery of subscription copies in Australia between May 26th and June 12th. 112 Silicon Chip unit is similar to ours, a reading of 84 ADC steps corresponds to 0A, with 21 more steps per additional amp; ie, 105 means 1A, 126 means 2A, 147 means 3A etc. We recommend adding a line “Serial.println(p);” to the main sketch loop() function; p is the sampled current sense analog value. This will allow you to quickly check the calibration of your unit as you apply test loads and possibly increase the current limit with safety. A simple fix might be to use a single-­ diode rectifier, which should reduce the inrush current by half. If the load on the converter is relatively low, a series resistor might work to limit the inrush current at the cost of dissipation in the resistor. An NTC thermistor rated at a few amps would be even better but more expensive. Since the DCC signal is an AC source, you could also use a capacitor (in series) dropper. Simulations suggest that values around 100nF to 1µF in one of the AC legs from the DCC signal (ie, before the bridge) might be in the workable range for the 220µF capacitor on the XC4514 buck converter. Still, it will depend on the load on your buck converter. Choosing a transformer for the Class-A amp The Altronics transformer specified for the 20W Class-A Amplifier (May-September 2007; siliconchip.au/ Series/58) is listed as 16-0-16V AC. I have an 18-0-18V AC transformer on hand. Is it OK to use this? If so, would I need to change any circuit values? (R. H., Berowra Heights, NSW) ● An 18-0-18V transformer would result in a higher DC voltage than the amplifier is designed for, and it isn’t easy to change it to handle that. You can use your transformer if you backwind the secondaries until you get an output closer to 16V AC for each. If you can’t get the 16-0-16 transformer, a 15-0-15 transformer might be available and would only reduce the output power slightly. Fixing the Automatic Rain Gauge Many years ago (in 2000), I built your tipping bucket rain gauge (June 2000; siliconchip.au/Article/4325), and it has been working without fail Australia's electronics magazine until recently. Now it wouldn’t record rainfall. I have diagnosed the fault to be the IR sensor in the bucket assembly. Not having the original documentation that came with it, I am stuck as to what the part is, but I have a bucket assembly from a failed Bunnings wireless unit. This bucket uses a reed switch and magnet. Would it be possible to get a copy of the circuit diagram so I can investigate if it’s possible to use a reed switch assembly? (C. L., Allingham, Qld) ● The sensor used in the Rain Gauge was the Jaycar Z1901 photo interruptor, which is still available. We still have plenty of June 2000 back issues if you need the circuit diagram, or you can get online access, via the following links: Print: siliconchip.au/ Shop/2/319; Digital: siliconchip.au/ Shop/12/3138 Replacing the sensor with a reed switch is easily possible. Just connect the reed switch between pin 6 of IC1 and circuit ground. That is the same connections as for the photo interruptor phototransistor collector (pin 6) and emitter (GND). If the bucket assembly from the Bunnings wireless unit tips the bucket each time it collects 1mm of rain, it should work with the Rain Gauge. Our Rain Gauge had an 86mm diameter collection area, so the volume of water collected for 1mm of rain is 5.808cm3 or 5.808mL (π × 43mm2 × 1mm). Optocoupler transistor base connection What do you connect the phototransistor base to when using an optocoupler like the 4N25, 4N26, 4N27 or 4N28? Leave it open, connect it to ground? (F. C., Maroubra, NSW) ● Generally, the base is left open. A resistor can be added between the base and the emitter to speed up the output response. This allows the transistor to switch off faster in the absence of light. However, it also reduces the sensitivity of the optocoupler, so more input current is required to switch on the output transistor. Care should be taken not to exceed the LED’s current ratings. When using a base resistor, its value is a compromise between output switch-off speed and input sensitivity. 10kW could be a good starting point. For more information, visit: siliconchip.au/link/abl5 SC siliconchip.com.au