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You would need to power the main controller section from 12V and the motor driver section separately from a suitable 180V supply. You could use a 500VA+ mains transformer with a 120V AC secondary (or 60V + 60V in series), then rectify and filter the output. Check that the transformer can handle the motor startup current, which likely will be well over 4A. If building this project, please read the relevant notes & errata in the 2017 PDF at siliconchip.au/Articles/Errata Displays for 2.5GHz Frequency Counter I am having trouble sourcing the four-digit, 7-segment LED displays used in the 2.5GHz 12-Digit Frequency Counter (December 2012 & January 2013; siliconchip.au/Series/21). They are specified in the parts list as coming from Futurlec, but they have no stock of the blue type. They can offer me a red type but the forward voltage is only 2.4V maximum at 20mA. The blue variety is rated at 3.2V <at> 20mA but can handle 4V maximum. Advertising Index Altronics.................................27-30 Dave Thompson........................ 103 DigiKey Electronics....................... 3 Emona Instruments.................. IBC Hare & Forbes............................. 13 Jaycar................... IFC, 9, 11, 14-15, ....................................43, 67, 90-91 Keith Rippon Kit Assembly....... 103 I have some similar red displays from AliExpress rated at 2V maximum <at> 20mA. Should I use the AliExpress parts, go with the alternative Futurlec displays, or wait for the blue ones to come back into stock? It could be a long wait. Changing the resistors to suit the alternative displays might be a solution, but what should their values be? I have built the main board but the display is holding me up from testing it. (E. B., Meadow Springs, WA) ● Readers asking where to find parts that have been discontinued or are out of stock is becoming something of a theme. While Futurlec doesn’t have stock of the displays we used, they are still available from other vendors. For example, AliExpress items: • 1005005352398426 • 1005001606190533 • 1005003246695690 You could use displays with a different colour if they are easier to get. Since, as you wrote, the red displays will have a lower voltage drop at the recommended segment current level of 20mA, we suggest replacing the eight 47W series segment resistors in the counter display board with 150W resistors to be on the safe side. The resistors concerned are at the upper left on the display PCB, looking from the front. PIR Mains Timer wiring question I have built your February 2008 PIR-Triggered Mains Switch project (siliconchip.au/Article/1751) from a Jaycar kit (KC5455). I am using Jaycar’s XC4444 PIR module. Unfortunately, I’m a bit stuck on this last step when connecting the PIR to the 3-way terminal block. The instructions state that I need to put a link between the ground on the PIR and the contact of the normally-­closed relay; could you please elaborate on this? Any help would be greatly appreciated. (E. C. H., via email) ● Before we get to wiring up the PIR module, we’d better check that it’s compatible with the PIR sensor shown in the article. That one had two normally-­closed (NC) switch outputs, ALARM and TAMPER. They were connected in series with one end to circuit GND so that they would usually hold the input low, but a resistor would pull it high if either switch opened. We downloaded the manual for Jaycar’s XC4444 PIR module from their website, and it appears to have a much simpler arrangement with just three terminals: Vcc, OUT and GND. The OUT pin idles low but goes high when the sensor detects movement (presumably to Vcc). Therefore, this appears compatible since it is also low when untriggered and goes high when triggered. The specifications for that module on the Jaycar website say it will operate from 5-20V, and our circuit is powered from 12V, so it should work. The connections for the 3-way terminal block are as follows: • Top terminal (+12V): goes to Vcc on the PIR detector • Middle terminal (IN): goes to OUT on the PIR detector • Bottom terminal (GND): goes to GND on the PIR detector Make sure you don’t get the +12V and GND connections mixed up. SC LEDsales................................... 103 LD Electronics........................... 103 Microchip Technology......... OBC, 7 Mouser Electronics....................... 4 SC Pico W BackPack................ 102 Silicon Chip Breadboard PSU... 66 Silicon Chip PDFs on USB....... 101 Silicon Chip Shop................ 89, 98 Silicon Chip Subscriptions........ 77 The Loudspeaker Kit.com.......... 97 Tronixlabs.................................. 103 Wagner Electronics....................... 6 104 Silicon Chip Mgazine Errata and Sale Date for the Next Issue Lazer Security........................... 103 Loudspeaker Testing Jig, June 2023: the 1kW resistor connecting to LK1 that filters the phantom power for the microphone should be 100W, not 1kW. It might work with 1kW, but it will depend on the microphone. Also, because pin 2 of XLR socket CON10 (“HOT”) connects to the INsignal and pin 3 (“COLD”) connects to IN+, the microphone phase will be inverted. To fix this, swap the wires to pins 2 & 3 of header CON11 on the PCB. Finally, the labels of transistors Q1 & Q2 in the circuit diagram (Fig.3) have been swapped, but they are correct on the PCB overlay and PCB. Vintage Radio, Astor APN, May 2023: there were some errors in the published circuit diagram for the set, mainly regarding the connection of capacitors #35, #36, #38 and resistors #6 & #10. The circuit diagram has been corrected in the online version of the magazine and has been made visible in the free preview of that issue on our website. Next Issue: the August 2023 issue is due on sale in newsagents by Thursday, July 27th. Expect postal delivery of subscription copies in Australia between July 26th and August 11th. Australia's electronics magazine siliconchip.com.au