Project: EQKit PSK-1 Electronic “Voice Control” Switch Kit

Continuing the kit-a-thon, I grabbed another EQKit out of the drawer – this one is a PSK-1 which was sold as an Electronic “Voice Control” Switch Kit for the princely sum of AU$1.98 including postage. As a kit that had nothing too complicated in it, how could it possibly do voice control?

The Kit

A zip-lock bag – but instead of containing contraband items, it contains components for the kit.

As seems to be classic with EQKits, they come with the extra frills – a JST cable and socket for power, aside from the necessary components. That’s a nice touch.

The PCB also is of a good quality, being single-sided this time, silkscreening on the top.

The underside having solder-resist and hot-air levelled tin finish for easier soldering. The pads do get somewhat close together, so a fine iron is probably best.


A quick count of the solder joints needed to build the kit:

14 x Resistors - 28
4 x Transistors - 12
6 x Capacitors - 12
2 x Diodes - 4
Microphone - 2
LED - 2
Power Socket - 2
Total: 62

Another straightforward construction – interestingly, nothing is provided to populate J1 and its purpose is not immediately apparent due to the lack of instructions or information.

Fairly neat solder joints – I did this after work in my time just before bed, so I was in a rush – but the boards from EQKit are always a joy to solder to.


Ever curious as to what it does, I hooked it up to power and tried speaking to it. Nothing. I tried tapping on the mic … but nothing happened. I even tried clapping … then I realized I mounted the LED backwards. D’oh! Just goes to show that experienced kids like myself make mistakes when they’re tired – so don’t build kits when you’re tired (or drunk)!

Take #2 was much more successful – now the LED was positioned correctly, I found that clapping or clicking would toggle the LED on or off. Quickly double-clapping would not trigger it twice, so it has some sort of “debounce” time. That actually reminds me of The Clapper switches which used to be rather popular. It doesn’t even need any adjustments.

Wanting some insight into how it worked, I tried to trace out the schematic which took multiple attempts due to the numerous cross-connections. I’m not even sure if the above is correct, but not having the time to analyse it in-depth, I’m none the wiser as to how it works.

Observing the bases of the transistors through the oscilloscope seemed to give me some hints – Q1 seems to be just biased with an “impuse” causing it to shut hard off. This seems to propagate to Q2 which shows a much harder “square” drive, all with about a 300ms time constant. Then Q3 seems to be triggered toggled between claps, whereas Q4 seems a bit of a mystery although it should be driving the output in some way … I’m not sure what happened there. But it does work and it seems to be a rather interesting module to integrate into another project (potentially).


As with most EQKit products, this one was rather straightforward to build despite the lack of instructions, and the board was fairly enjoyable to solder to. This one was rather interesting, as it was sold as a “voice control” kit but rather is more akin to a “clapper control” – clap to turn on/off.

The way it works is a slight mystery to me as well, as it has a rather interesting cross-connection of components, but from the oscilloscope trace, it seems to involve “just” biased transistors, some filtering, a time-constant of about 300ms somewhere and some diode logic of sorts.

Regardless, it does perform a rather neat function and it seems to work quite well. Speech doesn’t trigger it – but claps and clicks do. It seems useful as a module in other projects, hence the J1 output which could be input to a microcontroller (e.g. edge-triggered interrupt).

About lui_gough

I'm a bit of a nut for electronics, computing, photography, radio, satellite and other technical hobbies. Click for more about me!
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