You may and may not recall that I built a little optical theremin.

Basically, I’ve been trying to develop an electronic instrument project that could be built, in a workshop environment, at nwcMUSIC at Norwescon. It had to be really simple, but functional. And I can – what you can see in this picture totally works! It could be simplified further just by swapping those three resistors with one of similar value.

But the output is really, really quiet. Sure, I could – and did – add a matching impedance stage and hook it up to my amp, and that worked, but we can’t do that in a workshop.

So I wanted to add a pure amplification stage, using an amplifying transistor. I hooked all that up and: silence. After a few minutes, I realised that I was attempting to amplify a signal with a lower-power source than what I had to begin with. That won’t work.

And I could fix it, either by adding an impedence-matching voltage transformer (complexity rating no) or a second power stage, but it would take it well above my complexity limit for a one-hour workshop.

That won’t work either

So then I thought, “all these components are rated 40v, let’s just double the input power to 18v and see what happens.” And what happens is fire.

Or, at least, a surprisingly enthusiastic outbreak of magic blue smoke. And now nothing works, and now the little battery-powered air filter I built is running.

And that’s why there’s no DIY project today.

See you next week. XD