Comment by JKCalhoun
3 months ago
I was thinking Astable Multivibrators. Probably the same as your Metronome. The circuit I usually see uses two NPN transistors instead of the PNP+NPN your metronome does: https://www.electronics-tutorials.ws/waveforms/astable.html
It's a different principle, although I have a Ladybird Book of Electronics that my dad gave me when I was just about the age my son is now, that shows how to make a thing that flashes two lightbulbs using that astable circuit (and a few other things).
The two-transistor metronome one really is working more like an SCR, that rapidly charges the capacitor and allows it to discharge again.