The Atari Punk Circuit is a venerable old noise maker created by Forrest Mims III using the timed pulses out of 2 555 or 1 556 timers and some capacitors to make noise. The resistors change the rate of those pulses, and the capacitors discharge the pulse into a square-wave signal that is audible to humans if we have the capacitors in the right ranges.
I built one, but then, because I’m still electronaive, wasn’t certain where to put the speaker jack. Andrew helped me out, and we got it working by using his fancy fancy oscilloscope.
In the interests of full disclosure, I later quickly burnt out one of the 555 timers when I plugged it in to a power supply that had the voltage set too high. Now I get to dig through the shop’s bucket of ICs to find another 555, or, with luck, get to rebuild it with a 556. Maybe I’ll even solder up some flexible potentiometers at Build Night tonight!