This circuit fires with the noise captured by the touch of a sensor. Signal shapes are given next to the diagram. The circuit is from the 80s, using components from that time.
This circuit is like the previous one except that it can be triggered electronically. The circuit is...
Found in 90s Radio Electronics, this audio indicator makes use of an integrated circuit that is...
Found in the October 1992 Radio Electronics magazine, this oscillator is controlled by switch S1....