Published in Popular Electronics with the curious name of Obnoxious Noisemaker, this 1968 circuit generates random sounds that are reproduced on a loudspeaker. The power transistor can be a BD136.
This 2004 circuit is based on the ionization effect that occurs in old incandescent lamps with...
This circuit memorizes through an LED indicator if your phone was used during your absence. The...
Found in a 1969 Electronics World, this circuit generates low frequency signals with two...