This circuit was found in an English publication from 1967. The circuit is for listening on a phone. Transistors are types of germanium of the time.
This is a project that can easily be adapted for other purposes such as counting people, objects,...
A modulated (intermittent) siren, using the four gates of the 4001 integrated circuit is shown in the...
This circuit was found in July 1986 Radio Electronics magazine. The maximum current is 1.5 A. The...