This circuit was found in the July 1978 issue of Radio Electronics magazine. The circuit uses a common digital voltmeter as the indicator. The sensors are integrated circuits of the time.
This simple transistorized radio for listening on a crystal phone was found in a Japanese...
This very high voltage generator (VHV) uses a 555 and a power transistor with a heat sink. The...
Found in a 1969 documentation, this circuit is reset by a push button. The activation time is 100...