This circuit was found in a Popular Electronics from the 90's. Its purpose is to detect the ionization of the air. The meter can be replaced by the current scale of an ordinary multimeter.
This voltage controlled oscillator, which can be used as a shield, generates signals in the 1.5...
This circuit was obtained from the 1976 Siemens integrated circuits manual. It is the circuit for...
This instrumentation circuit was found in the September 1989 Radio Electronics magazine. The...