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.
With this circuit found in an American documentation from 1969 it is possible to vary the...
The reference voltage for this circuit can be selected digitally. The circuit is from Radio...
This circuit was found in an old factory documentation. The circuit uses single-junction...