This circuit was found in a 1985 documentation. It provides an audiovisual indication of the presence of moisture or water in the sensor. The circuit can be powered by voltages from 6 to 9 V.
I found this circuit in a Popular Electronics from November 1999. The magazine is no longer...
This tunnel diode circuit was found in American documentation from 1966. The tunnel diode is the...
This circuit provides two slightly different audio signal outputs from a monophonic audio signal, so...