This sensor circuit for currents of the order of nanoamperes was found in an American documentation from the 1980s. The components are from that time.
Found in a Popular Electronics from the 90's, this circuit detects the approach of objects by the...
This old 4-channel circuit was found in the December 1994 Electronics Now magazine. The circuit uses...
The figure shows how to implement an alarm buzzer in an LM3914 to warn about crossing the scale...