This circuit for incandescent lamps was found in the January 1980 Radio Elecronics magazine. The sensitivity can be controlled by a potentiometer and the microphone used is of the dynamic type.
We found this circuit in an old documentation. The instrument can be an ordinary multimeter in the...
This simple electroscope with bipolar transistors is not the most sensitive, but can detect static...
This circuit was found in an old Popular Electronics. It causes an LED to pulse and, at the same...