This circuit is from an 80's technical newsletter. The circuit can use any general purpose transistor and its power supply can be changed with a resistive divider to use a single 9V battery.
The presence of a low resistance between the terminals of the sensor causes this modulated...
TDK provides a wide range of EPCOS varistors for surge protection through Mouser Electronics....
This circuit was taken from a Popular Electronics from January 1967. Transistors are from the...