This circuit was found in the July 1992 Radio Electronics magazine. Sensitivity adjustment is made at R6. Supply voltage is matched to that of the relay.
This circuit was found in a Electronics Handbook (1989). The shown amplifier provides a few...
This circuit was found in the October 1993 Electronics Now magazine. The output transistors form...
Several types of OSEPP sensor modules can be obtained from Mouser Electronics for Arduino...