Indicated for activation by microcontrollers, this circuit was found in the Radio Electronics magazine of December 1987. The MOSFET can be of any type according to the buzzer.
This circuit was found in the July 1992 Radio Electronics magazine. Sensitivity adjustment is made...
This circuit was found in a 1967 Electronics World. We can design it with a BF245 for the FET and a...
Using a CA3030, this circuit was found in the May 1988 Radio Electronics magazine. The power...