This circuit was found in the July 1992 issue of Radio Electronics magazine. The circuit is based on a 741 that activates a buzzer with oscillator. R5 adjusts the sensitivity.
Two inverters of a 4069B type CMOS integrated circuit form this oscillator which is characterized by having...
Raytheon's used operational amplifier is rare today, but the configuration can be adapted to use...
Found in a radio amateur magazine of the 1980s, this circuit uses components that can still be...