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.
This circuit uses a 741 operational amplifier that must be powered by a symmetrical source of 6 to...
This oscillator generates a 1 kHz signal, using an old germanium PNP transistor. The circuit was...
This circuit was obtained from a Radio Electronics issue from January 1989. The indicator is a...