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.
Found in a Motorola documentation from the 70s, this circuit makes use of transistors of the time....
This circuit was found in Motorola documentation from 1968. SCRs can be modern equivalents and the...
I found this circuit in a documentation about thyristors from the 70s. The circuit uses a diac...