This circuit was found in the June 1991 issue of Radio Electronics magazine. The circuit uses two Hall effect sensors of the time. It can be assembled using modern equivalents.
We found this version of the siren that makes the American police siren sound in a 1980...
This circuit was found in old American documentation. The operational amplifiers are from the...
This simple very low power circuit can be used in a battery powered infrared tone trigger. We...