Based on the BA1404 integrated circuit, this circuit was found in the July 1992 issue of Radio Electronics magazine. The circuit is short range, but a power amplifier stage can be used.
In this circuit, obtained from a 1979 publication, IC1 is a 555 and IC2 is a 4020. The transistor is the...
The presented circuit uses a window comparator to keep a relay activated only when the sensor is...
Similar circuits can be found on this site. This is from an 80's American documentation. The...