This 2-quadrant modulator circuit was found in the May 1988 issue of Radio Electronics magazine. The CA3080 is an OTA operational amplifier.
The circuit shown triggers a relay when the current rises up to a value depending on R1 according...
This automotive circuit was obtained from an 80's schematic from the integrated circuit factory...
This circuit locks when the sensors are opened. The relay can be 6 or 12 V depending on the power...