This approach alarm circuit was found in the September 1970 Radio Electronics issue. The 1 mH coil is wound on a ferrite rod. The relay is 12 V sensitive.
For those who like experimental circuits, here is a sequential flasher system with LEDs, which can be...
This circuit can be used in broilers, greenhouses, drying chambers to regulate the temperature in a simple...
This circuit consists of an electrostatic sensor that can check if a cable is energized by simply...