This circuit that detects when the refrigerator is not working properly was found in the February 1997 Electronics Now magazine.
The output voltage depends on the zener diode. Zener in the range between 1.2 to 12 V rated to 1 W...
This shield with full-wave triggering was found in the Radio Electronics Experimenter magazine of 1989....
We obtained this circuit in a Maxim documentation from the 90s. The circuit is based on the...