Refrigerator door alarm circuit with two 555 timers
This refrigerator door alarm circuit alerts you when the door has been left open. Very important, because the power consumption increases when this happends. It uses the popular 555 timer IC
This light sensitive alarm is very simple and works using, as main components, a transistor, an LDR and a relay.
The alarm activates when the illumination level changes from almost total darkness to a moderately high illumination level. When this happens the alarm is locked and the alarm signal, be it a light or a sound, remains active.