This circuit will help you to save your electricity bill. Incase if you leave the fridge door open more than twenty seconds. The circuit consumes very little current as it can operates by a 3 volts battery. You can enclose this whole circuit in a small box and keep inside the fridge.
R2 is a photo resistor. Normally photo resister has a low resistance but when you close the fridge door, with the darkness the photo resister’s resistance will go high. When you open the door fridge lamp will light and photo resister’s resistance goes down.
Then the IC1 start its action. You can set the preset according to your wish but in this circuit it is set for 20 seconds delay. After 20 seconds the piezo starts beeps until you close the door.
Remember not to place the alarm box inside the freezer try to place it near the lamp.
