Fridge door Alarm using IC 4060
Beeps if you leave open the door over 20 seconds
3V battery operation, simple circuitry
The track, closed into a small box, placed in the refrigerator in the vicinity of the light (if any) or open. With the closed doors inside the refrigerator is in the dark, the photo resistor R2 made the anti-high ( “200,000), thus blocking the IC1 pin on the 12th held high. When the beam into the open, lights or light Fridge, photos Resistance to lower its resistance “(<2K), 12 do not have to pin low, IC1 started to count in the pre-delay time (20 seconds in such a case) of the piezoelectric sound beeps for 20 seconds. And then stopped at the same time, and repeat the cycle until the refrigerator door closed. Class D2 is connected to pin 6 IC1 so that the piezoelectric sound beeps 3 times per second.
