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A refrigerator door alarm circuit

2016-02-18 13:45  
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Next comes the refrigerator door alarm circuit theory. Generally, this circuit is enclosed in a small box in the refrigerator near the lamp (if available) or open. In the closed door of the refrigerator's interior is in the dark, this photo resistor R2 has a high  resistance  (> 200 k) thus clamping IC1 pin 12 held high. When a beam of light entering from the open, or in a refrigerator lamp light, this photo resistor reduces its resistance (<2 k), pin 12 is low, IC1 starts counting, after a preset delay (20 seconds in this case) Pressure electrical sounding beeps 20 seconds and then stops for the same period of time and the cycle is repeated until the refrigerator door closed. D2 connecting pin 6 of IC1 piezoelectric sounder beeps 3 times per second. The circuit is connected to pin 2 D1 IC1 half the delay time. Delay time can be varied changing C1 and / or R3 values. SW1 in the circuit can be eliminated. The circuit is close to lights and take it away when defrosting, to avoid circuit damage due to excessive moisture. Do not put it in the refrigerator.

 

FridgeAl refrigerator door alarm

Parts:

R1____________10K 1/4W Resistor
R2___________Photo resistor (any type)
R3,R4________100K 1/4W Resistors

C1____________10nF 63V Polyester Capacitor
C2___________100?F 25V Electrolytic Capacitor

D1,D2_______1N4148 75V 150mA Diodes

IC1___________4060 14 stage ripple counter and oscillator IC

Q1___________BC337 45V 800mA NPN Transistor

BZ1__________Piezo sounder (incorporating 3KHz oscillator)

SW1__________Miniature SPST slide Switch

B1___________3V Battery (2 AA 1.5V Cells in series)