Wednesday, September 19, 2012

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Buzzer Burglar Alarm Circuit For Refrigerator

This circuit, enclosed in a small box, is placed in the fridge near the lamp. With the door closed the interior of the fridge is in the dark, the LDR R2 has a high resistance about 1000K ohm thus clamping IC1 by holding pin 12 high. When a beam of light enters from the opening, or the fridge lamp lights, the photo resistor lowers its resistance, pin 12 goes low, IC1 starts counting and, after a preset delay, the piezo sounder beeps for 20 sec. then stops for the same lapse of time and the cycle repeats until the fridge door closes. D2 connected to pin 6 of IC1 makes the piezo sounder beeping 3 times per second.
Buzzer Burglar Alarm Circuit For  Refrigerator
Note:
  • Delay time can be varied changing C1 and/or R3 values.
  • Place the circuit near the lamp and take it away when defrosting, to avoid circuit damage due to excessive moisture Don't place it in the freezer.
List Componet Of  Buzzer Burglar Alarm Circuit
R1    : 10K 
R2    : LDR (any type)
R3,R4 : 100K 
C1    : 10nF Polyester Capacitor
C2    : 100µF/25VD1
D2    : 1N4148
IC1   : 4060
Q1    : BC337
BZ1   : Piezo sounder (incorporating 3KHz oscillator)
SW1   : SPST slide Switch

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