Tuesday, February 22, 2011
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.
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| Buzzer Burglar Alarm Circuit For Refrigerator |
- 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.
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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