This circuit, enclosed into a small box, is placed in the fridge near the lamp (if any) or the opening. With the door closed the interior of the fridge is in the dark, the photo resistor R2 presents a high resistance (up to 200K) thus clamping IC1 by holding pin 12 high. When a beam of light enters from the opening, or the fridge lamp illuminates, the photo resistor lowers its resistance (less 2K), pin 12 goes low, IC1 starts counting and, after a preset delay (20 seconds in this case) 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 allows the piezo sounder beeping 3 times per second.
Circuit diagram:
Parts:
R1 = 10K
R2 = LDR
R3 = 100K
R4 = 100K
D1 = 1N4148
D2 = 1N4148
Q1 = BC337
C1 = 10nF-63V
C2 = 100uF-25V
B1 = 3V Battery
IC1 = 4060 Ripple Counter & Oscillator IC
BZ1 = Piezo Buzzer Incorporating 3KHZ Oscillator
SW1 = Miniature SPST Slider Switch
Notes:
- Connecting D1 to pin 2 of IC1 will halve the delay time.
- Delay time can be varied changing C1 and/or R3 values.
- Any photo resistor type should work.
- Quiescent current drawing is negligible, so SW1 can be omitted.
- Place the circuit near the lamp and take it away when defrosting, to avoid circuit damage due to excessive moisture.
- Do not put this device in the freezer.
2 comments:
Hi !
Can you tell me about idle power consumption of this circut, how much is it ?
I want to make it as small as possible so can i use for example LR2032 as B1 (one or more - single battery is about 50mAh so package is possible)?
thanks for reply !
hye, recently am working on this circuit. but, am having a few problems and i hope u can help me.
1. the buzzer did not stop sounded and can i know why?
2. i've been understood that this circuit, when photoresistor did not detect any lights, the buzzer did not sounded. but mine, the buzzer goes on and on without stop. it will only stp when i remove the battery.
3. when i simulate this circuit, the buzzer goes on and its working. so do with the hardware. its working but the buzzer did not stop at all. it also did not stop when the photoresistor did not detect light. is there any problem with the ic u think? and others ic pins that we did not use, i connect it to the ground in the simulation but not hardware. is that okay?
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