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 NXP Semiconductors


  • Fridge Door Alarm

  • Created: Oct 21, 2014

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Summary

Keeping the door fridge open is costly considering that when cold air escapes, it is replaced by warm air causing the compressor to drive the warm air out to preserve the normal temperature. As much as it could contribute in elevating the monthly electric bill, it could also spoil the food. Thus, it does not only waste energy but also the food inside the fridge. However, this problem may be eliminated with fridge door alarm. The device beeps when the door is opened over 20 seconds which may annoy the last person who accidentally kept the fridge open. This project uses 74HC4060D, a high speed SI-gate CMOS device with 14 stage ripple-carry counter/divider and oscillator terminals, ten buffered outputs and an overriding asynchronous master reset.


This circuit will be enclosed in a small box which will be placed in the fridge near the lamp or at the opening. With the door closed, the interior of the fridge is dark. The photo resistor R2 has a high resistance greater than 200K and clamping at U2 is done by holding pin 12 (MR) high. When a beam of light enters from the opening, or when the fridge lamp lights, the photo resistor lowers its resistance less than 2K. Pin 12 goes low and U2 will start counting. After a preset delay of 20 seconds, the piezo sounder beeps for 20 seconds then stops for the same lapse of time and the cycle repeats until the fridge door closes. Moreover, D2 connected to pin 6 of U2 makes the piezo sounder beeping 3 times per second. Furthermore, delay time can be varied by changing C1 and/or R3 values.


Fridge door alarm is an essential alarm system in keeping the door closed at all times. It is an interesting project that can be constructed by anyone with components that are commonly available. This can be placed to any refrigerator so that an opened door is recognizable.

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