Build Your Fridge Door Alarm: 20-Second Timer Circuit

An audible alert is triggered if the door remains open for over 20 seconds.

Operation using a 3V battery, straightforward design.

Circuit Diagram:

Components:

Circuit Operation:

This circuit, housed within a small enclosure, is situated within the refrigerator alongside the illumination (if available) or the access point. When the refrigerator door is sealed, the interior is shadowed, resulting in a high resistance (>200K) exhibited by the photoresistor R2, thereby maintaining pin 12 of IC1 at a high level. Upon entry of a light beam from the opening or activation of the refrigerator lamp, the photoresistor's resistance decreases (<2K), causing pin 12 to drop, and IC1 commences counting. Following a predetermined delay (20 seconds in this case), the piezo sounder emits a beep for 20 seconds, then pauses for the identical period, and the cycle repeats until the refrigerator door is closed. D2, connected to pin 6 of IC1, ensures the piezo sounder generates a frequency of 3 times per second.

Integrated Circuit Description: IC1 4060

The 4060 is a widely utilized 14-stage ripple counter and oscillator IC. This integrated circuit functions as a precise timekeeping device, generating accurate delays and oscillations. Its core functionality lies in counting pulses to produce a specific delay duration, making it ideal for applications like timer circuits, frequency generation, and signal processing. It’s known for its stability and reliability, contributing to the overall performance of this circuit.

Notes: