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Last Updated on: Wednesday, June 02, 2021 06:28 AM

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More  Alarm Circuits   Freezer / Frost Alarms

Freezer Over-Temperature Alarm

A typical freezer can contain hundreds of dollars with of food.  If the device becomes unplugged or if the door is left open too long, the food inside can quickly become spoiled.  The hobby circuit below is a battery powered alarm system, which is attached to the outside of the freezer using a couple strong magnets.
Two small gage wires are fed from the alarm box to a thermistor temperature sensor, mounted inside the freezer.  The alarm beeper will be activated, whenever the electronic circuit detects a freezer temperature warmer than 0 degrees C (32 F).  The overall current is so low that the 9v battery powering the device will last for many years.

This circuit turns on a beeper whenever the inside temperature of a freezer is greater then zero degrees Centigrade.  The circuit draws only a few microamps from a 9 volt battery.  It uses a glass bead thermistor accurate to 1 degree C.


Click on Circuit Below to view PDF of Schematic

Alarm:  Freezer Over-Temp, David Johnson, 7/20/2006

More  Alarm Circuits   Freezer / Frost Alarms

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