Fridge Alarm Circuit

The simple fridge alarm circuit will alert the user in case the fridge malfunctions with its specified temperature cycle specifications.

The use of fridge in homes has become a de facto. Recent developments in fridge have defined sophisticated systems that can run even with less human intervention. But there are issue with the old fridge, which are not so equipped enough for self-control and need periodic checkup to if the system is running smoothly. One of the major issues in a refrigerator is to control the temperature and is mainly valid for those fridges which are not up-to-date. This article therefore aims to build an alert system to determine if the running temperature is not more than the temperature pre-set into the system.
The circuit below will show the way to design a circuit which will generate alarm as soon as the temperature of the fridge goes above 5C.
The following design is the circuit diagram of the proposed simple fridge alarm circuit project:

Circuit diagram of fridge alarm system
As per the above diagram, TH1 thermistor is deployed as the temperature sensor. The resistance of the thermistor changes with the surrounding temperature. Furthermore, CL7611 IC1is added with the thermistor to develop the entire process of the system. To indicate battery status, we have used IC2. The LED1 used in the circuit will glow once the temperature goes above 5C.
However, following are the parts that are needed to develop the system:
Resistors Semiconductors Others
R1, R2 = 4.7 MΩ IC1 = CL7611 Push-to-on switch = SW1
R3 = 2.2 MΩ IC2 = 8211 GL16 thermistor= TH1
R4 = 56 KΩ T1 = 2TX300
R5 = 12 KΩ LED1 = RED
R6 = 10 KΩ LED2 = Green
R7 = 270 Ω
R8 = 390 Ω

Designing an alarm circuit to control temperature of a refrigerator is not a complex procedure. The parts listed in the document are easily available in the market. Following this design will surely ease building up the the system.