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Car Radiator Hot Indicator Circuit

The proposed circuit is very useful which warns the car driver before hand once the radiator gets heated up above the preset level.

How it Works

The working of this circuit is very simple and works off on the car battery. The familiar IC555 is used here which is the heart of the circuit. The thermistor used here triggers the pin2 of the IC and it in turn makes its output high and it gives a buzzer indication when the temperature goes above the preset level.

The variable resistors should be suitably adjusted so that the buzzer rings at a certain temperature by using variable power supply of 12v.

How to Set up the Circuit

You may use a candle to set the circuit. BUT REMEMBER NOT TO PUT THE THERMISTOR TOO CLOSE TO CANDLE OR ELSE THE THERMISTOR DAMAGES. And after setting the circuit, clean the thermistor to remove soot deposits.



The setting of the circuit is now complete. You may keep the entire circuit in a plastic casing with hole for power supply and the sensor.

Keep the sensor (thermistor) near the car radiator and the circuit inside the car. If you feel difficult to use the key switch, you may include a small switch and connect the circuit directly to battery. But you should switch it on every time manually.

Circuit Diagram

Parts List 

R1-5k variable resistor,

R2-NTC thermistor, 50k,

R3-5k variable resistor,

R5-470ohms,

LED1-green,

LED2-red,

C1-10nf.

Written and Submitted by: ss kopparthy

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About the Author

I am an electronic engineer (dipIETE ), hobbyist, inventor, schematic/PCB designer, manufacturer. I am also the founder of the website: https://www.homemade-circuits.com/, where I love sharing my innovative circuit ideas and tutorials. If you have any circuit related query, you may interact through comments, I'll be most happy to help!



2 thoughts on “Car Radiator Hot Indicator Circuit”


  1. Howdy, Friend! Interested to Learn Circuit Designing? Let's Start Discussing below!
  2. While this simple design is good enough for basic temperature detection, it will give poor result in automotive environment.

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