High-temperature alarm circuit using Lm358 – Technoreview85

Last Updated on April 21, 2022 by technoreview85

It is a high-temperature alarm or over-temperature alarm system electronic project.

High-temperature alarm
High-temperature alarm

In this article, I am going to describe how you can make an easy temperature alarm circuit using an operational amplifier IC LM 358.

It is an easy electronic project idea. As a temperature sensor, I will use an NTC thermistor.

You can make this circuit on a breadboard or you can use a perf board.

Working of this project

I am using a thermistor as an analog sensor.

Actually, a thermistor is a resistor & Its value decreases when the temperature is increased.

 Generally, the same sensor is used in the 3D printer print bed & hot end to control temperature. 

When the thermistor’s value is decreased then the op-amp IC LM 358 output pin 1 becomes high. An active buzzer & a Led are connected to the IC output pin so the LED & buzzer are turned on. Ic pin 3 is an input pin so the thermistor is connected to ic pin 3.

Over heat alarm Adjust
Over heat alarm Adjust

You can control temperature sensitivity using a potentiometer that is connected to the ic pin 2.

What is an operational amplifier?

An operational amplifier or op-amp is an integrated circuit. It has two inputs. One of them is called an inverted pin which is marked as a (-) negative sign and another is called non-inverted pin which is marked (+) positive sign.


It has one output pin.

Its basic work is to amplify and output the voltage difference between the two input pins.

Ic lm358 has two op-amps.it is a dual op-amp Ic.

Applications of this circuit

Over heat alarm
Over heat alarm

Over-temperature alarm for industrial purposes. Alarm systems for big electrical appliances,

You can use it as a fire alarm to prevent disasters at the home, office, school etc.

You need to make

  1. Active Buzzer ( passive buzzer will not work )
  2. Resistor 1K, 2.2K
  3. Potentiometer 10K
  4. Perfboard 
  5. LED
  6. Ic LM358 & 8 pin Ic base
  7. 9V Battery & Battery connector
  8. Thermistor 10K
Active Buzzer
Active Buzzer

Project video 

Circuit diagram

High-temperature alarm circuit
High-temperature alarm circuit

Spacial connection diagram with practical components

High-temperature alarm circuit
High-temperature alarm circuit

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