Fire Alarm System Using Thermistor & LM358

In this article, I’ll walk you through building a basic fire alarm system that uses a small range to detect nearby fires. The sensor then triggers the op-amp LM358 to provide an audible output through a buzzer.

One component of a security system that helps in identifying or avoiding critical damages in commercial premises, apartment buildings, stores, workplaces, and numerous other places is a fire alarm circuit.

A variety of miniature fire alarms are available, including the LM358 alarm, NE555 timer alarm, LM341 alarm, transistor-type alarm, and several others. For my project, I’ll be utilizing the LM358 op-amp integrated circuit. Along with the circuit workings, connections, and thorough schematic, I’ll also show you the working principle and its applications.

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Fire alarm system using lm358

Circuit Schematic

Fire alarm system using lm358


  • 10 KΩ Thermistor
  • LM358 Op-Amp
  • 4.7 KΩ Resistor
  • 10 KΩ Potentiometer
  • Buzzer
  • Jumper Wire
  • Breadboard
  • 5V Power Supply

Circuit Connection of Fire Alarm System

The schematics and parts of the basic fire alarm circuit design are described above. Well, let’s see the connection we can find.

First, attach the 10 KΩ potentiometers to the LM358 IC’s inverting terminal. The middle terminal of the potentiometer is attached to the pin, one end is linked to GND, and the other end is connected to +5V.

As a potential divider, we will now add a 10 KΩ thermistor and 10 KΩ resistors. The non-inverting terminal of the LM358 op-amp is linked to the potential divider’s output, or junction point.

Next, a buzzer has been selected for this project in order to sound the alarm. Thus, directly link the buzzer to the LM358 IC’s output.

Following this, pin 8 of the LM358 IC will be directly linked to +ve, and pin 4 to -ve.

Working Principle of Fire Alarm System

As was previously mentioned, the design of the basic fire alarm circuit connections. Now let’s examine the basic fire alarm circuit’s operation. The 10 KΩ thermistor is the primary component used in this instance to detect the fire. As the temperature rises, the integrated thermistor’s resistance falls and the voltage divider’s output rises.

The voltage divider’s output will exceed the inverting input’s value since it is connected to the LM358 IC’s non-inverting input terminal. As a result, the op-amp’s output rises and the alarm buzzer is turned on.

Applications of Fire Alarm System

In residential situations, installing a fire alarm system with the LM358 IC offers a crucial safety feature. The circuit can identify heat or smoke and trigger an alarm to warn residents of any fire threats.

To improve safety in factories with the possibility of increased fire hazards, the LM358-based fire alarm system can be used. It can be included in systems to detect and address possible fire problems quickly, resulting in minimizing the risk of accidents and property damage.

It’s critical that office buildings have evacuation plans. Installing the LM358 IC-based fire alarm system would establish a reliable fire detection system that will ensure that residents are quickly notified in a situation of smoke or fire, allowing a quick escape.

Important infrastructure is kept in data centers, where fires can cause service interruptions and data loss. In data centers, installing a fire alarm system with the LM358 IC adds an additional degree of security by enabling early detection and immediate notification of potential fire risks.

It is also possible to modify the LM358-based fire alarm circuit for usage in automobiles. The installation of a fire detection system enhances passenger safety by assisting in the identification and reduction of possible fire hazards in vehicles, as cars, trucks, or other modes of transportation.

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