Smoke Detector Alarm Using LM358

I’ll demonstrate how to make a basic smoke detector alarm in this article without the need for a microcontroller. A smoke detector alarm is a device that indicates fire and detects smoke. Smoke alarms are a standard feature in homes, offices, schools, and businesses. Smoke alarms are incredibly useful devices since fire accidents can cause catastrophic damage. These days, smoke alarms and smoke warnings are minimal since their applications are growing and their assembly costs are decreasing. We are using simple equipment to create a rudimentary smoke detector alarm circuit in this project. To differentiate smoke, we used a Gas/Smoke sensor.

Smoke alarms are classified into two categories: photoelectric and ionisation.

A light source, such as an LED, and a light detector, such as a photocell, make up photoelectric smoke alarms. As long as it receives light, the photocell will function. Smoke obstructs the light from the source, preventing the photocell from conducting.

Two cathodes and an ionisation chamber filled with particles make up ionisation smoke alarms. The particles travel freely and the electrodes conduct normally when there is no smoke.

The chamber fills with smoke as soon as it is visible, interfering with the growth of the particles. The anodes are no longer conducting. The conductivity conditions can vary depending on the type of sensor and maker, but the idea remains the same.

Based on the smoke alarm’s output, a warning system may be implemented.

This project uses the MQ-2 Gas/Smoke sensor as its sensor. LPG, hydrogen, smoke, methane, propane, alcohol, butane, and other mechanically burnable gases are all harmful to it.

Its primary detecting layer is a warming component made of tin dioxide (SnO2), and it contains two anodes built of aluminium oxide (Al2O3).


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Circuit Schematic

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MQ-2 Gas Sensor
LM358 IC
Resistor (10 KΩ, 330 Ω
0.1µF Ceramic Capacitor
10 KΩ Potentiometer

Working Principle of Smoke Detector

The smoke detector alarm is a fantastic device because it is small, simple, and very functional. In this project, we implemented an affordable, simple smoke detector alarm circuit.

We used a MQ-2 smoke sensor as our primary physical device. The smoke detector alarm circuit’s basic operation is explained below.

This circuit uses the LM358 integrated circuit as a comparator. Because the LM358 IC’s transforming terminal is connected to POT, the circuit’s affectability can be balanced.

Although a buzzer can be used as an alert, the output of the LM358 IC is provided to an LED to serve as a marker. The smoke sensor’s output is connected to the non-modifying terminal of the LM358 IC.

When the air is ideal, there is initially less conductivity between the terminals because of a resistance of about 50 KΩ. The comparator’s inverting terminal input is higher than its non-inverting terminal input. The LED pointer is not on.

When a fire occurs, the conductivity between the terminals increases and the sensor’s resistance drops to 5 KΩ when it is filled with smoke.

As a result, the comparator’s output is high and its non-inverting terminal receives a larger contribution than its inverting terminal. As a warning that smoke is present, the unsettling LED turns on.

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