Smoke Detector Alarm Using LM358

In this tutorial, I will be going to show you a simple smoke detector alarm without using any microcontroller. A smoke detector alarm is a smoke detecting gadget that shows fire. Smoke alarms are exceptionally normal in homes, workplaces, schools, and industries. Smoke alarms are extremely helpful gadgets as the harm brought about by fire mishaps is disastrous. These days, smoke alarms and smoke cautions are modest as its use is expanding and the expense of assembling is diminishing. In this undertaking, we are executing a basic smoke detector alarm circuit utilizing basic equipment. We utilized a Gas/Smoke sensor for distinguishing smoke.

There are two kinds of smoke alarms i.e Photoelectric smoke alarms and Ionization smoke alarms.

Photoelectric smoke alarms comprise a light source like LED and a light detector like a photocell. The photocell leads as long as the light falls on it. When there is smoke, the light from the source is hindered and the photocell doesn’t conduct. 

Ionization smoke alarms comprise of two cathodes and an ionization chamber loaded up with particles. When there is no smoke, the particles move openly and the electrodes conduct typically.

Within the sight of smoke, the chamber is loaded up with smoke and intrudes on the development of particles. The anodes don’t conduct any longer. Contingent upon the kind of sensor and maker, the conductivity conditions may change yet the thought continues as before. 

In view of the output of the smoke alarm, a caution framework can be executed. 

The sensor utilized in this project is the MQ-2 Gas/Smoke sensor. It is delicate to LPG, Hydrogen, Smoke, Methane, Propane, Alcohol, Butane, and other mechanical burnable gases. 

It has two anodes made of Aluminum Oxide (Al2O3) and a warming component made of Tin dioxide (SnO2) which goes about as the principle detecting layer.

Circuit Diagram

smoke detector alarm

Components Required

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

Working of Smoke Detector

Smoke detector alarm is outstanding gadgets as they are little, modest yet helpful. In this project, we actualized a simple smoke detector alarm circuit with customizable affectability. 

We utilized a smoke sensor MQ-2 as the fundamental tangible gadget. The working of the smoke detector alarm circuit is simple and is clarified beneath. 

LM358 IC goes about as a comparator in this circuit. The transforming terminal of the LM358 IC is associated with POT so the affectability of the circuit can be balanced. 

The output of the LM358 IC is given to a LED as a marker although a buzzer can be utilized as an alert. The non-modifying terminal of LM358 IC is associated with the output of the smoke sensor. 

At first, when the air is perfect, the conductivity between the terminals is less, as the resistance is in the order of 50 KΩ. The inverting terminal input of the comparator is higher than the non-inverting terminal input. The pointer LED is OFF. 

In the case of a fire, when the sensor is loaded up with smoke, the resistance of the sensor falls to 5 KΩ, and the conductivity between the terminals increases. 

This gives a higher contribution at the non-inverting terminal of comparator than the inverting terminal and the output of the comparator is high. The disturbing LED is turned ON as a sign of the essence of smoke.

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