Simple Smoke Detector Alarm Circuit using MQ02

Last Updated on March 16, 2024

Simple Smoke Detector Alarm circuit using MQ02 designed with few easily available components. Main part of this circuit is Gas sensor MQ-02 which is capable of detecting Smoke, LPG, Propane and Hydrogen. It can be used in different types of applications where the smoke and other mentioned gas leak detection required.

The following prototype is a test circuit and it can be constructed through breakout board and PCB after calibration of each components. This smoke detector circuit will produce visible and audible alert when smoke detected.

Circuit Diagram

Components Required

  1. MQ-02 gas sensor
  2. IC LM358
  3. Resistor 10KΩ, 100Ω
  4. Variable Resistor 10KΩ
  5. Capacitor 0.1µF
  6. LED
  7. Buzzer
  8. Battery

Construction & Working

To construct this circuit start with gas sensor MQ-02 and combine B1,B2 and HB terminals and connect with bias terminal then combine A1, A2 terminals and connect to the Non inverting terminal of Operational amplifier. Connect HA to negative bias terminal. Variable Resistor is connected between positive and negative terminal of bias and variable terminal is connected to the inverting terminal of operational amplifier hence we can change the sensitivity by varying the value of RV1 (Variable Resistor).

Amplifier output is connected with the LED and Buzzer, when the smoke detected by MQ-02 sensor then it will change the sensing resistance value and operational amplifier increase the output by the way LED and Buzzer start to indicate and alert.

MQ-02 Sensor

Every gas sensor starts with MQ will have six terminals and two are Heater (H) and remaining A side and B side, depends on the sensor Resistance value between A and B terminals varies and during the operations A or B side Resistance taken as a Sensing Resistance value.

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