Lesson 22 Gas Sensor

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Gas Sensor MQ-2 is a sensor for flammable gas and smoke by detecting the concentration of combustible gas in the air. They are used in gas detecting equipment for smoke and flammable gasses in household, industry or automobile.

Required Components

 1 * Raspberry Pi

– 1 * Breadboard

 1 * Active Buzzer module

– 1 * PCF8591

– 1 * Gas sensor module

– 1 * 3-Pin anti-reverse cable

– 1 * 4-Pin anti-reverse cable

– Several Jumper wires

Experimental Principle

MQ-2 gas sensor is a kind of surface ion type and N-type semiconductors, which uses tin oxide semiconductor gas sensitive material. When ambient temperature is in 200 ~ 300℃, tin oxide will adsorb oxygen in the air and form oxygen anion adsorption to decrease electron density in semiconductor so as to increase its resistance. When in contact with the smoke, if grain boundary barrier is modulated by the smoke and changed, it could cause surface conductivity change. So you can gain the information of the smoke existence, The higher the smoke concentration is, the more conductive the material becomes, thus the lower the output resistance is.

In this experiment, if harmful gases reach a certain concentration, the buzzer will beep to warn. 

The schematic diagram of the module is as shown below:

Experimental Procedures

Step 1: Build the circuit. 

Raspberry PiGPIO Extension BoardPCF8591 Module
Gas Sensor ModuleGPIO Extension BoardPCF8591 Module
Raspberry PiGPIO Extension BoardActive Buzzer Module

For C Users:

Step 2: Change directory. 

    cd /home/pi/SunFounder_SensorKit_for_RPi2/C/22_gas_sensor/

Step 3: Compile.

    gcc gas_sensor.c -lwiringPi

Step 4: Run.

    sudo ./a.out

For Python Users:

Step 2: Change directory.

    cd /home/pi/SunFounder_SensorKit_for_RPi2/Python/

Step 3: Run.

    sudo python3 22_gas_sensor.py

Place a lighter close to the MQ-2 gas sensor, and press the switch to release gasses. A value between 0 and 255 will be displayed on the screen. If harmful gases reach a certain concentration, the buzzer will beep, and “Danger Gas!” will be printed on the screen.

You can also turn the shaft of the potentiometer on the module to raise or reduce the concentration threshold.

The MQ-2 gas sensor needs to be heated up for a while. Wait until the value printed on screen stays steady and the sensor gets warm, which means it can work normally and sensitively at that time.

Note: It is normal that the gas sensor generates heat. Actually, the higher the temperature is, the sensor is more sensitive.