How to Choose GAS sensor?



Confused, How to choose GAS detection sensor? Here this article gives detailed Information about gas sensors, it may fetch best GAS sensor to your Project design.

When we are search about gas sensors or detectors the first thing we get is MQ-XX series sensors. The MQ series of Gas sensors are used to detect different Gas forms. Basically every MQ sensors has one Heater inside with an electro-chemical sensor. They are best to smell Gas in indoors at room temperature, by connecting load resistor as variable one we can calibrate the sensor gas detection sensitivity more or less.

The MQ series sensors gives analog output hence it can be easily driven by the Arduino development boards, some breakout boards with ADC gives Digital and Analog outputs.

How the Sensor to be connected

Before get into the wiring of Gas sensor refer data sheet of that particular sensor, and follow wiring as per the instruction given in datasheet. Mostly the MQ series sensor can be connected as illustrated here.


Connect both A pins together and B pins together and apply +Vcc supply to the coupled A or B pins and apply Ground (Gnd) through variable load resistor (RL) to the remaining coupled A or B pins. Make sure that heater pins H & H connected with Vcc and Gnd. Don’t interconnect A and B pins or don’t make mistakes in the wiring if any thing goes wrong the sensor could get damaged, Otherwise you are advised to use breakout boards.

The Heater and Load Resistor


The sensor operation is mainly depends on heater coil, the sensor heater uses 5V Dc supply otherwise PWM pulses from 2V to 5V amplitudes. Important thing is No H pins (heater) directly connected to the micro-controller or Arduino board because it draws much current .

The sensor get warm by using this heater and this time taken for warm is called as “burn-in time” it may upto 3 minutes for MQ sensors.

The Load Resistor at the output to ground may valued from 2KΩ to 47KΩ, when you connecting lower value it brings the less sensitivity, and the higher value gives good sensitivity but less accurate for higher concentration of Gas. The best practice is to make RL as variable resistor.

GAS sensor Pinout


Consider this MQ-XX series sensor, these are have 6 pins namely two heater pins, two A terminals and two B terminals.

Both upside and down side we can use A and B pins as stated in How the sensor to be connected.

Before considering the pins refer corresponding sensor datasheet.



List of GAS sensors

Here the list of Gas sensors given, according to your design need you can adopt suitable one.

Name of Sensor Sensitive For
MQ2 Sensitive for Methane- Butane-LPG- smoke.
MQ3 Sensitive for Alcohol- Ethanol- smoke.
MQ4 Sensitive for Methane- CNG Gas.
MQ5 Sensitive for Natural gas- LPG.
MQ6 Sensitive for LPG- butane gas.
MQ7 Sensitive for Carbon Monoxide.
MQ8 Sensitive for Hydrogen Gas.
MQ9 Sensitive for Carbon Monoxide- flammable gasses.
MQ131 Sensitive for Ozone.
MQ135 For Air Quality Sensitive for Benzene-Alcohol- smoke.
MQ136 Sensitive for Hydrogen Sulfide gas.
MQ137 Sensitive for Ammonia.
MQ138 Sensitive for Benzene-Toluene- Alcohol- Acetone- Propane- Formaldehyde gas- Hydrogen gas.
MQ214 Sensitive for Methane- Natural gas.
MQ216 Sensitive for Natural gas-Coal gas.

How the Sensor Appears

Just for view here the appearance of Gas sensors are given.









Images are credited to their respective owners, and it is here for learning only.

Application Circuit


This application circuit can be used for any MQ-xx series Gas sensors and it gives visual par graph for Gas concentration sensed by the sensor.





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