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MQ135 Gas Sensor Module


The material of MQ135 is SnO2, it is a special material: when exposed to the clean air, it is hardly being conducted, however, when put it in an environment with combustible gas, it has a pretty performance of conductivity. Just make a simple electronic circuit, convert the change of conductivity to a correspond output signal. MQ135 gas sensor is sensitive to Ammonia, Sulfide, Benzene steam, smoke and other harmful gases. Used for family, surrounding environment noxious gas detection device, apply to ammonia, aromatics, sulfur, benzene vapor, and other harmful gases/smoke, gas detection, tested concentration range: 10 to 1000ppm. In normal environment, environment which don’t have detected gas, set senor’s output voltage as reference voltage, analog output voltage will be about 1V, when sensor detect gas, harmful gas’s concentration increases 20ppm per voltage increase 0.1V.


Technical Data

Input voltage: DC 5V

Current: 150mA

Digital Output: TTL 0 is 0.1V and TTL 1 is 5V

Analog Output: 0.1 to 0.3V (it seems that there’s almost no pollution), when harmful gas’ concentration reach max, analog output will become 4V

Tip: MQ5 sensor module needs about 20s to preheat, measuring data will be stable in this way, by the way, sensor module will heat, that’s normal, because there’s a heating wire in it, however, if it’s getting too hot, it must have problem in your circuit. 



Symbol        Detect Gas                      Detect Concentration

MQ-2          combustible gas                  300-10000ppm

                   Smoke, hydrogen


MQ-5          LPG, natural gas                  300-10000ppm

                              Town gas

MQ-135        Carbon oxide, coal gas        300-10000ppm


Working voltage: DC 5V

Working Current: 150mA

DOUT: TTL output

AOUT: Analog output

Preheat time: Over 20s

Dimension: 32mm x 22m x 27mm (HIGH 27mm)

low cost

suitable to any application

sensor module needs 20s to preheat, or the measuring data won’t be stable.

It’s normal that the sensor module is heat, because there’s the heat wire and it is not normal when sensor module is too hot



int LED=13;            //the build-in LED pin

int MQ135=5;            //MQ135’s output pin

void setup()


 pinMode(LED, OUTPUT);      //LED is output

 pinMode(MQ135, INPUT);       //MQ135 is input

 Serial.begin(9600);       //serial monitor's baud rate is 9600


  void loop()


    int MQValue=digitalRead(MQ135);



      digitalWrite(LED, HIGH);      //write high level to LED

      Serial.print("There is harmful gas");




        digitalWrite(LED, LOW);     //write low level to LED

        Serial.print("It's clean");