The MQ-135 gas sensor is used to measure air quality. The MQ series of gas sensors use a small heater inside with an electrochemical sensor. They are sensitive to a range of gasses and are used indoors at room temperature. The output is an analog signal and can be read with an analog input of the Arduino. Based on its fast response time. Measurements can be taken as soon as possible. Also, the sensitivity can be adjusted by the potentiometer.

Sensitive material of MQ-2 gas sensor is SnO2, which with lower conductivity in clean air. When the target combustible gas exists, The sensor’s conductivity is higher along with the gas concentration rising.


The MQ-135 alcohol sensor consists of a tin dioxide (SnO2), a perspective layer inside aluminum oxide microtubes (measuring electrodes) and a heating element inside a tubular casing. The end face of the sensor is enclosed by a stainless steel net and the back side holds the connection terminals. Ethyl alcohol present in the breath is oxidized into acetic acid passing through the heater element. With the ethyl alcohol cascade on the tin dioxide sensing layer, the resistance decreases. By using the external load resistance the resistance variation is converted into a suitable voltage variation.  The MQ135 gas sensor has high sensitivity to Ammonia, Sulphide and Benzene steam, also sensitive to smoke and other harmful gases. It is with low cost and suitable for different applications such as harmful gases/smoke detection.


They are used in air quality control equipment for buildings/offices, are suitable for detecting of NH3, NOx, alcohol, Benzene, smoke, CO2, etc.



  • Circuit voltage: 5V±0.1
  • Heating voltage: 5V±0.1
  • Load resistance: Adjustable
  • Heater resistance: 33Ω±5%
  • Heating consumption: less than 800mw
  • Using Temp: 10 to 45
  • Storage Temp: 20 to 70
  • Related humidity: less than 95%Rh
  • Oxygen concentration: 21%(standard condition)Oxygen concentration can affect sensitivity
  • Surface Sensing Resistance: 30KΩ-200KΩ (100ppm NH3 )
  • Concentration Slope rate: ≤0.65
  • Temp: 20±2
  • Vc:5V±0.1
  • Humidity: 65%±5%
  • Vh: 5V±0.1
  • Preheat time: Over 24 hour


Materials To Be Required:

  • Arduino
  • MQ-135 sensor
  • Breadboard
  • Jumper wires

Connection with Arduino: