MQ138 Volatile Organic Compound Gas Sensor


MQ138 gas sensor is a volatile organic compound gas sensor. MQ138 belongs to the MQ series of gas sensor modules, infamous for their quick and timely response to harmful concentrations of dangerous gases. The gas-sensitive layer of the MQ138 sensor determines the performance of the gas sensor and its capacity to detect harmful gases (volatile organic compounds and their corresponding fumes in particular) effectively and provides adequate warnings proactively. Whenever any volatile organic compound gas comes into contact with the sensing element, the resistivity of the element changes. The change is then measured to get the concentration of the gases present. The MQ138 gas sensor comes in a package similar to the MQ9 sensor and can be used with its corresponding breakout board.

MQ138 VOC gas sensor offers a wide array of features such as overvoltage protection and ESD protection. Analog data extraction from the sensor can be done easily by interfacing it with any generic microcontroller unit such as Arduino, Raspberry-pi, NodeMCU, etc.

MQ138 Volatile Organic Compound Gas Sensor

MQ138 Gas Sensor Key Features

  • Wide detecting scope
  • Fast response
  • High sensitivity
  • Stable and long life
  • The Sensitivity of the Digital pin can be varied using a potentiometer
  • Analog output is continuous
  • Compact size
  • Less cost
  • ESD Protection
  • Overvoltage Protection
  • Simple drive circuit
  • Pre-heat Duration: 20 Sec

MQ138 Gas Sensor Pinout

MQ138 Sensor Pinout
Pin NamePin No.Description
VCC4This pin powers the module, typically the operating voltage is +5V
GND3Used to connect the module to the system ground
DO2You can also use this sensor to get digital output from this pin, by setting a threshold value using the potentiometer
AO1This pin outputs 0-5V analog voltage based on the intensity of the gas.


  • Circuit voltage: 5V±0.1
  • Heating voltage: 5V±0.1
  • Load resistance: Adjustable
  • Heater resistance: 31Ω±3Ω
  • Heating consumption: less than 850mw
  • Operating Temperature: -10℃ – 45℃
  • Storage Temperature: -20℃-70℃
  • Related humidity: less than 95%Rh
  • Oxygen concentration: 21%(standard condition) Oxygen concentration can affect sensitivity
  • Sensing Resistance: 20KΩ-200KΩ (1000ppm Benzene )
  • Concentration Slope rate: ≤0.65


  • Domestic VOC gas alarm
  • VOC gas leakage alarm
  • They are used in air quality control equipment for buildings/factories and are suitable for detecting traces of VOC gases and fumes.
  • Portable VOC gas detector


You can download the datasheet for MQ138 Volatile Organic Compound Gas Sensor Module by clicking the link given below:

See Also: SIM900A Dual Band GSM/GPRS Module | DS3231 Precision I2C Real-Time Clock Module | MT8870D Integrated ISO2-CMOS DTMF Receiver Module