Methane Gas Sensor MQ-4

This semiconductor gas sensor detects the presence of methane (CNG) gas at concentrations from 200 ppm to 10,000 ppm, a range suitable for detecting gas leaks. The sensor’s simple analog voltage interface requires only one analog input pin from your microcontroller.

This methane gas sensor detects the concentration of methane gas in the air and ouputs its reading as an analog voltage. The concentration sensing range of  ppm to 10,000 ppm is suitable for leak detection. For example, the sensor could detect if someone left a gas stove on but not lit. The sensor can operate at temperatures from -10 to 50°C and consumes less than 150 mA at 5 V. Please read the MQ4 datasheet (161k pdf) for more information about the sensor.

Connections

Connecting five volts across the heating (H) pins keeps the sensor hot enough to function correctly. Connecting five volts at either the A or B pins causes the sensor to emit an analog voltage on the other pins. A resistive load between the output pins and ground sets the sensitivity of the detector. Please note that the picture in the datasheet for the top configuration is wrong. Both configurations have the same pinout consistent with the bottom configuration.The resistive load should be calibrated for your particular application using the equations in the datasheet, but a good starting value for the resistor is 20 kΩ.

This sensor comes with a carrier board (Not soldered on and other components excluded). This carrier board is designed to work with any of the MQ-series gas sensors, simplifying the interface from 6 to 3 pins—ground, power and analog voltage output—that are broken out with a 0.1" spacing, making the board compatible with 0.1" headers and standard breadboards and perfboards. This board has two mounting holes and provides convenient pads for mounting the gas sensor’s required sensitivity-setting resistor.

Connecting with the carrier board

Connect VCC to 5 V, GND to ground, and OUT to an analog-to-digital converter (ADC). The board has two pairs through-hole pins for the required (but not included) sensitivity-selecting resistor RL, providing two mounting options—horizontal or vertical—between GND and OUT as shown in the pictures below. The resistance of RL should be calculated using the datasheet for your particular gas sensor.

The MQ gas sensors have light to no polarity, so the gas sensor will work with the board all four ways it fits into the 6 pins (there are two possible orientations on each side of the board).