MQ-4 Methane CNG Gas Detector Module - Analog & TTL Output

The MQ-4 module is designed for a 5V DC supply. While the raw sensor can operate from 5V for the heater, the onboard circuitry requires a stable 5V input. Applying voltages outside this range may damage the module or provide incorrect readings.

Connect the module's VCC and GND to Arduino's 5V and GND pins. For analog readings, connect the AO pin to an analog input (e.g., A0). For the digital trigger, connect the DO pin to a digital input pin. The digital output goes LOW when gas concentration exceeds the threshold set by the onboard potentiometer.

The MQ-4 is primarily sensitive to methane (CH4) and compressed natural gas (CNG), which is predominantly methane. It has lower cross-sensitivity to other combustible gases like propane and butane, but its calibration is optimized for methane detection within its specified 300 to 10,000 ppm range.

For qualitative detection (digital trigger), calibration involves adjusting the onboard potentiometer to set the desired concentration threshold. For quantitative analog measurements, sensor calibration is recommended using known methane concentrations in clean air, as the analog output can drift over time and is sensitive to ambient temperature and humidity.