DFRobot Gravity Analog CO/Combustible Gas Sensor MQ9 Module

The module requires a 5V DC power supply for both its logic and sensor heater. The analog output signal ranges from 0V to approximately 5V, corresponding to the detected gas concentration. A higher output voltage indicates a higher gas density. This signal can be connected directly to an analog input pin on an Arduino or other microcontroller.

The MQ9 uses a controlled heating cycle. When the internal heater is run at a lower voltage (~1.5V), the sensor is optimized for detecting Carbon Monoxide (CO). When the heater is switched to a higher voltage (5.0V), it becomes sensitive to combustible gases like Methane and Propane. This high-temperature phase also helps burn off residues, cleaning the sensor for the next reading cycle.

Sensitivity can be adjusted using the blue potentiometer on the module. Turning it adjusts the reference point for the onboard comparator, effectively setting the threshold at which the analog signal is considered 'high'. For precise concentration measurement, a multi-point calibration in a known gas concentration is required, comparing ADC readings to reference values.

No, the MQ9 sensor itself cannot definitively differentiate between specific gases within its detection spectrum. It responds to a broad range of reducing gases, including CO, Methane, and Propane. Identification relies on the dual-heating cycle: the low-temperature phase is more sensitive to CO, while the high-temperature phase is more sensitive to combustible gases. Pattern analysis of the response at both temperatures can provide clues.