The MQ-9 is a gas sensor that detects carbon monoxide (CO), methane (CH₄), and liquefied petroleum gas (LPG). It uses a tin dioxide (SnO₂) sensing layer whose conductivity changes with gas concentration. Designed for indoor air quality and gas leak detection, it offers high sensitivity, fast response, and a simple analog output. The MQ-9 operates at 5V and is commonly used with microcontrollers like Arduino.
| Detection Gases: |
Carbon monoxide (CO), Methane (CH₄), Liquefied Petroleum Gas (LPG, primarily propane (C₃H₈) and butane (C₄H₁₀)) |
|---|---|
| Detection Range: |
CO: 10ppm to 1000ppm CH₄/LPG: 100ppm to 10000ppm |
| Working Voltage: | 5V |
| Heater Voltage (High/Low): | 5V / 1.5V |
| Heater Resistance: | 33Ω ±5% |
| Sensing Resistance: | 2kΩ to 20kΩ (in 100ppm CO) |
| Heating Consumption: | <340mW |
| Operating Temperature: | -20°C to 50°C |
| Relative Humidity: | <95% RH |
| Dimensions (L×W×H): | 32mm × 20mm × 22mm |
| Weight: | ~15g |
Please keep the following notes in mind before using/connecting the MQ-9:
| Pin name | Description |
|---|---|
| VCC | Power supply (5V) |
| GND | Ground connection |
| AO | Analog output |
| DO | Digital output |
Using the potentiometer on the back of the board, you can set the threshold at which the DO output switches from HIGH to LOW. The DO pin can be connected directly to a microcontroller or a development kit.
The sensor also has an AO analog output, which should be connected to the A/D converter (e.g.: analog input on Arduino). This allows for more accurate determination of the alcohol content by measuring the proportional voltage signal.
Due to the similarities in the module's structure and connections, all circuit diagrams and codes can be found under MQ-3.
Carbon monoxide (CO) is highly toxic, and even small amounts can be life-threatening so we will not use it here for testing the sensor!
Since the MQ-9 gas sensor can also detect methane (CH₄) and LPG (butane/propane), you can test it using safer, everyday sources:
Release a small puff of standard lighter gas near the sensor (without igniting it!)
Hold a tissue soaked with isopropyl alcohol or ethanol-based disinfectant near the sensor.