CO Carbon Monoxide Methane Liquefied Gas Sensor MQ-9

CO Carbon Monoxide Methane Liquefied Gas Sensor MQ-9

Sensors
DET659
Part.No: MQ-9
€4.95
Last items in stock
Immediate Dispatch
MQ-9 Carbon Monoxide, Methane & LPG Gas Sensor — detects CO, methane and propane using a dual-temperature heating cycle (1.5V / 5V) with a SnO2 sensitive element. Ideal for gas alarm and safety monitoring projects.

 

The MQ-9 (MPN: MQ-9) is a multi-gas sensor designed to detect carbon monoxide (CO), methane, and liquefied petroleum gases such as propane. It uses a tin dioxide (SnO₂) sensitive material whose electrical conductivity rises as target gas concentration increases. A unique dual-temperature heating cycle allows it to distinguish between gas types: low-temperature operation (1.5 V heating) targets carbon monoxide, while high-temperature operation (5.0 V heating) targets combustible gases like methane and propane. A simple external circuit converts conductivity changes into a measurable output signal, making this sensor a popular choice for DIY gas alarms, home safety devices, and educational projects.

Key Features

  • Dual-temperature detection cycle (1.5 V / 5 V heating): Enables separate detection of CO at low temperature and combustible gases (methane, propane) at high temperature → versatile multi-gas sensing in a single component
  • SnO₂ sensitive element: Conductivity increases with rising gas concentration → reliable and repeatable gas detection response
  • Simple signal conversion: Conductivity change can be converted to an output voltage via a basic load resistor circuit → easy integration with microcontroller ADC inputs
  • Targets CO, methane, and propane: Covers the most common household and industrial hazardous gases → broad safety monitoring coverage

Pinout & Wiring

PINSymbolDescription
1VHHeater voltage supply
2GND (H)Heater ground
3VCCCircuit supply voltage
4GND (A)Circuit ground
5 / 6A / BSensor output (connect load resistor to GND; read voltage across resistor)

Wiring note: Apply 5.0 V to VH during high-temperature phase and 1.5 V during low-temperature phase as per the recommended heating cycle. Connect a load resistor (RL) between the output pin and GND, then read the voltage across RL with an analog input pin.

Compatibility

  • Arduino UNO / Nano / Mega (5 V): Directly compatible — connect sensor output to any analog input pin (A0–A5). No level shifting required for the signal line.
  • ESP32 / Raspberry Pi (3.3 V logic): The heater and circuit supply can still be powered at 5 V; however, use a voltage divider or level shifter on the output signal line to protect 3.3 V ADC inputs.

Typical Applications

  • Home CO alarm systems: Detect dangerous carbon monoxide build-up from faulty heating appliances or blocked flues.
  • LPG / natural gas leak detectors: Monitor for methane or propane leaks in kitchens, boiler rooms, or storage areas.
  • Industrial safety monitors: Deploy in workshops or factories where combustible gases may accumulate.
  • Arduino / ESP32 maker projects: Build a portable multi-gas meter or a smart ventilation controller that activates a fan when gas levels rise.
  • Educational labs: Demonstrate gas sensing principles, ADC readings, and threshold-based alert logic for electronics and IoT courses.

Technical Specifications

InterfaceAnalog (resistive output)
Heater Voltage (VH) — low-temperature phase1.5 V
Heater Voltage (VH) — high-temperature phase5.0 V
Target GasesCarbon Monoxide (CO), Methane (CH₄), Propane (C₃H₈)
Sensitive MaterialTin Dioxide (SnO₂)
Detection MethodDual-temperature heating cycle
MPNMQ-9

Frequently Asked Questions

Q: What is the difference between the MQ-9 low-temperature and high-temperature phases?
A: At low temperature (1.5 V heater), the sensor is optimised to detect carbon monoxide. At high temperature (5.0 V heater), it detects combustible gases such as methane and propane. Cycling between these two states allows a single sensor to cover multiple gas types.

Q: Can I use the MQ-9 directly with an ESP32?
A: Yes, but with caution. The heater and circuit supply can run at 5 V, while the output signal should be attenuated (voltage divider or level shifter) before connecting to the ESP32's 3.3 V ADC to avoid damage.

Package Contents: 1 × MQ-9 Gas Sensor (bare sensor element)

⚠ Warning: Allow a warm-up / pre-heat period before taking measurements — the SnO₂ element requires stabilisation time after power-on. Keep away from high humidity environments for extended periods, as moisture can affect sensor accuracy.
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