Description

MQ-9 Carbon Monoxide Methane LPG Gas Sensor Module

Introduction

The MQ-9 Carbon Monoxide Methane LPG Gas Sensor Module is a compact semiconductor gas-detection board designed to respond to carbon monoxide and combustible gases including methane, propane and LPG. It combines an MQ-9 SnO₂ sensing element with an onboard comparator, sensitivity potentiometer, power indicator and digital-output indicator.

The module provides both an analog output for monitoring changes in sensor response and an adjustable digital output for threshold-based alarms. It can be integrated with Arduino boards, microcontrollers, alarm circuits and environmental-monitoring projects.

Key Features

• Sensitive to carbon monoxide, methane, propane, LPG and other combustible gases.
• SnO₂ semiconductor sensing material.
• 5V module operating voltage.
• Analog output for monitoring relative gas-concentration changes.
• TTL digital output with an adjustable trigger threshold.
• Onboard sensitivity potentiometer.
• Power and digital-output indicator LEDs.
• Simple four-pin interface.
• Compact module suitable for prototyping and embedded projects.
• Long service life when operated and stored correctly.

Technical Specifications

Pinout and Connections

How the Module Works

The MQ-9 uses tin dioxide, or SnO₂, as its sensitive material. Its conductivity is relatively low in clean air and increases as the concentration of target gases rises. The onboard circuit converts this change into an analog signal and compares it with the threshold selected by the potentiometer to generate the digital output.

The raw MQ-9 sensing element uses different heater conditions for carbon-monoxide and combustible-gas response. Common four-pin modules are normally powered from a 5V input and may not automatically implement a precision high/low heater-control cycle. Applications requiring selective or quantitative measurement should use suitable heater control, calibration and signal processing.

Arduino and ESP32 Usage

• Connect VCC to a regulated 5V supply.
• Connect GND to the controller ground.
• Connect DO to a digital input for threshold-based gas alarms.
• Connect AO to an analog input to monitor relative changes in sensor response.
• The analog output may approach 5V. Use a suitable voltage divider or level-scaling circuit before connecting AO to a 3.3V-only ADC such as an ESP32 input.
• Ensure that the power supply can provide the module’s heater current.

Calibration and Warm-Up

• Allow at least 24 hours of initial preheating for a new sensor to stabilize.
• Allow sufficient warm-up after each power-on before relying on readings.
• Calibrate the sensor in clean air and, when possible, with a known reference-gas concentration.
• The onboard potentiometer adjusts the digital-output threshold only.
• Converting AO readings directly into ppm requires calibration data, load-resistance information and compensation for temperature and humidity.

Applications

• Domestic gas-leakage detector projects.
• Industrial gas-monitoring prototypes.
• Portable gas-detector projects.
• Carbon-monoxide warning projects.
• Combustible-gas alarm circuits.
• Smart-home safety and ventilation systems.
• Arduino and microcontroller educational projects.

Related Products

For projects focused primarily on carbon monoxide, see the MQ-7 Carbon Monoxide Gas Sensor Module. For methane and LPG detection projects, compare it with the MQ-5 Methane and LPG Gas Sensor Module.

Package Contents

• 1 × MQ-9 carbon monoxide, methane and LPG gas sensor module.

Important Notes

• This module is intended for electronics projects, prototyping and educational use.
• It is not a certified life-safety, fire-alarm or industrial gas-measurement instrument.
• The sensor is cross-sensitive to multiple gases and cannot identify a gas from one reading alone.
• Readings are affected by temperature, humidity, sensor age, warm-up time and calibration.
• Avoid water, condensation, corrosive gases and silicone vapours around the sensing element.
• The actual PCB or component colour may differ from the displayed image.

Attachments & Datasheets

Download the MQ-9 Gas Sensor Datasheet (PDF)