The MQ-9 Gas Sensor Module is a sensitive gas detection module designed to detect carbon monoxide (CO), combustible gases, and liquefied petroleum gas (LPG). It uses a heated tin dioxide (SnO₂) sensing element whose resistance changes in the presence of target gases. This module is commonly used in gas leakage alarms, safety systems, air quality monitoring, and embedded electronics projects.
Core Sensor Specifications
• Sensor Type: Semiconductor gas sensor
• Sensor Model: MQ-9
• Target Gases: Carbon monoxide (CO), LPG, combustible gases
• Detection Principle: Change in sensor resistance due to gas concentration
Electrical & Interface
• Operating Voltage: 5 V DC
• Heater Voltage: 5 V DC
• Output Type: Analog and digital (module dependent)
• Interface Pins: VCC, GND, AO, DO
• Sensitivity Adjustment: Onboard potentiometer (for digital output threshold)
Performance Characteristics
• High sensitivity to CO and flammable gases
• Fast response after warm-up
• Stable output suitable for continuous monitoring
• Requires calibration for accurate readings
Physical Characteristics
• Module Type: PCB-mounted gas sensor module
• Sensing Element: Metal oxide semiconductor (SnO₂)
• Protective Mesh: Stainless steel cap
• Compact and durable construction
Compatibility
• Arduino Uno / Nano / Mega
• ESP8266 / ESP32
• Raspberry Pi (with ADC)
• Gas alarm and safety systems
• IoT air quality monitoring devices
Key Advantages
• Detects multiple combustible gases
• Simple analog and digital interfacing
• Low cost and widely available
• Suitable for safety and educational use
Technical Insights
• Requires initial burn-in and warm-up time
• Sensor readings affected by temperature and humidity
• Analog output preferred for precise measurement
• Digital output provides threshold-based alert only
Applications
• Carbon monoxide detection systems
• Gas leakage alarms
• Industrial and domestic safety devices
• Air quality monitoring
• DIY and educational electronics projects
Pro Tip
• Allow sufficient preheating time before use
• Calibrate using known gas concentration if accuracy is critical
• Use analog output for better resolution
• Avoid exposure to corrosive environments
Package Includes
• 1 × MQ-9 Gas Sensor Module