MQ7 MQ-7 Gas Sensor Module

The MQ-7 Gas Sensor Module is an electronic component used to detect and measure Carbon Monoxide (CO) concentrations in the surrounding air. It relies on a Tin Dioxide (SnO) semiconductor layer, which changes its electrical resistance when exposed to toxic CO gas. The module is widely integrated with microcontrollers like Arduino and Raspberry Pi for DIY electronics, home safety alarms, and industrial monitoring.Key Technical Specifications

• Target Gas: Carbon Monoxide (CO).
• Detection Range: Typical range is 20 to 2,000 ppm (parts per million), though some data sheets note detection from 10 to 10,000 ppm depending on calibration.
• Operating Voltage: 5V DC.
• Current Consumption: Less than 150 mA.
• Outputs: Dual output layout providing both Analog (AO) and Digital (DO) signals.
• Heater Mechanism: Requires a high/low heating cycle (5V for 60s to clean the sensor, then 1.4V for 90s to measure) for accurate ppm calculations.

Module Layout & Pin ConfigurationThe module usually includes a small potentiometer (adjustable dial) to manually tweak the digital threshold sensitivity and onboard LEDs to indicate power and digital signal status.

How It Works

1. Preheating: The internal heating wire warms the chemical material. A brief 20-second warm-up is normal before readings stabilize, though initial runtime calibration takes longer.
2. Chemical Reaction: In clean air, the SnO layer maintains low conductivity. When CO is introduced, oxygen molecules trapped on the surface react with the gas, releasing electrons and lowering the resistance.
3. Signal Translation: The circuit board interprets this drop in resistance as a voltage change.
   • Analog Line: Higher gas concentration yields a higher output voltage.
   • Digital Line: If the voltage passes the potentiometer’s limit, the DO pin drops to a Low TTL logic signal, triggering connected alarms or relays.