MQ-7 Gas Sensor For Carbon Monoxide Detector Module

What this sensor is

The MQ-7 Gas Sensor Module is a low-cost carbon monoxide (CO) detector commonly used in Arduino and IoT projects.

It detects:

• Carbon Monoxide (CO) a dangerous, odorless gas

Core Concept (VERY IMPORTANT)

This is a heating-type gas sensor (MQ series)

It works using a cyclic heating process:

• High temperature cleans sensor

• Low temperature detects CO

This makes it more selective to CO compared to other MQ sensors

Key Specifications

• Target Gas: Carbon Monoxide (CO)

• Detection Range: ~20 2000 ppm

• Operating Voltage:<(D0 with comparator)

Preheat Time: 2448 hours (important!)

Heater Current: ~150 mA

Working Principle

• Uses SnO (tin dioxide) sensing layer

• CO gas reduces sensor resistance

• Module converts it into voltage

More CO higher output signal

Unique Feature (IMPORTANT)

Unlike MQ-2 / MQ-135:

MQ-7 uses two-phase heating cycle:

• 5V heating (60s) cleaning phase

• 1.4V heating (90s) sensing phase

Accurate readings only in low-temp phase

Most modules don't control this automatically You must handle it in code (advanced use)< Ground

A0 Analog output

D0 Digital output (threshold adjustable)

Output Behavior

Analog output is non-linear

Applications

• Home CO alarm systems

• Fire detection

• Car exhaust monitoring

• Industrial safety

• Air quality projects

Important Notes (VERY IMPORTANT)

1. Requires long preheating

• Needs 2448 hours initially Otherwise readings are unstable

eeds calibration

3. High power consumption

• Heater uses significant current Not good for battery projects

4. Cross sensitivity

• Also reacts to:

  • Hydrogen

  • Methane Not 100% CO selective

5. Temperature cycle control (advanced)

For accurate CO detection:

• Must control heater voltage cycle Otherwise readings are less reliable

MQ-7 vs Other Sensors