MQ-7 Carbon Monoxide Gas Sensor Module - CO Detector

Specifications

• Target Gas: Carbon Monoxide (CO).

• Detection Range: 20ppm – 2000ppm.

• Operating Voltage: 5V DC (Circuit), 5V/1.4V (Heater Cycle - See Project Evolution).

• Output Format:

  • Analogue (A0): Voltage increases with CO concentration.

  • Digital (D0): Logic High/Low trigger based on adjustable threshold.

• Response Time: < 150s.

• Dimensions: 32mm x 20mm x 22mm.

Compatibility & Platform Support

• Arduino (Uno/Nano/Mega): Directly Compatible. The 5V logic works perfectly.

• ESP32 / ESP8266: ⚠️ Caution Required. The Analog output can reach up to 4V in high gas concentrations. You MUST use a voltage divider (e.g., 10kΩ & 20kΩ resistors) to reduce the signal to 3.3V to protect your ESP32 ADC.

• Raspberry Pi: ⚠️ Requires ADC. The Pi cannot read analogue voltages. Use an external ADC chip (MCP3008) or the Digital (D0) pin for a simple alarm.

Key Applications & Projects

• Home Safety Alarm: Trigger a loud buzzer if CO levels rise near a fireplace or gas heater.

• Car Cabin Monitor: Detect exhaust leaks entering the vehicle cabin.

• Industrial Air Quality: Monitor CO levels in parking basements or factories.

• Smart HVAC Controller: Automatically turn on ventilation fans when CO is detected.

Project Evolution

• The "Pro" Mode (Advanced): While hobbyists often run the MQ-7 at a constant 5V, the datasheet actually recommends a High/Low Heating Cycle for maximum accuracy (60s at 5V to clean the sensor, 90s at 1.4V to read it).

• The Upgrade: Use a MOSFET Module controlled by your Arduino to toggle the heater voltage. This unlocks "Lab-Grade" accuracy from this low-cost module.

• Effort Level: Advanced. Implementing the timing logic and voltage switching requires solid coding and circuit skills.

Virtual Technician: Wiring & Safety ⚠️

• VCC: Connect to 5V.

• GND: Connect to Common Ground.

• D0: Connect to Digital Pin (for threshold alarm).

• A0: Connect to Analogue Pin (for PPM measurement).

• Heater Warning: The sensor will get warm (~40°C). This is normal.

• Life Safety Warning: This module is for educational and prototyping purposes only. Do not use it as the sole safety device in a life-critical application. Always have a certified commercial CO alarm as a backup.

Accessories

• Included in the Package: 1 x MQ-7 Carbon Monoxide Gas Sensor Module

• Required Accessories (Not Included):

  • Controller: Arduino Uno or similar.

  • Power: 5V 1A Adapter (USB power is okay, but external power is more stable for the heater).

  • Wires: Female-to-Male Jumper Wires.

  • Optional: MOSFET Module (for advanced heater cycling).

Frequently Asked Questions (FAQ)

• Can I run this at constant 5V? Yes, for simple threshold detection (Alarm/No-Alarm), constant 5V works reasonably well. For precise PPM measurement, the High/Low cycle is better.
• Does it detect smoke? It has low sensitivity to smoke, but high concentrations of smoke might trigger it. Use MQ-2 for smoke.
• How do I calibrate it? You need a known concentration of CO (or clean air for a baseline). Measure the resistance (Ro) in clean air and use the datasheet curve.
• Can I test it with car exhaust? Yes, car exhaust contains CO. Warning: Do this in a well-ventilated area to avoid poisoning yourself!
• Is it sensitive to Hydrogen? Yes, Hydrogen can interfere with the readings.
• Why does the reading drift? Temperature and humidity affect the chemical reaction. The sensor needs to "warm up" for stabilization.
• What is the warmup time? Minimum 2-5 minutes for a rough reading. 24-48 hours for calibration.
• Can I use a 9V battery? No. 9V will destroy the heater. Use a 5V regulator.
• Is it waterproof? No. Keep it dry.
• What is the range? 20ppm to 2000ppm CO.
• Why is the LED always ON? Turn the blue potentiometer counter-clockwise to reduce sensitivity until the LED turns off.
• Can I use this with NodeMCU? Yes, but remember the Analog pin on NodeMCU is weird (some take 1V, some 3.3V). Use a voltage divider!
• How long does the sensor last? Typically 4-5 years.
• Does it detect Natural Gas? Very poorly. Use MQ-4 for Natural Gas.
• Can I use it to detect fire? Indirectly, as fires produce CO, but a Flame Sensor or Smoke Sensor is faster.
• Is the sensor pre-calibrated? No. Every sensor varies slightly. You must calibrate it in your code.
• What happens if I touch the mesh? Oils from skin can reduce sensitivity. Handle by the PCB.
• Can I control a fan directly? No, the output current is too low. Use a Relay Module to switch the fan.
• Does altitude affect readings? Yes, lower oxygen levels at high altitude can shift the baseline.
• Is this UL certified? No. It is a hobbyist component.