MQ Sensors EN

Overview

The MQ sensor is a low-cost electronic sensor that can detect various gas concentrations. Each sensor is designed to detect specific gases and can be easily used with microcontrollers like Arduino. It is widely used in air quality monitoring, gas leak detection, industrial safety, and other applications.

Main Models

The MQ series includes a variety of models, each detecting different gases.

Most sensors require a preheating time of around 24 hours. Considering measurement range and accuracy, they are better used for gas presence detection than precise safety applications.

Sensitivity can be adjusted via a variable resistor on the back.

Sensor Type	Detected Gas	Preheat Time	Detection Range	Operating Voltage	Output Type
MQ-2	LPG, Propane, Hydrogen, Methane, Alcohol, Smoke	24 hours	300–10000 ppm	5V	Analog
MQ-3	Alcohol, Benzene, CH4, Hexane, CO	24 hours	25–500 ppm (Alcohol)	5V	Analog
MQ-4	Methane, CNG	24 hours	200–10000 ppm	5V	Analog
MQ-5	LPG, Natural Gas, Town Gas	24 hours	200–10000 ppm	5V	Analog
MQ-6	LPG, Butane, Isobutane, Propane	24 hours	200–10000 ppm	5V	Analog
MQ-7	Carbon Monoxide	24 hours	20–2000 ppm	5V	Analog
MQ-8	Hydrogen	24 hours	100–10000 ppm	5V	Analog
MQ-9	Carbon Monoxide, Methane, LPG	24 hours	10–10000 ppm (CO), 100–10000 ppm (flammable gas)	5V	Analog
MQ-135	Ammonia, Benzene, Alcohol, Smoke	24 hours	10–1000 ppm (NH3, Alcohol, Benzene)	5V	Analog

Working Principle

MQ sensors contain a heater and a gas-sensitive component. When gas contacts the sensor, the resistance of the material changes, allowing gas concentration to be measured. The sensor element is usually made of SnO₂ (tin dioxide), whose resistance varies with the surrounding gas.

Electrical Characteristics

• Power supply: 5V (some models 3.3V)
• Output: Analog voltage (some models also support digital output)
• Heater current: ~150mA
• Response time: 1–2 minutes (for sensor stabilization)

Example Application

Example Hardware

• Arduino board
• Jumper wires
• MQ-6 module

Wiring

Digital pins are not used in this example but are included as a reference.

Arduino Uno	MQ-6
5V	VCC
GND	GND
A0	AO
D7	DO

Example Code

1. Basic Value Reading

int sensorPin = A0;
int sensorValue = 0;

void setup() {
  Serial.begin(9600);
}

void loop() {
  sensorValue = analogRead(sensorPin);
  Serial.println(sensorValue);
  delay(1000);
}

You can observe increasing values when gas is introduced.

2. Using a Library

Uses the MQUnifiedsensor library by Miguel Califa.

See the Library Usage Guide for installation and usage instructions.

Library Example Output

When gas is detected, the LED on the back of the sensor lights up.

The rightmost PPM value increases when exposed to lighter gas.

Application Fields

• Gas Leak Detection: Detect leaks in kitchens, factories, etc.
• Air Quality Monitoring: Monitor harmful gases in indoor environments.
• Alcohol Detection: Measure alcohol concentration for breathalyzers.
• Industrial Safety: Protect workers by detecting harmful gases in workplaces.