AtriBOTAtriBOT

MQ-135 Air Quality Sensor with Arduino UNO

MQ-135 Air Quality Sensor with Arduino UNO
Atribot team

Written by

Atribot team

Last updated

June 18, 2026

Introduction

The MQ-135 Air Quality Sensor is designed to detect various gases and air pollutants such as ammonia (NH₃), nitrogen oxides (NOₓ), alcohol, benzene, smoke, and carbon dioxide (CO₂). It is commonly used in air quality monitoring systems, environmental monitoring projects, smart home automation, and IoT-based pollution detection applications.

In this tutorial, you will learn how to interface the MQ-135 Air Quality Sensor with an Arduino UNO, upload the code, and monitor air quality levels using the Serial Monitor. By the end of this guide, you'll understand how to measure changes in air quality using analog sensor readings.

Components Required

Swipe right to view full table
Item NameQtyAction
Arduino UNO
1
MQ-135 Air Quality Sensor
1
Breadboard
1
USB Cable
1
Jumper Wires
4

Tools Required

Swipe right to view full table
Item NameAction
Soldering Iron
Screwdriver

Software Required

Swipe right to view full table
Item NameAction
Arduio IDE

Circuit Diagram

MQ-135 Air Quality Sensor with Arduino UNO Circuit Connections
MQ-135 Air Quality Sensor with Arduino UNO Circuit Connections

Source Code

MQ-135_Air_Quality_Sensor_with_Arduino_UNO.inocpp
const int mq135Pin = A0;

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

void loop()
{
  int airQuality = analogRead(mq135Pin);

  Serial.print("Air Quality Value: ");
  Serial.println(airQuality);

  delay(1000);
}

Step by Step Instructions

Step 1: Connect the MQ-135 Sensor

Make the following connections:

Swipe right to view full table

MQ-135

Arduino UNO

VCC

5V

GND

GND

A0

A0

Step 2: Open Arduino IDE

  1. Launch Arduino IDE.

  2. Connect Arduino UNO using USB.

  3. Select:

    • Board → Arduino UNO

    • Port → Correct COM Port

Step 3: Create a New Sketch

Create a new Arduino sketch and paste the provided code.

Step 4: Verify the Code

Click the Verify button to check for syntax errors.

Step 5: Upload the Code

Click Upload and wait until the upload process completes successfully.

Step 6: Open Serial Monitor

  1. Open Serial Monitor.

  2. Set the baud rate to 9600.

  3. Allow the MQ-135 sensor to warm up for 20–30 seconds.

  4. Observe the sensor values in normal air conditions.

The Serial Monitor will display air quality readings continuously.

Expected Output

Under normal air conditions:

Air Quality Value: 180
Air Quality Value: 185
Air Quality Value: 190

When exposed to smoke or polluted air:

Air Quality Value: 420
Air Quality Value: 580
Air Quality Value: 760

Higher values generally indicate poorer air quality and increased gas concentration.

Conclusion

In this tutorial, you learned how to interface the MQ-135 Air Quality Sensor with Arduino UNO and monitor air quality using analog readings. This setup can be used in environmental monitoring systems, indoor air quality detectors, smart home applications, and various IoT projects that require pollution and gas detection.