Interface MQ135 Air Quality Sensor with Arduino – ElectroVigyan

What is an air quality sensor? 

An air quality sensor is a device used to measure and detect various pollutants present in the air. These pollutants can include gases such as carbon monoxide (CO), nitrogen dioxide (NO2), and volatile organic compounds (VOCs), as well as particles such as dust and pollen.

Air quality sensors typically work by measuring changes in resistance, conductivity, or voltage caused by the presence of pollutants in the air. Some air quality sensors also use chemical reactions to detect specific gases. The output of the sensor is then processed and converted into numerical readings that can be used to evaluate the air quality.

In Arduino projects, air quality sensors can be connected to an Arduino board to monitor the air quality in real-time and to trigger an alarm or other response in the event of hazardous conditions. For example, an air quality sensor can be used to monitor the air inside a room or building to ensure that it meets specific air quality standards, or to detect the presence of gases that can be harmful to health.

There are many different types of air quality sensors available, each with its own strengths and limitations. When selecting an air quality sensor for an Arduino project, it is important to consider the pollutants that need to be detected, the required sensitivity and accuracy, and the operating conditions (such as temperature and humidity) that the sensor will encounter.

What is an MQ135 air quality gas sensor? 

MQ135 Semiconductor Sensor is an air quality gas sensor having high sensitivity to ammonia gas, sulfide, benzene series steam, smoke and other toxic gases as well. 

The SnO2 semiconductor material is used in the MQ135 for detecting the gases. It has a lower conductivity in clean air. It helps in detecting the rising levels of gases through rise in its conductivity. Users can convert the change of conductivity to gas concentration through a simple electronic circuit.

An MQ135 Air quality gas sensor has a wide array of applications such as:

• Air quality control equipment for buildings/offices
• Domestic gas alarm
• Industrial gas alarm
• Portable gas detector

The applicability of an MQ135 Air quality gas sensor is enhanced by the following features:

• Wide detecting scope
• Simple drive circuit
• Fast response
• High Stability
• High sensitivity
• Long-life
• Low cost

MQ135 Air Quality Sensor Specifications

• Operating Voltage: 2.5-5V 
• Operating Current: 150mA
• Heat-up time: 20s

MQ135 Air Quality Sensor pin diagram

Pin1: It is VCC Pin. It is used to connect 2.5-5V to the sensor.
Pin2: It is GND Pin. It is used to connect GND to the sensor.
Pin3: It is digital output Pin. From this pin you will get digital data HIGH/LOW.
Pin4: It is analog output Pin. From this pin you will get analog data.

Circuit diagram of MQ135 Air Quality Sensor with Arduino

Pin connection of MQ135 Air Quality Sensor with Arduino

Connect the VCC pin of the sensor to the 5V pin of the Arduino UNO board.
Connect the GND pin of the sensor to the GND pin of the Arduino UNO board.
Connect the AO pin of the sensor to the A4 pin of the Arduino UNO board.

Arduino code for interfacing MQ135 Air Quality Sensor with Arduino

int sensorPin=A4;
int sensorData;
void setup()
{  
  Serial.begin(9600);   
  pinMode(sensorPin,INPUT);                         
 }
void loop()
{
  sensorData = analogRead(sensorPin);       
  Serial.print("Air Quality:");
  Serial.print(sensorData, DEC);               
  Serial.println(" PPM");
  delay(100);                                   
}

Arduino code working

int sensorPin=A4;
int sensorData;

Create a variable named sensorPin to the pin number of the Arduino UNO board where you have connected the AO pin of the sensor. In our case, it is A4 pin of the Arduino UNO board.

Create another variable named sensorData. We will use this variable to store the data that will be received by the Arduino from the sensor.

void setup()
{  
  Serial.begin(9600);   
  pinMode(sensorPin,INPUT);                         
 }

Inside the void setup block, set the baud rate for the serial communication and initiate the serial communication using Serial.begin() command.

Then use the pinMode() function to set the sensorPin as INPUT. The Arduino will use this pin to get the analog data from the sensor.

void loop()
{
  sensorData = analogRead(sensorPin);       
  Serial.print("Air Quality:");
  Serial.print(sensorData, DEC);               
  Serial.println(" PPM");
  delay(100);                                   
}

Inside the void loop() function, use sensorData variable to store the data that is received by the Arduino from the sensor.

Then, print the data on the serial monitor using the print and println command. In the line”Serial.print(sensorData, DEC); “, we are converting the sensor data into decimal.