Air Quality Sensor MQ-135 w/ Breakout Board Digital & Analog Output

MQ135 is a semiconductor sensor which can detect the presence of Ammonia (NH₃), Mono-nitrogen oxides (NO_x), Alcohol, Benzene, Smoke, Carbon-dioxide (CO₂) etc. This module is commonly used as an Air Quality Sensor as it has good sensitivity to harmful gases in wide range. The sensitive material used for this sensor is SnO₂, whose conductivity is lower in clean air. It’s conductivity increases as the concentration of sensing gases increases. MQ135 Air Quality Sensor can be easily interfaced with Microcontrollers, Arduino Boards, Raspberry Pi etc using an Analog to Digital Converter (ADC).

Features:

• Low Cost
• Stable and Long Life
• High sensitivity to Ammonia, Sulfide and Benzene
• Good sensitivity to harmful gases in wide range
• Output voltage boosts along with the concentration of the measured gases increases
• Fast response and recovery
• Adjustable sensitivity
• On-board LED indicator
• Both digital and analog outputs

Specification:

• Operating Voltage : 5V ±0.1
• Operating Temperature : -10°C ~ 45°C
• Detection Concentration : 10 ~ 300 ppm of NH3, 10 ~ 1000 ppm of Benzene, 10 ~ 300 ppm of Alcohol
• Chip: LM393
• Board size: 32mm (L) x 20mm (W) x 22mm (H)

Applications

• Domestic air pollution detector
• Industrial air pollution detector
• Portable air pollution detector
• Air quality control equipment

Datasheet

• MQ135 Air Quality Sensor Datasheet

Interfacing MQ-135 Air Quality Sensor Module to Arduino

Here is a simple diagram of how your sensor should be wired to your Arduino.

We also wanted to convert the voltage readings of 0-1023 from the sensor to a 0.0-5.0 value which would reflect the true voltage being read.

Run this code to your Arduino and you will be ready to detect changes in the level of detectable gasses!

const int gasSensor =0;

void setup()
{
  Serial.begin(9600);      // sets the serial port to 9600
}

void loop()
{
  float voltage;
  voltage = getVoltage(gasSensor);
  
  Serial.println(voltage);
  delay(1000);
}

float getVoltage(int pin)
{
  return (analogRead(pin) * 0.004882814);
  // This equation converts the 0 to 1023 value that analogRead()
  // returns, into a 0.0 to 5.0 value that is the true voltage
  // being read at that pin.
}

Notes:  

• After doing some research about this sensor it was discovered that while the MQ-135 can detect all of the gasses listed above, it cannot distinguish between them.  If you are looking to specifically target one gas, it might be better to find a different sensor.
• This sensor also needs uses a heater to warm up the sensor.  It has been advised to not use this with a small battery source as it will quickly drain your battery.