Organic Steam MQ-138 w/ Breakout Board Digital & Analog Output

Sensitive material of MQ138 gas sensor is SnO_2, which with lower conductivity in clean air. When the target Organic Steam exist, The sensor’s conductivity is more higher along with the gas concentration rising. Please use simple electrocircuit, Convert change of conductivity to correspond output signal of gas concentration.

MQ138 gas sensor has high sensitity to Toluene, Acetone, Ethanol and Formaldehyde, also to other organic steam. The sensor could be used to detect different organic steam, it is with low cost and suitable for different application.

Sensor can be easily interfaced with Microcontrollers, Arduino Boards, Raspberry Pi etc using an Analog to Digital Converter (ADC).

Features

• Stable and Long Life
• High sensitivity to Organic Steam
• Good sensitivity to Toluene, Acetone and Ethanol, etc
• 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 : 20°C ~ 65°C
• Detection Concentration : 5 ~ 500 ppm

Interfacing MQ-138 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.