What is MQ2 Gas Sensor?
MQ2 is one of the commonly used gas sensors in MQ sensor series. It is a Metal Oxide Semiconductor (MOS) type Gas Sensor also known as Chemiresistors as the detection is based upon change of resistance of the sensing material when the Gas comes in contact with the material. Using a simple voltage divider network, concentrations of gas can be detected.
Here are the complete specifications
|Load resistance||20 KΩ|
|Heater resistance||33Ω ± 5%|
|Sensing Resistance||10 KΩ – 60 KΩ|
|Concentration Scope||200 – 10000ppm|
|Preheat Time||Over 24 hour|
This is how the sensor looks like when outer mesh is removed. The star-shaped structure is formed by the sensing element and six connecting legs that extend beyond the Bakelite base. Out of six, two leads (H) are responsible for heating the sensing element and are connected through Nickel-Chromium coil, well known conductive alloy.
The remaining four leads (A & B) responsible for output signals are connected using Platinum Wires. These wires are connected to the body of the sensing element and convey small changes in the current that passes through the sensing element.
Nickel-Chromium coil and Aluminum Oxide based ceramic forms a Heating System; while Platinum wires and coating of Tin Dioxide forms a Sensing System.
How does a gas sensor work?
When tin dioxide (semiconductor particles) is heated in air at high temperature, oxygen is adsorbed on the surface. In clean air, donor electrons in tin dioxide are attracted toward oxygen which is adsorbed on the surface of the sensing material. This prevents electric current flow.
In the presence of reducing gases, the surface density of adsorbed oxygen decreases as it reacts with the reducing gases. Electrons are then released into the tin dioxide, allowing current to flow freely through the sensor.
Hardware Overview – MQ2 Gas Sensor Module
Since MQ2 Gas Sensor is not breadboard compatible, we do recommend this handy little breakout board. It’s very easy to use and comes with two different outputs. It not only provides a binary indication of the presence of combustible gases but also an analog representation of their concentration in air.
The analog signal from MQ2 Gas sensor is further fed to LM393 High Precision Comparator (soldered on the bottom of the module), of course to digitize the signal. Along with the comparator is a little potentiometer you can turn to adjust the sensitivity of the sensor. You can use it to adjust the concentration of gas at which the sensor detects it.
The sensor is sensitive to multiple gasses – but cannot tell which it is! That’s normal; most gas sensors are like that. So, it is best for measuring changes in a known gas density, not detecting which is changing.
Calibrate MQ2 Gas Sensor Module
To calibrate the gas sensor you can hold the gas sensor near smoke/gas you want to detect and keep turning the potentiometer until the Red LED on the module starts glowing. Turn the screw clockwise to increase sensitivity or anticlockwise to decrease sensitivity.
MQ2 Gas Sensor Module Pinout
VCC supplies power for the module. You can connect it to 5V output from your Arduino.
GND is the Ground Pin and needs to be connected to GND pin on the Arduino.
D0 provides a digital representation of the presence of combustible gases.
A0 provides analog output voltage in proportional to the concentration of smoke/gas.
Wiring – Connecting MQ2 Gas Sensor Module to Arduino UNO
Now that we have a complete understanding of how MQ2 Gas sensor works, we can begin hooking it up to our Arduino!
Connecting the MQ2 Gas sensor module to the Arduino is pretty easy. Start by placing the sensor on to your breadboard. Connect VCC pin to the 5V pin on the Arduino and connect GND pin to the Ground pin on the Arduino.
x1 unit MQ2 Gas-Smoke Sensor