Grove - Gas Sensor(MQ2)

Introduction

5.0V Analog

The Grove - Gas Sensor(MQ2) module is useful for gas leakage detection (home and industry). It is suitable for detecting H2, LPG, CH4, CO, Alcohol, Smoke or Propane. Due to its high sensitivity and fast response time, measurement can be taken as soon as possible. The sensitivity of the sensor can be adjusted by potentiometer.

Note

The sensor value only reflects the approximated trend of gas concentration in a permissible error range, it DOES NOT represent the exact gas concentration. The detection of certain components in the air usually requires a more precise and costly instrument, which cannot be done with a single gas sensor. If your project is aimed at obtaining the gas concentration at a very precise level, then we don’t recommend this gas sensor.

There are 4 kinds of gas sensors, every can detect different type of gas, here we use a table to illustrate.

Sensor Gas Type Get One Now
MQ2 Combustible Gas, Smoke
MQ3 Alcohol Vapor
MQ5 LPG, Natural Gas, Town Gas
MQ9 Carbon Monoxide, Coal Gas, Liquefied Gas

Features

  • Wide detecting scope
  • Stable and long lifetime
  • Fast response and High sensitivity

Tip

More details about Grove modules please refer to Grove System

Specification

Item Parameter Min Typical Max Unit
VCC Working Voltage 4.9 5 5.1 V
PH Heating consumption 0.5 - 800 mW
RL Load resistance adjustable
RH Heater resistance - 33 - Ω
Rs Sensing Resistance 3 - 30

Platforms Supported

Application Ideas

  • Gas leakage detection.
  • Toys.

Hardware Overview

This is an Analog output sensor. It needs to be connected to any one Analog socket in Grove Base Shield. The examples used in this tutorial make uses of A0 analog pin. Connect this module to the A0 port of Base Shield.

It is possible to connect the Grove module to Arduino directly by using jumper wires, please refer to the connection in the table below:

Arduino Gas Sensor
5V VCC
GND GND
NC NC
Analog A0 SIG

The output voltage from the Gas sensor increases when the concentration of gas increases. Sensitivity can be adjusted by rotating the potentiometer. Please note that the best preheat time for the sensor is above 24 hours. For detail information about the MQ-2 sensor, please refer the data-sheet provided in Resources section.

Getting Started

What do we need

Name Function Qty Link
Base Shield V2 Provide Grove connectors 1 link
Seeeduino V4.2 Controller 1 link
Grove-Gas Sensor MQ2 Sensor 1 link

Connection

Connect the Grove - Gas Sensor(MQ2) to A0 port as shown in the picture above.

Gas Detection : Basic Example

In this example, the sensor is connected to A0 pin. The voltage read from the sensor is displayed. This value can be used as a threshold to detect any increase/decrease in gas concentration.

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

void loop() {
    float sensor_volt;
    float sensorValue;

    sensorValue = analogRead(A0);
    sensor_volt = sensorValue/1024*5.0;

    Serial.print("sensor_volt = ");
    Serial.print(sensor_volt);
    Serial.println("V");
    delay(1000);
}

Measurement : Approximation

These examples demonstrate ways to know the approximate concentration of Gas. As per the data-sheet of the MQx sensors, these equations are tested for standard conditions and are not calibrated. It may vary based on change in temperature or humidity.

  • Keep the Gas Sensor in clean air environment. Upload the program below.
void setup() {
    Serial.begin(9600);
}

void loop() {
    float sensor_volt;
    float RS_air; //  Get the value of RS via in a clear air
    float R0;  // Get the value of R0 via in H2
    float sensorValue;

    /*--- Get a average data by testing 100 times ---*/
    for(int x = 0 ; x < 100 ; x++)
    {
        sensorValue = sensorValue + analogRead(A0);
    }
    sensorValue = sensorValue/100.0;
    /*-----------------------------------------------*/

    sensor_volt = sensorValue/1024*5.0;
    RS_air = (5.0-sensor_volt)/sensor_volt; // omit *RL
    R0 = RS_air/9.8; // The ratio of RS/R0 is 9.8 in a clear air from Graph (Found using WebPlotDigitizer)

    Serial.print("sensor_volt = ");
    Serial.print(sensor_volt);
    Serial.println("V");

    Serial.print("R0 = ");
    Serial.println(R0);
    delay(1000);

}
  • Then, open the serial monitor of Arduino IDE. Write down the value of R0 and this will be used in the next program. Please write down the R0 after the reading stabilizes.

    Replace the R0 below with value of R0 tested above . Expose the sensor to any one of the gas listed above.

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

void loop() {

    float sensor_volt;
    float RS_gas; // Get value of RS in a GAS
    float ratio; // Get ratio RS_GAS/RS_air
    int sensorValue = analogRead(A0);
    sensor_volt=(float)sensorValue/1024*5.0;
    RS_gas = (5.0-sensor_volt)/sensor_volt; // omit *RL

          /*-Replace the name "R0" with the value of R0 in the demo of First Test -*/
    ratio = RS_gas/R0;  // ratio = RS/R0
          /*-----------------------------------------------------------------------*/

    Serial.print("sensor_volt = ");
    Serial.println(sensor_volt);
    Serial.print("RS_ratio = ");
    Serial.println(RS_gas);
    Serial.print("Rs/R0 = ");
    Serial.println(ratio);

    Serial.print("\n\n");

    delay(1000);

}

Now, we can get the concentration of gas from the figure below.

According to the graph, we can see that the minimum concentration we can test is 100ppm and the maximum is 10000ppm, in a other word, we can get a concentration of gas between 0.01% and 1%. However, we can’t provide a formula because the relation between ratio and concentration is nonlinear.

Resources

Suggest Reading / References

Schematic

Datasheet


ArduinoWioBeagleBoneRaspberry PiLinkIt ONE

Caution

The platforms mentioned above as supported is/are an indication of the module's hardware or theoritical compatibility. We only provide software library or code examples for Arduino platform in most cases. It is not possible to provide software library / demo code for all possible MCU platforms. Hence, users have to write their own software library.

Techsupport

For any technical issue, you are most welcome to contact techsupport@seeed.cc, our techsupport engineers will help you. Thank you!

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