Grove - Gas Sensor(MQ2)

Introduction

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.

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

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	kΩ

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

• How to choose a Gas Sensor
• What’s LEL

Schematic

• Grove Gas Sensor - EAGLE (Schematic and Board) files
• Grove Gas Sensor - PDF Schematic

Datasheet

• MQ-2 Datasheet

Help us make it better

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