Matrix - MQ-3 Gas Sensor

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1 Introduction

MQ-3 Alcohol sensor

• The Matrix-MQ_3_Gas_Sensor module uses the MQ-3 gas sensor which is sensitive to alcoholic vapors and thus can be used to detect the density of an alcoholic vapor.
• The output voltage of the module is non-linear but close to linear to the density of alcoholic vapors.
• In order to increase its accuracy before use it to detect a gas warm it up for one minute as long as it is not overheated.

2 Features

• Standard 3 PIN header
• PCB dimension(mm): 24 x 32

MQ-3 Gas Sensor.PCB

• Pin Description:

Pin	Description
S	GPIO
V	Supply Voltage 5V
G	Ground

3 工作原理

Matrix-MQ_3_Gas_Sensor模块的主要器件是一个具有快速响应和恢复特性的MQ-3气体传感器，传感器所使用的气敏材料是在清洁空气中电导率较低的二氧化锡(SnO2)，当传感器所处环境中存在酒精蒸汽时，传感器的电导率随空气中酒精蒸汽的浓度增加而增大，传感器将电导率的变化转换为与酒精蒸汽浓度相对应的模拟信号输出，灵敏度可以通过电位计进行调节。

4 Applications

The Matrix-MQ_3_Gas_Sensor module outputs analog signals which can be converted to digital signals through an ADC converter e.g. the Matrix-Analog_to_Digital_Converter module.
For more details about the Matrix-Analog_to_Digital_Converter module refer to wiki: Matrix_-_Analog_to_Digital_Converter.

4.1 Connect to NanoPi M1

Refer to the following connection diagram to connect the module to the NanoPi M1:
Matrix-MQ_3_Gas_Sensor_nanopi_m1

Connection Details:

Matrix-MQ_3_Gas_Sensor
GND	NanoPi M1 Pin9
5V	NanoPi M1 Pin2
S	Matrix-Analog_to_Digital_Converter A0

4.2 Connect to NanoPi 2

Refer to the following connection diagram to connect the module to the NanoPi 2:
Matrix-MQ_3_Gas_Sensor_nanopi_2

Connection Details:

Matrix-MQ_3_Gas_Sensor
GND	NanoPi 2 Pin9
5V	NanoPi 2 Pin2
S	Matrix-Analog_to_Digital_Converter A0

4.3 Connect to NanoPi M2 / NanoPi 2 Fire

Refer to the following connection diagram to connect the module to the NanoPi M2/ NanoPi 2 Fire:
Matrix-MQ_3_Gas_Sensor_nanopi_m2

Connection Details:

Matrix-MQ_3_Gas_Sensor
GND	NanoPi M2 Pin9
5V	NanoPi M2 Pin2
S	Matrix-Analog_to_Digital_Converter A0

4.4 Connect to NanoPC-T2

Refer to the following connection diagram to connect the module to the NanoPC-T2:
Matrix-MQ_3_Gas_Sensor_NanoPC-T2

Connection Details:

Matrix-Potentiometer
GND	NanoPC-T2 USB Host GND
5V	NanoPC-T2 USB Host 5V
S	Matrix-Analog_to_Digital_Converter A0

5 Compile & Run Test Program

Boot your ARM board with Debian and copy the matrix code:

$ apt-get update && apt-get install git
$ git clone https://github.com/friendlyarm/matrix.git

If your cloning is done successfully a "matrix" directory will be generated.

Compile and install Matrix:

$ cd matrix
$ make && make install

Run test program:

$ matrix-adc

Note: this module is not plug and play therefore before running the module please make sure it is connected to an ARM board.
Here is what you should observe:

The channel0 value is 2460

When the density of alcoholic vapors reaches a threshold value an event will be triggered. As the density increases the value will increase.

6 Code Sample

This Matrix code sample can work with all the ARM boards mentioned in this module's wiki. The name of this code sample is "matrix-analog_to_digital_converter". Here is its source code:

int main(int argc, char ** argv)
{
    int i = 0;
    int value = 0;
    int channel = 0;
 
    if (boardInit() < 0) {
        printf("Fail to init board\n");
        return -1;
    }
 
    if (argc == 2)
        channel = atoi(argv[1]);
    system("modprobe "DRIVER_MODULE);
    signal(SIGINT, intHandler);
    for (i=0; i<ADC_READ_TIMES; i++) {
        if (pcf8591Read(channel, &value) != -1) {
            printf("The channel%d value is %d\n", channel, value);
        } else {
            printf("Fail to get channel%d value\n", channel);
        }
    }
    system("rmmod "DRIVER_MODULE);
 
    return 0;
}

For more details about this APIs called in this code sample refer to Matrix API reference manual