Matrix - MQ-2 Gas Sensor

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1 Introduction

MQ-2 Gas Sensor

• The Matrix-MQ-2_Gas_Sensor uses the MQ-2 gas sensor which is sensitive to LPG, i-butane, propane, methane ,alcohol, Hydrogen, smoke and etc and is used to detect multiple gas leakage. This makes it suitable in various applications of gas leak detection.
• The output voltage of the module is positively proportional to the gas concentration.

2 Features

• Standard 3 Pin Interface
• PCB Dimension(mm): 24 x 32

• Pin Description:

Pin	Description
S	GPIO
V	Supply Voltage 5V
G	Ground

3 Basic Device Operation

• The MQ-2_Gas_Sensor module mainly consists of a MQ-2 gas sensor which is stable and responsive. The sensor uses SnO2 as its gas sensitive material. When its surrounding environment has combustible gases its conductivity change is positively proportional to the gas concentration and this change will be converted to analog output signals. Its sensitivity can be adjusted via the potentiometer.

4 Applications

模块Matrix-MQ_2_Gas_Sensor输出的是模拟信号，需要使用ADC转换模块Matrix-Analog_to_Digital_Converter将模拟信号转换为数字信号。
关于模块Matrix-Analog_to_Digital_Converter的使用方法可参考wiki：Matrix-Analog_to_Digital_Converter。

4.1 连接NanoPi M1

参考下图连接模块：

连接说明：

Matrix-MQ_2_Gas_Sensor
GND	NanoPi M1 Pin9
5V	NanoPi M1 Pin2
S	Matrix-Analog_to_Digital_Converter A0

4.2 连接NanoPi 2

参考下图连接模块：

连接说明：

Matrix-MQ_2_Gas_Sensor
GND	NanoPi 2 Pin9
5V	NanoPi 2 Pin2
S	Matrix-Analog_to_Digital_Converter A0

4.3 连接NanoPi M2 / NanoPi 2 Fire

NanoPi M2和NanoPi 2 Fire的40 Pin引脚定义是一模一样的，所以它们操作Matrix配件的步骤是一样的，这里仅以NanoPi M2为例。
参考下图连接模块：

连接说明：

Matrix-MQ-2_Gas_Sensor
GND	NanoPi M2 Pin9
5V	NanoPi M2 Pin2
S	Matrix-Analog_to_Digital_Converter A0

4.4 连接NanoPC-T2

参考下图连接模块：
Matrix-MQ-2_Gas_Sensor_NanoPC-T2

连接说明：

Matrix-MQ-2_Gas_Sensor
GND	NanoPC-T2 USB Host GND
5V	NanoPC-T2 USB Host 5V
S	Matrix-Analog_to_Digital_Converter A0

5 编译运行测试程序

启动开发板并运行Debian系统，进入系统后克隆Matrix代码仓库：

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

克隆完成后会得到一个名为matrix的目录。

编译并安装Matrix：

$ cd matrix
$ make && make install

运行测试程序：

$ matrix-adc

注意：此模块并不支持热插拔，启动系统前需要确保硬件连接正确。
运行效果如下：

The channel0 value is 2460

当有液化气、丙烷、氢气、天然气等泄露时会检测到事件，气体的浓度越大，读取到的值越大。

6 代码说明

所有的开发板都共用一套Matrix代码，本模块的测试示例代码为matrix-analog_to_digital_converter，内容如下:

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;
}

API说明参考维基：Matrix API reference manual

8 Update Log

8.1 Feb-24-2016

• Added Sections 1, 2, 3 and 4