Matrix - Soil Moisture Sensor

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1 Introduction

Soil Moisture Sensor Module

• The Matrix-Soil_Moisture_Sensor is a simple and straightforward-to-use soil moisture detection module.
• Before plug the module to a target soil make sure the target soil doesn’t contain rocks. Then point the pads perpendicular to the soil, push it in and make the module close contact to the soil and the module will output analog signals which are proportional to the soil’s moisture condition.
• To improve the test result it is suggested to take the average of multiple test results.
• The test result can be influenced by various factors: soil density, soil composition and etc.

2 Hardware Specification

• Standard 3 PIN Interface
• PCB Dimension(mm): 20 x 60

• Pin Description:

Pin	Description
S	GPIO
V	Supply Voltage 5V
G	Ground

3 Basic Device Operation工作原理

• 模块两片测试电极间的阻值与环境的湿度成比例，利用电极间电阻变化测量周围土壤水分湿度。土壤越干燥，输出电压越小。越湿润输出电压越大。模块输出的模拟信号再通过AD转换数字信号信号，即可得到土壤湿度值。
• 它利用电磁脉冲原理、根据电磁波在介质中传播频率来测量土壤的表观介电常数(ε)，从而得到土壤容积含水量(θv)。
• 使用说明：传感器模块使用的是adc模拟输入输出，这里直接把传感器模块接到PCF8591转换模块上即可检查到土壤湿度值。

4 Applications

4.1 Connect to NanoPi M1

Refer to the following connection diagram to connect the module to the NanoPi M1:

Connection Details:

Matrix-Soil_Moisture_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:

Connection Details:

Matrix-Soil_Moisture_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-Soil_Moisture_Sensor_nanopi_m2

Connection Details:

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

4.4 Connect to NanoPi M3

Refer to the following connection diagram to connect the module to the NanoPi M3:
Matrix-Soil_Moisture_Sensor_nanopi_m3

Connection Details:

Matrix-Soil_Moisture_Sensor
GND	NanoPi M3 Pin9
5V	NanoPi M3 Pin2
S	Matrix-Analog_to_Digital_Converter A0

4.5 Connect to NanoPC-T2

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

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