Matrix - Potentiometer

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1 Introduction

Potentiometer

• The Matrix-Potentiometer module is a Potentiometer module. It can be used in audio control, motion control, transducers, computation and etc.
• 3 Pin 2.54mm spacing pin header, V is supply voltage, G is ground and S is output analog signal. Users can convert output analog signals to digital signals via ADC conversion.
• Output Voltage: 0 ~ Vcc

2 Features

• GPIO
• Small
• 2.54mm spacing pin header
• PCB Dimension(mm): 8 x 24

• Pin Description:

Pin	Description
S	Analog GPIO
V	Supply Voltage 5V
G	Ground

3 Basic Device Operation

• A potentiometer is a three-terminal resistor with a sliding or rotating contact that forms an adjustable voltage divider.If only two terminals are used, one end and the wiper, it acts as a variable resistor or rheostat.
• This module mainly contains a potentiometer where the resistance changes with changes between the contact and one end terminal.

4 硬件连接

模块Matrix-Potentiometer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-Potentiometer
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-Potentiometer
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-Potentiometer
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-Potentiometer_NanoPC-T2

连接说明：

Matrix-Potentiometer
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

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 link to the Chinese version