Matrix - Analog to Digital Converter

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1 Introduction

Analog to Digital Converter

• The Matrix-Analog_to_Digital_Converter is a single-chip, single-supply low-power 8-bit CMOS data acquisition device.
• It utilizes the PCF8591 chip with four analog inputs, one analog output and a serial I2C-bus interface. Three address pins A0, A1 and A2 are used for programming the hardware address, allowing

the use of up to eight devices connected to the I2C-bus without additional hardware. Address, control and data to and from the device are transferred serially via the two-line bidirectional I2C-bus. The maximum conversion rate is given by the maximum speed of the I2C-bus.

• The I2C hardware address is configured to 1001000x
• The operating supply voltage is from 2.5V to 6.0V，Among the 2.54 mm spacing pin header the 5V pin is the supply voltage. If you need 0 - 3.3V analog signals and keep the acquisition resolution you can connect it to a 3.3V supply voltage.

2 Features

• Wide range supply voltage: 2.5V - 6.0V
• I2C interface: 3.3V/5V
• 8-bit A/D x 4
• 8-bit D/A x 1
• Small and easy to be used in various situations
• 2.54 mm spacing pin
• PCB dimension (mm): 16 x 24

• Pin Description:

Pin	Description
SDA	I2C SDA
SCL	I2C SCL
5V	Supply Voltage 5V
GND	Ground
AOUT	Analog Output
A3	Analog Input3
A2	Analog Input2
A1	Analog Input1
A0	Analog Input0

3 Basic Device Operation

The PCF8591's I2C-bus is for bidirectional, two-line communication between different ICs or modules. The two lines are a Serial DAta line (SDA) and a Serial CLock line (SCL). Both lines must be connected to a positive supply via a pull-up resistor. Data transfer may be initiated only when the bus is not busy. The AINT0 - AINT4 pins are analog inputs which can be configured to single-ended or differential inputs. The supply voltage is 0 - VDD.
1. Each PCF8591 device in an I2C-bus system is activated by sending a valid address to the device. The address consists of a fixed part and a programmable part. The programmable part must be set according to the address pins A0, A1 and A2. The address is always sent as the first byte after the start condition in the I2C-bus protocol. The last bit of the address byte is the read/write-bit which sets the direction of the following data transfer.
2. The second byte sent to a PCF8591 device is stored in its control register and is required to control the device function. The upper nibble of the control register is used for enabling the analog output, and for programming the analog inputs as single-ended or differential inputs. The lower nibble selects one of the analog input channels defined by the upper nibble.
3. The on-chip D/A converter and a high-gain comparator are used temporarily during an A/D conversion cycle. An A/D conversion cycle is always started after sending a valid read mode address to a PCF8591 device. The A/D conversion cycle is triggered at the trailing edge of the acknowledge clock pulse and is executed while transmitting the result of the previous conversion。

4 Applications

4.1 Connect to NanoPi M1

Please refer to the following connection diagram to connect the module to the NanoPi M1

Connection Details:

Matrix-Analog_to_Digital_Converter	NanoPi M1
SDA	Pin3
SCL	Pin5
5V	Pin4
GND	Pin6

4.2 Connect to NanoPi 2

Please refer to the following connection diagram to connect the module to the NanoPi 2:

Connection Details:

Matrix-Analog_to_Digital_Converter	NanoPi 2
SDA	Pin3
SCL	Pin5
5V	Pin4
GND	Pin6

4.3 Connect to NanoPi M2 / NanoPi 2 Fire

Please refer to the following connection diagram to connect the module to the NanoPi M2/ NanoPi 2 Fire:

Connection Details:

Matrix-Analog_to_Digital_Converter	NanoPi M2
SDA	Pin3
SCL	Pin5
5V	Pin4
GND	Pin6

4.4 Connect to NanoPC-T2

Please refer to the following connection diagram to connect the module to the NanoPC-T2
Matrix-Analog_to_Digital_Converter_NanoPC-T2

Connection Details:

Matrix-Analog_to_Digital_Converter	NanoPC-T2
SDA	Pin6
SCL	Pin5
5V	Pin29
GND	Pin30

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

当通道0接到5V时，能得到最大值2550，当通道0接到地时，能得到最小值0。

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

7 Resources

PCF8591.pdf

8 Update Log

8.1 Feb-19-2016

• Added Section 5