Matrix - Temperature and Humidity Sensor

查看中文

1 Introduction

Temperature and Humidity Sensor

• The Matrix-Temperature_and_Humidity_Sensor module is used to detect temperature and humidity.
• It utilizes the DHT11 temperature and humidity sensor. Its humidity range is 20% - 80% and the accuracy is 5%. Its temperature range is 0℃ - 50℃ and the accuracy is ±2℃.

2 Features

• Humidity range: 20 - 80%RH, Temperature range 0 ~ 50℃
• Accuracy of humidity: +-5%RH, accuracy of temperature: +-2℃
• One wire communication
• 2.54 mm spacing pin
• PCB dimension (mm): 16 x 32

Pin Description:

Pin	Description
S	GPIO
V	Supply Voltage 5V
G	Ground

3 Basic Device Operation

The DHT11 module uses a simplified single-bus serial communication. DATA controls communication and synchronization between the microprocessor and DHT11. A data transfer takes 4ms. The data format contains an integer part and a decimal part. The basic operation is as follows:

• a transmission of 40 data, the high first-out
• data format: 8bit humidity integer data + 8bit the Humidity decimal data
  
• 8bit temperature integer data + 8bit fractional temperature data
  
• 8 bit parity bit
  
• If a transmission is successful the “8bit humidity integer data + 8bit humidity decimal data +8 bit temperature integer data + 8bit temperature fractional data” 8bit checksum is equal to the results of the last eight.
  
• After the user host (MCU) sends a signal DHT11 is converted from low-power mode to high-speed mode, until the host begins to signal the end. Then DHT11 sends a response signal to send 40bit data, and trigger a letter collection. If DHT11 doesn't receive a signal from the host it will not begin a letter collection. After the letter collection is done DHT11 will turn to low power mode.

4 硬件连接

4.1 连接NanoPi M1

参考下图连接模块：

连接说明：

Matrix-Temperature_and_Humidity_Sensor	NanoPi M1
S	Pin7
V	Pin4
G	Pin6

4.2 连接NanoPi 2

参考下图连接模块：

连接说明：

Matrix-Temperature_and_Humidity_Sensor	NanoPi 2
S	Pin7
V	Pin4
G	Pin6

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-Temperature_and_Humidity_Sensor	NanoPi M2
S	Pin7
V	Pin4
G	Pin6

4.4 连接NanoPC-T2

参考下图连接模块：
Matrix-Temperature_and_Humidity_Sensor_NanoPC-T2

连接说明：

Matrix-Temperature_and_Humidity_Sensor	NanoPC-T2
S	Pin15
V	Pin29
G	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-temp_humidity

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 humidity is 35000
The temperature is 26000

成功读取温湿度值。

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-temperature_and_humidity_sensor，内容如下:

int main(int argc, char ** argv)
{
    int ret = -1;
    int dhtTemp=0, dhtHdty=0, board;
    char modStr[BUF_SIZE];
    int pin = GPIO_PIN(7);
 
    if ((board = boardInit()) < 0) {
        printf("Fail to init board\n");
        return -1;
    }    
    if (board == BOARD_NANOPI_T2)
        pin = GPIO_PIN(15);
 
    sprintf(modStr, "modprobe %s gpio=%d", DRIVER_MODULE, pintoGPIO(pin));
    system(modStr);
    if ((ret = dht11Read(DHT_HUMIDITY, &dhtHdty)) != -1) {
        printf("The humidity is %d\n", dhtHdty);
    } else {
        printf("Faided to get humidity\n");
    }
    if ((ret = dht11Read(DHT_TEMP, &dhtTemp)) != -1) {
        printf("The temperature is %d\n", dhtTemp);
    } else {
        printf("Faided to get temperature\n");
    }
    system("rmmod "DRIVER_MODULE);
    return ret;
}

API说明参考维基：Matrix API reference manual

7 Resources

DHT11.pdf

8 Update Log

8.1 Feb-23-2016

• Added the description for "NanoPi 2 branch" in Section 4
• Added Section 5: Connect to NanoPi 2