Matrix - Temperature and Humidity Sensor

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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 Applications

4.1 Connect to NanoPi M1

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

Connection Details:

Matrix-Temperature_and_Humidity_Sensor	NanoPi M1
S	Pin7
V	Pin4
G	Pin6

4.2 Connect to NanoPi 2

Refer to the following connection diagram to connect the module to the NanoPi 2:

Connection Details:

Matrix-Temperature_and_Humidity_Sensor	NanoPi 2
S	Pin7
V	Pin4
G	Pin6

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:

Connection Details:

Matrix-Temperature_and_Humidity_Sensor	NanoPi M2
S	Pin7
V	Pin4
G	Pin6

4.4 Connect to NanoPC-T2

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

Connection Details:

Matrix-Temperature_and_Humidity_Sensor	NanoPC-T2
S	Pin15
V	Pin29
G	Pin30

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-temp_humidity

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 humidity is 35000
The temperature is 26000

The module successfully read the environment's humidity and temperature values.

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-temperature_and_humidity_sensor". Here is its source code:

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;
}

For more details about this APIs called in this code sample refer to 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