Matrix - Temperature Sensor

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1 Introduction

Temperature Sensor

• The matrix-temperature_sensor module is used to measure temperature.
• We utilitze the DS18B20 chip with the To-92 package in this module. Its unique 1-wire interface requires only 1 port pin for reading/writing. Power for reading, writing, and performing temperature conversions can be derived from the data line itself with no need for an external power source. The DS18B20 can be powered from its data line. Each DS18B20 is assigned a unique ID.
• Its temperature range is -55 degree Celsius to +125 degree Celsius. The thermometer resolution is programmable from 9 to 12 bits. When the measured temperature is between -10 degree Celsius to +85 degree Celsius the accuracy can be at 0.5 degree. Among all three DS18B20 pins V is power, G is ground and S is data.

2 Features

• -55 degree Celsius to +125 degree Celsius
• One wire interface for communication
• Tiny, easy to be deployed in various situations
• 2.54mm spacing pin
• PCB dimension(mm): 8 X 24

• Pin Description:

Pin	Description
S	GPIO
V	Supply Voltage 5V
G	Ground

3 Basic Device Operation

The core functionality of the DS18B20 is its direct-to-digital temperature sensor. The resolution of the DS18B20 is configurable (9, 10, 11, or 12 bits), with 12-bit readings the factory default state. This equates to a temperature resolution of 0.5°C, 0.25°C, 0.125°C, or 0.0625°C. Following the issuance of the Convert T [44h] command, a temperature conversion is performed and the thermal data is stored in the scratchpad memory in a 16-bit, sign-extended two’s complement format. The temperature information can be retrieved over the 1-Wire interface by issuing a Read Scratchpad [BEh] command once the conversion has been performed. The data is transferred over the 1-Wire bus, LSB first. The MSB of the temperature register contains the “sign” (S) bit, denoting whether the temperature is positive or negative.

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_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_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_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_Sensor_NanoPC-T2

Connection Details:

Matrix-Temperature_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_sensor

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 temperature is 27.312 C

The module successfully read the environment's temperature.

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_sensor". Here is its source code:

int main(int argc, char ** argv)
{
    char temperature[BUF_SIZE], modStr[BUF_SIZE];
    int board;
    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);
 
    if (argc == 2)
        pin = atoi(argv[1]);
    sprintf(modStr, "modprobe %s gpio=%d", TEMP_GPIO_DRIVER_MODULE, pintoGPIO(pin));
    printf("%s\n", modStr);
    system(modStr);
    system("modprobe "TEMP_DRIVER_MODULE);
    sleep(1);
    memset(temperature, 0, BUF_SIZE);
    if (ds18b20Read(temperature) > 0) {
        printf("The temperature is %.3f C\n", atoi(temperature)/1000.0);
    } else {
        printf("Fail to get temperature\n");        
    }
    system("rmmod "TEMP_GPIO_DRIVER_MODULE);
    system("rmmod "TEMP_DRIVER_MODULE);
    return 0;
}

For more details about this APIs called in this code sample refer to Matrix API reference manual

7 Resources

DS18B20.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

8.2 June-24-2016

• Re-organized and simplified wiki