I2C Sensor Example C Code

README.txt

This gist contains code excerpts from the article:
https://www.nutsvolts.com/magazine/article/working-with-i2c-sensor-devices

example-usage.sh

root@ts-imx6:~/projects/altimeter-sensor$ gcc mpl3115a2.c -o mpl3115a2
root@ts-imx6:~/projects/altimeter-sensor$ ./mpl3115a2
Pressure : 85.36 kPa
Altitude : 20623.69 m
Temperature in Celsius : 23.56 C
Temperature in Fahrenheit : 74.41 F

mpl3115a2.c

#include <stdio.h>
#include <stdlib.h>
#include <linux/i2c-dev.h>
#include <sys/ioctl.h>
#include <fcntl.h>

void main()
{
    // Create I2C bus
    int file;
    char *bus = "/dev/i2c-1";
    if((file = open(bus, O_RDWR)) < 0)
    {
        printf("Failed to open the bus. \n");
        exit(1);
    }
    // Get I2C device, TSL2561 I2C address is 0x60(96)
    ioctl(file, I2C_SLAVE, 0x60);

    // Select control register(0x26)
    // Active mode, OSR = 128, altimeter mode(0xB9)
    char config[2] = {0};
    config[0] = 0x26;
    config[1] = 0xB9;
    write(file, config, 2);
    // Select data configuration register(0x13)
    // Data ready event enabled for altitude, pressure, temperature(0x07)
    config[0] = 0x13;
    config[1] = 0x07;
    write(file, config, 2);
    // Select control register(0x26)
    // Active mode, OSR = 128, altimeter mode(0xB9)
    config[0] = 0x26;
    config[1] = 0xB9;
    write(file, config, 2);
    sleep(1);

    // Read 6 bytes of data from address 0x00(00)
    // status, tHeight msb1, tHeight msb, tHeight lsb, temp msb, temp lsb
    char reg[1] = {0x00};
    write(file, reg, 1);
    char data[6] = {0};
    if(read(file, data, 6) != 6)
    {
        printf("Error : Input/Output error \n");
        exit(1);
    }

    // Convert the data
    int tHeight = ((data[1] * 65536) + (data[2] * 256 + (data[3] & 0xF0)) / 16);
    int temp = ((data[4] * 256) + (data[5] & 0xF0)) / 16;
    float altitude = tHeight / 16.0;
    float cTemp = (temp / 16.0);
    float fTemp = cTemp * 1.8 + 32;

    // Select control register(0x26)
    // Active mode, OSR = 128, barometer mode(0x39)
    config[0] = 0x26;
    config[1] = 0x39;
    write(file, config, 2);
    sleep(1);

    // Read 4 bytes of data from register(0x00)
    // status, pres msb1, pres msb, pres lsb
    reg[0] = 0x00;
    write(file, reg, 1);
    read(file, data, 4);

    // Convert the data to 20-bits
    int pres = ((data[1] * 65536) + (data[2] * 256 + (data[3] & 0xF0))) / 16;
    float pressure = (pres / 4.0) / 1000.0;
    
    // Output data to screen
    printf("Pressure : %.2f kPa \n", pressure);
    printf("Altitude : %.2f m \n", altitude);
    printf("Temperature in Celsius : %.2f C \n", cTemp);
    printf("Temperature in Fahrenheit : %.2f F \n", fTemp);
}