tmp102 from Pi.

temp.c

#include <errno.h>
#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <linux/i2c-dev.h>
#include <sys/ioctl.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>


#define TMP102_I2C	0x48
#define I2C_BUS		"/dev/i2c-0"

int main(void) {

	int file;
	char filename[40];
	int addr = TMP102_I2C; // The I2C address

	sprintf(filename, I2C_BUS);
	if ((file = open(filename, O_RDWR)) < 0) {
		printf("Failed to open the bus.");
		/* ERROR HANDLING; you can check errno to see what went wrong */
		printf("error: %s (%d)\n", strerror(errno), errno);
		exit(1);
	}

	if (ioctl(file, I2C_SLAVE, addr) < 0) {
		printf("Failed to acquire bus access and/or talk to slave.\n");
		/* ERROR HANDLING; you can check errno to see what went wrong */
		printf("error: %s (%d)\n", strerror(errno), errno);
		exit(1);
	}

	write(file, 0x00, 1);

	usleep(500);

	int errCount = 0;
	int i = 0;
	for (i=0;i<1;i++) {
		char buf[1] = { 0 };

		float data;

		// Read 2 uint8 using I2C Read
		int k = read(file, buf, 2);
		if ((k != 2)) {
			errCount++;
			printf("error: %s (%d) %d\n", strerror(errno), errno, errCount);
		} else {

			int temperature;

			temperature = ((buf[0]) << 8) | (buf[1]);
			temperature >>= 4;

			//The tmp102 does twos compliment but has the negative bit in the wrong spot, so test for it and correct if needed
			if (temperature & (1 << 11))
				temperature |= 0xF800; //Set bits 11 to 15 to 1s to get this reading into real twos compliment

      float fahrenheit = (temperature * 0.0625) * 9/5 + 32;
      printf("%0.1f\n", fahrenheit);
			//printf(" temp:  %04f \t error:  %d\n", fahrenheit, errCount);

		}
		usleep(5);

	}
	return 0;
}