ads1115a.c

// ads1115b.c read pot on ANC1
// output value in volts exit program.
// uses one-shot mode
// pull up resistors in module caused problems
// used level translator - operated ADS1115 at 5V
// by Lewis Loflin lewis@bvu.net
// www.bristolwatch.com
// http://www.bristolwatch.com/rpi/ads1115.html

#include <stdio.h>
#include <sys/types.h> // open
#include <sys/stat.h>  // open
#include <fcntl.h>     // open
#include <unistd.h>    // read/write usleep
#include <stdlib.h>    // exit
#include <inttypes.h>  // uint8_t, etc
#include <linux/i2c-dev.h> // I2C bus definitions
#include <sys/ioctl.h>

int fd;
// Note ads1115 defaults to 0x48!
int ads_address = 0x49;

//16 bit integer exactly
int16_t val;

//2 8-bit integers which become a 16-bit word
uint8_t writeBuf[3];
uint8_t readBuf[2];

//Float needed to return voltage from input being read
float myfloat;

//ADS1115 is a 16 bit A/D (0 - 32768 count)
//Max voltage is 4.096
//So, volt per step (or count) is this formula
const float VPS = 4.096 / 32768.0; //volts per step

/*
The resolution of the ADC in single ended 
mode we have 15 bit rather than 16 bit resolution, 
the 16th bit being the sign of the differential reading.
*/

int main(int argc, char *argv[])
{

  // open device on /dev/i2c-1 
  // Rapberry Pi really only has 1 i2c bus
  if ((fd = open("/dev/i2c-1", O_RDWR)) < 0) {
    printf("Error: Couldn't open device! %d\n", fd);
    exit (1);
  }

  // connect to ads1115 as i2c slave
  if (ioctl(fd, I2C_SLAVE, ads_address) < 0) {
    printf("Error: Couldn't find device on address!\n");
    exit (1);
  }

  // set config register and start conversion
  // ANC1 and GND, 4.096v, 128s/s

  writeBuf[0] = 1;    // config register is 1
  writeBuf[1] = 0b11010101; // bit 15-8 0xD3

  // bit 15 flag bit for single shot
  // Bits 14-12 input selection:
  // 100 ANC0; 101 ANC1; 110 ANC2; 111 ANC3
  // Bits 11-9 Amp gain. Default to 010 here 001 P19
  // Bit 8 Operational mode of the ADS1115.
  // 0 : Continuous conversion mode
  // 1 : Power-down single-shot mode (default)

  writeBuf[2] = 0b10000101; // bits 7-0  0x85

  // Bits 7-5 data rate default to 100 for 128SPS
  // Bits 4-0  comparator functions see spec sheet.

  // begin conversion
  if (write(fd, writeBuf, 3) != 3) {
    perror("Write to register 1");
    exit(-1);
  }

  // wait for conversion complete
  // checking bit 15
  do {
    if (read(fd, writeBuf, 2) != 2) {
      perror("Read conversion");
      exit(-1);
    }
  }
  while ((writeBuf[0] & 0x80) == 0);



  // read conversion register
  // write register pointer first

  readBuf[0] = 0;   // conversion register is 0
  if (write(fd, readBuf, 1) != 1) {
    perror("Write register select");
    exit(-1);
  }

  // read 2 bytes
  if (read(fd, readBuf, 2) != 2) {
    perror("Read conversion");
    exit(-1);
  }

  // convert display results
  val = readBuf[0] << 8 | readBuf[1];

  if (val < 0)   val = 0;

  myfloat = val * VPS; // convert to voltage

  printf("Values: HEX 0x%02x DEC %d reading %4.3f volts.\n",
         val, val, myfloat);

  close(fd);

  return 0;
}