adc.c

/*
read abelectronics ADC Pi V2 board inputs with repeating reading from each channel.

Based on ADC 1 demo code by Stephan Callsen from https://github.com/abelectronicsuk/adcpi/blob/master/adcon.c

Author:	Brian Dorey
Version:	1.0 
Date: 15 August 2013
Version History:
1.0 - Initial Release

	Required package:
	apt-get install libi2c-dev

	Compile with gcc: 
	gcc adc.c -o adc

	Execute with:
	./adc [channel] 
	default is channel 1

*/

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

// define adc chips addresses and channel modes
#define ADC_1 		0x68
#define ADC_2 		0x69
#define ADC_CHANNEL1	0x9C
#define ADC_CHANNEL2	0xBC
#define ADC_CHANNEL3 	0xDC
#define ADC_CHANNEL4	0xFC

const float varDivisior = 64; // from pdf sheet on adc addresses and config for 18 bit mode
static float varMultiplier = 0;


float getadc (int chn);  


int main(int argc, char **argv) {
  int i;
  float val;
  int channel;
  // setup multiplier based on input voltage range and divisor value
  varMultiplier = (2.4705882/varDivisior)/1000;

  if (argc>1) channel=atoi(argv[1]);
  if (channel <1|channel>8) channel=1;
  // loop for 500 samples and print to terminal
  for (i=0;i<500;i++){
    val = getadc (channel);
	if (val <= 5.5) {
		printf ("Channel: %d  - %2.4fV\n",channel,val);  
	}
    sleep (0.5);
  }
  return 0; 
}

float getadc (int chn){
  unsigned int fh,dummy, adc, adc_channel;
  float val;
  __u8  res[4];
  // select chip and channel from args
  switch (chn){
    case 1: { adc=ADC_1; adc_channel=ADC_CHANNEL1; }; break;
    case 2: { adc=ADC_1; adc_channel=ADC_CHANNEL2; }; break;
    case 3: { adc=ADC_1; adc_channel=ADC_CHANNEL3; }; break;
    case 4: { adc=ADC_1; adc_channel=ADC_CHANNEL4; }; break;
    case 5: { adc=ADC_2; adc_channel=ADC_CHANNEL1; }; break;
    case 6: { adc=ADC_2; adc_channel=ADC_CHANNEL2; }; break;
    case 7: { adc=ADC_2; adc_channel=ADC_CHANNEL3; }; break;
    case 8: { adc=ADC_2; adc_channel=ADC_CHANNEL4; }; break;
    default: { adc=ADC_1; adc_channel=ADC_CHANNEL1; }; break;
  }
  // open /dev/i2c-0 for version 1 Raspberry Pi boards
  // open /dev/i2c-1 for version 2 Raspberry Pi boards
  fh = open("/dev/i2c-1", O_RDWR);
  ioctl(fh,I2C_SLAVE,adc);
  // send request for channel
  i2c_smbus_write_byte (fh, adc_channel);
  usleep (50000);
  // read 4 bytes of data
  i2c_smbus_read_i2c_block_data(fh,adc_channel,4,res);
  // loop to check new value is available and then return value
  while (res[3] & 128){
	  // read 4 bytes of data
	  i2c_smbus_read_i2c_block_data(fh,adc_channel,4,res);
  }
  usleep(50000);
  close (fh);

  // shift bits to product result
  dummy = ((res[0] & 0b00000001) << 16) | (res[1] << 8) | res[2];

  // check if positive or negative number and invert if needed
  if (res[0]>=128) dummy = ~(0x020000 - dummy);
 
  val = dummy * varMultiplier;
  return val;
}