pigpio/EXAMPLES/C/PCF8591_YL-40/PCF8591.c

#include <stdio.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/ioctl.h>
#include <linux/i2c-dev.h>
#include <ncurses.h> /* libncurses5-dev */

/*
2014-08-26 PCF8591.c

sudo apt-get install libncurses5-dev

gcc -o PCF8591 PCF8591.c -lcurses -lpigpio -lpthread

sudo ./PCF8591
*/

/*
Connect Pi 3V3 - VCC, Ground - Ground, SDA - SDA, SCL - SCL.
*/

#define PCF8591_I2C_ADDR 0x48

/*
    P4 The thermister voltage is provided at AIN 1.
    P5 The photocell voltage is provided at AIN 0.
    P6 The single turn 10K ohm trim pot voltage is provided at AIN 3.
*/

/*
7 6 5 4 3 2 1 0
0 X X X 0 X X X
  | | |   | | |
  A B B   C D D

0 1 0 0 0 1 0 0

A 0 D/A inactive
  1 D/A active

B 00 single ended inputs
  01 differential inputs
  10 single ended and differential
  11 two differential inputs

C 0 no auto inc
  1 auto inc

D 00 select channel 0
  01 select channel 1
  10 select channel 2
  11 select channel 3

*/

int main(int argc, char *argv[])
{
   int i;
   int r;
   int handle;
   char aout;
   unsigned char command[2];
   unsigned char value[4];
   unsigned char str[8];

   int j;
   int key;

   if (gpioInitialise() < 0) return 1;

   initscr();
   noecho();
   cbreak();
   nodelay(stdscr, true);
   curs_set(0);

   printw("PCF8591 + or - to change aout, any other key to quit.");

   mvaddstr(10, 0, "Brightness");
   mvaddstr(12, 0, "Temperature");
   mvaddstr(14, 0, "?");
   mvaddstr(16, 0, "Resistor");

   refresh();

   handle = i2cOpen(1, PCF8591_I2C_ADDR, 0);

   command[1] = 0;
   aout = 128;

   while (1)
   {
      for (i=0; i<4; i++)
      {
         command[1] = aout;
         command[0] = 0x40 | ((i + 1) & 0x03); // output enable | read input i

         i2cWriteDevice(handle, &command, 2);

         usleep(20000);

         // the read is always one step behind the selected input
         value[i] = i2cReadByte(handle);

         sprintf(str, "%3d", value[i]);
         mvaddstr(10+i+i, 12, str);
         value[i] = value[i] / 4;
         move(10 + i + i, 16);

         for(j = 0; j < 64; j++)
            if(j < value[i]) addch('*'); else addch(' ');
      }

      refresh();

      key = getch();

      if      ((key == '+') || (key == '=')) aout++;
      else if ((key == '-') || (key == '_')) aout--;
      else if  (key != -1)                   break;
   }

   endwin();
 
   i2cClose(handle);

   gpioTerminate();

   return (0);
}