first re-commit.

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

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+#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);
+}
+

pigpio-master/EXAMPLES/C/PCF8591_YL-40/README

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+A program to display readings from the (I2C) PCF8591.