//
//  Code to read temperature from DLPDesign.com's DLP-TEMP-G
//  with DS18B20 digital thermometer from a Linux machine.  
//
//  Requires:
//     - Linux 2.6 kernel (newer 2.4's work too, but untested)
//     - USB core kernel modules
//     - USB FTDI kernel module for microcontroller on DLP-TEMP-G
//
//  Also Useful:
//     - 'lsusb' tool for viewing USB bus
//
//  License:
//     - Copyright (c) 2007 Tim Jensen, tim at jensens d0t org
//     - This code is FREE, so enjoy it.
//

#include <stdio.h>
#include <termios.h>
#include <unistd.h>
#include <fcntl.h>

int fd;

void init()
{
  // 9600 baud, 8n1, no flow control
  struct termios tc;                  
  fd = open("/dev/ttyUSB0", O_RDWR); // on my machine is ttyUSB0
  if (fd < 0) {
    perror("/dev/ttyUSB0");
    fprintf(stderr, "Cannot connect to temperature sensor\n");
    return;
  }
  tcgetattr(fd, &tc);
  tc.c_iflag = IGNPAR;
  tc.c_oflag = 0;
  tc.c_cflag = CS8 | CREAD | CLOCAL;
  tc.c_lflag = 0;
  cfsetispeed(&tc, B9600);
  cfsetospeed(&tc, B9600);
  tcsetattr(fd, TCSANOW, &tc);
}


int main(int argc, const char **argv)
{
  unsigned char buf[20];
  int b;

  memset(buf,0,sizeof(buf));

  init();

  if (argc == 2 && !strcmp(argv[1],"-p")) {
    //
    // Ping the device expect 'Q' as response
    //
    write(fd, "P", 1);
    read(fd, buf, 1);
    printf("%c\n", buf[0]);
    return 0;
  }

  //
  // Probe temperature sensor S1
  //
  write(fd, "S", 1);  

  //
  // Read 8 bytes back from S1
  //
  // 0 = temperature LSB
  // 1 = temperature MSB
  // 2-7 = Not used 
  //
  for (b=0; b < 8; b++)
    read(fd, &buf[b], 1);

  //
  // Convert to temperature per the DS18B20 specs
  //
  int temp = buf[1];
  temp = (temp << 8) | buf[0];  // combine MSB and LSB

  float C = (float)(temp) / 16.0;  // adjust the radix to get C
  float F = (9.0/5.0) * C + 32.0;  // convert to F for Americans
  
  if (argc == 2 && !strcmp(argv[1],"-i")) {
    printf("%d\n", (int)(F + 0.5));  // mrtg likes integers
  } else {
    printf("%1.2f\n", F);
  }

  return 0;
}