dht22.c

/*
 *      dht22.c:
 *	Simple test program to test the wiringPi functions
 *	Based on the existing dht11.c
 *	Amended by technion@lolware.net
 */

#include <wiringPi.h>

#include <ctype.h>
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <sys/types.h>
#include <unistd.h>


#include "locking.h"

#define MAXTIMINGS 85
static int DHTPIN = 7;
int printtemp = 1;
int printhumid = 1;
static int dht22_dat[5] = {0,0,0,0,0};

static uint8_t sizecvt(const int read)
{
  /* digitalRead() and friends from wiringpi are defined as returning a value
  < 256. However, they are returned as int() types. This is a safety function */

  if (read > 255 || read < 0)
  {
    fprintf(stderr, "Invalid data from wiringPi library\n");
    exit(EXIT_FAILURE);
  }
  return (uint8_t)read;
}

static int read_dht22_dat()
{
  uint8_t laststate = HIGH;
  uint8_t counter = 0;
  uint8_t j = 0, i;

  dht22_dat[0] = dht22_dat[1] = dht22_dat[2] = dht22_dat[3] = dht22_dat[4] = 0;

  // pull pin down for 18 milliseconds
  pinMode(DHTPIN, OUTPUT);
  digitalWrite(DHTPIN, HIGH);
  delay(10);
  digitalWrite(DHTPIN, LOW);
  delay(18);
  // then pull it up for 40 microseconds
  digitalWrite(DHTPIN, HIGH);
  delayMicroseconds(40); 
  // prepare to read the pin
  pinMode(DHTPIN, INPUT);

  // detect change and read data
  for ( i=0; i< MAXTIMINGS; i++) {
    counter = 0;
    while (sizecvt(digitalRead(DHTPIN)) == laststate) {
      counter++;
      delayMicroseconds(1);
      if (counter == 255) {
        break;
      }
    }
    laststate = sizecvt(digitalRead(DHTPIN));

    if (counter == 255) break;

    // ignore first 3 transitions
    if ((i >= 4) && (i%2 == 0)) {
      // shove each bit into the storage bytes
      dht22_dat[j/8] <<= 1;
      if (counter > 16)
        dht22_dat[j/8] |= 1;
      j++;
    }
  }

  // check we read 40 bits (8bit x 5 ) + verify checksum in the last byte
  // print it out if data is good
  if ((j >= 40) && 
      (dht22_dat[4] == ((dht22_dat[0] + dht22_dat[1] + dht22_dat[2] + dht22_dat[3]) & 0xFF)) ) {
        float t, h;
        h = (float)dht22_dat[0] * 256 + (float)dht22_dat[1];
        h /= 10;
        t = (float)(dht22_dat[2] & 0x7F)* 256 + (float)dht22_dat[3];
        t /= 10.0;
        if ((dht22_dat[2] & 0x80) != 0)  t *= -1;

    if(printhumid != 0) {
    	printf("%.2f", h);
	if (printtemp != 0) {
		putchar(',');
	}
    }

    if(printtemp != 0) {
    	printf("%.2f", t);
    }

    //printf("Humidity = %.2f %% Temperature = %.2f *C \n", h, t );
    return 1;
  }
  else
  {
    fprintf(stderr, "Data not good, skip\n");
    return 0;
  }
}

int main (int argc, char *argv[])
{
  //int lockfd;
  int c;
  int retries = 10;
  while ((c = getopt (argc, argv, "tmr:p:")) != -1)
  	switch (c)
  {
  	case 't':
  		printhumid = 0;
  		break;

  	case 'm':
  		printtemp = 0;
  		break;

	case 'r':
		retries = atoi(optarg);
		break;

  	case 'p':
  		DHTPIN = atoi(optarg);
  		break;

  	case '?':
  		if (optopt == 'p')
  			fprintf (stderr, "Option -%c requires port number an argument.\n", optopt);
        else if (isprint (optopt))
          fprintf (stderr, "Unknown option `-%c'.\n", optopt);
        else
          fprintf (stderr,
                   "Unknown option character `\\x%x'.\n",
                   optopt);
        return 1;

    default:
        fprintf(stderr, "This should never happen.\n");
      	abort();
  }

  //printf ("Raspberry Pi wiringPi DHT22 reader\nwww.lolware.net\n") ;

  //lockfd = open_lockfile(LOCKFILE);

  if (wiringPiSetup () == -1)
    exit(EXIT_FAILURE) ;
	
  //if (setuid(getuid()) < 0)
  //{
  //  perror("Dropping privileges failed\n");
  //  exit(EXIT_FAILURE);
  //}


  int fails = 0;
  while ((read_dht22_dat() == 0) && (fails < retries))
  {
     delay(500); // wait 1sec to refresh
     fails ++;
  }

  delay(1500);
  //close_lockfile(lockfd);

  return 0 ;
}