temp_rh_sensor.c

#include <wiringPi.h>
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <time.h>
#define MAX_TIME 85
#define DHT11PIN 5
int dht11_val[5]={0,0,0,0,0};
int res;

int dht11_read_val()
{
  uint8_t lststate=HIGH;
  uint8_t counter=0;
  uint8_t j=0,i;
  float farenheit;
  for(i=0;i<5;i++)
     dht11_val[i]=0;
  pinMode(DHT11PIN,OUTPUT);
  digitalWrite(DHT11PIN,LOW);
  delay(18);
  digitalWrite(DHT11PIN,HIGH);
  delayMicroseconds(40);
  pinMode(DHT11PIN,INPUT);
  for(i=0;i<MAX_TIME;i++)
  {
    counter=0;
    while(digitalRead(DHT11PIN)==lststate){
      counter++;
      delayMicroseconds(1);
      if(counter==255)
        break;
    }
    lststate=digitalRead(DHT11PIN);
    if(counter==255)
       break;
    // top 3 transistions are ignored
    if((i>=4)&&(i%2==0)){
      dht11_val[j/8]<<=1;
      if(counter>16)
        dht11_val[j/8]|=1;
      j++;
    }
  }
  // verify cheksum and print the verified data
  if((j>=40)&&(dht11_val[4]==((dht11_val[0]+dht11_val[1]+dht11_val[2]+dht11_val[3])& 0xFF)))
  {
    time_t timer;
    struct tm *date;
    char str[256];
    timer = time(NULL);
    date = localtime(&timer);
    strftime(str, 255, "%Y/%m/%d %H:%M:%S", date);
    printf("%s ,", str);
    printf("Humidity = %d.%d %% Temperature = %d.%d *C\n",dht11_val[0],dht11_val[1],dht11_val[2],dht11_val[3]);
    return 2;
  }
}

int main(void)
{
  if(wiringPiSetup()==-1)
    exit(1);
  while(1)
  {
     res = 1;
     res = dht11_read_val();
     if(res==2) {
      return 0;
      break;
     }
     delay(3000);
  }
  return 1;
}