Raspberry Pi + DHT11 Temperature and Humidity Sensor

Raspberry Pi + DHT11 Temperature and Humidity Sensor

I bought DHT11 Temperature and Humidity Sensor module on Akiduki denshi website in Japan.
http://akizukidenshi.com/catalog/g/gM-07040/
It's cheep sensor about 500 yen.
Datasheet is here.
http://akizukidenshi.com/download/ds/aosong/DHT11.pdf

It's Easy to handle on Raspberry Pi.
1. Connect to Raspberry Pi(RPi)
2. Programming
3. Execute

1.Connect to RPi
 The sensor has 3 ports. These ports are connected to harness, which are colored, red, black and green.
 I connected to RPi as following.
 (Sensor               ->         Rpi)
 Red code(VCC)    ->        +5V
 Black code(GND)  ->        GND
 Green code(Data) ->        GPIO23

 RPi GPIO
 http://www.pwv.co.jp/~take/TakeWiki/index.php?plugin=ref&page=raspberrypi%2FRaspberry%20Pi%E3%81%A7IO%E5%88%B6%E5%BE%A1&src=My-Pin-Layout.jpg

2.Programming
 I used these sample codes.
 http://dolls.orz.hm/?p=9000

 The remarkable point is PIN assign.
 I used DHT11PIN as "4".(the following code)
 "4" means wiringPi pin number. It is GPIO23.
 (connected to green code)

 I changed as continuous output in "main" function.
 because the sample code was one shot output.

 copy code and paste and save as dht11.c

#include <wiringPi.h>
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <time.h>
#define MAX_TIME 85
#define DHT11PIN 4
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 = dht11_read_val();
    delay(1600);
  }
  return 1;
}

3. Execute
 Before execute, install wiringPi.
    http://wiringpi.com/download-and-install/
 make the programming code.
    gcc -o a.out dht11.c -L/usr/local/lib -lwiringPi
 and execute.
   sudo ./a.out