TEMPERATURE + HUMIDITY (DHT11) []

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====== TEMPERATURE + HUMIDITY (DHT11) ======
{{:projets:atb:sensor_temp_humid:dht11-pinout-for-three-pin-and-four-pin-types-2.jpg?direct&400|}}
===== CHARACTERISTICS =====
  * Operating Voltage	3.3V to 5.5V
  * Humidity measurement range	20% to 90% RH
  * Humidity measurement accuracy	±5% RH
  * Humidity measurement resolution	1% RH
  * Temperature measurement range	0ºC to 50ºC [32ºF to 122ºF]
  * Temperature measurement accuracy	±2ºC
  * Temperature measurement resolution	1ºC
  * Signal transmission range	20m

===== ARDUINO WIRING =====
{{:projets:atb:sensor_temp_humid:arduino-dht11-tutorial-3-pin-dht11-wiring-diagram.png?direct&400|}}

===== HOT TO USE A DHTXX =====
  * https://learn.adafruit.com/dht/using-a-dhtxx-sensor

===== CODE SAMPLES =====

<code c>
#include <dht.h>

dht DHT;

#define DHT11_PIN 7

void setup(){
}

void loop(){
  int chk = DHT.read11(DHT11_PIN);
  delay(1000);
}
</code>

<code c>
int DHpin = 8; // input/output pin
byte dat[5];   

byte read_data()
{
  byte i = 0;
  byte result = 0;
  for (i = 0; i < 8; i++) {
      while (digitalRead(DHpin) == LOW); // wait 50us
      delayMicroseconds(30); //The duration of the high level is judged to determine whether the data is '0' or '1'
      if (digitalRead(DHpin) == HIGH)
        result |= (1 << (8 - i)); //High in the former, low in the post
    while (digitalRead(DHpin) == HIGH); //Data '1', waiting for the next bit of reception
    }
  return result;
}

void start_test()
{
  digitalWrite(DHpin, LOW); //Pull down the bus to send the start signal
  delay(30); //The delay is greater than 18 ms so that DHT 11 can detect the start signal
  digitalWrite(DHpin, HIGH);
  delayMicroseconds(40); //Wait for DHT11 to respond
  pinMode(DHpin, INPUT);
  while(digitalRead(DHpin) == HIGH);
  delayMicroseconds(80); //The DHT11 responds by pulling the bus low for 80us;
  
  if(digitalRead(DHpin) == LOW)
    delayMicroseconds(80); //DHT11 pulled up after the bus 80us to start sending data;
  for(int i = 0; i < 5; i++) //Receiving temperature and humidity data, check bits are not considered;
    dat[i] = read_data();
  pinMode(DHpin, OUTPUT);
  digitalWrite(DHpin, HIGH); //After the completion of a release of data bus, waiting for the host to start the next signal
}

void setup()
{
  Serial.begin(9600);
  pinMode(DHpin, OUTPUT);
}

void loop()
{
  start_test();
  Serial.print("Humdity = ");
  Serial.print(dat[0], DEC); //Displays the integer bits of humidity;
  Serial.print('.');
  Serial.print(dat[1], DEC); //Displays the decimal places of the humidity;
  Serial.println('%');
  Serial.print("Temperature = ");
  Serial.print(dat[2], DEC); //Displays the integer bits of temperature;
  Serial.print('.');
  Serial.print(dat[3], DEC); //Displays the decimal places of the temperature;
  Serial.println('C');

  byte checksum = dat[0] + dat[1] + dat[2] + dat[3];
  if (dat[4] != checksum) 
    Serial.println("-- Checksum Error!");
  else
    Serial.println("-- OK");
 
  delay(1000);
}
</code>
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