//

// FILE: dht.cpp

// AUTHOR: Rob Tillaart

// VERSION: 0.1.09

// PURPOSE: DHT Temperature & Humidity Sensor library for Arduino

// URL: http://arduino.cc/playground/Main/DHTLib

//

// HISTORY:

// 0.1.09 optimize size: timeout check + use of mask

// 0.1.08 added formula for timeout based upon clockspeed

// 0.1.07 added support for DHT21

// 0.1.06 minimize footprint (2012-12-27)

// 0.1.05 fixed negative temperature bug (thanks to Roseman)

// 0.1.04 improved readability of code using DHTLIB_OK in code

// 0.1.03 added error values for temp and humidity when read failed

// 0.1.02 added error codes

// 0.1.01 added support for Arduino 1.0, fixed typos (31/12/2011)

// 0.1.0 by Rob Tillaart (01/04/2011)

//

// inspired by DHT11 library

//

// Released to the public domain

//

#include "dht.h"

// #define TIMEOUT 10000

// uint16_t for UNO, higher CPU speeds => exceed MAXINT.

// works for DUE

// 16 MHz => 10000

// 84 MHz => 52500

// 100MHz => 62500

#define TIMEOUT (F_CPU/1600)

/////////////////////////////////////////////////////

//

// PUBLIC

//

// return values:

// DHTLIB_OK

// DHTLIB_ERROR_CHECKSUM

// DHTLIB_ERROR_TIMEOUT

int dht::read11(uint8_t pin)

{

// READ VALUES

int rv = read(pin);

if (rv != DHTLIB_OK)

{

humidity = DHTLIB_INVALID_VALUE; // invalid value, or is NaN prefered?

temperature = DHTLIB_INVALID_VALUE; // invalid value

return rv;

}

// CONVERT AND STORE

humidity = bits[0]; // bits[1] == 0;

temperature = bits[2]; // bits[3] == 0;

// TEST CHECKSUM

// bits[1] && bits[3] both 0

uint8_t sum = bits[0] + bits[2];

if (bits[4] != sum) return DHTLIB_ERROR_CHECKSUM;

return DHTLIB_OK;

}

// return values:

// DHTLIB_OK

// DHTLIB_ERROR_CHECKSUM

// DHTLIB_ERROR_TIMEOUT

int dht::read21(uint8_t pin)

{

return read22(pin); // dataformat identical to DHT22

}

// return values:

// DHTLIB_OK

// DHTLIB_ERROR_CHECKSUM

// DHTLIB_ERROR_TIMEOUT

int dht::read22(uint8_t pin)

{

// READ VALUES

int rv = read(pin);

if (rv != DHTLIB_OK)

{

humidity = DHTLIB_INVALID_VALUE; // invalid value, or is NaN prefered?

temperature = DHTLIB_INVALID_VALUE; // invalid value

return rv; // propagate error value

}

// CONVERT AND STORE

humidity = word(bits[0], bits[1]) * 0.1;

if (bits[2] & 0x80) // negative temperature

{

temperature = -0.1 * word(bits[2] & 0x7F, bits[3]);

}

else

{

temperature = 0.1 * word(bits[2], bits[3]);

}

// TEST CHECKSUM

uint8_t sum = bits[0] + bits[1] + bits[2] + bits[3];

if (bits[4] != sum) return DHTLIB_ERROR_CHECKSUM;

return DHTLIB_OK;

}

/////////////////////////////////////////////////////

//

// PRIVATE

//

// return values:

// DHTLIB_OK

// DHTLIB_ERROR_TIMEOUT

int dht::read(uint8_t pin)

{

// INIT BUFFERVAR TO RECEIVE DATA

uint8_t mask = 128;

uint8_t idx = 0;

// EMPTY BUFFER

for (uint8_t i=0; i< 5; i++) bits[i] = 0;

// REQUEST SAMPLE

pinMode(pin, OUTPUT);

digitalWrite(pin, LOW);

delay(20);

digitalWrite(pin, HIGH);

delayMicroseconds(40);

pinMode(pin, INPUT);

// GET ACKNOWLEDGE or TIMEOUT

unsigned int loopCnt = TIMEOUT;

while(digitalRead(pin) == LOW)

if (--loopCnt == 0) return DHTLIB_ERROR_TIMEOUT;

loopCnt = TIMEOUT;

while(digitalRead(pin) == HIGH)

if (--loopCnt == 0) return DHTLIB_ERROR_TIMEOUT;

// READ THE OUTPUT - 40 BITS => 5 BYTES

for (uint8_t i=0; i<40; i++)

{

loopCnt = TIMEOUT;

while(digitalRead(pin) == LOW)

if (--loopCnt == 0) return DHTLIB_ERROR_TIMEOUT;

unsigned long t = micros();

loopCnt = TIMEOUT;

while(digitalRead(pin) == HIGH)

if (--loopCnt == 0) return DHTLIB_ERROR_TIMEOUT;

if ((micros() - t) > 40) bits[idx] |= mask;

mask >>= 1;

if (mask == 0) // next byte?

{

mask = 128;

idx++;

}

}

return DHTLIB_OK;

}

//

// END OF FILE

//