/* DHT library
MIT license
written by Adafruit Industries
*/
#include "DHT.h"
DHT:
HT(uint8_t pin, uint8_t type, uint8_t count) {
_pin = pin;
_type = type;
_count = count;
firstreading = true;
}
void DHT::begin(void) {
// set up the pins!
pinMode(_pin, INPUT);
digitalWrite(_pin, HIGH);
_lastreadtime = 0;
}
//boolean S == Scale. True == Farenheit; False == Celcius
float DHT::readTemperature(bool S) {
float f;
if (read()) {
switch (_type) {
case DHT11:
f = data[2];
if(S)
f = convertCtoF(f);
return f;
case DHT22:
case DHT21:
f = data[2] & 0x7F;
f *= 256;
f += data[3];
f /= 10;
if (data[2] & 0x80)
f *= -1;
if(S)
f = convertCtoF(f);
return f;
}
}
return NAN;
}
float DHT::convertCtoF(float c) {
return c * 9 / 5 + 32;
}
float DHT::convertFtoC(float f) {
return (f - 32) * 5 / 9;
}
float DHT::readHumidity(void) {
float f;
if (read()) {
switch (_type) {
case DHT11:
f = data[0];
return f;
case DHT22:
case DHT21:
f = data[0];
f *= 256;
f += data[1];
f /= 10;
return f;
}
}
return NAN;
}
float DHT::computeHeatIndex(float tempFahrenheit, float percentHumidity) {
// Adapted from equation at:
Humidity Index formula · Issue #9 · adafruit/DHT-sensor-library · GitHub and
// Wikipedia:
Heat index - Wikipedia
return -42.379 +
2.04901523 * tempFahrenheit +
10.14333127 * percentHumidity +
-0.22475541 * tempFahrenheit*percentHumidity +
-0.00683783 * pow(tempFahrenheit, 2) +
-0.05481717 * pow(percentHumidity, 2) +
0.00122874 * pow(tempFahrenheit, 2) * percentHumidity +
0.00085282 * tempFahrenheit*pow(percentHumidity, 2) +
-0.00000199 * pow(tempFahrenheit, 2) * pow(percentHumidity, 2);
}
boolean DHT::read(void) {
uint8_t laststate = HIGH;
uint8_t counter = 0;
uint8_t j = 0, i;
unsigned long currenttime;
// Check if sensor was read less than two seconds ago and return early
// to use last reading.
currenttime = millis();
if (currenttime < _lastreadtime) {
// ie there was a rollover
_lastreadtime = 0;
}
if (!firstreading && ((currenttime - _lastreadtime) < 2000)) {
return true; // return last correct measurement
//delay(2000 - (currenttime - _lastreadtime));
}
firstreading = false;
/*
Serial.print("Currtime: "); Serial.print(currenttime);
Serial.print(" Lasttime: "); Serial.print(_lastreadtime);
*/
_lastreadtime = millis();
data[0] = data[1] = data[2] = data[3] = data[4] = 0;
// pull the pin high and wait 250 milliseconds
digitalWrite(_pin, HIGH);
delay(250);
// now pull it low for ~20 milliseconds
pinMode(_pin, OUTPUT);
digitalWrite(_pin, LOW);
delay(20);
noInterrupts();
digitalWrite(_pin, HIGH);
delayMicroseconds(40);
pinMode(_pin, INPUT);
// read in timings
for ( i=0; i< MAXTIMINGS; i++) {
counter = 0;
while (digitalRead(_pin) == laststate) {
counter++;
delayMicroseconds(1);
if (counter == 255) {
break;
}
}
laststate = digitalRead(_pin);
if (counter == 255) break;
// ignore first 3 transitions
if ((i >= 4) && (i%2 == 0)) {
// shove each bit into the storage bytes
data[j/8] <<= 1;
if (counter > _count)
data[j/8] |= 1;
j++;
}
}
interrupts();
/*
Serial.println(j, DEC);
Serial.print(data[0], HEX); Serial.print(", ");
Serial.print(data[1], HEX); Serial.print(", ");
Serial.print(data[2], HEX); Serial.print(", ");
Serial.print(data[3], HEX); Serial.print(", ");
Serial.print(data[4], HEX); Serial.print(" =? ");
Serial.println(data[0] + data[1] + data[2] + data[3], HEX);
*/
// check we read 40 bits and that the checksum matches
if ((j >= 40) &&
(data[4] == ((data[0] + data[1] + data[2] + data[3]) & 0xFF)) ) {
return true;
}
return false;
}
