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LDHT.cpp
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LDHT.cpp
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/* DHT library
MIT license
Written by Lin Wei Ting in National Taipei University of Technology Applied Network Laboratory. Taipei, Taiwan.
*/
#include "LDHT.h"
LDHT::LDHT(uint8_t pin, uint8_t type, uint8_t count) {
_pin = pin;
_type = type;
_count = count;
firstreading = true;
}
void LDHT::begin(void) {
// set up the pins!
pinMode(_pin, INPUT);
digitalWrite(_pin, HIGH);
temp = 25;
_lastreadtime = 0;
}
int readPin(int pin)
{
return digitalRead(pin);
}
//read the Humidity value.
float LDHT::readHumidity(void)
{
return humi;
}
//read the Temperature value.
//Select = true,Celcius ; Select = false,Fahrenheit ; Select default = true.
float LDHT::readTemperature(bool Select)
{
float f;
if(Select)
return temp;
else
{
f = convertCtoF(temp);
return f;
}
}
//convert Celcius to Kelvin.
float LDHT::convertCtoK(float tempCelcius)
{
return tempCelcius + 273.15;
}
//convert Celcius to Fahrenheit.
float LDHT::convertCtoF(float tempCelcius)
{
return tempCelcius * 9 / 5 + 32;
}
//convert Fahrenheit to Celcius.
float LDHT::convertFtoC(float tempFahrenheit)
{
return (tempFahrenheit - 32) * 5 / 9;
}
// read the Heat Index value.
//https://en.wikipedia.org/wiki/Heat_index
float LDHT::readHeatIndex(float tempCelcius, float percentHumidity)
{
return convertFtoC(-42.379 +
2.04901523 * convertCtoF(tempCelcius) +
10.14333127 * percentHumidity +
-0.22475541 * convertCtoF(tempCelcius)*percentHumidity +
-0.00683783 * pow(convertCtoF(tempCelcius), 2) +
-0.05481717 * pow(percentHumidity, 2) +
0.00122874 * pow(convertCtoF(tempCelcius), 2) * percentHumidity +
0.00085282 * convertCtoF(tempCelcius)*pow(percentHumidity, 2) +
-0.00000199 * pow(convertCtoF(tempCelcius), 2) * pow(percentHumidity, 2));
}
// read the Dew Point value.
//https://en.wikipedia.org/wiki/Dew_point
float LDHT::readDewPoint(float tempCelcius, float percentHumidity)
{
double A0= 373.15/(273.15 + tempCelcius);
double SUM = -7.90298 * (A0-1);
SUM += 5.02808 * log10(A0);
SUM += -1.3816e-7 * (pow(10, (11.344*(1-1/A0)))-1) ;
SUM += 8.1328e-3 * (pow(10,(-3.49149*(A0-1)))-1) ;
SUM += log10(1013.246);
double VP = pow(10, SUM-3) * percentHumidity;
double T = log(VP/0.61078);
return (241.88 * T) / (17.558-T);
}
int LDHT::read()
{
uint8_t laststate = HIGH;
unsigned long counter = 0;
uint8_t j = 0, i;
unsigned long currenttime;
// pull the pin high and wait 250 milliseconds
digitalWrite(_pin, HIGH);
delay(250);
currenttime = millis();
if (currenttime < _lastreadtime) {
// ie there was a rollover
_lastreadtime = 0;
}
if (!firstreading && ((currenttime - _lastreadtime) < 2000)) {
return true; // return last correct measurement
}
firstreading = false;
_lastreadtime = millis();
data[0] = data[1] = data[2] = data[3] = data[4] = 0;
// now pull it low for ~20 milliseconds
pinMode(_pin, OUTPUT);
digitalWrite(_pin, LOW);
delay(20);
digitalWrite(_pin, HIGH);
delayMicroseconds(40);
pinMode(_pin, INPUT);
unsigned char count_buf[MAXTIMINGS];
int count_len = 0;
// read in timings
for ( i=0; i < MAXTIMINGS; i++)
{
counter = 0;
while (1)
{
if(readPin(_pin) != laststate)
{
//if(counter > 9)
break;
}
counter++;
// delayMicroseconds(1);
if (counter == 100)
{
break;
}
}
count_buf[count_len++] = counter;
laststate = readPin(_pin);
if (counter == 100) break;
if ((i >= 4) && (i%2 == 0))
{
// shove each bit into the storage bytes
data[j/8] <<= 1;
if (counter > 25)
data[j/8] |= 1;
j++;
}
}
float f = 0.0;
switch(_type)
{
case DHT11:
f = data[2];
if(f>=(temp-15) && f<=(temp+15))
{
temp = f;
f = data[0];
humi = f;
return true;
}
else
return false;
break;
case DHT21:
case DHT22:
f = data[2] & 0x7F;
f *= 256;
f += data[3];
f /= 10;
if (data[2] & 0x80)
f *= -1;
if(f>=(temp-15) && f<=(temp+15))
{
temp = f;
f = data[0];
f *= 256.0;
f += data[1];
f /= 10.0;
humi = f;
return true;
}
else
return false;
break;
}
}