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DHTSensor.cpp
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DHTSensor.cpp
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/* DHT library
MIT license
written by Adafruit Industries
*/
#include "DHTSensor.h"
#define DELAY_BETWEEN_READ 2000
DHTSensor::DHTSensor(uint8_t pin, DHTSensorType type)
{
_pin = pin;
_type = type;
}
const char *DHTSensor::sensorClass(void)
{
return "DHT";
}
const char *DHTSensor::sensorType(void)
{
switch(_type) {
case DHTSensorType_11:
return "DHT11";
case DHTSensorType_21:
return "DHT21";
case DHTSensorType_22:
return "DHT22";
case DHTSensorType_AM2301:
return "AM2301";
}
}
boolean DHTSensor::begin(void)
{
// set up the pins!
pinMode(_pin, INPUT);
digitalWrite(_pin, HIGH);
_lastreadtime = 0;
return true;
}
boolean DHTSensor::printValues(Stream *serial)
{
serial->print(this->temperature());
serial->print(" ");
serial->print(this->humidity());
return true;
}
boolean DHTSensor::loop(void)
{
uint8_t data[6];
uint8_t laststate = HIGH;
uint8_t counter = 0;
uint8_t j = 0, i;
unsigned long currentMillis = millis();
if ((unsigned long)(currentMillis - _lastreadtime) < DELAY_BETWEEN_READ) {
return true; // return last correct measurement
}
_lastreadtime = currentMillis;
// pull the pin high and wait 250 milliseconds
digitalWrite(_pin, HIGH);
delay(250);
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);
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 > 6)
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)) ) {
switch (_type) {
case DHTSensorType_11:
_humidity = data[0];
break;
case DHTSensorType_22:
case DHTSensorType_21:
case DHTSensorType_AM2301:
_humidity = data[0];
_humidity *= 256;
_humidity += data[1];
_humidity /= 10;
break;
}
switch (_type) {
case DHTSensorType_11:
_temperature = data[2];
break;
case DHTSensorType_22:
case DHTSensorType_21:
case DHTSensorType_AM2301:
_temperature = data[2] & 0x7F;
_temperature *= 256;
_temperature += data[3];
_temperature /= 10;
if (data[2] & 0x80)
_temperature *= -1;
break;
}
return true;
}
return false;
}