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179
DHT/DHT.cpp
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179
DHT/DHT.cpp
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/* DHT library
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MIT license
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written by Adafruit Industries
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*/
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#include "DHT.h"
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DHT::DHT(uint8_t pin, uint8_t type, uint8_t count) {
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_pin = pin;
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_type = type;
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_count = count;
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firstreading = true;
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}
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void DHT::begin(void) {
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// set up the pins!
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pinMode(_pin, INPUT);
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digitalWrite(_pin, HIGH);
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_lastreadtime = 0;
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}
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//boolean S == Scale. True == Farenheit; False == Celcius
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float DHT::readTemperature(bool S) {
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float f;
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if (read()) {
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switch (_type) {
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case DHT11:
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f = data[2];
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if(S)
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f = convertCtoF(f);
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return f;
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case DHT22:
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case DHT21:
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f = data[2] & 0x7F;
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f *= 256;
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f += data[3];
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f /= 10;
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if (data[2] & 0x80)
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f *= -1;
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if(S)
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f = convertCtoF(f);
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return f;
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}
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}
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return NAN;
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}
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float DHT::convertCtoF(float c) {
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return c * 9 / 5 + 32;
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}
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float DHT::convertFtoC(float f) {
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return (f - 32) * 5 / 9;
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}
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float DHT::readHumidity(void) {
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float f;
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if (read()) {
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switch (_type) {
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case DHT11:
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f = data[0];
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return f;
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case DHT22:
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case DHT21:
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f = data[0];
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f *= 256;
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f += data[1];
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f /= 10;
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return f;
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}
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}
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return NAN;
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}
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float DHT::computeHeatIndex(float tempFahrenheit, float percentHumidity) {
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// Adapted from equation at: https://github.com/adafruit/DHT-sensor-library/issues/9 and
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// Wikipedia: http://en.wikipedia.org/wiki/Heat_index
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return -42.379 +
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2.04901523 * tempFahrenheit +
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10.14333127 * percentHumidity +
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-0.22475541 * tempFahrenheit*percentHumidity +
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-0.00683783 * pow(tempFahrenheit, 2) +
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-0.05481717 * pow(percentHumidity, 2) +
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0.00122874 * pow(tempFahrenheit, 2) * percentHumidity +
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0.00085282 * tempFahrenheit*pow(percentHumidity, 2) +
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-0.00000199 * pow(tempFahrenheit, 2) * pow(percentHumidity, 2);
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}
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boolean DHT::read(void) {
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uint8_t laststate = HIGH;
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uint8_t counter = 0;
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uint8_t j = 0, i;
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unsigned long currenttime;
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// Check if sensor was read less than two seconds ago and return early
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// to use last reading.
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currenttime = millis();
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if (currenttime < _lastreadtime) {
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// ie there was a rollover
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_lastreadtime = 0;
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}
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if (!firstreading && ((currenttime - _lastreadtime) < 2000)) {
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return true; // return last correct measurement
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//delay(2000 - (currenttime - _lastreadtime));
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}
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firstreading = false;
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/*
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Serial.print("Currtime: "); Serial.print(currenttime);
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Serial.print(" Lasttime: "); Serial.print(_lastreadtime);
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*/
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_lastreadtime = millis();
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data[0] = data[1] = data[2] = data[3] = data[4] = 0;
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// pull the pin high and wait 250 milliseconds
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digitalWrite(_pin, HIGH);
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delay(250);
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// now pull it low for ~20 milliseconds
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pinMode(_pin, OUTPUT);
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digitalWrite(_pin, LOW);
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delay(20);
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noInterrupts();
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digitalWrite(_pin, HIGH);
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delayMicroseconds(40);
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pinMode(_pin, INPUT);
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// read in timings
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for ( i=0; i< MAXTIMINGS; i++) {
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counter = 0;
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while (digitalRead(_pin) == laststate) {
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counter++;
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delayMicroseconds(1);
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if (counter == 255) {
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break;
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}
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}
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laststate = digitalRead(_pin);
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if (counter == 255) break;
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// ignore first 3 transitions
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if ((i >= 4) && (i%2 == 0)) {
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// shove each bit into the storage bytes
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data[j/8] <<= 1;
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if (counter > _count)
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data[j/8] |= 1;
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j++;
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}
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}
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interrupts();
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/*
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Serial.println(j, DEC);
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Serial.print(data[0], HEX); Serial.print(", ");
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Serial.print(data[1], HEX); Serial.print(", ");
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Serial.print(data[2], HEX); Serial.print(", ");
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Serial.print(data[3], HEX); Serial.print(", ");
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Serial.print(data[4], HEX); Serial.print(" =? ");
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Serial.println(data[0] + data[1] + data[2] + data[3], HEX);
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*/
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// check we read 40 bits and that the checksum matches
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if ((j >= 40) &&
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(data[4] == ((data[0] + data[1] + data[2] + data[3]) & 0xFF)) ) {
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return true;
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}
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return false;
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}
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41
DHT/DHT.h
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41
DHT/DHT.h
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#ifndef DHT_H
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#define DHT_H
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#if ARDUINO >= 100
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#include "Arduino.h"
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#else
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#include "WProgram.h"
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#endif
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/* DHT library
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MIT license
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written by Adafruit Industries
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*/
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// how many timing transitions we need to keep track of. 2 * number bits + extra
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#define MAXTIMINGS 85
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#define DHT11 11
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#define DHT22 22
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#define DHT21 21
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#define AM2301 21
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class DHT {
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private:
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uint8_t data[6];
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uint8_t _pin, _type, _count;
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unsigned long _lastreadtime;
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boolean firstreading;
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public:
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DHT(uint8_t pin, uint8_t type, uint8_t count=6);
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void begin(void);
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float readTemperature(bool S=false);
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float convertCtoF(float);
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float convertFtoC(float);
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float computeHeatIndex(float tempFahrenheit, float percentHumidity);
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float readHumidity(void);
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boolean read(void);
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};
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#endif
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3
DHT/README.txt
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3
DHT/README.txt
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This is an Arduino library for the DHT series of low cost temperature/humidity sensors.
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To download. click the DOWNLOADS button in the top right corner, rename the uncompressed folder DHT. Check that the DHT folder contains DHT.cpp and DHT.h. Place the DHT library folder your <arduinosketchfolder>/libraries/ folder. You may need to create the libraries subfolder if its your first library. Restart the IDE.
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71
DHT/examples/DHTtester/DHTtester.ino
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71
DHT/examples/DHTtester/DHTtester.ino
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// Example testing sketch for various DHT humidity/temperature sensors
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// Written by ladyada, public domain
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#include "DHT.h"
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#define DHTPIN 2 // what pin we're connected to
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// Uncomment whatever type you're using!
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//#define DHTTYPE DHT11 // DHT 11
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#define DHTTYPE DHT22 // DHT 22 (AM2302)
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//#define DHTTYPE DHT21 // DHT 21 (AM2301)
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// Connect pin 1 (on the left) of the sensor to +5V
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// NOTE: If using a board with 3.3V logic like an Arduino Due connect pin 1
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// to 3.3V instead of 5V!
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// Connect pin 2 of the sensor to whatever your DHTPIN is
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// Connect pin 4 (on the right) of the sensor to GROUND
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// Connect a 10K resistor from pin 2 (data) to pin 1 (power) of the sensor
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// Initialize DHT sensor for normal 16mhz Arduino
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DHT dht(DHTPIN, DHTTYPE);
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// NOTE: For working with a faster chip, like an Arduino Due or Teensy, you
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// might need to increase the threshold for cycle counts considered a 1 or 0.
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// You can do this by passing a 3rd parameter for this threshold. It's a bit
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// of fiddling to find the right value, but in general the faster the CPU the
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// higher the value. The default for a 16mhz AVR is a value of 6. For an
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// Arduino Due that runs at 84mhz a value of 30 works.
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// Example to initialize DHT sensor for Arduino Due:
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//DHT dht(DHTPIN, DHTTYPE, 30);
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void setup() {
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Serial.begin(9600);
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Serial.println("DHTxx test!");
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dht.begin();
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}
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void loop() {
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// Wait a few seconds between measurements.
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delay(2000);
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// Reading temperature or humidity takes about 250 milliseconds!
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// Sensor readings may also be up to 2 seconds 'old' (its a very slow sensor)
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float h = dht.readHumidity();
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// Read temperature as Celsius
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float t = dht.readTemperature();
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// Read temperature as Fahrenheit
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float f = dht.readTemperature(true);
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// Check if any reads failed and exit early (to try again).
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if (isnan(h) || isnan(t) || isnan(f)) {
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Serial.println("Failed to read from DHT sensor!");
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return;
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}
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// Compute heat index
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// Must send in temp in Fahrenheit!
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float hi = dht.computeHeatIndex(f, h);
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Serial.print("Humidity: ");
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Serial.print(h);
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Serial.print(" %\t");
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Serial.print("Temperature: ");
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Serial.print(t);
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Serial.print(" *C ");
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Serial.print(f);
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Serial.print(" *F\t");
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Serial.print("Heat index: ");
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Serial.print(hi);
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Serial.println(" *F");
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}
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