Humidity&Temperature Sensor

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Humidity_Temperature_Sensor/DHT.cpp

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+/* DHT library 
+
+MIT license
+written by Adafruit Industries
+*/
+
+#include "DHT.h"
+
+DHT::DHT(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;
+    }
+  }
+  Serial.print("Read fail");
+  return NAN;
+}
+
+float DHT::convertCtoF(float c) {
+	return c * 9 / 5 + 32;
+}
+
+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;
+    }
+  }
+  Serial.print("Read fail");
+  return NAN;
+}
+
+
+boolean DHT::read(void) {
+  uint8_t laststate = HIGH;
+  uint8_t 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
+    //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;
+  
+  // now pull it low for ~20 milliseconds
+  pinMode(_pin, OUTPUT);
+  digitalWrite(_pin, LOW);
+  delay(20);
+  cli();
+  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++;
+    }
+
+  }
+
+  sei();
+  
+  /*
+  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;
+
+}

Humidity_Temperature_Sensor/DHT.h

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+#ifndef __DHT_H__
+#define __DHT_H__
+#if ARDUINO >= 100
+ #include "Arduino.h"
+#else
+ #include "WProgram.h"
+#endif
+
+/* DHT library 
+
+MIT license
+written by Adafruit Industries
+*/
+
+// how many timing transitions we need to keep track of. 2 * number bits + extra
+#define MAXTIMINGS 85
+
+#define DHT11 11
+#define DHT22 22
+#define DHT21 21
+#define AM2301 21
+
+class DHT 
+{
+private:
+    uint8_t data[6];
+    uint8_t _pin, _type, _count;
+    boolean read(void);
+    unsigned long _lastreadtime;
+    boolean firstreading;
+
+public:
+    DHT(uint8_t pin, uint8_t type, uint8_t count=6);
+    void begin(void);
+    float readTemperature(bool S=false);
+    float convertCtoF(float);
+    float readHumidity(void);
+};
+
+#endif

Humidity_Temperature_Sensor/README.txt

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+This is an Arduino library for the DHT series of low cost temperature/humidity sensors. 
+
+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.

Humidity_Temperature_Sensor/examples/DHTtester/DHTtester.ino

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+// Example testing sketch for various DHT humidity/temperature sensors
+// Written by ladyada, public domain
+
+#include "DHT.h"
+
+#define DHTPIN 2     // what pin we're connected to
+
+// Uncomment whatever type you're using!
+//#define DHTTYPE DHT11   // DHT 11 
+#define DHTTYPE DHT22   // DHT 22  (AM2302)
+//#define DHTTYPE DHT21   // DHT 21 (AM2301)
+
+// Connect pin 1 (on the left) of the sensor to +5V
+// Connect pin 2 of the sensor to whatever your DHTPIN is
+// Connect pin 4 (on the right) of the sensor to GROUND
+// Connect a 10K resistor from pin 2 (data) to pin 1 (power) of the sensor
+
+DHT dht(DHTPIN, DHTTYPE);
+
+void setup() 
+{
+    Serial.begin(9600); 
+    Serial.println("DHTxx test!");
+
+    dht.begin();
+}
+
+void loop() 
+{
+    // Reading temperature or humidity takes about 250 milliseconds!
+    // Sensor readings may also be up to 2 seconds 'old' (its a very slow sensor)
+    float h = dht.readHumidity();
+    float t = dht.readTemperature();
+
+    // check if returns are valid, if they are NaN (not a number) then something went wrong!
+    if (isnan(t) || isnan(h)) 
+    {
+        Serial.println("Failed to read from DHT");
+    } 
+    else 
+    {
+        Serial.print("Humidity: "); 
+        Serial.print(h);
+        Serial.print(" %\t");
+        Serial.print("Temperature: "); 
+        Serial.print(t);
+        Serial.println(" *C");
+    }
+}