Merge branch 'jmdana-master'

Steadman's equations. As a result, it allows a larger range of
temperatures and more accurate results for extreme conditions.

DHT.cpp

@@ -6,10 +6,11 @@ written by Adafruit Industries
 
 #include "DHT.h"
 
+#define MIN_INTERVAL 2000
+
 DHT::DHT(uint8_t pin, uint8_t type, uint8_t count) {
   _pin = pin;
   _type = type;
-  _firstreading = true;
   _bit = digitalPinToBitMask(pin);
   _port = digitalPinToPort(pin);
   _maxcycles = microsecondsToClockCycles(1000);  // 1 millisecond timeout for
@@ -20,17 +21,19 @@ DHT::DHT(uint8_t pin, uint8_t type, uint8_t count) {
 
 void DHT::begin(void) {
   // set up the pins!
-  pinMode(_pin, INPUT);
-  digitalWrite(_pin, HIGH);
-  _lastreadtime = 0;
+  pinMode(_pin, INPUT_PULLUP);
+  // Using this value makes sure that millis() - lastreadtime will be
+  // >= MIN_INTERVAL right away. Note that this assignment wraps around,
+  // but so will the subtraction.
+  _lastreadtime = -MIN_INTERVAL;
   DEBUG_PRINT("Max clock cycles: "); DEBUG_PRINTLN(_maxcycles, DEC);
 }
 
 //boolean S == Scale.  True == Fahrenheit; False == Celcius
-float DHT::readTemperature(bool S) {
+float DHT::readTemperature(bool S, bool force) {
   float f = NAN;
 
-  if (read()) {
+  if (read(force)) {
     switch (_type) {
     case DHT11:
       f = data[2];
@@ -64,7 +67,7 @@ float DHT::convertFtoC(float f) {
   return (f - 32) * 5 / 9;
 }
 
-float DHT::readHumidity(void) {
+float DHT::readHumidity(bool force) {
   float f = NAN;
   if (read()) {
     switch (_type) {
@@ -85,23 +88,17 @@ float DHT::readHumidity(void) {
 
 //boolean isFahrenheit: True == Fahrenheit; False == Celcius
 float DHT::computeHeatIndex(float temperature, float percentHumidity, bool isFahrenheit) {
-  // Adapted from equation at: https://github.com/adafruit/DHT-sensor-library/issues/9 and
-  // Wikipedia: http://en.wikipedia.org/wiki/Heat_index
-  if (!isFahrenheit) {
-    // Celsius heat index calculation.
-    return -8.784695 +
-             1.61139411 * temperature +
-             2.338549   * percentHumidity +
-            -0.14611605 * temperature*percentHumidity +
-            -0.01230809 * pow(temperature, 2) +
-            -0.01642482 * pow(percentHumidity, 2) +
-             0.00221173 * pow(temperature, 2) * percentHumidity +
-             0.00072546 * temperature*pow(percentHumidity, 2) +
-            -0.00000358 * pow(temperature, 2) * pow(percentHumidity, 2);
-  }
-  else {
-    // Fahrenheit heat index calculation.
-    return -42.379 +
+  // Using both Rothfusz and Steadman's equations
+  // http://www.wpc.ncep.noaa.gov/html/heatindex_equation.shtml
+  float hi;
+
+  if (!isFahrenheit)
+    temperature = convertCtoF(temperature);
+
+  hi = 0.5 * (temperature + 61.0 + ((temperature - 68.0) * 1.2) + (percentHumidity * 0.094)); 
+
+  if (hi > 79) {
+    hi = -42.379 +
              2.04901523 * temperature +
             10.14333127 * percentHumidity +
             -0.22475541 * temperature*percentHumidity +
@@ -110,22 +107,25 @@ float DHT::computeHeatIndex(float temperature, float percentHumidity, bool isFah
              0.00122874 * pow(temperature, 2) * percentHumidity +
              0.00085282 * temperature*pow(percentHumidity, 2) +
             -0.00000199 * pow(temperature, 2) * pow(percentHumidity, 2);
+
+    if((percentHumidity < 13) && (temperature >= 80.0) && (temperature <= 112.0))
+      hi -= ((13.0 - percentHumidity) * 0.25) * sqrt((17.0 - abs(temperature - 95.0)) * 0.05882);
+
+    else if((percentHumidity > 85.0) && (temperature >= 80.0) && (temperature <= 87.0))
+      hi += ((percentHumidity - 85.0) * 0.1) * ((87.0 - temperature) * 0.2);
   }
+
+  return isFahrenheit ? hi : convertFtoC(hi);
 }
 
-boolean DHT::read(void) {
+boolean DHT::read(bool force) {
   // Check if sensor was read less than two seconds ago and return early
   // to use last reading.
   uint32_t currenttime = millis();
-  if (currenttime < _lastreadtime) {
-    // ie there was a rollover
-    _lastreadtime = 0;
-  }
-  if (!_firstreading && ((currenttime - _lastreadtime) < 2000)) {
+  if (!force && ((currenttime - _lastreadtime) < 2000)) {
     return _lastresult; // return last correct measurement
   }
-  _firstreading = false;
-  _lastreadtime = millis();
+  _lastreadtime = currenttime;
 
   // Reset 40 bits of received data to zero.
   data[0] = data[1] = data[2] = data[3] = data[4] = 0;
@@ -154,7 +154,7 @@ boolean DHT::read(void) {
     delayMicroseconds(40);
 
     // Now start reading the data line to get the value from the DHT sensor.
-    pinMode(_pin, INPUT);
+    pinMode(_pin, INPUT_PULLUP);
     delayMicroseconds(10);  // Delay a bit to let sensor pull data line low.
 
     // First expect a low signal for ~80 microseconds followed by a high signal

DHT.h

@@ -39,18 +39,17 @@ class DHT {
   public:
    DHT(uint8_t pin, uint8_t type, uint8_t count=6);
    void begin(void);
-   float readTemperature(bool S=false);
+   float readTemperature(bool S=false, bool force=false);
    float convertCtoF(float);
    float convertFtoC(float);
    float computeHeatIndex(float temperature, float percentHumidity, bool isFahrenheit=true);
-   float readHumidity(void);
-   boolean read(void);
+   float readHumidity(bool force=false);
+   boolean read(bool force=false);
 
  private:
-  uint8_t data[6];
+  uint8_t data[5];
   uint8_t _pin, _type, _bit, _port;
   uint32_t _lastreadtime, _maxcycles;
-  bool _firstreading;
   bool _lastresult;
 
   uint32_t expectPulse(bool level);

library.properties

@@ -1,5 +1,5 @@
 name=DHT sensor library
-version=1.1.1
+version=1.2.1
 author=Adafruit
 maintainer=Adafruit <info@adafruit.com>
 sentence=Arduino library for DHT11, DHT22, etc Temp & Humidity Sensors