Update example to show temp in Fahrenheit and add computeHeatIndex function to resolve issue #9.

Author: tdicola

DHT.cpp

@@ -74,6 +74,20 @@ float DHT::readHumidity(void) {
   return NAN;
 }
 
+float DHT::computeHeatIndex(float tempFahrenheit, float percentHumidity) {
+  // Adapted from equation at: https://github.com/adafruit/DHT-sensor-library/issues/9 and
+  // Wikipedia: http://en.wikipedia.org/wiki/Heat_index
+  return -42.379 + 
+           2.04901523 * tempFahrenheit + 
+          10.14333127 * percentHumidity +
+          -0.22475541 * tempFahrenheit*percentHumidity +
+          -0.00683783 * pow(tempFahrenheit, 2) +
+          -0.05481717 * pow(percentHumidity, 2) + 
+           0.00122874 * pow(tempFahrenheit, 2) * percentHumidity + 
+           0.00085282 * tempFahrenheit*pow(percentHumidity, 2) +
+          -0.00000199 * pow(tempFahrenheit, 2) * pow(percentHumidity, 2);
+}
+
 
 boolean DHT::read(void) {
   uint8_t laststate = HIGH;

DHT.h

@@ -33,6 +33,7 @@ class DHT {
   void begin(void);
   float readTemperature(bool S=false);
   float convertCtoF(float);
+  float computeHeatIndex(float tempFahrenheit, float percentHumidity);
   float readHumidity(void);
 
 };

examples/DHTtester/DHTtester.ino

@@ -28,7 +28,13 @@ 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();
+  // Read temperature as Celsius
   float t = dht.readTemperature();
+  // Read temperature as Fahrenheit
+  float f = dht.readTemperature(true);
+  // Compute heat index
+  // Must send in temp in Fahrenheit!
+  float hi = dht.computeHeatIndex(f, h);
 
   // check if returns are valid, if they are NaN (not a number) then something went wrong!
   if (isnan(t) || isnan(h)) {
@@ -39,6 +45,12 @@ void loop() {
     Serial.print(" %\t");
     Serial.print("Temperature: "); 
     Serial.print(t);
-    Serial.println(" *C");
+    Serial.print(" *C ");
+    Serial.print(f);
+    Serial.print(" *F\t");
+    Serial.print("Heat index: ");
+    Serial.print(hi);
+    Serial.println(" *F");
+
   }
 }