Merge pull request #7 from DevanceJ/feat/heat-index

adds ftoc and ctof functions along with a getHeatIndex function using…

DHT22.cpp

@@ -15,16 +15,54 @@ String DHT22::getRawStrData(){
   return r;
 }
 
+// Convert Celsius to Fahrenheit
+float DHT22::convertCtoF(float c) { return c * 1.8 + 32; }
+// Convert Fahrenheit to Celsius
+float DHT22::convertFtoC(float f) { return (f - 32) * 0.55555; }
+
 float DHT22::getHumidity(){
   if (readSensor() != OK) return -1;
   else return _h16bits/10.0;
 }
 
-
-float DHT22::getTemperature(){
+// M = true : Celsius ; M = false : Fahrenheit
+float DHT22::getTemperature(bool M){
   if (readSensor() != OK) return -273;
-  if (bitRead(_t16bits,15)) return (_t16bits & 0x7FFF)/-10.0;
-  else return _t16bits/10.0;
+  float temperature = (bitRead(_t16bits, 15)) ? (_t16bits & 0x7FFF) / -10.0 : _t16bits / 10.0;
+  return M ? temperature : convertCtoF(temperature);
+}
+
+// https://www.weather.gov/media/ffc/ta_htindx.PDF
+float DHT22::getHeatIndex(float temperature, float percentHumidity, bool isCelsius){
+  float hi;
+
+  if (isCelsius)
+    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 +
+         -0.00683783 * pow(temperature, 2) +
+         -0.05481717 * pow(percentHumidity, 2) +
+         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 isCelsius ? convertFtoC(hi) : hi;
 }
 
 uint8_t DHT22::getLastError(){

DHT22.h

@@ -52,8 +52,18 @@ class DHT22{
     /** @return humidity %rH **/
     float getHumidity();
 
-    /** @return temperature in °C **/
-    float getTemperature();
+    /** if M=true, return temperature in °C, else in °F **/
+    /** @return temperature in °C or °F **/
+    float getTemperature(bool M = true);
+
+    /** @return temp in °C **/
+    float convertCtoF(float);
+
+    /** @return temp in °F **/
+    float convertFtoC(float);
+
+    /** @return heat index in °C or °F **/
+    float getHeatIndex(float t, float h, bool isCelsius = true);
 
     /** @return code from last readSensor() request **/
 	  uint8_t getLastError();