Add imperial unit support

Added imperial units support to MKRENV library

- Added enum scale factors
- Renamed  readLux in readIlluminance to comply the others illuminance scale factors
- Added scale factor support to pressure temperature and illuminance API
- added example to show how to read in fahrenheit and foot candle the temperature and the illuminance sensor
- added PSI unit Support to readPressure
- Added enum's words in keywords.txt

Author: Rocketct

examples/ReadSensorsImperial/ReadSensorsImperial.ino

@@ -0,0 +1,69 @@
+/*
+  MKR ENV Shield - Read Sensors Imperial
+
+  This example reads the sensors on-board the MKR ENV shield
+  and prints them in imperial units to the Serial Monitor once a second.
+
+  The circuit:
+  - Arduino MKR board
+  - Arduino MKR ENV Shield attached
+
+  This example code is in the public domain.
+*/
+
+#include <Arduino_MKRENV.h>
+
+void setup() {
+  Serial.begin(9600);
+  while (!Serial);
+
+  if (!ENV.begin()) {
+    Serial.println("Failed to initialize MKR ENV shield!");
+    while (1);
+  }
+}
+
+void loop() {
+  // Passing in FAHRENHEIT as the unit paramter to ENV.readTemperature(...),
+  // PSI to readPressure(...) and FOOTCANDLE to readIlluminance(...)
+  // allows you to read the sensors values in imperial units
+  float temperature = ENV.readTemperature(FAHRENHEIT);
+  float humidity    = ENV.readHumidity();
+  float pressure    = ENV.readPressure(PSI);
+  float illuminance = ENV.readIlluminance(FOOTCANDLE);
+  float uva         = ENV.readUVA();
+  float uvb         = ENV.readUVB();
+  float uvIndex     = ENV.readUVIndex();
+
+  // print each of the sensor values
+  Serial.print("Temperature = ");
+  Serial.print(temperature);
+  Serial.println(" °F");
+
+  Serial.print("Humidity    = ");
+  Serial.print(humidity);
+  Serial.println(" %");
+
+  Serial.print("Pressure    = ");
+  Serial.print(pressure);
+  Serial.println(" psi");
+
+  Serial.print("Illuminance = ");
+  Serial.print(illuminance);
+  Serial.println(" fc");
+
+  Serial.print("UVA         = ");
+  Serial.println(uva);
+
+  Serial.print("UVB         = ");
+  Serial.println(uvb);
+
+  Serial.print("UV Index    = ");
+  Serial.println(uvIndex);
+
+  // print an empty line
+  Serial.println();
+
+  // wait 1 second to print again
+  delay(1000);
+}

keywords.txt

@@ -26,3 +26,12 @@ readUVIndex	KEYWORD2
 #######################################
 # Constants
 #######################################
+
+FAHRENHEIT	LITERAL1
+CELSIUS	LITERAL1
+PSI	LITERAL1
+MILLIBAR	LITERAL1
+KILOPASCAL	LITERAL1
+FOOTCANDLE	LITERAL1
+METERCANDLE	LITERAL1
+LUX	LITERAL1

src/MKRENV.cpp

@@ -109,7 +109,7 @@ void ENVClass::end()
   pinMode(LIGHT_SENSOR_PIN, INPUT);
 }
 
-float ENVClass::readTemperature()
+float ENVClass::readTemperature(int units)
 {
   // trigger one shot
   i2cWrite(HTS221_ADDRESS, HTS221_CTRL2_REG, 0x01);
@@ -121,8 +121,12 @@ float ENVClass::readTemperature()
 
   // read value and convert
   int16_t tout = i2cRead16(HTS221_ADDRESS, HTS221_TEMP_OUT_L_REG);
-
-  return (tout * _hts221TemperatureSlope + _hts221TemperatureZero);
+  float reading = (tout * _hts221TemperatureSlope + _hts221TemperatureZero);
+  if (units == FAHRENHEIT) { // Fahrenheit = (Celsius * 9 / 5) + 32
+    return (reading * 9.0 / 5.0) + 32.0;
+  } else {
+    return reading;
+  }
 }
 
 float ENVClass::readHumidity()
@@ -141,7 +145,7 @@ float ENVClass::readHumidity()
   return (hout * _hts221HumiditySlope + _hts221HumidityZero);
 }
 
-float ENVClass::readPressure()
+float ENVClass::readPressure(int units)
 {
   // trigger one shot
   i2cWrite(LPS22HB_ADDRESS, LPS22HB_CTRL2_REG, 0x01);
@@ -151,19 +155,31 @@ float ENVClass::readPressure()
     yield();
   }
 
-  // read value and convert
-  return (i2cRead(LPS22HB_ADDRESS, LPS22HB_PRESS_OUT_XL_REG) | 
+  float reading = (i2cRead(LPS22HB_ADDRESS, LPS22HB_PRESS_OUT_XL_REG) |
           (i2cRead(LPS22HB_ADDRESS, LPS22HB_PRESS_OUT_L_REG) << 8) | 
           (i2cRead(LPS22HB_ADDRESS, LPS22HB_PRESS_OUT_H_REG) << 16)) / 40960.0;
+
+  if (units == MILLIBAR) { // 1 kPa = 10 MILLIBAR
+    return reading * 10;
+  } else if (units == PSI) {  // 1 kPa = 0.145038 PSI
+    return reading * 0.145038;
+  } else {
+    return reading;
+  }
 }
 
-float ENVClass::readIlluminance()
+float ENVClass::readIlluminance(int units)
 {
   // read analog value and convert to mV
   float mV = (analogRead(_lightSensorPin) * 3300.0) / 1023.0;
 
   // 2 mV per lux
-  return (mV / 2.0);
+  float reading = (mV / 2.0); // Readings are in Lux scale
+  if (units == FOOTCANDLE) { // 1 Lux = 0.092903 Foot-Candle
+    return reading * 0.092903;
+  } else {
+    return reading; // 1 Lux = 1 Meter-Candle
+  }
 }
 
 // UV formula's and constants based on:

src/MKRENV.h

@@ -23,6 +23,16 @@
 #include <Arduino.h>
 #include <Wire.h>
 
+enum {
+  FAHRENHEIT,
+  CELSIUS,
+  PSI,
+  MILLIBAR,
+  KILOPASCAL,
+  FOOTCANDLE,
+  METERCANDLE,
+  LUX = METERCANDLE
+};
 
 class ENVClass {
 public:
@@ -31,16 +41,16 @@ class ENVClass {
   int begin();
   void end();
 
-  float readTemperature();
+  float readTemperature(int units = CELSIUS);
   float readHumidity();
-  float readPressure();
-  float readIlluminance();
+  float readPressure(int units = KILOPASCAL);
+  float readIlluminance(int units = LUX);
   float readUVA();
   float readUVB();
   float readUVIndex();
 
   // deprecated, use readIlluminance() instead
-  float readLux() { return readIlluminance(); }
+  float readLux() { return readIlluminance(LUX); }
 
 private:
   int i2cRead(uint8_t address, uint8_t reg);