Support for BME280 Temperature Correction (#1062)

* Support for BME280 Temperature Correction

The Spark Fun BME 280 library has support for Temperature correction, and this pull request implements the ability to apply a correction via a compiler directive ( BME280Correction ).

main/ZsensorBME280.ino

@@ -107,6 +107,12 @@ void setupZsensorBME280() {
   //  1 through 5, oversampling *1, *2, *4, *8, *16 respectively
   mySensor.settings.humidOverSample = 1;
 
+  // tempCorrection - Correction in celcius of temperature reported by bme280 sensor.  Both Celcius and Farenheit temperatures are adjusted.
+  // -------------------------
+  // Value is a float
+  // ie Compiler Directive '-DBME280Correction=-3.4'
+  mySensor.settings.tempCorrection = BME280Correction;
+
   delay(10); // Gives the Sensor enough time to turn on (The BME280 requires 2ms to start up)
 
   int ret = mySensor.begin();

main/config_BME280.h

@@ -62,4 +62,16 @@ int BME280_i2c_addr = 0x76; // Bosch BME280 I2C Address
 int BME280_PIN_SDA = SDA; // PIN SDA
 int BME280_PIN_SCL = SCL; // PIN SCL
 
+// Temperature correction for BME280 devices
+
+#ifndef BME280Correction
+
+// BME280Correction - Correction in celcius of temperature reported by bme280 sensor.  Both Celcius and Farenheit temperatures are adjusted.
+// -------------------------
+// Value is a float
+// ie Compiler Directive '-DBME280Correction=-3.4'
+
+#  define BME280Correction 0
+#endif
+
 #endif

platformio.ini

@@ -236,6 +236,7 @@ build_flags =
   '-DZsensorADC="ADC"'
   '-DZsensorBH1750="BH1750"'
   '-DZsensorBME280="BME280"'
+  '-DBME280Correction=-3.4'
   '-DZsensorHTU21="HTU21"'
   '-DZsensorAHTx0="AHTx0"'
   '-DZsensorTSL2561="TSL2561"'