added set_temp_offset function and example

Author: ayeks

examples/temp-offset.py

@@ -0,0 +1,46 @@
+#!/usr/bin/env python
+import bme680
+
+print("""Display Temperature, Pressure and Humidity with different offsets.
+""")
+
+sensor = bme680.BME680()
+
+# These oversampling settings can be tweaked to
+# change the balance between accuracy and noise in
+# the data.
+
+sensor.set_humidity_oversample(bme680.OS_2X)
+sensor.set_pressure_oversample(bme680.OS_4X)
+sensor.set_temperature_oversample(bme680.OS_8X)
+sensor.set_filter(bme680.FILTER_SIZE_3)
+
+print("Initial readings")
+sensor.get_sensor_data()
+output = "{0:.2f} C,{1:.2f} hPa,{2:.3f} %RH".format(sensor.data.temperature, sensor.data.pressure, sensor.data.humidity)
+print(output)
+
+print("SET offset 4 degrees celsius")
+sensor.set_temp_offset(4)
+sensor.get_sensor_data()
+output = "{0:.2f} C,{1:.2f} hPa,{2:.3f} %RH".format(sensor.data.temperature, sensor.data.pressure, sensor.data.humidity)
+print(output)
+
+print("SET offset -10 degrees celsius")
+sensor.set_temp_offset(-10)
+sensor.get_sensor_data()
+output = "{0:.2f} C,{1:.2f} hPa,{2:.3f} %RH".format(sensor.data.temperature, sensor.data.pressure, sensor.data.humidity)
+print(output)
+
+print("SET offset -100 degrees celsius")
+sensor.set_temp_offset(-100)
+sensor.get_sensor_data()
+output = "{0:.2f} C,{1:.2f} hPa,{2:.3f} %RH".format(sensor.data.temperature, sensor.data.pressure, sensor.data.humidity)
+print(output)
+
+print("SET offset 0 degrees celsius")
+sensor.set_temp_offset(0)
+sensor.get_sensor_data()
+output = "{0:.2f} C,{1:.2f} hPa,{2:.3f} %RH".format(sensor.data.temperature, sensor.data.pressure, sensor.data.humidity)
+print(output)
+

library/bme680/__init__.py

@@ -36,7 +36,7 @@ def __init__(self, i2c_addr=I2C_ADDR_PRIMARY, i2c_device=None):
         self.set_temperature_oversample(OS_8X)
         self.set_filter(FILTER_SIZE_3)
         self.set_gas_status(ENABLE_GAS_MEAS)
-
+        self.set_temp_offset(0)
         self.get_sensor_data()
 
     def _get_calibration_data(self):
@@ -56,6 +56,19 @@ def soft_reset(self):
         self._set_regs(SOFT_RESET_ADDR, SOFT_RESET_CMD) 
         time.sleep(RESET_PERIOD / 1000.0)
 
+    def set_temp_offset(self, value):
+        """Set temperature offset in celsius
+
+        If set, the temperature t_fine will be increased by given value in celsius.
+        :param value: Temperature offset in Celsius, eg. 4, -8
+        """
+        if value == 0:
+            self.offset_temp_in_t_fine = 0
+        elif value < 0:
+            self.offset_temp_in_t_fine = -int((((abs(value) * 100) << 8) - 128) / 5)
+        else:
+            self.offset_temp_in_t_fine = int((((abs(value) * 100) << 8) - 128) / 5)
+
     def set_humidity_oversample(self, value):
         """Set humidity oversampling
         
@@ -293,7 +306,7 @@ def _calc_temperature(self, temperature_adc):
         var3 = ((var3) * (self.calibration_data.par_t3 << 4)) >> 14
 
         # Save teperature data for pressure calculations
-        self.calibration_data.t_fine = (var2 + var3)
+        self.calibration_data.t_fine = (var2 + var3) + self.offset_temp_in_t_fine
         calc_temp = (((self.calibration_data.t_fine * 5) + 128) >> 8)
 
         return calc_temp