Merge pull request #26 from barbudor/master

fix #25 + fix #19 + refactor `pressure` property

Author: ladyada

.gitignore

@@ -1,6 +1,7 @@
 __pycache__
 _build
 *.pyc
+*.mpy
 .env
 build*
 bundles

adafruit_bme280.py

@@ -74,8 +74,8 @@
 IIR_FILTER_X8 = const(0x03)
 IIR_FILTER_X16 = const(0x04)
 
-_BME280_IIR_FILTERS = frozenset((IIR_FILTER_DISABLE, IIR_FILTER_X2,
-                                 IIR_FILTER_X4, IIR_FILTER_X8, IIR_FILTER_X16))
+_BME280_IIR_FILTERS = (IIR_FILTER_DISABLE, IIR_FILTER_X2,
+                       IIR_FILTER_X4, IIR_FILTER_X8, IIR_FILTER_X16)
 
 """overscan values for temperature, pressure, and humidity"""
 OVERSCAN_DISABLE = const(0x00)
@@ -93,7 +93,7 @@
 MODE_FORCE = const(0x01)
 MODE_NORMAL = const(0x03)
 
-_BME280_MODES = frozenset((MODE_SLEEP, MODE_FORCE, MODE_NORMAL))
+_BME280_MODES = (MODE_SLEEP, MODE_FORCE, MODE_NORMAL)
 """
 standby timeconstant values
 TC_X[_Y] where X=milliseconds and Y=tenths of a millisecond
@@ -107,9 +107,9 @@
 STANDBY_TC_500 = const(0x04)    #500ms
 STANDBY_TC_1000 = const(0x05)   #1000ms
 
-_BME280_STANDBY_TCS = frozenset((STANDBY_TC_0_5, STANDBY_TC_10, STANDBY_TC_20,
-                                 STANDBY_TC_62_5, STANDBY_TC_125, STANDBY_TC_250,
-                                 STANDBY_TC_500, STANDBY_TC_1000))
+_BME280_STANDBY_TCS = (STANDBY_TC_0_5, STANDBY_TC_10, STANDBY_TC_20,
+                       STANDBY_TC_62_5, STANDBY_TC_125, STANDBY_TC_250,
+                       STANDBY_TC_500, STANDBY_TC_1000)
 
 class Adafruit_BME280:
     """Driver from BME280 Temperature, Humidity and Barometic Pressure sensor"""
@@ -344,23 +344,21 @@ def pressure(self):
         var3 = self._pressure_calib[2] * var1 * var1 / 524288.0
         var1 = (var3 + self._pressure_calib[1] * var1) / 524288.0
         var1 = (1.0 + var1 / 32768.0) * self._pressure_calib[0]
-        if var1 == 0:
-            return 0
-        if var1:
-            pressure = 1048576.0 - adc
-            pressure = ((pressure - var2 / 4096.0) * 6250.0) / var1
-            var1 = self._pressure_calib[8] * pressure * pressure / 2147483648.0
-            var2 = pressure * self._pressure_calib[7] / 32768.0
-            pressure = pressure + (var1 + var2 + self._pressure_calib[6]) / 16.0
-
-            pressure /= 100
-            if pressure < _BME280_PRESSURE_MIN_HPA:
-                return _BME280_PRESSURE_MIN_HPA
-            if pressure > _BME280_PRESSURE_MAX_HPA:
-                return _BME280_PRESSURE_MAX_HPA
-            return pressure
-        else:
+        if not var1: # avoid exception caused by division by zero
+            raise ArithmeticError("Invalid result possibly related to error while \
+reading the calibration registers")
+        pressure = 1048576.0 - adc
+        pressure = ((pressure - var2 / 4096.0) * 6250.0) / var1
+        var1 = self._pressure_calib[8] * pressure * pressure / 2147483648.0
+        var2 = pressure * self._pressure_calib[7] / 32768.0
+        pressure = pressure + (var1 + var2 + self._pressure_calib[6]) / 16.0
+
+        pressure /= 100
+        if pressure < _BME280_PRESSURE_MIN_HPA:
             return _BME280_PRESSURE_MIN_HPA
+        if pressure > _BME280_PRESSURE_MAX_HPA:
+            return _BME280_PRESSURE_MAX_HPA
+        return pressure
 
     @property
     def humidity(self):
@@ -416,7 +414,7 @@ def _read_coefficients(self):
         self._humidity_calib = [0]*6
         self._humidity_calib[0] = self._read_byte(_BME280_REGISTER_DIG_H1)
         coeff = self._read_register(_BME280_REGISTER_DIG_H2, 7)
-        coeff = list(struct.unpack('<hBBBBb', bytes(coeff)))
+        coeff = list(struct.unpack('<hBbBbb', bytes(coeff)))
         self._humidity_calib[1] = float(coeff[0])
         self._humidity_calib[2] = float(coeff[1])
         self._humidity_calib[3] = float((coeff[2] << 4) |  (coeff[3] & 0xF))