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Added function to calculate real/absolute pressure at sea level #56

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Added function to calculate real/absolute pressure at sea level #56

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9 changes: 9 additions & 0 deletions Adafruit_BMP085/Adafruit_BMP085.py
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Original file line number Diff line number Diff line change
@@ -1,6 +1,7 @@
#!/usr/bin/python

import time
from decimal import Decimal
from Adafruit_I2C import Adafruit_I2C

# ===========================================================================
Expand Down Expand Up @@ -257,3 +258,11 @@ def readAltitude(self, seaLevelPressure=101325):
return altitude

return 0

# With the measured pressure and the absolute altitude the pressure at sea level can be calculated
# see BMP085 datasheet: 3.7 Calculating pressure at sea level
def getRealPressure(self, altitude):
pressure = self.readPressure()
denominator = pow(Decimal(1) - (Decimal(altitude) / Decimal(44330)), Decimal(5.255))

return pressure / denominator
5 changes: 5 additions & 0 deletions Adafruit_BMP085/Adafruit_BMP085_example.py
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Expand Up @@ -21,6 +21,10 @@
# Read the current barometric pressure level
pressure = bmp.readPressure()

# get the real barometric pressure on sea level
# pass the absolute altitude of the sensors position as parameter
realPressure = bmp.getRealPressure(720)

@F481 F481 Sep 5, 2013

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Forgot to make the altitude parameter variable.
Best would be to use a global variable where the user could set the altitude.


# To calculate altitude based on an estimated mean sea level pressure
# (1013.25 hPa) call the function as follows, but this won't be very accurate
altitude = bmp.readAltitude()
Expand All @@ -32,4 +36,5 @@

print "Temperature: %.2f C" % temp
print "Pressure: %.2f hPa" % (pressure / 100.0)
print "Real pressure: %.2f hPa" % (realPressure / 100)
print "Altitude: %.2f" % altitude