User Manual

Data sheet
BMP085
Page 11
BST-BMP085-DS000-06 | Revision 1.3 | August 2011 Bosch Sensortec
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third parties. BOSCH and the symbol are registered trademarks of Robert Bosch GmbH, Germany.
Note: Specifications within this document are subject to change without notice.
3.3 Measurement of pressure and temperature
For all calculations presented here an ANSI C code is available from Bosch Sensortec
(“BMP085_SMD500_API”).
The microcontroller sends a start sequence to start a pressure or temperature measurement.
After converting time, the result value (UP or UT, respectively) can be read via the I
2
C interface.
For calculating temperature in °C and pressure in hPa, the calibration data has to be used.
These constants can be read out from the BMP085 E
2
PROM via the I
2
C interface at software
initialization.
The sampling rate can be increased up to 128 samples per second (standard mode) for
dynamic measurement. In this case, it is sufficient to measure the temperature only once per
second and to use this value for all pressure measurements during the same period.
By using different modes the optimum compromise between power consumption, speed and
resolution can be selected, see below table.
Start temperature
measurement
Read UT
Start pressure
measurement
Read UP
Start
Calculate pressure and
temperature in physical
units
wai
t 4.5ms
wai
t (depends on mode, see below)
Figure 2
: Measurement of pressure and temperature