BMP085

Data sheet

Bosch Sensortec

Rev. 1.2

Page 10

15 October 2009

© Bosch Sensortec GmbH reserves all rights even in the event of industrial property rights. We reserve all rights of disposal such

as copying and passing on to third parties. BOSCH and the symbol are registered trademarks of Robert Bosch GmbH, Germany.

Specifications 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

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

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

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.

Overview of BMP085 modes, selected by driver software via the variable oversampling_setting:

Mode

Parameter

oversampling_setting

Internal

number of

samples

Conversion

time pressure

max. [ms]

Avg. current

@ 1 sample/s

typ. [µA]

RMS noise

typ. [hPa]

RMS noise

typ. [m]

ultra low power

0

1

4.5

3

0.06

0.5

standard

1

2

7.5

5

0.05

0.4

high resolution

2

4

13.5

7

0.04

0.3

ultra high

resolution

3

8

25.5

12

0.03

0.25

The noise data is calculated as standard deviation of 10 data points. For further information on

noise characteristics see the relevant application note “Noise in pressure sensor applications”.

Start temperature

measurement

Read UT

Start pressure

measurement

Read UP

Start

Calculate pressure and

temperature in physical

units

wait 4.5ms

wait (depends on mode, see below)