BMP085

Data sheet

Bosch Sensortec

Rev. 1.2

Page 13

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.

Calculation of pressure and temperature for BMP085

C code function:

type:

bmp085_get_cal_param

AC1 (0xAA, 0xAB)

(16 bit)

AC1 =

408

short

AC2 (0xAC, 0xAD)

(16 bit)

AC2 =

-72

short

AC3 (0xAE, 0xAF)

(16 bit)

AC3 =

-14383

short

AC4 (0xB0, 0xB1)

(16 bit)

AC4 =

32741

unsigned short

AC5 (0xB2, 0xB3)

(16 bit)

AC5 =

32757

unsigned short

AC6 (0xB4, 0xB5)

(16 bit)

AC6 =

23153

unsigned short

B1 (0xB6, 0xB7)

(16 bit)

B1 =

6190

short

B2 (0xB8, 0xB9)

(16 bit)

B2 =

4

short

MB (0xBa, 0xBB)

(16 bit)

MB =

-32768

short

MC (0xBC, 0xBD)

(16 bit)

MC =

-8711

short

MD (0xBE, 0xBF)

(16 bit)

MD =

2868

short

bmp085_get_ut

UT =

27898

long

oss =

0

= oversampling_setting

short (0 .. 3)

(ultra low power mode)

bmp085_get_up

UP =

23843

long

bmp085_get_temperature

X1 = (UT - AC6) * AC5 / 2

1 5

X1 =

4743

long

X2 = MC * 2

X2 =

-2344

long

B5 = X1 + X2

B5 =

2399

long

T = (B5 + 8) / 2

4

T =

150

temp in 0.1°C

long

BMP085_calpressure

B6 = B5 - 4000

B6 =

-1601

long

X1 = (B2 * (B6 * B6 / 2

X1 =

1

long

X2 = AC2 * B6 / 2

11

X2 =

56

long

X3 = X1 + X2

X3 =

57

long

B3 = ((AC1*4+X3) << oss + 2) / 4

B3 =

422

long

X1 = AC3 * B6 / 2

13

X1 =

2810

long

X2 = (B1 * (B6 * B6 / 2

12

)) / 2

16

X2 =

59

long

X3 = ((X1 + X2) + 2) / 2

2

X3 =

717

long

B4 = AC4 * (unsigend long)(X3 + 32768) / 2

15

B4 =

33457

unsigned long

B7 = ((unsigned long)UP - B3) * (50000 >> oss)

B7 =

1171050000

unsigned long

if (B7 < 0x80000000) { p = (B7 * 2) / B4 }

p =

70003

long

else { p = (B7 / B4) * 2 }

long

X1 = (p / 2

8

) * (p / 2

8

)

X1 =

74529

long

X1 = (X1 * 3038) / 2

16

X1 =

3454

long

X2 = (-7357 * p) / 2

16

X2 =

-7859

long

p = p + (X1 + X2 + 3791) / 2

4

p =

69964

press. in Pa

long

display temperature and pressure value

calculate true pressure

calculate true temperature

read uncompensat ed pressure value

write 0x34+(oss<<6) into reg 0xF4, wait

read reg 0xF6 (MSB), 0xF7 (LSB), 0xF8 (XLSB)

example:

Read calibration data

from the E

2

PROM of the BMP085

read out E

read uncompensated temperature value

UT = MSB << 8 + LSB

UP = (MSB<<16 + LSB<<8 + XLSB) >> (8-oss)

write 0x2E into reg 0xF4, wait 4.5ms

read reg 0xF6 (MSB), 0xF7 (LSB)

Start