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Datasheet

BMP280 Digital Pressure Sensor

Page 22

BST-BMP280-DS001-19 | Revision 1.19 | January 2018

Bosch Sensortec

parties. BOSCH and the symbol are registered trademarks of Robert Bosch GmbH, Germany.

Note: Specifications within this document are subject to change without notice. Not intended for publication.

The variable t_fine (signed 32 bit) carries a fine resolution temperature value over to the pressure

compensation formula and could be implemented as a global variable.

The data type “BMP280_S32_t” should define a 32 bit signed integer variable type and can

usually be defined as “long signed int”.

The data type “BMP280_U32_t” should define a 32 bit unsigned integer variable type and can

usually be defined as “long unsigned int”.

For best possible calculation accuracy, 64 bit integer support is needed. If this is not possible on

your platform, please see appendix 8.2 for a 32 bit alternative.

The data type “BMP280_S64_t” should define a 64 bit signed integer variable type, which on most

supporting platforms can be defined as “long long signed int”. The revision of the code is rev.1.1.

// Returns temperature in DegC, resolution is 0.01 DegC. Output value of “5123” equals 51.23 DegC.

// t_fine carries fine temperature as global value

BMP280_S32_t t_fine;

BMP280_S32_t bmp280_compensate_T_int32(BMP280_S32_t adc_T)

{

BMP280_S32_t var1, var2, T;

var1

= ((((adc_T>>3) – ((BMP280_S32_t)dig_T1<<1))) * ((BMP280_S32_t)dig_T2)) >> 11;

var2

= (((((adc_T>>4) – ((BMP280_S32_t)dig_T1)) * ((adc_T>>4) – ((BMP280_S32_t)dig_T1))) >> 12) *

((BMP280_S32_t)dig_T3)) >> 14;

t_fine = var1 + var2;

= (t_fine * 5 + 128) >> 8;

return T;

}

“”–

// Returns pressure in Pa as unsigned 32 bit integer in Q24.8 format (24 integer bits and 8 fractional bits).

// Output value of “24674867” represents 24674867/256 = 96386.2 Pa = 963.862 hPa

BMP280_U32_t bmp280_compensate_P_int64(BMP280_S32_t adc_P)

{

BMP280_S64_t var1, var2, p;

var1 = ((BMP280_S64_t)t_fine) – 128000;

var2 = var1 * var1 * (BMP280_S64_t)dig_P6;

var2 = var2 + ((var1*(BMP280_S64_t)dig_P5)<<17);

var2 = var2 + (((BMP280_S64_t)dig_P4)<<35);

var1 = ((var1 * var1 * (BMP280_S64_t)dig_P3)>>8) + ((var1 * (BMP280_S64_t)dig_P2)<<12);

var1 = (((((BMP280_S64_t)1)<<47)+var1))*((BMP280_S64_t)dig_P1)>>33;

if (var1 == 0)

{

return 0; // avoid exception caused by division by zero

}

p = 1048576-adc_P;

p = (((p<<31)-var2)*3125)/var1;

var1 = (((BMP280_S64_t)dig_P9) * (p>>13) * (p>>13)) >> 25;

var2 = (((BMP280_S64_t)dig_P8) * p) >> 19;

p = ((p + var1 + var2) >> 8) + (((BMP280_S64_t)dig_P7)<<4);

return (BMP280_U32_t)p;

3.12 Calculating pressure and temperature

The following figure shows the detailed algorithm for pressure and temperature measurement.

This algorithm is available to customers as reference C source code (“BMP28x_ API”) from Bosch

Sensortec and via its sales and distribution partners.

Please contact your Bosch Sensortec representative for details.

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