Data Sheet

Final Datasheet
BME280 Environmental sensor
Page 23
BST-BME280-DS001-10 | Revision 1.1 | May 2015 Bosch Sensortec
© 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.
Note: Specifications within this document are subject to change without notice.
0xE4 / 0xE5[3:0]
dig_H4 [11:4] / [3:0]
signed short
0xE5[7:4] / 0xE6
dig_H5 [3:0] / [11:4]
signed short
0xE7
dig_H6
signed char
4.2.3 Compensation formulas
Please note that it is strongly advised to use the API available from Bosch Sensortec to perform
readout and compensation   
risk. Both pressure and temperature values are expected to be received in 20 bit format,
positive, stored in a 32 bit signed integer. Humidity is expected to be received in 16 bit format,
positive, stored in a 32 bit signed integer.
The variable t_fine (signed 32 bit) carries a fine resolution temperature value over to the
pressure and humidity compensation formula and could be implemented as a global variable.
   BME           

BMEnsigned integer variable type and can

For best possible calculation accuracy in pressure, 64 bit integer support is needed. If this is not
possible on your platform, please see appendix 8.2 for a 32 bit alternative.
T BME  
 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
BME280_S32_t t_fine;
BME280_S32_t BME280_compensate_T_int32(BME280_S32_t adc_T)
{
BME280_S32_t var1, var2, T;
var1 = ((((adc_T>>3) – ((BME280_S32_t)dig_T1<<1))) * ((BME280_S32_t)dig_T2)) >> 11;
var2 = (((((adc_T>>4) – ((BME280_S32_t)dig_T1)) * ((adc_T>>4) – ((BME280_S32_t)dig_T1))) >> 12) *
((BME280_S32_t)dig_T3)) >> 14;
t_fine = var1 + var2;
T = (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
BME280_U32_t BME280_compensate_P_int64(BME280_S32_t adc_P)
{
BME280_S64_t var1, var2, p;
var1 = ((BME280_S64_t)t_fine) – 128000;
var2 = var1 * var1 * (BME280_S64_t)dig_P6;
var2 = var2 + ((var1*(BME280_S64_t)dig_P5)<<17);
var2 = var2 + (((BME280_S64_t)dig_P4)<<35);
var1 = ((var1 * var1 * (BME280_S64_t)dig_P3)>>8) + ((var1 * (BME280_S64_t)dig_P2)<<12);
var1 = (((((BME280_S64_t)1)<<47)+var1))*((BME280_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 = (((BME280_S64_t)dig_P9) * (p>>13) * (p>>13)) >> 25;
var2 = (((BME280_S64_t)dig_P8) * p) >> 19;
p = ((p + var1 + var2) >> 8) + (((BME280_S64_t)dig_P7)<<4);
return (BME280_U32_t)p;
}
// Returns humidity in %RH as unsigned 32 bit integer in Q22.10 format (22 integer and 10 fractional bits).
// Output value of “47445” represents 47445/1024 = 46.333 %RH
BME280_U32_t bme280_compensate_H_int32(BME280_S32_t adc_H)
{
BME280_S32_t v_x1_u32r;
v_x1_u32r = (t_fine – ((BME280_S32_t)76800));
v_x1_u32r = (((((adc_H << 14) – (((BME280_S32_t)dig_H4) << 20) – (((BME280_S32_t)dig_H5) * v_x1_u32r)) +
((BME280_S32_t)16384)) >> 15) * (((((((v_x1_u32r * ((BME280_S32_t)dig_H6)) >> 10) * (((v_x1_u32r *