Data Sheet

ManualsBrandsSparkfun Electronics ManualsLight SensorsSparkFun ESP32 Thing Environment Sensor Module

Final Datasheet

BME280 Environmental sensor

Page 49

BST-BME280-DS001-10 | Revision 1.1 | May 2015 Bosch Sensortec

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.

8. Appendix A: Alternative compensation formulas

8.1 Compensation formulas in double precision floating point

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 compensation formula and could be implemented as a global variable.

 BMEhould define a 32 bit signed integer variable type and could

       The revision of the code is rev. 1.1 (pressure and

temperature) and rev. 1.0 (humidity).

Compensating the measurement value with double precision gives the best possible accuracy

but is only recommended for PC applications.

// Returns temperature in DegC, double precision. Output value of “51.23” equals 51.23 DegC.

// t_fine carries fine temperature as global value

BME280_S32_t t_fine;

double BME280_compensate_T_double(BME280_S32_t adc_T)

{

double var1, var2, T;

var1 = (((double)adc_T)/16384.0 – ((double)dig_T1)/1024.0) * ((double)dig_T2);

var2 = ((((double)adc_T)/131072.0 – ((double)dig_T1)/8192.0) *

(((double)adc_T)/131072.0 – ((double) dig_T1)/8192.0)) * ((double)dig_T3);

t_fine = (BME280_S32_t)(var1 + var2);

T = (var1 + var2) / 5120.0;

return T;

}

// Returns pressure in Pa as double. Output value of “96386.2” equals 96386.2 Pa = 963.862 hPa

double BME280_compensate_P_double(BME280_S32_t adc_P)

{

double var1, var2, p;

var1 = ((double)t_fine/2.0) – 64000.0;

var2 = var1 * var1 * ((double)dig_P6) / 32768.0;

var2 = var2 + var1 * ((double)dig_P5) * 2.0;

var2 = (var2/4.0)+(((double)dig_P4) * 65536.0);

var1 = (((double)dig_P3) * var1 * var1 / 524288.0 + ((double)dig_P2) * var1) / 524288.0;

var1 = (1.0 + var1 / 32768.0)*((double)dig_P1);

if (var1 == 0.0)

{

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

}

p = 1048576.0 – (double)adc_P;

p = (p – (var2 / 4096.0)) * 6250.0 / var1;

var1 = ((double)dig_P9) * p * p / 2147483648.0;

var2 = p * ((double)dig_P8) / 32768.0;

p = p + (var1 + var2 + ((double)dig_P7)) / 16.0;

return p;

}

// Returns humidity in %rH as as double. Output value of “46.332” represents 46.332 %rH

double bme280_compensate_H_double(BME280_S32_t adc_H);

{

double var_H;

var_H = (((double)t_fine) – 76800.0);

var_H = (adc_H – (((double)dig_H4) * 64.0 + ((double)dig_H5) / 16384.0 * var_H)) *

(((double)dig_H2) / 65536.0 * (1.0 + ((double)dig_H6) / 67108864.0 * var_H *

(1.0 + ((double)dig_H3) / 67108864.0 * var_H)));

var_H = var_H * (1.0 – ((double)dig_H1) * var_H / 524288.0);

if (var_H > 100.0)

var_H = 100.0;

else if (var_H < 0.0)

var_H = 0.0;

return var_H;

}