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finitespace / BME280

Provides an Arduino library for reading and interpreting Bosch BME280 data over I2C, SPI or Sw SPI.
GNU General Public License v3.0
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Absolute humidity measurement #25

Closed milan-de closed 7 years ago

milan-de commented 7 years ago

Hi all,

as I am new to arduino and BME280 world I am not sure if my question I should ask under "Issues" or somwhere else, but in case I am on right place my question would be how to retrieve absolute humidity using this BME280 ? In library "finitespace/BME280" is mention only relative humidity, right ? Thanks!

cheers, Milan

coelner commented 7 years ago

IMHO that is not a functionality of this sensor so it should not be part of the library either. There are thoughts about another library, maybe this code snippets helps you `#include

double calculationAbsHum(float t, float h) { double temp; temp = pow(2.718281828, (17.67 t) / (t + 243.5)); return (6.112 temp h 2.1674) / (273.15 + t); } String(calculationAbsHum(temperature, humidity)) + " g/m3");`

milan-de commented 7 years ago

Thanks, is there any scientific reference on the Internet where this approximation is listed ?

coelner commented 7 years ago

I'm not sure, but I guess here: https://carnotcycle.wordpress.com/2012/08/04/how-to-convert-relative-humidity-to-absolute-humidity/ Otherwise: http://www.vaisala.com/Vaisala%20Documents/Application%20notes/Humidity_Conversion_Formulas_B210973EN-F.pdf

milan-de commented 7 years ago

Thanks!