use compensation from reference implementation

[el-han]

This PR is a proposed fix for #78

It uses the reference implementation of the compensation algorithm from the datasheet. This implementation uses division operations instead of bit shifts.

[caternuson]

Current code seems to match section 4.2.3 of datasheet: https://www.bosch-sensortec.com/media/boschsensortec/downloads/datasheets/bst-bme280-ds002.pdf Can you clarify where you are seeing the implementation you have coded?

[el-han]

I used the driver which is provided by Bosch as a reference: https://github.com/BoschSensortec/BME280_driver

[caternuson]

Thanks, so:

• temperature from here
  • pressure from here
  • humidity from here

Running the library example bme280test with your updated code seems to work OK except for pressure, which looks to be off by a factor of 256 (or 2.56?). Test was run near sea level, so ~14.7 psi -> 101352.9 Pa = 1013.5 hPa

[el-han]

Aw bummer! Seems like I have overlooked the return line in readPressure(). Sorry for that! Yes, the pressure is off by factor 2.56. I will fix that.

[caternuson]

@elli89 Sorry for not getting back to this in a while. See suggested code change above. Also - did you test this, similar to my test above, to make sure the readings come out generally as expected?

[caternuson]

I'm going to go ahead and merge this. The one code suggestion was fairly cosmetic. Hopefully these updates help with #78.

Just tested one more time with latest updates and looks good.