Humidity value always 0.0

[christoph-7]

Hi,
when running the sample.py, the humidity value is always 0.0.
Temperature and pressure seem fine. The sensor is also working with the Adafruit library on an Arduino.

EDIT1:
I'm using Python 2.7
Looking into the init.py, the error seems to occur in the calculating of the variable res, which is in my case calculated to ~ -3798. Therefore line 92 is evaluated to 0.0

[rm-hull]

Interesting.... line 92 clamps the value between 0% and 100% (obviously, any value outside this range doesn't/shouldn't make sense)

• Do the temperature and pressure values correspond with what the adafruit library results?
• Are you using an unbranded BME280 or the adafruit breakout board?
• Can you print out the bme280.compensation_params and paste into this issue

[christoph-7]

The value of temperature is ~3 °C higher with the Adafruit library and pressure is the same.
I'm using an unbranded BME280 breakout board.

bme280.compensation_params delivers
{'dig_P9': 4285, 'dig_P8': -10230, 'dig_T1': 28814, 'dig_T3': 50, 'dig_T2': 26441, 'dig_P1': 35567, 'dig_P3': 3024, 'dig_P2': -10609, 'dig_P5': -40, 'dig_P4': 7295, 'dig_P7': 9900, 'dig_P6': -7, 'dig_H1': 75, 'dig_H3': 0, 'dig_H2': 358, 'dig_H5': 131075, 'dig_H4': 329, 'dig_H6': 30, 'x8': 4, 'x2': 2, 'x1': 1, 'x4': 3, 'x16': 5}

EDIT1:
I looked up the compensation value for the humidity with the Adafruit library. The only difference is dig_H5, which is only 50

EDIT2:
I think that you did made a mistake in the register shifting in line 156
I changed
compensation_params.dig_H5 = (e5 & 0xF0) << 12 | e6
to
compensation_params.dig_H5 = ((e5 >> 4) & 0xF0) | (e6 << 4)
and now I'm getting reasonable results. I will later try to verify the measurements to clarify if this is just another incorrect value.

[rm-hull]

Yes, I think you're right, it is definitely an issue with H5 - looking at the datasheet, I think I made a transcription error when I coded it up:

I believe your calc is correct, so I will push out a new version

[rm-hull]

I've published 0.1.3 on pypi with the fix in it, and have improved the debug logging of uncompensated readings:

$ python examples/sample.py 
compensation_params = {'dig_P9': 4285, 'dig_P8': -10230, 'dig_T1': 28441, 'dig_T3': 50, 'dig_T2': 26357, 'dig_P1': 36127, 'dig_P3': 3024, 'dig_P2': -10788, 'dig_P5': 45, 'dig_P4': 6191, 'dig_P7': 9900, 'dig_P6': -7, 'dig_H1': 75, 'dig_H3': 0, 'dig_H2': 364, 'dig_H5': 0, 'dig_H4': 313, 'dig_H6': 30, 'x8': 4, 'x2': 2, 'x1': 1, 'x4': 3, 'x16': 5}
uncompensated_reading(temp=0x00081930, pressure=0x00058A70, humidity=0x00006C49, block=58:A7:00:81:93:00:6C:49)
compensated_reading(id=e5b9d160-b697-4799-bcd6-dce26ae9ebfd, timestamp=2017-05-23 20:40:07.209791, temp=23.782 °C, pressure=1011.74 hPa, humidity=43.29 % rH)

[cmur2]

Sorry for necromancy, I got a similar issue reported in cmur2/python-bme280#35 and thus came to this thread.

@rm-hull one question:
Shouldn't compensation_params.dig_H5 = ((e5 >> 4) & 0xF0) | (e6 << 4) be compensation_params.dig_H5 = ((e5 >> 4) & 0x0F) | (e6 << 4) (0x0F instead if 0xF0) to avoid ignoring e5 completely?

Edit: It looks like a missed a later modification to the code, my apologies.

[rm-hull]

@cmur2 if you look at the code https://github.com/rm-hull/bme280/blob/master/bme280/__init__.py#L179, is that not what it does?

I think that #11 made this observation, and it was fixed in commit ad21381.