Weather Board 2 shows incorrect temperature from BME280

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Moan
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Weather Board 2 shows incorrect temperature from BME280

Unread post by Moan » Sun Jun 16, 2019 7:09 pm

Hi.
I've a problem with Weather Board 2's BME280 sensor. The shown temperature is at least +5°C higher than in reality.
I use Odroid N2. Weather Board 2 is connected to I2C-2. I use 50cm long jumper wires, so the WB2 is afar from the potential heat source. It has no Sun contact.
Output at the moment:

Code: Select all

UV_index : 0.01
Visible : 103 Lux
IR : 77 Lux
======== bme280 ========     WEATHER-BOARD v1.6
temperature : 26.48  'C
humidity : 58.36 %
pressure : 984.75 hPa
altitude : 330.533478 m
There it is currently 19 °C outdoors, and 20-21 °C in the room with the device (checked by two other "normal" thermometers).

What's strange, when the temperature was higher (29 °C in the room) it showed only +1 °C higher (30 °C),
I could set an offset (delta_temperature) in Home Assistant, but this measure differs depending on temperature, so -5 °C delta wouldn't be good in all cases.

What can I do to improve it? I'm totally new at single board computers, so any, even obvious tips would be welcome.

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Re: Weather Board 2 shows incorrect temperature from BME280

Unread post by odroid » Mon Jun 17, 2019 2:02 pm

According to the BME280 datasheet, the temperature sensor accuracy must be +/- 1.0 °C at 0~65 °C range.
So the difference between other thermometers must be lower than 2°C.
Can you check the accuracy of other "normal" thermometers.

It is also worth to check whether Bosch's compensation formulas must be used or not.
Please see page 49 of the BME280 datasheet.
https://ae-bst.resource.bosch.com/media ... -DS002.pdf

Moan
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Re: Weather Board 2 shows incorrect temperature from BME280

Unread post by Moan » Mon Jun 17, 2019 2:37 pm

According to the BME280 datasheet, the temperature sensor accuracy must be +/- 1.0 °C at 0~65 °C range.
So the difference between other thermometers must be lower than 2°C.
Can you check the accuracy of other "normal" thermometers.
Unfortunately, I can't check the accuracy of other thermometers as they are normal, home thermometers, bought years ago.

The current outdoors temperature is +15 °C (confirmed by the outdoors thermometer). The window is open. Two other thermometers in room show 19 °C and 20 °C.
Home Assistant screenshot:
temp-now.PNG
temp-now.PNG (124.31 KiB) Viewed 116 times
I think this difference is too high, however, when I touched sensors with a finger, it jumped to around 36 °C within 2 minutes.
It is also worth to check whether Bosch's compensation formulas must be used or not.
Please see page 49 of the BME280 datasheet.
Could you please give me some tips how to check this method? Am I supposed to edit file: WEATHER-BOARD/c_weather/bme280.c from https://github.com/hardkernel/WEATHER-B ... /c_weather ?

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