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Bmp280 Sensor gives wrong readings

See original GitHub issue

While testing the Bmp280 sensor, I found that mine was giving very wrong readings (~940hPa when it should be in the order of ~1010hPa). There’s definitelly no storm outside now, and it’s cold but sunny.

Investigating further, I found a small bug in the calibration calculation for temperatures:

Line 181 of Bmxx80Base.cs should be changed to:

double var1 = ((((double)adcTemperature / 16384.0) - ((double)_calibrationData.DigT1) / 1024.0)) * (double)_calibrationData.DigT2;

There are missing parentheses in that formula.

I’ll come up with a patch for this (including an unit test), however, since my sensor still gives the wrong values (also with the python reference implementation), it’s hard for me to know that’s really all.

Issue Analytics

State:
Created 3 years ago
Comments:14 (14 by maintainers)

Top GitHub Comments

2reactions

djaus2commented, Apr 1, 2020

Ok will do in next 24hrs

David Jones MVP

From: Patrick Grawehr notifications@github.com Sent: Wednesday, April 1, 2020 4:28:56 PM To: dotnet/iot iot@noreply.github.com Cc: David Jones (MVP) davidjones@sportronics.com.au; Mention mention@noreply.github.com Subject: Re: [dotnet/iot] Bmp280 Sensor gives wrong readings (#1027)

Since my sensor is apparently broken (or is incorrectly calibrated) I would be glad if @djaus2 https://github.com/djaus2 could verify the fix. I have ordered a new one, but I’m not sure when this arives.

— You are receiving this because you were mentioned. Reply to this email directly, view it on GitHubhttps://github.com/dotnet/iot/issues/1027#issuecomment-607040796, or unsubscribehttps://github.com/notifications/unsubscribe-auth/AC7U2EPBTAZEMPBFTVSWZQLRKLGJRANCNFSM4LUADORA.

0reactions

pgrawehrcommented, May 7, 2020

Actually, I’m a bit confused, because I think I didn’t really change anything (the parentheses on that line are extra-confusing). But I’ve done it together with an unit test and an improved calcuation formula (using doubles instead of fixed-point math). I can finish that PR pretty quickly, but I don’t want to have to many PRs open at a time.

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