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From: Catrike Ryder <Soloman@old.bikers.org>
Newsgroups: rec.bicycles.tech
Subject: Re: Garmin altitude problems
Date: Sat, 10 Aug 2024 04:39:21 -0400
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On Fri, 09 Aug 2024 17:36:48 -0700, Jeff Liebermann <jeffl@cruzio.com>
wrote:

>On Sat, 10 Aug 2024 07:02:48 +0700, John B. <slocombjb@gmail.com>
>wrote:
>
>>The basic system sounds much like my old airplane altimeter. But how
>>is atmospheric pressure due to temperature handled?
>
>The MEMS barometric sensor, which I guessed was being used by Garmin,
>has a built in temperature sensor and compensates internally.
><https://www.st.com/resource/en/datasheet/lps28dfw.pdf>
>The data sheet claims "embedded temperature compensation" and +/-1.5C
>temperature accuracy.  However, I can't tell if the pressure numbers
>the sensor produces are pre-compensated internally in the sensor, or
>if the pressure is calculated externally with a connected micro
>controller.  In other words, I don't know how Garmin does temperature
>compensation.
>
>The supplied code from Sparkfun shows that both pressure and
>temperature are output by the sensor.  However, it does not show any
>external processing which would be needed to provide compensation.
><https://learn.sparkfun.com/tutorials/sparkfun-absolute-digital-barometer---lps28dfw-qwiic-hookup-guide#lps28dfw-arduino-library>
>Once again, I don't know how Garmin does temperature compensation.
>
>I blundered across this explanation of how temperature compensations
>works in an aircraft altimeter:
>"What does setting an altimeter actually do to the altitude?"
><https://aviation.stackexchange.com/questions/87848/what-does-setting-an-altimeter-actually-do-to-the-altitude>
>I don't really know if that helps answer your question but it is
>interesting reading.


Calculating altitude with GPS seems to me to make more sense.