Re: Garmin altitude problems

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.


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Jeff Liebermann                 jeffl@cruzio.com
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