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PICList Thread
'Barometric pressure sensing stability'
1999\07\08@043528 by Andy Holdaway

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Piclist Gurus,
I am trying to interface an MPX5100 absolute pressure sensor to a PIC via an
LTC1298 12 bit A/D, where I require an accuracy of +/-2ft between ref.
ground level and 1000 ft..
Using the CCS compiler (can't cope with asm!) and the example prog. and
header written for the LTC1298, I can't get a stable reading off the A/D.
I have seen various examples of this on the 'net, especially 'Barom.c'
(http://www.phanderson.com)which reads pressure and wind speed, but can't get this
to compile.
As an aside, I have tried voltage to frequency conversion, then measure
pulses as well, which also proved to be unstable.
I have no doubt that the problem is my maths/code, and not the hardware, as
a DVM on the measured output on all the schemes I have tried is solid.
Any help/pointers greatly appreciated - I need to sleep!
Andy Holdaway

1999\07\08@123533 by Dan Creagan

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Andy,

Since I'm playing in this area right now, I would be happy to help with the
C code. Please send me (offlist) the exact error message you got with
Barom.c and I will see what I can do.  I will be meeting with Peter next
week at his workshop and if there is a general problem, it would be good to
know for all.

Dan

Simple CCS Code at: http://204.233.101.40/robots/pic1.html

>Piclist Gurus,
>I am trying to interface an MPX5100 absolute pressure sensor to a PIC via
an
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1999\07\08@133650 by Jamil J. Weatherbee

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Do what the DVM does and integrate the signal.
Maybe you need a low-pass filter, check the pressure sensor data sheet and
take a look out the output on a scope.



On Thu, 8 Jul 1999, Andy Holdaway wrote:

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1999\07\10@192517 by Mark Willis

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Definitely low-pass (1/4-second to 1/2-second Tau, RC filter at least)
the signal.  Or active filter it.

There can be a surprisingly large AC component in wind (Some geophysical
researchers are thinking that causes some of the under-snow temperature
rises they're trying to figure out) - I did a sensor package for this
that was actively filtering the output differential put out by an
Atmospheric differential sensor, inputs were atmospheric pressure and
the output of a mechanical low-pass filter (large chamber with tiny
orifice to outside air), to try to FFT the power at various
frequencies.  Some think Avalanches are enhanced by air being pumped in
& out of the pores in snow, causing friction heating.  I know that I
sure saw some interesting temperature changes in buried thermistors when
weather fronts hit in the Arctic, while up there installing that
beast...  Amazed the heck out of me, I'm "somewhat of a believer" due to
the effects I've seen.

 Mark

Jamil J. Weatherbee wrote:
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