Newsgroups: comp.robotics
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From: exujet@exu.ericsson.se (Jerry Ethridge)
Subject: Re: Altitude sensors
Message-ID: <1994Jan18.184525.24685@exu.ericsson.se>
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Organization: Ericsson Network Systems, Inc.
References: <2hh6g5INNpec@matt.ksu.ksu.edu>
Date: Tue, 18 Jan 1994 18:45:25 GMT
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In article 2hh6g5INNpec@matt.ksu.ksu.edu, nhowland@matt.ksu.ksu.edu (Neal Patrick Howland) writes:
>I would like to know if anyone has ever tried to do any kind of altitude
>sensing.  Is there a pressure sensor sensitive enough to detect a change
>in altitude of a foot or less?  The best method I could think of was to
>mount an ultrsonic sensor pointing downward and take a reading to determine
>the distance.  What is the best way to do implement this sonar array?  Is
>there any device out there that controls this easily?
>Any info would be greatly appreciated.
>
>Neal Howland
>nhowland@matt.ksu.ksu.edu
>


Since I build electronic packages to send up in model rockets, I have looked
into pressure sensors extensively. There are several manufactueres that make
pressure sensors sensitive to do this. In addition, there have been several 
articles over the years in Radio Electrinic, Popular Electronics, Modern
Electronics, and others on how to build digital altimiters with a 1 foot 
resolution. I have used sensors made by SenSym, and Motorolla makes many
pressure sensors. Call both of these and they will send you free literature
on there pressure sensors.

Ultrasonic sensor is ok if you take into consideration the doppler shift
while you are moving. Might need a PLL to lock into the return signal, or
use a continuous signal that is modulated with a bit stream, and do a correlation
on the return signal.

If your purpose is for indoors, you have to really worry about multipath 
distortion. If your altimiter is for a mobile flying robot outdoors, then the 
pressure sensors should be ok.

Hope that helps,
Jerry
