Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!wuarchive!psuvax1!psuvm!psuecl!peg
From: peg@psuecl.bitnet (PAUL E. GANTER)
Newsgroups: sci.electronics
Subject: Re: Can anyone recommend a sensor?
Message-ID: <69060@psuecl.bitnet>
Date: 30 Nov 89 13:17:14 GMT
References: <472202ca.20b6d@apollo.HP.COM>
Distribution: na
Organization: Engineering Computer Lab, Pennsylvania State University
Lines: 22

> I guess Polaroid sells a "hacker's kit" with the sonar gizmo they use
> on their autofocus cameras, and I think for under $200.  But I seem to
> recall reading that the range was more like 12" - dozens of feet, with
> an accuracy of 1" or worse.  Does anyone know if that's a fundamental
> limit on the sensor itself, or only the way the electronics were
> designed in the kit?  (Be gentle; I'm mostly a software person.  I

Recently my robotics class was discussing distance sensing, and one
of the methods we covered was acoustics  (my prof is doing research
on them).  One large problem with acoustic transceivers involves the
air they travel through:  the speed of sound in air varies quite a bit
with temperature, humidity, barometric pressure, etc.  I don't have
quantitative figures on the variation; I will ask my prof.  Try playing
with the formula for speed of sound in most physics texts.  I see that
speed of sound varies about 10% from 0C to 100C.  Add the effects of
humidity and pressure and you are probably much higher.

Maybe you could build timing circuits to measure transit time of
light (if you do, I'll buy them for $1000 cash !! :)

Good luck!

Paul


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