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From: mahaun@sactoh0.sac.ca.us (Mark A. Haun)
Newsgroups: sci.electronics
Subject: Re: Hall Effect Sensor
Summary: fluxgate compass radio shack
Message-ID: <1991Jun26.020259.279@sactoh0.sac.ca.us>
Date: 26 Jun 91 02:02:59 GMT
References: <1991Jun24.232559.3004@helios.physics.utoronto.ca> <1991Jun25.161850.11815@helios.physics.utoronto.ca>
Organization: Sacramento Public Access Unix
Lines: 40

In article <1991Jun25.161850.11815@helios.physics.utoronto.ca>, neufeld@aurora.physics.utoronto.ca (Christopher Neufeld) writes:
> In article <16869@ganymede.inmos.co.uk> kevin@cheetah.inmos.co.uk (Kevin Cameron) writes:
> >
> >I'm sure you're right about it working, but $3000 seems a bit expensive
> >compared to an ordinary magnetic compass. You could probably buy a global
> >positioning system for that price (Inmos have developed a pocket one based
> >on transputers).
> >
>    Well, that one is more sophisticated than it has to be for your
> purposes. Potted in epoxy, intensities measured to high precision, you
> could probably use it to detect submarines. A cobbled-together fluxgate
> magnetometer shouldn't run $3000. I just gave that as an example. A
> similar Hall effect sensor would contain a variable current power
> supply, a precision variable voltage source and meter, and some logic to
> calculate the field given current and voltage values. That stuff isn't
> cheap if bought as commercial products.
> 
> >It only needs to be accurate to ~1 degree to be competitive with a
> >magnetic compass on performance, but it would need to cost nearer $100
> >in total to be worth buying instead.

For anyone not aware, Radio Shack sells a fluxgate compass for
$54.95 (Cat. # 63-641, page 50 in '91 catalog).  I don't know its
accuracy.

Keep in mind that designing a working electronic compass is a lot
easier than actually measuring changes in the Earth's field.  For a
compass, all you need to sense are the relative strengths of the
field in two directions.  I would not be suprised if Hall devices
*can* be used in a crude electronic compass.  Of course, if you
want to actually watch the field and see changes in it, you need to
attain a resolution down to at least 100 nT or so (10 nT would be
more realistic).  That is a tricky thing to do, even with
fluxgates.

-- 
Mark A. Haun / 3445 Del Mesa Ct. / Sacramento, CA 95821 / Phone: (916) 488-2965
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