Path: utzoo!utgpu!news-server.csri.toronto.edu!rutgers!ucsd!swrinde!cs.utexas.edu!uunet!kitty!larry
From: larry@kitty.UUCP (Larry Lippman)
Newsgroups: sci.electronics
Subject: Re: position sensor
Summary: Shaft encoders
Keywords: rotary position, shaft encoders
Message-ID: <4699@kitty.UUCP>
Date: 16 Feb 91 05:28:04 GMT
References: <14570@mcdphx.phx.mcd.mot.com>
Followup-To: sci.electronics
Distribution: usa
Organization: Recognition Research Corp., Clarence, NY
Lines: 33

In article <14570@mcdphx.phx.mcd.mot.com> hbg6@citek.mcdphx.mot.com writes:
>Does anyone out there know of an INEXPENSIVE sensor for determining
>the position of a shaft?
>A standard shaft encoder would be nice but they run about $85 which is a
>bit steep for this home project.

	If you have a microprocessor-based system which can count pulses,
then an optical incremental encoder is pretty inexpensive.  If you need
absolute angular position with binary or BCD output, then an $ 85.00
encoder sounds like a pretty good deal to me!

	An incremental encoder can be made with a toothed wheel that
interrupts an LED/phototransistor pair.  For finer resolution, you will
need an optical disk with ruled lines.  Such a disk can be made by
plotting the radial ruling lines, making a transparency thereof, and
carefully gluing the transparency to a clear plastic disk which fits
over the shaft.

	Using two LED/phototransistor pairs positioned over inner and
outer rulings with the same number lines, but which have a suitable
angular offset will give you a quadrature output that can be used to
sense direction (i.e., cw or ccw).

>I'd also like to avoid potentiometer / AtoD systems because there such
>a pain to build.

	A resolver with a packaged resolver->digital converter is a better
method for an analog approach.  You may be able to find something in a
surplus store.

Larry Lippman @ Recognition Research Corp.  "Have you hugged your cat today?"
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