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From: Chuck Simmons
Organization: You jest.
X-Mailer: Mozilla 4.61 [en] (X11; U; Linux 2.0.33 i586)
Subject: Re: A simple angular positioning solution?
Date: Tue, 29 Oct 2002 12:44:54 GMT
NNTP-Posting-Date: Tue, 29 Oct 2002 04:44:54 PST
> Hi all,
> I was wondering if anybody out there had come up with a solution to
> problem similar to this or even whether they had ideas on how this
> might be done?
> I am designing something that has a plastic mechanical dial on it,
> which can click into 1 of 4 locations. Each of these locations will
> signify a mode of operation for the device. I must get the processor
> to recognise what position the dial is in, to determine what mode has
> been selected.
> I have experimented with hall effect proximity sensors, and having a
> different 2 bit binary number on each segment of the dial, but both of
> these require having some electronics on the dial which is not the
> ideal situation.
> Another idea I had was to have holes and blanks in each segment
> representing binary 1's and 0's. This would require having some
> optical transmitting and sensing circuitry on either side of the dial
> to determine which position it is in.
> Anyway All ideas would be appreciated.
A friend of mine uses hall switches for determining the angle of a
filter wheel in a 26.5 inch telescope. No electronics is required on the
wheel. The wheel is drilled near the edge for the code for each angle
and tiny "cow" magnets are glued in the holes, The hall switches are
mounted to the frame. Edmund Scientific probably has the tiny "cow"
A word about encoding position in this way. 2 bits for 4 positions
probably won't work. In the system above, there is a sync sensor, 3 data
bits and a parity bit making in all 5 sensors for 3 bits. This is
minimal to eliminate ambiguity. For your 4 position device, 4 sensors
would work with pretty good reliability. The filter wheel was originally
built with microswitches but mechanical wear was a problem. That
application could not use optical sensors but yours could in similar
fashion to the hall switch method. The extra bits to improve reliability
are still needed.
... The times have been,
That, when the brains were out,
the man would die. ... Macbeth
Chuck Simmons firstname.lastname@example.org
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