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Topic: Codewheels
Replies: 1   Last Post: Jun 24, 2002 8:11 PM

 Messages: [ Previous | Next ]
 Guillermo Phillips Posts: 37 Registered: 12/8/04
Codewheels
Posted: Jun 24, 2002 1:51 PM

Hello, here's a problem I've been working on, but can't see an immediate
easy solution.

I'm designing a codewheel for a piece of apparatus that rotates. A (binary)
code is printed on the rim of a wheel that defines the position of the wheel
and read off with LEDs. A black square indicates a 0 and a white square a
1. Of course I want to use a coding scheme which will be optimal and give
me good resolution. As such I've come up with the following scheme for
detecting eight different positions of the wheel for example.

The following set of squares is printed on the rim of the wheel:

00010111

and read off three at a time by three LEDs. As you can see taking three
'bits' at a time you can define eight positions. Reading from the left we
would get:

000
001
010
101
011
111
110 (code wraps around)
100

The electronics can then convert this into a binary number and use a lookup
table to work out the position of the wheel.

In fact if I wanted 16 possible positions I could use the following sequence
on the rim:

0010100110111100

Which would give 16 unique positional values: 0010 0101 1010 0100 1001 0110
1101 1011 1111 1110 1100 1000 0000.

Since I had to find these sequences by trial and error it would be nice to
have an algorithm which would generate me a sequence for any number of bits
of resolution I wanted. Is there a general method for higher numbers of
bits and if not, why not? Can I also generate other sequences of different
sizes such as 7 positional values or 100 positional values?

Cheers.

Guillermo.

Date Subject Author
6/24/02 Guillermo Phillips
6/24/02 Gerry Myerson