1970's digitizer tablets

From: John Allain <allain_at_panix.com>
Date: Tue Jul 15 08:52:00 2003

> Anybody else try depositing carbon ( either pencil
> lead or other substances )
> on a flat surface and work out the math to get X-Y?

More like everybody.
The math is not hard at all. With two sample points, you read
two voltages, from that mathematically get two circle radii, intersect
them and get at most two points. Sample three points and get just
the one point with a degree of redundancy to it. I would take the samples
by chopping back and forth from the different sampling points.
Others may have other methods, I don't claim to know them all.

Try finding a premanufactured carbon surface, or antistatic plastic
that is partially conductive. Trouble with carbon contact is that once
you put paper on top of it you've insulated it, so it is to be used as
mouse substitute only. An electromagmetic digitizer can take a
paper above it just fine.

John A.
Received on Tue Jul 15 2003 - 08:52:00 BST