Summagraphics tablet?

From: Peter C. Wallace <pcw_at_mesanet.com>
Date: Sat May 8 09:06:51 2004

On Sat, 8 May 2004, der Mouse wrote:

> > Oh, it's a Kriz tablet (after Stan Kriz at 3 rivers).
>
> > I have never fully understood how they work either. The 'wires' in
> > the PCB carry electrical currents, and are sequenced in some way by
> > the microcontroller. The puck/pen contains a pickup coil, the output
> > of which is amplified and fed back to the microcontroller.
> [...]
> > And the resolution is _much_ higher than the spacing between the
> > 'wires'.
>
> Much. The manual documents resolution settings as high as 20 counts
> per mm; experimenting with it, I find it actually includes settings
> that appear to attempt 1000 lines/inch and 1000 lines/mm, based on
> dividing full-scale counts by pad size (in-my-head estimates; I could
> be out by a factor of two or so). Of course, I doubt it's accurate to
> anything like ±1 count at those settings. :-)

Most likely the relative signal levels of the 2 closest wires to the puck are
measured and the position is then interpolated...

Peter Wallace
Received on Sat May 08 2004 - 09:06:51 BST