Summagraphics tablet?

From: der Mouse <mouse_at_Rodents.Montreal.QC.CA>
Date: Sat May 8 01:49:29 2004

> 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. :-)

Actually, it's not accurate to ?1 count even at the documented
settings. I find that when I turn on stream mode and don't move the
puck, I get a stream of identical samples. If I turn on request mode
and request reports (at human typing speeds), I get identical reports -
but they are a few counts different from the reports I get in stream
mode. I conjecture that there is some kind of residual carryover when
doing two readings in quick succession, as stream mode does....

> One day I'll disassemble the microcontroller ROM and make sense of it
> all...

Mine has a 27xxx-series UVEPROM (2732, I think it was), and it's
socketed. I'm very tempted to pull it and dump it, and see how much of
a schematic I can extract from the pcb (the only real problem is
component-side etch runs that run under components).

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Received on Sat May 08 2004 - 01:49:29 BST