Summasketch graphics tablet

From: Max Eskin <>
Date: Mon Apr 6 19:11:09 1998

>> > Can I make one,
>> > get one REALLY cheap, or operate the thing without one? Also, it
>> Don't know. I bet it emits RF, and the tablet probably has a circuit
board with
>> traces running horizontally on one side an vertically on the other.
My Dauphin
>> detects the pen in this manner.
>The older sumagraphics tables like the Bit Pad 1, the ID series and the
>Apple graphics tablet worked by sending a magnetic pulse along some
>made of special alloy. I believe this pulse travelled at approximately
>the speed of sound in the wires - there was a shock wave that travelled
>along them caused by magnetostriction.
>The puck was a simple sense coil. I had to rewind one of mine once, and
>seem to remember it was something like 11 turns of 30swg wire. That
>be a start anyway.
>Also I seem to remember that the buttons on the puck had 100k resistors
>in series with them. The other side of the button was grounded. This is
>also critical - otherwise noise breaks through into the sense coil
> / 100k
>Gnd----/ o---\/\/\---- Button input
Do you know the pinout for the plug?

>Certainly the Bit Pad 1 came in a serial version (and also a GPIB
>version and a parallel version).
>There's another type of tablet that consists of an XY matrix of PCB
>tracks - plain copper PCB tracks. They are individually driven by a set
>of decoder/driver chips which are driven by a simple microcontroller.
>Again the puck is a simple sense coil.
>Thing is, it has a much better resolution than the spacing between the
>tracks. And there's no extra hardware, like high-speed-ish counters.
>never figured out how that one works - any clues?
Well, I have this second one. My guess is that it uses capacitance,
like touch-to-turn on lamps.

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Received on Mon Apr 06 1998 - 19:11:09 BST

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