6 May
2004
6 May
'04
5:57 p.m.
Basically, the microcontroller triggers a
thyristor (SCR) on the
tablet driver PCB (actually iside the tablet, at one corner) which
discharges a capacitor through a 1-turn coil around one side of the
tablet. This causes a magnetic pulse to propagage down metal wires
across the tablet. IIRC, it sets up magnetostrictive strains in the
wires, and thus propagates essentially at the speed of sound.
I'm not sure how accurate this is for the pad I have.
The pad is a two-layer PCB, with the working area covered by a grid of
printed-circuit "wires", in one direction on one side of the PCB and
the other direction on the other side. They are surprisingly far apart, on the order of =BE". I haven't
traced the circuitry enough to
know how accurate your description is, though I didn't see anything
like the one-turn coil you describe - everything electrical, besides
the serial connector, power, and the puck, is on the PCB. Two parallel
etch runs could form a one-turn coil; I don't recall seeing them, but I
I was assuming this was a magnetostrictive tablet, like the older
Summagraphics ones. Obviously not.
-tony