Re: Apple Graphics Tablet info?

[Michael Mahon <mahon@cup.hp.com>]

Frank McKenney wrote:

> I don't really need the adapter...  just the pinouts and what they
> represent.

I don't think that will help as much as you think (see below).

> I'm hoping to connect this tablet to either a Macintosh or an Intel PC by
> building an interface using a PIC microprocessor ("Hi!  You thing I'm a
> mouse...  but I'm really not!").  Trouble is, I have no idea what the
> lines from the board - and the stylus - represent.  Makes converting it a
> bit tricky (;-).
> 
> I'm guessing that the tablet senses position via resistance, and, since
> there's no power connections or batter holder, that I need to supply the
> power myself.  But...  what voltage, and what resistance values represent
> what position?

Ah, but it doesn't use resistance.  It is an RF device which operates
at about 20 MHz if I remember correctly.  The pen is an inductive pickup
which detects the RF pulse as it propagates through a tapped delay line
for each axis.  The board contains the pulsed exciter for the delay
lines
and the RF "sense amplifier" for the pen, plus a high frequency counter
to capture the time delay, and thus the position, of the pen.

Driving this tablet without the original board is not for the faint
of heart!   ;-(

> Anyone have any ideas who might still have documentation on this device?
> I checked Apple's 'web site, but no luck.

There was a little (~25 page) manual for the tablet which was widely
available as a separate manual up to about 1986 or so.  I have one,
and it contains the schematic for the adapter.  Unfortunately, I haven't
seen mine since 1990 and I haven't seen them for sale for even longer.

If you're still in the mood, I can try to find my copy...

-michael

===============================================================
This is my personal opinion, and does not in any way represent
the position of my employer, etc...