Re: Apple Graphics Tablet info?

[rrs0059@ibm.net (Frank McKenney)]

Michael,

One of the problems with getting both a Usenet post-back and an e-mail 
reply is that it's not clear how to reply (;-). And, it looks like my 
e-mail reply to you got lost.

Even if you were willing to take the time to reproduce the entire 123-page
manual, I'd need to send you $12 (or more) to just cover your reproduction
costs (;-).

How many pages to the "Theory of operation" and circuit diagram pages?

Whose manual is it? If it has an Apple part number, I can at least try 
sending it to Apple on the off chance one is mouldering away somewhere.

> ...   From the schematic, it appears to be just a current wavefront
>that's sent down the delay lines.  There are separate I/O addresses to
>fire the X- and Y-axis SCR's, which start a nice sharp edge propagating
>down each axis in its turn.  A 12-bit counter is reset at the same time,
>and counts up at a multiple of 7 MHz between 38 MHz and 54 MHz--
>so either 42 MHz or 49 MHz.  When the inductive pen senses the
>current edge, it stops the counter.  The Apple can then read the
>counter value at other I/O addresses.

Okay...  so I need to at least find out the SCR supply voltage and the
signal specs to fire them.  And how to detect the return signal pulse.
Hm...  counter running at 42 MHz is a little trickier... it's be nice if I
could find a CMOS counter... wonder where I put the Newark catalog? (;-) 

Anyway, thank you.  This is exactly the kind of information I was looking
for.


Frank McKenney            / OS/2 Advisor (OS2BBS)
McKenney Associates       / Richmond, Virginia / (804) 320-4887
Internet: rrs0059@ibm.net / TalkLink: WZ01123
==========================================================================
In <19980308072101.CAA14831@ladder02.news.aol.com>, mjmahon@aol.com (MJMahon) writes:
>I just found the manual, so here's a correction to my post (!):
>
>>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!   ;-(
>
>Yes, but...   From the schematic, it appears to be just a current wavefront
>that's sent down the delay lines.  There are separate I/O addresses to
>fire the X- and Y-axis SCR's, which start a nice sharp edge propagating
>down each axis in its turn.  A 12-bit counter is reset at the same time,
>and counts up at a multiple of 7 MHz between 38 MHz and 54 MHz--
>so either 42 MHz or 49 MHz.  When the inductive pen senses the
>current edge, it stops the counter.  The Apple can then read the
>counter value at other I/O addresses.
>
>All in all, probably the fastest circuit ever to go into a //e!
>
>>> 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...
>
>I did, and its 123 pages--a little thicker than I remembered!  ;-)
>
>
>-michael
>
> Email:  mjmahon@aol.com
> Home page:  http://members.aol.com/MJMahon/