[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: Anybody with an oscilloscope as an Apple II display?

Charlie Springer wrote:

On Wed, 2 Apr 2008 14:32:07 -0700, Michael J. Mahon wrote
(in article <ba-dnWXeJ-XFZm7anZ2dnUVZ_hGdnZ2d@comcast.com>):



Charlie Springer wrote:


On Tue, 1 Apr 2008 12:52:56 -0700, Michael J. Mahon wrote
(in article <07CdnQbALc4HD2_anZ2dnUVZ_oOnnZ2d@comcast.com>):




Fun with scopes is probably what led me to interactive graphics
as my first excursion into interactive computer programs (around
1964).  The graphical capabilities of the Apple II were one of
its strongest attractions to me in 1980.
Micheal, you may not be aware, but Jef Raskin's thesis from 1967 is entitles "QuickDraw, A graphical computer interface". I think I have it right. 

I've been curious about his thesis, but haven't yet found it.
I don't have a copy. There may be one in his papers in the Stanford archives or at, hmmm. UCSD? 



When the photomultiplier was pointed toward an operating TV, the
video waveform was visible on the scope, and could be displayed
(with some smearing) on another monitor.  This same approach, when
used with a telescope, can be used to see what TV shows are on in
nearby houses, even if the light from the screen is only indirect!
Cool. The smearing must have been from the decay of the phosphors. I think there is a typical half life of less than 1/60 second for TV. I analysed a bazillion tubes and phosphors for the Swyft project but can't remember the details. We didn't need them that fast and were after a paper white with no green ghosting when scrolling and such -- Swyft and Cat had black type on white background for WYSIWYG. 

The TV I was using in the 1950's was a B&W model--in fact, an
RCA 630TS--the 30-tube grandaddy of all TVs!

The P4 phosphor then used had a blue fast-decay component and a
slower yellow component.  If you shifted your eyes, you could
sometimes notice the color shift, but if you looked steadily at
it (pretty common behavior sitting across the room from a 10"
CRT ;-), it looked fine.

The 931A was more sensitive to the blue component, but it also
responded to the yellow, so there was a slightly blurred picture
(from the blue) convolved with a lighter smeared picture (from
the yellow).  I cleaned it up a great deal by putting a blue
filter over the 931A.

I don't know what the composition of P4 phosphors are these days...

BTW, the P7 phosphor was a *very* exaggerated version of the P4,
with a *very* fast, intense blue component, and a *very* slow
(several seconds) greenish-yellow component.  You've probably
seen P7 displays on RADARs, often with a yellow filter so the
bright blue doesn't wash out the long tail of the yellow.

I used P7 CRTs with blue filters for my flying spot scanners,
since I couldn't find surplus P15's.  The only downside is the
"texture" produced by the translucency of the front yellow
phosphor layer.


BTW, you may have been a little late for the light pen, since the
first use of a light-sensitive device (a light "gun") that I know
of was developed in the 1950s (using a photomultiplier) to designate
targets on a computer-driven radar scope.  It was the SAGE system,
running on IBM's AN/FSQ-7, IIRC.
Well, to be fair, the pen in that case would be a bit bulky without an optical fiber and have 600 to 1,200 volt supply. But I do remember some really neat half inch PMTs (Hamamatsu?). I suppose a plain old phototube would have worked fine as a light pen with a piece of lucite light guide or some such. 

That's probably why the first such devices were light "guns"--looking
a bit like a hair dryer.  ;-)  They were pretty heavy to hold onto, so
there was a "holster" for them at the side of the display.
This is getting very retro. I want to find a nice inexpensive 7 to 12 inch LCD to use with my //e and //GS stuff. With a CFFA card inside and a nice tilt-up LCD it could be very convenient. 

It sure would be.

-michael

NadaPong: Network game demo for Apple II computers!
Home page:  http://members.aol.com/MJMahon/

"The wastebasket is our most important design
tool--and it's seriously underused."