Re: Beagle Bros and Wonderful disk drive noises

[ard12@eng.cam.ac.uk (A.R. Duell)]

dbryant@netcom.com (David K. Bryant) writes:

>ard12@eng.cam.ac.uk (A.R. Duell) writes:

>>I can _trivially_ prove that an unmodifed Apple CRT monitor cannot read 
>>any information off a card held against it. 

>I wouldn't bet any meals with an American ex-patriot on that one.

Actually, I would. Wozniak was not a god, he was not even a particularly good
designer IMHO (his circuits went for minimum component count, even if the
result was a kludge). And there is no way that a CRT is sensitive to 
something held on the screen (and I speak as someone who has _designed_ 
monitors)


>Rumor has it that Wozniak had managed to get an Apple ][ to send
>rudimentary fax documents.  You would hold the original up against
>the screen and the scanning program would move the block cursor
>across the page.  The downfall was that the resolution wasn't
>very good and it took a long time to complete.

Seriously, there was a thing called a 'flying spot scanner' used to
transfer frames of cine (movie) film to television. It used a CRT with the
light from the screen being optically focused onto the the frame of the
film. A single photodector (originaly a vacuum photocell or
photomultiplier) recorded the ammount of light that passed through the
frame. The electron beam was scanned over the CRT screen as normal (at a
constant intensity), and the output of the photocell was an electronic
representation of the image on the film. 

Now, that would be possible (just) on an Apple ][. You could move a white 
object (either the cursor, or a low-res graphics block) over the screen, 
focus the screen onto the object you wanted to digitise and detect the 
amount of transmitted or reflected light using a photomultiplier. The 
output of that, after some analogue processing, could be fed into an A-D 
on Apple (or even into one of those kludged paddle inputs). You'd have to 
run it in a darkened room, though.

If the above posting is not a troll, then I think that's what you are 
refering to. It's a lot more hardware than just a monitor and Apple ][ 
though.


--
-tony
ard12@eng.cam.ac.uk
The gates in my computer are AND,OR and NOT, not Bill