> > Imagine one made from audio tape -- it's pretty narrow, so the
> >
> > Of course a microcassette tape is probably orders of magnitude too
>
> As far as I got it, wouldn't be some kind of a film tape better?
Film would work -- same concept. Rapidly moving plastic passing
by a "viewing window."
Imagine it this way. Place a light at the center of a microcassette case
and have the tape speed past where the read head would be in a tape
player. If holes were made in the tape (film, cloth, whatever) then
these
holes would scribe a line across your field of view. Modulate the light
source, ala Nipkow/Baird disk television, and the effect would be similar
to the electron beam scanning across a CRT -- effectively a television in
a small rectangular form, without the "pie slice" distortion of the disk
or
the cylindrical distortion of the next best option.
Should be able to make a simple 1/4 or 3/8" diagonal display this way,
and with cheap off the shelf parts.
> But looks like I got something wrong. You are talking about a normal
> audio
> cassette? How should that work to produce an almost-square picture?
Yep...an endless loop cassette (like for answering machines) has a
continual loop of tape within the casing, and is designed specifically to
track well. Replace the audio tape with something more opaque (if
necessary) and feed *it* through an off the shelf cassette.
The *tape* is essentialy a very long, very narrow rectangle. The
cassette
is only a means by which it could be utilized effectively.
I like not having to reinvent the wheel, when possible. The
microcassette
case is a good, proven design that works well, and is already mass
produced by the millions.
-- Chuck Knight
Just for fun, let's see how much tape would be needed. Since I don't
have
a microcassette handy, I'll make a few assumptions. The results should
be scalable.
30 line display
3x4 aspect ratio
1/4" tape
Horizontal scanning:
3x4 aspect ratio produces an image 1/4" high by 1/3" long. 30 lines
would
require 30x1/3" = 10" of tape. 30 frames per second requires this to be
looped 30 times each second -- 10"x30 = 300" per second = 25 feet per
second.
Vertical scanning:
Now...let's do it the other direction. 3x4 aspect ratio produces an
image
3/16" high by 1/4" wide. 30 columns requires 30x3/16" = 5 5/8". 30 fps
requires 30x5 5/8" = 168 3/4" per second = 14' 3/4" per second.
How fast do audio tapes move, in normal use? I know video tapes move
pretty fast. I don't think audio tapes do. Movie film must move pretty
fast
too -- their frames are bigger, but move at a similar rate.
-- Chuck Knight
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