Stef Mientki wrote:
> Maybe I wasn't clear enough, we are going to look outside onto the
> half sphere,
> just like in the EyeBall. So projection is maybe the wrong word ???
> But I think projecting gives a much better image, because of the
> radiation pattern of the LEDs.
> If you look at a narrow beamed LED, you'll see a second radiation
> pattern, which is very widespread.
> So the idea is to project the LEDs on the innerside of a
> semi-transparant sphere and have a better picture.
> I just tested it with some semi-transparent white plexiglass
> (Litterary translated from Dutch we call this color "milkglass") and
> the effect is disappointing.
> But if you just shine the LED through a piece of (white) paper, you
> get the widespread beam completely vanished, so that's what we really
> want. But how do we make a (strong enough) paper sphere, or is there
> some
> other coating which has the same effect  ??

The EyeBall works on direct viewing of the LEDs, and I think this method
makes sense.  I don't see what you gain with a diffuser.  It would fuzz the
pixels and decrease brightness.  Also the cool thing people seem to like
about the EyeBall is that the image appears to hang in space.  You don't see
the rotating arm, just the pixels.

> BTW, how many LEDs did you have to control in the EyeBall ?

The first EyeBall had 16 LEDs taking up about 3 1/2 inches on a 12 inch
diameter sphere.  It was designed to display text with a single built in
font.  The second EyeBall is 18 inches in diameter and has 96 RGB LEDs
creating a vertical display height of about a foot.  That's 188 total LEDs
that can each be modulated to 2 bits of intensity per pixel.  That is
sufficient to display recognizable individual faces, although that's mostly
a bonus.  They originally cared most about arbitrary downloadable fonts and
simple low-color logos.  They didn't complain though when we added an extra
bit per color per pixel.

The total display is 512 x 96 pixels.  There is a dsPIC handling the data
from the rendering processor (which is another dsPIC) and managing a CPLD
that clocks the data to the LEDs.  If you work it out, 512 x 96 pixels x
30Hz x 8 bits/pixel comes out to a significant data rate.


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