(I mumble about clocks as that's MY use for this, it's the idea that
counts <G>)

  One option:  Laser scanner projects the digits onto a flat surface, "a
la" those cheap surplus red laser scanner mechanisms, this might be much
cheaper than all those LEDs (for hardware costs anyways!) & would be
really visible indoors (if no human's in the beam path!)  Or fairly
visible outdoors in shadow.  I've been mumbling about building this for
large-digit house clocks since my favorite clocks were discontinued
(drat!)  If you have a continuous-on laser, use a mask to block the
light beam when no output desired.  (i.e. 2 voicecoils, one for H
aiming, one for V aiming, when you don't want light output aim the laser
down out of the open hole in the mask.)

  That might be far cheaper, & take less power, than a bunch of LEDs.
And you could also spread out the scans into multiple parallel scans if
needed, for more visibility?  Or use one laser per digit (for a 5 digit
display, 5x the light available to dump onto the surface) for a brighter
clock.  Would take more development time, potentially.

  As laser beams are quite visible, at quite a distance, I'm also
wondering: do you NEED 2" wide groups of LEDs, or just a single row?
(Anyone done this?  I've been thinking of playing with it, my
girlfriend's physically disabled & partially visually disabled, and I'm
a little nearsighted, so for convenience for us both it'd be neat to
have a large digit clock in each room, networked to the master clock,
always easily visible & on time!  I could go 12" clocks from one laser,
indoors...)

  Mark Willis, mwillis@nwlink.com

Troy P. wrote:
>
> Hi all,
> I have an opportunity make a little money if I can design a display that
> has 5 - 36" tall digits on it. I have always wanted to make one of these
> anyway but I wanted to do it with LEDs. Does anyone have any experience
> with this type of design. Questions that came to my mind were:
> 1. What should the width of each segment be? The height will be 18".
>
> 2. What should the spacing on the LEDs be? I was thinking about
> stagering them for more coverage.
>
> 3. How should the current and voltage be made? First calculations show
> about 30amps at around 5v per digit. This didn't sound right to me. This
> was based on 8LEDs/square inch and each segment being 18" x 2" and this
> seems too skinny.
>
> Any thoughts will help before I start spending money on development.
>
> Thanks in advance.
> Troy Powledge
> TCo. Systems
> tpow@eramp.net