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'driving 1000's of leds'
2000\03\21@132723 by Steven Rightnar

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Hi all:
OK maybe my last post didnt make it or maybe my ?'s were blown off. I
seriously want to build this gaint computer monitor out of three different
colored leds as my pixels. I have seen huge ones biult to cover the streets
in down town Las Vegas of course these are alot bigger than the one I want
to build. So at first sight for 100000 leds I need appprox 10000+ PICs
however since I have not got a clue about how to start this could someone
please direct me... even if it is over a cliff. Thanks (flame me as needed).

Steven

2000\03\21@140851 by Harold M Hallikainen

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On Tue, 21 Mar 2000 10:26:14 -0800 Steven Rightnar
<spam_OUTrightnarTakeThisOuTspamDOMINION.LLUMC.EDU> writes:
> Hi all:
> OK maybe my last post didnt make it or maybe my ?'s were blown off.
> I
> seriously want to build this gaint computer monitor out of three
> different
> colored leds as my pixels. I have seen huge ones biult to cover the
> streets
> in down town Las Vegas of course these are alot bigger than the one
> I want
> to build. So at first sight for 100000 leds I need appprox 10000+
> PICs
> however since I have not got a clue about how to start this could
> someone
> please direct me... even if it is over a cliff. Thanks (flame me as
> needed).
>
> Steven

       Well, a simple way would be to use an Allegro UCN5832 to drive each
group of 32. Then just cascade however many you need. The 5832 is a
serial in parallel out shift register - latch - driver.
       You could try to multiplex the whole thing, reducing the number of
drivers by some factor (maybe 8 to 16).

Harold


FCC Rules Online at http://hallikainen.com/FccRules
Lighting control for theatre and television at http://www.dovesystems.com

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2000\03\21@141058 by douglas.burkett

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Not certain what your intent is, however, before I'd employ thousands of
pics.  I'd look into setting up something like is used with a regular
monitor.  A memory matrix that was 3 bits deep and just scan it out to the
LED's.  Not certain what the X,Y size of your matrix is but at some speed
the persistance of the eye will have an effect, you may even need to
subdivide the matrix into smaller quicker scanned submatrices.  But no way
I'd employ thousands of PIC's to do this.

My 2 cents.
Doug

{Original Message removed}

2000\03\21@150043 by Cor Grooff

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On Tue, 21 Mar 2000 10:26:14 -0800, you wrote:

>Hi all:
>OK maybe my last post didnt make it or maybe my ?'s were blown off. I
>seriously want to build this gaint computer monitor out of three different
>colored leds as my pixels. I have seen huge ones biult to cover the streets
>in down town Las Vegas of course these are alot bigger than the one I want
>to build. So at first sight for 100000 leds I need appprox 10000+ PICs
>however since I have not got a clue about how to start this could someone
>please direct me... even if it is over a cliff. Thanks (flame me as needed).
>
>Steven

Go to:
http://www.sharpmeg.com/products/opto/html/dot_matrix_led_unit.html

At the bottom of the list you will find full-color types, of which the
LT1550W probably is the cheapest.
Expect to shell out big $$$ though.

C

2000\03\21@151504 by Alice Campbell
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What you are describing is creating a color graphics lcd except at
a different scale.  If i were you, i would look at the chips that
control graphics lcds, they are made up of thousands of pixels.  i
suspect that an lcd controller chip and, lets see, about 5000 power
mosfets, and some shift registers, one pic controlling the controller
chip, plus of course a memory chip to hold the
patterns,..hmm.....and do a search on pic projects that include lcd
graphics , i remember a electrocardiogram one on the Scenix site
that describes the basic approach you will need.  Sorry i dont have
URLs, but they wont be too difficult to find.

alice

{Quote hidden}

2000\03\21@151744 by andy howard

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> Hi all:
> OK maybe my last post didnt make it or maybe my ?'s were blown off. I
> seriously want to build this gaint computer monitor out of three
different
> colored leds as my pixels. I have seen huge ones biult to cover the
streets
> in down town Las Vegas of course these are alot bigger than the one I
want
> to build. So at first sight for 100000 leds I need appprox 10000+ PICs
> however since I have not got a clue about how to start this could
someone
> please direct me... even if it is over a cliff. Thanks (flame me as
needed).


I too was intrigued when I saw these displays and gave some thought to
doing this with LEDS -here's a couple of musings for you.

Resolution.

If you want to use it as an RGB computer display at, e.g. 600 x 480
you'll need 864,000 LEDs rather than the 100,000 you mention. Of these
288,000 will be the rather expensive blue ones.
I'm guessing here that your boxful doesn't include blue LEDs.

(As an aside, you can now buy three-colour RGB leds in a single package.
Seimens make them and they're ludicrously expensive.)

Anyway, the power you'll need to drive these is something to consider.
To make the things easy let's assume each type of LED draws 10mA for
maximum brightness. Your total power drain will then be close on 10,000
Amps @ e.g. 5V to light the LEDs for an all-white image. Allowing a bit
for driving circuitry and I2R losses it could even be more.

Say 50,000 kVA anyway. I don't think that's very far off unless I've
dropped a digit or two in the arithmetic.

Of course if you can scan them fast enough you can divide down the power
requirements significantly, just like multiplexing a seven-segment
display, but as always there's tradeoffs in visibility and drive
complexity.

I suspect these displays don't use LEDs as we know them at all, possibly
they use something like TI's steerable reflective discs and coloured
laser sources. 50,000 kVA sounds like a heck of an electricity bill,
even for Vegas.


If anyone has any first hand experience or knowlege of these things I'd
be keen to hear about them...





..

2000\03\21@154058 by Thomas C. Sefranek

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Steven Rightnar wrote:

> Hi all:
> OK maybe my last post didnt make it or maybe my ?'s were blown off. I
> seriously want to build this gaint computer monitor out of three different
> colored leds as my pixels. I have seen huge ones biult to cover the streets
> in down town Las Vegas of course these are alot bigger than the one I want
> to build. So at first sight for 100000 leds I need appprox 10000+ PICs
> however since I have not got a clue about how to start this could someone
> please direct me... even if it is over a cliff. Thanks (flame me as needed).
>
> Steven

I DON'T want to rain on your parade, I will let you know some facts.

Fact 1  A LOW resolution TV screen is about 380 dots per line
and 525 lines per screen (Interlaced).
That requires 199,500 leds for just one color,
3 leds for a color scheme would require 598,500 LEDs.

That s for LOW resolution, now a computer screen is HIGH resolution...

Enough?
--
 *
 |  __O    Thomas C. Sefranek  .....tcsKILLspamspam@spam@cmcorp.com
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2000\03\21@160342 by jamesnewton

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Just incase you haven't caught the theme here, we are most all saying "this
just isn't going to get done by a hobbyist."

Now, I for one would just love to be proven wrong on this point, so I'm
looking forward to your posting a .jpg of the finished project, but.... just
getting data to the drivers (what ever type you manage to afford buying in
that quantity) in real time is going to be pure hell. You might be able to
get a sequence programmed into individual PICs (each driving a few LEDs) via
a daisy chain serial bus of some sort in a few seconds and then play back
the sequence in real time but moving 100000 bits of data in real-time to
something that big is a challenge. Maybe 8 LED's per PIC (no.. too dim..
need driver) or Latch/driver chip and then all the latch inputs connected to
a 8 bit bus, lets see that's... 12500 PICs or Latches so you will need some
sort of driver for the bus that can put out current for 12500 devices to
accurately and quickly read? How about a hierarchy? What is the "fan out"
for components these days? I've stopped looking as I never seem to connect
more that one or two of anything to any one signal.

I was thinking about a electro-mechanical version of this some time ago,
with big Christmas lights and a drum with metal contacts and brushes turned
by a small motor. Slip different insulating cylinders with patterns cut out
to flash the lights with a message. Very low tech and all kinds of RF
interference from the arcing on the brushes, but it would be an inexpensive
fire hazard.... Disclaimer: I am not advising that anyone build such a
monster as it could be hazardous.

---
James Newton jamesnewtonspamKILLspamgeocities.com 1-619-652-0593
http://techref.massmind.org NEW! FINALLY A REAL NAME!
Members can add private/public comments/pages ($0 TANSTAAFL web hosting)


{Original Message removed}

2000\03\21@171738 by Matthew Fries

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> Fact 1  A LOW resolution TV screen is about 380 dots per line
> and 525 lines per screen (Interlaced).
> That requires 199,500 leds for just one color,
> 3 leds for a color scheme would require 598,500 LEDs.
>
> That s for LOW resolution, now a computer screen is HIGH resolution...


Well, how about the worlds largest monochrome gameboy? Anyone know what
the resolution is on one of those?

2000\03\21@172410 by David VanHorn

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At 04:16 PM 3/21/00 -0600, Matthew Fries wrote:
>> Fact 1  A LOW resolution TV screen is about 380 dots per line
>> and 525 lines per screen (Interlaced).
>> That requires 199,500 leds for just one color,
>> 3 leds for a color scheme would require 598,500 LEDs.

When I visited the Futaba VFD factory in Taiwan, I saw some pixels they
were making for an ourdoor TV.
Red, Green, and Blue screens, each about 1 x 1.5 ". Each pixel had three of
these sections, one for each color, with separate filament, grid, and plate
connections.  That's a HUGE project.

Just the filament power is pretty scary.
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2000\03\21@172443 by Severson, Rob

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With 25,600 LEDs you could make a very large Palm device. (160 X 160) I
think you could get away with using a pool que as a stylus.

Couldn't you make an Apple II ? Now THAT would be cool. <smirk>

-Rob
usbsimm.home.att.net


> {Original Message removed}

2000\03\21@185539 by William Chops Westfield

face picon face
[1000's of LEDs.]

OK, I've actually thought about this sort of thing, since I sorta wanted to
do it with xmas lights...

First of all, you need LOTS of LEDs.  A pitiful (by modern standards)
100x100 dot resolution is 10,000 LEDs, and of course it goes up as N^2.
The physical construction is daunting as well, IMHO.  Soldering 20k leads
is not for the faint of heart or people with flux allergies!  Power
consumption is remarkable, as well.  Most large LED arrays (signs) start
with matrix based LED arrays (5x8 or whatever.)  (probably not the very
large, very bright ones you're talking about, though.)

Now, you want to animate this, right?  So your "main" processor needs to
have storage for the equivilent of (minimally?) animated GIF files.  Your
100x100x16frames is a good 20kbytes of storage, so PICs are probably out
for the main processor as well.  (or not, if you hang a big external EPROM
of some kind on the PICs.)

As for electronics, LEDs are easilly drivable in a matrix using row and
column drivers, which probably ARE appropriate for PICs.  Multiplex, but
watch your duty cycle (1 in 100 is probably not enough.)  One possible
"attack" would be to assign a PIC to as many LEDs as it could easilly
drive (25, in a 5x5 array, for a small PIC?  8x8 for a somewhat bigger PIC
is probably about optimal.)  Have larger PICs divide up your pictures into
appropriate sub-pictures and send the appropriate data to each PIC via
some comm link.  This set of PICs (N/256 + N*x) for N LEDs is your
self-refeshing Light controller for a single frame.  A larger systems
(think old, used, PC) feeds the frame controllers pictures in succession
to achieve animation.

So the 100x100 array would require fewer than 500 PICs.  The "low end"
PICs are being used as pretty trivial drivers, and it might be cheaper to
replace them with fixed logic of some kind (especially since that would
get you quickly past the difficulties you'd see past 8x8 arrays per PIC.)
You should probably read a couple of data sheets for the self-driven LED
dot-matrix display chips that are out there (ie those HP 4 character by
5x7 dot array displays.  140 LEDs in a .5 x 1 inch package.)  They ought
to be relatively representative of how the problem is handled in the "real
world."

BillW

2000\03\21@194153 by John Mullan

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Unless a hobbiest has very deep pockets, I wouldn't really see this being
done.  Not at the suggested resolution anyway.

The "Jumbo-Tron" used at Toronto Skydome (I think or is it the one in times
square), is actually done with 5" crt as elements/pixels.  One can just
imagine the power consumption.  So power is not necessarily the limiting
factor.

I tend to agree with the "sub-picture" idea.  Feed your video signal
commonly to all subs and let each sub capture the portion of the signal that
they need.  A little manipulation at each element will produce the desired
results.  There would be no need for a common processor with outrageous
computational and memory requirements.

I realize the goal is to make a fairly high resolution image, but unless you
plan to replace the times square display, you would probably not get the
effect of high resolution at such close range.  If you can afford to put
this thing in such a spot, then the cost of building it won't much matter
either.

Just some of my random thoughts :)

John

2000\03\21@210349 by picxpert

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The Jumbotron is in the Skydome.

-Randy Glenn
.....PICxpertKILLspamspam.....techie.com - http://i.am/PICxpert

Ineptitude is a sure indicator of intellect.

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