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'[EE]: big led display (kind of)'
2001\12\27@172135 by Dave King

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This isn't quite the same problem but the title still fits. I'm working on
a real big LED
display that's on the order of 2 miles long. Think of it as the worlds
longest Christmas
tree light string. When my mouth opened it yap and said "oh yah I can do
that" my
brain wasn't paying too much attention. Now I need to find a way to power
this "thing"
so it works without making the smoke come out of something. Right now I'm
thinking
along the lines of using a Pic controlled switching power supply to
generate pwm and
slowly ramping things up. I'm sure I need to have several feed points but
I'd like to be
sure.

Anyway I was wondering if anyone has run across any good information on
working with
something this sized. I've got a few ideas on it but I'd like to be a bit
more sure before I
start.

Cheers

Dave


The only thing that helps me maintain my slender grip on reality is the
friendship I share
with my collection of singing potatoes

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2001\12\27@173814 by Michael Coop

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My first questions are -
       How many segments (shape?)
       Size of each segment length x width

You may do better with lasers scanning prismatic targets to scatter the
light

Thinking...
MC

{Original Message removed}

2001\12\27@181102 by Jinx

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> This isn't quite the same problem but the title still fits. I'm
> working on a real big LED display that's on the order of 2
> miles long. Think of it as the worlds longest Christmas tree
> light string

Sounds like the sort of thing that nutcase Christo would get
up to ;-)

A redwood in your living room he he, you'd be sweeping up
needles and shooing squirrels for months

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2001\12\27@210348 by Dave King

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At 09:35 AM 12/28/01 +1100, you wrote:
>My first questions are -
>         How many segments (shape?)
>         Size of each segment length x width
>
>You may do better with lasers scanning prismatic targets to scatter the
>light
>
>Thinking...
>MC

The problem with the laser is the layout (looked at that one already ;-]).
it doesn't easily support line of sight. I would have some concerns about
eye damage or exposure to that.

The strings are up to 10,000 feet long with a light every 25-30 meters (100ft).
It's one light wide and 100 plus long. The layout is linear more or less over
broken ground. As long as I can control them so they appear as one string
I can break them down into smaller segemnts.

Dave

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2001\12\27@210421 by Dave King
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>A redwood in your living room he he, you'd be sweeping up
>needles and shooing squirrels for months
Its not the squirrels, (lots of em running around here anyway) its
the barr's dat eb the problem ;-]

Dave
(head nut picker)

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2001\12\27@213358 by Bob Barr

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On Thu, 27 Dec 2001 18:00:32 -0800, Dave King wrote:

>>A redwood in your living room he he, you'd be sweeping up
>>needles and shooing squirrels for months
>Its not the squirrels, (lots of em running around here anyway) its
>the barr's dat eb the problem ;-]

What'd I do this time? :=)

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2001\12\27@220344 by Jinx

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>Its not the squirrels, (lots of em running around here anyway)
> its the barr's dat eb the problem ;-]

What'd I do this time? :=)

Dunno. Have you s*** in the woods lately ?

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2001\12\28@025706 by Peter L. Peres

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> 2 mile long christmas lights

The closest I have comes was custom stage lighting where 2 miles of cable
looks small. But none of it was low voltage ...

I'd go with a normal voltage supply (ac 220V or whatever you have), with
PSUs spread along the way to feed a segment each, of, as big as you dare
(but less than 100 feet each probably). You may have to use several feed
points for mains (how much power do you plan to put into it ?! - more than
about 5kW mandates several feedpoints).

Signalling would be Manchester or carrier current WITH TRANSFORMER
INSULATION at each station. The ground loops formed over such a distance
are truly amazing even if nothing goes wrong.

hope this helps,

Peter

PS: I do not normally shout, but take the transformer insulated signalling
very seriously. All the shortcuts tried to remove that resulted in
spectacular failures in my experience.

PS2: I do not know what the longest X-mas light is but I suspect that it
may be longer than 2 miles.

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2001\12\28@051550 by Roman Black

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Dave King wrote:
>
> This isn't quite the same problem but the title still fits. I'm working on
> a real big LED
> display that's on the order of 2 miles long. Think of it as the worlds
> longest Christmas
> tree light string. When my mouth opened it yap and said "oh yah I can do
> that" my
> brain wasn't paying too much attention. Now I need to find a way to power
> this "thing"
> so it works without making the smoke come out of something.


You need a HV distribution system, because of
the length. 240vac mains would do it depending on
your exact needs.

Then divide the whole display into shorter chunks.
For each chunk;
* use a Xc supply from 240vac to run a string
of leds
* it's own fuse

This will be cool and transofrmerless. There is a
sample of a Xc circuit to drive a heap of leds
from 120vac at the bottom of this web page:
http://centauri.ezy.net.au/~fastvid/tube4w.htm
-Roman

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2001\12\28@095927 by Lawrence Lile

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2 MILES???  as in 5280 feet MILES???  What are they going to do with it -
signal aliens on Arcturus?
{Original Message removed}

2001\12\28@103102 by David VanHorn

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At 08:57 AM 12/28/01 -0600, Lawrence Lile wrote:
>2 MILES???  as in 5280 feet MILES???  What are they going to do with it -
>signal aliens on Arcturus?


Scrolling display  "IF YOU CAN READ THIS,  YOU'RE TOO CLOSE".

:)

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2001\12\28@120606 by Michael Coop

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VERY cute !


At 08:57 AM 12/28/01 -0600, Lawrence Lile wrote:
>2 MILES???  as in 5280 feet MILES???  What are they going to do with it -
>signal aliens on Arcturus?


Scrolling display  "IF YOU CAN READ THIS,  YOU'RE TOO CLOSE".

:)

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2001\12\28@142932 by Dave King

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At 04:02 AM 12/29/01 +1100, you wrote:
>VERY cute !
>
>
>At 08:57 AM 12/28/01 -0600, Lawrence Lile wrote:
> >2 MILES???  as in 5280 feet MILES???  What are they going to do with it -
> >signal aliens on Arcturus?
>
>
>Scrolling display  "IF YOU CAN READ THIS,  YOU'RE TOO CLOSE".
>
>:)

Actually it's going to read:

"I hope there is intelligent life in space as there is bugger all down here
on Earth"


It's also 3x 2 miles strings with about 6 shorter ones thrown in to make
life interesting.


Dave

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2001\12\28@164806 by Michael Coop

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It's also 3x 2 miles strings with about 6 shorter ones thrown in to make
life interesting.

How can making something shorter make life more interesting,...
Everything I've ever read says 'SIZE DOES MATTER'

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2001\12\28@191909 by David VanHorn

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My orange leds just arrived.  600+ 10000 mcd LEDS.  :)

Driving the whole mess would only be about 60W. <veg>




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2001\12\28@202155 by Jinx

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> My orange leds just arrived.  600+ 10000 mcd LEDS.  :)
>
> Driving the whole mess would only be about 60W. <veg>

Here's a surprise (pleasantly surprised me anyway) -

This message board I've designed

http://home.clear.net.nz/pages/joecolquitt/message.html

uses just 40mA at 5V and is quiet viewable under indoor
lighting, even with 270 ohm resistors. Battery back-up is a
distinct possibility for one application. The LEDs are bog-
standard 3mm 5mA 5mCd

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2001\12\29@031658 by Peter L. Peres

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> Arcturus

Most likely roadside decoration.

Peter

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2001\12\29@152529 by Bob

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I've never worked on anything like this, but here are a few thoughts off the top
of my head.

Do the LED's have to blink in unison, turn on in sequence, or anything fancy
like that?  I.e., what are the exact specs.?

If not, you could just plug in a two watt series resistor and diode into each
one every so far apart, in parallel (very small circuit board encapsulated in
epoxy comes to mind), and run it off of either 120 or 240 VAC.  If you used
LED's with the resistor and diode built in (I think someone makes that, but a
bit more spendy), all you'd need is some sort of plastic LED connector you can
crimp onto the cord that the LED's neatly fit into (not unlike christmas tree
lights), and that works reliably (I'd hate to have to climb that tree to fix a
bulb).  Obviously, you'd want some sort of fuse and/or power crowbar setup where
it plugged in at for safety.

To light up sections of LED's, like one section of a 7 segment LED display, you
could have a PIC at each segment, that turned on the HV power to that segment
via a zero crossing triac (or pre-rectify, and use a HV Mosfet), and have an
X-cap or VB409 there to power the PIC.  You'd need something like an X-10 setup
or RF reciever on each segment to communicate with each PIC.  Obviously you'd
need a "master" PIC to control the others, via X-10 or RF transmitter, that
would also communicate with a PC or something.

I know, running high voltage to each led is a bit more "dangerous", but low
voltage ain't gonna go far unless your using really big wires between each LED
(more cost).  Even high voltages drop a bit at those distances.  I make a power
supply that sends out 1.5~1.7vac down a four foot 16 gauge cord to a resistive
load (at upwards of 16 amps), and the voltage drops to less than half near the
load.  Obviously an LED won't drop the voltage that much, but by the time it
gets to the last one (I'm assuming several in parallel), it may not be very
bright.  At 100 LED's per 10,000 feet (1 LED per 100ft/25~30m), you'd need at
least 2 amps of low voltage DC to power it (including line losses, add another
amp or two per 100ft), or more likely, you'd need a lot more sections.  At any
rate, unless you have "a lot" of small sections, or your probably going to have
the LED's up front running a lot brighter than the ones on the end of the line,
with a low voltage DC supply.

Again, these are thoughts just off the top of my head, no flamage please.....

Bob


{Original Message removed}

2001\12\30@012448 by Alexandre Domingos F. Souza

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>My orange leds just arrived.  600+ 10000 mcd LEDS.  :)

       Wow! :oD


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