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'[EE]: big led display'
2001\12\27@150609 by uter van ooijen & floortje hanneman

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How much LEDs (of the average, 5mm/20mA kind) must I roughly use to make a
7-segment display that has good visibility in 'average' outdoor daylight?
The application is a countdown display for a car race, each digit 20 .. 50
cm high. Any experience, URLs?

Wouter van Ooijen

Van Ooijen Technische Informatica: http://www.voti.nl
Jal compiler for PIC uC's:  http://www.voti.nl/jal
PICs kopen? http://www.voti.nl/shop

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2001\12\27@153019 by Jinx

face picon face
> How much LEDs (of the average, 5mm/20mA kind) must I roughly
> use to make a 7-segment display that has good visibility in
> 'average' outdoor daylight? The application is a countdown display
> for a car race, each digit 20 .. 50 cm high. Any experience, URLs?

Hi, I got asked to look at something similar a couple of years
ago and in the end rejected LEDs. Each segment would have
needed around 3 rows of 40, so a single digit was 7 x 3 x 40 =
840 LEDs. At the time that was around $160. Plus the PCBs
and components was another $100 / digit. For a 6-digit display
total came in at around $1500 + assembly costs + housing + PSU.
Ouch.

I thought it would be far simpler and cheaper to use magnetic
segments made of aluminium. One side is black, the other side
is fluoro-yellow, and they can be flipped using a (home-made ?)
solenoid pulling a lever. They can also be made larger with no
increase in cost. A good source of thin aluminium sheet is printing
plate. Ask at any decent-sized printers, they throw a lot out

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2001\12\27@153805 by Dale Botkin

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On Fri, 28 Dec 2001, Jinx wrote:

> > How much LEDs (of the average, 5mm/20mA kind) must I roughly
> > use to make a 7-segment display that has good visibility in
> > 'average' outdoor daylight? The application is a countdown display
> > for a car race, each digit 20 .. 50 cm high. Any experience, URLs?
>
> I thought it would be far simpler and cheaper to use magnetic
> segments made of aluminium. One side is black, the other side
> is fluoro-yellow, and they can be flipped using a (home-made ?)
> solenoid pulling a lever. They can also be made larger with no
> increase in cost. A good source of thin aluminium sheet is printing
> plate. Ask at any decent-sized printers, they throw a lot out

Another option would be a colored plasic sheet with 7 segments masked off,
lit by brake lamps under PIC control with MOSFET drivers.  No moving
parts, which I like better.

Dale

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2001\12\27@154830 by Scott.Touchton

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The other day I followed a truck that utilized LED brake lights and turn
signals.  Plenty bright even in direct sunlight.  Don't know if these are
special high brightness led's, but they would make a good 7 segment sign.
They appeared to be about 3/8" in diameter and were red.  The turn signal
arrow was made up of 11 LEDS, and was about 4" x 3".  Really looked good.

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2001\12\27@160351 by Jinx

face picon face
> Another option would be a colored plasic sheet with 7 segments
> masked off, lit by brake lamps under PIC control with MOSFET
> drivers.  No moving parts, which I like better

Filament bulbs ? Not fussy about those unless you run them under-
voltage to extend lifetime. "grain of wheat" neons perhaps behind
a diffuser

What I really objected to with LEDs was all that soldering. It took
me the best part of half a day to solder up a 7 x 64 and I reckon
you'd be looking at 30 hours (at what cost ?) to make a large
7-seg display. Imagine the tedium - LED after LED after LED....

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2001\12\27@160547 by Jinx

face picon face
> The other day I followed a truck that utilized LED brake lights
> and turn signals.  Plenty bright even in direct sunlight

Buses around these here parts use yellowish LEDs in the
destination signs. Wash out completely when the sun is
directly on them. Wouter's sign is fixed in one position, I
presume, so maybe that wouldn't be an issue

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2001\12\27@161008 by Dale Botkin

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On Fri, 28 Dec 2001, Jinx wrote:

> > Another option would be a colored plasic sheet with 7 segments
> > masked off, lit by brake lamps under PIC control with MOSFET
> > drivers.  No moving parts, which I like better
>
> Filament bulbs ? Not fussy about those unless you run them under-
> voltage to extend lifetime. "grain of wheat" neons perhaps behind
> a diffuser

For one that big I'd be more tempted to use bigger bulbs.  Run 'em off a
12V source...  I only lose bulbs in my car every few years, and they run
on 13V+ and get a lot of abuse.  Anything much smaller I'd be concerned
about the brightness in direct sunlight.

> What I really objected to with LEDs was all that soldering. It took
> me the best part of half a day to solder up a 7 x 64 and I reckon
> you'd be looking at 30 hours (at what cost ?) to make a large
> 7-seg display. Imagine the tedium - LED after LED after LED....

Oh, yeah.  It would be *almost* enough to make you wish for a wave
soldering machine.  I say "almost" because I've seen what is involved
in owning one, was tempted a few years back.  I could have had one fo next
to nothing, complete with 800# of solder -- still in the machine, of
course!!  No thanks...

Dale

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2001\12\27@163112 by Jinx

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> Oh, yeah.  It would be *almost* enough to make you wish for
> a wave soldering machine

The thing about ultra-bright LEDs is that with their narrow
beam angle, get one out of place and it sticks out like the
proverbial dog's wassnames

And consider this Wouter - you would need 70A of DC to
display worst-case "88:88", assuming 7 x 4 x 120 LEDs
pulling 20mA each. A 25A supply for each digit ? Not trying
to put you off (especially as LEDs are "in" these days), but I
got a surprise when I did the calcs for my request

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2001\12\27@163902 by uter van ooijen & floortje hanneman

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> And consider this Wouter - you would need 70A of DC to
> display worst-case "88:88", assuming 7 x 4 x 120 LEDs
> pulling 20mA each. A 25A supply for each digit ? Not trying
> to put you off (especially as LEDs are "in" these days), but I
> got a surprise when I did the calcs for my request

The customer only wants two digits, and I guess I can put at least 5 in
series, so that would be 7 x 2 x 120 x 0.02 / 5 = 6.72 A. No problem for a
car race environment where accu's are found all over the place. But how
large were your digits?

Wouter

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2001\12\27@164704 by David VanHorn

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>
>The customer only wants two digits, and I guess I can put at least 5 in
>series, so that would be 7 x 2 x 120 x 0.02 / 5 = 6.72 A. No problem for a
>car race environment where accu's are found all over the place. But how
>large were your digits?


I'm pulling a similar project, a replacement for a whelen slimlighter.

The original is driven by an 8 pin PIC, but it failed after only an hour of
use, and is stuck on one flash pattern.  I'll use an AVR2343 of course.

The slimlighter uses two banks of 4x20 orange leds.  I'm using two banks of
HP hyperbright 10,000 mcd lamps Eacn bank will draw about an amp with the
LED current set to 50mA at 15V input.

I don't know what the slimlighter led specs are, but it puts an impressive
spot on the wall across the room.

They go for about $0.22 each in moderate quantities.
Doing projects like these, it's easy to see where 1000 leds could dissapear
real fast.
(until you turn them on!)

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2001\12\27@165703 by Aaron Blohowiak

picon face
why not use EL (electroluminescent cable)? it can be spliced like normal
wire, and i am sure it wouldnt be hard to wire up a quick circuit to
control.

Aaron

{Original Message removed}

2001\12\27@165713 by Jinx

face picon face
> But how large were your digits?

They wanted 30cm by 5cm segments, which worked out to 3
rows of 40 5mm LEDs at 0.3 inch spacing. So each digit was
around 70cm high by 45 wide. Putting the LEDs further apart
just didn't look right so it needed that many. They choked on
the price, but never followed up on the magnetic idea. Not a
clue what, if anything, they ended up with. If you need only two
digits sounds like yours is still feasible in LEDs. Have you
thought about 12V fluorescent tubes ? Length and shape is
right, don't know about brightness though

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2001\12\27@170146 by Aaron Blohowiak

picon face
more on el:
http://www.elwire.com/faq/faq.html

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2001\12\27@170157 by Jinx

face picon face
----- Original Message -----
From: wouter van ooijen & floortje hanneman <wfEraseMEspam.....XS4ALL.NL>
To: <EraseMEPICLISTspamMITVMA.MIT.EDU>
Sent: Friday, December 28, 2001 6:04 AM
Subject: Re: [PICLIST] [EE]: big led display


{Quote hidden}

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2001\12\27@170348 by Tal Bejerano - AMC

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EL is only good for dark places and suffer a lot from direct sun light

Tal

-----Original Message-----
From: pic microcontroller discussion list [RemoveMEPICLISTTakeThisOuTspamspamMITVMA.MIT.EDU]On
Behalf Of Aaron Blohowiak
Sent: Thursday, December 27, 2001 11:55 PM
To: EraseMEPICLISTspamspamspamBeGoneMITVMA.MIT.EDU
Subject: Re: [EE]: big led display


why not use EL (electroluminescent cable)? it can be spliced like normal
wire, and i am sure it wouldnt be hard to wire up a quick circuit to
control.

Aaron

----- Original Message -----
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To: <PICLISTSTOPspamspamspam_OUTMITVMA.MIT.EDU>
Sent: Thursday, December 27, 2001 4:47 PM
Subject: Re: [EE]: big led display


{Quote hidden}

of
> use, and is stuck on one flash pattern.  I'll use an AVR2343 of course.
>
> The slimlighter uses two banks of 4x20 orange leds.  I'm using two banks
of
> HP hyperbright 10,000 mcd lamps Eacn bank will draw about an amp with the
> LED current set to 50mA at 15V input.
>
> I don't know what the slimlighter led specs are, but it puts an impressive
> spot on the wall across the room.
>
> They go for about $0.22 each in moderate quantities.
> Doing projects like these, it's easy to see where 1000 leds could
dissapear
> real fast.
> (until you turn them on!)
>
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>
>

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2001\12\27@170547 by Jinx

face picon face
> The customer only wants two digits, and I guess I can put
> at least 5 in series, so that would be 7 x 2 x 120 x 0.02 / 5
> = 6.72 A. 8

BTW, set your PSU voltage to match series forward voltage
of the LEDs. For example, a yellow is typically around 2.1V,
so you could put 3 in series on ~ 6.5V supply with no current
limiting resistor, makes life simpler (no heat) and a little cheaper

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2001\12\27@170754 by Tal Bejerano - AMC

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what about using those transparent tubes that can deliver the led light, so
you need less leds to use, each led can cover about 4-5cm along the tube.

it also used in thus brake lights at cars

Tal

{Original Message removed}

2001\12\27@171030 by David VanHorn

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At 04:55 PM 12/27/01 -0500, Aaron Blohowiak wrote:
>why not use EL (electroluminescent cable)? it can be spliced like normal
>wire, and i am sure it wouldnt be hard to wire up a quick circuit to
>control.

Does it grab your attention in daylight?

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2001\12\27@171219 by Dave King

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>The customer only wants two digits, and I guess I can put at least 5 in
>series, so that would be 7 x 2 x 120 x 0.02 / 5 = 6.72 A. No problem for a
>car race environment where accu's are found all over the place. But how
>large were your digits?
>
>Wouter

Have you looked at the luminescent digits? They are about a foot tall, not
sure if they would be visible enough in daylight. If it's only during the day
I built a timing system for marathons a few years back. This display was
18" using electromechanical segments. The company had smaller and
larger versions. We used ultrasonic wristbands and the runners had to pass
within a few feet of a sensor pad. The problem was by about the second
stage the "runners" tended to get a bit focused and zoned out on things
so you almost had to grab em and direct them towards things. Otherwise
it was a bit like herding a bunch of cats.

Dave

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2001\12\27@172341 by Lawrence Lile

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Ha! a wave soldering machine can be had for a song.  I've got one made out
of an electric skillet.

HERES HOW THEY DO high volume cheap production over in China.  It's likely
your clock radio, toaster, and Tamaguchi pet are all made this way.  Heat a
big bucket of bulk solder, deep enough to not bottom out on component leads
and wide enough to carry your circuit board.  Stuff all the components in
the proper holes.  Pick up the board by the edges with a pair of wood(or
more likely bamboo) tongs and dunk it solder side down into a tank of flux.
Squeegee off the dross on the top of the molten solder with a metal
spackling knife, then carefully dunk the sodler side of the board into the
molted solder, just deep enough that the bottom of the board gets wet, but
the top of the board stays dry.  Hold for about 2 seconds, then remove
quickly.  Hold time and dunking depth are kind of critical, but not beyond
the capabilities of a human hand.

You can snip off the component ends, but they are mostly cut off in a saw
fixture.  Clean by dunking in a bucket of  flux solvent and fish them out
with a big spoon.

I'm serious, I've toured the plants, and this is how the high volume low
cost suppliers wave solder through-hole components.  If you really need to
do a short production run, and can't afford to have it made outside, this is
the way to go.  Even in a production palnt the whole setup probably cost
them $100.

With a few boards practice, the quality obtainable with this method is
admirable, probably better than you'd do your self after the 1000th LED.

-- Lawrence


{Original Message removed}

2001\12\27@174559 by Douglas Butler

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> BTW, set your PSU voltage to match series forward voltage
> of the LEDs. For example, a yellow is typically around 2.1V,
> so you could put 3 in series on ~ 6.5V supply with no current
> limiting resistor, makes life simpler (no heat) and a little cheaper
>
This sounds like it could get you into trouble if temperature or
something changes the LED voltages a little.  If your supply doesn't
track the current will change wildly.  You really ought to have some
ballast resistance, or use a current driver.

Sherpa Doug

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2001\12\27@180158 by Benjamin Bromilow

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>> so you could put 3 in series on ~ 6.5V supply with no
>> current limiting resistor, makes life simpler (no heat)

There was a discussion on this topic a few months back in a NG. The overall
decision was no current limiting resistor that is a bad idea unless you are
current limiting some other way. The voltage will hover around the forward
voltage (if you're lucky). If you get less than the forward voltage, you get
no light emited. If you get more than the forward voltage, the current can
vary greatly, resulting in frazzled LEDs. Like most components nowadays, the
LEDs will tolerate the abuse for a long while- probably just until the units
are hauled into place at the race track- or until you've sold enough units
to be a real pain in the arse to have to mend....

Ben

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2001\12\27@180808 by Jinx

face picon face
> >> so you could put 3 in series on ~ 6.5V supply with no
> >> current limiting resistor, makes life simpler (no heat)
>
> There was a discussion on this topic a few months back in
> a NG. The overall decision was no current limiting resistor
> that is a bad idea

Slowly, ever so quietly, places paper bag over head

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2001\12\27@181444 by David VanHorn

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At 12:06 PM 12/28/01 +1300, Jinx wrote:
> > >> so you could put 3 in series on ~ 6.5V supply with no
> > >> current limiting resistor, makes life simpler (no heat)
> >
> > There was a discussion on this topic a few months back in
> > a NG. The overall decision was no current limiting resistor
> > that is a bad idea
>
>Slowly, ever so quietly, places paper bag over head

Well, a series string of LEDs could be driven by an SMPS, sensing the
current through the string, rather than the voltage applied. That works,
though you might want to limit the output voltage compliance in case of an
open circuit.

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2001\12\28@025652 by Peter L. Peres

picon face
Wouter, I have no numbers here but 'average outdoor lignting' is a trap.
If you put them in the shade (roof or shade above) you can assume
illumination <3000 lux in most cases. There are IEC/ISO standards for
display sizes and contrast factors etc. I will look if I can find
something here, I used to have a book that contains pointers.

Anyway try to look at products from LED makers for special elements for
outdoor panels. And take into account the angle of view. Their data sheets
and application notes are very helpfull.

Peter

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2001\12\28@051638 by Roman Black

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Jinx wrote:

> > > And consider this Wouter - you would need 70A of DC to
> > > display worst-case "88:88", assuming 7 x 4 x 120 LEDs
> > > pulling 20mA each. A 25A supply for each digit ? Not trying
> > > to put you off (especially as LEDs are "in" these days), but I
> > > got a surprise when I did the calcs for my request
> >
> > The customer only wants two digits, and I guess I can put at least 5 in
> > series, so that would be 7 x 2 x 120 x 0.02 / 5 = 6.72 A. No problem for a
> > car race environment where accu's are found all over the place. But how
> > large were your digits?

Hi Wouter, the easiest and cheapest electronic
solution which gives enough brightness etc is
to use 240vac or 120vac bulbs, at 2 or 3 bulbs per
segment. They can be switched easily with any cheap
triac. You can get millions+ of on/off cycles from
normal mains bulbs if you do this:

* run 40w bulbs at about 32w (80%)
* drop 20% on a series resistor - soft starts them
* keep filaments warm and JUST glowing with a
simple parallel resistor across your triac.
* consider a 4" fan in your cabinet.
* also put a "hood" on the display like traffic
lights have to keep the sun off the digits?

My preferred solution, being cheap, reliable,
and has excellent visibility even in HUGE
sizes; Make each segment mechanical, like a
2" x 2" wooden length (or something lighter like
PVC pipe), painted black and fluoro yellow on
different sides. Use a cheap "toy" type dc motor
one end, acting as rotary solenoid and bearing and
and a simple greased pin as bearing on the other
end. They rotate to change appearance, and simply
"hit the stop" at each end of the rotation. You
apply enough power to the motor to turn it, but
low enough power so that the motor "stalls" at each
side without getting too hot. Saves limit switches
etc. :o)

Controlling them cheaply is a challenge, I would
use a 0v,+6v,+12v power supply, common for all the
segments. The +6v connects to one motor terminal,
The other needs a half-bridge ie a cheap NPN and PNP
transistor and a series resistor to set stall
current. You could PWM the half bridge also for no
extra cost, giving adjustable motor current in each
direction. Really they just need to be on or off,
with the resistor size chosen to give good motion
with minimum heat.

Those hobby motors in the larger sizes are about $2
each, and have a LOT of quite reliable power in a
"rotary solenoid" of that price range. I've done
similar things in robotics projects. :o)
-Roman

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2001\12\28@053818 by Jinx

face picon face
> 2" x 2" wooden length (or something lighter like
> PVC pipe), painted black and fluoro yellow on
> different sides. Use a cheap "toy" type dc motor

Nice touch using pipe and a cheapo motor. We thought
of something like it as a probable alternative to aluminium
strips and levers but like I say, nothing got made anyway.
The only concern I'd have is the torque of a very small (eg
slot car) motor, and whether it would be enough to get
something as large as pipe moving. Maybe it could be
an indirect drive, say a rubber clutch, like a CD drawer
mechanism, and a leaf switch. Two bumps on opposite
sides of the pipe (ie 180deg apart) would operate on the
same switch to tell the driver to stop

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2001\12\28@054506 by Roman Black

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Jinx wrote:
>
> > 2" x 2" wooden length (or something lighter like
> > PVC pipe), painted black and fluoro yellow on
> > different sides. Use a cheap "toy" type dc motor
>
> Nice touch using pipe and a cheapo motor. We thought
> of something like it as a probable alternative to aluminium
> strips and levers but like I say, nothing got made anyway.
> The only concern I'd have is the torque of a very small (eg
> slot car) motor, and whether it would be enough to get
> something as large as pipe moving. Maybe it could be
> an indirect drive, say a rubber clutch, like a CD drawer
> mechanism, and a leaf switch. Two bumps on opposite
> sides of the pipe (ie 180deg apart) would operate on the
> same switch to tell the driver to stop

The motors I mentioned are quite large, about 3cm
or 4cm long, torques up to 1300g/cm, see the new
Jaycar catalogue or their web site. PLENTY of torque
to direct drive, no drama. :o)
-Roman

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2001\12\28@071929 by Anand Dhuru

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How about the conventional approach (about 8 LEDs per segment), but using
the LARGER 1cm LEDs? They light up quite brightly at 20 ma, and because of
the larger size, you would have a longer, wider segment for the same number.

Regards,

Anand Dhuru

{Original Message removed}

2001\12\30@004328 by Alexandre Domingos F. Souza

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>The motors I mentioned are quite large, about 3cm
>or 4cm long, torques up to 1300g/cm, see the new
>Jaycar catalogue or their web site. PLENTY of torque
>to direct drive, no drama. :o)

       Plenty of torque, plenty of amps too ;o) It is usual to use some 20 amps or more.


---8<---Corte aqui---8<----

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'[EE]: big led display'
2002\01\08@140502 by Larry G. Nelson Sr.
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I did an outdoor sign that you can see on my web site http://www.ultranet.com/~nr
. I used 4 superbright leds for each segment of each 7 segment digit. It
works fine outdoors in sunlight. I use T 1 3/4 superbright from HP that are
an orange - yellow in color.

Larry


At 04:37 PM 12/27/01 +0100, you wrote:
{Quote hidden}

Larry G. Nelson Sr.
L.NelsonEraseMEspamieee.org
http://www.ultranet.com/~nr

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2002\01\20@135241 by Joris van den Heuvel

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face
>
> Do you recall the intensity of these LEDs? The site (no at aligent) has a
> wide ratenge of 5mm LEDs. A typical value a found is 10..20 mcd, which
seems
> to be quite low compared to some superlamps I see quotes at 20.000 mcd!
>
> Wouter van Ooijen

Wouter, please note that the intensity is very dependent on the viewing
angle of the LED.

I have used 1..5 mcd diffuse LEDs that emitted more light than a 20 mcd LED.
They just don't focus the light into a narrow beam.

The intensity doesn't have anything to do with the output power.

Someone correct me if I'm wrong.

Regards,
Joris.

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'[EE]: big led display'
2002\02\05@122419 by Larry G. Nelson Sr.
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I think they were 2000 mcd. I bought them from Newark but they have been
discontinued.


At 10:01 AM 1/20/02 +0100, you wrote:
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Larry G. Nelson Sr.
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'[EE]: big led display'
2002\04\04@090034 by Larry G. Nelson Sr.
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I thought it was 10,000 mcd or more.

At 10:01 AM 1/20/02 +0100, you wrote:
> > I did an outdoor sign that you can see on my web site http://www.ultranet.com/~nr
> > . I used 4 superbright leds for each segment of each 7 segment digit. It
> > works fine outdoors in sunlight. I use T 1 3/4 superbright from HP that
>are
> > an orange - yellow in color.
>
>Do you recall the intensity of these LEDs? The site (no at aligent) has a
>wide ratenge of 5mm LEDs. A typical value a found is 10..20 mcd, which seems
>to be quite low compared to some superlamps I see quotes at 20.000 mcd!
>
>Wouter van Ooijen
>
>Van Ooijen Technische Informatica: http://www.voti.nl
>Jal compiler for PIC uC's:  http://www.voti.nl/jal
>PICs kopen? http://www.voti.nl/shop
>
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Larry G. Nelson Sr.
L.NelsonspamBeGonespamieee.org
http://www.ultranet.com/~nr

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