# Largest 7-seg LED displays?

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#### DaveC

Jan 1, 1970
0
Would like to build a clock with very large display. I'd like 7 to 10-inch
high digits. The largest I can find is 5-inch.

I've considered doing a single LED array, but cost becomes an issue with
large digits.

Ideas? References?

Thanks,

T

#### Tim Jackson

Jan 1, 1970
0
DaveC said:
Would like to build a clock with very large display. I'd like 7 to 10-inch
high digits. The largest I can find is 5-inch.

I've considered doing a single LED array, but cost becomes an issue with
large digits.

Ideas? References?

This firm makes custom large 7segment displays:
www.london-electronics.com
However you do it it winds up expensive though.

Tim Jackson

J

#### John Woodgate

Jan 1, 1970
0
I read in sci.electronics.design that Tim Jackson <[email protected]
This firm makes custom large 7segment displays:www.london-
electronics.com However you do it it winds up expensive though.

Do you wind up LED clocks? Or is this a wind-up?

W

#### William P.N. Smith

Jan 1, 1970
0
DaveC said:
Would like to build a clock with very large display. I'd like 7 to 10-inch
high digits. The largest I can find is 5-inch.

Make your own with flourescent tubes.

F

#### Frank Bemelman

Jan 1, 1970
0
DaveC said:
Would like to build a clock with very large display. I'd like 7 to 10-inch
high digits. The largest I can find is 5-inch.

I've considered doing a single LED array, but cost becomes an issue with
large digits.

Ideas? References?

Fluorescent tubes? Perhaps single leds aren't that expensive,
with a single segment of ~20 5mm dia. leds (some spacing between led).
About 140 leds for a digit. 850 for a clock. 1000 leds on Ebay
for $20.00 (search for item #2576358167) M #### [email protected] Jan 1, 1970 0 Followups set to sci.electronics.components. In sci.electronics.components DaveC said: Would like to build a clock with very large display. I'd like 7 to 10-inch high digits. The largest I can find is 5-inch. I've considered doing a single LED array, but cost becomes an issue with large digits. Maybe this is what you mean by a "single LED array", but you can get "bar graph" arrays of rectangular LEDs that might do what you want. They will probably make it a lot easier to get straight lines. Mouser (USA) sells some Kingbright arrays that may work - DD12HWB has 12 rectangular LEDs with their short sides together and DC20/20EWA has 20 rectangular LEDs with their long sides together. Digi-Key (USA) has some Lumex 12-LED parts that should also work. Here, I'm going to talk about the Kingbright parts. The illuminated length of the 12-LED one is about 1.8" and of the 20-LED one about 2.0". They aren't very bright; the 12-LED one is rated at 900 _micro_candelas minimum. and the 20-LED one is rated at 2200 _micro_candelas minimum. Compare to a high-brightness single red LED of 2800 _milli_candelas or more. There is a higher-cost 20-LED version rated at 9000 _micro_candelas minimum. All of the Kingbright ratings are at 10 milliamps forward current. There is lots of information about LED efficiencies (and LEDs in general) at Don Klipstein's excellent site: http://members.misty.com/don/ledx.html . You'd have to stack these up to get the size you want. The 12-LED one might have a little bit of trouble with this, as there is about 3.4 mm of "dead space" between the edge of the LED on the end and the housing. You will end up with about a 1.5 LED-width gap if you stack two of these displays end-to-end; this may or may not be important depending on the proposed viewing distance of the clock. Also, this will yield a "line width" of 1.5 mm, which might be too narrow for easy long-distance viewing. The sketch of the 20-LED one also shows an unspecified gap between the edge of the last LED and the housing, although it appears much smaller than on the 12-LED one. This one will have a "line width" of about 5 mm, which may be better for distant viewing. With the 12-LED displays, four of them would give you about a 7.2" high display (14 required per digit, cost per digit US$33) and six would yield
a 10.8" high display (21 required per digit, cost per digit US$49). With the 20-LED displays, four would give you about an 8.0" high display (14 required per digit, cost per digit US$82) and six would yield about a
12.0" high display (21 required per digit, cost per digit US$124). Probably you want to run a relatively high voltage so you can run the LEDs of each segment in series. It will make the wiring a lot easier in any case. Two 12-LED displays in series at 20 mA will drop 60 V max, and three will drop 90 V max. Two 20-LED displays in series at 20 mA will drop 100 V max, and three will drop 150 V max. Worst case, for a 24-hour clock, you'll need to provide around 150 V at 0.52 A (about 80 watts). I hope this helps! Matt Roberds T #### Tim Jackson Jan 1, 1970 0 John Woodgate said: I read in sci.electronics.design that Tim Jackson <[email protected] Do you wind up LED clocks? Or is this a wind-up? No, don't get the wind up! I was after large panel meters. They quoted me about £500 UK each for 2" high voltmeters. Tim M #### Mark Zenier Jan 1, 1970 0 Would like to build a clock with very large display. I'd like 7 to 10-inch high digits. The largest I can find is 5-inch. I've considered doing a single LED array, but cost becomes an issue with large digits. Ideas? References? The biggest displays seem to be those magnetic flipper panel types that switch a flap between a fluorescent painted side and a black one F-P Electronics have/had 7 segment displays up to 18 inches. Try the EEM web site and look up "Displays, Electromagnetic" Mark Zenier [email protected] Washington State resident M #### Michael A. Terrell Jan 1, 1970 0 Tim said: I was after large panel meters. They quoted me about £500 UK each for 2" high voltmeters. Tim Two inch panel meters are not "Large" ;-) -- I say, the boy is so stupid that he tried to make a back up copy of his hard drive on the Xerox machine! Michael A. Terrell Central Florida R #### Roger Gt Jan 1, 1970 0 Made a seven segment display many years ago with four 12V incandescent lamps per segment, Needed to read from fifty feet away. This lamps were spaced evenly and the character was 16 inches high and 8 inches wide. Did several smaller versions at long gone "Robotomics" in Tempe AZ from .75 inches to 4 inches. A mask defines the shape. Lamps aren't very expensive, but are power hogs! Bright LEDs should work just as well..... G #### Guy Macon Jan 1, 1970 0 William P.N. Smith said: Make your own with flourescent tubes. The seconds display would go through tubes rather quickly and the tubes might have problems starting/stopping that fast, depending on the ballast/starter design. I would suggest incadescent lights behind red transluscent plexiglass with a custom mask between the lights and the plexiglass. Some nice Solid State Relays and a Basic Stamp getting it's sync from the 60Hz. would do nicely. Or he could buy one, but the prices are rather ... interesting. http://www.brgprecision.com/ http://www.brgprecision.com/arc77.html http://www.google.com/search?q="giant+digital+clock" J #### Joel Kolstad Jan 1, 1970 0 Roger Gt said: Made a seven segment display many years ago with four 12V incandescent lamps per segment, Needed to read from fifty feet away. How about using four foot long fluorescent tubes for each segment? ---Joel Kolstad J #### Jeff Jan 1, 1970 0 DaveC said: Would like to build a clock with very large display. I'd like 7 to 10-inch high digits. The largest I can find is 5-inch. I've considered doing a single LED array, but cost becomes an issue with large digits. Check out "Neon Wires" R #### Roger Gt Jan 1, 1970 0 Joel Kolstad said: How about using four foot long fluorescent tubes for each segment? ---Joel Kolstad Why not? But the rate of display change would be slow. We thought about using 60W bulbs for an advertising sign, but opted instead for neon. For a British flag display three lamps per segment were just too much power. Shipped two prototypes to LV but never got another order for the MONSTERS! Mounted on the top of a van! Thirty feet of glass tubing lamps. Had to switch a lot of 20KV signals.... Fun! Arc-Arc! P #### petrus bitbyter Jan 1, 1970 0 Frank Bemelman said: Fluorescent tubes? Perhaps single leds aren't that expensive, with a single segment of ~20 5mm dia. leds (some spacing between led). About 140 leds for a digit. 850 for a clock. 1000 leds on Ebay for$20.00 (search for item #2576358167)

A 5" single row of leds may be to a little bit to thin to light a segment.
So you will need two or three rows. Boards to mount them, electronics to
drive them.....

But what are the costs of it compared to that of 5" devices that are
available? How about the costs of conventional bulbs or a specialized firm?
Even if you can find of the shelve displays, they will not by cheap either.

As far as I can see, the best way to obtain the required displays is
designing your own 3.5 - 5" segment boards. It should be possible to make
one universal type that fits for all seven positions in a display. Then you
*only* have to make copies....

petrus

T

#### Tim Jackson

Jan 1, 1970
0
Guy Macon said:
The seconds display would go through tubes rather quickly and
the tubes might have problems starting/stopping that fast,
depending on the ballast/starter design.

Fluorescent tubes normally switch on and off 100 or 120 times per second so
tube wear is not a problem per se. The trick would be maintaining the
electrode temperature during the off periods to get a hot restart. You
would need something a bit fancier than the typical snap starter to control
the heater current, but it wouldn't be particularly difficult to achieve.

Sounds like a fun research project for a bright young guy with time on his
hands.

Tim Jackson

T

#### Tim Jackson

Jan 1, 1970
0
Michael A. Terrell said:
Two inch panel meters are not "Large" ;-)
--

Is this relevant?

Statement 1. They make large displays. As large as you like.
Statement 2. I happen to have had a quote from them for 2" high panel
meters.

These two statements are not connected except as guide to pricing, which was
necessary because the company do not show prices on their website - you have

OK?

2" high is large as panel meters go. If you know where I can get them off
the shelf and cheap then I'd be interested in buying some. My customer
turned down the £500 quote. I can't build them myself any cheaper, my time
is too expensive.

Tim

G

#### Guy Macon

Jan 1, 1970
0
Tim Jackson said:
Fluorescent tubes normally switch on and off 100 or 120 times per second so
tube wear is not a problem per se. The trick would be maintaining the
electrode temperature during the off periods to get a hot restart. You
would need something a bit fancier than the typical snap starter to control
the heater current, but it wouldn't be particularly difficult to achieve.

That's an iinteresting idea, but I suspect that it wouldn't work.

The reason why the lamp restarts 120 times per second is not because
the electrodes are hot, but because the gas is ionized. The lower
left seconds segment is off for three seconds (digits 3, 4, and 5),
and the gas loses it's ionization in a fraction of a second. While
the electrodes are hot, they are being eroded. Keeping them hot won't
stop that from happening.

J

Jan 1, 1970
0
Guy Macon said:
Do you know what happens to fluorescent tubes when you tirn them
on and off once every couple of seconds, 24 hours a day?

Perhaps using cold cathode tubes would be much better then? As far as I
know, the whole point of having a hot cathode is to make starting (a whole
bunch!) easier -- with a sufficiently high voltage you should be able to
'jump start' the lamp directly, just as is done with neon tubes. (And of
course you can use a regular fluorescent tube as a CCFL tube by just not
heating the cathode!)

Come to think of it, seeing neon tubes switching on and off every second or
so all night long isn't that unusual...

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