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Largest 7-seg LED displays?

Discussion in 'Electronic Basics' started by DaveC, Nov 30, 2003.

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  1. DaveC

    DaveC Guest

    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,
     
  2. Tim Jackson

    Tim Jackson Guest

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


    Tim Jackson
     
  3. I read in sci.electronics.design that Tim Jackson <[email protected]
    Do you wind up LED clocks? Or is this a wind-up?
     
  4. Make your own with flourescent tubes.
     
  5. 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)
     
  6. Guest

    Followups set to sci.electronics.components.

    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
     
  7. Tim Jackson

    Tim Jackson Guest

    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
     
  8. Mark Zenier

    Mark Zenier Guest

    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 Washington State resident
     
  9. 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
     
  10. Roger Gt

    Roger Gt Guest

    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.....
     
  11. Guy Macon

    Guy Macon Guest

    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"
     
  12. Joel Kolstad

    Joel Kolstad Guest

    How about using four foot long fluorescent tubes for each segment? :)

    ---Joel Kolstad
     
  13. Jeff

    Jeff Guest

    Check out "Neon Wires"
     
  14. Roger Gt

    Roger Gt Guest

    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!
     
  15. 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
     
  16. Tim Jackson

    Tim Jackson Guest

    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
     
  17. Tim Jackson

    Tim Jackson Guest

    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
    to ask for a quote.

    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
     
  18. Guy Macon

    Guy Macon Guest

  19. Guy Macon

    Guy Macon Guest

    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.
     
  20. Joel Kolstad

    Joel Kolstad Guest

    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...

    ---Joel Kolstad
     
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