Large LED Display

Discussion in 'The Projects Forum' started by allenpitts, Jun 27, 2015.

  1. allenpitts

    Thread Starter Active Member

    Feb 26, 2011
    77
    7
    Hello All About Circuits,

    Have been experimenting with LED displays
    connecting 555 timers to 4017 decade counters
    to creates sequences of running lights.

    Have branched out to a larger display. This
    one has about 300 LEDs.

    [​IMG]

    This is an animated GIF of the effect that is sought.
    This animation shows four of the eight characters
    that are the complete plan.
    This shows about 150 green LEDS. The project will
    have a little over 300.

    The set up is an Arduino Uno to a Max7219 to a
    breakout board.
    The Max7219 controls 64 lights and can be daisy chained
    so five Max7219s are needed.

    The Max7219 is actually designed to operate either an
    eight-by-eight matrix or a seven segment LED.

    This is the schematic of the Max7219 to an 8x8 matrix.
    [​IMG]

    To translate the matrix layout into a linear layout
    the schematic was redrawn. (This shows 24 of the
    64 connections. 40 more would be done using
    this pattern and four more boards would be daisy-chained
    from the first.)
    [​IMG]

    This is a pictorial of the PCB (Datak 21-117) which holds the 7219
    and the PCB (Vector 8022) used to break out the matrix.
    [​IMG]

    The design works well with a dozen LEDs on a bread board
    but now, with over thirty connections made to LEDs set in holes
    drilled in an acrylic sheet the rats nest is becoming
    unworkable. An eight inch long female to female
    two position Dupont jumper connector is connected to two leads
    on the Vector 8022 on one end and to the LED leads at the other end.
    [​IMG]

    So the question is more one of construction than electronic design.
    Or perhaps the electronic design chosen is causing the
    the construction nightmare.

    One of the problems is the wires leads from Vector 8022
    tend to get loose from the Dupont connectors. Perhaps
    cutting and stripping the female to female jumpers and soldering
    the stripped end to the leads coming off the Vector 8022
    so the only connector would be at the LED would improve things.
    The female Dupont connections at the LEDs seem to be more stable.

    Conceptually some way of simplifying the connection between
    the Max7219 and the LEDs is sought. Maybe another plane of
    acrylic sheet with wiring to make the Vector 8022 to LED connection
    less hectic.

    If anyone has any ideas about to simplify the wiring I would appreciate
    it greatly.

    Thanks.

    Allen in Dallas
     
  2. Bernard

    AAC Fanatic!

    Aug 7, 2008
    4,176
    397
    To simplify the wiring, I would use shift registers which can be distributed along the display. My choice would be the 74AC164 in DIP pkg. 8 bit, ser. in parallel out which can directly drive 25 mA LEDs. Best price around $.50 from Futurlec or Mouser?
     
  3. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
    2,812
    834
    Also, you can buy jumpers (both sexes) that are connected in a ribbon cable construction. That may help. Also, I think you can buy female to male headers which can be used to make your own custom cable for your connection. If you made a PCB that serves as a backing to your acrylic front plate, the traces can be brought to the edge where connector(s) can be used.
     
  4. korchoi

    Member

    Jun 5, 2015
    59
    6
    To avoid this rat's nest monstrosity, mount the LED's into a selfmade PCB(You can make a design in eagle) and route their external connections to a Ribbon cable, which then goes to the controller board. Won't reduce the wire count, but will make your board far more visible and uncluttered.
     
  5. AnalogKid

    Distinguished Member

    Aug 1, 2013
    4,546
    1,252
    Bernard beat me to the shifter idea. There will be more chips since each chip drives 8 LEDs as opposed to 64, but the wiring is much less complicated, and 8 LEDs take 8 wires (plus 1 common Vcc wire for the entire display) instead of 16. Also, the arduino can be replaced by a 555.

    ak
     
  6. #12

    Expert

    Nov 30, 2010
    16,345
    6,831
    I found a rats nest in my attic. It was much neater than this wiring job.
    I think we need a nastier word to describe the wiring in the first post. :D
     
  7. korchoi

    Member

    Jun 5, 2015
    59
    6
    How about "copper tentacle"? it sure looks like a giant squid tentacle.
     
    #12 likes this.
  8. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
    2,812
    834
    ...Or copper worms!
    [​IMG]
     
  9. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
    2,812
    834
    What a great idea!
     
  10. Bernard

    AAC Fanatic!

    Aug 7, 2008
    4,176
    397
    If thinking about shift registers, & this is a one time project, I would use something like hard aluminum for back panel ( clean drilling & good heat sinking ), mount 38 SR IC's dead bug style in two rows, use copper tape for buss bars, attach current limiting resistors to LED cathodes & ground above LED's, SR's below, use wire wrap wire for SR connections, about 5 turns per pin, soldered.
    LED's light at about 5/ sec., at end remain on for 10 sec., then sequently reset at a faster clock, 25 led.s / sec., all off for 10 sec., then repeat???
     
  11. allenpitts

    Thread Starter Active Member

    Feb 26, 2011
    77
    7
    Hello AAC Forum,

    Thanks for the replies.
    DjsFantasi said 'PCB that serves as a backing'.
    Korchoi wrote 'Selfmade PCB'
    Working on these ideas I am creating a plane that holds
    the break out from the 7219 using a large PCB based on this schematic
    [​IMG]
    Thanks to every one who offered ideas including Bernard and the AnalogKid.
    Will post results when I get the project finished.

    Allen Pitts, Dallas Texas
     
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