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LED SignBoard 64X8 - PIC 16F628A

Discussion in 'Microcontrollers' started by Gayan Soyza, Mar 8, 2009.

  1. Gayan Soyza

    Gayan Soyza Active Member

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    LED Sign Board 64X8 - PIC 16F628A

    Here is a recent signboard I have designed under a PIC 16F628A, 4MHz.

    It’s a 64 X 8 led matrix board (64 columns & 8 rows).

    Didn’t work much hard with code stuff. Just added some basic scrolling.

    I cannot resist I want to show what I had in my mind.

    Here is a video of my project & some pictures of that.(Photography from - Pasans camera)

    Light - YouTube - SignBoard Light

    Dark- YouTube - SignBoard Dark
     

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    Last edited: Mar 8, 2009
  2. edeca

    edeca Active Member

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    Very nice! Do you have a schematic to show how you did the multiplexing?

    It looks great.
     
  3. Gayan Soyza

    Gayan Soyza Active Member

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    Hi thanks.

    I do a row scan.I use 74HC164 shift register + ULN2803 per 8X8 matrix.Likewise I have cascaded 8 sets together.

    I'll post a schematic recently.
     
  4. dave

    Dave New Member

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  5. Mike - K8LH

    Mike - K8LH Well-Known Member

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    Very nice Gayan.

    I would like to see the schematic too just to see how you're latching column data.

    Mike
     
    Last edited: Mar 11, 2009
  6. Gayan Soyza

    Gayan Soyza Active Member

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    Hi thanks for your view.

    I'm doing a column scan in this project & I was doing a row scan in some other design.

    Here is a schematic of the design.
     

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    • Like Like x 1
  7. be80be

    be80be Well-Known Member

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    That's sweet looks real good
     
  8. Mike - K8LH

    Mike - K8LH Well-Known Member

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    Well your display looks surprisingly nice with such a low 1.5625% (1/64th) duty cycle.
     
  9. mabauti

    mabauti Member

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    Awesome! (º<
     
  10. Gayan Soyza

    Gayan Soyza Active Member

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    Thanks guys.

    I was making some boxes these days actually its harder than designing the project.

    Reg brightness you can still reduce the 47R resister but I wont' recommend.Don't know when uC will stop run & the particular column would be blown :O

    With column scanning method I'd like to add some more columns & see if its fine then ok otherwise shift to row scanning technic.
     
    Last edited: Mar 15, 2009
  11. muralieb

    muralieb New Member

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    kindly publish the codes....
     
  12. colin55

    colin55 Well-Known Member

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    I's a "run of 8" not 64.
     
  13. Mike - K8LH

    Mike - K8LH Well-Known Member

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    Gayan has daisy-chained the column driver shift registers so he is only lighting one of sixty-four columns at a time.

    Mike
     
  14. be80be

    be80be Well-Known Member

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    I couldn't get how he came up with 8 seeing he was rolling threw 64 one at a time lol
     
    Last edited: Apr 11, 2009
  15. colin55

    colin55 Well-Known Member

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    He's loading 64 and scanning from top to bottom in a "run of 8."
     
  16. Mike - K8LH

    Mike - K8LH Well-Known Member

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    The schematic shows the current limiting resistors placed on the row driver outputs which implies that he's scanning columns.

    Hey Gayan, how are you doing it?
     
  17. Gayan Soyza

    Gayan Soyza Active Member

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    :D

    I'm doing a column scan like Mike, K8LH mentioned.You can see when it displays the word "CONTACT" it shows the direction I'm scanning :D
     
  18. AtomSoft

    AtomSoft Well-Known Member

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    hey Gayan can you write some notes on the operation of this signboard. I know it may seem like a silly question but how did you center the text? was it like a auto center or was it manual? Manual being you typed spaces to make it looked center?

    Do you mind if i use this design? If i was to ever make any money from something i use from someone else i would of course give them some royalty if you understand :)
     
  19. Gayan Soyza

    Gayan Soyza Active Member

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    Hi AtomSoft

    First of all you need to multiplex your display what ever the method you like.
    The two methods I use is column scanning & row scanning. You can do that using shift registers or using direct I/O ports.
    The above project I used a column scan because it has only 64 columns. If I have 100 columns & above then I might do a row scanning method.

    In column scan I’m scanning one column at a time like multiplexing SSDs.
    Load 1st column –show for a while—turn off previous column—load next column-- show for a while-- turn off previous column--…………………
    If you have 5 columns then you need 5 column registers.
    If you have 20 columns then you need 20 column registers.

    The column registers contains data or pattern. When you multiplexing rapidly then the data will show on the matrix display.

    I think the above things you know very well.

    Regarding balance (centering) you don’t need special code to do that. For a 5 column display if you want to show only the middle column, you need to turn off (clear) the 1st, 2nd, 4th, 5th column registers & leave the 3rd column with data. So when multiplexing rapidly it will show only the middle column data.

    When a letter moves from right to left I use a “Shift Count Register” so it’s easily to place the text on what ever the place you like.
     
  20. Mike - K8LH

    Mike - K8LH Well-Known Member

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    While Gayan's 1/64th duty cycle matrix seems to work well, I would recommend scanning rows at a 1/8th duty cycle instead to improve brightness and better manage 'peak' current requirements. You could do this by replacing the 74HC164's with 74HC595's + ULN2803's, or better yet use TPIC6C595's or MIC5821's or one of the other serial-to-parallel sinking driver IC's. Then remove the current limiting resistors from the row driver and put them on the column drivers.

    Mike
     
    Last edited: Apr 18, 2009
  21. AtomSoft

    AtomSoft Well-Known Member

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    ok how about for controlling BI-Color LEDs Matrixs. I have 5x7 Matrix LED but they are BI color. Some info:

    Orange red and yellow green

    Unit is column cathode
    row anode

    Can you tell me or give me your opinion on the best way to control this? Im sure i can add or alter it for Many without issue but thoughts would be nice.
     

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