LED Tile Wall (Micro Controller Help)

Discussion in 'Embedded Systems and Microcontrollers' started by acefire, Aug 22, 2010.

  1. acefire

    Thread Starter New Member

    Aug 21, 2010
    9
    0
    Hi i have posted in The Projects Forum but i thought it may reach people quicker if i posted a small amount in here about the MC side of the system.

    Here is the basic rundown so far
    Hi there, i am a beginner when it comes to electrical circuits but i am a motor vehicle engineer so i do understand how to diagnose problems and understand V=IR to some extent.
    What i dont really know is what type of ucontroller to use i have looked into Picaxe and i think it may be possible but do not know the right one to go for or if i have to just get a chip or if i can use the experimental ucontrollers on the website.

    Thank you.
     
  2. debjit625

    Well-Known Member

    Apr 17, 2010
    790
    186
    In simple way I would do it using multiplexing you need a microntroller of just 14 output pins i.e.. 8*6 = 48 and thats more than 42.

    Good Luck
     
  3. acefire

    Thread Starter New Member

    Aug 21, 2010
    9
    0
    Ok sounds good, could you go into any detail for what i would need to multiplex? And would it let me control any led at any time?

    Thank you.
     
  4. tom66

    Senior Member

    May 9, 2009
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  5. acefire

    Thread Starter New Member

    Aug 21, 2010
    9
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    Yes this does seem very familiar to mine but mine is quite a lot smaller than this design. Shame they do not post much helpful information.
     
  6. wannaBinventor

    Member

    Apr 8, 2010
    179
    4

    I disagree with this because the tricolors are going to have three leads versus two. I'm guess two anodes and a common cathode.
    1 anode will be one color, 1 will be the other color, and both will be the third color.

    Then I think you also wanted a white LED. So thats a total of 84 cathodes. With the TRi-colors and the white LEDs, you are looking at 84+42 = 126 anodes. 84 + 126 = 210 pins. You could also consider a multiplexer IC or some data buffers to lower your uC pin requirements.

    You're an engineer, so I'm sure you can come up with optimum arrangements/pin requirements from here.
     
  7. acefire

    Thread Starter New Member

    Aug 21, 2010
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    0
    Im a motor vehicle engineer not an electrical engineer. But do i need the "earth" side of the LED to go back to a pin? would it not be possible to just use a joint earth for all pins going straight to the negative side of the power supply and just use the anodes as pins?
     
  8. Markd77

    Senior Member

    Sep 7, 2009
    2,803
    594
    This is a pretty good description of multiplexing, should get you started.
    They use a counter chip but you could use 8 more output pins for their application.
    You have 168 (42X4) LEDs so it will be more complicated.
    This could be thought of as 12 rows by 14 columns, so 26 pins required without using a counter. However the LEDs would only be on 1/12 of the time which could make them very dim. One method is to increase the current to them - LEDs can take more current if it is only for a fraction of the time (check the datasheet). <ed> You have to be very careful with this method because if yuor code goes wrong you could burn the LEDs. </ed> The other way is to use more pins and make a 6 row by 28 column array or an 8 by 21.
    http://www.best-microcontroller-projects.com/led-dot-matrix-display.html
     
    Last edited: Aug 22, 2010
  9. debjit625

    Well-Known Member

    Apr 17, 2010
    790
    186
    Ok I missed that its tri color and one white extra so every set will give 4 connection and a common ,so make 7 set of 6 tiles and multiplex it,every set will need 6*4 = 24 pin and plus 1 for switching the set ,i.e.. for all the tiles you need 24 + 7 = 31 pins on a mcu to multiplex.

    For know about the process of multiplexing do a google search ,I did it and found some here is one http://www.winpicprog.co.uk/pic_tutorial13.htm

    Good Luck
     
  10. nickelflipper

    Active Member

    Jun 2, 2010
    280
    35
    Many popular microcontrollers can only source 200-300ma maximum current. The power budget could easily be exceeded, especially if higher power led's are selected.

    They make led drivers that handle adustable constant current sourcing, without the need for individual resistors, and include individual pwm control. If full brightness is not required, then a multiplex board like the Rainbowduino, would easily handle your requirements.

    Consider the more expensive plcc6 rgb leds by Osram or Cree for beautiful color mixing and wide angle dispersion for your 20cm2 tiles. If those aren't in the budget, then at least some other wide angle types, like the straw hat or piranha.
     
    Last edited: Aug 22, 2010
  11. tom66

    Senior Member

    May 9, 2009
    2,613
    214
    You can get darlington driver chips. These can source upwards of 200mA per channel, usually with a maximum total limit. They come in anywhere from 2 channels to 16 channels (the max I've seen, but they could go bigger.)
     
  12. acefire

    Thread Starter New Member

    Aug 21, 2010
    9
    0
    So for this i would need an "tricked" PSU to power an Arduino board connected using 7 Rainbowduino's to power all of the LED's? And also the plcc6 are 6 pins and i think that will make a lot of hastle as i am already going to have to use a lot of multiplexing to get this to work in the first place. And on the website for rainbowduino it says that it gives each output 200mA each from what i gather, so that means each LED would get full brightness even with them all on assuming only all the tri colour ones would be on at a time and the white would be on seperatly to them never at the same time.

    Thank you all so much for the help. I get soldering, fuses, relays, programming language, but when it comes to the acutal board making... them some big holes in my knowledge do seem to arise.
     
  13. nickelflipper

    Active Member

    Jun 2, 2010
    280
    35
    I mentioned the Rainbowduino in the context of it being a multiplexed row driver for a 1/8 or 12.5% duty cycle. It will not have full brightness. If you intend to have a full on or 100% duty cycle display, then each led has its own driver input (i.e. no multiplexing). In that case, the Rainbowduino doesn't make much sense cost wise.

    Nine 16 bit led drivers would handle the rgb duties, add three more for the white if necessary. A single Arduino (or nearly any other micro) could talk to all those drivers. One of the few pdip package versions available is the tlc5940. You will see many projects built with that chip when looking for ideas. If you are lucky, someone has already made up a board that could be adapted to the project.

    As far as the plcc6 is concerned, three of the wires will be shorted, most likely to make a common anode (CA). Unless you make/get some breakout boards, the smt chips will not be much fun. The Osram plcc6 rgb led that I have, has a nice "paper white" color with all chips on.

    All I,m trying to say is, check out a few different led options first, with the proposed tile size, before committing to the full project.
     
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