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Ideas for large LED RGB display (how to drive, etc).

Discussion in 'Electronic Design' started by klaas langhout, Oct 16, 2005.

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  1. I'm trying to set up a rather large RGB LED display. In specific,
    approximately 1000 RGB LED's in a way where I have individual control of ea.
    LED (color must have, brightness nice to have).

    My current plan (though I need to see if this will work, no previous
    experience) is to use a MAXIM MAX7219 serial in/out 8 digit, 8 segment
    driver to multiplex 64 LED's for a single color. So, for RGB each panel of
    64 LED's will have 3 MAX7219 chips to drive R, G, B separately across the
    entire set.

    The MAX7219 can be put in series up to 16 so, i'll end up with muliple sets
    of 16 to control all 1000 led's.

    My question is this, what other methods / ideas do people have to do this.
    I just ordered some chips/led's to do some experiementation as i'm not sure
    I can PWM the LED's enough to get different shades. One additional note,
    I can't use an intergrated LED display as I want the ability to move/space
    out the LED's in a custom physical arrangement (e.g. space them out every
    1-6 inches).

    Any ideas appreciated....
     
  2. Don McKenzie

    Don McKenzie Guest

    have a look at:
    http://www.dontronics.com/micro-vga.html
    may be a idea worth considering

    Don...


    --
    Don McKenzie
    E-Mail Contact Page: http://www.e-dotcom.com/ecp.php?un=Dontronics

    Micro,TTL,USB to 1.5" color LCD http://www.dontronics.com/micro-lcd.html
    USB,RS232 or TTL to VGA Monitor http://www.dontronics.com/micro-vga.html
    World's smallest USB 2 TTL Conv http://www.dontronics.com/micro-usb.html
     
  3. Cool board and I fully agree that it would be much cheaper / easier to go
    with VGA out to an LCD display. I can't do this however as, each LCD
    element in what I'm putting together is 6" apart so, I have to go with
    discrete LED's. Now, if there were a board that can control a ~ 30 x 30
    matrix of LED's (say, a really small LCD display) that I could hack in, that
    would be something :)

    Cheers.
    -------------------------------------------------
     
  4. Don McKenzie

    Don McKenzie Guest

    small LCD, OK here is another:
    http://www.dontronics.com/micro-lcd.html
    again, it may not suit your application.

    Don...

    --
    Don McKenzie
    E-Mail Contact Page: http://www.e-dotcom.com/ecp.php?un=Dontronics

    Micro,TTL,USB to 1.5" color LCD http://www.dontronics.com/micro-lcd.html
    USB,RS232 or TTL to VGA Monitor http://www.dontronics.com/micro-vga.html
    World's smallest USB 2 TTL Conv http://www.dontronics.com/micro-usb.html
     
  5. Erik, good information thanks.

    For the questions:
    - This is for an art piece and, i believe 10fps should provide a good degree
    of dynamic image quality. I don't need video quality :
    - Only nighttime viewing (no external lighting) so, i suspect 10ma per pin
    may be enough.
    - I'm open. for the ATMega48's at $1.69 ea for 6 rgb led's that works out
    to $281- for 1k LED's which is still less than the LED's.

    ~ klaas
     
  6. What system are you going to be using to control these? Whatever it is
    that holds and updates the framebuffer is going to have to manage the
    240+Kbps datastream, which has to be distributed to each of the
    controlling chips. I2C at 400KHz may or may not do it, as you have to
    deal with the bus overhead as well as the fact that depending on how the
    code is written for the ATmega, it may have to block for short periods
    of time, somewhat randomly. SPI would work better, since you can
    "broadcast" the data, but you'll have to have buffers to handle that
    many devices on the bus.

    I don't know how much of this engineering you're planning on doing
    yourself, but I'd be interested in at least writing the microcontroller
    code (since I need it for another project anyway, and is probably
    saleable as a unit), and even engineering the PCBs if necessary. Would
    probably put 8 ATmega48's on one board with power and signal buffering,
    controlling 48 RGB LEDs each. Headers for flying wires to each LED, or
    potentially to a stacked board with spaced LEDs if your spacing
    requirements are consistent anywhere.

    BTW, the chips drop to $1.56 in purchased q.100 or higher, and you'd
    need 167 for 1000 LEDs totalling $260.52. However, depending on the
    resulting brightness you might end up needing ATmega88's, which have
    twice the Flash space for code (irrelevant here) but can put out 100mA
    per group instead of 70mA. The most LEDs on one group will be 7, so
    that's either 10mA or ~14mA depending on the chip.

    Something else to consider is that depending on how it's all
    interconnected, you could easily spend that much money again in
    connectors. For instance if you stacked all the boards (for power and
    control) and used dual-row 0.1" right-angle headers to connect LEDs one
    at a time, you'd use Jameco 203991CE on the board at $0.47 per chip (24
    pins), plus 6 4-pin housings at $0.19 each, and 24 crimp pins at $0.07
    each. Totals $3.29 in connectors (not counting wire, etc.) per $1.56
    chip... If you can solder 4-wire bundles or entire ribbon cables to
    each board you'd be a lot better off ;-)
     
  7. Terry Given

    Terry Given Guest

    just buy these:

    www.monstavision.com

    Cheers
    Terry
     
  8. klaasl

    klaasl Guest

    The monstavision won't work: the led's have to have more space between the
    ;)

    I was planning on driving the whole thing with a mini-itx or lapto
    equivalent to source the 'image' and send it to the 'display'.

    I'm still in the initial r&d phase so not quite sure how much i want to d
    myself: the end project is an art display where i want both canne
    sequences as well as camera based input. I'm setting up a prototype pane
    just to see what the output looks like in full darkness.

    The below is good info :)
     
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