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Wall of RAM

Discussion in 'Electronic Basics' started by logjam, Jan 2, 2006.

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  1. logjam

    logjam Guest

    A while back on ebay I was just looking around and came upon 50,000

    Ebay is a dangerous place, I can understand how women go to the store
    and spend $800 window shoping.

    $300 later and I have 50,000 LEDs in the mail

    Anyway, I gave away around 1,500 to friends. I still have MANY of them

    I thought a "fun" project would be to create a "Wall of RAM". Now it
    would be fairly easy to emulate the ram and display the results on the
    wall using a CPLD, but what about actually making real ram?

    Does anyone think its possible to use capacitors and high current
    drivers to use the LED+capacitor combination as ram?

    The goal of the project would be a wall of cards, say 4k of ram max.
    This wall of ram would interface to either the Altair that I bought OR
    the Apple 1 kit that I bought on ebay.

    What do you guys think? It seems that with some RAS/CAS decoding logic
    that it shouldn't be too hard. The cons of this project are the cost
    of 4,096 capacitors and PCBs. The pros of the project are, well, it
    would look really neat. :)

    Tell me what you think.

  2. logjam

    logjam Guest

    Well, in the excitement I forgot that 4,096 bytes is 32,768 bits. A
    little out of my range.

    So maybe we settle on 1k of ram. I don't think I have 32,000 leds of
    wall space to spare!!! ;)
  3. logjam

    logjam Guest

    On second thought, a 1k ram wall would be 121x121" square. I just got
    done drafting it. I think maybe I should consider one 256 byte array
    and see how it goes.

    What considerations will I have to make for wire length? Possibly use
    a differential transciever set?
  4. Jasen Betts

    Jasen Betts Guest

    when you said 4K I thought you meant bits. and that it sounded possible
    but lots of work.
    reduce the clock speed until it starts working?

  5. logjam

    logjam Guest

    All right, I'm not crazy any more. If I even try this I'll just use
    some dual port sram and fake it. That should be easier and allow a
    switch to choose which 1k bank of the memory to look at. A little more
    flexible. ;)
  6. Bart

    Bart Guest

    How many lights/led's would that be? Calculating your original thoughts
    showed scary amperage and blinding candle-power. I could be wrong, just a
  7. logjam

    logjam Guest

  8. Sjouke Burry

    Sjouke Burry Guest

    Put all of them in an array (~220 * 220) ,wire them in
    groups serial an parallel, and in desert sun you have a nice
    solar panel.(I do not know what the output would be) -)-)-)
  9. logjam

    logjam Guest

  10. Bart

    Bart Guest

    Just a thought, if you're going thru so much labor, maybe have a board
    drilled to make a significant sign, shape, or lettering that you could sell
    to a business or school, donate to a church.
  11. Tim Williams

    Tim Williams Guest

    Say, do you have a range of colors? I'm probably stupid to ask for it, but
    a couple hundred LEDs could be nice for a whacky project. Probably is
    stupid since about the only indicator I use regularly is my oscilloscope...
    Ooo, nice.
    Not that I know of. LEDs are exponential, not negative-resistance, like
    neon lights are. If you had gotten a couple ten-thousand neon lights, you
    could do it (although clock would have to be slowed to the 10kHz range!).
    You'll need at least 8,192 transistors and 16,384 resistors, to make yea
    many RTL inverter R-S flip-flops. To burn LEDs, I suggest using a red to
    indicate OFF and a green to indicate ON for each bit. A negative or
    positive pulse to the base (supplied by resistor or capacitor) sets state,
    while electrical state is read by collector voltage. RTL with typical
    transistors will switch in a 100-200 nanoseconds, so should be able to keep
    up with a standard clock. I'm not sure how you're going to address it,
    since you need essentially eight 9 to 512 decoders!

    Lesse, at 5mA per LED, that's a good 25 amperes supply current. 'Gonna want
    that as low as possible, i.e., 5V or so. Total dissipation will be on the
    order of 125W, not too bad.

    For the wiring, runs several feet long will want to be coax or at least laid
    against a ground plane or something. Terminating resistors might be a good

  12. Rich Grise

    Rich Grise Guest

    Yes, but it'd be a nightmare to design; you'd have to come up with
    a whole refresh scheme. I'd use flip-flops or real RAM.
    I think you're crazy, but it does sound like a kewl idea. :)
    If you want to do it, (and have the cash) do it. "If you build it,
    they will come". :) Take pictures, and _then_ see what other people
    think. :)

    Good Luck!
  13. Daniel Pitts

    Daniel Pitts Guest

    I've been looking for some for a similar type of project.
    My idea was to have a computer case that displays certain patterns,
    graphics effects such as:
    Conway's Game of Life (Haven't posted the applet for that one yet)

    I might be interested in buying a few thousand LEDs from you :)
    Depending on their specs.
  14. logjam

    logjam Guest

    This started as a little thought. Now I'm kind of excited about it!

    Rather than have gaps all over the place I've designed it to have LEDs
    that are always off in binary view mode. Labels could be placed over
    the dead LEDs. Then in a normal mode the display could be used as a
    giant bitmapped display. This might make the LED wall more attractive
    to other people. ;)

    I know, I messed up on all the captions. The COST is correct. $255 vs

    1296 bytes
    400 mil spacing, 10368 bits of display, 4212 LEDs wasted in binary view

    1280 bytes
    300 mil spacing, 10240 bits of display, 4160 LEDs wasted in binary view
  15. logjam

    logjam Guest

    The 400mil display would be a 180x81 pixel display.
    The 300mil display would be a 160x90 pixel display.
  16. logjam

    logjam Guest

  17. Bob Monsen

    Bob Monsen Guest

    Ah, that explains it. Winter darkness... You crave LIGHT!

    Bob Monsen

    "False facts are highly injurious to the progress of science, for they
    often endure long; but false views, if supported by some evidence, do
    little harm, for every one takes a salutary pleasure in proving their
    -- Charles Darwin

  18. What part of Alaska? That's a very large area. I was there in '73 &
    '74 at Ft Greely.

    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
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