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Electronics question on LED sign circuit

Discussion in 'Modding' started by bigal, 8 Jun 2005.

  1. bigal

    bigal Fetch n Execute

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    some of you may remember my topic of quite a few months ago (seems alot longer) about a LED sign i got off ebay, 6ft long with 784 LED's made by newscanner.. Well its been lying around my room getting slowly more and more broken so i have decided to finally have a go at making a control circuit based mostly (if not i dentically) on this one here

    It works using shiftregistes and TIP transistors the same as mine, infact the display is identical except mine has the 7 row transistors encoded into BCD... i guess to reduce I/O lines.. anyway, due to my lazyness when it comes to modifiying PIC code, i plan to simply cut out the BCD - decimal decoders and solder onto the outputs and copy the controller circuit from that site, it _SHOULD_ work, i think (if it doesnt this sign meets the skip!).

    HOWEVER

    that site is pretty sparse on information, for one thing it doesnt say at all how the sign is programmed, it shows how to wire it to a PC, but no VB code or info at all and the code contains some default messages... so i cant work that one out.. I have tried emailing the author but to no reply :wallbash:

    and second, my sign uses 74LS164N shift registers and ULN2083A buffers on the columns, there sign uses 74LS154N shift registers.. shouldent be a problem i think... also my rows use TIP 115's and theirs TIP 30's.

    so in conclusion:

    Does anyone have any idea how one would program this thing once i built it? (going by the ASM code on that site) and do you think this will work too? :idea:


    thanks alot people
    Alex :cooldude:
     
  2. bigal

    bigal Fetch n Execute

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    BUMPAGE ^_^


    any ideas?
     
  3. hcker2000

    hcker2000 What's a Dremel?

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    Well it shows an example of what to put where on there but I'm not sure if there is any actual code to put stuff from the serial port (i.e. your text) onto the pic. I supose that is all you realy need to do is write up some serial code to store the text in memory on the pic. Probably the best way would be to put a button on the controler board that when you switch it to program mode ("on") then the pic just sits and listens for stuff from the serial port and stores it (kind of like a boot loader).

    If you wanted you could add an I2C EEprom for more memory for messages. This is all theory on my part as I'm new to pic's. If you havn't done any serial stuff there is a decent tutorial at Sparkfun
     
  4. bigal

    bigal Fetch n Execute

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    why is nothing ever easy. ever.
     
  5. hcker2000

    hcker2000 What's a Dremel?

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    So say we all.
     
  6. TheAnimus

    TheAnimus Banned

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    erm this is easy, this guy's just made a rather complex one, it has font support.

    If you really want i can help you design a simple circuit driven by a PIC, that will be able to talk to the serial port, should be no more than 100 lines of asm. (very simple really).

    How big is your LED matrix, common annode or cathode, how much current neaded?

    Also remeber that with micro's programmign asm is better and cleaner, and for things like this much easer.
     
  7. Wolfe

    Wolfe What's a Dremel?

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    And a hell of a lot harder to lean on short term.

    Also, everyone i know who learned ASM on X86 hates the PIC ASM, so, go figure.
     
  8. TheAnimus

    TheAnimus Banned

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    I learnt ASM on the ARM (Advanced RISC Machine) so i find PIC ASM great, these "most people" something tells me there pure computer scientists who don't ever try to make things interface with a BUS.

    You have to remeber learning a RISC uC's ASM is nothing like as hard as learning the x86. Nothing like as hard!

    I think a bit of the RISC vrs CISC debate has come in hear, generally pureists people who want control over everything go for RISC, people who don't want to have to think about all the code needed to piss about because you can only handle one instruction, tend to hate low end RISC micro's.
     
  9. bigal

    bigal Fetch n Execute

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    HI!

    thanks for the offer of help!

    the rows are active high (the TIP transistors here have the input tied high..) so the shift registers bust give a low output to trigger the columns it wants lit.

    It is almost i dentical to the design here:

    http://www.acm.uiuc.edu/sigarch/projects/sign2003/driver_board.gif

    but all the outputs on the shift registers are used (not in "modules" of 5)

    in totals there are 112 columns * 7 rows of leds (784 tot)

    since characters are 5*7 in size, i dont know how they origionally split this up, assuming a 1 column gap between the letters... about 18 letters MAX.

    Pictures:

    http://hellzbellz.net/screen_dumps/LEDSIGN/DSCK0014.JPG (PSU)
    http://hellzbellz.net/screen_dumps/LEDSIGN/DSCK0015.JPG (display boards)


    .pdf really really bad schematic of the sign section (really bad)

    http://hellzbellz.net/screen_dumps/LEDSIGNDISPLAY11.pdf

    should give some idea though.. :)

    again, thanks for the offer to help, consider it taken up! :cooldude:
     
  10. TheAnimus

    TheAnimus Banned

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    Right well you'll need to use either a micro, or an old computer for to control this.

    I'd say for this make life easy on yourself, a high end PIC.

    You'll need a prototype board, the PIC a programmer (the useual).

    JDM or PonyProg are the cheapest, if you've got $50 doing nothing and want to "get into" PIC'ing, get an ICD2, this allows you to see what code is running inside the micro, what line its on, and other great stuff.

    then you need to work out how the PIC can turn on the LEDs, i'm guessing you know the principels of matrix LED-ing?
     
  11. bigal

    bigal Fetch n Execute

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    • Yes, i have a USB max 40DIL job..
    • I have a couple of 16f877's in stock
    • Yes i understand most of how they work

    Mign works 99% the same way as that link i posted, so isnt it possible to reuse most of the code he used? Just to impliment the serial programming routines? :confused:
     
  12. SteveyG

    SteveyG Electromodder

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    You could re-use his code (you'd have to translate it back into 16F instruction set), but it really isn't very difficult to drive this display, and wouldn't take you very long to write some code to drive it. The thing that took the longest when I created my matrix display was creating all the ASCII characters. The rest of the coding only took a few hours. I initially used a 16F648A@10MHz, so you don't need a particularly powerful PIC unless you're wanting powerful effects/lots of storage space for messages.

    So long as you know the principles behind driving the display you shouldn't have any difficulties.

    One thing you'll have to be careful of when creating the code is that you'll probably blow the LEDs instantly unless you drive it correctly first time as there will be little to no current limiting on those LEDs (they were probably pulsed at their peak current). I suggest you find some way of limiting the current to the LEDs before trying to drive it for the first time.
     
  13. bigal

    bigal Fetch n Execute

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    hmm, my programmer supports 18f252 anyway, so i could always spend a massive £3ish on one of them and just use his code entirely (i dont know how to program in ASM, so writing new code for this is very hard for me.. I just want the simplist way..

    as for the led curent issue, i have got these to chase very slowly and they didnt blow then, so i guess they are ok..
     

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