Prototyping a modular LED matrix


[Will] was toying with the idea of creating a scrolling LED marquee to display messages as his wedding in May. But you’ve got to crawl before you can walk so he decided to see what he could do with the MAX7219 LED driver chips. They do come in a DIP package, but the 24-pin 0.1″ pitch chip will end up being larger than the 8×8 LED modules he wanted to use. So he opted to go with a surface mount part and spun a PCB which makes the LEDs modular.

These drivers are great when you’re dealing with a lot of LEDs (like the motorcycle helmet of many blinking colors). Since they use SPI for communications it’s possible to chain the chips with a minimum of connections. [Will] designed his board to have a male header on one side and a female socket on the other. Not only does it make aligning and connecting each block simple, but it allows you to change your mind at any time about  which microcontroller to use to command them. For his first set of tests he plugged the male header into a breadboard and drove it with an Arduino. We hope to hear back from him with an update when gets the final device assembled in time for the big day.


  1. Hack Man says:


  2. Kelvin Mead says:

    got a lot of love for this… would love to see a corner version also!

  3. asciimation says:

    There are also the Maxim ICM7211 and ICM7212:

    Interestingly some of these ICs output Code B which is ‘0123456789-EHLP ‘ instead of hex which gives ‘0123456789ABCDEF’.

    I’ve been trying to find out what ‘Code B’ is actually for. I’ve asked the questions on several forums and got unhelpful answers, usually from people who don’t read the question.

    I even asked Maxim support and the best they could come up with was this old Intersil datasheet:

    Some engineer at some point must have decided that those Code B values were useful for something. They made a chip to output them. But what exactly are they for?

    Has anyone ever actually build something and said ‘what we need for this display is Code B output’. In which case was what that something?

    You can get free samples of the Maxim Code B outputting one and I have requested some but I don’t think Maxim know where New Zealand is as nothing I order from them ever arrives!


    • SavannahLion says:

      Thanks for nothing jerk. If I may posit a solution to your quandry? What I have may not be correct but based on my limited knowledge it’s a thought.

      It’s kind of strange that A: The order of 0123456789-EHLP space was chosen and B: It’s still being made.

      So following that train of thought, it’s painfully obvious that EHLP does not spell out HELP nor does the inclusion of P mean that words like HI or LO can be spelled. If HELP was the intent, then a smart engineer would have ordered it accordingly to reduce unnecessary work on MCU’s. The inclusion of the MCU AND multiplexed BCD interface makes the intents pretty clear. There is some kind of legacy support going on.

      So my first and only theory is:

      It’s used to represent British Sterling, eg in calculators that probably convert from older Sterling numbers to modern Sterling. Given that – is minus and E is ERROR then H could be HalfPence, L for Pound and P for Pence. I don’t know how to do the conversion so…. Meh.

      I was curious about a working example though. I poked around some data sheets and it’s a damn nightmare. The CD4055/CD4056 data sheets show 0123456789LHPA-blank. Another Google showed that the 74LS47 or 74*48 has an entirely different >9th digit scheme not worth typing here. Strangely the 7447/7448 series seems to be older and bit more common that Maxim’s Code B. I really can’t fathom what the *47/*48 series the extended digits was used for.

      Once I encountered that crap, I gave up. Not much point in going further with such obscure stuff getting in the way. :(

  4. asciimation says:

    I should add the ICM7211 and ICM7212 are for 7 segment displays, not matrix ones.

  5. John C. says:

    I’d love to see this up on Kickstarter! I’d be in for a bundle of 10 or 20 of them.

  6. anverx says:

    This kindda looks similar to LED matrix controller that sparkfun are selling
    ( except theirs has an atmega that you can program. You can chain them same way (mechanically).
    Images can be either stored inside the microcontroller or sent over the input lines. While those things aren’t cheap, this looks like reinventing the wheel to me.

  7. charles says:

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