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Thread: DMX and the Helix

  1. #11
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    Default Re: DMX and the Helix

    Greg, I've been looking at pixel possibilities with the Helix, which for the moment at least, appears to require a DMX pixel driver board. There are a few around, but the new boards from Joshua 1 Systems (http://doityourselfchristmas.com/for...ighlight=j1sys) look very interesting.

    I assume I could connect one of these boards directly to a Helix channel bank for a single universe of 170 RGB pixels. But the intriguing thing is that the boards have a capability to drive 4 universes using the hyperDMX protocol. The boards are brand new, so info is a bit thin, but quoting from the above thread:
    "*hyperDMX is a non-standard extension of the DMX protocol developed by Joshua 1 Systems that can increase the bandwidth and capacity of a single RS-485 connection. hyperDMX can run at speeds up to 1500Kbps and deliver up to 4 universes of DMX data."


    Now speed and sheer volume of data could obviously be a problem (as mentioned before), but the protocol appears to be flexible (note use of words "up to") and I have to wonder whether we could squeeze maybe a couple of universes into each DMX channel.

    So, Greg, in your spare time while you're looking at pixelnet, perhaps you could look at the possibilities with hyperDMX?

    Cheers
    Dave

  2. #12
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    Default Re: DMX and the Helix

    Quote Originally Posted by adski View Post
    So, Greg, in your spare time while you're looking at pixelnet, perhaps you could look at the possibilities with hyperDMX?
    If you can find some additional information about the protocol I would be willing to look into it.
    Greg

  3. #13
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    Default Re: DMX and the Helix

    Thanks Greg

    I've emailed Ed at J1sys asking for a spec document, but meanwhile, you could check http://auschristmaslighting.com/foru...hp?topic=405.0 where there's a bit more info.

    There appear to be only 2 significant differences between hyperDMX and standard DMX:
    1) the use of alternate start codes to specify which of the 4 possible universes,
    2) option of higher transmission rates - 2x, 3x, 4x and 6x the standard 250 Kbps

    I'm sure it's more complicated when you get into the detail, but hopefully not too difficult.

    Dave

  4. #14
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    Default Re: DMX and the Helix

    I haven't heard back from Ed yet - he's busy getting his new boards finalised. But I've spoken to AussiePhil who developed the idea in the first place, and I've re-read the above thread. All the information is in there - just scattered around a bit.

    So, here's the essence of hyperDMX:

    hyperDMX supports up to 4 universes on a single RS-485 DMX line.
    For the 1st universe, the default DMX start code of 0 is used.
    Alternate start codes of 1, 2 & 3 are used for the other 3 universes.

    Non-standard transmission rates are allowed (multiples of the standard 250Kbps).
    Allowed rates are 250Kbps, 500Kbps, 750Kbps, 1Mbps & 1.5Mbps.
    The higher (non-standard) bit rates are only used within the channel slots (start code & data).
    All other timing conforms to the DMX standard.
    So for bit rates higher than 250kbps, the DATA will be faster but the DMX packet will still satisfy the standard timing requirements for Break, Mark After Break, Mark Time Between Slots, Mark Before Break and total packet length.

    In practice, data rates and multiple universes are functionally independent.

    So, it's not that complicated after all. The limitation will probably be in the compute power of the Helix hardware, but as you've mentioned previously, it could be (at least partially) possible on a Helix Network Node.

    Fingers crossed
    Dave

  5. #15
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    Default Re: DMX and the Helix

    Thank you for the additional information. How does the end device know the data rate for the channel slots? Would it be a problem to standardize on 1Mbps? This would allow up to four DMX universes to be updated at the same rate as standard DMX. It would also make the code fairly simple.

    As you pointed out the problem will be getting the data off of the microSD card fast enough. I have done some speed tests with the file system I use on the Helix and I'm getting better than 1300 KB/s read speeds. This is fast enough to support four DMX universes w/50ms event periods on each of the four channel banks for a total of 16 DMX universes (8,192 channels). Of course this will need to be verified and tested.

    Do you have the necessary equipment to do a test? I have several other things I'm trying to finish before this holiday season but once I finish those I may be able to get at least some rough code together. However, I don't have any way to test it.
    Greg

  6. #16
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    Default Re: DMX and the Helix

    Hi Greg

    The end device needs to be set up in advance to match the transmitted data rate - for the j1sys boards, I believe this is done through a USB port.
    I think a fixed 1Mbps hyperDMX option for the Helix would be just fine. In fact, I'd be delighted with that.

    I don't have the equipment YET, but I've pre-ordered 3 of the uDCG-P2 boards (see http://auschristmaslighting.com/foru...ic,2349.0.html) and hope to have them sometime next month. And I'll be ordering some pixels shortly, once I firm up on the display layout and figure out how much I can afford.

    So I'd be happy to test the code for you.

    Dave

  7. #17
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    Default Re: DMX and the Helix

    Greg and Dave,

    This is very exciting. I'll be following this closely and I can't wait to see the progress.

    Thanks for all the work.

    Bryan

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