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Thread: DMX Splitter - Isolation needed?

  1. #1
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    Question DMX Splitter - Isolation needed?

    So I'm debating buying or building a DMX splitter in order to split my yard into 'zones' and avoid so much wire criss-crossing the yard.

    I understand the reasoning/advantage behind opto-isolation, but the question is, do I really NEED isolation as it substantially increases the complexity and cost. There are some very cheap RS-485 to TTL converters on fleabay, 5 for $5 (US seller, even cheaper from China) and I was thinking of using 1 as the receiver, and connecting it's TTL data output to the TTL data input of the other 4 (as transmitters), and driving them all from the same 5V power supply that runs my controllers and other stuff. All my controllers are grounded and on the same circuit. Any problem with this? Seems to me like it would be the same electrically as just having them all daisy-chained (as it has been in the past).
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    Default Re: DMX Splitter - Isolation needed?

    It's not a necessity to have isolation, but obviously it's at your own risk - a fault in one zone could potentially knock out all the others.

    Your solution sounds feasible though, but a 1 to 4 splitter can be picked up for $50 (and rackmount ones for about $80) so keep in mind that there are options available that are purpose-built for what you're trying to achieve and won't break the bank!

  3. #3
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    Default Re: DMX Splitter - Isolation needed?

    Thanks Mark for your input!
    a fault in one zone could potentially knock out all the others
    So how is having a non-isolated splitter any different or any more risky than having everything daisy chained?
    but a 1 to 4 splitter can be picked up for $50
    Actually found an 8-way as cheap as $23 with free shipping. But they all* use XLR connectors and of course LOR, Renard, and most other home Christmas light controllers use RJ-45, thus I would need to build or buy a bunch of adapters. (Of course the RS485 -> TTL adapters I mentioned above only include screw terminals so still need to buy connectors anyway.) Also, none of the cheap ones, and not even many of the expensive ones say anything about isolation or transient voltage protection in the description.

    *Found some with RJ-45 connectors, starting at almost $500 which seems absurd because the circuitry is exactly the same and the RJ-45 connectors in bulk are considerably cheaper than XLR connectors.
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    Default Re: DMX Splitter - Isolation needed?

    So how is having a non-isolated splitter any different or any more risky than having everything daisy chained?
    It's a very good point - it's no difference but usually splitters are being used in an environment with longer cable runs between fixtures so probably more likely to happen, but if you were having to run back and forth across you're garden you'd be no better off!

    XLR to RJ45 adaptors would be very easy to put together, so a cheap off-the-shelf unit wouldn't need much work to be compatible with your connectors.

    I would've assumed that most splitters contain isolation, but if they don't advertise it then it's impossible to know without cracking the cover off!

  5. #5
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    Default Re: DMX Splitter - Isolation needed?

    Another thing to consider:
    Many daisy-chained DMX fixtures don't do a thing to the signal. They simply tap the line, and watch for their assigned address to come through and then act on that.
    Most splitters that I had (no longer) had active components. They provided isolation of signal, and repeated the incoming signal to each of the outputs.

    https://www.sweetwater.com/store/detail/DataStream4--chauvet-dj-data-stream-4-4-port-dmx-splitter

    This one worked very well. (I do not work for Sweetwater, but I have purchased a bunch of stuff from them.)

    Even this one has both types (non-repeated and repeated) outputs. "Thru" is usually just that with no added signal boost. "Out" has a signal regeneration and isolation on each output.
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    Default Re: DMX Splitter - Isolation needed?

    Most of the cheap DMX splitters have zero isolation even though some of them imply that they do. Isolation on the input side will protect the data source. Isolation of all outputs will help with ground issues.

    So a fully isolated DMX splitter is best, but a non isolated one can still give you better data integrity. It also makes it possible to have a star wiring layout which may suit the application better.
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    Default Re: DMX Splitter - Isolation needed?

    makes it possible to have a star wiring layout which may suit the application better.
    which is exactly my point of all this. Sure, isolation would be nice, but I've run a bunch of daisy-chained controllers for 15 years now and never had a blow-out. Likewise, a splitter typically "amplifies" (or more accurately, regenerates) the signal, good for long cable runs, but that hasn't been my problem either.

    I have a hunch there is a small market for something like this in the Christmas lighting community, especially if the price was right. So I think after the crush of the season, I may design a schematic and have some PCBs made, maybe a dozen or so. I also figured it could have jumpers to select LOR, Renard, or standard DMX pinouts for each jack. It's aggravating that all 3 of these (and I have all 3 types) use the same cables and connectors but different pinouts and thus I have to make crossover cables and make sure I have them all connected correctly.

    I suspect that in kit form (PCB + components) it would sell for $30-40. Anyone interested?
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    Default Re: DMX Splitter - Isolation needed?

    I thought I'd seen a few DMX splitter designs on this forum over the years?

    You could certainly make one with RJ45 connectors with jumpers behind each one to set the ESTA / LOR / Renard pinouts.
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