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Thread: Clarification on suitable ILDA cables?

  1. #1
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    Default Clarification on suitable ILDA cables?

    There are countless threads on this topic yet none seem to offer any concrete answers and I am hellava confused. I hope people in future will be able to reference this thread for clarification and answer their questions.


    1) Many advise that each twisted pair should be individually shielded when doing a "diy-style" run. But I took apart ILDA cable today and the only shielding present was a single outer shield, nor was it twisted in pairs. So what about non-twisted cable: Is a single outer shield sufficient for say 30m non-twisted runs? I have access to this for about $0.3 per meter.


    2) Stanwax's ILDA over cat5 brings in even more confusion. There is no shielding whatsoever within generic cat5 cable (please correct me if wrong) yet it allows runs of 50m. Now I believe this is because the twisted pairs cancel out noise - fine. But if the projector only uses R+,G+,B+ and gnd on the projector side what then? Or is the mere presence of R-,G-,B- running along the cable sufficient to cancel out noise (even though not connected to anything on the projector side). Or does the product use fancy circuitry to make up for single-ended projectors?


    3) What is stopping me from making up my own ILDA cable with 2x cat5 totally unshielded running next to one another and soldering DB25 connectors on each end? If I pay attention to the twisted pairs (ie: R+R-, X+X-) and so forth will I be good to go with 50m for a projector that uses only positive colour signals?


    4) For the above, would I want to use in each colour pair
    a) R+Gnd, G+Gnd, B+Gnd
    or b) R+R-, G+G-, B+B- even though the negatives remain completely isolated from the negative side of the lasers as the lasers are instead connected to ground.
    c) R+R-, G+G-, B+B- and connect the negative input to ground on my lasers (logic tells me that even though laser drivers are not built for differential inputs, anything below 0v will register as 0v so all will be fine)

    That is all I can think of at the moment.
    Thanks in advance!
    Last edited by Humphry; 09-04-2012 at 05:35.

  2. #2
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    Smile

    I can't speak to the ILDA over Cat-5 solution that Stanwax sells, as I've never used it. But I have run over 125 ft of standard ILDA cable (single external shield around all wires, individual wires *not* twisted with a ground and no individual shielding) with no problems.

    My understanding is that a Max-spec cable (with each wire twisted with a ground and individual shielding on each pair) is overkill for our application. Maybe if you were looking at an exceptionally long run of ILDA cable (say, 300 ft or so) this might be advisable, but I wonder if voltage drop on such a long run wouldn't end up being an even bigger issue.

    As for your idea of trying to build your own ILDA cables using a couple runs of Cat-5 cable and then soldering some DB-25's on the end - I have heard of people doing this for temporary shows. (Think one-night gigs at a nightclub where you need to run cable overhead.) It's easier to run cat-5 than ILDA, and it's cheap, so you don't care if you damage it when you pull it down, because you're going to toss it anyway. (I've even heard of people leaving it in place.) It's probably not recommended, but it should work. Worst case, bodge together a few cables in your garage and give it a shot. But no way would I ever plan to use this as a permanent solution.

    As for which pairs to use, it depends on how you have the ILDA connector on your projector wired. Either option A or C in your post above will work, but the standard is to use R+ and R-, G+ and G-, and B+ and B- (which would be your option C). However, many people cheat and just wire the positive color modulation signal up, and then connect all the negatives to pin 25, which is ILDA ground.

    This usually works just fine, because the negative modulation input lead on almost all lasers is tied to ground inside the driver. And since ground on the laser should always be connected to ILDA ground, it's all the same potential. (In fact, for a while the Pangolin Qm-2000 boards actually had the negative color output pins tied internally to pin 25 right on the board.)

    I've never seen a laser driver that had the modulation input completely isolated from the DC ground, so your "option B" above should be impossible. (That is, it should be functionally equivalent to option C, since the negative input will be at DC ground. So long as you have all your grounds connected to pin 25, it's all the same.)

    But to be true to the ILDA standard, you should use the individual negative color pins. (That's the way I wired my projectors.)

    Adam

  3. #3
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    i look at it as this yes they all will work just like with DMX however with dmx as low z mic cable will work issues can arrive due to that esp with long runs longer the run the bigger the "antenna" for interference. i go with the best cable budget allows. play it safe the cables do pump the blood of the show!

  4. #4
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    Didn't Marc (Insanity) post a link a long while ago on here to a heavy duty Cat 5 cable that he uses?

    I seem to remember it wasn't cheap but apparently very very tough.

  5. #5
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    I see - So basically it's not worth it to cut corners with cabling in the long run. It's interesting as I originally come from a purely hobbyist background where cheap=best and am now having to teach myself that quality investments (even if pricey) are better.

    @White Light - Probably something like this http://www.cat5ecableguy.com/inc/sdetail/27979

    I will still give a bash at using some super cheap shielded cable I found at $0.3 per meter and let you guys know how it goes. It can be kept as backup cable

    Once again thanks for your answers guys.

  6. #6
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    For what it's worth, I use Cables2Go pre-made cables, often using runs of 60-90 metres with no problems and at least one or 2 joins along the way. Voltage drop is your enemy, not interference. These are often taped up into a loom along with power and DMX signals to run from front of house.
    Frikkin Lasers
    http://www.frikkinlasers.co.uk

    You are using Bonetti's defense against me, ah?

    I thought it fitting, considering the rocky terrain.

  7. #7
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    Quote Originally Posted by Humphry View Post

    @White Light - Probably something like this http://www.cat5ecableguy.com/inc/sdetail/27979
    No I found the thread its this:

    http://www.fuzion.co.uk/ftproot/Fuzi..._Datasheet.pdf

    Someone suggested this was probably the same cable in the US:

    http://www.markertek.com/Cables/Bulk...l?BL-1304A-500

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