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DMX Opto/Relfections

Discussion in 'Lighting and Electrics' started by Jezza, Jan 18, 2007.

  1. Jezza

    Jezza Active Member

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    I'm in the pre-production mode for a concert we are producing at my high school and had a few questions about the proper way to wire up some moving heads. So far, I know I've got 4 StudioSpot 575s coming in, giving us a nice little moving package. However, they are 3pin and my board is 5pin. I know I can just use a 3 to 5 step down adapter but I'm wondering how that adversely effects the cable. I was once told that only 3pins are really used with most movers--5 are there for instruments that can talk back to the console. Is there any truth to that statement.
    Additionally, I might also be acquiring 4 Mac250s for the concert and would "like" to place them on the same DMX run as the StudioSpots. The Mac250s can recieve either a 3pin or 5pin signal from what I understand. Being that they are two different instruments, will I receive odd reflections in the line? Should I isolate the two different types of units using an optical splitter? In any case, both lines will be terminated. Any suggestions would be great.

    Thanks-
     
  2. soundman

    soundman Well-Known Member

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    If you have the opto I would suggest using it but it is by no means nesessary. Make sure the 3 pin cable is real data cable not just mic cable.
     
  3. Footer

    Footer Senior Team Senior Team Premium Member

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    Heres how DMX works... Pin 1 is a ground, Pin 2 is Data 1-, pin 3 is data 1+, pin 4 is data 2-, and pin 5 is data 2+. That is the "1990" standard pinup, Now you ask, where do I get this data 2 thing? Well you don't. It was in there so "someday" someone could do something with it. To be "true" 1990 DMX 512 USITT said that everything had to be 5 pin. So being intelligent folks, most intelligent light manufactures started producing gear that only had 3 pin in's and out's, because they were only using data 1, but (usually) supplied a 3-5 and 5-3 adapter with them to say they were 1990 DMX 512. Console manufacturers however only produced gear with the 5 pin in/outs. So basicly pins 4 and 5 do nothing (sorta). You can convert 3-5 and 5-3 all day long as long as pins 1-3 are connected to each other. This will not hurt anything. Just make sure you use legit cable that is made for data, not crappy mic cable.

    .....now my other rant....
    Pins 4 and 5 actually do something NOW.... RDN uses those pins for feedback from anything thats hooked up to it for remote monitoring, addresses, all that good stuff. RDN gear however is few and far between because it is such a new technology.

    ......rant #3.....
    Personally, I think RDN is a waste of time. Because most gear does not have 5 pin ins/outs it can not be upgraded to work with RDN. ACN (which also just got standardized) is the Ethernet standard for entertainment networks. It is a much better technology then anything DMX related, you can buy about 5x as much switching gear as one opto isolator, and you don't have to think about universes ever again!
     
  4. soundlight

    soundlight Well-Known Member

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    If you have a splitter, yes, use it, but if not, there should be no problem. DMX is just a control protocol, it is not bothered by different fixtures. BUT...make sure that you are using 3 pin data cable, not mic cable, and that you are terminating the last fixture in each DMX chain that you use. You probably already know all this, but just to recap the necessities. But, if your board doesn't have an opto-isolated DMX out, get an opto-isolator for the DMX line unless it goes through an opto-splitter for dimmers vs. movers or whatever. IMO, opto-isolating a DMX line is very important because you don't want to toast the board. It almost never happens, but in the one time out of a few hundred thousand or so that it does happen, you want to be ready.
     
  5. Van

    Van CBMod CB Mods Premium Member

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    As everyone else has stated, If you have the use of a splitter by all means use it. running to different types/brands/versions of fixtures will not cause reflections. Bad solders, bad kinks in the cable, and not terminating connections will cause reflections. I agree with Footer < I do that a lot lately > and his rants on DMX protocol. Follow his advice on the pinouts and you can build all the 3-5, 5-3 pin converters you want. Building your own terminators is also very simple. Double check your addressing and you'll be in business ! Good luck !
     
  6. SteveB

    SteveB Well-Known Member

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    [QUOTE= But, if your board doesn't have an opto-isolated DMX out, get an opto-isolator for the DMX line unless it goes through an opto-splitter for dimmers vs. movers or whatever. IMO, opto-isolating a DMX line is very important because you don't want to toast the board. It almost never happens, but in the one time out of a few hundred thousand or so that it does happen, you want to be ready.[/QUOTE]
    When I went to ETC End User Training in '04 I was shocked to discover that the Express consoles had NO optical isolation !.
    Then I learned that the reason, which was that it is as easy to replace the DMX output chip - which is what usually goes, as it is to replace an opto-isolater. In some consoles, the opto isolater circuit might well use the same type of chip. Thus, in ETC's logic, why bother putting in a separate opto-isolater when the DMX chip does the same basic thing - isolating the primary control electronics from damage.
    Made sense to me and I stopped worrying about it.
    What you do want to do is make sure that the console has some form of data isolation. Some cheaper controllers might not, and in that case a splitter will do the trick.
    SB
     
  7. Jezza

    Jezza Active Member

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    Guys, this has been great, really informative thank you. But a few follow up questions: I assume that when one puts an opto in line, its will a. split and boost the signal over multiple outputs but also b. "isolates" the signal. I am confused as to what this term "isolating" means as it pertains to DMX signal--please advise.
    Also, more and more I am seeing/hearing about ethernet replacing DMX as a control protocol as you all have mentioned. Aside from the obvious increase in channel control over one cable, what are the other advantages over standard 512 DMX? How do ethernet nodes and relays play into that? Additionally, the standard ethernet jack, at least the ones I am familiar with are very flimsy and would all be busted up after even one load out. Are there/is there any push towards a new, more robust connector/jack situation?

    Just to clarify, I don't have an opto, but I was considering renting one if I had to. Thank though!
     
  8. soundlight

    soundlight Well-Known Member

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    Basically, isolating means that you have a break in the line where there is an opto (opto as in light) circuit that transmits the signal via emitters and receptors to physically isolate the signal. Basically, this means that only signal (and not harmful voltages) can pass over the emitter/receptor circuit.
     
  9. Footer

    Footer Senior Team Senior Team Premium Member

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    http://www.btx.com/Categories.aspx?Category=8b5c6bab-e19d-4c61-a695-8aafc21acfbe
    Then there is tourflex which makes a very rugged cat 5e cable.
    DMX was not made for what we do to it today. It was meant to control dimmers, not tons of accessories and movers. Most moving lights take around 25-30 DMX addresses. DMX 512 has 512 addresses available. So that comes to about 15-20 fixtures per DMX universe. The reason there is so many slots per fixture is because DMX transmits data with 255 values per slot, so a unit that pans 400 to 560 degrees would pan 2 degrees (or so) per value. In order to give the unit more "resolution" 2 slots get doubled up to do one function (pan and fine pan, and tilt and fine tilt). This now gives you 65025 values for that action. With ACN you would not have to do this convoluted stuff. Also, you would not have to think of universes (Ethernet can carry around 30 (of the top of my head) or so DMX universes). The biggest thing though would be addressing as we know it will go away. Instead spending time going through truss addressing every fixture, DHCP will be address everything for you. The console will then be able to go out and discover each fixture, wiggle it, and then you patch it to what channel it needs to be. Right now your console knows nothing more then what you tell it whats out there. As far as the DMX line is concerned there is nothing but dimmers on the line. It doesnt know if you have a DL2 or a lightronics dimmer on the line.
    Right now we are in the converter phase of the revolution. ETC (etcnet3) Strand (Shownet and SN110 nodes) and Artnet are all ACN like protocols. I believe ETCnet3 uses the ACN standard. Dimmers are starting to be manufactured that takes ACN strait in, however I know of no intelligent fixtures that take ACN as of yet. So basically heres what we got... A console that puts out ACN or some similar protocol, goes into a switch, the switch then spits out data to the dimmers which take ACN strait in, and then to nodes which convert the ACN to one universe of DMX. This solution makes running DMX to positions much easier (you only have to run 1 line to stage), but is not the full solution.
     
    Last edited: Jan 19, 2007
  10. Jezza

    Jezza Active Member

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    Footer-

    Those are some pretty rugged jacks--I'll check out the TourFlex. That is a really great, simplified explanation of where the industry stands on the use of Ethernet as a means of communication. Thanks. It seems as though the posotive aspects of ACN would be pushing it through the industry much faster than it is at the moment. I'm sure ML manufacturues are reticent to a. build lights that are accept exlusively ACN protocol or b. consoles that step out of the DMX 255 relm. Hopefully, we'll see more of that in the comming years. In addition to some of the newer, truely innovate consoles out there (such as the Eos) the next few years sound like they are going to be really exciting and tumultuous. I'm still waiting on the L.E.D. Leko! Thanks a bunch.
     
  11. Andrewr

    Andrewr Member

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    Actually DMX was intended to control both inteligents and dimmers. (its just a higher baud rate version of CMX, which was developed by Colortran to control scrollers IIRC)

    As everbody has said, the fixture don't know the difference between 3 and 5 pin cable. If you are using Mac250 Entours (the regular 250 is only 3 pin IIRC) they make a very handy 3-5 coverter! the sockets are connected in parrallel, just don't try and use them as splitters too ;)

    As for ACN......well a couple of manufacturers are pushing alternative products... DMX only came about because it was something better than any existing protocol, and Strand gave away the analog alternative as part of the deal (not literarally, they just published that standard for AMX192)

    Oh, and the LED profile.....give me some time I'm kind of busy!
     
  12. SteveB

    SteveB Well-Known Member

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    Colortran CMX was simply a proprietary console-to-dimmers control protocol, same as Strands analog (which to be fair to Strand was adopted as AMX-192), NSI's, Electrol Control's. Kliegl and ETC's own, proprietary control console to dimmer protocols.

    Nobody was using these signals to do much else except console to dimmer. Very few scrollers existed (if any, they really didn't get popular until DMX had become viable) while the ML companies, such as VariLite and Morpheus, developed their own console-to-fixture protocols.

    If memory serves, the 3 biggie lighting companies in the early 90's were Strand, Kliegl and Colortran. C-Tran was a relative latecomer, but went the most intelligent route by adopting and modifying an electronic industry standard RS485 (if memory serves) standard digital control signal for their systems.

    Steve Terry - now at ETC, was one of the owners of Production Arts Lighting, in NYC and was moving the company into what is known as System Integration, as well as being a leader in the lighting rental market, especially for high end and sophisticated lighting packages. He was one of the early proponents of the industry developing a standard for anybodies control console to talk to any one's dimmers. This obviously made economic sense from the renters standpoint and the idea quickly moved forward under the auspices of the United States Institute for Theater Technology (USITT).

    FWIW, I'm of the understanding that the new ACN Ethernet based protocol was based on the VariLite network control protocol - VariLite being gracious enough to allow ESTA to adopt their technology.

    SB
     
  13. Footer

    Footer Senior Team Senior Team Premium Member

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    Its pretty simular to Shownet as that it runs on a TCP/IP network, not some weird thing that re-invents the wheel. One thing that I am really happy about with ACN is that is it is fully rout able and upgradeable. If anyone wants it, I have a powerpoint presentation put together by USITT for a lecture last year that pretty much explains everything you need to know in the short term about entertainment networks. PM me your email and I can send it (its a large file, i can't post it even zipped)
     
  14. gafftaper

    gafftaper Senior Team Senior Team Fight Leukemia

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    I mentioned this before in another thread I really recommend "Practical DMX" by Nick Mobsby for those of us who are a little shaky in our understanding of control networks. It has the whole history of DMX, explains in simple terms exactly how DMX works, covers all the components of a DMX network, Then it moves toward the future and covers Ethernet, ACN, and RDM. It'll set you back about $30 but it's well worth it.
     
  15. Van

    Van CBMod CB Mods Premium Member

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    If everybody want's it I could Talk to Gordon on monday and see if he'll talk me through his original visioning and give me a more accurate historical perspective on the evolution of dmx and where he thinks things are going. I spent all day Thursday working with him on some dimmable battery operated lanterns and we chatted all day about stuff dealing with the begining of intelligent fixtures and how several companies got thier start. It was fascinating.
     
  16. RonaldBeal

    RonaldBeal Active Member

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    Actually, DMX specs have never specified any use for pins 4 and 5, other than the connectors had to be 5 pin.
    In RDM's early stages of development, they discussed using pins 4 and 5 for return data, but in the final spec, the retun data comes down pins 1 and 2. It is sent on the same wire pair as the normal DMX stream, in between packet breaks. No new wiring is needed, just RDM compliant opto splitters, (that can pass the return data)
    On opto splitters:
    They provide electrical isolation between DMX streams so a fault in 1 wire will not take out other streams. The "opto" comes from the optical isolation circuits used to provide the isolation. Think of it as a IR remote control, and reciever on the same chip, so other than sharing a common power supply, there is no physical connections between DMX outputs.
    Hope this helps
    RB
     

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