DMX Opto/Relfections

[Jezza]

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-

[soundman]

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.

[Footer]

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!

[soundlight]

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.

[Van]

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 !

[SteveB]

[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

[Jezza]

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!

[soundlight]

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.

[Footer]

http://www.btx.com/Categories.aspx?C...5-8aafc21acfbe
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.

[Jezza]

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.