# DMX out from ETC wall jack panels?



## austio (Feb 19, 2015)

I have been a long-time browser of Control Booth forums, and always learn something new to use in my shows. 

But today I need help. 

I have an ETC wall panel with "Console Input" "RFU" & "ETCNet" (NOTE: it is called ETCnet1 now...)

I need to get a DMX signal out of this panel. Is that possible? The reason is, the panel is located on the stage wing, so it is the nearest most logical place to plug in a DMX controlled fixture I want to use. My console is plugged in BOH, but only uses "Console Input" on its panel.

The venue was originally wired with ETC stuff and an Expression 24/48, and had an RFU, all of which plugged into the three jacks. However, they now use an ETC Element. Someone recommended it as an "upgrade" for use with newer DMX controlled fixtures and LED lighting (venue has none), failing to notice that there are NO (zero, none, nada) DMX outputs anywhere else in the venue, so unless it is possible to get DMX from the 3 jacks mentioned above, I will need to run lots of extra wire.

Any thoughts?


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## derekleffew (Feb 19, 2015)

derekleffew said:


> lightman02 said:
> 
> 
> > You can use a gender changer to tap off that connection if you wanted to, those pins become live with DMX when DMX is fed into the system from the board. ...
> ...




> The building is likely wired one of three ways:
> 1) Booth DMX Input goes to dimmers' DMX Input A and Stage DMX Input goes to dimmers' DMX Input B, and dimmers are set to take either or both on an HTP basis. This is the only "proper" wiring, but means that the Stage Input cannot be used as an output.
> 2) The Booth DMX Input loops through the Stage DMX Input, then onto the dimmers.
> 3) The Booth DMX Input and the Stage DMX Input are both homerun to the dimmers, where they are two-fered on the same dimmer input.


Probably #2. A quick call to ETC Tech Services at 1-800-688-4116 and they can look up your job number and confirm how your building was wired.


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## SteveB (Feb 19, 2015)

austio said:


> I have been a long-time browser of Control Booth forums, and always learn something new to use in my shows.
> 
> But today I need help.
> 
> ...



Sounds like the stage box has a chassis mount male 5 pin XLR (console input), a 6 pin XLR - maybe chassis mount male ? (RFU), and either a Cat5 connector or a BNC connector for the ETC Net1.

From that configuration I would assume the 5 pin XLR for console connection would allow a local console to send DMX only to the dimmer rack, possibly on the B DMX connections in the dimmer rack(s). I would then also assume the 6 pin and the Cat5/BNC to run to a similar box in the booth where they would have hooked up to the console.

If the ETC Net is Cat5, you can get adapters to 5 pin XLR to get a DMX output off the Element at that stage jack location. If not Cat5 and it's a BNC, you might be able to get adapters made from 6 pin RFU to 5 pin XLR's to allow DMX to use the RFU cable - which I believe is DMX compliant. Best option would be to change out the 6 pin connectors to 5.

I'd be calling Steve Short at LiteTrol Service. If you e-mail him pictures of the boxes he can advise and figure out the best solution.

http://www.litetrol.com/


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## derekleffew (Feb 20, 2015)

SteveB said:


> you might be able to get adapters made from 6 pin RFU to 5 pin XLR's to allow DMX to use the RFU cable - which I believe is DMX compliant. Best option would be to change out the 6 pin connectors to 5.


@SteveB, thank you. I always forget about using the RFU wiring for DMX512 porpoises!

starksk said:


> If the wire was pulled according to ETC Spec (Belden 9728 or approved equal), the only difference with the RFU cable would be the extra set of conductors and shielding. Technically, RFU uses the same type of underlying data protocol (RS-485) that DMX uses, so data transmission down the pairs would not be a problem.


Changing the RFU's XLR6 s to XLR5 s is the best solution.
-----
Minor niggle:

austio said:


> ... and an Expression 24/48, and had an RFU, ...


'Taint no such animal as "Expression 24/48"; you mean an Express 24/48.


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## jfremm (Feb 21, 2015)

Hello everyone,

This question may not make sense and I apologize in advance, but I am really looking for some help. In our auditorium, we have a DMX input(male pins) in one of our wings. My question to you all is if you think the purpose of that input is for a light board, or if I could use it for a fixture I want to hang. I'm not really sure where to go with regards to this question, but perhaps other technicians might have a plausible answer. 

Basically, we are looking at upgrading our current cycle to the Altman Spectra Series LED fixtures. I was wondering what the best way to run this back to our board would be. I figured if this DMX input worked, if at possible, just use that which connects to our board (I think). 

Thank you


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## Les (Feb 21, 2015)

A DMX input is for a console or RFU. What you need is a DMX output.

You could possibly turn the input in to an output by changing the connector to female and re-routing the other end, but it all depends on how your system is wired.

The other options are to A). put an opto-splitter and the booth and run a separate DMX line to the stage or B). Tap off the DMX in your dimmer rack which may require surgery and is best left to qualified personnel.


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## SteveB (Feb 21, 2015)

jfremm said:


> Hello everyone,
> 
> This question may not make sense and I apologize in advance, but I am really looking for some help. In our auditorium, we have a DMX input(male pins) in one of our wings. My question to you all is if you think the purpose of that input is for a light board, or if I could use it for a fixture I want to hang. I'm not really sure where to go with regards to this question, but perhaps other technicians might have a plausible answer.
> 
> ...



I'm guessing, but and most of the time, the purpose of an additional input jack located other then the booth, is to allow a visiting or house console to activate the dimmers from the "other then booth" location. As such the wiring usually goes to the dimmers. If an ETC Sensor system, there's a "B" input to the dimming system for this 2nd DMX signal and I would suspect that's what your Input connection does. One clue is the male chasis connector being typical of a connection designed to receive a DMX signal from a console.

No way to really know unless you have access to the installation wiring plans. Or you can hookup a console and see if it activates dimmers, but I'd rather see the plans first. 

One solution and I'd check with ETC, is if this connection port is indeed on the DMX B port of the dimmers would be to have this changed at the very first dimmer rack to land on the A port, which would then route the booth console signal to the dimmers and back this connection. Then change the connector to a chassis female 5 pin. I believed you are "allowed" one pass thru of this type without issue.


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## RickR (Feb 22, 2015)

A vote for calling ETC, and some warnings!

Their drawings are how it was designed and only sometimes updated to 'as built'. Then life happens to the building and things get really interesting. Before making any wiring changes (especially in a school) someone should trace out the actual wires.

I have had bad luck converting RFU wiring to DMX. Yes the wire should work, but there are often many more input locations. They are also wired 'touch-n-go' which is not to the DMX/RS485 standard. There may be other issues but I suspect it would take a fair bit of detective work and an oscilloscope to sort out. 

In another post I detailed using the second pair of the base DMX runs. This too is off the standard if only in philosophy, but it does classify as "future use"


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## austio (Mar 2, 2015)

My original post had a few mistakes, as some of you noticed. First off, it was not ETCnet, it was ETCLink.


SteveB said:


> Sounds like the stage box has a chassis mount male 5 pin XLR (console input), a 6 pin XLR - maybe chassis mount male ? (RFU), and either a Cat5 connector or a BNC connector for the ETC Net1.



But the Steve was right on the rest of the box.


derekleffew said:


> Probably #2. A quick call to ETC Tech Services at 1-800-688-4116 and they can look up your job number and confirm how your building was wired.



I called ETC, and was confirmed that the console input on the box could not be used. However, I was wondering about your description of possible wiring schemes, and took the box off the wall, and saw that it is a chain from another jack in the house, so DMX does flow through Console In, but putting that to a daisy chain to get DMX out would be a huge pain, though not impossible. It would also make for a very large worrisome daisy-chain before it gets to the main Unison/Sensor dimmer system that I would not like to deal with.


derekleffew said:


> Changing the RFU's XLR6 s to XLR5 s is the best solution.



Thank you for this insight. I thought about this, but was wondering; would I then loose the ability to use the RFU, or does the RFU only work with the retired Express, and therefor its functionality is already gone (cannot be used with Element)? There are multiple RFU locations, as well (more than Console or ETCnet jacks), so converting these for DMX might be the ticket, as you suggest. In such a situation, is the DMX signal coming from the Unison system (as the Element is already sending DMX to that), or would I need to be plugging the re-purposed RFU line into the DMX output on the back of the Element?


derekleffew said:


> 'Taint no such animal as "Expression 24/48"; you mean an Express 24/48.



You are right.

I have actually purchased some wireless DMX units, and I will just use the second universe on the Element, but the venue (and I) will need a more permanent and robust setup in the future, so I will keep this thread handy.

I know this was in response to the other person's question on my thread, but it pertains to me as well I think... I have no idea what wired 'touch-n-go" means...?


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## lightman02 (Mar 3, 2015)

austio said:


> My original post had a few mistakes, as some of you noticed. First off, it was not ETCnet, it was ETCLink.
> 
> 
> 
> ...


You can use the DMX input port on the box as an output when you are feeding DMX from one of the other existing ports such as the booth by using a gender changer as I stated before. It's all on the same data bus and there is no issue when using it that way and if ETC is telling you no, then I'm sorry they are misleading you. It's thesame is if you were daisy chaining fixtures, the only difference is the gender in this case. If you do decide to use that port as an output and have a lot of DMX fixture off that line then go into an OPTO from there. As long as that port is on the same side as your control console it will work.


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## robartsd (Mar 3, 2015)

lightman02 said:


> You can use the DMX input port on the box as an output when you are feeding DMX from one of the other existing ports such as the booth by using a gender changer as I stated before. It's all on the same data bus and there is no issue when using it that way and if ETC is telling you no, then I'm sorry they are misleading you. It's thesame is if you were daisy chaining fixtures, the only difference is the gender in this case. If you do decide to use that port as an output and have a lot of DMX fixture off that line then go into an OPTO from there. As long as that port is on the same side as your control console it will work.


I'm guessing that ETC is telling him no because the project information they have shows that this would not work because either 1) it would create a Y in the DMX because this port is between the booth and the dimmers (may work with possible reliability issues) or 2) this port goes to a secondary input on the dimmers and does not see the booth output (will not work at all).


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## lightman02 (Mar 3, 2015)

Well like I was saying, it has to be on the same port, most I have seen are. As far as a Y split, you are not creating a Y split, you are actually treating the dimmers as sort of a fixture that you would daisy chain out of, it the same wiring path flow wise.


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## robartsd (Mar 3, 2015)

austio said:


> Thank you for this insight. I thought about this, but was wondering; would I then loose the ability to use the RFU, or does the RFU only work with the retired Express, and therefor its functionality is already gone (cannot be used with Element)? There are multiple RFU locations, as well (more than Console or ETCnet jacks), so converting these for DMX might be the ticket, as you suggest. In such a situation, is the DMX signal coming from the Unison system (as the Element is already sending DMX to that), or would I need to be plugging the re-purposed RFU line into the DMX output on the back of the Element?


The RFU port was for a wired remote for the Express. The Element does not use this remote, so the wiring could be repurposed without a loss of functionality. The Element supports network, USB, and phone remotes. As you've stated that there are many RFU ports, you'll want to make sure that your reuse of the wiring does not create problematic topography for your DMX signal.


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## DavidNorth (Mar 3, 2015)

robartsd said:


> I'm guessing that ETC is telling him no because the project information they have shows that this would not work because either 1) it would create a Y in the DMX because this port is between the booth and the dimmers (may work with possible reliability issues) or 2) this port goes to a secondary input on the dimmers and does not see the booth output (will not work at all).


 

lightman02 said:


> Well like I was saying, it has to be on the same port, most I have seen are. As far as a Y split, you are not creating a Y split, you are actually treating the dimmers as sort of a fixture that you would daisy chain out of, it the same wiring path flow wise.


 
It was very common, when those system were designed, to have DMX Input jacks daisy-chained through the facility on the way to the dimmer racks. This is what creates the moniker, "touch and go." What we did was take DMX from the booth Input, run the wire to the next DMX Input jack [touch], and then run the wire [go] to the next DMX Input jack, and so on, until we reached the dimmer racks. The reason we did this is because users wanted the ability to plug the console in at various places in the building [booth, FOH, backstage] depending on what they wanted to do for their show. This means that there was only ever one DMX source and then DMX racks on the other end without a plan for other uses. The notion of having DMX Outputs around the building only became prevalent after DMX scrollers and moving lights came in to popularity.

So yes, in this wiring scenario, you would indeed create a "Y" if an Input was used as an output, however, you would be ok if you placed a splitter or booster right at the Input being used as an Output every time you want to use that data. If the dimmers were in the middle of the wiring run, instead of the end, then you would not have a "Y" situation. This one is a "Y". Use a splitter/booster or don't use the Input as an Output, please, as you could end up with corrupted data and loss of control.

Yes, the RFU wiring could indeed be reused as another data run given installation of the correct connectors. Do be warned that this is also a "touch and go," which means you could use one Input and one Output only, unless of course each Output also utilized a splitter/booster.

Later ETC systems did use splitters and data homeruns to distribute DMX throughout a space until network solutions took over.

David


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## lightman02 (Mar 3, 2015)

David, I was assuming that the connections were terminated at the dimmer itself and not intercepted in the middle of the data run. But you do agree that and input is not always have to be used as an input and can be output under certain situations which is my point. However if you look up schematics of how dimmers and fixtures pass dmx u will see where I'm coming from. Also DMX really doesn't have an in and out.


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## SteveB (Mar 3, 2015)

Well, and as a quibble, DMX does indeed have and in and out. The out would be the transmitting device and would have a female 5 pin XLR connector on the transmitting source. The "in" is of course at the receiving device(s), which would have male XLR 5pin (one hopes).

The fact of this is why we were able to ascertain from the OP description that the chassis mounted male connectors in a stage located box, were likely to be additional input locations for additional consoles (the touch and go system that DN describes). Had it been a female connector, it would have probably been a DMX send port from a DMX source - booth control ?, splitters somewhere ?. 

And as described in posts above, certainly the input connections "could" be re-purposed, but as they in this scenario probably don't go back to the booth, re-purposing as an output from a booth located console isn't going to work, as the existing DMX cable might well be the only connection from the booth console to the dimmers. Thus a recommendation to maybe re-use the Link cable, having disconnected it at the dimmers with appropriate 5 to 6 pin adapters.


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## lightman02 (Mar 3, 2015)

Dmx is transmitted from the board it's then looped through every dimmer, mover, fog machine, etc. It is not retransmitted from device to device with an opto being an exception to this rule.
This is why dmx still passes even when your dmx devices are unplugged from their power source. As I stated DMX does not have an in and out really it has transmit and receive only. The console being the transmitter.


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## DavidNorth (Mar 3, 2015)

lightman02 said:


> Dmx is transmitted from the board it's then looped through every dimmer, mover, fog machine, etc. It is not retransmitted from device to device with an opto being an exception to this rule.
> This is why dmx still passes even when your dmx devices are unplugged from their power source. As I stated DMX does not have an in and out really it has transmit and receive only. The console being the transmitter.


 
Well, it's not always true that the DMX In and Out are the same on DMX products. It does indeed depend on how they are designed, and yes, I have looked at many schematics. [My degree is in electrical engineering and I have done product repair and support for several decades. ]

Since some products do receive DMX and then retransmit a new DMX stream as an output, I am making a general statement that an In is an In and Out is an Out. Technically, an In is tied to a Pass Through and an Out is a transmitted DMX signal. it is unfortunately very common that we interchange the terms DMX Out and DMX Pass Through when they are not the same thing. Thomas I think you mean to use Pass Through.

So, to do some fun ASCII graphics, since I don't have time to sketch today.....here's the system the OP posted.

[Console] - [DMX In] - - - - - - - - - - - - - [DMX In] - - - - - - - - - - - - - [DMX In] - - - - - - - - - - - - - - - [Dimmers]

If he was to patch a DMX cable into the backstage DMX In jack, he will have a "Y" as seen here:

[Console] - [DMX In] - - - - - - - - - - - - - [DMX In] - - - - - - - - - - - - - [DMX In] - - - - - - - - - - - - - - - [Dimmers]
--------------------------------------------------------------------------------------------|
--------------------------------------------------------------------------------------------|
--------------------------------------------------------------------------------------------|- - - - - [LED] - - - - - - - - - [LED]

You can in fact cheat, but you have to use turnarounds and you have to always use a splitter or booster and do this:

[Console] - [DMX In] - - - - - - - - - - - - - [DMX In] - - - - - - - - - - - - - [DMX In] - - - - - - - - - - - - - - - [Dimmers]
--------------------------------------------------------------------------------------------|
----------------------------------------------------------------------------------[Splitter/Booster]
--------------------------------------------------------------------------------------------|
--------------------------------------------------------------------------------------------|- - - - - [LED] - - - - - - - - - [LED]

But, that splitter or booster needs to be at the jack. Steve has the cleaner solution to reuse the now unused ETCLink cabling. Better yet, get a technician in there that knows how to correctly reuse the wiring and install new connectors, and then this is a system that will always work no matter who uses it in the future. Isn't that what we should really be looking for?

David


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## SteveB (Mar 3, 2015)

lightman02 said:


> This is why dmx still passes even when your dmx devices are unplugged from their power source. .



With an opto again being an exception to the rule.


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## lightman02 (Mar 4, 2015)

DavidNorth said:


> Well, it's not always true that the DMX In and Out are the same on DMX products. It does indeed depend on how they are designed, and yes, I have looked at many schematics. [My degree is in electrical engineering and I have done product repair and support for several decades. ]
> 
> Since some products do receive DMX and then retransmit a new DMX stream as an output, I am making a general statement that an In is an In and Out is an Out. Technically, an In is tied to a Pass Through and an Out is a transmitted DMX signal. it is unfortunately very common that we interchange the terms DMX Out and DMX Pass Through when they are not the same thing. Thomas I think you mean to use Pass Through.
> 
> ...



It's like I said the port is part of the same data bus as long as it was wired properly even though it is labeled as input it can be used to carry the same data signal to another device and you should use an OPTO as the cable length from the transmitter is


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## lightman02 (Mar 4, 2015)

It's like I said the port is part of the same data bus as long as it was wired properly even though it is labeled as input it can be used to carry the same data signal to another device and you should use an OPTO in either case as the cable length from the transmitter is probably lengthy at that point anyway. I’m assuming they would like to branch it out to several locations on the grid beyond that. As far as re-purposing unused cable, yes that can be done but I don’t see it adding any integrity at all in this case. The original question for this thread was can a port that is labeled as input is used as an output and the answer is, YES. No need to hack or change wiring or make thing over complicated however if they wanted a whole extra universe I can see the reason for wiring however that can also be done using the same cable if it has enough conductors. If you know of any devices that re-broadcast and don't pass through DMX besides OPTOS and processors, I would love to know what those are. As far as electrical engineering degrees go, well I’m a broadcast engineer for a major television network, I kind of know how signal flow and distributions work.


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## DavidNorth (Mar 4, 2015)

DMX data system "Y" cable runs do provide unmanaged data reflections and the possibility of corrupting the data thereby causing unwanted or loss of control. There are only two ways to eliminate the possibility of a "Y" in the specific system listed above: place a splitter/booster at the DMX In jack backstage with as short a DMX cable as possible between the wall jack and the splitter/booster, or use a different cable such as the ETCLink wiring. The opto must be used to eliminate data reflections, not because of cable length issues. DMX is good for well over 1000' feet and I highly doubt these systems have that much cable in them even when a "Y" is added.

For me, this is about data integrity, system stability and system usability. So, I agree with you that the In can be used as an Out, but only under very specific caveats that have to be remembered each time. I do not agree that system integrity is not improved when using the other cable system. It is far improved. I would like to somehow convince you that "Y" wiring in DMX data systems is not a solid system. Since you know how signal flows and distribution works, I would hope that you agree that many "Y" and "T" systems do not work.

So sure, you can always have an opto bolted to the wall, with a turn around cable plugged in to the DMX In backstage, and for that the answer of YES does work. I will argue that it is not best practice and likely someone in the near future [especially at a school] will remove the opto and wonder why on certain days the DMX system doesn't work.

As far as devices that rebroadcast, let's remember that we started with an absolute statement that none did, that changed to add optos, then changed to add boosters and then changed again to add processors. Some older DMX devices did indeed rebroadcast. I do not have a list, but there were some old movers and scrollers that did this before people really understood everything they needed to do in their designs. My guess is that we could place a table full of DMX devices in front of people and ask them which ones rebroadcast and almost no one would get them all right. We want to avoid people having to think about the use of their cabling plant to make it work for this specific show. As has been said before, DMX system failures only occur when you least expect them to. Perhaps that should be called Terry's Law.

I am trying to use this forum to educate people in the robust design and use of their system so that they never spend hours troubleshooting something that could have been easily corrected for in their system design.

David


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## austio (Mar 4, 2015)

Wow. As a first timer, my opening post has garnered way more information and replies than I expected. Thank you to everyone who has responded.

In the past, I installed a very small DMX system using an opto between the console and the rest of the system, to support future use of other DMX fixtures and LEDs, so I am aware of the need for such things to maintain reliability and integrity.

I did not know how such a device (or any, for that matter) could be reliably used given the situation I found in the OP.


DavidNorth said:


> ... There are only two ways to eliminate the possibility of a "Y" in the specific system listed above: place a splitter/booster at the DMX In jack backstage with as short a DMX cable as possible between the wall jack and the splitter/booster, or use a different cable such as the ETCLink wiring. The opto must be used to eliminate data reflections, not because of cable length issues.
> ...
> So sure, you can always have an opto bolted to the wall, with a turn around cable plugged in to the DMX In backstage, and for that the answer of YES does work. I will argue that it is not best practice and likely someone in the near future [especially at a school] will remove the opto and wonder why on certain days the DMX system doesn't work.



As David points out, he has drawn an exact schematic of the situation I have, and how a "Y" would have been created had I just used a gender-bender at the wall jack. This was one reason I posted (though not explained) as I thought could be problematic, and hoped a solution would present itself.

Indeed, it seems we can thus break it down to two permanent or semi-permanent solutions (other than my temporary wireless solution).
1) A quick hack, without an opto at the jack, would be possible, yes. Probably would work in this situation as runs from the jack are short. _A better solution_ would be to use an opto. But potential user ignorance issues in the future.
2) Future rewiring of the existing RFU jacks for a permanent, robust solution, using optos to avoid the linked topology of the jacks that is likely present, especially if multiple DMX drops are needed at one time.

Everyone's insight has been great. I hope others will find this thread as informative as I have.


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## lightman02 (Mar 4, 2015)

So it's ok to send a signal at the middle of a data bus according to your design. But it's not ok to go out from the same data stream because of a wall plate label. Is that correct?


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## SteveB (Mar 4, 2015)

lightman02 said:


> So it's ok to send a signal at the middle of a data bus according to your design. But it's not ok to go out from the same data stream because of a wall plate label. Is that correct?



Tom,

You are arguing about a system that isn't built these days. It was not un-common to see the touch-and-go input systems as DN described, but this was before the widespread use of other devices listening that were other then the dimming system. Thus ETC found it acceptable (and likely never had issues with) a touch-and-go. So yes, you would see an input in the middle of the data bus, but in reality and use, the primary console, as the initial source of DMX at the start of the data buss, would have been off-line, as this system typically had no ability to merge DMX.. So, yes it was considered OK.

It would obviously not be today, but we are talking 20 years ago on that type of design, with lots learned about how to better configure systems.


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## BillConnerFASTC (Mar 4, 2015)

As Steve Terry once said, you can run DMX on a couple pieces of barbed wire and it will work .... until it doesn't. I'll adhere to the DMX standard which I don't think even allows the mid tap with a "very short cable" to a splitter. Too many DMX problems on actual installs that I can't afford not to insist it be done to best practice. While the consequences for a non-professional production of DMX going flaky are usually not catastrophic, why do it wrong?


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## lightman02 (Mar 5, 2015)

BillConnerASTC said:


> As Steve Terry once said, you can run DMX on a couple pieces of barbed wire and it will work .... until it doesn't. I'll adhere to the DMX standard which I don't think even allows the mid tap with a "very short cable" to a splitter. Too many DMX problems on actual installs that I can't afford not to insist it be done to best practice. While the consequences for a non-professional production of DMX going flaky are usually not catastrophic, why do it wrong?




How do you know my way is wrong, you’re not proving anything to me to prove it either? Not to mention the original post talked about using the end of the DMX chain and not the center tap. Most fixtures the two DMX ports are wired directly to each other with a center tap for the transceiver chip. Most quality fixtures have an isolation circuit to protect the DMX lines from chatter, cheap stuff does not. If you want me to post actual traces and schematics to prove a point, I would be more than happy to spend the time. So don’t tell me I’m wrong when you aren’t providing any hard documentation from anyone just your opinion. Do things the way you want to, it’s not my problem and I’m done with this thread. As far as a system made 20years ago; you want to tell me they don’t put a DMX port in the control booth and on the stage tied to the same universe anymore?? DMX hasn’t really changed in 20 years if you haven’t noticed.


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## GreyWyvern (Mar 5, 2015)

lightman02 said:


> DMX hasn’t really changed in 20 years if you haven’t noticed.


While DMX hasn't really changed, the way it is being used has, quite a bit. There is this neat, new thing called RDM. You should check it out! 

@lightman02, please read the replies from SteveB and DavidNorth a little more carefully. You'll see why you are getting flak for your replies, they kind of don't make sense. Look at @DavidNorth's signature. See where he works? He said that ETC does do things differently now because of the way things have changed. It's also clear you didn't even read the original post carefully either, as there is no mention of where in the line the OP would be connecting. Truth is, he probably doesn't even know himself.
If you are going to reply, take the time to know what you are replying to. After you write your reply, don't just hit post. Do what SteveB says, "Read it again, before pressing Send". Also, remember, no one is forcing you to pay any attention to anything in this thread, or anywhere on CB. If you don't like something that is said, just ignore it and move on. You don't have to reply if you don't want to. No sense in trying to start an argument, especially someplace like CB where there are plenty of people that probably know much more than you or I. Don't reply just for the sake of doing so. Let's keep CB a happy place!


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## lightman02 (Mar 5, 2015)

GreyWyvern said:


> While DMX hasn't really changed, the way it is being used has, quite a bit. There is this neat, new thing called RDM. You should check it out!
> 
> @lightman02, please read the replies from SteveB and DavidNorth a little more carefully. You'll see why you are getting flak for your replies, they kind of don't make sense. Look at @DavidNorth's signature. See where he works? He said that ETC does do things differently now because of the way things have changed. It's also clear you didn't even read the original post carefully either, as there is no mention of where in the line the OP would be connecting. Truth is, he probably doesn't even know himself.
> If you are going to reply, take the time to know what you are replying to. After you write your reply, don't just hit post. Do what SteveB says, "Read it again, before pressing Send". Also, remember, no one is forcing you to pay any attention to anything in this thread, or anywhere on CB. If you don't like something that is said, just ignore it and move on. You don't have to reply if you don't want to. No sense in trying to start an argument, especially someplace like CB where there are plenty of people that probably know much more than you or I. Don't reply just for the sake of doing so. Let's keep CB a happy place!



Yeah, I know what RDM is and this is not about RDM, it's about DMX but RDM would still not be an issue either. As far as saying someone else is right because they work for ETC or Apollo, well sorry no thanks.


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## GreyWyvern (Mar 5, 2015)

lightman02 said:


> As far as saying someone else is right because they work for ETC or Apollo, well sorry no thanks.


Umm... not sure why Apollo is being brought up....

So, what are you saying? When you have an issue with a product, do you not call the manufacturer because even though they made the product, their solution may not be right because of what you think? You might not agree, but industry leaders are typically right. If they weren't, they likely wouldn't be an industry leader. Just because you might not like something, that doesn't mean it is wrong. There are different ways of doing the same thing, some may be better than others, and one person may prefer one over another. That doesn't make any of them wrong. Opinions are exactly that.
I apologize, I didn't realize you didn't know who David North is. He happens to be one of the people on CB that I was talking about that knows more than you and me about things like DMX. Just because he is the GM for ETC's rigging department, doesn't mean he only knows rigging.


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## lightman02 (Mar 5, 2015)

Like I said I'm done with this conversation. David North I do not know personally and don't care who he works for, ETC is not the DMX rulers of the world and neither is David North. So it's safe to say that just because he works for ETC that it's said and done and whatever he says is set in stone.; that his opinion is final. I work on things a hell of a lot more complex then DMX data so my stance does not change. Once again I am done posting in this thread. Have a nice day, been doing lighting since 1996 and no DMX problems. Just because I don't work for ETC or any lighting manufacturer does not mean I don't know what I am doing and my thoughts are less important. That's my point, lets not have hard feelings, we are all trying to help each other so let's not get out of hand. I do appreciate vendors taking the time but that doesn't mean they are always right. I've had several vendor reps on sites that had no clue what they were doing. I am not saying that about you or David but the vendor isn't always perfect either.


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## GreyWyvern (Mar 5, 2015)

Like I already said,

GreyWyvern said:


> If you are going to reply, take the time to know what you are replying to.


You were so quick to reply that you didn't even realize that I never implied or said that you knew him personally or that ETC is "the DMX rulers of the world".


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## lightman02 (Mar 5, 2015)

GreyWyvern said:


> I apologize, I didn't realize you didn't know who David North is. He happens to be one of the people on CB that I was talking about that knows more than you and me about things like DMX. Just because he is the GM for ETC's rigging department, doesn't mean he only knows rigging.



I don't know how much he knows, like I said never worked with.


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## DavidNorth (Mar 5, 2015)

Thomas,

I wish I could have a one on one conversation with you. This is not, and has not ever been, personal. I've tried to make it clear that I am representing information and tried to also address your questions and points. Clearly I have failed. Do not listen to me because of where I work - I've never asked for that or expect it.

For those that are interested, I will try to address some of these topics.

In fixtures, and other devices that have a DMX connection, there is indeed a stub. This is defined as the amount of distance between the transceiver chip and the DMX transmission line. In some cases this distance is zero because the lines connect at the input of the chip which means the chip is sitting directly on the data bus. In other products, this distance might be 6" or so as the DMX In and Thru connectors will be soldered together at the front panel and then a single twisted pair then goes to the board and chip. Best practice design [elicited by the standard and several use docs] say that any stubs should be kept as short as possible. So yes, at each device that has a non-zero stub, that is a "Y" or "T". 

It is true that a DMX console plugged into the middle of a line is sending data in two directions, ie a "Y" or "T". Technically, an RS-485 line can be terminated at each end and this will eliminate reflections on the line. This is not what was done many years ago, nor to this day when such systems are installed. I can tell you, however, that I have installed terminators on both ends in cases where data reflections caused issues. Reflections are based on several parameters, the most notable being distance of the DMX cable. Time is distance down a wire and with wire at the perfect length, data waveforms can be altered or canceled out due to reflections off the unterminated end.

RDM does require specific, non-DMX termination and it must be held correctly at each location due to bi-directional data flow and transmit status. I have found, on a number of installations, that the termination is even more critical. RDM places transmitters all over the data bus, not just at the ends, which is why data integrity is even more important than DMX.

Isolation chips are not designed to isolate chatter as they do not know about proper timing. If a reflected signal is the dominate signal, the receiver chip and isolator accept the changed timing and send it on the CPU for processing. Isolators are designed to provide galvanic or optical isolation to reduce the possibility that an out of tolerance signal will get coupled into the main electronics. It's just like the galvanic isolation that is provided on each port of an ENET switch where it just passes on anything it gets but doesn't know if it's a real signal or not. Yes, more expensive products do have them and they are wonderful when someone sends the wrong signal down a data line or there's a nearby lightning strike.

Somehow I have missed where the OP stated his DMX In port is at the end of a DMX chain. Unless we are talking about where the console is plugged in.

I have scope shots of corrupted DMX, copies of DMX specs and best practices, schematics of products and I can post that if that will help people reading this. I want a healthy discourse and to work using standards and best practices. Thomas, you can do what you are saying - I never said you couldn't. I did say I wouldn't and that other methods are more sure.

Anyone that has now spent the time reading through all my dribble and has an interest in knowing more about DMX practices, I would highly recommend Recommended Practice for DMX512, by Adam Bennette. It takes the DMX standard it turns it into a doc that can more easily be interpreted to use cases in the field and with product design.

Thomas, if I have failed to explain things clearly, I would appreciate a phone call when you have a free moment. It's possible that things are just getting lost in translation.

David
eight eight eight - 908-2142 reaches my desk toll free


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## DavidNorth (Mar 5, 2015)

Well, my long posting surely missed a lot of activity. I can delete the last post if people think it's wise.

David


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## lightman02 (Mar 5, 2015)

David I appreciate your post and it is very informative. I'm not trying to downgrade your intelligence in any way even though that's what it seems. I don't want there to be any hard feelings and maybe this has gone a bit far being the way DMX passes is why I am looking at it the way I am. I would be more then happy to call you and talk if you want.


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## BillConnerFASTC (Mar 5, 2015)

lightman02 said:


> How do you know my way is wrong, you’re not proving anything to me to prove it either? Not to mention the original post talked about using the end of the DMX chain and not the center tap. Most fixtures the two DMX ports are wired directly to each other with a center tap for the transceiver chip. Most quality fixtures have an isolation circuit to protect the DMX lines from chatter, cheap stuff does not. If you want me to post actual traces and schematics to prove a point, I would be more than happy to spend the time. So don’t tell me I’m wrong when you aren’t providing any hard documentation from anyone just your opinion. Do things the way you want to, it’s not my problem and I’m done with this thread. As far as a system made 20years ago; you want to tell me they don’t put a DMX port in the control booth and on the stage tied to the same universe anymore?? DMX hasn’t really changed in 20 years if you haven’t noticed.



I expressed my view as a consultant that I'd follow the dmx standard. I know it can be disregarded and "usually" still work. I think that is not the best practice which i promise my clients.

I have no need torove anything to you. You have proved to me that I should never approve you as a bidder on a project of mine. Thank you. It might save me time someday.


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## lightman02 (Mar 5, 2015)

Oh well, no loss here.


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## ScottT (Mar 5, 2015)

DavidNorth said:


> I have scope shots of corrupted DMX, copies of DMX specs and best practices, schematics of products and I can post that if that will help people reading this. I want a healthy discourse and to work using standards and best practices. Thomas, you can do what you are saying - I never said you couldn't. I did say I wouldn't and that other methods are more sure.



David,

I for one am curious. Can you either post these or PM/email them?

Thanks


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## DavidNorth (Mar 9, 2015)

ScottT said:


> David,
> 
> I for one am curious. Can you either post these or PM/email them?
> 
> Thanks



Here is a shot of a normal DMX signal. The verticals are upright and occur at the same time, and the pulses are equal and opposite. The amplitude shown is quite high due to a short distance of DMX cable.



Here is an over-terminated DMX signal. In this case, two terminators are enabled on the DMX line and the only real issue here is loss of amplitude. All this really means is that the DMX signal could not be sent as far and/or to as many devices.



This is an un-terminated line. The DMX signal can be a prime contributor to DMX reflections and is easy to recognize due to overshoots. I do not have at hand a reflected signal but will create one soon and post it.



The next shot is from a capacitive system. This is what DMX looks like on a bunch of mic cable. Note the rounded corners, which doesn't look too bad, but in extreme conditions, the timing placement of DMX transitions [the rises and falls of each pulse] changes. When timing changes, DMX no longer becomes DMX and you have flicker or level changes due to frame shifting. In very extreme conditions, this leads to total loss of recognizable data. This is the reason why people say it worked fine in the shop on 150' of cable and then failed in the field at 500'.



This last one is rare but I have talked about it on other posts before. [EDIT by Mod.: http://www.controlbooth.com/threads/moving-light-freakout-terminator-was-the-problem.28635/ ] When someone says that everything worked fine until they placed a terminator on the end of the line, this is one of the reasons that could have caused it. What you are looking at is DMX signal that has a broken Data - wire and termination is on. Data + goes down the line, through the terminator and then back up the Data - line at low amplitude. As soon as that happens, DMX goes away. Yes, many devices can run on DMX + only - that is until the terminator gets added.



More as soon as I get to it.

Thanks,
David


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## robartsd (Mar 9, 2015)

DavidNorth said:


> More as soon as I get to it.


Thanks for illustrating the issue.


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## BillConnerFASTC (Mar 9, 2015)

I appreciate that also. I had a sense of what was happening but not so clearly. Now I can whip these out to make my point to follow the standard.

PS - does it look different when transmitted on Cat5?


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## DavidNorth (Mar 9, 2015)

BillConnerASTC said:


> PS - does it look different when transmitted on Cat5?


 
It would look exactly the same. Well all would be the same except for the capacitive scope shot, as that would not occur with Category cable.

David


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## DavidNorth (Mar 10, 2015)

Here is a shot of a reflected signal. In this case, the two different amplitudes show DMX from two different lengths of cable interfering with each other. This is only one of many way that this can be seen on a scope as many factors can play into reflections including cable length, cable type, number and types of devices on the line, etc. When it is this bad, it is very easy to see but many times it is not this pronounced and much more difficult to sort out.



David


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## Wood4321 (Mar 11, 2015)

@DavidNorth Thanks for your insight into this, this has been an awesome thread.


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## SteveB (Mar 11, 2015)

Wood4321 said:


> @DavidNorth Thanks for your insight into this, this has been an awesome thread.



Ditto. I'm saving the images.


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## Dionysus (Mar 12, 2015)

Wood4321 said:


> @DavidNorth Thanks for your insight into this, this has been an awesome thread.


Awesome indeed (Perhaps there is due course for a thread more properly addressed (ie titled) to discuss DMX standards and issues?). I know I've had discussions about this many times in the past with many different people, many people saying that Im full-of-crap when I talk about "reflections" and "capacitance" possibly causing an issue with the DMX signal.

Indeed as said before, DMX can be run down barbed wire and microphone-XLR and work just fine... But then all of a sudden its not working so fine. It also depends on how accurate you really care about your dmx signal being. I know Ive seen a few of these issues before a number of times, usually just a slight "flickering", which is fine with a bunch of conventionals. But once you get a bunch of LEDs or other intelligent fixtures it can be really annoying.

It's great seeing these scope shots as it fairly clearly illustrates what happens to the digital signal. The truth is, while we all use DMX, many have no clue (and don't care) about how it actually works and functions.


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## RickR (Mar 12, 2015)

This discussion has the makings of a great WIKI article. @DavidNorth are you willing to assemble it? (If not or nobody else jumps in, I'll make a first attempt.)


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## kicknargel (Mar 14, 2015)

RickR said:


> This discussion has the makings of a great WIKI article. @DavidNorth are you willing to assemble it? (If not or nobody else jumps in, I'll make a first attempt.)



TWO wiki articles. One about DMX, and one about professionalism.


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