DMX out from ETC wall jack panels?

[robartsd]

More as soon as I get to it.

Thanks for illustrating the issue.

 

[BillConnerFASTC]

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?

 

[DavidNorth]

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

 

[DavidNorth]

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

 

[Wood4321]

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

 

[SteveB]

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

Ditto. I'm saving the images.

 

[Dionysus]

@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.

 

[RickR]

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.)

 

[kicknargel]

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.