Control/Dimming DMX refresh flash on cheaper LED's

[RonHebbard]

Maybe I'm getting the term "ground" confused here, but in a DMX system pin 1 of the XLR should never be connected to the shell of the connector per Bennette's "Recommended Practice for DMX512". Quote from page 8: "The shield must not be connected to, or be in contact with, the shell or body of either the male or female connectors because chassis mounted connectors are generally connected to mains ground and this could cause problems with ground loop currents." (Itallics are his). In fact, some imported 3-pin cables do have pin 1 tied to the shell and this will likely cause problems in a DMX system.

@microstar and @James Mierkey The DMX shield(s) should be grounded at one, and only one, point; normally the chassis ground of the DMX source. Grounding at multiple points, such as within the shells of XLR connectors, is a definite No, NO as it leads to hum and interference inducing ground loops.
Multiple ground points is BAD. Leaving the shield floating un-grounded is also bad.
Toodleoo!
Ron Hebbard

 

[Malabaristo]

Surprised no one has said this yet, but it looks like that Enttec interface supports RDM. Have you looked into how to disable that? That's definitely the most common issue I see with these kinds of cheap fixtures.

 

[Amiers]

Surprised no one has said this yet, but it looks like that Enttec interface supports RDM. Have you looked into how to disable that? That's definitely the most common issue I see with these kinds of cheap fixtures.

Good catch.

 

[RonHebbard]

And if the flicker is still present with one fixture, what's next? The ground problem?

@James Mierkey Have you resolved your problem with flickering when using your Entec to control your DMX gear? If so, how; what worked for you??
Toodleoo!
Ron Hebbard

 

[James Mierkey]

@James Mierkey Have you resolved your problem with flickering when using your Entec to control your DMX gear? If so, how; what worked for you??
Toodleoo!
Ron Hebbard

Malabaristo wins the prize. RDM was enabled in the entec and as soon as I disabled it and rebooted the interface, the flicker went away. In the process of troubleshooting, I learned a ton though. Thank you all for the awesome info! Now to tackle my randomly dousing lamp in the VL2500.

 

[Harrison Hohnholt]

Malabaristo wins the prize. RDM was enabled in the entec and as soon as I disabled it and rebooted the interface, the flicker went away. In the process of troubleshooting, I learned a ton though. Thank you all for the awesome info! Now to tackle my randomly dousing lamp in the VL2500.

The big tell here was the consistent flicker. RDM packets are sent out at a set speed which can sometimes be adjusted.

The reason for this is if you are in testing or tech you might want RDM to be more stable so you would adjust it to cut out DMX more and send more RDM packets. Now you can leave RDM running during the show, not recommended, but if you did you would want to reduce the DMX cutouts so you would get fewer RDM packets sent.

 

[dmx512rdm]

We recently moved to controlling our lights through QLab using an entec ODE interface. As soon as we did that, we started getting a flash on all of our LED fixtures every 120 seconds. We were previously using an ETC console. I have played with the refresh rate on the entec and can slow it down or speed it up but it doesn't go away completely. I have double checked every single DMX cable for issues. As soon as I switch from the entec back to the ETC console, the flashing stops. I realize that this is an unfortunate reality when using less expensive LED fixtures (prosumer/DJ level stuff). We're a small community theatre and we get a lot of bang out of those cheaper fixtures. Is there anything I can put inline on the DMX chain to reduce or remove this flash? A splitter/isolator? Anything?

I appreciate any help you can give.

While I would normally repeat some of the grounding comments, I'm not sure this is a grounding problem. But a short comment on grounding follows - ideally consoles earth ground pin 1 of the data line, and fixtures isolate pin 1 from chassis ground. This can be found by application of an ohm meter measuring the resistance between pin 1 and chassis. If you have groundrd fixtures, having an isolated console can help. But with most consoles you can't change that status. So having an optoisolator that segregates fixtures that are mechanically far apart can be useful. The bigger the ground loop, the bigger the problem.
However you say the problem appears at a regular interval. Grounding problems seldom have a regular period. I would suggest that you borrow, rent, or buy some level of DMX test equipment that could see whether the controller throws errors even when the tester is the only thing connected to the line. If the tester supports timing analysis and reporting, look to see if every flash period equates to a change in timing. (FlickerFinder on a DMXter or MiniDMXter is good for this)
If your tester can generate framing errors, check to see whether sending a framing error causes a blink. A properly designed receiver can reject framing errors and makes random line errors less of an issue.
Does the system work correctly when driven by the tester alone? If it does, then you should suspect that there is a software/hardware issue in the Entec interface and/or the QLab software.
Bob Goddard/Goddard Design Co.

 

[derekleffew]

Well, this is what happens when one answers the question asked, rather than what should have been asked. Inlight of this new information, it does make one wonder... @jfleenor How does the DMX DECELERATOR feel about/deal with RDM?