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Author Topic: DMX, LED, Cat6, and flicker  (Read 529 times)

Peter Gothold

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DMX, LED, Cat6, and flicker
« on: January 23, 2020, 01:53:00 pm »

This may be basic knowledge, but I'm somewhat new to DMX system design and troubleshooting.

Background: I'm 4 months in to a position at a church and figuring out what's existing while wanting to add functionality.

What I did: add floor lamps with dimmable LED bulbs to the stage by adding a 4ch dimmer pack to the daisy chain with 150' cat6 cables and adapters.

Problem: the lamps flicker every couple seconds

I wanted to add DMX control to our stage, but all the dimmers are in the back of the balcony, so I ran cat6 cable under the floor all the way to the stage and back to keep the daisy chain. The lamps flicker, and I thought it could be ground issues so I tried an optoisolator, then the Fleenor DMX Decelerator before the dimmer pack, but that didn't fix the issue.

Complications: We have 3 architectural controls that come after the added dimmer pack in the chain, and they seem to be what's causing the flicker. When the lamps are controlled by the board they don't flicker, only when they are controlled by the presets on the wall controller. We use the wall controls to run our show (not ideal, I know), so it would be best to figure out the flicker while keeping the wall controls in the mix.

Board: Sweet old NSI MC 7024

Added Dimmer pack: ADJ DP-DMX-20L

Problem lights: 10 Floor lamps with 4w LED bulbs all one 1 circuit in the dimmer

Wall controls: Doug Fleenor PRE10

Any input would be welcome, thanks in advance!
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Brian Jojade

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Re: DMX, LED, Cat6, and flicker
« Reply #1 on: January 23, 2020, 02:18:18 pm »

Dimmable LED bulbs are sometimes barely dimmable, and depend heavily on the type of dimmer used.  Dimming with supply voltage is MUCH more complex than just lowering the total voltage/power like you can do with an incandescent light.

With some dimmers, the extremely small load of LEDs isn't enough for them to function properly either.

Cheap solution: Replace the LED bulbs with incandesants.
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Brian Jojade

Taylor Hall

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Re: DMX, LED, Cat6, and flicker
« Reply #2 on: January 23, 2020, 02:30:46 pm »

Brian nailed it. Either replace the LEDs with filament bulbs or replace the dimmer packs for ones specifically designed to use with LED bulbs.
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Jeff Lelko

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Re: DMX, LED, Cat6, and flicker
« Reply #3 on: January 23, 2020, 03:04:23 pm »

Hi Peter, two things jump out to me.

- The LED bulbs, as Brian already mentioned.  LED bulbs do exist that play well with dimmers, but this is still a minority and given that the flickering occurs only when using the wall controllers I'm not convinced that the bulbs are the problem.

- How many controllers do you have in the daisy chain?  DMX doesn't work as a mesh nor is it intended to be bidirectional.  It's a serial path that starts with a controller and ends with a terminator.  Having a setup such as Controller -> Fixtures -> Another controller -> More Fixtures won't work.  Some devices such as offerings from Doug Fleenor allow for DMX input as either a redundancy or a merger, but this should all be done upstream of your first fixture.  The proper way to set up a multiple controller system is to use a DMX merger with a discrete input from each controller merging into a single output that then runs to your fixtures.  If I understand your system correctly then I suspect this is where you're getting the glitching.  Hope this helps! 
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Peter Gothold

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Re: DMX, LED, Cat6, and flicker
« Reply #4 on: January 23, 2020, 03:19:08 pm »

Thanks for the info. I'm not totally sure of the overall flow of the controllers, but I know before I added the dimmer pack it was board>wall controllers (3 of them: 2 on rear wall and one backstage)>dimmers>fixtures. I put the dimmer pack before the wall controllers as I don't have ability to run conduit for new cable from the balcony to the stage at the moment. If I knew which order the wall panels were wired, and could jump in after the last one, would that help? I have yet to find a schematic of the architectural wiring for this stuff, so that has been frustrating..

Hi Peter, two things jump out to me.

- The LED bulbs, as Brian already mentioned.  LED bulbs do exist that play well with dimmers, but this is still a minority and given that the flickering occurs only when using the wall controllers I'm not convinced that the bulbs are the problem.

- How many controllers do you have in the daisy chain?  DMX doesn't work as a mesh nor is it intended to be bidirectional.  It's a serial path that starts with a controller and ends with a terminator.  Having a setup such as Controller -> Fixtures -> Another controller -> More Fixtures won't work.  Some devices such as offerings from Doug Fleenor allow for DMX input as either a redundancy or a merger, but this should all be done upstream of your first fixture.  The proper way to set up a multiple controller system is to use a DMX merger with a discrete input from each controller merging into a single output that then runs to your fixtures.  If I understand your system correctly then I suspect this is where you're getting the glitching.  Hope this helps!
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Jeff Lelko

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Re: DMX, LED, Cat6, and flicker
« Reply #5 on: January 23, 2020, 03:30:36 pm »

Thanks for the details Peter.  I can say that what you describe is very bad practice at best, and likely the cause of the problems at worst (through no fault of your own).  Even though the wall panels may allow for a DMX input so that they can function as a redundant controller, stringing a total of 4 controllers together that way isn't how they're meant to be used.  Ideally you would have your controller and the three wall panels running to a dedicated merge device that then flows a single DMX universe out to your lights. 

Having these controllers downstream of your new dimmers mean that when the wall panels are in control, you're flowing DMX into the dimmer's output.  While most DMX I/Os are simply wired in parallel, this still isn't advisable, especially with the controller then in the middle of the daisy chain.  You'll be getting a lot of strange signal reflections that can lead to what's called a framing error - often manifesting as flickering and erratic behavior from fixtures. 

I'd suggest finding a few incandescent lights just to check that the LEDs aren't the source of the problem (a simple halogen desk lamp will work fine), but barring that you'll need to get your daisy chain sorted out and routed properly to resolve the problem.  I'm not an advocate for using wireless solutions, but it's a thought if running wires just isn't doable.  Good luck!
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Dave Garoutte

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Re: DMX, LED, Cat6, and flicker
« Reply #6 on: January 23, 2020, 06:01:59 pm »

LEDs on a dimmer pack need a bleed resistor.
Chauvet makes a dimmer pack specifically for LEDs.
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Scott Hofmann

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Re: DMX, LED, Cat6, and flicker
« Reply #7 on: January 23, 2020, 11:09:07 pm »

I've installed quite a few Fleenor PRE10 units and they have always worked amazingly well. Fleenor's tech support is wonderful as well. As mentioned by others, you have undoubtedly corrupted the DMX chain by adding the dimmer between controllers.
If you consult the PRE10 manual, it shows signal flow goes from your console to PRE10 #1, then to PRE10 #2, (then to PRE10 #3), then to your dimmers (also daisy-chained). No merge device is needed; in fact the PRE10's may not work as designed if you do so. As detailed in the manual, only one PRE10 in a system should be set as a Master and the others should be set as Slaves. Recording of presets takes place on the Master unit and the Slave faceplates pull the info from it. Each unit echoes the button presses from the others. I would encourage you to give Fleenor tech support a call if you have any questions on how to determine if the units are configured correctly.
« Last Edit: January 23, 2020, 11:11:35 pm by Scott Hofmann »
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Scott Hofmann

Jeff Lelko

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Re: DMX, LED, Cat6, and flicker
« Reply #8 on: January 24, 2020, 07:07:22 am »

As detailed in the manual, only one PRE10 in a system should be set as a Master and the others should be set as Slaves. Recording of presets takes place on the Master unit and the Slave faceplates pull the info from it. Each unit echoes the button presses from the others.

I saw that, and that's how DFD addresses the situation of which unit should take precedence over another.  I was under the impression that these were being used independently and not in master/slave configuration.  I have a high regard for DFD products so I'm confident that they'll work as designed when used properly - I just don't know the mechanics of how they handle injecting DMX into the daisy chain along with their other metadata without causing corruption.  I have no doubt that putting these downstream of fixtures can cause issues though! 
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Scott Hofmann

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Re: DMX, LED, Cat6, and flicker
« Reply #9 on: January 24, 2020, 03:17:50 pm »

I saw that, and that's how DFD addresses the situation of which unit should take precedence over another.  I was under the impression that these were being used independently and not in master/slave configuration.  I have a high regard for DFD products so I'm confident that they'll work as designed when used properly - I just don't know the mechanics of how they handle injecting DMX into the daisy chain along with their other metadata without causing corruption.  I have no doubt that putting these downstream of fixtures can cause issues though!
Hi Jeff.... I agree. Unless the original poster removes the faceplates and looks at the jumper which determine Master/Slave assignment, it's anyone's guess as to how the PRE10's are actually configured. And everyone's guess is different!

I was recently involved in a renovation that utilized two of the relatively new PRE10E-A stations (able to handle 4 universes of sACN) as the architectural controllers with an ETC ION Xe-20 as the console with an extensive Net3 distribution system. The stations would stay locked out when the ION was turned off instead of their becoming active. Fleenor tech support spent a lot of time with me trying to resolve the issue, including sending diagrams with a lengthly explanation of how the units worked. The cause turned out to be one of the ETC Net3 gateways holding a last look (HLL) which contained a channel and universe far removed from normal operation (probably keyed in in error). Because that channel was being held indefinitely by the HLL function of the gateway, the PRE10E-A's sensed that activity and stayed locked out. Check out the PRE10E-A... quite a nice piece of engineering.Very happy with it.
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Scott Hofmann

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Re: DMX, LED, Cat6, and flicker
« Reply #9 on: January 24, 2020, 03:17:50 pm »


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