DMX Buffer / Booster

[scottbramall]

Hi,

Currently got a small lighting rig set up running from a Velleman PC USB thing.

 

Some of the lights every so often flicker. For example (on the movers) it will twitch and then the gobo will flick of the color will flick to a different one. Dosent last a second but is noticable. Its usually the last light that does it. The last light is terminated.

 

Could this be because there is not enough power signal getting to the lights?

 

If it is, Whats the propper term for the device I need?

 

Thanks a lot

Scott

[Ynot]

Could this be because there is not enough power signal getting to the lights?

Nope.

 

You either:

Have not used proper DMX quality cables;

Have not terminated the end of the DMX run at the last unit;

Have run DMX cables (esp if (a) is the case) near noisy mains cables;

Your DMX cable is poorly terminated somewhere;

You have a sharp kink in the DMX cable;

 

Any of several other possibilities wrt the DMX cable.

 

Tony

[Tomo]

The issue may well be the Velleman USB > DMX adapter, as a few of the cheaper ones can produce spurious levels from time to time.

 

How many fixtures are on the DMX line?

[niclights]

There are other possible reasons:

 

Fixtures cannot accept data at full rate. Many desks allow adjustment to compensate.

 

A unit in the chain is doing bad things to the data occasionally.

[ChrisD]

It's possible that the USB > DMX box isn't sending out a full universe of DMX (i.e. is going up to the highest channel then skipping to the start again.) In your software, send data to channel 512 (any arbitry value other than 0) and see if that helps.

 

It sounds far fetched, but I had a problem with some cheap LED battens which would go into demo mode (i.e. had no DMX signal) for a split second then jump back. It was eventually figured out they were also doing this on cheap lighting desks but worked fine on a Strand 300 series (which outputs a full universe).

 

HTH

 

Chris D

[scottbramall]

I have 8 fixtures on the ring and it is terminated.

 

The DMX is run next to and tangled into the mains power. This might be causing it then. Its just currently set up in my room but when its set up properly ill separate the cables.

 

Ill also try sending data to channel 512. Would this be done by just making a new fixture (such as a flood) on the software and constantly having it on - but obviously without the light on the rig.

 

I'm using freestyler

[niclights]

Personally I would say that running next to mains cable is the least likely cause even if using mic cable. Obviously rule out by all means but instinct tells me this is a DMX fault caused either by the output device itself, a faulty DMX lead (esp. soldering in XLR) or poorly implemented or faulty DMX on a fixture. What are the fixtures?

[David A]

you can waste a lot of time trying all the suggestions on this site or get it checked out with a proper DMX tester which will give you some real data to work with and probably give you the answer instantly.

[Don Allen]

Hello Scott

 

Does the velleman usb DMX interface have a microcontroller withing the interface to provide a constant DMX output stream of data or does the usb DMX interface rely on your pc's cpu to run it. If it uses the pc's cpu then the usb DMX interface may miss out on processor time which can cause loss of DMX output.

 

This is why the enttec professional usb DMX interface is four times the price of the enntec open source usb DMX interface, as the professional one has it's own microcontroller.

 

Some DMX devises such as dimmers and demuxes have a latch function to cover for loss of DMX data so you do not end up with a blackout on the stage during glitches, not sure of what movers do.

 

The other timing points need investigating also, a DMX tester is nice but expensive and cro's need an external DMX trigger to see what is happening.

[scottbramall]

Fixtures are:

2 Funky Daddys

2 3D Magic's

2 Sound Lab ColourScans

2 Sound Lab Four channel Dimmers

 

 

 

I think the velleman kit uses the CPU becuase it only cost £45 so it was a cheap budget unit to see if PC based controll is worth going into

[niclights]

I guess is fair to say that these might not have the best DMX implementation but unless someone has specific experience of problems with one of these units it would be wrong to accuse them!

 

@David A: Maybe. Or you could waste a lot of time/money getting a DMX tester only to tell you everything is fine when it is not - ie. our friend the intermittent fault. I would say this is another good suggestion for eliminating, but certainly not the absolute answer :)

 

When you get the glitch do all the fixtures in the chain do something odd or is it only one unit?

[Ekij]

Since you have at least two of everything, have you tried swapping the misbehaving unit and it's twin in the DMX chain and seeing whether the misbehaving moves with the unit or stays at the end of the DMX line?