Q Light Controller+

We ran a show last night which went pretty well unless we moved the laptop mouse.

We had 12 COLORados, two sunstrips and a dimmer running two profiles.
As expected, the sunstrips and profiles were fine (i.e. didn't show the problem) but the LED COLORados would flicker if we moved the mouse.

We're running v4.10.5b on a reasonably old Dell laptop under Win10 (4GB RAM, i5 2.50GHz) with an Enttec Open DMX USB dongle. The last fixture did not have a terminator.

Given that the problem only occurs when we move the mouse, is the answer to use a faster machine? I know that it's usual to check cabling and terminate first, but when we leave the laptop alone it's fine. The faster we move the mouse around the more flicker we have.
Will cabling make a difference? The reason I ask is that we ran a much smaller event earlier this month where we only had eight COLORados with a much shorter dmx cable and we didn't have flicker.
Would it be better to install Ubuntu?

Can you describe your USB connections? Can you try to plug the mouse to a different USB port? Can you try a different mouse?

It's possible that the mouse causes USB bus to fallback to the slowest speed (12 mbps) and or stall it for some time.

I forgot to mention that the problem was caused by both the trackpad and an external mouse.
I didn't have the opportunity to try a different USB port. This coming weekend I may do more tests.

The laptop in question is a Dell Latitude E6420 and the dongle plugged directly into one of the 3 USB ports, the mouse into another USB port.

If I recall, mouse movement in Windows is done with a hardware interrupt: a way for the computer to stop what it's doing and instead do something else like updating the pointer position. USB devices also use hardware interrupts to keep data flowing to them. If the computer is trying to do too much at once, some devices won't get a smooth flow of data because the computer is busy jumping from one task to another.

What I strongly suspect is that, when the mouse pointer is moving, your computer becomes too busy to keep data flowing smoothly to the Open DMX interface. When DMX frames are skipped, some lights say "uh.... I forgot what I was doing" and blank out until they receive the next (correct) DMX frame.

Some DMX devices have an internal mini-CPU to keep data flowing smoothly out of the DMX port even when the computer can't supply updates fast enough. This technique is called Frame Buffering, and more advanced interfaces like the DMX USB Pro have it. I don't believe the Open DMX interfaces have that - they instead rely on the computer to refresh the frames fast enough.

If what I described above is in fact the cause of the problem, then you can fix it by either:

1) Using a more advanced "pro" DMX interface with frame buffering; or
2) Using a newer/faster computer; or (possibly)
3) Reducing the amount of things the computer has to keep up with

If your computer is just too slow/old then #3 might not be enough, but Windows tends to be pretty inefficient on old hardware, so one cost-free thing to try is to boot the computer into Linux and run your project there.

If you decide to try this, I would recommend the Ubuntu MATE distribution of Linux which is available for free here: https://ubuntu-mate.org/download/ You can boot your computer into Linux without altering your Windows installation using these instructions: https://www.ubuntu.com/download/desktop ... on-windows Good luck!

Thanks mdmayfield

We tried the same computer & dongle at another venue. No problem at all. I moved both the USB mouse and trackpad quite aggressively. The fixtures were nearly the same but with extra sunstrips and a much bigger dimmer running 12 lights. The cables were all different. So same pc, same dongle, similar lights and different cable and dimmer setup - no issues.

We have another event in two weeks time at a different venue where I'll be running a fairly small rig. I'll prepare a linux setup to compare with the Windows machine.

Hm, strange. A mystery, for sure. It is possible that the issue is what I described, but the fact that another setup doesn't flicker is odd.

It may be that the other lights or dimmers smooth out occasional 0s in the data by reacting slower, or maybe I was wrong and something completely unrelated to everything posted above is happening. Good luck with the next steps in diagnosing the problem.

Hi,

to me these issues sound very familiar.
Could you give us some approximate information as to what the cable runs looked like in the two venues?

We experienced a lot of weird behavior with 5 pin-DMX cables from a specific manufacturer up from a specific length with only few fixtures behind and no endresistor at the end of the chain.
It seems that signal reflexion going back to an interface can lead to these faulty values being submitted from what I understand.
Because we tested with another configuration with 12 fixtures at the end of the cable and were not experiencing this weird behaviour.
Looks like the more fixtures you have the more reflections get dampened...


Hope this helps you.

I've tried a few times to replicate the problem - everything runs perfectly.

The only thing that I haven't been able to replicate is the dimmer we hired for the event. We have since bought our own which is faultless.

So ... go figure!
Was it the dimmer or was Windows doing heavy garbage collection at the time?

Anyway, thanks for all the help and comments folks.
I'll be running a few events over the coming month - let's see if it happens again.