DMX shield woks with some dimmer packs but not others

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dodger

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Oct 30, 2009, 11:38:00 AM10/30/09
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Hay there

I have built a custom DMX shield and have had it up and running
controlling a DMX dimmer pack for some time now. It has been working
beautifully.

But last weekend the dimmer pack was replaced by another pack ( a more
professional one) so that it could control much more powerful lights.
The lights stopped responding correctly. Shame as this was an exciting
event and we had hired out a bunch of equipment for it.

The original dimmer pack is the Sound Lab 4 channel power DMX dimmer
pack. This still works perfectly

The other packs that failed are:

Starivill DDS 405, Beta pack 3 and the Alpha pack 3

The Arduino and the DMX shield appear to be working fine. Power LED’s
on both boards are on. There are two LED’s that indicate the signal
coming from two stretch sensors. The stretch sensors are calibrated
and working perfectly and the two corresponding LED’s are responding
well. When using the original dimmer pack (Sound LAB) everything works
perfectly.

I have tried many different cables and connectors so I don’t think
it’s a connector/ cable problem. I am not using terminal resistors
however I tried a splitter with a terminal block and that did not
solve it. All the channels seem to be set correctly.

My fear is it is a timing issue in the code???
Is it possible that the refresh rate for the frames is to fast on an
Arduino???
I do not know that much about DMX and I don’t want to mess about with
the DMXsimple library.

Any help would be greatly appreciated.
Thanks
D

Peter Knight

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Oct 30, 2009, 2:13:15 PM10/30/09
to DmxSimple
On Oct 30, 3:38 pm, dodger <davidmcgo...@gmail.com> wrote:
> ...
> The lights stopped responding correctly. Shame as this was an exciting
> event and we had hired out a bunch of equipment for it.

That's a real shame. I hope we can get everything sorted so your
installation has another chance.

Could you describe 'stopped responding correctly'? Were all the lights
dead? Did some work? Did they flicker and flash? Maybe a silly
question - but do you know the dimmer packs actually work?

> ...
> My fear is it is a timing issue in the code???

That is very unlikely. The code is has been tested on multiple DMX
lamps, a logic analyser and a CPU simulator, and checked against the
DMX512-A specification. A lot of work has gone into testing that part
- as that was the central flaw with the old Arduino DMX solutions. The
timing critical part of DmxSimple is written in hand-coded assembly
language to guarantee timing accuracy.

Are you using any libraries outside the built-in Arduino ones? Are you
using any interrupts in your own code?

> Is it possible that the refresh rate for the frames is to fast on an
> Arduino???

Unlikely, but possible. The specified minimum frame time is 1.204ms,
but the internet seems to suggest not all DMX devices can work that
fast. Try setting DmxSimple.maxChannel(100); to slow things down.

> I do not know that much about DMX and I don’t want to mess about with
> the DMXsimple library.

Here are some things to check.

1) Are you sending enough channels? Some dimmer packs need all the
channels transmitting, even if you're only using the first one. So
make sure you are sending all 6 channels to the Zero88 Betapack 3, for
example.
2) Does a trivial example work? Modify FadeUp from the examples and
see if you can get a lamp working. If so, maybe part of your code or a
library you are using breaks DmxSimple.
3) I know you said you checked your wiring, but have you checked it
works, or checked the connections manually? Beware - DMX often seems
to function even with faulty wiring, and only fails when you start
using different equipment or longer cables. Swapping earth and one of
the data lines is one common problem.
4) Have you used a decoupling capacitor on your DIY shield? A
capacitor (of about 100nF) between the power pins of the driver chip.
You might need one.


I hope that helps. Please report back what works and what doesn't.
Then I can use the feedback to improve the library and/or
documentation to banish this problem in the future.


Peter

david mcgoran

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Oct 31, 2009, 6:06:16 AM10/31/09
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v

2009/10/30 Peter Knight <cath...@gmail.com>

david mcgoran

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Oct 31, 2009, 6:12:46 AM10/31/09
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Thanks for your response.

Things seem to be working now, at least with the Starivill DDS 405.

 

Very strange but switching the data lines around solved the problem.

So now having them one way works for the Sound Lab dimmer and having them the other way around works for the Starvill dimmer. We no longer have the other dimmer packs to test now but my hunch is that the Sound Lab pack is the odd one out? This was misleading as seeing that it worked perfectly on one pack we didn’t want to touch the wiring for the others.

 

Perhaps the Sound Lab pack is wired up incorrectly? Or are there variations in how they are wired up? The Sound Lab pack defiantly stops working correctly with the data lines switched (by incorrectly I mean the lamps do not fade smoothly and flash on and off as if it’s struggling to receive a clean signal). It would be interesting to test a second Sound Lab unit to see if the one we have is faulty.

 

Anyway I think we have it ready for our next event so we can redeem ourselves after the last one. Moral of the story don’t hire you equipment at the last moment so you have time to test ahead of time. Aw well live and learn.

 

Thanks again.



2009/10/30 Peter Knight <cath...@gmail.com>

Peter Knight

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Oct 31, 2009, 6:48:51 AM10/31/09
to DmxSimple
On Oct 31, 10:12 am, david mcgoran <davidmcgo...@gmail.com> wrote:
>...
> Perhaps the Sound Lab pack is wired up incorrectly? Or are there variations
> in how they are wired up?

I think this solves the mystery:

http://www.blue-room.org.uk/index.php?s=d1617dd3f1b06fd3cd82bd9a6f67f41f&showtopic=37362&pid=313114&st=0


A quick history of DMX:
DMX committee decides on a data cable specification. It's different to
normal audio cables.
DMX committee decides on a different XLR connector (5 pin) so no-one
will use the wrong cable type.
Roadies get fed up with carrying two types of cable, and use audio
cables anyway. Everything works fine.
DMX companies find they sell more lamps if they use 3 pin XLR
connectors on their products.
Because it isn't standardised, everyone invents their own mapping to 3
pin connectors. Chaos ensues.

If it's got a 5 pin XLR on it, it's standard. If it has a 3 pin (and
almost everything does), tread carefully.
If you get a 3->5 pin adapter and a phase reversal adapter, you should
can cover all pinout combinations.

And yes, it's a mess ;-)


Peter
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