DMX Stage Lighting Systems - Is Anyone Listening?
If you have any experience of stage lighting you have probably used the DMX512 protocol to control your lighting rig. Apart from being able to control your dimmers, DMX lighting control is at the heart of intelligent lighting, moving lights and accessories. This article explains the basics of a full DMX stage lighting system while busting some of the myths surrounding DMX lighting control.
An Overview of DMX.
Image by VeldaZ
Digital Multiplex (DMX) was developed as a standard digital theatre lighting control which replaced the older analogue systems that were used to control the dimmers in a stage lighting rig. Despite the advance in use of ethernet networking at the top of the professional lighting industry, DMX is still the best answer for most lighting control applications. DMX had the advantage in that a total of 512 (hence the name DMX512) dimmer channels could be controlled using only a 2-core and Ground signal cable. The other plus point to DMX was (and still is) the fact that a signal cable could be daisy chained from one DMX unit to the next and the next until all the lighting equipment was connected by one single chain of signal cables. This is particularly important when controlling moving lights as it minimises the cable required.
How does DMX work?
This article was originally called “DMX Stage Lighting Systems - Get Them To Talk” but, apart from being a bit of a lame title, this actually misses the point of the serial DMX signal. Unlike modern networks, DMX lighting fixtures and their controller do not all “talk” to each other.
When a DMX Lighting Control talks - everyone else listens!
Information about each “DMX Channel” (in the old days, a dimmer number) and it’s level (0 - 100%) is transmitted down the DMX “Universe” cable and each DMX stage lighting fixture, moving light or smoke machine listens for it’s own part of the signal stream and ignores everything else. The signal is then transmitted over and over in “packets”, giving a regularly updated stream for the rig to obey. The lighting console recieves no information in this one-way street.
In order for all the DMX stage lighting fixtures to have their own part of the signal stream, each one has it’s own “address” which is set on the fixture using buttons or switches. If a dimmer channel has a DMX address of 001 then it listens for the 001 part of the DMX signal then obeys the “channel level” value, 75% for instance.
Once all intelligent lighting fixtures, dimmers and accessories are connected up and “addressed” the lighting desk can control each part of the rig indiviually using their own unique DMX address.
Masters of the Universe
Back when we only controlled dimmers using DMX, life was simple. 1 DMX Channel = 1 Dimmer No. Then we started to use more complicated fixtures, moving lights and intelligent (?) lighting that needed more than 1 DMX channel per fixture. This means that fixtures are assigned a DMX “start address” which is the first channel in a sequential batch that the fixture listens to. If your fixture uses 6 DMX channels and you set it to a “start address” of 001 then it listens to channels 001,002,003,004,005 and 006. Your next free address for another fixture is then 007 because if you set it to 006 then the “channel overlap” would create a conflict of control. Setting fixtures to the same start address can be useful some circumstances and is a common method of DMX fault finding.
With many DMX moving lights requiring the use of 20 or more channels, those 512 don’t look too many now, huh? A few moving lights, 100+ Dimmers, Strobes and a couple of smoke machines and you’ve run out of channels already! The solution to this problem is to connect and address some of your equipment on a second DMX “universe”, a different signal stream with even more cables. Many lighting control desks have more than one DMX output these days and the principles of fixture addresses and channel numbers apply to this, and subsequent, universes. The first DMX channel on a second universe is also 001 and each DMX universe is a totally separate stream, independent of each other.
Myths busted about DMX stage lighting systems
- It does NOT matter which order you connect up all the fixtures in a DMX chain, so long as they all have a signal going to them.
- The DMX cable chain should NOT return to a create circular control signal loop. (If your lighting desk has a DMX IN connector, leave it alone!)
- A DMX signal cannot be split into two using a Y-cord. A DMX splitter/buffer (somestimes called an Optisplit) is required.
- If does not matter which order your fixtures are addressed in just as long as they are unique and don’t overlap. Make sure you find out how many DMX channels each of your fixture uses for control.
- A DMX chain will usually work without a termination resistor although it is recommended by the equipment manufacturers and can solve some tricky problems with a complex rig. Here is a good article on why you should terminate your DMX lines.
- The “DMX received” indicator on a piece of equipment does not neccessarily mean that all is well with your DMX signal.
- You can set two pieces of DMX equipment to the same start address on the same universe without problems. They will both do exactly the same thing , however.
Hopefully, you now have a better understanding of how DMX stage lighting systems work. A good book on the use of DMX systems is Practical DMX
Related Articles:
- DMX Fault - Finding and Fixing DMX Problems
- DMX Over Ethernet - The Ethernet To DMX Converter
- RDM DMX - A Guide to the Basics
- Intelligent Lighting Control - Lighting Desk Basics 2
- LED Light Control - DMX Controllers for LED Stage Lighting
25 Responses to “DMX Stage Lighting Systems - Is Anyone Listening?”
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August 22nd, 2007 at 9:20 pm
I’m working on a synchronized music and light show and have the 06 PC DMX lighting control system. Last year i used it with 100,000 christmas lights and now i want to add 60,000 led lights. Will i need additional dimmers? I already have 15 4 channel dimmers and 40 single channel dimmers.
thank you!
August 23rd, 2007 at 8:13 am
Welcome,
Wow, that’s a lot of tiny lights.
Dimming genuine LED lights can only be achieved using specialist technology and they cannot be plugged into your usual dimmers.
If your synchonised show requires live control of then you might be better to use traditional incandescent christmas lights.
If you are technically confident enough, you could buy/make/modify a DMX controlled switching system that just switched the power to your LED circuits, rather than dimming them.
It is sometimes possible to change the settings on more advanced stage lighting dimmers to achieve this but it requires a knowledge of dimmer technology to make sure your don’t ruin the LED transformer or dimmer.
I assume you wish to use LED lights for colours/brightness?
HTH
November 25th, 2007 at 11:59 pm
hey
im surposed to be hireing equipment for a school production and it was suggest we use DMX cables and LED stage lights so we can mix colors im not very informed on these things so i need your help. DMX cables do they have to go through a dimmer because the dimmer we have at our school is not controlled by DMX cables but with another dimmer with cables that have i think 8 or 9 pins in them not sure hwat they are called. but if so can you suggest one. LED stage lights are they just like regular stage lights but can be controlled by DMX to mix the colour and can you possibly suggest a good company to hire from in the uk that also have moving light
thanks much appreciated
muz
November 26th, 2007 at 8:30 am
Hi Muzzy
Just to clarify - LED stage lighting does not need any dimmers. All the LED fixtures need is power and a DMX signal, they dim themselves. If your dimmers are connected by 8 pin DIN cables, then your system is using analogue control, not DMX. Check to see if your desk does not also have a socket marked DMX too. If not, you could get round this by hiring a simple DMX desk to control the LED fixtures and the cable to connect them.
If you are only controlling simple LED PARS or Battens, you could evn get away with using a simple manual conventional desk. It depends on how much control you need. If you are also looking at moving lights, you will need some kind of moving light controller.
There are loads of good lighting hire companies in the UK that have LED kit as well as moving lights. It depends where you based. Give your local lighting hire company a call and they will be able to help you with which cable/kit/control you need.
HTH
January 21st, 2008 at 5:23 pm
Hiya!
My school has a old lighting system that connects via 8-pin DIN. We are hoping to purchase some DMX lights very soon. But, we need some way of controlling DMX lights (possibly some moving heads as well) & our original lights. Can we buy a DMX mixer and convert the output to
DIN? Can we buy a mini DMX mixer for just our DMX lights?
We have a tight budget - as we are a school.
Please Help!
From Andy
January 24th, 2008 at 8:57 am
Hi Andy,
If you are planning to use DMX fixtures in the future, you can indeed buy a DMX lighting controller and then convert a DMX signal to analogue lighting signal (the 8-pin DIN).
To convert the DMX signal for the new lighting controller for your old lighting system, you will need a Demultiplexer or DEMUX. Some dimmer systems use a positive (+ve) analogue control signal, and some negative (-ve) so make sure that buy a DEMUX that is compatible with your dimmers. eg. if the dimmmers are made by Strand, they will need a 0 to -10v (negative) signal.
Some DMX to Analogue converters can output both type of analogue control signal.
HTH
March 1st, 2008 at 9:41 pm
hi do you have any idea how the person above used dmx to control his xmas light display? computer controling my display is somthing i am wanting to do this christmas but i seem to be struggling to get hold of suitable technology! any ideas are very much apreciated, thankyou
March 9th, 2008 at 7:01 am
Wayne,
Although I don’t know for sure, Griselda mentioned DMX dimmers and I presume that these were used to control the intensity of “normal” decoration light strings (with additional “load lamp” if required).
The problem was that conventional stage lighting dimmers can’t be used to feed LED christmas lights.
March 25th, 2008 at 10:35 pm
Yes you can control led rope lights with standard dimmers but you must use a load lamp If you do not the leds do not go fully off this is due to the very low current of led
The dimmers leak a few mili amps They dim well also
I to am trying to use DMX and a computer to drive christmas lights 30 channels to date
I am finding normal stage lighting software a nightmare to program Christmas lights to music one step at a time then back to start again each time
Some people do not use dmx but a system called lightarama as it is better for this job
I think we need some special DMX software can anyone help
Mike Shrewsbury
March 25th, 2008 at 11:06 pm
Hi It Mike again FIRE RISK
The LED rope Lights MUST BE MAINS DIRECT and not have transformers or chase function boxes in. The wave forms from dimmers WILL cook the transformers and even the dimmers
They must be 230v static sets and all will be fine
Mike
March 26th, 2008 at 6:30 am
Hi Mike
Thanks for pointing that out. As usual with transformed mains, it all really depends on the type of transformers. I have worked with cheap 12v transformers (with MR16 dichroics) that were supposed to dim but they have lasted a few minutes before being fried.
I wouldn’t recommened that anyone attached domestic equipment to stage lighting dimmers unless they really understood what they doing.
Re : Your timed music show - have you looked into the various sync control systems to fire your cues; timecode etc? A common way of sync-ing stage lighting control.
Thanks for visiting.
April 7th, 2008 at 11:07 pm
Has anyone come across dimmers that do not work But work fine with a cross in the DMX data wires ie pins 2/3 This has the effect of inverting the data
Have now made up a short cords Male female plugs with cross in
The item in question is a Soundlab 3pin XLR Barrel scan Nightclub Disco light
Tried this as last resort before item went in skip Have herded of this fix from someone else but I had never come across it
Will play some more and report back
Mike
April 8th, 2008 at 7:29 am
Hi Mike
You have an interesting problem and I don’t really know the Soundlab kit in question. If you find that a hot/cold swap makes your fixtures work completely - great. I suggest that the “fix” does work in the way you think it does.
I am not a DMX boffin, but I can tell you that hot/cold swapping the data lines (pins 2 and 3) does not invert the DMX signal. Being a digital DMX signal, changing the “polarity” (for want of a better word) does not mean that a 255 signal suddenly becomes 0 or vice versa.
Early Martin disco equipment, such as the Robocolor, was built with pins 2 and 3 inverted and most of this kit was made DMX compatible (-ish) by either resoldering the connectors internally or using a hot/cold swap jump lead to feed DMX into the fixture.
Another problem with dimmer or other attribute inversions on intelligent lighting comes down to the way the fixtures interprets the DMX signal. Many intelligent lights see a DMX signal of 255 as “dimmer open” or “full” with 0 being “off”. But this is not always the case.
Occasionally, the set up of the controller and the fixture are different - meaning that when you push up a fader, the fixture fades out. Colour attributes of both RGB and CMY fixtures can also vary in this way, depending the the manufacturer. The solution in this case is either in the fixture set-up, controller patching or personality file used.
Let us know how you get on.
April 8th, 2008 at 11:33 pm
Hi Rob
Mike again
An update on this SoundLAB pin 2and 3 cross thing
It is now become even more interesting
Some months ago i purchased off e bay a pair of identical 4 port standard generic lighting dimmers
On test one worked fine but the other had no DMX sync led on but worked in local test mode OK
I went back on Ebay and the words said Sold as seen
I said to my self Mike you have been had again
Have been hunting the web for a circuit diagram with no success
But guise what. Thease dimmers are made by SoundLab
Can you gues the next bit Yes with the Pin 2/3 crossing cord in the input it works fine
Have opened both dimers up expecting to fine a simple
wiring cross on the input plug to PCB wiring but no it is soldered direct to PCB The units have no link options on th PCB,s
At the moment I am at a lost to explain
ALL Units are as new looking
Crossing the data Pin inverts data bit 1,s to 0,s and 0,s to 1,s
ie Data 1 IS pin 3 {+pin) high +5 v and pin 2 (-pin) at -5v
A data 0 is pin 3 (+pin low -5 v and pin 2 (-pin) at +5v
Each bit is use to make up a 8 bit word to give 256 brightness levels for each in channel in turn
As a final prof I put the reversing cord on the input to 4 other working dimmer of differing makes and sync is lost as you would expect
This problem cannot be unique to me NEED REPORTS FROM OTHERS PLEASE
I will try to get to bottom of problem and report further
Mike
April 9th, 2008 at 7:15 pm
Hi Rob again
Have been looking for any ref of problems with DMX
and SoundLAB for days. Have at last found ref to the very same problem. A bit hard to understand but!
In the last line the same FIX but not explained very well This is dated 2006 how many good lighting units and dimmers have gone for scrap since then. See link
http://discolitez.com/phpbb/viewtopic.php?p=7827&sid=59a03dd5274fa959d22c3a6fc3bdab74
Mike
April 9th, 2008 at 10:45 pm
Hi Its Mike yet again
Think I understand it all
DMX 512 standards call for a 5 pin plug to be used Pin 1 earth pin 2 data neg cold .Pin 3 hot pos 4 and 5 are not often, but are for return data from dimmers etc
Some kit now often uses 3 pin plugs for cost and also mic leads can be used BUT SHOLD NOT as IN audio Pin one is also conected to plug outer in dmx it is not and can give probs in big rigups if used
Most 3 pin makers use the same pin out as in 5 pin (1to 3)
BUT some say its 3 pin AND as sutch in the audio world PIN 2 is the hot or pos and pin3 is the cold.
I think SoundLAB is one of these makers. If ALL KIT in rig is SoundLAB all would work fine Mix kit PROBLEMS start
This would mean the 1 unit I have that works with no cross cord is the odd one out now! It may be modified in some way to make it standard.I will investigate this new idea ASAP
See this new link It the same but more up to date than the last one and explains all wellhttp://discolitez.com/phpbb/viewtopic.php?p=7827&sid=59a03dd5274fa959d22c3a6fc3bdab74
Think a DMX rigger needs in his tool box a 5pin to 3 straight shot male/female patch cord
and 3 pin to 3 M/F crossed cord two off
. As after a soundlab the cross must be taken out
to get back to normal
Sorry for so much info in one day. Hope it is of interest
Mike
April 9th, 2008 at 10:53 pm
Sorry Link to new site is
http://www.usbdmx.com/forum/viewtopic.php?t=57
Mike
April 10th, 2008 at 8:32 pm
Hi Mike
I did a search and found some references to DMX hot/cold swapping for Soundlab kit (like I said, not really familiar with it myself). Your information will be a great help to anyone else searching for an answer. A quick Google didn’t seem to find anything much like a user manual though.
A few of the disco manufacturers followed this DMX pin configuration, particularly early Martin kit ( particularly the Robocolour as I mentioned). All the lighting companies that I have worked with have, as well as 5-3pin / 3-5 pin jumper cables, some specially marked hot/cold swap jumpers to solve this problem.
But to be honest, we don’t really use that kind of kit anyway. Thanks for your work and for letting us know your findings.
April 16th, 2008 at 7:13 am
Hi Rob
Just to sum up. Even SoundLAB equipment can be found wired to both standards
The only saving grace is that if You look at the XLR plug diagram by the plug,it shows the pin out polarity.However even this is not foolproof. Have a dimmer not as diagram
Mike
April 24th, 2008 at 6:59 pm
Hi
Just purchased a soundlab package.8 Par 56 cans on 2 T bars with 2 x IEC blocks for the lights into bulgin coonector to the controller. Fine so far but I have no contol over it as it either chases at different speeds of sound activates. This is OK but I need to isolate some of the lights for dimmer purposes. What do I need to do this?
Thanks
May 20th, 2008 at 12:17 am
Hi Mark
Sound to me like you need to take external or manual control in some way
What sort of controller is it please Is it a dimmer unit with programed chase function and sound to light.
The main Question is Has it got a DMX input
If it has got DMX in then you could use a laptop computer
with DMX software and a DMX interface to convert USB to
DMX protocol
I use a unit made by a firm called Afterglow This firm also provide the software. Popsoft DMX control 2.9
With this software you can do any think you like If you can get your head round the software fully
ie
Manual fade of any channel via on screen faders and mouse
Automatic lighting changes set in time and/or with sound or manual triggering
Sound to light disco style With manual override of any channel (Sounds like this is what you may need)
Lighting displays set to music. Programed by hand
Lighting displays are what I am currently working on. Now having more success with the software a bit hard to understand at first
Maplin also do a unit as a kit with software
Or you could use a small DMX Dimmer control console as a better option maybe. Not sure of sound to light function on low cost console units
This is more in Robs line I think
Over to you Rob
Mike
May 20th, 2008 at 7:23 am
Mark/Mike
Mike has pretty much hit the nail on the head. If the controller only does sound to light chases, then you need to split out a few of the PARs to another supply.
The simplest way to do this would be a 13A to IEC cable, plugging a PAR into a wall socket. No dimmer control but…
You can get small dimmer units or a single channel “followspot” dimmer for a bit more control. It sounds unlikely that you would need much in the way of a DMX console controller - 8 PARs is good for lighting a band or a dancefloor but you don’t usually need complex control.
Sorry, missed this comment. Thanks Mike, I am always pleased to see OSL readers helping each other.
July 7th, 2008 at 4:23 am
I am new to DMX. I have a small musical group I am considering using the Led Lights controlled by DMX(dmx-512). I am planning on using at least 8 led light units, each unit has 4 channels. Channel 1 (Blackout/Strobe/Dimmer. Channel 2 Red. Channel 3 Green. Channel 4 Blue. My question is on the controller how many channels do I need to controll this system to have an effective system for chase programs on these units
July 7th, 2008 at 7:54 am
Hi Al,
It depends on how fancy you need your chases, but even just 8 DMX channels will give you some flexibilty. Half your LEDs set to DMX 001 and half to DMX 005 will mean you can flip-flop chase between two sets of LEDs.
Don’t forget that LED chases can flip between colours, not just turn on and off. Take a look at DMX Control for LED Lighting
July 7th, 2008 at 4:19 pm
So 16 channel controller should be adaquate then?