DMX? is being discussed in the ControlBooth Lighting and Electrics forum; Can someone explain to me how DMX works in a simple way? I'm sure that's a stupid question, but I'm ...

1. ## DMX?

Can someone explain to me how DMX works in a simple way? I'm sure that's a stupid question, but I'm very confused. I'm from the old school - rack of dimmers that you have to patch by hand. I've managed to upgrade my knowledge w/ an ETC board, but have never had to set up intelligent lights. I've programmed intelligent lights, but never hung or set them up. Can someone explain this to me?

Thanks a lot!

2. ## Re: DMX?

Kind of a 512 channel lighting snake run over a single twisted pair as serial data. Each channel can be set between 0 and 255. Dimmers, movers, etc are programed to listen to one or more specific channels, so "patching" can be done at the fixture/dimmer, or by rearranging control assignments at the board.

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amberjel (December 22nd, 2010)

4. ## Re: DMX?

One simple analogy I heard is to think of a coal train with an engine and 512 coal cars. Multiple trains are sent down a track 44 times per second. A "device" watches to see how much coal is in car 1, or 2 or 57, etc... and translates that (digital) information to a particular command. If it's dimmer 57 and the car is at 28% full, then the dimmer varies the voltage to 28%. If it's a color scroller the motor(s) move (the scroll of color) to a position at about 28% of travel. If a moving light, it listens to 24 coal cars per ML and uses car 1 to control position on a tilt motor, car 3 is for pan motor, car 5 might be how far to open the mechanical shutter (dimmer). Car 6 says move to gobo 1.

If you screw up and put scroller 1 at DMX address 1, then everytime you try to bring up dimmer 1, you will move scroller 1 as well, because they are both configured to listen to that address.

The use of DMX to control things other then dimmers is one of the reasons the term Address is in use to define a particular DMX "coal car".

Because a single DMX "Universe (512 addresses) can only fit on one cable (or track), multiple cables are run for a 2nd, or 3rd, or multiple "universes" of DMX, each sending 512 addresses of data. Or the DMX data streams can be combined using Ethernet systems to allow up to 32 universes of DMX to be run on a single Cat5 Ethernet cables. Assorted companies use proprietary Ethernet protocols or they can us a new standard called ACN, for Advanced Control Network to send the data.

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amberjel (December 22nd, 2010)

6. ## Re: DMX?

For a few practical setup things (if that's what you need): DMX devices (dimmers, scrollers, moving lights, etc) can be daisy chained together. Each device should have a port for in and out. So, DMX comes out of the console, runs to the first device (often the dimmer rack) then out of that and to the next device, etc etc. You cannot make a "two-fer" or Y-splice. You can split the signal with a device know as an optical isolator, which has one in and multiple outs. These are a good idea anyway, as they protect your devices in the case of a wiring fault that could cause line voltage to pass down the control cable. Often you'll run from your console to an "Opto," then out of that to the dimmers and other devices.

DMX traditionally runs on 5-pin cable, but only uses 3 of the pins. So now some devices have 3-pin connectors and you can end up having to convert back and forth in your data chain. The connectors are XLR connectors, and you can sometimes get away with using mic cable, but it's not twisted pair and not properly shielded, and can lead to problems. Better to use specific cable (there are many discussions about this on CB). At the end of your data chain, it's a good idea to plug in a DMX terminator. This can prevent "reflections" of signal and bad data getting to the devices.

Troubleshooting DMX can be tricky. If, for example, a cable gets melted or there's a bad connector, the problem can manifest anywhere along the chain, not necessarily at the problem spot. You may have to start from the back of the chain and unplug one connection at a time until the devices snap back to where they're supposed to be.

In a quick search, I didn't find an article about DMX best practices. Might be a good idea.

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amberjel (December 22nd, 2010)

8. ## Re: DMX?

These have been very good explanations amberjel, and if you would like additional reading our friend and resident DMXpert Doug Fleenor has a few helpful pieces:

Doug Fleenor Design - DMX Basics

Doug Fleenor Design - DMX Primer

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amberjel (December 22nd, 2010)

10. ## Re: DMX?

Thanks everyone!!

11. ## Re: DMX?

Don't let 'em fool ya ! DMX Is Magick ! It's Black Magick of the foulest kind ! Doug Fleenor is the Lich King and all electricians will be bound to him in the Afterlife !

12. ## Re: DMX?

Originally Posted by Van
Don't let 'em fool ya ! DMX Is Magick ! It's Black Magick of the foulest kind ! Doug Fleenor is the Lich King and all electricians will be bound to him in the Afterlife !
Ya just HAD to tell everyone now, didn't cha?

:D

13. ## Re: DMX?

So if DMX is Black Magick, what is ETC's dimmer doubling?

14. ## Re: DMX?

Originally Posted by chausman
So if DMX is Black Magick, what is ETC's dimmer doubling?
Don't. Go. There.

Oh. No. You. Didn't.

15. ## Re: DMX?

Ok, so this might be a stupid question and I think I know the answer but just want to double check. If I have DMX from my console do I need a separate DMX box to power units? Ex: we have four Apollo color scrollers and the way it was explained to me, they needed to be plugged into the separate Apollo box (which is plugged in a grounded edison plug) in order to work. Do I need to do this or can't I just use the DMX output and be done with it?

16. ## Re: DMX?

The DMX coming out of your console is only a control signal. It tells whatever is on the other end what to do. However, it doesn't provide power for those things. If you ran DMX to your brand new moving light, but never plugged the moving light into a power source, it obviously wouldn't work, right? With devices like scrollers and gobo rotators, the manufacturers basically decided it was easier to run both data AND power through a single cable, instead of having to run two cables to every device. Scrollers generally use a special 4-pin connector which carries data from the console as well as low-voltage power from a "power box," more commonly referred to as a PSU. You provide both DMX and power to the PSU, then it moves all that around until it comes out the other side with both power and data in the same connector. This power and data then runs out to each scroller or other smaller device, and they work without you needing to run more than one cable. Pretty smart, eh?

For your purposes, you might be best off going with the Apollo Smart Power 200W Power Supply. This will power up to six Smart Color scrollers, or 8 Smart Color Pros. If you have any thought of upgrading in the near future, or you have other devices that run off of a 4-pin 24VDC power supply (like Apollo gobo rotators), you may want to get a higher capacity PSU.

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Jamyo (February 18th, 2011)

18. ## Re: DMX?

Someone will know about these specifically, but many scrollers have their own proprietary "brain." This is a box that sends control signal (I don't know if it's DMX or a proprietary signal) plus 24v power to the scrollers via 4-pin cable. So you do need the box. There are some scrollers that get DMX run straight to them, but they will each need to plug into A/C power.

MOD: this may want to be a new thread.

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Jamyo (February 18th, 2011)

20. ## Re: DMX?

Thank you both - that is very helpful and thank also for the quick response time!

21. ## Re: DMX?

There are LED fictures that need a brain to run also, ColorBlasts are an example. Also, remember there is a limit of devices per DMX chain and not all devices play nicely with dissimilar devices. Sometimes you have to seperate them to a seperate daisey chain but not necessarily a seperate universe. Always try terminating before seperation. I had a TV shoot the other day that when they added the LEDs the whole rig started flickering. He had terminated everything except that run, fixed in seconds.

22. ## Re: DMX?

Originally Posted by chausman
So if DMX is Black Magick, what is ETC's dimmer doubling?
Necromancy or something.

23. ## Re: DMX?

Originally Posted by chausman
So if DMX is Black Magick, what is ETC's dimmer doubling?
Dimmer Doubling - Electronic Theatre Controls