DMX?

[amberjel]

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!

[JD]

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.

[SteveB]

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.

Thus a dimmer rack is listening to the entire DMX data stream of 512 addresses and is typically set for dimmer 1 to respond to address 1, with the color scrollers and moving lights listening to that same data stream. If you have 300 dimmers, dimmer 1 will respond to whatever the console is telling dimmer 1 to do, right thru 300. If you want 10 color scrollers to function, you choose a starting "DMX address" to be at 301 thru 310 as example (assuming the scroller uses one DMX addresses - some use 2) You then set console channels to patch those DMX addresses to appropriate channels to get the scollers to move from Home (zero value on DMX address 301) to the end of the scoll (100% for that same address). The scroller moves thru all the assorted colors on the way. If you add 2 moving lights, say High End Studio Spot CMY Zooms, which uses 24 DMX addresses to get control of all of these features, you tell the fixture to start listening at 311 thru 334, with the 2nd fixture at 335 and up. Those 24 DMX addresses control the assorted functions of the fixture, Intensity, Pan, Tilt, Zoom, Iris, Gobo 1 position, Gobo 2 position, dichroic color flag 1 position, flag 2 position, etc... which is why it uses 24 addresses per fixture.

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.

[kicknargel]

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.

[Kelite]

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

Please let us know how else we may help you!

[amberjel]

Thanks everyone!!

[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 !

[Kelite]

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

[chausman]

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

[techno89]

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

Don't. Go. There.

Oh. No. You. Didn't.

[Jamyo]

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?

[rochem]

Short answer: yes you do.

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.

[kicknargel]

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.

[Jamyo]

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

[mstaylor]

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.

[shiben]

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

Necromancy or something.

[SteveB]

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

Dimmer Doubling - Electronic Theatre Controls

[mstaylor]

Dimmer Doubling - Electronic Theatre Controls

Dimmer Doubling=Voodoo