A Simple Guide to DMX by Nicky Burke

April 8, 2008 by Mobile Beat Staff Writer

Introduction:I’ve written this document with the intent of providing the DMX novice a quicker understanding of what is going on in his/her ‘new realm’ of intelligent lighting. I’ve made every attempt at providing this insight from a mobile DJ’s perspective. For whatever their reasons, I’ve come across entirely too many DJ’s who dive head first into intelligent lighting, at great expense and without a clue as to what’s involved or without realizing the tremendous learning curve that lies before them. One must understand the basics prior to just getting a start much less becoming an expert. I’ve been at it since 1989 and I am by no means an expert although many think of me as such. I do have a distinct advantage over many in that I posses a high degree of electronics knowledge mostly thanks to my USAF days, nearly 35 years of computer programming experience at NASA, a rather lucrative 18 year part time career as a professional musician, not to mention it helps having been a mobile DJ like yourself for the past 17+ years.

What do I need to build a decent lightshow?
Any decent lightshow, whether it’s built using basic garden variety floodlights, sound active analog fixtures (more commonly referred to as “spin & pukes” at the street level) or fully DMXable intelligent luminaires, requires and should have a solid foundation. The ideal position for lighting relative to the human eye, is at 90 degrees which means directly overhead or in the floor. This is totally impractical for a mobile DJ, therefore we seek a reasonable compromise in using tripod stands, T-bars and trusses. Since this obviously changes the lighting perspective, we split the difference and shoot for 45 degrees to the eye but, the higher the better. Anything to keep the clients and guests from complaining about the bright lights.

Keep one thing in mind when you purchase such items; preplan your lightshow and buy quality so as to only do it once. Otherwise you’ll be replacing those stands very soon because the average weight of an intelligent fixture is around 20 lbs. and it doesn’t take many to reach or exceed a safe load rating of cheaper stands. Before you say a light stand is a light stand, remember whose head they’ll be hanging over. And while you’re at it, safety cables are a really cheap insurance policy for everyone involved as well as those expensive fixtures.

The absolute base of any light show should always be color fill and since we’re talking about dmx intelligent fixtures, color changers or wash type moving yokes to be more specific. This major ingredient can affect a crowd’s attitude and mood and for some strange reason, nearly always gets overlooked and skipped by beginning light show planners. If you think color fill is unimportant, think again. It is the basis for all stage type shows whether it’s for a guest speaker, fashion show, stage play, a DJ or even a full TV production or Hollywood movie. A deep blue color fill, reminicent of moonlight, can establish a kind of romantic, easy-going and laid back atmosphere with soft music playing. Add a little primary green, a little low lying fog and now you’re in the midst of one of those eerie scenes you see in horror movies. On the other end of that color spectrum, red, orange and yellows often times generate feelings of angst and mentally are associated with feelings of rage or anger which infuses bursts of energy.

If you still don’t believe it, pay more attention to the color atmosphere at your more popular big time night clubs. Take notes on how the ambiance of the dance floor changes as the BPM’s rise and fall. Notice how that UV blacklight color sets up the glow of bright irridescent colors. No matter how much you want those scanners, strobes and other effects, remember they will always look better contrasted against a full wash of color. Your first investment should be in the biggest, baddest, most powerful color changers or moving yoke wash lights you can afford. A one time purchase that can be a show in themselves, and once that good background is in place, then you can add the “Wow Factor”. Often times beginners start with the effects because they think they’re “kewl” and then once they have and use them a couple times, discover they’re boring or plain and just don’t have the impact they really expected from such a big investment. It’s because they failed to see the big picture and didn’t realize the importance of that preset mental state that made the effects jump out at you. This is a subtle yet very important fact.

Intelligent fixtures – What are they and what do they do?

Intelligent luminaires or intels as we DJs refer to them, are much the same as all those analog or sound active fixtures we’re all so familiar with, but with one major and distinct difference. That being control. With those S&P’s, a heavy bass beat can make it move but that’s about all. The only control you have is whether it’s ON or it’s OFF and most of the time, they have duty cycles; a time period it needs to relax and cool down, otherwise it’ll go up in smoke because it doesn’t have sufficient cooling mechanisms to disipate the heat of those high powered halogen lamps. Minimal control but for the remainder of what the effect does, you’re at the mercy of whatever it was the designer wanted the fixture to do. An intel on the other hand, puts control in the operators hand. An intel may be triggered by that same heavy bass beat or some other source but you, as the operator, can decide not only when it’s ON or OFF, but what COLOR it will be, WHERE the beam will be directed and what SHAPE the beam will be as well as strobing or constant.

Fixtures generally fall into five categories.

FILL LIGHTS – which includes flood lights and color changers/scrollers
MOONFLOWERS – Includes mirrored balls and many other fixtures whose source is bounced off some form of mirrored base.
BEAMERS – probably the largest group including followspots, pin spots, scanners, and all those that generate very sharp, crisply defined beams.
STROBES – a highly specialized form of flashing light
LASERS – a highly specialized light source, mostly monochromatic (one color) but are getting better with technological advances.
Nearly every fixture made, either S&P or intel, can be placed into one of these five basic categories.

DMX – What is it and how does it work?
DMX, in so far as a DJ need be concerned, is an acronym for the term “digital multiplex”. If you know absolutely nothing about electronic multiplexing techniques and how they work, don’t worry about it. Just understand that it merely means that there are multiple signals all sharing a common path at the same time. For simplicity sake, think of it like the cable TV connection into your home; a single cable from the outside world that comes into your home. Surely you have more than one TV set in your home so let’s assume there’s one in the downstairs family room with the second being upstairs in the master bedroom. So you’re downstairs watch Monday night football on Channel 5 while the little lady is up in the bedroom watching the LifeTime channel’s Golden Girls on channel 42. How can this be …. two shows on the same wire at the same time?

As a matter of fact, there are many more shows on that same wire than the two being watched. All the TV station’s shows are there, being multiplexed onto a common FM carrier frequency. What determines the show you’re watching is the tuner inside the TV. The correlation here is that in a DMX domain, your intel fixtures also have a form of tuner, that being their DIP switches. There is one major difference and we’ll see that very shortly in the next section.

DMX ADDRESSING or setting the fixture’s tuner!

This is likely the most difficult part to understanding DMX protocols and mistakes here are most often the cause of most problems you’ll encounter while attempting to learn about it. There are a few basic rules to remember:

RULES:

The DIP switches are used to establish the starting address for a fixtures. DMX fixtures generally require more than one DMX channel with very few exceptions.
The number of DMX channels required is determined by the number of functions a fixture allows you to control.
DMX channels can be shared by more than one fixture BUT those fixtures should be of the same type and manufacturer. Otherwise you’re leaving the potential for control problems later. When DMX addresses are shared, all fixtures sharing that address should remain in sync.

There are 512 addresses available (soon to be expanded to 1024). The address you set for a DMX fixture is the starting address for that fixture (Rule #1). The fixture will actually occupy an address block equal to it’s starting address, plus the number of DMX channels it requires, minus 1.

Applying these basic rules, you should understand that each DMX fixture should have it’s very own DMX address block for control and that no other fixture’s DMX address should fall within another fixture’s DMX address block unless sharing that address is intentional. To do so would cause a situation known as DMX crosstalk which means making an intended change to a setting for one fixture would inadvertantly make a change to a setting of the other.

The time is here to discuss those little DIP switches and how to set them; basically setting the tuner in each of your fixtures. There are usually ten DIP switches used for setting the starting address on each fixture. These switches are numbered 1 thru 10 respectively. Each switch carries a numeric DMX address value equal to 2 times the value of the previous switch. Any switch in it’s OFF position carries a value of zero (“0”). When a switch is turned ON, then it’s associated numeric value is accumulated as part of the total starting address. The values for the DIP switches are as follows: Switch No. Value
Switch #1 1
Switch #2 2
Switch #3 4
Switch #4 8
Switch #5 16
Switch #6 32
Switch #7 64
Switch #8 128
Switch #9 256
Switch #10
Note:
Switch #10 is generally used for some special setting within the fixture. On newer fixtures, it will carry a value of 512 so it may be addressed into the larger 1024 address domain.

Using the DIP switches and the address values in our table, if you wanted to address a 6 channel DMX fixture like the ADJ Concept-1 to have a DMX starting address of 49, then you’d turn ON switches 1, 5 and 6 which accumulatively would yield an address of (1 + 16 + 32) 49. That ADJ Concept-1 is now tuned in to a DMX starting address of 49 and it’s DMX address block would be DMX channels 49 through 54 (49 + 6 -1). DO NOT confuse DMX starting address with DMX address block. The DMX starting address is only one channel; the DMX address block is a grouping of contiguous DMX channels as determined by the number required by the fixture for control.

Are you confused yet? Well, to make things easier, I highly recommend you visit the American DJ Website. On the left hand column of their website, select SUPPORT. Once the SUPPORT page loads, select “Click Here for Product Manuals”. Download the DMX-512 CHART.pdf file and print a copy to keep with your fixtures and/or controller. Believe me when I tell you it’ll save lots of setup time and troubleshooting in your dmx environment.

Now return to the ADJ Website Home Page. Under PRODUCTS select LIGHTING, then under LIGHTING select INTELLIGENT. Once the INTELLIGENT LIGHTING page loads, select Concept-1 and download the User’s Manual for that fixture. Print a copy for yourself as reference because you’ll most likely need this to understand the next section.

Now, you might ask “How is it you know that the ADJ Concept-1 fixture uses 6 DMX channels?” The answer can be found in the “Owner’s Manual” for that fixture and every fixture has one. Therein lies a table commonly referred to as the fixture’s DMX Protocol. Defined in that table are each channel number, the function it controls, a list of numeric values and the effect it causes on that particular channel. In the case of the ADJ Concept-1, the 1st channel controls the left/right PAN function of the mirror and in our example that would correspond to dmx channel 49, the dmx starting address that we set with the DIP switches. In that same table we’d find that the 2nd channel controls the up/down TILT function of the mirror and that would be on channel 50 which is the 2nd channel within our fixtures’s dmx address block. The 3rd channel controls the position of the COLOR WHEEL which would be on channel 51. The 4th, 5th and 6th channels with respect to our dmx starting address control the GOBO WHEEL, SHUTTER and MIRROR SPEED on channels 52, 53 and 54 respectively.

OK … Got it tuned to a dmx address, so now what?

Hopefully you’ve got a basic understanding that each fixture has a starting address and listens for input on any of the channels within it’s respective address block. What exactly is it listening for? It’s waiting to receive numeric values on the channels within its address block. These DMX values, not to be confused with DMX addresses, are numeric values from 0 to 255 that will instruct our intelligent fixture what posture to assume. These values, in order to be represented as a single byte of information, will not be transmitted in the decimal format we’ve discussed, but rather in a computerized hexidecimal format. I don’t want to get into detail on the basic internals of computers, so the actual control values will be transmitted as 00 thru FF, where x’00’ equals zero (0) and x’ff’ equals 255. To analyze what would happen, we’ll stick to the decimal equivalent values for the sake of our discussion which are the values you’ll see published in the dmx protocol tables for fixtures.

Internally, the functions of an intel are controlled by special motors called stepper motors. Unlike a standard motor that merely spins when you apply power, stepper motors have specially designed windings that allow the armature (the center part that spins) to be turned and then held at specific points in a 360 degree arc. It is this controllable positioning that makes them useful for this application. An intel may contain many of these motors to perform all its various functions and each will require at least one DMX channel and sometimes more for that control. Attach a circular disc with color glass or punched images, locate it to be within the light beam and we’ve got color and/or gobo control.

In the previous section, channel 49 controls the left/right PAN position of our ADJ Concept-1 scanner. The mirror is attached to one of our stepper motors. A value of 0 would force the mirror position to one extreme, lets say far left. By the same token, a value of 255 then should force the mirror to the extreme right. This means that a vlue in the middle, say 127, should set the mirror aroud the midpoint. The same could be applied to channel 50 which would be the mirror TILT, channel 51 the COLOR WHEEL, channel 52 the GOBO WHEEL, channel 53 the SHUTTER and channels 54 the MIRROR MOTOR SPEEDS.

Congratulations, upon reaching this point you should have a good idea on how to address a single dmx intelligent fixture and how to make that fixture do the task it was designed to perform. There you have it; DMX in a NUTSHELL! The next step is to apply this basic knowledge on a larger scale.

But how large?

To answer that depends on how many intelligent fixtures you have, how many dmx channels each requires for full control and how many channels and fixtures can your controller handle simultaneously. Today’s dmx market offers many different controllers from simple to complex and everything in between. A simple controller like the Martin 2518 can control 72 channels. An example of a mid-level controller would be the Chauvet DMX-50 which can handle 192 channels that also includes additional fog/haze control and offers a jogwheel for followspot control. On the upper end would be the NSI MLC-128 capable of all 512 channels and contains a full library of various manufacturer’s fixture traits so you don’t have to remember what channel does what. These are all known as hardware controllers.

There are software based controllers available as well. These run on some form of PC based computer platform, mostly WINDOWs based. PC based control generally is more expensive but offers better control capabilities than hardware based controllers. Light motions are often “precanned” in the form of macros which is prewritten software to perform repetitive tasks like mirror positioning in circles, arc, horizonal and vertical sweeps or figure 8’s. The software is often able to address the largest of DMX domains (i.e. the full 1024 DMX channels). Examples are Chauvet’s ShowXpress package, Martin’s LightJockey. As technology progresses, we’ll be seeing more and more 1024 channel domains and maybe even 2048 channel domains. Eventually all this growth could lead to a complete changeover in the protocol itself; a new standard. An example of a protocol changeover would be something akin to the switchover from normal TV transmission to HDTV which is currently scheduled to take place within the next couple of years.

So what is DMX programming?

Programming is nothing more than performing a series of steps in a logical order or sequence. In lighting, were going to preset multiple intelligent fixtures to some preset set of conditions and save those settings for later recall. There are three basic rudimentary building blocks to DMX programs and these are SCENEs, PATTERNs and SHOWs. The most basic is the SCENE and each builds upon the other.

A SCENE is a static setting …. a group of fixtures that are set to establish a baseline. In a SCENE there can be color wash, spots, gobos, a variety of intensities for highlights but there can not be motion in any of the X-Y-Z geometrical planes. This being the case, a rotating gobo would be permitted so long as it doesn’t move laterally.

Next is the PATTERN. What establishes a PATTERN? Let’s look at the basic scene … all fixtures aimed at a fixed point, all are red in color and at full intensity. Save those setting into your controller’s first memory location. Next switch the colors to blue and reposition the beams to alternative points and save this in the controller’s memory. Repeat again with orange or yellow, save it and then again with green. Now playback time! Cycle through the four SCENEs we’ve just saved and do it repetitively; you’ve created a PATTERN. As you can see, stacking simple basic scenes and sequencing them results in a pattern. If we were to do the same enough times to the point where we can now sequence patterns, we will have created a SHOW. This is basic dmx programming.

As one could well understand, DMX programming is a tedious and time consumming task but that is what I’ve been attempting to tell you all along. This is the part most DJ’s don’t realize … the time element required to make a great show. There is no mystery to it; only hard work and a lot of imagination!

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Mobile Beat Staff Writer (228 Posts)

This is the general editors account for Mobile Beat Magazine and Website. Who reads Mobile Beat online and in print and attends Mobile Beat events? DJs, VJs and KJs to start with, especially those who own and operate mobile entertainment services. They provide music, video, lighting and a myriad other entertainment choices for corporate events, wedding receptions, dances and innumerable other gatherings.


Filed Under: Lighting