Control/Dimming "Facts" about DMX

[derekleffew]

From http://www.cheaplights.com/cart/page38.html :

Let's talk about DMX cables... I recently received and email from a blog monitor that said... "There are MICROPHONE cables and there are DMX cables and one can NOT be used for the other". That's a very strong statement. Very "Black and White". Unfortunately, it's also very untrue. That statement would be like saying that Chevy's are for taking your kids to school and Ferrari's are for racing and one can not be used for the other. I have seen many people race Chevy's successfully and I have also seen a few Ferrari's in the school pick up lanes. I don't know exactly why people make those black and white statements about DMX cables. Perhaps they merely lack real world experience in the field. If they had real world experience, they would know that there were companies like NSI making digitally controlled lighting boards and dimmer packs with signals carried thru 3 pin XLR cables long before the term DMX was ever heard of here in America. (NSI calls their proprietary signal MICROPLEX and they still use it today). What do you think those digital signals were carried thru back before the late 90's when DMX was introduced to the commercial market here in America? MICROPHONE CABLES. That's all we had back then, that's what was used and that's what worked for years. Perhaps some cables marked "DMX Cable" might perform better than some cables marked "MICROPHONE Cable", but it can also be proven that some mid to high grade MIC cables work better than some DMX cables and if you and your audience can't tell the difference, who cares? What does matter is which pins the wires are connected to on the 3 pin XLR plug. At High Energy Lighting (CheapLights.com), we currently buy "MIC" cables and "DMX" cables from over 22 different suppliers. Regardless of how they are marked, we test samples from each different "MIC" and "DMX" cable model to make sure they work in a DMX chain before we ever offer them to our customers. Here's an interesting fact... In the ten to fifteen years that we have been selling cables for transmitting digital signals for light processors, we have never had any cables returned by customers saying they didn't work as a DMX cable, unless the cable actually had a physical defect, such as a wire not connected to the plug or a cut in the wire. That's a great statement to be able to make!
Here's a few more interesting facts...
1. "DMX" was created in 1986, but not widely used or known. At that time, the popular method for transmitting signal to dimmer packs was zero to ten volts.
2. "DMX" was revised in a major way and started gaining recognition in 1990. (But not in America).
3. The first DMX lighting controllers were displayed at the American LDI Lighting convention in 1999 by LitePuter.
4. "DMX" was introduced as the "Standard" digital signal for the World Wide lighting industry in 2000.

I have issues with each of the four "interesting facts" presented, as well as other statements I've bolded.

Don't believe everything you read on the Internet, kids.

 

[gafftapegreenia]

I...just...wow...

 

[Van]

I...just...wow...

and again..... wow I need to forward this to a friend....
wow

 

[gafftaper]

3. The first DMX lighting controllers were displayed at the American LDI Lighting convention in 1999 by LitePuter.

WHAT?!? It's not just wrong, it's wrong in VERY strange ways.

The basic premise that microphone cable can be substituted for DMX is true for a lot of low budget, small rig, non-critical applications... a very limited number of fixtures and a very short travel distance. Got it. The purists among us don't like to admit it, but it is true under certain conditions. But how do you get from that to some of the completely random and very wrong statements in there?

 

[Lotos]

If you really want to die of shock... Cruise on over to:
136: DMX Dimmer & Relay Packs and read the product description for 136-DMXDP4-08

4 channel DMX dimmer pack for use with 3 pin DMX controllers or as a stand alone controller with 16 built in chase patterns, programmable speed and dimming. 10 amps per channel. Pack has a max of 20 amps on at one time unless you remove the power cord and hard wire the unit. 2 sockets per channel. 2.75x7.5x10.25. 8 lbs. Fuses (4) ea. 156-F10-S

Seriously, wait, what?!

 

[fredthe]

Ouch. It's interesting that they are basically saying that because Microplex works over mic cables, then DMX should. Even worse, they admit to selling "microphone" cables as DMX cables.

-Fred

 

[fredthe]

If you really want to die of shock... Cruise on over to:
136: DMX Dimmer & Relay Packs and read the product description for 136-DMXDP4-08



Seriously, wait, what?!

Then, on the 6-pack right below it, they state

Comes with (2) NEMA 5-20P 120 V 2-pole 3 wire grounding plugs. If the plugs need to be changed they must be done by a licensed electrician.

I understand the need for caution when putting 5-15P plugs on this unit, but a licensed electrician? Sure, go ahead and hard-wire our 4-pack yourself, who is this UL guy, anyway. But, don't think about touching a plug on our 6-pack. Sheesh.

-Fred

 

[dramatech]

Of the several incorrect assumptions made in this poorly, non-researched, statement, let us start off withe one that says that DMX was not the first digital lighting signal. He goes on to state that Microplex was the first digital, and had been around for many years. Also he states that NSI created microplex.
Let us take this one point at a time. Microplex is an analog signal. The only thing that it has in common with DMX, is that it is multiplexed. This means that various signals are sent down a cable in a serial fashion. If you look at a multiplexed signal with an oscilliscope, you will see one pulse or packet of pulses one after another. In the case of Microplex and AMX192, you will see that the pulses rise and fall in amplitude as the channel controlling that pulse is changed on the control board. This is analog, as the amplitude is increasing and decreasing in voltage. In a digital signal, the amplitude remains the same,it is a series of pulses in binary fashion that create a binary number that relates to steps in an increasing intensity. In DMX there are eight such pulses per channel that in binary create 256 steps. These pulses are either on or off, but do not vary in intensity. There are of course several other pulses per channel in the multiplexed chain that tell a receiving device when to move to the next channel, and pulses that tell the device when to restart the count.

As for which was first, NSI had their analog micropex signal under the name NMX. Lightronics had a very similar signal called LMX128. I believe that Leprocaun had a similar system, but others could correct me on that. These signals were compatible in their analog information, but not in a voltage that was sent down a third wire to power the control board. Over a period of time Lightronics changed that voltage so that there was complete compatability. This then became Microplex and became a standard that was very popular among the small club bar band circuit, until the chinese started building inexpensive lighting control and dimming systems using DMX on 3 pin connectors.
AMX192 was a very similar system but a bit more sophisticated.

As to who created the first Digital control protocal, Colortran had CMX, Strand had SMX, and EDI had their own. All of these and probably more preceeded DMX and it is my uderstanding, that DMX is a system that used the best parts of these to create a standard that could be used through out the industry.

Now what I have stated here, is stuff that I have learned by personal use of the systems, a little reading, info told to me by others, some with questionable qualifications. So as Derek said "Don't always believe what you read on the web," or words of that sort. Now let the people who are better qualified than I, fill in the blanks and make the corrections. I would have to say, though, I think that I have at least researched my statement better than the uninformed egotist, that we are commenting about.

 

[Kelite]

This seems an opportune time to ask a question regarding 'three pin DMX' acceptance, but first a brief comment/statement from the USITT.org site

"Is any connector besides an XLR–5 allowed?
No ! Using anything besides the XLR–5 connectors as prescribed in all versions of the standard is not allowed and defeats the interoperability the standard is intended to provide. Equipment using an XLR–3 connector is not compliant with the standard and should not be marked as such. In very special circumstances, the ANSI version of the standard allows for the use of a non–XLR style connector. One of the provisions for this is that the manufacturer must supply an adapter.
USITT DMX512 FAQ

With the multitude of DMX operated devices offered within the US market, a number of them are 3-pin only, with no 5-pin connector/s on the device. These products seem to target the DJ market due perhaps to the rampant availability of 3-pin cable. (We can assume microphone cable is substituted for 'real' DMX cable- but that's another story/thread.)

Now- Q: Bearing in mind the DMX standard, do YOU as theater technicians regard these 3-pin only devices as legitimate within the market, or half-breeds trying to fit into the legitimate market?

(Canada/overseas is an important market, but this question is directed to US technicians and the US market only, please.)

 

[BillESC]

I'm stunned by the level of wrong in Cheaplights statement.

 

[dramatech]

Being a community theatre, with no lighting budget, (I am retired, and give what I am paid to be the ME, back to the theate, by purchasing lighting equipment for the theatre) I sometimes purchase lesser expensive items that have 3 pin XLR as their DMX connectors. If the item is pretty much a semipermanent install, I make an adapter to 3 pin. If it is an item that moves around a lot, such as a shoebox dimmer, I change the connectors on the chassis to 5 pin.
Keith, I am not sure that answers your question, but I think that it will reflect many CB members, as this is a forum that by it's very nature has many users of low budget equipment. If you ask this question on the Lightnetwork forum I would expect the answers to be quite different, but no more or less valid.

 

[derekleffew]

...fill in the blanks and make the corrections. ...

No corrections needed that I can see, dramatech. Except as an enhancement, to redirect your attention to this post: http://www.controlbooth.com/forums/lighting/8493-lmx-128-mpx-microplex-rs-232-a.html#post99619. And to say that Strand-Century released the CD-80 protocol, that which would later become AMX192-1986, in 1979 (although Darthrob13 says 1977). See also Lighting Control Protocols - Part 2.

 

[STEVETERRY]

From 137: Cables (DMX & Analog) :
I have issues with each of the four "interesting facts" presented, as well as other statements I've bolded.

Don't believe everything you read on the Internet, kids.

I cannot find one statement in this Cheaplights post that is correct. I recommend ignoring it. Unfortunately, I do not have the time or energy to correct each of the multitude of egregious errors.

Steve Terry
--Chair, USITT Dimmer Standards Committee (authors of the 1986 and 1990 DMX512 standards)
--Founding Co-Chair, ESTA Control Protocols Working Group (authors of ANSI E.11-2004 and E1.11-2008, USITT DMX-512A standard)

 

[photoatdv]

A school I worked with had a bunch of stuff from Cheap Lights... It mostly worked for very simple stuff. However, it had this strange fault where it started flashing on and off and nothing short of turning off the controller would stop it-- and sometimes not even that. We were never able to determine the fault-- it kinda just went away after 2 days.

And buy I wish I had a copy of the manual to post--- the first part told you to pleasure keep this manual for your pleasure. It also called pages "bands" and cues "banks" of something like that... it kinda gave up on it quickly.

 

[gafftaper]

Don't believe everything you read on the Internet, kids.

I cannot find one statement in this Cheaplights post that is correct. I recommend ignoring it.

Exception: When Steveterry is talking about DMX, you can bet your children that it's true. Somehow I doubt think the guys at cheap lights attended any of the meetings with Steve and the USITT standards team.

Perhaps the name "cheap lights" should be considered a hint at the quality of equipment and advice you get there.

 

[icewolf08]

Part of me wants to buy one of their 3-pin "DMX" cables and then return it saying it didn't work. How can they test it? Then send them a letter about how wrong they are.

 

[photoatdv]

Do it......

 

[misterm]

having little money left in our budget, we bought some cables from them this year along with some clamps because we couldnt find them anywhere that was even half as cheap. the cables are 3 ft cables and work fine for our LED pars. the clamps are a pain to tighten (they use a thumbscrew) and generally worry me. i only use them for the cheap/lightweight LED pars we have and am going to replace the thumpscrew on them soon.

 

[icewolf08]

Here's the thing, with the right adapter one could run DMX down an edison extension cord. Would it work? Probably. Is it a good idea? Not at all. It is all about using the correct tool for the job. Mic cables might work in a pinch, when you just have to get something working 5 minutes before a show, but they should not be used for long term, show critical use.

 

[photoatdv]

While we're on this topic... I was thinking about recommending 2x light trees w/ 4x 300w parcans and 2x shoebox dimmers from there to a school with no front lighting. Plan is to get the lamps elsewhere though. What do you'll think? Anyone know of an alternative that is about as cheap? They have a console that I'm fixing/upgrading so control is taken care of.

Do you think that stuff will be too crappy for me to get working for them?