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DMX originally considered unsuitable for lighting


micromusic

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DMX was designed for lighting, so I can't see how it was ever considered unsuitable for the purpose (and if so, by who?)

 

I imagine it's reasonable to believe that someone may have considered unsuitable for Automated Lighting (the subject matter of the book you linked to) as it was originally designed to control dimmers, and it isn't maybe the ideal protocol for some of the automated fixtures we have these days (like LED Washes that take 166 channels for a single fixture!) ;-)

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As Ross says, I find that idea quite difficult to believe. I don't really know much about the genesis and history of DMX512 as a control protocol, but I also was under the impression that it was designed with control of lighting equipment firmly in mind. Perhaps, as Ross also mentions, what you read was an anecdote concerning an expression of doubt regarding its suitability as a protocol for control of later generations of lighting equipment requiring greater control resolution, etc.? Not having read the book that you linked to, though, I can't offer any more than that.
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Two comments:

 

No matter what the technology, there will always be nay-sayers. People said it about the horseless carriage, and they'll say it about the hovercar, too.

 

Chances are, many of the nay-sayers will have some sort of interest in maintaining the status quo.

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Surely all Status Quo use are full par rigs, negating the need for DMX control (of moving lights) B-)

 

Not funny :P

 

As far as I was aware, DMX was just an extension of the RS485 industrial serial communication protocol.

 

Wiki article http://en.wikipedia.org/wiki/RS-485

 

The DMX512 'Website?'

 

http://www.usitt.org/Resources/Standards2/DMX512

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"Just an extension???"

 

And there was me convinced that the RS485 was the volty stuff and DMX512 was the bitty/bytey stuff.

 

RS485 being chosen for being capable of working in electrically noisy environs.

 

And what about IF SQ needed colour changers cobbled onto their Pars?

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And what about IF SQ needed colour changers cobbled onto their Pars?

 

Dwarf and a windy handle on a scroller! Job done :P

 

Edit to add, you'll need to attach a croc clip to his right ear, and left big toe and wire him into the mains, then communication is simply morse code ...---... :P

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Before DMX was widely used for moving lights there were at least two competing protocols, the one that Vari*lite used, which was something or other wierd manchester coded over coax if my adulled brain is working at all right, and the other was Martin's properietry protocol which was RS485 based on 3 pin XLRs. Both manufacturers provided both ends of the chain, ie lights and controllers.

 

When Vari*lite capitulated they made a rack box that converted DMX to Vari*speak. Martin just changed the firmware in their fixtures to accept DMX rather than their protocol, leaving the 3 pin XLR in place. And thats why theres a lot of DMX on 3 pin XLR about.

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When Vari*lite capitulated they made a rack box that converted DMX to Vari*speak. Martin just changed the firmware in their fixtures to accept DMX rather than their protocol, leaving the 3 pin XLR in place. And thats why theres a lot of DMX on 3 pin XLR about.

 

It should also be noted though that Martin's protocol had the data pins reversed - which is why the older fixtures need a phase-reverse cable in line with the DMX - which is a pain if they are sitting in the middle of a chain of fixtures - phase reverse in, then phase reverse at the other end. This then made 3 pin appear "acceptable" - being so much cheaper than 5 pins meant that cheap manufacturers started using them... and now we end up with the situation we have now, where people think using any old mic lead as a DMX cable is somehow okay.

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It should also be noted though that Martin's protocol had the data pins reversed

 

"Reversed"? Compared to what? The standard? There is no actual standard for DMX on 3 pin XLR, so although Martin used to do it differently to most people in the early days, they weren't "wrong", just "different".

 

Martin (in the pre-DMX days) adopted the audio convention of "pin 2 hot", which you would have to think was a decent choice, as audio had been through the "is pin 2 or pin 3 hot" battle of the preceeding decades, finally settling on pin 2 hot. Everyone else in lighting who came later than Martin (ie post DMX) used the same pin numbering as DMX does on the XLR 5 pin, which has pin 3 as +ve.

 

Edited for multiple spelling errors.

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It should also be noted though that Martin's protocol had the data pins reversed

 

"Reversed"? Compared to what? The standard? There is no actual standard for DMX on 3 pin XLR, so although Martin used to do it differently to most people in the early days, they weren't "wrong", just "different".

 

There is a defacto standard for 3 pin - it is the same as for 5 pin - you just drop the redundant pins. Maybe I should have said "Martins protocol used pin 2 hot whilst DMX is pin 3 hot requiring the use of phase-reverse cables" or something. It does not change the fact that Martin fixtures of that era that got firmware upgraded to accept DMX also needed the hot and cold pins to be swapped.

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While we're on the subject of proprietory control standards, let's not forget Pulsar's PMX - used for the first generation of Golden Scans, and the only option on the original Masterpiece 48 desks. They soon 'saw the light' and added DMX as well though!
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