The DMX World

[zac850]

Ok, im really curious to learn about DMX and how it really works. Currently all I have ever done with DMX is to hook our bad light bord (an American DJ desk, DMX 512) to 2 dimmer's, (daisy chained, out of the bord, into the first box, out of the first box, into the secound box). I want to learn how to really use DMX. For instance, what are the different DMX universes? Also, how do (inteligent) lights take up more then one DMX channel? The way i've always done it (with the 12 lights my school has) is use DMX to run the dimmer's which are connected (with extention coards) to the lights. Also, how would you run this in a show? I'm assuming that theres a DMX in type of port in the inteligent lights, but how do you program it so that circut 27-34 or whatever is for this light, and circut 34 to whatever is this other thing....

As you can see, im confused with DMX and how to use it.

Thanks
Zac

[DMXtools]

I've got something posted on my website that might be a decent place to start. Check out http://www.dmx-tools.com/DMX512_Primer.html - I tried to write it so you don't need an engineering degree to understand.

John

[zac850]

Thanks!!! Thats just what I was looking for!!!

I had a funny feeling that you would be the one to respond to that post...

[cruiser]

I used http://www.dmx512-online.com/ to learn DMX, it has animations and stuff that might help you understand a bit easier, its also explained in every day language

The guy that wrote that sight is an absolute electronic genius, he is also very helpful... I have often emailed him with some questions or problems and he is always more than happy to help!

[The_Terg]

Well, Im into some DIY projects... Maybe if I have the time I can give a really simple DMX controller a shot.

what kind of IC/capacitor circuit can I use to get a clock cycle of 4 microseconds? I would need a circuit that simply gives a clock pulse output every 2 or 4 microseconds. Thats really the only part that I have no idea about. After that, I could just use some kind of BASIC Programmable IC chip to store lists of binary commands for controlling a dimmer. For a kind of test rig.

[DMXtools]

what kind of IC/capacitor circuit can I use to get a clock cycle of 4 microseconds? I would need a circuit that simply gives a clock pulse output every 2 or 4 microseconds. Thats really the only part that I have no idea about. After that, I could just use some kind of BASIC Programmable IC chip to store lists of binary commands for controlling a dimmer. For a kind of test rig.

It's not just putting out binary data at 250Kbps, but generating the break between packets and the mark-after-break that turns serial data into DMX-512.

I do everything with a little 8031-family microcontroller. Philips has a nice, cheap little chip, the 87LPC762, that does a nice job. The 87LPC762 is a little 20-pin DIP IC with an 8-bit microprocessor, a couple 16-bit counters, a serial port, ram and EPROM (...and a partridge in a pear tree) all on the same piece of silicon, for under $3. I used it for the internal DMX-512 upgrade I designed for James Lighting controllers.

All the critical timings for DMX-512 can be generated by hooking it up to an 8MHz crystal (80 cents) and setting up the right sequence of instructions.

I believe you can find a link to a shareware assembler for it on the Philips website - along with some sample applications (none DMX-512) and a .PDF of the data book... or Keil Software has a demo version of their UV2 development environment for programming in C. It does everything my full version does, but is limited to programs of 4K bytes or less (the EPROM on the LPC family is 2K).

If you want to do more of a real controller, the 87LPC767 adds a 4-channel, 8-bit analog-to-digital converter on the same chip - still in a 20-pin DIP. Use the A to D to read the positions of up to four faders and the serial port to turn that information into a DMX packet. Uses the same development software and still costs under $4.

String together a couple 4051 analog multiplexers to be able to read more faders and you could easily make a decent 2-scene controller on the cheap.

John

[The_Terg]

Cool, I was hoping to find an all-purpose IC like that... Hmmm, i definately feel the need for a new DIY project... (DMX Tester/controller)

After all, focusing lights is really a two man job in our auditorium... one needs to be up in the booth fiddling with the board, and the other doing the actual dirty work. If I could DIY up a simple little DMX tester, I wouldn't end up running my ass off between the stage and the booth. Besides, I want more of a challenge after I built myself a little pocket headphone amp.

Ill take a bigger dig at it when I get back from DC on monday..

[Nephilim]

Cool - I never realised that the channel numbers are implied rather than expicitly stated - I guess you need as much speed as possible. This puts the onus on the decoder to get the right channel data, I suppose.

[cruiser]

What kind of desk do you have? A generic remote control might work? i know that you can get ones that you run out the end of your daisy chain for desks unlike the strands that dont have a dmx remote port!

We have one for our event, looks quite similar to the ones for the strands too....

[The_Terg]

I unfortunately know that my board doesnt have any remote capabilities. Its a Lee/Colortan 'scenemaster', and I havent seen it anywhere