20-channel DMX Controller

[Joshua] shares his details on building this 20-channel DMX controller. He’s sourced some extension cords to cut up for the complicated wiring project. He plans to drive 120V lights with the system so he’s also using the extension cords to connect a bunch of outlet boxes to the main controller. Inside you’ll find a set of AVR chips ready for your commands. Instead of using jumpers or DIP switches to set their addresses he set them in the firmware and burned a different version to each chip. The key here is writing the address right on the chips to prevent any confusion.

This will be used of Halloween and Christmas displays. We love Halloween hacks just about as much as we love Christmas hacks, so hit the basement and don’t forget to share the result of your labors with us.

29 thoughts on “20-channel DMX Controller

  1. While cool these things always make me cringe, Those outlet boxes + extension cords makes me question the safety of a setup like this.

    especially if it is planned on being used outside, or inside.

    If I was going to use something like this outside I would employ some type of weatherproof outlet boxes and GFCI outlets.

    this may add some considerable cost to a project like this but when it comes to safety I think it is worth the extra money.

  2. Nice build. I personally don’t like the use as the ground cable as neutral and the neutral cable being used as a hot. Should have gone to a hardware store and bought a 4 conductor wire. (black-red-white-gnd)

    Also, would be cool if it supported triac-dimming.
    And if the site was readable :P

  3. @poiso:
    Good call on GFCI. Though, since this this runs off only 2 circuits, might as well put 2 upstream rather than buying a pile of them.

    But yes, weatherproofed boxes are a great idea.

  4. Am I missing something here? DMX has 512 channels, right? So, is this even DMX? Why not run all the power separate from the controller channels? This seems a little backwards from any professional hardware I’ve used…

  5. “This seems a little backwards from any professional hardware I’ve used…”

    I bet any professional hardware you have used was not built on the kitchen table either

    Good stuff, and I am not sure what the big deal is about the extension cords, and that short length, take a trip to your local stage before or after shows you see the same thing (although usually bigger boxes and thicker cords to hold those bigger boxes)

  6. I don’t get it 100% either. Normally the DMX controller is the master, for instance a programmable light board or a computer.

    The DMX interface itself is a serial RS485 multidrop with a slightly odd clock frequency that I can’t remember right now.

    Anyway to the controller, slaves like DMX dimmer packs and other DMX controllable units would be attached, normally daisy chained, with one in and one out XLR type connector for each unit.

    Since RS485 can be transmitted over some distance the DMX “slaves” can be placed where needed. The last unit will be terminated with a resistor usually inside an XLR connector.

    When you are controlling lights for instance with a dimmer pack, the dimmer always lets some current through the light. That because tungsten and halogen lights don’t last long if you turn them completely off and then on repeatedly.

    So I guess this should really be called a DMX relay and not a DMX controller.

  7. Neat and useful project. But the web site is something to behold. Honestly… blue text on a black and green background! Did he learn HTML in 1991 and never return to the web?

  8. 1) If this project even uses DMX, it shouldn’t be labeled as such.
    – Each channel is either on or off. Not DMX
    2) He has twice as many relays as he needs
    – Neutrals can also be bridged together.
    3) Website is impossible to read.

    On the plus side
    1) Nice PCBs
    2) Shitton of pictures (almost make up for the lack of readable text)

  9. I applaud the built spirit. Some of the execution, however, makes me cringe.

    Get rid of the extension cord wire. As someone else already said, find some decent four-conductor cable. Most hardware stores have it.

    Red and blacks are ok for hot.
    White for neutral.
    Green for ground ONLY. BTW, make sure you have ground continuity from your outlets all the way back to your source.

    Get some waterproof outlet boxes.

    I’ve been told that if you Macguyver something that is not to code, and you end up killing someone or burning your house down, your insurance may not pay up.

  10. why even use the extention cords, there only a few feet long, why not just mount all the outlets in a nice box.

    would make it more portable and easier to use. would be less of a mess to.

    but I like the work he did, if he added fading and such it could be a powerful tool.

    how many watts per channel?

  11. Not that I disagree with the 4 wire and ground wire comments, but if this is strictly for Christmas lights then they tend not to have a ground anyway.

    Also the colours don’t matter, who cares if ground is green, if no one else is going to look at it then you can use whatever wire you want for whatever. Just be consistant

  12. DMX is an electrical spec and protocol for controlling lights and other stage devices. It is packets of up to 512 8-bit “channels” that a device can interpret in any way. Fog machines and light truss wenches understand DMX these days. A dimmer pack is just one of many types of devices that use the protocol.
    What this guy built is a switcher or relay pack, not a controller. Looks great. Triac dimming is much more complicated than switching, especially at 20 channels. I think he should have gone for 24 channels to fully utilize 3 dmx channels (24-bits), and he could have used better wiring with fuses, but I bet this box is going to make one awesome Christmas display.

  13. Dmx is broken into universes. Each universe has up to 512 channels. A single fixture can use several channels. An inteli-light for example. You have channels for x and y axis, filters, and light control. The diyc site mentioned has been offering plans to build light control systems for several years. I have 96 channels built from the plans at DIYC. Each channel is designed to handle 1-2 amps of lighting. But even at that you can see that the amps can quickly add up. The switch to LEDs has helped immensely though. The systems I have built have worked incredibly well for Christmas and Halloween. A little common sense goes a long way towards keeping the systems safe.

  14. Cool project. Have to remember to add up total load on all the controlled devices + power on surge currents to pick the right size wire for the main power plug. The two plugs as shown in the photos with that wire size is not enough for 20 outlets unless all outlets are under 1A and even then you may have issues because some circuits have breakers that trip at 15A.

    Really need something like a 10AWG sized wire for the plug if you plan to have any length to the wire going to the wall outlet.

    Something else to consider is using opto isolated relay drivers so that if something does go wrong , a relay shorts out for instance, the current will not run back through the setup controlling everything. A part like the 4n25 only cost about 30 cents and could be put on a board in between the wires that go to the relay control . Well worth the time and cost for what it adds.

  15. Something else I just noticed. The relay control board and the 120VAC side are both in the same box that when closed will put them right on top of each others. That is a BAD idea. If anything shorts or a wire pulls out of a screw whatever is connected to that setup controlling it will fry.

  16. @catzburg “Also the colours don’t matter, who cares if ground is green”

    It also doesn’t _REALLY_ matter that you pair up the “right” color wires in a Cat5 cord, or that you use black for positive polarity in your car, or that you use blue for hot water and red for cold, or even that you have personally renamed backslash to “sloppy joe”. None of those things would prevent anything from working as long as you were the only one that ever used, maintained, or created your equipment.
    Adhering to standards saves you headaches in the long run and in many cases prevents potential safety hazards, but it IS entirely up to you whether you want to use them or not.

  17. dmx is the perfect protocol for a project like this, and those who think it’s not have no idea about professional lighting control… and should shut their little blogging fingers in the door of their car. Dmx does much more than dimming.

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