DMX Light Control For Home Automation

Generally, the only time I’ve ever seen DMX in use is for stage productions. [Dan] sent in his home light control project – he used a RS-232 to DMX interface and a bunch of commercial DMX dimmers. His light switches were replaced with potentiometers connected to the system via CAT5 cabling. The POTs send 0-10v up the line to the dimmers, and the manual control can override the automated(DMX) settings. The system is simple, robust and responsive – avoiding the delay pitfalls usually incurred by systems like X10.

21 thoughts on “DMX Light Control For Home Automation

  1. If I recall correctly, normal household dimmers use triacs/scrs to do the dimming, with a standard pot as the control. This means that the whole dmx dimmer system could have just been normal household dimmers, and digital pots hooked to the server. Would probably cost somewhat less than a professional dmx solution. Also, there would only be 1 line going to the control unit, not both the pot and the light itself.

    Still awesome though.

  2. Did anyone notice the plumbing located next to his mess of a DMX server?

    Nice setup tho ;) You must work on stage in lighting or something… You have a very clean DMX installation.

  3. Soundlab’s 4 channel dimmers can be had for about $75. Lowes sells (single channel) household dimmers for $10-$25.

    So, it is not _too_ expensive (especially if he recently upgraded a theatre and had these left over), and it has a pretty high cool factor.

    Good work [dan].

  4. atrain – yes standard dimmers are triac based, but your idea wont work as you think. The goal of using both DMX and the 10volt signal was to allow in room control as well as automated.
    in a normal household dimmer, the pot controls pulses to determine ‘on time’ (maby its off time, I dont *exactly* remember).
    In order for the automated server to take over, an override switch would need to be added to the dimmer module, in order to route the automated signal to the triac and bypass the pulse signal from the module’s internal logic. This would involve complete dissasembly of the module and likely some extensive mods (at the very least, cutting wires/traces and adding a few components.)
    Ultimately, it would be cumbersome, as the home user would almost always leave the switch in ‘room control mode’ for practical daily living.
    a completely custom made dimmer module might be a better solution, but at the very least requires bi-directional talk (dimmer to server: “someone is turning my knob. dont dim me out.”) and would be an expensive, ‘per knob’ solution.

    All in all, a pasive remote as done here is the *best* solution (tried and tested in thousands of performance spaces around the world.)

  5. also, a digital pot would give the server a way to *read* the pot value on the dimmer, but not a way to *affect* the value on the dimmer without a complete overhaul of the dimmer unit and a bidirectional communication line.
    digipots come in multiple formats and price ranges (as well as levels of intelligence, communication format, etc). a digipot that models a mechanical pot (with endstops for Off and full on) would need the ability to turn itself based on the data from the server thus representing in the real world the value given. These are quite expensive. Especially when talking about fitting the whole house with them.

  6. ok. 3 wires from board, 3 wires to pot (for watching if someone is playing with it), 2 wires control relay that swaps between digital pot + normal pot. thats 8 wires, perfect for CAT5 cables. A 4ch dmx dimmer is $125. Go to Analog Devices, digital pots are 50c -> $1, ADC’s can be had for $5 (for determining if pots being used). Household dimmers are $15. $60 + $20 + 4 relays = $100ish, and now don’t have to send power back from wherever the relay is located.

    I’m biased towards my schematic cause this seems to be a great project to do, and I already have dimmers and relays and don’t want to go out and buy a new set wrapped in a pretty metal box.

    BTW: Can’t access / on his server! Is this the only page he has? I want to see how he detects when you enter/exit a room, that sounds like fun!

  7. he could put a rotary encoder at the light ‘switch’ and have it tell the server to turn a light up/down. it might also be a good idea to put a backlit push button. When you move the encoder the software detects it and puts the light in manual mode. When the light is in manual mode the server tuns the push button’s backlight on. To switch the light back to auto you push the button and the backlight tuns off.

    This would let you have a software ‘admin’ app which could toggle the manual/auto state. Which would be handy if you left a light in manual mode and don’t want to get up to change it. :p

  8. Thanks for the comments guys!

    The dimmers I used aren’t as expensive as you would think, about £50 each – and for that you get 4 channels! A normal dimmer here is about £7 (for 1 channel) so the extra cost isn’t that great.

    I intend to post more HA stuff, as the rest of my house is automated too, the heating (all that plumbing you can see) is probably the most impressive (I think)

    Anyway, glad you enjoyed it, and thanks for the positive comments.


  9. DMX is dead easy to read with a PIC, the signal is a standard UART form but sent over balanced line RS422/485. The form of the signal is – Line held low (break) which will read as an overrun, then the line idles (high) and then the data comes as a byte stream with the channels identified by their order (start counting at zero).

    a very simple protocol which simply repeats, so no need for error checking as the data is corrected on the next pass

  10. Interesting project.
    I’m curious about how you interfaced your home wiring into the system Dan. Is it through receptacles and cords? Or through a bunch of J-Boxes?
    The single light sensor seems a touch inadequate, if you have a basement it is probably always darker than your upstairs and if programmed in the same line as the upstairs might then not come on when you needed it too.
    As far as knobs go- try this as a starting point-
    As an electrician I find rotory knobs distasteful- I would rather see slide fader.

  11. Nice setup. A pity you can only use regular incandescent light bulbs with systems like these; not very energy-efficient.
    I thought of building something similar, but went for a remote with a bunch of relays instead, as all of my lighting is either LED’s or Energy-efficient.

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