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I have an existing project using an Arduino Yun that controls Christmas lights with relays to turn them on/off. There are currently 13 separate rows of lights on the (60 foot) tree, each plugged into a wall wart that's controlled by its own relay.

I'm considering adding the ability to dim the lights, so I wanted to figure out the best way to do it. The lights can all be dimmed "in unison" - there's no need for 13 seperately controlled dimmers. But I have to be mindful not to cause any "buzzing" in the audio equipment on stage where the tree is.

I've read about PWN, zero cross, and other terms and saw the zero cross tail from powerswitchtail.com that seem useful in the typical project. I'd like to be able to pull this off with no more than 2 "dimmers" for the whole project, if possible.

Where do I start, and how do I do it?

dlu
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chris.nesbit1
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  • What voltage lights? What kind of lights? Where are the relays - mains or low voltage side? – Majenko Dec 19 '15 at 13:49
  • Traditional 120v white Christmas lights. The relays are currently powertail switch relays, but as I add more modules in the future (for additional colors) I plan to use sainsmart 8 channel SSR relays (so, low voltage side in both setups). – chris.nesbit1 Dec 19 '15 at 14:06
  • Do you have the budget to get some DMX dimmers? You could use the Arduino as your DMX controller. For example, something like this [4 channel dimmer](http://smile.amazon.com/American-Dp-415-Channel-Dimmer-Pack/dp/B000FVZUMM). – dlu Dec 19 '15 at 16:29
  • @dlu I'm powering all my lights from 2 power strips. so if I do as you suggest, with an arduino fix shield, could I plug my 2 power strips (for my 60 foot Christmas tree) into 2 (or 4, at most) outlets on a DMX dimmer? Or does each row need to be on its own outlet on the DMX dimmer? – chris.nesbit1 Dec 19 '15 at 19:46
  • Basically the DMX dimmer gives you an outlet with a remote control that you can talk to programmatically. I suppose the big question is how much power you need to control. I think the DMX dimmer that I linked to is capable of handling about 5 A (~600 W) per channel (or maybe per outlet, there are two outlets per channel on that one. So depending on how much power you need you could divide up the load amongst the channels. Another approach would be to get one or more X10 dimmers. Looks like they run about $20 US for a 500 W dimmer. – dlu Dec 19 '15 at 19:58
  • "Traditional 120v white Christmas lights." does not fully describe the problem. Presumably you mean a series (and possibly secondarily parallel) string of incandescent bulbs which are presumably dimmable, but your mention of "wallwart" instead implies something else like low-voltage LED which is not AC dimmable but rather requires a PWM source. – Chris Stratton Dec 19 '15 at 21:04
  • @ChrisStratton my apologies for probably not being expert enough to give more specific detail. I don't have on-demand access to the actual lights or tree once it's put away. I assume the lights to be regular Walmart Christmas lights. My use of the word "wallwart" can be ignored for now given the current use of powertail switch relays. What would be the deciding factor that differentiates DMX dimmers from a PWM implementation, and could that implementation run the risk of interfering with audio equipment in close proximity? – chris.nesbit1 Dec 19 '15 at 21:12
  • The primary concern shouldn't be audio interference, but utter failure and/or fire. This is a task which you simply **cannot undertake** without determining the **exact** nature of the lights to be controlled. If they won't unpack samples for you, run away from the project as quickly as you can. – Chris Stratton Dec 19 '15 at 21:14
  • @ChrisStratton again, what determines which implementation I should pursue? How can I tell what I'm dealing with, and what characteristics would determine whether I should go with DMX or PWM? – chris.nesbit1 Dec 19 '15 at 21:16
  • You need to determine if they are incandescent running directly off the mains supply or if they are LED with some sort of power supply or control module. With the latter, you must assume that they **cannot be dimmed** unless you entirely understand and/or replace that power supply. – Chris Stratton Dec 19 '15 at 21:18

1 Answers1

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I can think of a couple of ways to approach this:

  1. Use a DMX dimmer, something like this 4-channel dimmer, or

  2. Use an household X10 dimmer.

DMX is used for stage lighting and there is some information on controlling DMX devices with an Arduino in the Playground where there is also some information on the hardware interface and shields, it looks pretty simple. DMX is a differential RS485 interface.

X10 is used for home automation, the signaling is done over the AC line. There is some information on using X10 and an Arduino library in the Tutorials.

Both seem like viable approaches, if you're working in a theater it is likely that they might already have DMX equipment and it would be as simple as hooking up to the gear in the house. Then you'd only need to add a shield or build the interface hardware.

dlu
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  • For the DMX dimmer, since it's meant for stage/DJ use, does that also mean there won't be a hum in the sound system from nearby microphones, speakers, etc? And is there more compact DMX dimmers out there that might fit more nicely into a project box (smaller than, maybe, 6 inches on its biggest side)? – chris.nesbit1 Dec 19 '15 at 20:46
  • I think that will depend on the dimmer, but yes, I'd expect them to be designed to take interference with other equipment into account. As to size, I don't know off hand. Since they are often close to the load they typically include the outlets and that makes them pretty big – the one I linked to has 8 outlets. But, there are probably DMX chips out there and the triacs they control aren't all that big you might be able to build something pretty small. But in a theatre the equipment might already be there, it might be as simple as hooking up to it with the tree & the Arduino. – dlu Dec 19 '15 at 20:53