Mood lights FTW

June 2, 2010 5:40 PM

How do I wire up a bunch of LEDs in my ceiling?

Me and a couple of others share an approximately 1000 sq feet space in the basement of an old building as kind of a shared hangout / workshop area. When we moved in, the landlord installed adequate fluorescent tubes, but we'd like to have another option.

What I was thinking of was, since there's wood beams every 3 feet or so, hang white fabric between the beams, and put clusters of LEDs in the corners of the beams. Maybe like 8 LEDs per cluster... two each of white, blue, green, and red, and have sliders or an arduino, or something, to control the color composition from a central control panel / switch bank.

So, how do I make my diffuse LED lighting dream a reality?

posted by fvox13 to technology (9 answers total)

So something like this, only with like several million more LEDs?

Tediously.
posted by Threeway Handshake at 6:07 PM on June 2, 2010 [1 favorite]

I would use ethernet cable to carry power to each cluster from the controller, because it's widely available, cheap, and pretty easy to work with. Also, you can get four different colors on a single cable. I assume you know that you'll need a pulldown resistor paired with every LED (let me know if you want to know how to calculate the value).

Make sure you don't have the ethernet cable carry too much current - each LED will draw around 20 mA, so I wouldn't connect more than 10-12 of them on one ethernet cable. If you want more, use some other kind of cable.

If you organize the LEDs so all the LEDs of one color are powered by the same strand of the ethernet cable in one of your clusters, then you can easily switch one color on or off by wiring up a few switches, one for each color.

A dimmer would be cool, but I've heard that dimming LEDs can lower their lifespan. Not clear on exactly why though.
posted by Salvor Hardin at 6:07 PM on June 2, 2010

These are quite popular in DIY projects these days.

Pity there's no obvious way to control a bunch of them at once.
posted by schmod at 6:10 PM on June 2, 2010

How budget-limited are you? The easy answer is one Shiftbrite at each node, and all of them connected in series (for data) and across power rails. They're the most plug & play answer I know for "I want to control ~1 bazillion RGB LEDs." As far as I know there's no real upper limit to the number of these you can control at once, though for extremely long strings it becomes harder to do real-time (30fps) animation. The downside is that they're about $5/ea, and your description above leads to a count of about 100.

"Tediously" is definitely the answer, by the way -- before you get too invested, try to do a quick (time for 1 solder connection) * (# of solder connections needed) calculation to figure out if you really want to go through with this. When East Campus @ MIT built their Disco Dance Floor they were practically kidnapping people on the sidewalk and forcing them to solder at gunpoint, at the end.
posted by range at 7:11 PM on June 2, 2010 [2 favorites]

You have two choices for the LEDs - you can either buy the discrete components (LEDs and resistors and a little circuit board) and solder them yourselves, or you can buy a pre-built package like the Shiftbrite. Go with the Shiftbrite, or something comparable; the cost will be similar or even cheaper, since the pre-built product gets volume discounts on parts, and it will save you shitloads of time.

The annoying part is running wires all over the place. You want to avoid having to buy a pack of headers and several rolls of wire and spending a few days making cables. Fortunately Shiftbrite comes through again; they sell pre-made cables up to 19 inches long. It really does seem like a good solution. You won't need to solder a thing! If you need longer than that, I think you can probably buy a male-male plug which would let you daisy-chain two cables together, though you should maybe ask the Shiftbrite people about maximum cable length, or if they could sell you longer cables.
posted by PercussivePaul at 9:23 PM on June 2, 2010

Might also try one of the many sources in Hong-Kong. I just received my 5m roll of warm-white from Hero-LedStore.
posted by mmdei at 11:01 PM on June 2, 2010 [1 favorite]

You do not want a resistor on every LED at all. Assuming the usual little 5-10mm ~200mW devices, put a bunch in series so that their junction voltages add up to a volt or two less than your supply, which should be on the order of 12-24V and the one resistor for the whole chain. Way more efficient, way less parts count.

Dim them with pulse-width modulation. CAT5 cable would be good for distributing the power but beware of your PWM switching frequency (keep it to about 100-200Hz) and (especially if your dimmer is centrally located) use snubbers so that your cables don't radiate RF on the transitions.

I think the tediousness of assembly is the biggest problem here. You might be better off instead to use a smaller number of very bright (5W-class) LEDs instead of a larger number of smaller (200mW-class) LEDs. Power supply and heatsinking the LEDs gets a bit more complicated but the total effort is probably less.

You can also buy LED rope. Makes the assembly problem go away.
posted by polyglot at 4:16 AM on June 3, 2010

definitely check out mmdei's link. A couple of those strips with a dimmer (sold at the same store) totally does it all for you. No effing about with soldering, resistors, etc.
posted by polyglot at 4:22 AM on June 3, 2010

Maybe some of the links in this instructables post on creating a fiber optic starfield ceiling will help you. If not, it's just a damn fine piece of work to admire.
posted by Jambi at 5:47 AM on June 3, 2010