Computing stuff tied to the physical world

RGB strips, revisited

In Hardware on Sep 8, 2010 at 00:01

A while back, I reported about hooking up an RGB strip. That was then.

Now there is the MOSFET Plug to make such hookups a lot simpler. So it’s time to revisit that experiment, because I want to find out how well RGB strips would work for < w a r m > white lighting in the house. Theoretically, RGB can generate any color, so that would include any “temperature” of white, right? Trouble is, I’m not convinced that LED strips are color matched well enough across their entire length to accomplish such lighting conditions over a few meters. The other concern is that RGB LEDs have the Red, Green, and Blue LEDs sitting next to each other, so there may be some fringe colorization – maybe diffusers will be needed.

Then again, I do have one LED lamp of 1 meter long which generates an abolutely great tint of white (“white tint” – interesting concept, eh?).

Time to find out:

Dsc 1912

I obtained some samples of “5050” RGB self-adhesive LED strip, one with 30 LEDs per meter, the other with 60 LEDs. They are mounted on nice white flexible strips, and the whole thing was tacked onto my all-time favorite material: foam board!

Since 2 x 3 is 3 x 2, I used 3 MOSFET plugs to connect this together, these are in turn plugged into a Carrier Board with a JeeNode on its back, and the whole kaboodle is placed in half a box. Since the plan is to later attach this unit to much longer LED strips, I don’t really want to close that box – the MOSFETs will no doubt generate too much heat once they drive several amps each.

Here is how everything is wired together:

Screen Shot 2010 09 07 at 22.31.09

Oh, there’s one more wire: on the photo you can see a red jumper wire running from +12V to a PWR pin on the Carrier Board (I used the FTDI connector) – so the same 12V supply is used to power the JeeNode itself.

That’s it. Six output lines to control the on-off state of two independent strips of RGB LEDs.

Tomorrow – the software…

  1. Very very neat…

    The photographer in me is dying to see how well these work, and how much light they put out… With an eye towards a mobile setup powered by some SLAs.

    The soldering iron geek in me just wants to see the pretty colours changing :-)

  2. Interesting as always. Software tomorrow… yes please!

    tankslappa, these low cost leds cannot produce high CRI or “good quality” light for photography. Unless you’re focused on some weirdo abstract material :D

    • Ah, didn’t know about CRI, thanks. Found this page about some of the issues involved. It sort of makes sense, intuitively, that you won’t see the same colors when the light mixes a smooth range of wavelengths, versus the strict 3-wavelength RGB cocktail produced by LEDs.

  3. Interesting test. Regarding the colour and temperature: You could steal some idea from the Philips LED lamps. They can change colour temperature. They use 4 LEDs 2*Red, G and B and a diffuser. Even with the diffuser you do see RGB separately on the edges of shadows the lamp creates.

  4. One thing I just realized, is that the RGB brightness is controlled through PWM. So even if the white that comes out looks ok, this means that for small fractions of time the R, G, or B will be on while the others are off. So whatever comes out, it won’t be a pure color and there are bound to be visual artifacts (if you move your eye quickly, the “timing strips” will show).

    Maybe some larger caps – one per color – can help overcome the PWM artifacts and produce a more constant source of energy?

    Lots of unknowns. We’ll see…

    • Hey jcw, I know a remedy for this partial color artefact.. you should come up with a PWM plug. But wait — you got it already! I have one, just haven’t used it yet. Next weekend, hopefully.

  5. I realise the “white” mix will be lacking in a few places, but I’m quite an experimental type of photographer. Only the other night I removed a perfect good f/2.8 zoom from my Nikon and replaced it with a piece of aluminium foil with a small hole in it!

    Okay, maybe not experimental, just mental!

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