Computing stuff tied to the physical world

RGB multi-meter?

In Hardware on Sep 12, 2010 at 00:01

How’s that for a weird title, eh? ;)

Just got around to hooking up a test set of 2x 5 meter RGB LED strips to the MOSFET Plugs – using the setup created and described here a few days ago.

These are water-proof strips, with only 30 LEDs/m and a somewhat unfortunate brown strip background color:

Dsc 1925

That’s with all LEDs full on.

Now some more color and power experiments, in the evening – full on:

Dsc 1920

You can see the current reading, the JeeNode setup, and the power supply.

And with 100% / 45% / 15% settings for red, green, and blue, respectively:

Dsc 1923

The color came out much more yellow on this picture than it actually was, btw.

Some power measurements on the 12V line:

  • full on: 2.4 amps @ 12 V = 28.8 watt
  • color-adjusted: 1.9 amps @ 12V = 22.8 watt

The power supply is a beefy 12A @ 12V cage which draws 4.4 watt even without anything connected. That’s very unfortunate, because I’d like to turn the LEDs off on the 12V side and leave the power supply on at all times. Will need to find a better supply – 4A would be plenty.

These results are slightly disappointing. First of all, 60 LEDs per meter will be a minimum to provide a decent level of (indirect) house lighting at full power. But also, it’s frustrating to see how the power gets eaten up in the supply and by the resistors (especially with red LEDs dimmed less than the others).

No doubt this is way better than incandescent lighting, but still…

Another surprising outcome, is that the RGB settings for this strip are completely different from the 5050 RGB test setup I used a few days ago. It looks like I’m going to have to adjust each strip individually to get a nice consistent white balance.

And then there’s the issue of fringing. Looking directly at these LED strips clearly shows the distinct RGB components, with the color balance very much dependent on the viewing angle. I sure hope that the 60 LED/m strip with white background and used as indirect lighting will even this out.

On the plus side, the ≈ 300 Hz PWM of the new rgbAdjust.pde sketch I’m using on the JeeNode seems to make these LED strips completely flicker-free.


  1. What white balance was the camera on JC? If it was auto then the rendition will be all over the place as the camera tries to work out the ambient lighting.

    Is 30 LEDs/M such a problem? You could always lay two strips side by side :-)

    • You’re right about the while balance (it was on auto, silly me…). I was too lazy to go back and redo the shots.

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