The Color Mixing Christmas Light Project

Discretely Controllable DMX Driven RGB Pixels

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2010 RGB Node & Controller FAQ

(Page is still under construction…  If we’ve missed something, leave a note in the comment section below.)

Why only 42 nodes on a string?

As with all things engineering, this is a study in compromises.

The controller chip in each node requires an input voltage which falls in a fairly tight range.  Too high and the smoke comes out, too low and there’s no output at all.

To keep the inter-node cable flexible, we need to use a fairly small wire gauge.

Each node draws about 65 mA at 5V when fully illuminated.  Nearly all the power used by the string passes between the first and second nodes.

A DMX universe contains 512 discrete channels.  Each RGB node requires 3.  512 / 3 = 170.6. To make the best use of a universe, we divide 170 available RGB clusters by 4.  170 / 4 rounds conveniently down to 42.

Et Voila… 42 nodes on a string, plus a compromise between cable weight, cable thickness, voltage drop, copper prices, DMX channel usage, etc.

I Need a Power Supply

Both the node strings and the T3 controller require a tightly regulated 5V switching power supply.  Rather than ordering a bunch of supplies, paying shipping to get them here, then charging shipping (again) to send them to you, here’s a couple useful links.

Each node draws 65 mA at full power.

65 mA X 42 nodes = 2.73 A.

We round up to give a bit of headroom and specify 5V @ 12A for a T3 controller loaded with 4 strings.

Here’s an open-frame 5V 11A supply which has been tested and works well.  If you pick a supply like this, be sure to mount it properly and shield it from the elements.

Here’s something similar, but enclosed.

Surplus PC power supplies also work well.  Just use the +5v & GND leads.

In any case (and for many reasons), the T3 controller and node strings are not protected against reverse polarity. Therefore, it’s very, very critical that everything is connected properly the first time.

Otherwise, the smoke which escapes will be expensive and difficult to replace.

The T3 includes a polarized circular connector for power input, and we also have pigtails (stripped wires –> circular connector) and extension cables (circular connector –> circular connector) for reaching between the T3 and the power supply location.

7 Responses to “2010 RGB Node & Controller FAQ”

  1. neil Says:

    cool, that leaves me 8 dmx channels per controller to use for other dmx devices

  2. Dave Says:

    What is the length of one 42 node string?

  3. JEC Says:

    Standard spacing is 10 cm, which makes an entire string 4.2 meters (13.7995 feet) long.

    In practice, nodes can be set on 4″ centers without putting too much strain on the wires.

  4. John Says:

    These look great but I was wondering if you’ve look into using the LOR protocol as well as DMX? That would allow for more channels without having multiple LOR to DMX converter.

  5. JEC Says:

    It’s been a while since I’ve checked… Is the LOR protocol open and fully documented? If so, it’s something we might consider.

    Otherwise, we’ll be sticking to published standards such as DMX512, Art-Net and E1.31.

  6. GregF Says:

    Are the RGB nodes individually addressable with a microcontroller such as an arduino?

  7. JEC Says:

    Yes they are.

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