So you need more than 4000 addressable LEDs

Maybe you want to build something for a big thing in the desert. And the desert is wide and large and your thing is going to be really, really, big. For example, the Tree of Ténéré by Zachary Smith and team has 175,000 LEDs.

A photograph of the multi-colored Tree of Tenere at night; each leaf has 7 LEDs.
Photo by Duncan Rawlinson under CC Attribution / Non Commercial License
duncan.co

That is significantly higher than the 4416 LEDs that you can drive off of a single Teensy 3.2 with an OctoWS2811 adapter and ultimately you’re going to need some kind of central controller sending signals out to multiple branch controllers that each handle a set of LEDs.

There are a bunch of ways to think about how to do this, but a good approach might be just using simple ethernet. That way you can use a lot of off-the-shelf equipment. For example, the popular WizNET W5500 can provide internet access for the branch controllers. Indeed the Tree of Ténéré people apparently used custom boards with a W5500 and a cheapo ESP32 controller. Now you can just use generic CAT5 cables and any kind of Ethernet hub you want. As the main controller, you have a single PC. It blasts pixel data out to all the branch controllers.

There are a couple of interesting design considerations:

Do you want to use Power-over-Ethernet?

It seems like it might simplify wiring a bit to deliver some power over the CAT-5 cables. The trouble is that this would not supply nearly enough power to drive the number of LEDs that each branch controller is going to drive, so you still need a separate power distribution system for the LEDs. Given that you are already distributing power for the LEDs, it doesn’t simplify the wiring as much has you might think. It seems like what the Tree people did was distribute 12V throughout the project and then had a simple low drop regulator on their custom board to drop 12v to 3.3v.

Are you sending every single pixel?

If you are really using 175,000 pixels with 24 bits of data at 60Hz, that’s about 252Mbps. After adding the overhead of ethernet with real protocols, you might be able to crank this out using Gigabit ethernet but the W5500 is apparently limited to 100Mbps (100baseT). Unless you want to get really complicated and run multiple ethernet segments, you’re going to have to take shortcuts.

Luckily, we have a pretty good computer sitting at each of the branches, so there are a lot of ways to do that. We can send a packet down to each branch controller containing arbitrary parameters and let the controller decide how to map that onto its pixels.

For example, on the Tree project, which had 7 LEDs per leaf, you might just decide it’s OK for each leaf to be a single color. Then you could send custom pixel data for each leaf. You could also use other arbitrary custom compression schemes that are appropriate for your particular project.

Next Steps

Here’s what I’m working on next:

  • get an Ethernet switch and something to test W5500
  • build some software that distributes data from PCs to branch controllers

Useful links:

Published by Blinky Lights Blogger

I'm a programmer in New York City working on addressable LED art projects.

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