Interlude: BeagleBones

BeagleBone Black

The Story So Far

In investigating how to drive enormous numbers of WS2812b LEDs from Arduino-style controllers at 60 fps or faster, I found that a pretty solid option is the Teensy 3.2 with the OctoWS2811 adapter board which can drive up to 4400 pixels. But what if you need more pixels? A common approach seems to be using a TCP/IP network with CAT-5 cable to connect a bunch of controllers, then using a central PC to coordinate everything.

I was about to start working on this when I thought of maybe using a Linux-style development platform (like Raspberry Pi or BeagleBone) instead of Arduino. Let’s look at some specs:

Teensy 3.2Teensy 4.0BeagleBone Black
CoreMark Benchmark Speed12623142497
RAM64K1024K512M
Flash256K2048K4GB
Price$19.80$19.95$62.38

The neat thing about the BeagleBone is that it has two PRUs. Those are tiny little 32-bit computers running at 200MHz which have access to 16 of the output pins. You can leave the PRUs in charge of sending output to the LED strips, which frees up 100% of the BeagleBone CPU for your own image processing. There’s also an insane amount of flash memory for storing images, animations, and even videos. There’s onboard ethernet so you don’t have to mess around with wiring up a W5500 to your controller.

Still, there are some disadvantages:

  • You have to wait about 10 seconds for Linux to boot up when you power up
  • Since the PRUs can only access 16 output pins, you can’t really drive insane numbers of pixels from a single BeagleBone, so you still need some kind of distribution protocol
  • BeagleBone doesn’t have FastLED and not a lot of people are using it for addressable pixels, so you’ll have to do a lot more work trying to drive pixels than you would on the Arduino-type controllers
  • And, it’s more expensive.

One obvious idea is to use BeagleBones at the center of your architecture, sending commands over Ethernet to an army of Teensy 3.2s which serve as low-cost WS2812b drivers. You can even get industrial-strength BeagleBones like this one which support Gigabit ethernet in case the 10/100 ethernet doesn’t pump enough pixels for your design.

So now the idea would be that you can run arbitrary Linux software at the center of your architecture using tons of CPU, RAM, Flash, and even all kinds of cool 3D accelerators and stuff that are built into the BeagleBone Black. We would then design a little board for the branch controllers with Teensy 3.2, W5500 ethernet, level shifters and resistors, and use one of those for each 8 WS2812b strips.

A fancier version of this board could also include a power distribution bus for the LEDs themselves. If you were driving 4400 LEDs you would theoretically need 242 amps (1210 watts) so if you were thinking “PoE” please stop thinking that.

Published by Blinky Lights Blogger

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

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