The OctoWS2811

My first experiment in speeding up the LEDs is to use something called OctoWS2811 which is designed to let you drive 8 strips of LEDs in parallel. Theoretically, this would allow me to boost the speed of my antenna from the dismal 9 frames per second to a much more attractive 72 frames per second.

OctoWS2811 started out a library from PJRC for their Teensy 3.2 development board (an Arduino-type board based on a Cortex M4). The main thing you need to know about this library is that it uses direct memory access to drive eight output pins at the same time. You hook up those 8 output pins to eight separate LED strips and, boom!, you’re in business.

PJRC also makes an adapter board that looks like this:

The OctoWS2811 is a small board, about 55mm by 35mm. One end has two RJ-45 ethernet jacks. The rest of the board can be used to mount a Teensy 3.2 controller.
The OctoWS2811 is a small board, about 55mm by 35mm. One end has two RJ-45 ethernet jacks. The rest of the board can be used to mount a Teensy 3.2 controller.

The adapter board basically takes your eight output pins, level-shifts them from 3.3v to 5.0v, and pushes them through 100 ohm resistors. Then it wires them out to two RJ-45 jacks.

The idea is that you mount a Teensy 3.2 controller on that thing. Each RJ-45 jack then provides four twisted pairs (ground + data) which can be sent reliably over longish distances to the LED strips themselves (I found that 25 feet of CAT-6 worked fine).

I wish the adapter had sockets so you could just snap in the controller, but they weren’t too hard to solder on.

For my first test, I made 8 little strips of 8 WS2812b pixels. Here is what the whole thing looks like:

Teensy 3.2 mounted on an OctoWS2811 adapter, with two CAT-6 cables connecting it to a small dual RJ-45 breakout board, which is wired to 8 strips of 8 WS2812b LEDs.
Teensy 3.2 mounted on an OctoWS2811 adapter, with two CAT-6 cables connecting it to a small dual RJ-45 breakout board, which is wired to 8 strips of 8 WS2812b LEDs.

I ran this with the OctoWS2811 library without problems, even up to 1100 pixels per strip.

I also tried using the FastLED library driving the OctoWS2811 library; that worked fine too but was limited to about 680 pixels per strip, presumably due to memory usage.

There are more powerful Teensy boards available than the 3.2, and you might be tempted to use them in your LED projects:

Teensy 3.2Teensy 3.6Teensy 4.0
Speed72 MHx180 MHz600 MHz
Memory256K1M1M

Should you consider the 3.6 or the 4.0 instead of the 3.2? Maybe, if you are planning to do a ton of processing on the chip to prepare the visuals that you send to the LEDs and need the memory or speed for that. But the truth is that if you are driving WS2812s and want a reasonable frame rate, the Teensy 3.2 is powerful enough. If you hook it up to 8800 pixels (8 strips of 1100) it will use 86% of available memory, and those strips of 1100 pixels will only get a 30 Hz refresh rate due to the limitations of the protocol. So adding more memory or processing power is not going help you push more pixels. If you want to build something like Mark Lottor’s Hextron, with 213,840 pixels, you’ll need to use a lot of Teensy’s and figure out how to synchronize them.

Hexatron, by Mark Lottor, was a forest of 486, 20-foot tall LED light poles, each containing 440 LEDs.

Published by Blinky Lights Blogger

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

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