What about the Teensy 4.0?

The Teensy 4.0 development board, by PJRC

Oh man, this thing looks amazing.

No sooner had I soldered pins on the Teensy 3.2 than a newer Teensy 4.0 arrived in the mail. The new Teensy is insanely more capable for the same price and in the same form factor. It’s 10-15 times faster on benchmarks, has 16 times as much RAM and 8 times the flash. It uses the new ARM Cortex M7. This is a 600 MHz chip. This is basically a Pentium III-class processor, with tons of memory, tons of IO, and all kinds of amazing things.

Teensy 3.2Teensy 4.0
CoreMark Benchmark Speed1262314

I would love to use this development board to drive tons and tons of WS2812b-type LEDs, but I just can’t get it to work.


  1. The Teensy 4.0 uses different pins for parallel output than the 3.2. I am pretty sure that means that it will not work with the OctoWS2811 library, which has not been updated.
  2. That would be OK, because FastLED seems to have new native support for parallel output on the Teensy 4.0, and FastLED is a much better library than OctoWS2811.
  3. But, because the pins have changed, the OctoWS2811 adapter board won’t work with the Teensy 4.0 (even though it is the same form factor), so I think I would be on my own in terms of providing level-shifting, resistors, and RJ-45 connectors.
  4. Another problem with the Teensy 4.0 is that a lot of its output pins seem to be in the form of tiny pads on the bottom (digital pins 24-33). These might be ok to use in an emergency but seem like a real mess in real projects.
The bottom of the Teensy 4.0 includes a stunning number of annoying little solder pads
The bottom of the Teensy 4.0 includes a stunning number of annoying little solder pads

I prototyped a little circuit that level shifts eight of the pins (19,18,14,15,17,16,22,23) from 3.3v to 5.0v:

Unfortunately, this is just not working for me no matter what I try. I even tried using an oscilloscope to figure out where it’s going wrong, but at this point, I’m in way over my head. From the current discussion on Reddit I see a lot of other people having problems so I’m pretty much ready to give up on Teensy 4.0 for a while until someone smarter than me figures out how to make it work.

(By the way, by my calculations, even the Teensy 3.2 is powerful enough to drive eight strips of 500-1000 LEDs at 30Hz- 60Hz. Putting any more WS2812b-type LEDs on a Teensy 4.0 would actually just reduce the frame rate due to limitations in the protocol. So there’s no compelling case for a Teensy 4.0 right now.)