Teensy-Arduino Cross-over (Adapter) Board

Note: this page serves as a technical reference for Teensy-Arduino Cross-over (TAX) board.

What is it?

The TAX or Teensy-Arduino Cross-over (X) board is an Arduino-style prototyping board containing the Teensy 3.1 micro-controller, together with some nice extras. It brings the powerful features of the Teensy together with the form factor of the Arduino Uno, resulting in a board which you can program through the familiar Arduino IDE and which is compatible with all your Arduino shields.


Ethernet shield on TAX

TAX running the Ethernet sketch with an Arduino Ethernet shield


Key features

  • Fully compatible with Arduino IDE (requires Teensy application)
  • Fully compatible with all official Arduino shields and nearly all other shields
  • 5V input, even on analog pins!
  • 3.3V regulator for ripple free voltage rail
  • Robust USB type B receptacle for power and programming
  • Automatic power selector circuit (USB, barrel jack, Vin pin)
  • FTDI header for UART access and power
  • Combined 5V/3.V reset (resetting a shield also resets TAX and vice versa)


SpecificationTAXTeensy 3.1Arduino UNO
CPUMK20DX256 @ 72MHzMK20DX256 @ 72MHzATmega328 @ 16MHz
Flash memory256kB256kB32kB
Digital in/out14 @ 5V-3.3V (in)/3.3V (out)34 @ 5V-3.3V (in)/3.3V (out)14 @ 5V
Analog in6 @ 5V21 @ 3.3V6 @ 5V
Analog out110
Max power1A @ 5V, 500mA @ 3.3V150mA @ 3.3V500mA @ 5V, 50mA @ 3.3V

TAX header

Where you would normally have the Atmega 16U2 ICSP header on a regular Arduino Uno board, this has been replaced with a TAX header (or rather: a socket) on this board. The TAX header provides access to the following features:

  • Analog out
  • Analog input 10 (for simultaneously sampling two analog inputs)
  • Battery input for RTC
  • 3.3V power output
  • Ground
  • Reset
Teensy-Arduino Crossover Board

4 TAX prototypes

Why this board?

As you can see, the amount of I/O offered by the Teensy 3.1 vastly outnumbers that of the TAX. So why even bother with this board?

Truth is, I don’t want TAX to be a competitor to the Teensy. Rather, I want it to be an augmentation to the Teensy, providing some new features while omitting some others. The main goal is to make it possible to (re)use all the existing Arduino shields while still enjoying the power of the MK20 micro controller and the familiarity of the Arduino IDE and language.

In addition, there are some other features stemming mainly from my own personal needs such as a powerful and noise-free 3.3V line, buffered analog inputs for accurate high speed sampling, easy access to the UART, a more durable USB connector and multiple ways to provide power to the board.


TAX is currently in prototype production, and it will go into limited production runs when I receive at least 50 expressions of interest. You can leave yours in the comment section. Be sure to leave a reply address so I can contact you with updates!

How much?

Ah yes, the one thing on everyone’s mind: the price. While it’s hard to predict an definite price at this stage, I’m aiming to position it at the same price level of a regular Arduino Uno. The more interest, the better it will be to achieve or even surpass this goal.

9 Responses to Teensy-Arduino Cross-over (Adapter) Board

  1. […] Teensy-Arduino Cross-over (Adapter) Board […]

  2. Black Ink says:

    I have a project (a pilot for a larger project) that I’d like to use this board for.
    The project would require 50 units – does that help you with the qty’s to have a run?



  3. mani says:

    very useful I would like to buy

  4. Tim Wyatt says:


    this is exactly what I’m looking for.

    Is it available for purchase?

  5. Bernard Sypniewski says:

    I’m definitely interested, especially if the price is right. Keep me posted.

  6. mike says:

    What are possibilities on this shield to connect Adafruit 2.8 tft touch – ICSP headers /microSD for use with Teensy 3.1 ??


  7. VERY INTERESTED. The company I work for would possibly purchase this by the hundreds.

  8. David says:

    Hi! Did you ever decide to pursue this? If you did, you can count me in!


  9. I hope you make the arduino adapter for teensy. I need Ethernet in my application and would buy a few if you did, at least 3x.

    Please advise if and when you make a decision on this.

    Livermore, CA

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