How to Load MicroPython on a Microcontroller Board

Contributors: Shawn Hymel
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Teensy 3.x

The Teensy is development platform that easily fits on a breadboard, can be programmed with the Arduino IDE, and offers many advanced features over most basic Arduino boards. It is well-loved among many embedded engineers and hobbyists for its powerful microcontroller while still being relatively inexpensive.

Teensy 3.2


As of the time of this writing (Aug. 2018), MicroPython is compatible with the following Teensy boards:

Heads up! A MicroPython build for the Teensy is not actively maintained by the MicroPython community. That means you will need to install the ARM toolchain and compile the MicroPython interpreter yourself. As a result, this is recommended for advanced users only!

Note that while it is possible to install the ARM toolchain and build MicroPython on Windows, the instructions and scripts were written for Linux. As a result, they might work on macOS, and to use them on Windows, you will need something like the Cygwin environment. For now, the steps will be shown for Linux only (and only for certain Debian variants).

Note: These steps were tested with Ubuntu 18.04.

Install the ARM Toolchain

In a terminal, enter the following commands:

sudo add-apt-repository ppa:team-gcc-arm-embedded/ppa
sudo apt-get update
sudo apt-get install -y gcc-arm-embedded

This should install the GCC ARM Embedded toolchain.

If you run unto any problems or want to download the packages (or source code), head to GNU Arm Embedded Toolchain page.

Build MicroPython for Teensy

Download the latest ZIP file from the MicroPython GitHub repository:


Unzip the repository and navigate to the Teensy port directory:

cd micropython-master/ports/teensy

Determine which Teensy board you are using (MicroPython has thus far only been ported to the Teensy 3.x variants). The BOARD argument will be set to one of the following:

  • For Teensy 3.1 or 3.2, use TEENSY_3.1
  • For Teensy 3.5, use TEENSY_3.5
  • For Teensy 3.6, use TEESNY_3.6

Since I tested this process with a Teensy 3.2 board, I will show TEENSY_3.1 in the following commands. Replace TEENSY_3.1 with the argument for your particular board.


If you wish to create MicroPython build for a different board, call make clean first before calling make BOARD=TEENSY_3.x again.

For more information on how to build MicroPython for the Teensy, see the MicroPython Teensy wiki page.

Build the Teensy Flashing Tool

To upload the build MicroPython interpreter to the Teensy, we will use Paul Stroffregen's teensy_loader_cli tool (the repository for which can be found here). We need to download the repository, make it, and install it.

To start, install the libusb library:

sudo apt-get install -y libusb-dev

If you have not already done so, head back to your home directory and delete the MicroPython file:

cd ~

Download and build the tool:

cd teensy_loader_cli-master

Install the tool to the local user's application directory:

sudo cp teensy_loader_cli /usr/local/bin

Flash the Teensy

To avoid having to use sudo to upload programs to the Teensy, install the following udev rule:

cd ~
sudo cp 49-teensy.rules /etc/udev/rules.d/
sudo udevadm control --reload-rules

Plug in your Teensy board to an available USB port (if it was already plugged in, unplug it first to allow udev to see it after reloading the new udev rules).

To flash the MicroPython firmware, determine which board you have and use the microcontroller name as the mcu argument for teensy_loader_cli:

  • For Teensy 3.1 or 3.2, use mk20dx256
  • For Teensy 3.5, use mk64fx512
  • For Teensy 3.6, use mk66fx1m0

Finally, we flash the built MicroPython firmware. Note that as I am using the Teensy 3.2 board, I will use mk20dx256 as the mcu argument. Change it to match your Teensy board.

cd micropython-master/ports/teensy
teensy_loader_cli --mcu=mk20dx256 -w build/micropython.hex

After entering that last command, your terminal should wait for your Teensy to show up in bootloader mode. With the Teensy plugged in to your computer, press the reset button on the Teensy. After a few seconds, the Teensy's LED should flash twice rapidly, and the teensy_loader_cli command should finish executing in the terminal.

MicroPython should now be installed on your Teensy!

Test It

Install the minicom utility:

sudo apt-get install minicom

Open a serial connection to REPL running on the Teensy:

minicom -D /dev/ttyACM0 -b 115200

Press enter once to see the REPL command prompt (>>>). Enter the following commands:

import pyb
led = pyb.Pin.board.LED

This should turn on the Teensy's LED. Turn it off with:


Blinking the LED on a Teensy board with MicroPython

Exit out of minicom by pressing Ctrl+A followed by pressing X. Press enter when you are asked if you really want to leave.