So, you've got this new CircuitPython compatible board. You plugged it in. Maybe it showed up as a disk drive called CIRCUITPY. Maybe it didn't! Either way, you need to know where to go from here. Well, we've got you covered!

This guide will get you started with CircuitPython!

There are many amazing things about your new board. One of them is the ability to run CircuitPython. You may have seen that name on the Adafruit site somewhere. Not sure what it is? We can help!

"But I've never coded in my life. There's no way I do it!" You absolutely can! CircuitPython is designed to help you learn from the ground up. If you're new to everything, this is the place to start!

This guide will walk you through how to get started with CircuitPython. You'll learn how to install CircuitPython, get updated to the newest version of CircuitPython, how to setup a serial connection, and how to edit the files.

Welcome to CircuitPython!

What is CircuitPython?

CircuitPython is a programming language designed to simplify experimenting and learning to program on low-cost microcontroller boards. It makes getting started easier than ever with no upfront desktop downloads needed. Once you get your board set up, open any text editor, and get started editing code. It's that simple.

CircuitPython is based on Python

Python is the fastest growing programming language. It's taught in schools and universities. It's a high-level programming language which means it's designed to be easier to read, write and maintain. It supports modules and packages which means it's easy to reuse your code for other projects. It has a built in interpreter which means there are no extra steps, like compiling, to get your code to work. And of course, Python is Open Source Software which means it's free for anyone to use, modify or improve upon.

CircuitPython adds hardware support to all of these amazing features. If you already have Python knowledge, you can easily apply that to using CircuitPython. If you have no previous experience, it's really simple to get started!

Why would I use CircuitPython?

CircuitPython is designed to run on microcontroller boards. A microcontroller board is a board with a microcontroller chip that's essentially an itty-bitty all-in-one computer. The board you're holding is a microcontroller board! CircuitPython is easy to use because all you need is that little board, a USB cable, and a computer with a USB connection. But that's only the beginning.

Other reasons to use CircuitPython include:

  • You want to get up and running quickly. Create a file, edit your code, save the file, and it runs immediately. There is no compiling, no downloading and no uploading needed.
  • You're new to programming. CircuitPython is designed with education in mind. It's easy to start learning how to program and you get immediate feedback from the board.
  • Easily update your code. Since your code lives on the disk drive, you can edit it whenever you like, you can also keep multiple files around for easy experimentation.
  • The serial console and REPL. These allow for live feedback from your code and interactive programming.
  • File storage. The internal storage for CircuitPython makes it great for data-logging, playing audio clips, and otherwise interacting with files.
  • Strong hardware support. There are many libraries and drivers for sensors, breakout boards and other external components.
  • It's Python! Python is the fastest-growing programming language. It's taught in schools and universities. CircuitPython is almost-completely compatible with Python. It simply adds hardware support.

This is just the beginning. CircuitPython continues to evolve, and is constantly being updated. We welcome and encourage feedback from the community, and we incorporate this into how we are developing CircuitPython. That's the core of the open source concept. This makes CircuitPython better for you and everyone who uses it!

Frequently Asked Questions

These are some of the common questions regarding CircuitPython and CircuitPython microcontrollers.

As we continue to develop CircuitPython and create new releases, we will stop supporting older releases. Visit to download the latest version of CircuitPython for your board. You must download the CircuitPython Library Bundle that matches your version of CircuitPython. Please update CircuitPython and then visit to download the latest Library Bundle.

I have to continue using CircuitPython 3.x or 2.x, where can I find compatible libraries?

We are no longer building or supporting the CircuitPython 2.x and 3.x library bundles. We highly encourage you to update CircuitPython to the latest version and use the current version of the libraries. However, if for some reason you cannot update, you can find the last available 2.x build here and the last available 3.x build here.

Is ESP8266 or ESP32 supported in CircuitPython? Why not?

We are dropping ESP8266 support as of 4.x - For more information please read about it here!

Is there asyncio support in CircuitPython

We do not have asyncio support in CircuitPython at this time

My RGB NeoPixel/DotStar LED is blinking funny colors - what does it mean?

The status LED can tell you what's going on with your CircuitPython board. Read more here for what the colors mean!

What is a MemoryError?

Memory allocation errors happen when you're trying to store too much on the board. The CircuitPython microcontroller boards have a limited amount of memory available. You can have about 250 lines of code on the M0 Express boards. If you try to import too many libraries, a combination of large libraries, or run a program with too many lines of code, your code will fail to run and you will receive a MemoryError in the serial console (REPL).

What do I do when I encounter a MemoryError?

Try resetting your board. Each time you reset the board, it reallocates the memory. While this is unlikely to resolve your issue, it's a simple step and is worth trying.

Make sure you are using .mpy versions of libraries. All of the CircuitPython libraries are available in the bundle in a .mpy format which takes up less memory than .py format. Be sure that you're using the latest library bundle for your version of CircuitPython.

If that does not resolve your issue, try shortening your code. Shorten comments, remove extraneous or unneeded code, or any other clean up you can do to shorten your code. If you're using a lot of functions, you could try moving those into a separate library, creating a .mpy of that library, and importing it into your code.

You can turn your entire file into a .mpy and import that into This means you will be unable to edit your code live on the board, but it can save you space.

Can the order of my import statements affect memory?

It can because the memory gets fragmented differently depending on allocation order and the size of objects. Loading .mpy files uses less memory so its recommended to do that for files you aren't editing.

How can I create my own .mpy files?

You can make your own .mpy versions of files with mpy-cross.

You can download the CircuitPython 2.x version of mpy-cross for your operating system from the CircuitPython Releases page under the latest 2.x version.

You can build mpy-cross for CircuitPython 3.x by cloning the CircuitPython GitHub repo, and running make in the circuitpython/mpy-cross/ directory. Then run ./mpy-cross path/to/ to create a foo.mpy in the same directory as the original file.

How do I check how much memory I have free?

import gc

Will give you the number of bytes available for use.

Does CircuitPython support interrupts?

No. CircuitPython does not currently support interrupts. We do not have an estimated time for when they will be included.

Does Feather M0 support WINC1500?

No, WINC1500 will not fit into the M0 flash space.

Can AVRs such as ATmega328 or ATmega2560 run CircuitPython?


Commonly Used Acronyms

CP or CPy = CircuitPython
CPC = Circuit Playground Classic
CPX = Circuit Playground Express

Installing Mu Editor

Mu is a simple code editor that works with the Adafruit CircuitPython boards. It's written in Python and works on Windows, MacOS, Linux and Raspberry Pi. The serial console is built right in so you get immediate feedback from your board's serial output!

Mu is our recommended editor - please use it (unless you are an experienced coder with a favorite editor already!)

Download and Install Mu

Download Mu from Click the Download or Start Here links there for downloads and installation instructions. The website has a wealth of other information, including extensive tutorials and and how-to's.


Using Mu

The first time you start Mu, you will be prompted to select your 'mode' - you can always change your mind later. For now please select Adafruit!

The current mode is displayed in the lower right corner of the window, next to the "gear" icon. If the mode says "Microbit" or something else, click on that and then choose "Adafruit" in the dialog box that appears.

Mu attempts to auto-detect your board, so please plug in your CircuitPython device and make sure it shows up as a CIRCUITPY drive before starting Mu

Now you're ready to code! Lets keep going....

Installing CircuitPython

As we continue to develop CircuitPython and create new releases, we will stop supporting older releases. If you are running CircuitPython 2, 3 or 4, you need to update to 5.x. Generally Adafruit will support the last two major versions.

Some of the CircuitPython compatible boards come with CircuitPython installed. Others are CircuitPython-ready, but need to have it installed. As well, you may want to update the version of CircuitPython already installed on your board. The steps are the same for installing and updating. Here we will cover how to install or update CircuitPython on your board.

You only have to install CircuitPython ONCE, after that you are free to code all you like without going through this process again until it's time to upgrade!

Download the latest version!

The first thing you'll want to do is download the most recent version of CircuitPython.

If you're already running CircuitPython, make sure you're running the latest version! If you're unsure,  you can follow the steps below to ensure you have the latest version installed.

ALWAYS BACKUP YOUR CODE BEFORE INSTALLING OR UPDATING CIRCUITPYTHON. Most of the time, nothing will be removed from your board during the update, but it can happen. If you already have code on your board, be sure to back it up to your computer before following the steps below.

Download the latest software for your board by clicking the green button below to go to

Next, you'll want to plug in your board using a known-good USB data cable. Make sure the USB cable is a data cable! There are some that work only for charging and can lead to a lot of frustration.

Windows 7 Drivers

If you're using Windows 7, you need to install a driver before plugging in your board.

If you're using Windows 7, use the link below to download the driver package. You will not need to install drivers on Mac, Linux or Windows 10.

Start the UF2 Bootloader

Nearly all CircuitPython boards ship with a bootloader called UF2 (USB Flasher version 2) that makes installing and updating CircuitPython a quick and easy process. The bootloader is the mode your board needs to be in for the CircuitPython .uf2 file you downloaded to work. If the file you downloaded that matches the board name ends in uf2 then you want to continue with this section. However, if the file ends in .bin then you have to do a more complex installation - go to this page for how to do that.

Find the reset button on your board. It's a small, black button, and on most of the boards, it will be the only button available. (On Circuit Playground Express, it's the smaller button located in the center of the board.)

Tap this button twice to enter the bootloader. If it doesn't work on the first try, don't be discouraged. The rhythm of the taps needs to be correct and sometimes it takes a few tries. If you have a Circuit Playground Express, and it's fresh-out-of-the-bag try pressing the button once.

Once successful, the RGB LED on the board will flash red and then stay green. A new drive will show up on your computer. The drive will be called boardnameBOOT where boardname is a reference to your specific board. For example, a Feather will have FEATHERBOOT and a Trinket will have TRINKETBOOT etc. Going forward we'll just call the boot drive BOOT

The board is now in bootloader mode! This is what we need to install or update CircuitPython.

Now find the file you downloaded. Drag that file to the BOOT drive on your computer.

The lights should flash again, BOOT will disappear and a new drive will show up on your computer called CIRCUITPY.

Congratulations! You've successfully installed or updated CircuitPython!

What's the difference between CIRCUITPY and boardnameBOOT?

When you plug a CircuitPython board into your computer, your computer will see the board's flash memory as a USB flash drive where files can be stored. When you have successfully installed CircuitPython, you'll see the CIRCUITPY drive. When you double-tap the reset button, you'll see the boardnameBOOT drive. You can drag files to both, but only CIRCUITPY will run your CircuitPython code.

Normally, when you drag a file to a mounted USB drive, the file copies to the drive and then is able to be seen in your file explorer. However, when you drag the CircuitPython UF2 file to the boardnameBOOT drive, it seems to disappear, and the drive disconnects. This is normal! The UF2 is essentially an installer file, and does not simply sit on the drive, but installs CircuitPython if the board is in bootloader mode (i.e. boardnameBOOT).

You will be able to copy other files to the bootloader drive (boardnameBOOT) but they will not run or be accessible to CircuitPython. So make sure that once you're done installing CircuitPython, that you're dragging to and editing files on the CIRCUITPY drive!

Bootloader Drive Names

This list is not exhaustive, but should give you an idea what to look for in a bootloader drive name.

  • Trinket M0 = TRINKETBOOT
  • Gemma M0 = GEMMABOOT
  • Circuit Playground Express = CPLAYBOOT
  • ItsyBitsy M0 Express = ITSYBOOT
  • ItsyBitsy M4 Express = ITSYM4BOOT
  • Feather M0 Express = FEATHERBOOT
  • Feather M4 Express = FEATHERBOOT
  • Metro M0 Express = METROBOOT
  • Metro M4 Express = METROM4BOOT
  • Grand Central M4 Express = GCM4BOOT
  • NeoTrelis M4 Express = TRELM4BOOT 


When CircuitPython finishes installing, or you plug a CircuitPython board into your computer with CircuitPython already installed, the board shows up on your computer as a USB drive called CIRCUITPY.

The CIRCUITPY drive is where your code and the necessary libraries and files will live. You can edit your code directly on this drive and when you save, it will run automatically. When you create and edit code, you'll save your code in a file located on the CIRCUITPY drive. If you're following along with a Learn guide, you can paste the contents of the tutorial example into on the CIRCUITPY drive and save it to run the example.

CircuitPython looks for and runs the contents of the file automatically when the board starts up, reloads, or when you save changes to the file. This is what makes it so easy to get started with your project and update your code!

Working with Multiple Devices

There are many boards that work with CircuitPython. You may find yourself in a situation where you're working with more than one board at the same time. What happens when you have multiple boards plugged into your computer? You have multiple CIRCUITPY drives! How do you know which one is which? You can rename each CIRCUITPY drive to avoid confusion.


When you rename CIRCUITPY, it writes the name to the filesystem. This means that the name change will persist through disconnecting the board, as well as reloading CircuitPython!

The name must be 11 characters or less! This is a limitation of the filesystem. You will receive an error if you choose a name longer than 11 characters.

Renaming CIRCUITPY on Mac

Renaming your CIRCUITPY drive on Mac is simple. Click on the drive in Finder so you can see the contents. Then, right click on the drive in Finder and choose "Rename".

Once you click "Rename", in the right-click menu, the drive name will show up in a text box where you can rename the drive. Type in the new name.

Renaming CIRCUITPY on Windows

Renaming the CIRCUITPY drive on Windows is easy. Open File Explorer and find the CIRCUITPY drive. Right click on it, and click "Rename".

Renaming the CIRCUITPY drive on Windows is easy. Open File Explorer and find the CIRCUITPY drive. Right click on it, and click "Rename".

You can also rename the drive through the "Properties" menu, which can be opened several different ways through the Windows File Explorer, including right clicking on the CIRCUITPY drive and choosing "Properties".

Once you click "Rename" in the right-click menu, the drive name will show up in a text box where you can rename the drive. Type in the new name.

Renaming CIRCUITPY on Linux

Renaming CIRCUITPY on Linux requires a couple of steps. You'll need to identify the mount point, and then run a command to rename the drive.

Open a terminal program. Run the following to find out where your board is mounted:

Download: file
df | grep CIRCUITPY

You will see CIRCUITPY on the right end of the resulting line. The dev/foo (where foo is the name of the mount point) on the left end of that line is the mount point.

Next you can run the following to unmount the board, replacing foo with your specific mount point.

Download: file
sudo umount /dev/foo

To rename the board, run the following:

Download: file
sudo fatlabel /dev/foo NEW_NAME

Then, eject your board, unplug it, and plug it back in to force it to remount with the new name.

To check to see if it worked, look for the drive in your file manager. Or, you can run the following:

Download: file
df | grep NEW_NAME

Renaming CIRCUITPY through CircuitPython

You can also rename the board using CircuitPython. Create a new file on your CIRCUITPY drive called Copy the following code into the new file:

Download: file
import storage

storage.remount("/", readonly=True)

m = storage.getmount("/")
m.label = "NEW_NAME"

storage.remount("/", readonly=False)

Eject your board, and reboot the board either by pressing the reset button once, or unplugging it and plugging it back in. After a moment, it should show up in your file explorer with the NEW_NAME you chose for it! You can delete after the newly named board shows up in your file explorer.

Reverting to CIRCUITPY

You can follow the same processes above to rename the drive back to CIRCUITPY.

You will also revert to CIRCUITPY by erasing the filesystem. If you are in a situation where you need to erase the filesystem on your CircuitPython board, the drive name will revert to CIRCUITPY on completion.

Creating and Editing Code

One of the best things about CircuitPython is how simple it is to get code up and running. In this section, we're going to cover how to create and edit your first CircuitPython program.

To create and edit code, all you'll need is an editor. There are many options. We strongly recommend using Mu! It's designed for CircuitPython, and it's really simple and easy to use, with a built in serial console!

If you don't or can't use Mu, there are basic text editors built into every operating system such as Notepad on Windows, TextEdit on Mac, and gedit on Linux. However, many of these editors don't write back changes immediately to files that you edit. That can cause problems when using CircuitPython. See the Editing Code section below. If you want to skip that section for now, make sure you do "Eject" or "Safe Remove" on Windows or "sync" on Linux after writing a file if you aren't using Mu. (This is not a problem on MacOS.)

Creating Code

Open your editor, and create a new file. If you are using Mu, click the New button in the top left

Copy and paste the following code into your editor:

Download: file
import board
import digitalio
import time

led = digitalio.DigitalInOut(board.D13)
led.direction = digitalio.Direction.OUTPUT

while True:
    led.value = True
    led.value = False
If you are using Adafruit CLUE, you will need to edit the code to use board.D17 as shown below!

For Adafruit CLUE, you'll need to use board.D17 instead of board.D13. The rest of the code remains the same. Make the following change to the led = line:

Download: file
led = digitalio.DigitalInOut(board.D17)

It will look like this - note that under the while True: line, the next four lines have spaces to indent them, but they're indented exactly the same amount. All other lines have no spaces before the text.

Save this file as on your CIRCUITPY drive.

On each board you'll find a tiny red LED. It should now be blinking. Once per second

Congratulations, you've just run your first CircuitPython program!

Editing Code

To edit code, open the file on your CIRCUITPY drive into your editor.


Make the desired changes to your code. Save the file. That's it!

Your code changes are run as soon as the file is done saving.

There's just one warning we have to give you before we continue...

Don't Click Reset or Unplug!

The CircuitPython code on your board detects when the files are changed or written and will automatically re-start your code. This makes coding very fast because you save, and it re-runs.

However, you must wait until the file is done being saved before unplugging or resetting your board! On Windows using some editors this can sometimes take up to 90 seconds, on Linux it can take 30 seconds to complete because the text editor does not save the file completely. Mac OS does not seem to have this delay, which is nice!

This is really important to be aware of. If you unplug or reset the board before your computer finishes writing the file to your board, you can corrupt the drive. If this happens, you may lose the code you've written, so it's important to backup your code to your computer regularly.

There are a few ways to avoid this:

1. Use an editor that writes out the file completely when you save it.

Recommended editors:

Recommended only with particular settings or with add-ons:

  • vim / vi safely writes all changes. But set up vim to not write swapfiles (.swp files: temporary records of your edits) to CIRCUITPY. Run vim with vim -n, set the no swapfile option, or set the directory option to write swapfiles elsewhere. Otherwise the swapfile writes trigger restarts of your program.
  • The PyCharm IDE is safe if "Safe Write" is turned on in Settings->System Settings->Synchronization (true by default).
  • If you are using Atom, install the  fsync-on-save package so that it will always write out all changes to files on CIRCUITPY.
  • SlickEdit works only if you add a macro to flush the disk.

We don't recommend these editors:

  • notepad (the default Windows editor) and Notepad++ can be slow to write, so we recommend the editors above! If you are using notepad, be sure to eject the drive (see below)
  • IDLE in Python 3.8.0 or earlier does not force out changes immediately
  • nano (on Linux) does not force out changes
  • geany (on Linux) does not force out changes
  • Anything else - we haven't tested other editors so please use a recommended one!

2. Eject or Sync the Drive After Writing

If you are using one of our not-recommended-editors, not all is lost! You can still make it work.

On Windows, you can Eject or Safe Remove the CIRCUITPY drive. It won't actually eject, but it will force the operating system to save your file to disk. On Linux, use the sync command in a terminal to force the write to disk.

Oh No I Did Something Wrong and Now The CIRCUITPY Drive Doesn't Show Up!!!

Don't worry! Corrupting the drive isn't the end of the world (or your board!). If this happens, follow the steps found on the Troubleshooting page of every board guide to get your board up and running again.

Back to Editing Code...

Now! Let's try editing the program you added to your board. Open your file into your editor. We'll make a simple change. Change the first 0.5 to 0.1. The code should look like this:

Download: file
import board
import digitalio
import time

led = digitalio.DigitalInOut(board.D13)
led.direction = digitalio.Direction.OUTPUT

while True:
    led.value = True
    led.value = False

Leave the rest of the code as-is. Save your file. See what happens to the LED on your board? Something changed! Do you know why? Let's find out! 

Exploring Your First CircuitPython Program

First, we'll take a look at the code we're editing.

Here is the original code again:

Download: file
import board
import digitalio
import time

led = digitalio.DigitalInOut(board.D13)
led.direction = digitalio.Direction.OUTPUT

while True:
    led.value = True
    led.value = False

Imports & Libraries

Each CircuitPython program you run needs to have a lot of information to work. The reason CircuitPython is so simple to use is that most of that information is stored in other files and works in the background. These files are called libraries. Some of them are built into CircuitPython. Others are stored on your CIRCUITPY drive in a folder called lib.

Download: file
import board
import digitalio
import time

The import statements tells the board that you're going to use a particular library in your code. In this example, we imported three libraries: board, digitalio, and time. All three of these libraries are built into CircuitPython, so no separate files are needed. That's one of the things that makes this an excellent first example. You don't need any thing extra to make it work! board gives you access to the hardware on your board, digitalio lets you access that hardware as inputs/outputs and time let's you pass time by 'sleeping'

Setting Up The LED

The next two lines setup the code to use the LED.

Download: file
led = digitalio.DigitalInOut(board.D13)
led.direction = digitalio.Direction.OUTPUT

Your board knows the red LED as D13. So, we initialise that pin, and we set it to output. We set led to equal the rest of that information so we don't have to type it all out again later in our code.


The third section starts with a  while statement. while True: essentially means, "forever do the following:". while True: creates a loop. Code will loop "while" the condition is "true" (vs. false), and as True is never False, the code will loop forever. All code that is indented under while True: is "inside" the loop.

Inside our loop, we have four items:

Download: file
while True:
    led.value = True
    led.value = False

First, we have led.value = True. This line tells the LED to turn on. On the next line, we have time.sleep(0.5). This line is telling CircuitPython to pause running code for 0.5 seconds. Since this is between turning the led on and off, the led will be on for 0.5 seconds.

The next two lines are similar. led.value = False tells the LED to turn off, and time.sleep(0.5) tells CircuitPython to pause for another 0.5 seconds. This occurs between turning the led off and back on so the LED will be off for 0.5 seconds too.

Then the loop will begin again, and continue to do so as long as the code is running!

So, when you changed the first 0.5 to 0.1, you decreased the amount of time that the code leaves the LED on. So it blinks on really quickly before turning off!

Great job! You've edited code in a CircuitPython program!

What if I don't have the loop?

If you don't have the loop, the code will run to the end and exit. This can lead to some unexpected behavior in simple programs like this since the "exit" also resets the state of the hardware. This is a different behavior than running commands via REPL. So if you are writing a simple program that doesn't seem to work, you may need to add a loop to the end so the program doesn't exit.

The simplest loop would be:

while True:


And remember - you can press <CTRL><C> to exit the loop.

See also the Behavior section in the docs.

More Changes

We don't have to stop there! Let's keep going. Change the second 0.5 to 0.1 so it looks like this:

Download: file
while True:
    led.value = True
    led.value = False

Now it blinks really fast! You decreased the both time that the code leaves the LED on and off!

Now try increasing both of the 0.1 to 1. Your LED will blink much more slowly because you've increased the amount of time that the LED is turned on and off.

Well done! You're doing great! You're ready to start into new examples and edit them to see what happens! These were simple changes, but major changes are done using the same process. Make your desired change, save it, and get the results. That's really all there is to it!

Naming Your Program File

CircuitPython looks for a code file on the board to run. There are four options: code.txt,, main.txt and CircuitPython looks for those files, in that order, and then runs the first one it finds. While we suggest using as your code file, it is important to know that the other options exist. If your program doesn't seem to be updating as you work, make sure you haven't created another code file that's being read instead of the one you're working on.

Connecting to the Serial Console

One of the staples of CircuitPython (and programming in general!) is something called a "print statement". This is a line you include in your code that causes your code to output text. A print statement in CircuitPython looks like this:

print("Hello, world!")

This line would result in:

Hello, world!

However, these print statements need somewhere to display. That's where the serial console comes in!

The serial console receives output from your CircuitPython board sent over USB and displays it so you can see it. This is necessary when you've included a print statement in your code and you'd like to see what you printed. It is also helpful for troubleshooting errors, because your board will send errors and the serial console will print those too.

The serial console requires a terminal program. A terminal is a program that gives you a text-based interface to perform various tasks.

If you're on Linux, and are seeing multi-second delays connecting to the serial console, or are seeing "AT" and other gibberish when you connect, then the modemmanager service might be interfering. Just remove it; it doesn't have much use unless you're still using dial-up modems. To remove, type this command at a shell:
Download: file
sudo apt purge modemmanager

Are you using Mu?

If so, good news! The serial console is built into Mu and will autodetect your board making using the REPL really really easy.

Please note that Mu does yet not work with nRF52 or ESP8266-based CircuitPython boards, skip down to the next section for details on using a terminal program.

First, make sure your CircuitPython board is plugged in. If you are using Windows 7, make sure you installed the drivers.

Once in Mu, look for the Serial button in the menu and click it.

Setting Permissions on Linux

On Linux, if you see an error box something like the one below when you press the Serial button, you need to add yourself to a user group to have permission to connect to the serial console.

On Ubuntu and Debian, add yourself to the dialout group by doing:

sudo adduser $USER dialout

After running the command above, reboot your machine to gain access to the group. On other Linux distributions, the group you need may be different. See Advanced Serial Console on Mac and Linux for details on how to add yourself to the right group.

Using Something Else?

If you're not using Mu to edit, are using ESP8266 or nRF52 CircuitPython, or if for some reason you are not a fan of the built in serial console, you can run the serial console as a separate program.

Windows requires you to download a terminal program, check out this page for more details

Mac and Linux both have one built in, though other options are available for download, check this page for more details

Interacting with the Serial Console

Once you've successfully connected to the serial console, it's time to start using it.

The code you wrote earlier has no output to the serial console. So, we're going to edit it to create some output.

Open your file into your editor, and include a print statement. You can print anything you like! Just include your phrase between the quotation marks inside the parentheses. For example:

Download: file
import board
import digitalio
import time

led = digitalio.DigitalInOut(board.D13)
led.direction = digitalio.Direction.OUTPUT

while True:
    print("Hello, CircuitPython!")
    led.value = True
    led.value = False

Save your file.

Now, let's go take a look at the window with our connection to the serial console.

Excellent! Our print statement is showing up in our console! Try changing the printed text to something else.

Keep your serial console window where you can see it. Save your file. You'll see what the serial console displays when the board reboots. Then you'll see your new change!

The Traceback (most recent call last): is telling you the last thing your board was doing before you saved your file. This is normal behavior and will happen every time the board resets. This is really handy for troubleshooting. Let's introduce an error so we can see how it is used.

Delete the e at the end of True from the line led.value = True so that it says led.value = Tru

Save your file. You will notice that your red LED will stop blinking, and you may have a colored status LED blinking at you. This is because the code is no longer correct and can no longer run properly. We need to fix it!

Usually when you run into errors, it's not because you introduced them on purpose. You may have 200 lines of code, and have no idea where your error could be hiding. This is where the serial console can help. Let's take a look!

The Traceback (most recent call last): is telling you that the last thing it was able to run was line 10 in your code. The next line is your error: NameError: name 'Tru' is not defined. This error might not mean a lot to you, but combined with knowing the issue is on line 10, it gives you a great place to start!

Go back to your code, and take a look at line 10. Obviously, you know what the problem is already. But if you didn't, you'd want to look at line 10 and see if you could figure it out. If you're still unsure, try googling the error to get some help. In this case, you know what to look for. You spelled True wrong. Fix the typo and save your file.

Nice job fixing the error! Your serial console is streaming and your red LED Is blinking again.

The serial console will display any output generated by your code. Some sensors, such as a humidity sensor or a thermistor, receive data and you can use print statements to display that information. You can also use print statements for troubleshooting. If your code isn't working, and you want to know where it's failing, you can put print statements in various places to see where it stops printing.

The serial console has many uses, and is an amazing tool overall for learning and programming!

The other feature of the serial connection is the Read-Evaluate-Print-Loop, or REPL. The REPL allows you to enter individual lines of code and have them run immediately. It's really handy if you're running into trouble with a particular program and can't figure out why. It's interactive so it's great for testing new ideas.

To use the REPL, you first need to be connected to the serial console. Once that connection has been established, you'll want to press Ctrl + C.

If there is code running, it will stop and you'll see Press any key to enter the REPL. Use CTRL-D to reload. Follow those instructions, and press any key on your keyboard.

The Traceback (most recent call last): is telling you the last thing your board was doing before you pressed Ctrl + C and interrupted it. The KeyboardInterrupt is you pressing Ctrl + C. This information can be handy when troubleshooting, but for now, don't worry about it. Just note that it is expected behavior.

If there is no code running, you will enter the REPL immediately after pressing Ctrl + C. There is no information about what your board was doing before you interrupted it because there is no code running.

Either way, once you press a key you'll see a >>> prompt welcoming you to the REPL!

If you have trouble getting to the >>> prompt, try pressing Ctrl + C a few more times.

The first thing you get from the REPL is information about your board.

This line tells you the version of CircuitPython you're using and when it was released. Next, it gives you the type of board you're using and the type of microcontroller the board uses. Each part of this may be different for your board depending on the versions you're working with.

This is followed by the CircuitPython prompt.

From this prompt you can run all sorts of commands and code. The first thing we'll do is run help(). This will tell us where to start exploring the REPL. To run code in the REPL, type it in next to the REPL prompt.

Type help() next to the prompt in the REPL.

Then press enter. You should then see a message.

First part of the message is another reference to the version of CircuitPython you're using. Second, a URL for the CircuitPython related project guides. Then... wait. What's this? To list built-in modules, please do `help("modules")`. Remember the libraries you learned about while going through creating code? That's exactly what this is talking about! This is a perfect place to start. Let's take a look!

Type help("modules") into the REPL next to the prompt, and press enter.

This is a list of all the core libraries built into CircuitPython. We discussed how board contains all of the pins on the board that you can use in your code. From the REPL, you are able to see that list!

Type import board into the REPL and press enter. It'll go to a new prompt. It might look like nothing happened, but that's not the case! If you recall, the import statement simply tells the code to expect to do something with that module. In this case, it's telling the REPL that you plan to do something with that module.

Next, type dir(board) into the REPL and press enter.

This is a list of all of the pins on your board that are available for you to use in your code. Each board's list will differ slightly depending on the number of pins available. Do you see D13? That's the pin you used to blink the red LED!

The REPL can also be used to run code. Be aware that any code you enter into the REPL isn't saved anywhere. If you're testing something new that you'd like to keep, make sure you have it saved somewhere on your computer as well!

Every programmer in every programming language starts with a piece of code that says, "Hello, World." We're going to say hello to something else. Type into the REPL:

print("Hello, CircuitPython!")

Then press enter.

That's all there is to running code in the REPL! Nice job!

You can write single lines of code that run stand-alone. You can also write entire programs into the REPL to test them. As we said though, remember that nothing typed into the REPL is saved.

There's a lot the REPL can do for you. It's great for testing new ideas if you want to see if a few new lines of code will work. It's fantastic for troubleshooting code by entering it one line at a time and finding out where it fails. It lets you see what libraries are available and explore those libraries.

Try typing more into the REPL to see what happens!

Returning to the serial console

When you're ready to leave the REPL and return to the serial console, simply press Ctrl + D. This will reload your board and reenter the serial console. You will restart the program you had running before entering the REPL. In the console window, you'll see any output from the program you had running. And if your program was affecting anything visual on the board, you'll see that start up again as well.

You can return to the REPL at any time!

CircuitPython Hardware

Now it's time to do something great with what you've learned! Every CircuitPython board is perfect for projects. However, each one excels in different areas. We're going to give you some details about each board, and highlight Learn guides where each one is used. You can try these out or get ideas for your own project!

Trinket M0

The Adafruit Trinket M0 is the smallest CircuitPython board we carry. But don't let that fool you! It's a tiny board with a lot of power. We wanted to design a microcontroller board that was small enough to fit into any project, and low cost enough to use without hesitation. Planning to test a proof of concept and need a CircuitPython board to throw in? Not ready to disassemble the project you worked so hard to design to extract the board you used last time? Trinket M0 has you covered. It's the lowest cost CircuitPython board available but it easily holds its own with the bigger boards!

Trinket M0 ships with CircuitPython and comes with demo code already on the board. You can open and edit the file found on the CIRCUITPY drive to get started, or create your own! The Trinket M0 guide gives you everything you need to know about your board. Check out the CircuitPython section to find a huge list of examples to try.

You can use Trinket M0 to make the Chilled Drinkibot which uses the Trinket to control thermoelectric cooling of a beverage. Or build a spooky Halloween project that turns your candy bucket into a Screaming Cauldron!

Gemma M0

The Adafruit Gemma M0 is a tiny CircuitPython board with just enough built-in to build many simple projects. It's designed to be worked into your wearable projects, with big holes around the outside for sewing (and they're alligator clip friendly too!). Gemma M0 will super-charge your wearables and is easier to use than ever. There are capacitive touch pads, an on-off switch and an RGB DotStar LED built right into the board so there's plenty you can do without adding a thing. Add conductive thread and LEDs and you'll have a blinky wearable in no time!

Like Trinket, Gemma M0 ships with CircuitPython and has demo code already on the board. You can open and edit the file on the CIRCUITPY drive, or create your own! The Gemma M0 guide shows you all the info about your board, and has a great list of CircuitPython examples to try out.

Use Gemma M0 to create a pair of Clockwork Goggles with fun light patterns on NeoPixel rings. Or accessorise with this 3D printed Sheikah Pendant to add a bit of light to your next costume!

Circuit Playground Express

The Adafruit Circuit Playground Express is the next step towards a perfect introduction to electronics and programming. It's packed full of sensors, LEDs, buttons and switches, and it's super easy to get started with! This board is super versatile. Whether you're new to electronics and programming, or a seasoned veteran, Circuit Playground Express is an amazing board to work with. With so much built into the board, you can learn how different types of electronics work and learn to program them all without purchasing any other parts. All you need is a USB cable and the board! But, that's just the beginning. Many of the pads around the outside of the board function in multiple ways allowing you to wire other things to the board. For example, you could wire up a servo or a potentiometer. The possibilities are endless!

The Circuit Playground Express guide has tons of information on all the fantastic features of the board. The CircuitPython section of the guide has an extensive list of examples using the built-in features of the CircuitPython and the board. There is also a section called Python Playground with more demos and a Drum Machine project to try out.

You can turn your Circuit Playground Express into a capacitive touch tone Piano in the Key of Lime using the touch pads on the board. Use the built in accelerometer to make a UFO Flying Saucer complete with lights and alien sounds using your board, and some extra supplies from around the house or a 3D printed saucer!

Feather M0 Express

The Adafruit Feather M0 Express is the first Feather designed specifically for CircuitPython. It's part of a line of Adafruit Feather development boards designed to work standalone or stacked, and is powered by USB or lithium ion battery so it works for both stationary and on-the-go projects. Feather M0 Express comes with two headers for use with a solderless breadboard, or you can solder wires directly to the pins on the board. This allows for prototyping while you're working on your project and permanent installation when you're ready. One of the things that makes the Feather M0 Express amazing is the the huge array of boards called Featherwings which are designed to fit right on the Feather. There are CircuitPython libraries for many of these boards and more are being written all the time.

Feather M0 Express ships CircuitPython-ready with the UF2 bootloader installed and ready for you to install CircuitPython when you receive your board. Create your first program, save it to the board, and off you go! The Feather M0 Express guide has all the details about your board, and a CircuitPython section to get you started.

Feather M0 Express can be used to power all kinds of projects. Build a CircuitPython Painter POV LED wand using 3D printed parts and DotStar strips. Create an engraved edge-lit LED Acrylic Sign with NeoPixels. There are guides to go with the Featherwings that explain how to use them with CircuitPython, like the OLED Display and Adalogger Featherwing.

Metro M0 Express

Metro M0 Express is the first Metro board designed to work with CircuitPython. This is not a beginner board. If you're just getting started, we'd recommend one of the previous boards. It has a lot of the same features as Feather M0 Express, as well as some development specific features (like the SWD port built in!). The Metro M0 Express is designed to work with the Arduino form-factor, so if you've already got Arduino shields, this board would be great for you. There are CircuitPython libraries for some shields already. It has 25 GPIO pins (the most of any of these boards!) so it's great if you're looking for a lot of options.

Metro M0 Express ships CircuitPython-ready with the UF2 bootloader installed and is ready for you to install CircuitPython when you receive your board. Create your first program, save it to the board, and you're good to go! The Metro M0 Express guide gives you all the details about your board, and the CircuitPython section is available to get you started.

All sensors and breakout boards with CircuitPython libraries will work with the Metro M0 Express running CircuitPython. Find the guide for your sensor and follow the guide to find out how to wire it up. There are a ton of options available.

What's Next?

Now you're ready to jump into some more Learn Guides or simply get started with a brand new project. Great job, and good luck!

CircuitPython Libraries

As we continue to develop CircuitPython and create new releases, we will stop supporting older releases. Visit to download the latest version of CircuitPython for your board. You must download the CircuitPython Library Bundle that matches your version of CircuitPython. Please update CircuitPython and then visit to download the latest Library Bundle.

Each CircuitPython program you run needs to have a lot of information to work. The reason CircuitPython is so simple to use is that most of that information is stored in other files and works in the background. These files are called libraries. Some of them are built into CircuitPython. Others are stored on your CIRCUITPY drive in a folder called lib. Part of what makes CircuitPython so awesome is its ability to store code separately from the firmware itself. Storing code separately from the firmware makes it easier to update both the code you write and the libraries you depend.

Your board may ship with a lib folder already, it's in the base directory of the drive. If not, simply create the folder yourself. When you first install CircuitPython, an empty lib directory will be created for you.

CircuitPython libraries work in the same way as regular Python modules so the Python docs are a great reference for how it all should work. In Python terms, we can place our library files in the lib directory because its part of the Python path by default.

One downside of this approach of separate libraries is that they are not built in. To use them, one needs to copy them to the CIRCUITPY drive before they can be used. Fortunately, we provide a bundle full of our libraries.

Our bundle and releases also feature optimized versions of the libraries with the .mpy file extension. These files take less space on the drive and have a smaller memory footprint as they are loaded.

Installing the CircuitPython Library Bundle

We're constantly updating and improving our libraries, so we don't (at this time) ship our CircuitPython boards with the full library bundle. Instead, you can find example code in the guides for your board that depends on external libraries. Some of these libraries may be available from us at Adafruit, some may be written by community members!

Either way, as you start to explore CircuitPython, you'll want to know how to get libraries on board.

You can grab the latest Adafruit CircuitPython Bundle release by clicking the button below.

Note: Match up the bundle version with the version of CircuitPython you are running - 3.x library for running any version of CircuitPython 3, 4.x for running any version of CircuitPython 4, etc. If you mix libraries with major CircuitPython versions, you will most likely get errors due to changes in library interfaces possible during major version changes.

If you need another version, you can also visit the bundle release page which will let you select exactly what version you're looking for, as well as information about changes.

Either way, download the version that matches your CircuitPython firmware version. If you don't know the version, look at the initial prompt in the CircuitPython REPL, which reports the version. For example, if you're running v4.0.1, download the 4.x library bundle. There's also a py bundle which contains the uncompressed python files, you probably don't want that unless you are doing advanced work on libraries.

After downloading the zip, extract its contents. This is usually done by double clicking on the zip. On Mac OSX, it places the file in the same directory as the zip.

Open the bundle folder. Inside you'll find two information files, and two folders. One folder is the lib bundle, and the other folder is the examples bundle.

Now open the lib folder. When you open the folder, you'll see a large number of mpy files and folders

Example Files

All example files from each library are now included in the bundles, as well as an examples-only bundle. These are included for two main reasons:

  • Allow for quick testing of devices.
  • Provide an example base of code, that is easily built upon for individualized purposes.

Copying Libraries to Your Board

First you'll want to create a lib folder on your CIRCUITPY drive. Open the drive, right click, choose the option to create a new folder, and call it lib. Then, open the lib folder you extracted from the downloaded zip. Inside you'll find a number of folders and .mpy files. Find the library you'd like to use, and copy it to the lib folder on CIRCUITPY.

This also applies to example files. They are only supplied as raw .py files, so they may need to be converted to .mpy using the mpy-cross utility if you encounter MemoryErrors. This is discussed in the CircuitPython Essentials Guide. Usage is the same as described above in the Express Boards section. Note: If you do not place examples in a separate folder, you would remove the examples from the import statement.

Example: ImportError Due to Missing Library

If you choose to load libraries as you need them, you may write up code that tries to use a library you haven't yet loaded.  We're going to demonstrate what happens when you try to utilise a library that you don't have loaded on your board, and cover the steps required to resolve the issue.

This demonstration will only return an error if you do not have the required library loaded into the lib folder on your CIRCUITPY drive.

Let's use a modified version of the blinky example.

Download: file
import board
import time
import simpleio

led = simpleio.DigitalOut(board.D13)

while True:
    led.value = True
    led.value = False

Save this file. Nothing happens to your board. Let's check the serial console to see what's going on.

We have an ImportError. It says there is no module named 'simpleio'. That's the one we just included in our code!

Click the link above to download the correct bundle. Extract the lib folder from the downloaded bundle file. Scroll down to find simpleio.mpy. This is the library file we're looking for! Follow the steps above to load an individual library file.

The LED starts blinking again! Let's check the serial console.

No errors! Excellent. You've successfully resolved an ImportError!

If you run into this error in the future, follow along with the steps above and choose the library that matches the one you're missing.

Library Install on Non-Express Boards

If you have a Trinket M0 or Gemma M0, you'll want to follow the same steps in the example above to install libraries as you need them. You don't always need to wait for an ImportError as you probably know what library you added to your code. Simply open the lib folder you downloaded, find the library you need, and drag it to the lib folder on your CIRCUITPY drive.

You may end up running out of space on your Trinket M0 or Gemma M0 even if you only load libraries as you need them. There are a number of steps you can use to try to resolve this issue. You'll find them in the Troubleshooting page in the Learn guides for your board.

Updating CircuitPython Libraries/Examples

Libraries and examples are updated from time to time, and it's important to update the files you have on your CIRCUITPY drive.

To update a single library or example, follow the same steps above. When you drag the library file to your lib folder, it will ask if you want to replace it. Say yes. That's it!

A new library bundle is released every time there's an update to a library. Updates include things like bug fixes and new features. It's important to check in every so often to see if the libraries you're using have been updated.

Welcome to the Community!

CircuitPython is a programming language that's super simple to get started with and great for learning. It runs on microcontrollers and works out of the box. You can plug it in and get started with any text editor. The best part? CircuitPython comes with an amazing, supportive community.

Everyone is welcome! CircuitPython is Open Source. This means it's available for anyone to use, edit, copy and improve upon. This also means CircuitPython becomes better because of you being a part of it. It doesn't matter whether this is your first microcontroller board or you're a computer engineer, you have something important to offer the Adafruit CircuitPython community. We're going to highlight some of the many ways you can be a part of it!

Adafruit Discord

The Adafruit Discord server is the best place to start. Discord is where the community comes together to volunteer and provide live support of all kinds. From general discussion to detailed problem solving, and everything in between, Discord is a digital maker space with makers from around the world.

There are many different channels so you can choose the one best suited to your needs. Each channel is shown on Discord as "#channelname". There's the #help-with-projects channel for assistance with your current project or help coming up with ideas for your next one. There's the #showandtell channel for showing off your newest creation. Don't be afraid to ask a question in any channel! If you're unsure, #general is a great place to start. If another channel is more likely to provide you with a better answer, someone will guide you.

The help with CircuitPython channel is where to go with your CircuitPython questions. #help-with-circuitpython is there for new users and developers alike so feel free to ask a question or post a comment! Everyone of any experience level is welcome to join in on the conversation. We'd love to hear what you have to say! The #circuitpython channel is available for development discussions as well.

The easiest way to contribute to the community is to assist others on Discord. Supporting others doesn't always mean answering questions. Join in celebrating successes! Celebrate your mistakes! Sometimes just hearing that someone else has gone through a similar struggle can be enough to keep a maker moving forward.

The Adafruit Discord is the 24x7x365 hackerspace that you can bring your granddaughter to.

Visit to sign up for Discord. We're looking forward to meeting you!

Adafruit Forums

The Adafruit Forums are the perfect place for support. Adafruit has wonderful paid support folks to answer any questions you may have. Whether your hardware is giving you issues or your code doesn't seem to be working, the forums are always there for you to ask. You need an Adafruit account to post to the forums. You can use the same account you use to order from Adafruit.

While Discord may provide you with quicker responses than the forums, the forums are a more reliable source of information. If you want to be certain you're getting an Adafruit-supported answer, the forums are the best place to be.

There are forum categories that cover all kinds of topics, including everything Adafruit. The Adafruit CircuitPython and MicroPython category under "Supported Products & Projects" is the best place to post your CircuitPython questions.

Be sure to include the steps you took to get to where you are. If it involves wiring, post a picture! If your code is giving you trouble, include your code in your post! These are great ways to make sure that there's enough information to help you with your issue.

You might think you're just getting started, but you definitely know something that someone else doesn't. The great thing about the forums is that you can help others too! Everyone is welcome and encouraged to provide constructive feedback to any of the posted questions. This is an excellent way to contribute to the community and share your knowledge!

Adafruit Github

Whether you're just beginning or are life-long programmer who would like to contribute, there are ways for everyone to be a part of building CircuitPython. GitHub is the best source of ways to contribute to CircuitPython itself. If you need an account, visit and sign up.

If you're new to GitHub or programming in general, there are great opportunities for you. Head over to adafruit/circuitpython on GitHub, click on "Issues", and you'll find a list that includes issues labeled "good first issue". These are things we've identified as something that someone with any level of experience can help with. These issues include options like updating documentation, providing feedback, and fixing simple bugs.

Already experienced and looking for a challenge? Checkout the rest of the issues list and you'll find plenty of ways to contribute. You'll find everything from new driver requests to core module updates. There's plenty of opportunities for everyone at any level!

When working with CircuitPython, you may find problems. If you find a bug, that's great! We love bugs! Posting a detailed issue to GitHub is an invaluable way to contribute to improving CircuitPython. Be sure to include the steps to replicate the issue as well as any other information you think is relevant. The more detail, the better!

Testing new software is easy and incredibly helpful. Simply load the newest version of CircuitPython or a library onto your CircuitPython hardware, and use it. Let us know about any problems you find by posting a new issue to GitHub. Software testing on both current and beta releases is a very important part of contributing CircuitPython. We can't possibly find all the problems ourselves! We need your help to make CircuitPython even better.

On GitHub, you can submit feature requests, provide feedback, report problems and much more. If you have questions, remember that Discord and the Forums are both there for help!


ReadTheDocs is a an excellent resource for a more in depth look at CircuitPython. This is where you'll find things like API documentation and details about core modules. There is also a Design Guide that includes contribution guidelines for CircuitPython.

RTD gives you access to a low level look at CircuitPython. There are details about each of the core modules. Each module lists the available libraries. Each module library page lists the available parameters and an explanation for each. In many cases, you'll find quick code examples to help you understand how the modules and parameters work, however it won't have detailed explanations like the Learn Guides. If you want help understanding what's going on behind the scenes in any CircuitPython code you're writing, ReadTheDocs is there to help!

Advanced Serial Console on Windows

Windows 7 Driver

If you're using Windows 7, use the link below to download the driver package. You will not need to install drivers on Mac, Linux or Windows 10.

What's the COM?

First, you'll want to find out which serial port your board is using. When you plug your board in to USB on your computer, it connects to a serial port. The port is like a door through which your board can communicate with your computer using USB.

We'll use Windows Device Manager to determine which port the board is using. The easiest way to determine which port the board is using is to first check without the board plugged in. Open Device Manager. Click on Ports (COM & LPT). You should find something already in that list with (COM#) after it where # is a number.

Now plug in your board. The Device Manager list will refresh and a new item will appear under Ports (COM & LPT). You'll find a different (COM#) after this item in the list.

Sometimes the item will refer to the name of the board. Other times it may be called something like USB Serial Device, as seen in the image above. Either way, there is a new (COM#) following the name. This is the port your board is using.

Install Putty

If you're using Windows, you'll need to download a terminal program. We're going to use PuTTY.

The first thing to do is download the latest version of PuTTY. You'll want to download the Windows installer file. It is most likely that you'll need the 64-bit version. Download the file and install the program on your machine. If you run into issues, you can try downloading the 32-bit version instead. However, the 64-bit version will work on most PCs.

Now you need to open PuTTY.

  • Under Connection type: choose the button next to Serial.
  • In the box under Serial line, enter the serial port you found that your board is using.
  • In the box under Speed, enter 115200. This called the baud rate, which is the speed in bits per second that data is sent over the serial connection. For boards with built in USB it doesn't matter so much but for ESP8266 and other board with a separate chip, the speed required by the board is 115200 bits per second. So you might as well just use 115200!

If you want to save those settings for later, use the options under Load, save or delete a stored session. Enter a name in the box under Saved Sessions, and click the Save button on the right.

Once your settings are entered, you're ready to connect to the serial console. Click "Open" at the bottom of the window. A new window will open.

If no code is running, the window will either be blank or will look like the window above. Now you're ready to see the results of your code.

Great job! You've connected to the serial console!

Advanced Serial Console on Mac and Linux

Connecting to the serial console on Mac and Linux uses essentially the same process. Neither operating system needs drivers installed. On MacOSX, Terminal comes installed. On Linux, there are a variety such as gnome-terminal (called Terminal) or Konsole on KDE.

What's the Port?

First you'll want to find out which serial port your board is using. When you plug your board in to USB on your computer, it connects to a serial port. The port is like a door through which your board can communicate with your computer using USB.

We're going to use Terminal to determine what port the board is using. The easiest way to determine which port the board is using is to first check without the board plugged in. On Mac, open Terminal and type the following:

ls /dev/tty.*

Each serial connection shows up in the /dev/ directory. It has a name that starts with tty.. The command ls shows you a list of items in a directory. You can use * as a wildcard, to search for files that start with the same letters but end in something different. In this case, we're asking to see all of the listings in /dev/ that start with tty. and end in anything. This will show us the current serial connections.

For Linux, the procedure is the same, however, the name is slightly different. If you're using Linux, you'll type:

ls /dev/ttyACM*

The concept is the same with Linux. We are asking to see the listings in the /dev/ folder, starting with ttyACM and ending with anything. This will show you the current serial connections. In the example below, the error is indicating that are no current serial connections starting with ttyACM.

Now, plug your board. Using Mac, type:

ls /dev/tty.*

This will show you the current serial connections, which will now include your board.

Using Mac, a new listing has appeared called /dev/tty.usbmodem141441. The tty.usbmodem141441 part of this listing is the name the example board is using. Yours will be called something similar.

Using Linux, type:

ls /dev/ttyACM*

This will show you the current serial connections, which will now include your board.

Using Linux, a new listing has appeared called /dev/ttyACM0. The ttyACM0 part of this listing is the name the example board is using. Yours will be called something similar.

Connect with screen

Now that you know the name your board is using, you're ready connect to the serial console. We're going to use a command called screen. The screen command is included with MacOS. Linux users may need to install it using their package manager. To connect to the serial console, use Terminal. Type the following command, replacing board_name with the name you found your board is using:

screen /dev/tty.board_name 115200

The first part of this establishes using the screen command. The second part tells screen the name of the board you're trying to use. The third part tells screen what baud rate to use for the serial connection. The baud rate is the speed in bits per second that data is sent over the serial connection. In this case, the speed required by the board is 115200 bits per second.

MacOS screen command using example board name

Press enter to run the command. It will open in the same window. If no code is running, the window will be blank. Otherwise, you'll see the output of your code.

Great job! You've connected to the serial console!

Permissions on Linux

If you try to run screen and it doesn't work, then you may be running into an issue with permissions. Linux keeps track of users and groups and what they are allowed to do and not do, like access the hardware associated with the serial connection for running screen. So if you see something like this:

then you may need to grant yourself access. There are generally two ways you can do this. The first is to just run screen using the sudo command, which temporarily gives you elevated privileges.

Once you enter your password, you should be in:

The second way is to add yourself to the group associated with the hardware. To figure out what that group is, use the command ls -l as shown below. The group name is circled in red.

Then use the command adduser to add yourself to that group. You need elevated privileges to do this, so you'll need to use sudo. In the example below, the group is adm and the user is ackbar.

After you add yourself to the group, you'll need to logout and log back in, or in some cases, reboot your machine. After you log in again, verify that you have been added to the group using the command groups. If you are still not in the group, reboot and check again.

And now you should be able to run screen without using sudo.

And you're in:

The examples above use screen, but you can also use other programs, such as putty or picocom, if you prefer.

PyCharm and CircuitPython

THIS PROCESS DOES NOT WORK. This plugin was never designed to work with CircuitPython. The process described here is a work-around that is of limited functionality. IF YOU WANT TO USE THE REPL WITHIN PYCHARM, USE THE BUILT IN TERMINAL AND screen.

PyCharm is a full featured Python editor including super helpful things like code completion and error highlighting. It's available for free in a Community Edition.

Recently, they added a MicroPython plugin that enables use of the REPL from within the editor. CircuitPython isn't officially supported, however we have some steps to make it work!

Download and install PyCharm on your computer. Then, plug in your board and follow the steps below!

Create a new project or open an existing project.

Open PyCharm Preferences/Settings. Click on Plugins and search for "micropython". Click on Search in repositories.

THIS PROCESS DOES NOT WORK. This plugin was never designed to work with CircuitPython. The process described here is a work-around that is of limited functionality. IF YOU WANT TO USE THE REPL WITHIN PYCHARM, USE THE BUILT IN TERMINAL AND screen.

Click Install.

Once it's finished installing, click Restart PyCharm.

Once restarted, open Preferences/Settings. Click on Languages & Frameworks and choose MicroPython.

THIS PROCESS DOES NOT WORK. This plugin was never designed to work with CircuitPython. The process described here is a work-around that is of limited functionality. IF YOU WANT TO USE THE REPL WITHIN PYCHARM, USE THE BUILT IN TERMINAL AND screen.

Choose your project directory from the list.

Choose ESP8266 from the list of Device Names.


For now, you'll use this option regardless of what board you are using.

You'll need to manually add your Device Path. This is the path to your serial connection. Once entered, click Ok.



If you need help finding your device's serial connection, see Advanced Serial Console on Windows and Advanced Serial Console on Mac and Linux.

THIS PROCESS DOES NOT WORK. This plugin was never designed to work with CircuitPython. The process described here is a work-around that is of limited functionality. IF YOU WANT TO USE THE REPL WITHIN PYCHARM, USE THE BUILT IN TERMINAL AND screen.

Now, open any Python file from the project directory you chose.


A message may pop up stating, "Packages required for ESP8266 support not found," followed by a list of packages. Click Install Requirements on this message to install the required packages.

Now, you can click on the Tools menu and you should find a MicroPython menu. Highlight this, and you'll find MicroPython REPL available.

The REPL will open at the bottom of the PyCharm window. Now you can begin coding!

If you want to use the built in REPL with a different board, you'll need to go in and change the Device Path to the path that matches the board you'd like to use.

To change the Device Path, follow the steps above starting with manually adding the Device Path.

The PyCharm REPL will not work with multiple boards at the same time. Going through the steps above on multiple projects did not result in consistently being able to open multiple REPL connections at the same time.

The "Remove All Files from MicroPython Device" and "Flash Project" features do not work, but could corrupt your board. Do not try to use these functions. Remember, CircuitPython isn't officially supported and the steps above are a workaround.
THIS PROCESS DOES NOT WORK. This plugin was never designed to work with CircuitPython. The process described here is a work-around that is of limited functionality. IF YOU WANT TO USE THE REPL WITHIN PYCHARM, USE THE BUILT IN TERMINAL AND screen.

CircuitPython for ESP8266

We are no longer supporting CircuitPython on ESP8266. This page is for historical purposes only. There is no guarantee that the instructions will continue to work.

Why are we dropping support for ESP8266?

CircuitPython on ESP8266 has not been a great experience for users. Its hard to send files to the device because it has no native USB, and you can quickly run out of RAM (there's less than you think once the networking stack is added). We've decided to only use ESP as a co-processor. Specifically, the ESP32 because it has good TLS/SSL support which is now essential for even the most basic interactions.

If you'd like to use ESP8266, please keep to version 3.x with the knowledge that it isn't supported. You can also check out MicroPython for ESP8266 which is still supported!

If you'd like to add WiFi support, check out our guide on ESP32/ESP8266 as a co-processor.

About ESP8266 for CircuitPython (3.x)

We have two 'strains' of CircuitPython, the primary one is the ATSAMD21/51-based boards that have native USB connectivity. Native USB means that the board can show up as a disk drive called CIRCUITPY and hold all your files on it.

There's also CircuitPython for boards like the ESP8266 and nRF52832, these are really nice chips with WiFi and Bluetooth, respectively, built in. But they do not have native USB! That means there is no way for the chip to appear as a disk drive. You can still use them with CircuitPython but its a lot tougher, so we don't recommend them for beginners. Here's what you have to know about using non-native chips for CircuitPython:

  • You only get a REPL connection! No HID keyboard/mouse or other USB interface
  • No disk drive for drag-n-drop file moving, files must be moved via a special tool such as ampy that 'types' the file in for you via the REPL
  • Loading CircuitPython requires command line tools

Installing CircuitPython on the ESP8266

To use CircuitPython with the ESP8266 you'll need to first flash it with the latest firmware.

Download esptool

First install the software which enables firmware flashing on the ESP8266.  The easiest way to install this tool is from Python's pip package manager.  If you don't have it already you'll need to install Python 2.7 (make sure you check the box to put Python in your system path when installing on Windows) and then run the following command in a terminal: pip install esptool

Note on Mac OSX and Linux you might need to run the command as root with sudo, like: sudo pip install esptool

If you receive an error that only supports Python 2.x try running again with the pip2 command instead of pip (likely your system is using Python 3 and the pip command is getting confused which version to use).

Download Latest CircuitPython Firmware

Next download the latest CircuitPython ESP8266 firmware file:

Get ESP8266 Ready For Bootloading

Now you'll need to put the ESP8266 into its firmware flashing mode.  Each ESP8266 board is slightly different:

  • For a raw ESP8266 module you'll need to wire up buttons to ground for the GPIO0 and RESET pins.  Hold the GPIO0 button down (or connect the line to ground) and while still holding GPIO0 to ground press and release the RESET button (or connect and release the line from ground), then release GPIO0.
  • For the HUZZAH ESP8266 breakout buttons for GPIO0 and RESET are built in to the board.  Hold GPIO0 down, then press and release RESET (while still holding GPIO0), and finally release GPIO0.
  • For the Feather HUZZAH ESP8266 you don't need to do anything special to go into firmware flashing mode.  This board is built to detect when the serial port is opened for flashing and automatically configure the ESP8266 module to receive firmware.  Be sure to first install the SiLabs CP210x driver on Windows and Mac OSX to make the board's serial port visible!  On Windows you want the normal VCP driver, not the 'with Serial Enumeration' driver.

Erase ESP8266

It's recommended to erase the entire flash memory of the ESP8266 board before uploading firmware. Run the following command in a terminal to perform this erase:

Download: file --port ESP8266_PORTNAME erase_flash

Where ESP8266_PORTNAME is the path or name of the serial port that is connected to the ESP8266.  The exact name of the device varies depending on the type of serial to USB converter chip so you might need to look at the serial ports with and without the device connected to find its name.

Program ESP8266

Now put the ESP8266 back into firmware flashing mode and run the following command to load the downloaded firmware file:

Download: file --port ESP8266_PORTNAME --baud 115200 write_flash --flash_size=detect 0 firmware.bin

Again set ESP8266_PORTNAME to the path or name of the serial port that is connected to the ESP8266.  In addition set firmware.bin to the name or path to the firmware file you would like to load.

Once the tool finishes flashing the firmware (you'll usually see a blue light on the ESP8266 module flashing during this process) press the RESET button on the ESP8266 board or disconnect and reconnect it to your computer.  You should be all set to start using the latest CircuitPython firmware on the board!

Note that if you see an error that "detect is not a valid flash_size parameter" you might be using an older version of  To upgrade to the latest version run the following command pip install --upgrade esptool

Upload Libraries & Files Using Ampy!

The biggest difference you'll find with ESP8266 is that you need to use a special tool to move files around. Check out ampy by reading this guide. It's about MicroPython but CircuitPython is nearly identical so the the overall installation and usage is identical!

Other Stuff To Know!

  • The REPL works as you'd expect, so check out that introductory page.
  • File storage is in the same chip as CircuitPython so if you update, you may lose your files! Keep backups.
  • Libraries and API are also the same as for other CircuitPython boards.
  • Note that the ESP8266 does not have a ton of pins available, and only one analog input with 0-1.0V range. There is no UART port available (it's the one used for the REPL!)
  • There are no analog outputs.
  • For SPI and I2C, you can use them! But you will need to use bitbangio to create the bus objects

Uninstalling CircuitPython

A lot of our boards can be used with multiple programming languages. For example, the Circuit Playground Express can be used with MakeCode, CS Discoveries, CircuitPython and Arduino.

Maybe you tried CircuitPython and want to go back to MakeCode or Arduino? Not a problem

You can always remove/re-install CircuitPython whenever you want! Heck, you can change your mind every day!

Backup Your Code

Before uninstalling CircuitPython, don't forget to make a backup of the code you have on the little disk drive. That means your or any other files, the lib folder etc. You may lose these files when you remove CircuitPython, so backups are key! Just drag the files to a folder on your laptop or desktop computer like you would with any USB drive.

Moving Circuit Playground Express to MakeCode

On the Circuit Playground Express (this currently does NOT apply to Circuit Playground Bluefruit), if you want to go back to using MakeCode, it's really easy. Visit and find the program you want to upload. Click Download to download the .uf2 file that is generated by MakeCode.

Now double-click your CircuitPython board until you see the onboard LED(s) turn green and the ...BOOT directory shows up.

Then find the downloaded MakeCode .uf2 file and drag it to the ...BOOT drive.

Your MakeCode is now running and CircuitPython has been removed. Going forward you only have to single click the reset button

Moving to Arduino

If you want to change your firmware to Arduino, it's also pretty easy.

Start by plugging in your board, and double-clicking reset until you get the green onboard LED(s) - just like with MakeCode

Within Arduino IDE, select the matching board, say Circuit Playground Express

Select the correct matching Port:

Create a new simple Blink sketch example:

Download: file
// the setup function runs once when you press reset or power the board
void setup() {
  // initialize digital pin 13 as an output.
  pinMode(13, OUTPUT);

// the loop function runs over and over again forever
void loop() {
  digitalWrite(13, HIGH);   // turn the LED on (HIGH is the voltage level)
  delay(1000);              // wait for a second
  digitalWrite(13, LOW);    // turn the LED off by making the voltage LOW
  delay(1000);              // wait for a second

Make sure the LED(s) are still green, then click Upload to upload Blink. Once it has uploaded successfully, the serial Port will change so re-select the new Port!

Once Blink is uploaded you should no longer need to double-click to enter bootloader mode, Arduino will automatically reset when you upload

Non-UF2 Installation

This installation page is only required if you do not have UF2 bootloader installed (e.g. boardBOOT drag-n-drop)! This page is for non-Express Feather M0's, Arduino Zero's & M0's, and other custom ATSAMD21 boards.

Flashing with Bossac - For Non-Express Feather M0's & Arduino Zero

Our older Feather M0 boards don't come with UF2, instead they come with a simpler bootloader called bossa. This is also what is installed on Arduino Zero's and other  CircuitPython compatible boards that use the ATSAMDx1 or nRF52840. It is the only method you can use if your CircuitPython installation file is a .bin rather than a .uf2

Command-Line ahoy!

Flashing with bossac requires the use of your computer's command line interface. On windows, that's the cmd or powershell tool. On mac and Linux, use Terminal!

Download Latest CircuitPython Firmware

The first thing you'll want to do is download the most recent version of CircuitPython.

As of April, 2019, there are two sites to download the appropriate .bin file. Adafruit is migrating files to It is suggested to look for the .bin file for your compatible board there first by searching for the board. Only compatible boards that have a pull request for the appropriate pin definition files will be listed on that site, developers should submit their materials to be included if they have a new CircuitPython board they would like to see listed.

Click the green button below to search for your board to find the appropriate file.

Alternatively, use GitHub

For now, CircuitPython board files are also in the Adafruit CircuitPython GitHub repo, although they may migrate to a dedicated CircuitPython repo in the future. If you have issues with, look to download from GitHub using this second green button below.

Once downloaded, save the .bin file onto your desktop, you'll need it soon!

If you are running Windows 7, you must install the driver set (we cover it on this page) so you have access to the COM port.

Download BOSSA

Once you have a firmware image you'll need to download the BOSSA tool, which that can load firmware on SAMD21/51 boards. This tool is actually used internally by the Arduino IDE when it programs these boards, however you can use it yourself to load custom firmware

Be aware you must use 1.7.0 or higher version of bossac to program SAMD21 and SAMD51 boards! Versions of  BOSSA before version 1.7.0 won't work because it doesn't support the SAMD21/51 chips. Also note that bossac versions 1.9.0 and newer have incompatibly changed their command-line parameters, and can erase your bootloader if it is not protected. (Adafruit boards ship with protected bootloaders.) Follow the directions below carefully, depending on which version you have.

To flash with bossac (BOSSA's command line tool) first download the latest version from here. The ming32 version is for Windows, apple-darwin for Mac OSX and various linux options for Linux.

bossac works with .bin files only, it will not work with .uf2 files!

Test bossac

Open a terminal and navigate to the folder with the bossac tool. Then check the tool runs by running it with the --help option:

Open a terminal and navigate to the folder with the bossac tool. Then check the tool runs by running it with the --help option with bossac --help

Or if you're using Linux or Mac OSX you'll need to add a ./ to specify that bossac is run from the current directory like ./bossac --help

Make sure you see BOSSA version 1.7.0 or higher!  And see the warning below about version 1.9.0 and higher. If you see a lower version then you accidentally downloaded an older version of the tool and it won't work to flash SAMD21 chips.  Go back and grab the latest release from this BOSSA GitHub repository as mentioned above.

Port Selection for Mac OS

You'll need to know what port to use if you're on a Mac.

In your same terminal window, run the command ls /dev/cu.*. Note the ports listed, then plug in your board and run the command again.  The device may be listed something like /dev/cu.usbmodem14301. Make note of the port name for the bossac section below.

Get Into the Bootloader

You'll have to 'kick' the board into the bootloader manually. Do so by double-clicking the reset button. The red "#13" LED should pulse on and off. If you are using an Arduino Zero, make sure you are connected to the native USB port not the debugging/programming port.

One special note, if you're using the Arduino M0 from you'll need to replace its bootloader with the Arduino Zero bootloader so it can work with BOSSA.  To do this install the Arduino/Genuino Zero board in the Arduino IDE board manager and then follow these steps to burn the Arduino Zero bootloader (using the programming port on the board).  Once you've loaded the Arduino Zero bootloader you should be able to use the M0 with bossac as described below.

Run the bossac Command

With your board plugged in and running the bootloader you're ready to flash CircuitPython firmware onto the board. Copy the firmware .bin file to the same directory as the bossac tool, then in a terminal navigate to that location and run one ofthe following commands, depending on which version of bossac you have.

With bossac versions 1.9 or later, you must use the --offset parameter on the command line, and it must have the correct value for your board.

With bossac version 1.9 or later, you must give an --offset parameter on the command line to specify where to start writing the firmware in flash memory. This parameter was added in bossac 1.8.0 with a default of 0x2000, but starting in 1.9, the default offset was changed to 0x0000, which is not what you want in most cases. If you omit the argument for bossac 1.9 or later, you will probably see a "Verify Failed" error from bossac.  Remember to change the option for -p or --port to match the port on your Mac.

Replace the filename below with the name of your downloaded .bin: it will vary based on your board!

Using bossac Versions 1.7.0, 1.8

There is no --offset parameter available. Use a command line like this:

bossac -p /dev/cu.usbmodem14301 -e -w -v -R adafruit-circuitpython-boardname-version.bin

For example,

bossac -p /dev/cu.usbmodem14301 -e -w -v -R adafruit-circuitpython-feather_m0_express-3.0.0.bin

Using bossac Versions 1.9 or Later

For M0 boards, which have an 8kB bootloader, you must specify -offset=0x2000, for example:

bossac -p /dev/cu.usbmodem14301 -e -w -v -R --offset=0x2000 adafruit-circuitpython-feather_m0_express-3.0.0.bin

For M4 boards, which have a 16kB bootloader, you must specify -offset=0x4000, for example:

bossac -p /dev/cu.usbmodem14301 -e -w -v -R --offset=0x4000 adafruit-circuitpython-feather_m4_express-3.0.0.bin

This will erase the chip, write the given file, verify the write and Reset the board. On Linux or MacOS you may need to run this command with sudo ./bossac ..., or add yourself to the dialout group first.

After BOSSA loads the firmware you should see output similar to the following:

After reset, CircuitPython should be running and the CIRCUITPY drive will appear. You can always manually reset the board by clicking the reset button, sometimes that is needed to get it to 'wake up'. Express boards may cause a warning of an early eject of a USB drive but just ignore it. Nothing important was being written to the drive!


From time to time, you will run into issues when working with CircuitPython. Here are a few things you may encounter and how to resolve them.

As we continue to develop CircuitPython and create new releases, we will stop supporting older releases. Visit to download the latest version of CircuitPython for your board. You must download the CircuitPython Library Bundle that matches your version of CircuitPython. Please update CircuitPython and then visit to download the latest Library Bundle.

Always Run the Latest Version of CircuitPython and Libraries

As we continue to develop CircuitPython and create new releases, we will stop supporting older releases. You need to update to the latest CircuitPython..

You need to download the CircuitPython Library Bundle that matches your version of CircuitPython. Please update CircuitPython and then download the latest bundle.

As we release new versions of CircuitPython, we will stop providing the previous bundles as automatically created downloads on the Adafruit CircuitPython Library Bundle repo. If you must continue to use an earlier version, you can still download the appropriate version of mpy-cross from the particular release of CircuitPython on the CircuitPython repo and create your own compatible .mpy library files. However, it is best to update to the latest for both CircuitPython and the library bundle.

I have to continue using CircuitPython 3.x or 2.x, where can I find compatible libraries?

We are no longer building or supporting the CircuitPython 2.x and 3.x library bundles. We highly encourage you to update CircuitPython to the latest version and use the current version of the libraries. However, if for some reason you cannot update, you can find the last available 2.x build here and the last available 3.x build here.


You may have a different board.

Only Adafruit Express boards and the Trinket M0 and Gemma M0 boards ship with the UF2 bootloader installed. Feather M0 Basic, Feather M0 Adalogger, and similar boards use a regular Arduino-compatible bootloader, which does not show a boardnameBOOT drive.


If you are running a MakeCode program on Circuit Playground Express, press the reset button just once to get the CPLAYBOOT drive to show up. Pressing it twice will not work.

Windows 10

Did you install the Adafruit Windows Drivers package by mistake? You don't need to install this package on Windows 10 for most Adafruit boards. The old version (v1.5) can interfere with recognizing your device. Go to Settings -> Apps and uninstall all the "Adafruit" driver programs.

Windows 7

Version or later of the Adafruit Windows Drivers will fix the missing boardnameBOOT drive problem on Windows 7. To resolve this, first uninstall the old versions of the drivers:

  • Unplug any boards. In Uninstall or Change a Program (Control Panel->Programs->Uninstall a program), uninstall everything named "Windows Driver Package - Adafruit Industries LLC ...".


DriveDx and its accompanything SAT SMART Driver can interfere with seeing the BOOT drive. See this forum post for how to fix the problem.


  • Now install the new (or higher) Adafruit Windows Drivers Package:
  • When running the installer, you'll be shown a list of drivers to choose from. You can check and uncheck the boxes to choose which drivers to install.

You should now be done! Test by unplugging and replugging the board. You should see the CIRCUITPY drive, and when you double-click the reset button (single click on Circuit Playground Express running MakeCode), you should see the appropriate boardnameBOOT drive.

Let us know in the Adafruit support forums or on the Adafruit Discord if this does not work for you!

Windows Explorer Locks Up When Accessing boardnameBOOT Drive

On Windows, several third-party programs we know of can cause issues. The symptom is that you try to access the boardnameBOOT drive, and Windows or Windows Explorer seems to lock up. These programs are known to cause trouble:

  • AIDA64: to fix, stop the program. This problem has been reported to AIDA64. They acquired hardware to test, and released a beta version that fixes the problem. This may have been incorporated into the latest release. Please let us know in the forums if you test this.
  • Hard Disk Sentinel
  • Kaspersky anti-virus: To fix, you may need to disable Kaspersky completely. Disabling some aspects of Kaspersky does not always solve the problem. This problem has been reported to Kaspersky.
  • ESET NOD32 anti-virus: We have seen problems with at least version 9.0.386.0, solved by uninstallation.

Copying UF2 to boardnameBOOT Drive Hangs at 0% Copied

On Windows, a Western DIgital (WD) utility that comes with their external USB drives can interfere with copying UF2 files to the boardnameBOOT drive. Uninstall that utility to fix the problem.

CIRCUITPY Drive Does Not Appear

Kaspersky anti-virus can block the appearance of the CIRCUITPY drive. We haven't yet figured out a settings change that prevents this. Complete uninstallation of Kaspersky fixes the problem.

Norton anti-virus can interfere with CIRCUITPY. A user has reported this problem on Windows 7. The user turned off both Smart Firewall and Auto Protect, and CIRCUITPY then appeared.

Serial Console in Mu Not Displaying Anything

There are times when the serial console will accurately not display anything, such as, when no code is currently running, or when code with no serial output is already running before you open the console. However, if you find yourself in a situation where you feel it should be displaying something like an error, consider the following.

Depending on the size of your screen or Mu window, when you open the serial console, the serial console panel may be very small. This can be a problem. A basic CircuitPython error takes 10 lines to display!

Download: file
Auto-reload is on. Simply save files over USB to run them or enter REPL to disable. output:
Traceback (most recent call last):
  File "", line 7
SyntaxError: invalid syntax

Press any key to enter the REPL. Use CTRL-D to reload.

More complex errors take even more lines!

Therefore, if your serial console panel is five lines tall or less, you may only see blank lines or blank lines followed by Press any key to enter the REPL. Use CTRL-D to reload.. If this is the case, you need to either mouse over the top of the panel to utilise the option to resize the serial panel, or use the scrollbar on the right side to scroll up and find your message.

This applies to any kind of serial output whether it be error messages or print statements. So before you start trying to debug your problem on the hardware side, be sure to check that you haven't simply missed the serial messages due to serial output panel height.

CircuitPython RGB Status Light

Nearly all Adafruit CircuitPython-capable boards have a single NeoPixel or DotStar RGB LED on the board that indicates the status of CircuitPython. A few boards designed before CircuitPython existed, such as the Feather M0 Basic, do not.

Circuit Playground Express and Circuit Playground Bluefruit have multiple RGB LEDs, but do NOT have a status LED. The LEDs are all green when in the bootloader. They do NOT indicate any status while running CircuitPython.

Here's what the colors and blinking mean:

  • steady GREEN: (or code.txt,, or main.txt) is running
  • pulsing GREEN: (etc.) has finished or does not exist
  • steady YELLOW at start up: (4.0.0-alpha.5 and newer) CircuitPython is waiting for a reset to indicate that it should start in safe mode
  • pulsing YELLOW: Circuit Python is in safe mode: it crashed and restarted
  • steady WHITE: REPL is running
  • steady BLUE: is running

Colors with multiple flashes following indicate a Python exception and then indicate the line number of the error. The color of the first flash indicates the type of error:

  • GREEN: IndentationError
  • CYAN: SyntaxError
  • WHITE: NameError
  • ORANGE: OSError
  • PURPLE: ValueError
  • YELLOW: other error

These are followed by flashes indicating the line number, including place value. WHITE flashes are thousands' place, BLUE are hundreds' place, YELLOW are tens' place, and CYAN are one's place. So for example, an error on line 32 would flash YELLOW three times and then CYAN two times. Zeroes are indicated by an extra-long dark gap.

ValueError: Incompatible .mpy file.

This error occurs when importing a module that is stored as a mpy binary file that was generated by a different version of CircuitPython than the one its being loaded into. In particular, the mpy binary format changed between CircuitPython versions 2.x and 3.x, as well as between 1.x and 2.x.

So, for instance, if you upgraded to CircuitPython 3.x from 2.x you’ll need to download a newer version of the library that triggered the error on import. They are all available in the Adafruit bundle.

Make sure to download a version with 2.0.0 or higher in the filename if you're using CircuitPython version 2.2.4, and the version with 3.0.0 or higher in the filename if you're using CircuitPython version 3.0.

CIRCUITPY Drive Issues

You may find that you can no longer save files to your CIRCUITPY drive. You may find that your CIRCUITPY stops showing up in your file explorer, or shows up as NO_NAME. These are indicators that your filesystem has issues.

First check - have you used Arduino to program your board? If so, CircuitPython is no longer able to provide the USB services. Reset the board so you get a boardnameBOOT drive rather than a CIRCUITPY drive, copy the latest version of CircuitPython (.uf2) back to the board, then Reset. This may restore CIRCUITPY functionality.

If still broken - When the CIRCUITPY disk is not safely ejected before being reset by the button or being disconnected from USB, it may corrupt the flash drive. It can happen on Windows, Mac or Linux.

In this situation, the board must be completely erased and CircuitPython must be reloaded onto the board.

You WILL lose everything on the board when you complete the following steps. If possible, make a copy of your code before continuing.

Easiest Way: Use storage.erase_filesystem()

Starting with version 2.3.0, CircuitPython includes a built-in function to erase and reformat the filesystem. If you have an older version of CircuitPython on your board, you can update to the newest version to do this.

  1. Connect to the CircuitPython REPL using Mu or a terminal program.
  2. Type:
Download: file
>>> import storage
>>> storage.erase_filesystem()

CIRCUITPY will be erased and reformatted, and your board will restart. That's it!

Old Way: For the Circuit Playground Express, Feather M0 Express, and Metro M0 Express:

If you can't get to the REPL, or you're running a version of CircuitPython before 2.3.0, and you don't want to upgrade, you can do this.

       1.  Download the correct erase file:

       2.  Double-click the reset button on the board to bring up the boardnameBOOT drive.
       3.  Drag the erase .uf2 file to the boardnameBOOT drive.
       4.  The onboard NeoPixel will turn yellow or blue, indicating the erase has started.
       5.  After approximately 15 seconds, the mainboard NeoPixel will light up green. On the NeoTrellis M4 this is the first NeoPixel on the grid
       6.  Double-click the reset button on the board to bring up the boardnameBOOT drive.
       7.  Drag the appropriate latest release of CircuitPython .uf2 file to the boardnameBOOT drive.

It should reboot automatically and you should see CIRCUITPY in your file explorer again.

If the LED flashes red during step 5, it means the erase has failed. Repeat the steps starting with 2.

If you haven't already downloaded the latest release of CircuitPython for your board, check out the installation page. You'll also need to install your libraries and code!

Old Way: For Non-Express Boards with a UF2 bootloader (Gemma M0, Trinket M0):

If you can't get to the REPL, or you're running a version of CircuitPython before 2.3.0, and you don't want to upgrade, you can do this.

       1.  Download the erase file:

       2.  Double-click the reset button on the board to bring up the boardnameBOOT drive.
       3.  Drag the erase .uf2 file to the boardnameBOOT drive.
       4.  The boot LED will start flashing again, and the boardnameBOOT drive will reappear.
       5.  Drag the appropriate latest release CircuitPython .uf2 file to the boardnameBOOT drive.

It should reboot automatically and you should see CIRCUITPY in your file explorer again.

If you haven't already downloaded the latest release of CircuitPython for your board, check out the installation page You'll also need to install your libraries and code!

Old Way: For non-Express Boards without a UF2 bootloader (Feather M0 Basic Proto, Feather Adalogger, Arduino Zero):

If you are running a version of CircuitPython before 2.3.0, and you don't want to upgrade, or you can't get to the REPL, you can do this.

Just follow these directions to reload CircuitPython using bossac, which will erase and re-create CIRCUITPY.

Running Out of File Space on Non-Express Boards

The file system on the board is very tiny. (Smaller than an ancient floppy disk.) So, its likely you'll run out of space but don't panic! There are a couple ways to free up space.

The board ships with the Windows 7 serial driver too! Feel free to delete that if you don't need it or have already installed it. Its ~12KiB or so.

Delete something!

The simplest way of freeing up space is to delete files from the drive. Perhaps there are libraries in the lib folder that you aren't using anymore or test code that isn't in use. Don't delete the lib folder completely, though, just remove what you don't need.

Use tabs

One unique feature of Python is that the indentation of code matters. Usually the recommendation is to indent code with four spaces for every indent. In general, we recommend that too. However, one trick to storing more human-readable code is to use a single tab character for indentation. This approach uses 1/4 of the space for indentation and can be significant when we're counting bytes.

MacOS loves to add extra files.

Luckily you can disable some of the extra hidden files that MacOS adds by running a few commands to disable search indexing and create zero byte placeholders. Follow the steps below to maximize the amount of space available on MacOS:

Prevent & Remove MacOS Hidden Files

First find the volume name for your board.  With the board plugged in run this command in a terminal to list all the volumes:

Download: file
ls -l /Volumes

Look for a volume with a name like CIRCUITPY (the default for CircuitPython).  The full path to the volume is the /Volumes/CIRCUITPY path.

Now follow the steps from this question to run these terminal commands that stop hidden files from being created on the board:

Download: file
mdutil -i off /Volumes/CIRCUITPY
cd /Volumes/CIRCUITPY
rm -rf .{,_.}{fseventsd,Spotlight-V*,Trashes}
mkdir .fseventsd
touch .fseventsd/no_log .metadata_never_index .Trashes
cd -

Replace /Volumes/CIRCUITPY in the commands above with the full path to your board's volume if it's different.  At this point all the hidden files should be cleared from the board and some hidden files will be prevented from being created.

Alternatively, with CircuitPython 4.x and above, the special files and folders mentioned above will be created automatically if you erase and reformat the filesystem. WARNING: Save your files first! Do this in the REPL:

>>> import storage
>>> storage.erase_filesystem

However there are still some cases where hidden files will be created by MacOS.  In particular if you copy a file that was downloaded from the internet it will have special metadata that MacOS stores as a hidden file.  Luckily you can run a copy command from the terminal to copy files without this hidden metadata file.  See the steps below.

Copy Files on MacOS Without Creating Hidden Files

Once you've disabled and removed hidden files with the above commands on MacOS you need to be careful to copy files to the board with a special command that prevents future hidden files from being created.  Unfortunately you cannot use drag and drop copy in Finder because it will still create these hidden extended attribute files in some cases (for files downloaded from the internet, like Adafruit's modules).

To copy a file or folder use the -X option for the cp command in a terminal.  For example to copy a foo.mpy file to the board use a command like:

Download: file
    cp -X foo.mpy /Volumes/CIRCUITPY

(Replace foo.mpy with the name of the file you want to copy.) Or to copy a folder and all of its child files/folders use a command like:

Download: file
cp -rX folder_to_copy /Volumes/CIRCUITPY

If you are copying to the lib folder, or another folder, make sure it exists before copying.

Download: file
# if lib does not exist, you'll create a file named lib !
cp -X foo.mpy /Volumes/CIRCUITPY/lib
# This is safer, and will complain if a lib folder does not exist.
cp -X foo.mpy /Volumes/CIRCUITPY/lib/

Other MacOS Space-Saving Tips

If you'd like to see the amount of space used on the drive and manually delete hidden files here's how to do so.  First list the amount of space used on the CIRCUITPY drive with the df command:

Lets remove the ._ files first.

Whoa! We have 13Ki more than before! This space can now be used for libraries and code!

CircuitPython Essentials

You've gone through the Welcome to CircuitPython guide. You've already gotten everything setup, and you've gotten CircuitPython running. Great! Now what? CircuitPython Essentials!

There are a number of core modules built into CircuitPython and commonly used libraries available. The Essentials guide will introduce you to these and show you an example of how to use each one.

It's time to get started learning the CircuitPython Essentials!

This guide was first published on Dec 19, 2017. It was last updated on Dec 19, 2017.