The serial supports serial communication between the BBC micro:bit and another computer. Basically, this allows you to send data from the micro:bit to your own computer. This is very useful for debugging purposes: you can add write line statements in your code and see them display on your computer as the program executes.

The code below shows a simple script that sends a line when the BBC micro:bit starts and another line each time the button A is pressed.

input.onButtonPressed(Button.A, () => {
    serial.writeLine("A pressed")

Data is also automatically streamed to serial by the bar graph block and picked up by the editor. This data can be streamed to the cloud as well.

basic.forever(() => {
   led.plotBarGraph(input.acceleration(Dimension.X), 0);

How to read the micro:bit’s serial output from your computer

Unfortunately, using the serial library requires quite a bit of a setup.

Windows earlier than 10

If you are running a Windows version earlier than 10, you must install a device driver (for the computer to recognize the serial interface of the micro:bit).

Also, if you don’t see the serial port as one of your computer’s devices, you might need to update the firmware on the micro:bit. Find the device name for the attached serial port in the following instructions for your operating system.

Windows > Tera Term

  • Install the terminal emulator Tera Term. At the time of this writing, the latest version is 4.88 and can be downloaded from here. Follow the instructions from the installer.

Once both the driver and the terminal emulator are installed, plug in the micro:bit and wait until the device is fully setup. Then, open TeraTerm.

  • Hit File > New Connection
  • Check “Serial”; in the dropdown menu, pick the COM port that says “mbed Serial Port”. Hit Ok.
  • In the menus, hit Setup > Serial Port and set the baud rate to 115200.

You should be good. Feel free to hit Setup > Save Setup in the menus to erase the default configuration file with a new one so that you don’t have to type in the settings again.

Please note that Windows will assign you a different COM port if you plug in another micro:bit. If you’re juggling between micro:bits, you’ll have to change the COM port every time.

Windows > Putty

If you prefer another terminal emulator (such as PuTTY), here are some instructions.

  • Open Windows’s Device Manager; expand the section called “Ports (COM & LPT)”; write down the com number for “mbed Serial Port” (e.g. COM14)
  • Open PuTTY; on the main screen, use the following settings: Serial / COM14 / 115200. Replace COM14 with the COM port number you wrote down previously. Feel free to type in a name and hit “Save” to remember this configuration.

  • (optional): in the “Terminal” section, check “implicit cr in every lf”


  • Install the program screen if it is not already installed.
  • Plug in the micro:bit.
  • Open a terminal.
  • Find which device node the micro:bit was assigned to with the command ls /dev/ttyACM*.
  • If it was /dev/ttyACM0, type the command screen /dev/ttyACM0 115200. If it was some other device node, use that one in the command instead. Note: You may need root access to run screen successfully. You can probably use the command sudo like this: sudo screen /dev/ttyACM0 115200.
  • To exit screen, type Ctrl-A Ctrl-D.

Alternative programs include minicom and so on.

Mac OS

  • Plug in the micro:bit
  • Open a terminal
  • ls /dev/cu.* will return to you a list of serial devices; one of them will look like /dev/cu.usbmodem1422 (the exact number depends on your computer)
  • screen /dev/cu.usbmodem1422 115200 will open up the micro:bit’s serial output. To exit, hit Ctrl-A Ctrl-D.