CircuitPython 4.0.0 Alpha 2 Released! — @adafruit @CircuitPython

Download the 4.0.0 Alpha 2 release here.

4.0.0 is the latest major revision of CircuitPython and features support for the nRF52840 BLE chipset, display support and translated messages.


This is alpha release number 2 of 4.0.0. Alpha releases do not have the complete API from 3.x on the nRF buildsand are only meant for testing. (Beta release will have the full existing API but still need work.) Please use the latest 3.x stable release when first starting with CircuitPython. It is stable.

When you find a bug please check the current known issues and file an issue if something isn’t already known.


To install follow the instructions in our new Welcome to CircuitPython! guide. To install the latest libraries, see this page in that guide.

Try the latest version of the Mu editor for creating and editing your CircuitPython programs and for easy access to the CircuitPython serial connection (the REPL).

Most builds are available as both UF2 and bin files here along with test builds.

New Features, Updates, and Fixes

  • Add new audioio.Mixer class to provide multiple simultaneous sample playback. Thanks @tannewt.
  • Add pulseio.PWMOut and pulse.PulseOut to nrf port. Thanks @dhalbert.
  • Add busio.UART to nrf port. Thanks @hathach.
  • Add supervisor.runtime.serial_bytes_available to see if input is available to read. Thanks @ATMakersBill.
  • Add auto-reload for nrf port. Thanks @hathach.
  • framebuf has been removed. displayio is its replacement, and will be enhanced as 4.0 progresses to include framebuf‘s functionality.
  • Fix storage.erase_filesystem() on nrf port. Thanks @jerryneedell.
  • Enable optional support for inline assembly. Thanks @urish.
  • Continued work on Spanish translation. Thanks @C47D and @carlosperate.
  • Italian translation. Thanks @platipo.
  • Brazilian Portuguese translation. Thanks @furlaneto@xpecex, and @gcvasconcelos.
  • Travis build improvements. Thanks @sajattack and @jepler.
  • Fix bugs in nrf SPI and I2C. Thanks @dhalbert.
  • Frozen libraries updated to latest released versions. Thanks @dhalbert.
  • Merge latest fixes from 3.x. Thanks @tannewt.

Breaking Changes!

  • None so far, but expect some later!

Known Issues

  • On nRF52840, using ubluepy with first allocated busio.SPI object will cause a reset. The first SPI object created is always be the high speed 32MHz SPIM3 peripheral. To avoid this, if you need SPI, create but do not use the first SPI object, and create subsequent SPI objects to use. The second and later objects will run at a maximum of 8MHz.
  • Due to a bug, the SPIM3 peripheral is not allocated. Only one SPI peripheral, running at 8MHz, is available. This accidentally works around the problem above.


Thank you to all who used, tested, contributed, helped out, and participated on GitHub and/or Discord:
@ladyada@dhalbert@tannewt@kattni@microbuilder@hathach@arturo182@nickzoic@glennrub@siddacious@deshipu@sommersoft@jerryneedell@brentru@caternuson@jepler@urish@sajattack,, @notro@Jahor@Makdaam@mrmcwethy@jepler@notro@mattyt@furlaneto@ATMakersBill@Klowner@klardotsh@C47D@carlosperate@platipo@xpecex@gcvasconcelos@saspa@uhrheber, and surely more we have missed. Join us on the Discord chat to collaborate.


Documentation is available in

Here are all the changes since 4.0.0-alpha.1.
Here are all the changes since 3.0.2.

This release is based on MicroPython 1.9.4 @25ae98f. Support upstream MicroPython by purchasing a PyBoard(from Adafruit here).


Check out this guide for info on common problems with CircuitPython. If you are still having, then post to the Adafruit Support Forums and join Discord.

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