Older versions of the nRF52840 were shipped with a bootloader that does not handle large UF2's, and has other issues. To check whether you need to update the bootloader, double-click the reset button, and look in the NRF52BOOT drive for INFO_UF2.TXT. Inside that file, check the version number. It should be 0.6.1 or newer. This one is older:

UF2 Bootloader 0.2.9 lib/nrfx (v1.1.0-1-g096e770) lib/tinyusb (legacy-755-g55874813) s140 6.1.1
Model: Adafruit Feather nRF52840 Express
Board-ID: nRF52840-Feather-revD
Bootloader: s140 6.1.1
Date: Feb 22 2019

Adafruit nRF52 Bootloader can be upgraded/downgraded without any additional hardware. There are 3 different ways to update bootloader, each has its pros and cons:

  • Use UF2: This is the fastest and safest way to update bootloader. However, it requires your existing bootloader is at least 0.4.0 and only work with nRF52840 (not nRF52832).
  • Use Arduino IDE: work with all Adafruit nRF52 boards and bootloader version, typo free but may not be the latest bootloader version due to BSP release cycle.
  • Use Command Line: work with all boards and bootloader version (including 3rd party one). This command line is back-end of the Arduino IDE method above. 

This guide was first published on Jan 02, 2019. It was last updated on Jul 27, 2022.

This page (Update Bootloader) was last updated on Mar 08, 2019.

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