There are numerous examples available for the Bluefruit nRF52/nRF52840 Feathers in the Examples menu of the nRF52 BSP, and these are always up to date. You're first stop looking for example code should be there:
The latest example source code is always available and visible on Github, and the public git repository should be considered the definitive source of example code for this board.
To help explain some common use cases for the nRF52 BLE API, feel free to consult the example documentation in this section of the learning guide:
- Advertising: Beacon - Shows how to use the BLEBeacon helper class to configure your Bleufruit nRF52 Feather as a beacon
- BLE UART: Controller - Shows how to use the Controller utility in our Bluefruit LE Connect apps to send basic data between your peripheral and your phone or tablet.
- Custom: HRM - Shows how to defined and work with a custom GATT Service and Characteristic, using the officially adopted Heart Rate Monitor (HRM) service as an example.
- BLE Pin I/O (StandardFirmataBLE) Shows how to control Pin I/O of nRF52 with Firmata protocol
For more information on the Arduino nRF52 API, check out this page.