This is a sample project using the Zephyr RTOS and Nordic nRF Connect to create a BLE watch. This device is composed with:

• nRF52840 DK Nordic board.
• OLED monochrome displays SSD1306 128x64 pixels.
• and the DS3231 real-time clock (RTC).

Both display and RTC communicates with the nRF52840 MCU via I2C bus.

Some topics covered:

• Tested on nRF52840 DK board.
• Embedded system with Zephyr RTOS and nRF Connect SDK.
• Bluetooth Low Energy (LE) technology.
• The device works as GAP Peripheral and GATT server.
• Implemented BLE services officially adopted by Bluetooth SIG and custom services too.
• Continuous integration (CI) with GitHub Actions.
• Use of Docker container.

Exposes the device information.

• Device Information Service: <UUID: 0x180A>
  • Characteristic: Model number string <UUID: 0x2A24>
    • Data format: < string >
    • Properties: Read.
  • Characteristic: Manufacturer name string <UUID: 0x2A29>
    • Data format: < string >
    • Properties: Read.
  • Characteristic: Serial number string <UUID: 0x2A25>
    • Data format: < string >
    • Properties: Read.
  • Characteristic: Firmware revision string <UUID: 0x2A26>
    • Data format: < string >
    • Properties: Read.
  • Characteristic: Hardware revision string <UUID: 0x2A27>
    • Data format: < string >
    • Properties: Read.
  • Characteristic: Software revision string <UUID: 0x2A28>
    • Data format: < string >
    • Properties: Read.

Simulates the battery level voltage.

• Battery Service: <UUID: 0x180F>
  • Characteristic: Battery level <UUID: 0x2A19>
    • Data format: < UINT8[1 byte]> percentage battery level
    • Properties: Notify, Read.

Receives messages to be shown on the display screen.

• Unknown Service: <UUID: 3C134D60-E275-406D-B6B4-BF0CC712CB7C>
  • Characteristic: Unknown <UUID: 3C134D61-E275-406D-B6B4-BF0CC712CB7C>
    • Data format: < TEXT (UTF-8) > limit up to 31 characters
    • Properties: Read, Write.

.
├── app
│   ├── inc
│   │   ├── device_information_service.h
│   │   ├── display_ssd1306.h
│   │   ├── gatt_central.h
│   │   └── rtc_ds3231.h
│   └── src
│       ├── device_information_service.c
│       ├── display_ssd1306.c
│       ├── gatt_central.c
│       └── rtc_ds3231.c
├── build_nrf52840dk
├── CMakeLists.txt
├── docs
│   ├── Assigned Numbers.pdf
│   ├── DS3231.pdf
│   └── DTS_v1.0.pdf
├── Kconfig
├── Makefile
├── nrf52840dk_nrf52840.overlay
├── prj.conf
├── README.md
├── sample.yaml
└── src
    └── main.c

Access the project folder.

cd BLE-Watch

And run the docker image.

docker run --rm -it -v ${PWD}:/workdir/project -w /workdir/project charlesdias/nrfconnect-sdk /bin/bash

After that, run the command below to build the firmware.

make build

Test the BLE Watch application with the nRF Connect app, which is available for iOS (App Store) and Android (Google Play).

• Create dedicate task to update the display.
• Implement Bluetooth service to set the date and time.
• Flash the application project running west on Docker container.
• Add Doxygen configuration.