Bluetooth LE Watch

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, as SonarCloud integration.
• Use of Docker container.

Bluetooth Services

Device information service (dis)

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.

Battery service (bas)

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.

Custom service

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.

Project Structure

.
├── CMakeLists.txt
├── docs
│   ├── Assigned Numbers.pdf
│   ├── DS3231.pdf
│   ├── DTS_v1.0.pdf
│   └── images
├── Kconfig
├── Makefile
├── nrf52840dk_nrf52840.overlay
├── prj.conf
├── README.md
├── sample.yaml
├── sonar-project.properties
├── src
│   ├── 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
│   └── main.c

Building and Running

Building with Docker image in interactive mode

Navigate to the project folder.

$ cd BLE-Watch

Then, run the Docker image. Replace the --device=/dev/bus/usb/001/xxx with the correct value.

$ docker run --rm -it --device=/dev/bus/usb/001/xxx --device=/dev/ttyACM0 --device=/dev/ttyACM1 -v ${PWD}:/workdir/project -w /workdir/project charlesdias/nrfconnect-sdk /bin/bash

Afterwards, execute the command below to build the firmware.

$ make build

You should expect an output similar to the following:

.
.
. 

[390/400] Linking C executable zephyr/zephyr_pre0.elf
[394/400] Linking C executable zephyr/zephyr_pre1.elf

[400/400] Linking C executable zephyr/zephyr.elf
Memory region         Used Size  Region Size  %age Used
           FLASH:      353588 B         1 MB     33.72%
             RAM:       55624 B       256 KB     21.22%
        IDT_LIST:          0 GB         2 KB      0.00%

Flashing the firmware

After the build is complete, run the following command to flash the firmware:

$ make flash

The expected output should be similar to:

.
.
.
[ ######               ]   0.000s | Verifying image - block 1 of 2
[ #################### ]   0.000s | Verifying image - Verify successful
[ #################### ]   2.377s | Verify file - Done verifying

Applying system reset.
Run.
-- runners.nrfjprog: Board with serial number <serial-number-value> flashed successfully.

Running

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

Unit Testing with Ztest

Ztest is a simple testing framework for Zephyr applications. It provides basic structures for writing test cases and test suites.

To run the unit tests for this project, follow these steps:

1. Navigate to the project's directory.

$ cd BLE-Watch

2. Open the /dev/ttyACM0 using your preferable serial communication program.

3. Build the tests with the following command:

$ make tests

4. After building, flash the tests firmware into the board with:

$ make flash

The output will show the results of the tests on /dev/ttyACM0, indicating which tests passed and which failed.

Next improvements

• 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.