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:

Navigate to the project's directory.

$ cd BLE-Watch

Open the /dev/ttyACM0 using your preferable serial communication program.
Build the tests with the following command:

$ make tests

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.

wmrsouza / BLE-Watch