ZephyrWatch

ZephyrWatch is an open-source smartwatch project designed to bring a modern, modular firmware experience to wearable hardware. Built on the Zephyr Real-Time Operating System (RTOS), it leverages a robust ecosystem of drivers and stacks to create a functional and extensible timepiece. The project specifically targets the Waveshare ESP32-S3-Touch-LCD-1.28, a circular display module that combines a powerful dual-core SoC with a capacitive touch interface.

Core Features and Capabilities

The firmware provides the essential building blocks of a smartwatch experience, focusing on timekeeping, connectivity, and user interface:

• Time Synchronization: Using the Bluetooth Low Energy (BLE) Current Time Service (CTS), the watch can synchronize its internal Real-Time Counter with a connected smartphone or computer.
• Graphics and UI: The Light and Versatile Graphics Library (LVGL) is used for all rendering, providing a smooth and responsive interface. The project includes several Montserrat font weights to ensure high-quality typography on the 1.28-inch display.
• Device Metadata: It implements the BLE Device Information Service (DIS), allowing host devices to identify the hardware model, manufacturer, and firmware revision.
• System Reliability: A hardware watchdog is integrated to handle unexpected software hangs, ensuring the device remains operational in the field.

Technical Architecture

ZephyrWatch is built using the Zephyr west build system and follows a modular architecture. The configuration is managed through Zephyr’s Kconfig system, enabling various subsystems such as:

• Input Subsystem: Handles touch events from the circular LCD.
• Settings Subsystem: Utilizes Non-Volatile Storage (NVS) and the Flash Map to persist user settings and pairing information across reboots.
• Bluetooth Stack: Implements a peripheral role with support for Security Manager Protocol (SMP) and privacy features to allow secure pairing with mobile devices.

One of the project’s core philosophies is the Single-Responsibility Principle. Developers are encouraged to isolate subsystem logic, making components self-sufficient and testable. For inter-component communication, the project utilizes a specialized “devicetwin” subsystem to share attributes like date and time between different parts of the firmware.

Hardware Support

The primary target is the ESP32-S3-Touch-LCD-1.28 from Waveshare. This board is a popular choice for DIY wearables due to its integrated ESP32-S3 chip, which provides both Wi-Fi and BLE, and its compact form factor. The project includes specific Devicetree overlays and board configurations to support the display controller and touch interface out of the box.

Getting Started

To build the project, developers need the Zephyr SDK and the Espressif HAL (obtained via west blobs fetch). The build process uses standard Zephyr commands:

west build -p always . --board esp32s3_touch_lcd_1_28/esp32s3/procpu
west flash

For developers looking to contribute or customize the watch, the project maintains a Kanban board and clear contribution guidelines focusing on code quality and responsibility isolation.