OpenWatch

I needed a smartwatch so i tried making one, with a custom PCB, a printed case, and custom firmware, here's what i came up with.

OpenWatch follows my earlier Potato Watch project. This version moves to a more serious nRF52840 (very cool chip, also used in apple airtags) and a monochrome e-paper touchscreen, with a focus on battery efficiency and features that are commonly not found on a smartwatch, like full openness of the software/hardware stack, full mifare nfc emulation and more.

This project is still very much a work in progress. for now i have a working prototype, once testing is over i will publish everything here.

What it does

• Always-on e-ink display. Readable in sunlight, with a fairly quick refresh rate. The current firmware refreshes in around 300 ms without ghosting or blinking. An experimental version reached 30 fps, but still needs refining.
• Full MIFARE NFC support. Mifare 1k based NFC cards can be stored on the watch for use with generic Mifare-based access control systems.
• Onboard sensors and timekeeping. An accelerometer and magnetometer provide motion sensing, shake detection, and a tilt-compensated compass. A dedicated RTC keeps time independently of the phone, while a fuel gauge tracks battery level and electrical measurements. Capacitive touch handles input, with vibration for alerts and feedback.
• Bluetooth phone integration. Sync notifications and time, see what's playing, and control media playback and volume. Currently iPhone only, using its built-in Bluetooth services without a companion app.
• Easy to add custom apps. A small app system makes it straightforward to implement new applications alongside the included watch faces, games, and utilities.
• A layered OS. Drivers feed services, and services feed apps. Each layer respects that hierarchy, keeping hardware details out of applications and making individual parts easier to edit, replace, and update.
• Wireless firmware updates. Load new firmware over Bluetooth using MCUboot, without opening the watch (swd interface is present but is basically only needed for first firmware flash).
• Crash and stall recovery. The firmware detects crashes and freezes and can automatically send the watch into update mode, allowing recovery without opening the case.
• Unibody design. Touch controls and wireless charging allow a case with no buttons or charging ports.
• Qi wireless charging. Recharge on a compatible Qi charger, with the receiver, battery charger, and protection circuitry built into the mainboard.

Hardware

The PCB was designed in EasyEDA Pro and manufactured by JLCPCB. The board uses 0.8 mm thickness. Schematics, manufacturing files, and the BOM are in pcb/; for future and more detailed remarks and manufacturing details check PCB notes.

Case

The current prototype uses a 3D-printed case around the square display and custom board. once i reach a final design i will cnc manufacture the final case in metal and add a protective custom glass with silkscreen to the display (also hiding the undesirable touch layer lines on the sides):

Project status

There is a working wearable prototype, and both the hardware and firmware are still being refined. Battery-life figures will be added once measured.

I'll post further updates here as the project develops, followed by the full firmware source.