Valentine Is Targeting a 10-Year Runtime for This Nordic nRF52-Powered BLE Smartwatch Design

Pseudonymous maker "Valentine" is working on a Bluetooth Low Energy smartwatch, emphasis on the "low energy" — targeting a 10-year runtime on a single charge, with the potential to add a compact solar panel to power the device forever.

"Developing a smart watch from scratch would be a great learning experience to advance my knowledge of low-power, self-contained powered devices. Hence, we learn about watches, smartwatches, and wearables in general by designing one," Valentine explains of the project. "This is not a commercial effort. I doubt that we are making anything new per se, however, we are trying to advance the art a lot further than others into the low-power domain."

Valentine has some big asks for his smartwatch design, even before you get into the desire for a decade-long runtime. It should be maintenance-free, he says, with no need to open the device, and it should have no buttons or other moving parts. It should be tough enough to "crush rocks," operate in the depths of the ocean, and could include on-board sensors, sync to atomic clocks, and even provide a compass — though, at the time of writing, the project was focusing on core watch functionality, including alarms.

"Testing the power consumption with a 200mA[h] battery, BLE at -40db. Estimated life of that setup without any power tuning would be about 5,000 hours (~200 days)," Valentine writes of initial testing with a "pre-alpha" board. "To give you an idea how hard this is, it takes a team of highly qualified people working for months to get to this stage. I did it over a few weekends in my bedroom listening to Gert van Hoef."

The initial design is built around a Sharp memory display, offering a sunlight-readable monochrome panel which draws less power than rival liquid-crystal display technologies, connected to a Nordic Semi nRF52 providing the controlling logic and Bluetooth Low Energy (BLE) connectivity to a smartphone and a five-parts-per-million temperature-compensated crystal oscillator (TCXO) for timekeeping.

Initially, Valentine found the antenna design causing issues with reaching a low enough power draw — until Nordic offered to optimize the design in-house. "I was extremely impressed by the level of customer service," Valentine writes. "I'll take them up the offer once I finalize my case design."

Valentine isn't only thinking about what's going into the watch, though, but about what the outside will look like — showing off a chunky body which protects the display behind a mineral crystal glass panel and encloses the electronics in a completely-sealed stainless steel body. Further experiments have shown that the device draws so little power it can run from a solar cell — though the maker is working on building the self-contained version first before potentially investigating adding solar charging to the design.

More information on the work-in-progress project is available on Valentine's Hackaday.io page; no design files or source code have yet been released.