Maker Hari R. has designed a 3D-printable ePaper watch that, unlike its arguably more polished rivals, doesn’t require a custom PCB — instead simply packing an off-the-shelf Seeed Studio XIAO nRF52840 board and compatible display in a 3D-printed housing.
“There are plenty of better built [watches],” Hari R. admits of the functional if somewhat-bulky design of his own wrist-worn gadget, “but those require PCBs to be fabricated. A PCB is better because the watch can be compact while we add features like buttons and all that. But I wanted to do try something simple, just with soldering. No flashy features. Just shows time, changes watchface every 10 mins. Fun.”
Graytimer is a simple ePaper watch powered by a XIAO nRF42840, with full (pictured) and partial refresh modes. (📹: Hari R.)
The heart of the project is a Seeed Studio XIAO nRF52840, one of the growing XIAO family of ultra-compact yet USB-ready development boards — in this case using the Nordic Semi nRF52840 chip on-board. This is connected to a GoodDisplay 1.54″ 200×200 ePaper screen, which keeps the power draw down by requiring energy only when changing states. There’s an Analog Devices DS3231 real-time clock with battery backup to keep time, and a 3.7V lithium-polymer battery to keep everything running.
The watch features two refresh modes. Every minute, the display performs a partial refresh to update the time; every ten minutes, it performs a full refresh while automatically switching to a randomly-selected graphic. “I did spend a lot of time creating watchfaces,” Hari R. admits, with 54 available at the time of writing. The software also includes three level of power optimization, depending on how precise you want the per-minute updates to be.
Source code for the project has been published on GitHub under an unspecified license, with more information available in Hari R.’s Reddit thread.