Aaron Christophel's Triink Is an Upcycled Low-Power BLE ePaper Desk Clock

Developer Aaron Christophel has designed a 3D-printed desk clock with a difference: based around an ePaper display and a Nordic Semi nRF52832 system-on-chip (SoC), it can run for over a year on a single 18650 cell — and uses upcycled components.

"This is a mix of two gadgets I love to play with," Christophel explains of the project. "An E-Paper display out of old unused Electronic Shelf Labels [ESLs] and the [Nordic] nRF52832 out of countless smartwatch hacking projects. The goal was to create a nice looking ePaper Clock that will show the current time all the time, so a refresh every minute is needed."

Electrophoretic displays, commonly known as ePaper, are designed for use where low power draw and sunlight readability are desired. Their key defining feature is that no power is required unless the display is actively being refreshed — great for keeping the power draw of a shelf label or electronic book to a minimum, but not so great for a clock updating once every minute throughout the day.

"This goal was reached," Christophel explains, "by implementing a custom LUT (Look-Up Table) driving the ePaper display as well as implementing an algorithm that will only update the changing pixels of the ePaper display. Every hour the screen will be fully refreshed to prevent ghosting or burn in."

This partial refresh approach minimizes the power draw of the display, despite is relatively frequent refresh cycle, while leaving enough charge in the battery to take advantage of the nRF52832's Bluetoth Low Energy (BLE) capabilities — meaning it's possible to set the time from a smartphone device or even synchronize notifications to the clock.

This clock is far from Christophel's first experiments with ePaper displays. Back in April 2021 he designed a tool which could hijack and overwrite common ePaper-based electronic shelf labels, as part of an ongoing effort to prevent them from becoming landfill at the end of their life. In June 2022, he released an ePaper sniffer designed to break out the signals required to analyze communication between a microcontroller and an unknown ePaper display panel to ease reverse engineering and reuse.

Design files and source code for the clock, which includes a 3D-printable desk housing, are available on Christophel's Hackaday.io page.