A Custom Flip-Dot Ring Makes for a Unique Clock
Pierre Muth’s flip-dot ring clock sounds every bit as good as it looks.
Before there was E Ink, there were flip-dots. No, they couldn’t exactly be used for an e-book display, but flip-dots could show a persistent image without being powered. There isn’t a lot of practical use for this aging mechanical technology today, but people still love flip-dots because of their unique appearance and the way they click when images change.
For this reason, there are lots of DIY flip-dot display projects still making the rounds. These usually take the form of a rectangular display, which is most commonly used to show the time and weather, or information from a home automation system. But Pierre Muth had a different idea. He designed and built a custom flip-dot ring that is perfect for a unique clock.
Instead of arranging segments into a grid, Muth created a circular display made from roughly 300 salvaged 7-dot segments. By tightening the angle between each segment to under two degrees, the result appears nearly continuous to the human eye.
Each of the 12 custom-built boards handles 24 segments and includes dedicated driver circuitry based on FP2800a half-bridge chips. Because flip-dots behave like tiny solenoids, they generate electrical noise and require precise timing. To handle this, Muth implemented daisy-chained microcontrollers that coordinate dot updates over SPI, achieving speeds up to 100 kHz after optimizing interrupt routines.
Each board maintains a circular buffer and uses a custom communication protocol to latch display updates. Timing is critical: a brief pause in SPI data signals the system to refresh the display. Additional configuration bits allow fine-tuning of coil activation time and refresh behavior, offering flexibility for performance and experimentation.
Powered by five 18650 lithium-ion cells, it steps voltage up to the ~24V needed for flipping dots while stepping down for logic circuits. Thanks to careful component selection and aggressive power management — including deep sleep on the ESP32 controller — the system can run for around 40 days on a charge.
Mechanically, the build balances strength and aesthetics. A waterjet-cut aluminum backplate provides rigidity, while 3D-printed housing components keep the design visually appealing.
Further build details are available on Muth’s personal website, and you can find the open-source software on GitHub.