Joren Heit's Clock Keeps Perfect Time with an Unmoving Hand — By Rotating Its Entire Face

Maker Joren Heit has designed a "broken" clock that is right more than twice a day — because a static hand remains exactly where it is while the entire clock face rotates to keep time.

"This project was inspired by a student of mine who told me he was programming a JavaScript analog clock," Heit explains of the project's origins. "A bug in his code caused the number to rotate rather than the hands… True or not, my immediate thought was: I want that in real-life. It was the perfect excuse for finally buying a 3D printer."

The heart of the build is a standard commercial off-the-shelf wall clock, working as most do on a quartz mechanism. It's this which keeps time: the clock itself is entirely unmodified, and keeps time exactly as it did from the factor. The trick with the "static" hand comes in how it's housed: a 3D-printed shell that turns the clock into a giant gear in a machine under the control of an Arduino Nano microcontroller board.

The Arduino Nano is linked to a real-time clock (RTC) module and programmed to drive a stepper motor based on precise timing — matching the ticking of one of the clock's hands. By rotating the whole clock as the hand ticks, its movement is canceled out; from the observer's perspective, the hand stays entirely motionless while the clock face rotates instead.

"A switch lets you select the hand that is being canceled," Heit explains. "Based on the switch-setting, the Arduino calculates exactly how many milliseconds should be between subsequent steps of the stepper-motor. It turned out however that the millis()-function will drift slightly over time, so a real-time clock is used for long-term synchronization."

The project is documented over on Hackaday.io, with source code and 3D print files available on GitHub under an unspecified open-source license.