Digital Geneva Clock
This clock uses a microcontroller of your choice, plus the Geneva mechanism for timing.
The Geneva mechanism, also known as a Maltese Cross, is an ingenious method for mechanically turning continuous rotary motion into intermittent motion. First used in watchmaking hundreds of years ago, it’s also the mechanism that is employed to advance film frame-by-frame in projectors, and the mechanism is prominent in industrial automation.
Of course, mechanical timekeeping is still in the Geneva mechanism’s purview, and in this project shiura leverages two of them in sequence to display the time in digits. Here the ones place of the minutes is shown by a dial directly driven by an inexpensive 28BYJ-48 geared stepper motor. This in turn advances a six-lobed cross once every 10 minutes to display the 10s place. Finally, the six-lobed 10s cross advances the 12-lobed hours cross once an hour.
The crosses are linked together with the driving digit wheel via a 3D-printed base, and held in tension with a rubber band. This allows one to easily reset the time as needed by pulling things apart.
Most of the magic of this device resides in the Geneva mechanism setup, and to actuate the stepper one needs a commonly available driver plus a microcontroller/dev board with four available outputs. This could be an Arduino Nano as illustrated, an ESP32, a Raspberry Pi device, or one of many other options, though you would need a way to keep it from unacceptably drifting over time.
If you’d like to build your own, code for the build, along with print files and its rather modest list of purchased parts, are available via the project writeup!
