Large mechanical seven-segment displays have a certain presence that you just don’t get in electronic screens. Part of this comes from the rather satisfying click-click-clack sound they make at every transition. Unfortunately, such a noise quickly becomes annoying in your living room; David McDaid therefore designed a silent electromechanical seven-segment clock that has all the presence of a mechanical display; without the accompanying sound.
As David describes in a very comprehensive blog post; the key to this silent operation is to use stepper motors instead of servos; and to drive them using a TMC2208 stepper motor driver. This chip has a unique method of regulating the current that does not introduce mechanical vibrations inside the motor. A drawback compared to servos is the number of control wires required: with four wires going to each motor; cable management becomes a bit of an issue when you try to assemble four seven-segment displays.
The clock is built up on a large piece of MDF; with all 28 motors on the front and the electronics on the back. Custom mounting brackets and the display segments are all 3D printed; while four large PCBs hold the stepper motor drivers and connectors to hook them up to the motors. Additional PCBs hold an Arduino Mega 2560 that runs the whole show; a DS3231 real-time clock for accurate time-keeping, and a power supply to manage the 40-odd watts consumed by the display.