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.
Apart from showing the current time, the clock also includes an alarm, a strip of LED lights, and a “random word generator”: press a button and the display will show a random four-letter word. We’re not sure about the exact use case for that feature, but it’s a neat addition to a very neat build. If you’re into mechanical seven-segment clocks, you’re in luck: we’ve featured ones based on a single stepper motor, tiny ones full of wooden gears, one with protruding segments, and one with lots of servos that make really smooth movements.