Silent stepper motors make an electromechanical clock suitable for a living room

Large seven-segment mechanical displays have a certain presence that you just don’t get in electronic displays. Part of this comes from the rather satisfying click-click-clack sound they make with each transition. Unfortunately, such a sound quickly becomes annoying in your living room; [David McDaid] therefore designed a silent seven-segment electromechanical clock that has all the presence of a mechanical display without the accompanying sound.

Such as [David] describes in a very comprehensive blog post, the key to this quiet 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 controlling the current that does not cause mechanical vibrations in the motor. One drawback compared to servos is the number of control wires needed: with four wires going to each motor, cable management becomes a bit of an issue when trying to mount four seven-segment displays.

The clock is built 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 connect them to the motors. Additional PCBs include an Arduino Mega 2560 that powers the entire show, a DS3231 real-time clock for accurate timekeeping, and a power supply to manage the 40 watts consumed by the display.

In addition to 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 shows a random four-letter word. We’re not sure of the exact use case for that feature, but it’s a neat addition to a very neat build. If you like seven-segment mechanical clocks, you’re in luck: we’ve featured ones based on a single stepper motor, small ones full of wooden gears, one with protruding segments, and one with lots of servos that move really smoothly.

An electromechanical wall clock that displays random words when a button is pressed

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