Check Out This 7-Segment Clock with Zero Electronics

We spend so much time working with digital devices in a digital world these days that anything mechanical can seem like a relic from the past. However, before the digital revolution, mechanical systems got the job done just fine, thank you very much. Even computer processors and memory existed in mechanical forms at that time. They were certainly primitive by today’s standards, but the fact that they existed at all goes to show that mechanical systems can accomplish quite a lot with some ingenuity.

Consider the clock recently built by creator Müjin, for instance. If you wanted to make a clock, you would probably grab an Arduino, a real-time clock module, and some type of digital display. But Müjin took a different approach and built a working clock — display and all — from purely mechanical components. It may not be the most practical thing to do — there are better approaches, to be sure — but Müjin’s clock is something you won’t want to take your eyes off of.

The device is built around a mechanical implementation of a seven-segment display, the familiar format used in digital clocks. Instead of LEDs, however, each segment is physically actuated by a network of cams, linkages, and gears. As the clock advances, carefully shaped cams rotate and push thin metal rods that bring individual segments into view, forming the correct numeral at any given time.

The structure itself is built largely from precision-cut plywood, machined using a CNC setup that required its own custom workholding system. Müjin devised clamps and fixtures to ensure repeatability and accuracy, which is important for components like gears and cams where even small deviations can lead to major issues. Brass standoffs and shafts hold the layered assembly together, while cyanoacrylate adhesive secures many of the smaller parts in place.

Driving the entire mechanism is a low-speed synchronous motor, chosen for its reliability. Because its speed is tied to the electrical grid frequency, it provides a consistent rotational rate without the need for electronic regulation. That motion feeds into a series of gear trains and Geneva drive mechanisms, which convert continuous rotation into the precise intermittent steps needed to advance each digit correctly. For example, the tens-of-minutes digit only advances once the minutes digit completes a full cycle.

As with any complex mechanical system, the project wasn’t without setbacks. Tolerance issues caused misaligned digits and interference between moving parts, forcing multiple redesigns and remachining passes. Cam timing also required careful calibration, with markings added manually to ensure the digits advanced in the correct sequence.

In the end, the clock succeeded in its goal of keeping time using nothing but mechanical logic. In doing so, it offers an interesting glimpse into an alternate approach to computation and display — one where carefully coordinated motion does all the work.