Single-Servo Mechanical Seven-Segment Display

Seven-segment displays have long been used by industry and makers alike to convey simple numerical values. While normally LED-powered, such displays can also be implemented with physical segments, moving each into place via servo motors or other means. And while using a single servo to move one segment setup is fairly self-explanatory — though somewhat complicated wiring-wise — Shinsaku Hiura (AKA Shiura) instead created a one-servo, all-seven-segments display through a clever cam system.

The device’s internals, as illustrated in the image above, uses a total of four servos to actuate each digit in a clock-like arrangement. As a small SG-90 servo spins, an attached gear spins a camshaft. This in turn clicks each of the seven segments into show and no-show orientations, depending on the number to be displayed.

The entire system arranged in a 3D-printed housing, and controlled by a micro:bit control board via a KS0360 sensor shield. While it doesn’t appear to be implemented yet, the obvious application for such a device is a clock, though one could see it used in a myriad of other devices as well. This type of device it would continue to display when the power is off, so it would be ideal when information updates only intermittently.

Generally-speaking, the cam system simplifies this type of mechanical display tremendously from an electronics standpoint, transferring coordinated switching duties to the mechanism itself. One might keep such a concept in mind for future display projects, or anything else requiring the use of a repeating mechanical pattern.