Who Needs Luminescence? This Seven-Segment Display Works Mechanically

Digital displays are extremely practical, now that they’re affordable to manufacture. There are reasons that even fast-food restaurants use digital displays for their menus: they’re dynamic and the business can update them arbitrarily without dealing with printing. But with the notable exception of e-ink screens, those displays require power to maintain the image. To eliminate that requirement, Tin Foil Hat used flip-dot technology to build this clock with mechanical seven-segment displays that don’t need power to show static characters.

Flip-dot displays, which used to be common in places like train stations, were the peak of electromechanical display technology. They work using “pixels” that are bistable mechanisms. A light switch is the most common everyday example of a bistable mechanism. When you flip the switch “on,” it stays in that position until you introduce enough force to move it to its other stable position (off). It doesn’t need power to maintain its position and neither does a flip-dot display mechanism. That mechanism relies on electromagnetism, but only when toggling the dot between one side and the other. Once set, the dot will remain in its current state until changed again.

Tin Foil Hat’s display works in a similar manner, except each “dot” is a segment in the conventional seven-segment arrangement we’re all so familiar with. There are 28 segments in total: seven for each of the four digits necessary to show the time.

The advantage of this design — aside from simply looking awesome — is that it will retain the last set characters, even if it loses power. That isn’t particularly useful for a clock (other than indicating when the power went out), but it does make sense for any messages displayed as alphanumeric characters.

Tin Foil Hat 3D-printed the mechanical parts and designed his own circuitry for driving the electromagnets that flip the segments. The circuits are mostly shift registers, transistors, and relays that direct power to those electromagnets, operating under influence of an ESP8266-based development board.

The use of the ESP8266, which has a built-in Wi-Fi adapter, meant that Tin Foil Hat could connect this display to the internet. A custom web interface lets users select what to show on the display. There are different modes available, such as a countdown, a clock, and a random number generator. But users can also manually enter messages, if they want to display specific alphanumeric messages.

Best of all, this is all open source if you’d like to build your own display.