We’ve all used LED and LCD 7-segment displays in calculators, home theater systems, and the like to show us pertinent information. While useful and extremely common, one alternative you may not have considered is an electromechanical 7-segment display.
These displays could be considered to be a simplified version of the flip-disc or flip-dot displays that were at one time common in mass transit systems, even being used in the game show Family Feud until 1995. In both systems a colored segment is moved into place using mechanical means, and uses no more power until the digits are adjusted once again.
While largely replaced by newer technology, you can still find these displays for sale via a quick web search. Unfortunately, they tend to be quite expensive, so if you’d like to build one using this technology plan on spending several hundred dollars or more on a multi-digit display. But check out the video below and you’ll hear (and see) why they’re so much fun to build into a project. That clicky action is addictive!
The good news is that if you do manage to obtain one or more of these devices, the Sig7Seg i2c controller for this type of device is available at a small fraction of this display’s price. It’s shown in the video taking signals from a Particle Photon, but will also work with a Raspberry Pi, Arduino board, or similar. The hardest part of driving these segments (other than getting your hands on them) is wiring the reversible voltage necessary to change to either state. This driver takes care of that with a port expander and two DMOS transistor array chips.