These Digital Dominos work just like regular dominos knocking each other down, only virtually. Each domino-sized PCB has a button that triggers an LED to blink (which corresponds to the domino “falling”). An IR sensor on one end and an IR LED on the other allow each domino to trigger any adjacent domino to blink, and so on.
Created by Daryll Strauss of Los Angeles hackerspace Crash Space, these open source boards come four to a pack and are the perfect large-group build for people just learning to solder. They’re easy to assemble, and a hundred people building them can collaborate to create gigantic, blinking trails of light. Best of all, to see the dominoes fall another time, you don’t have to stack them all back up. Just press the first domino’s button again.