Here’s a fun entry into our coin cell challenge. The power source is the actuating force in [Frank]’s blinky LED Christmas tree, which takes advantage of the physical structure of coin cells and our old pal gravity to roll out some holiday cheer. Talk about forward voltage!
We love the concept, and the circuit couldn’t be more simple. A coin cell is released at the top of the tree and rolls down a series of angled foam board railings covered with 1/4″ copper tape. As the coin cell travels, the negative terminal shimmies along the face of the tree, which has corresponding ground rail tapes. There’s no microcontroller here—all that’s needed for blinks are breaks in the negative rail tape.
The challenging part of a project like this is the execution. Getting a coin cell to ride the rails without falling off required angle experimentation prior to and during the build. Now that it’s done, keeping the tree tilted back against the wall is key. [Frank] explored several options for returning the coin cell to the top using a camera motor and the gear assembly from an old inkjet, but for now, his six-year-old does the job without complaint. Check out his work ethic after the break.
Before going too far, they cut out a cardboard mock-up of the tree. This an easy step to skip, but it can save headaches later! Once happy with the prototype, they printed off the design stencils and cut the chunks of clear acrylic using power tools — you don’t need a laser cutter to produce good stuff — and drilled dozens of holes in the plastic to mount LEDs, and run wires.
