We’ve seen Raspberry Pi hologram projects before but this is the first one we’ve seen that functions as a Christmas tree. This project, created by Sean Hodgins, uses a Raspberry Pi 4 and relies on the principle of persistence of vision. This principle uses an LED strip to "paint" light at a specific speed. Using the tree's rotation, it displays custom 3D effects in mid-air that in this case resemble a festive holiday evergreen.
This tree is made from a metal, triangular frame. It’s mounted to a larger frame that has a motor capable of spinning the triangle into a cone at 10 Hz. The tree is capable of displaying both static and moving images. This makes it possible to display a simple tree or cartoon images and, in one demonstration, a flaming tree.
Hodgins was kind enough to share a video breaking down the project’s construction process. The metal frame was built entirely from scratch. Hodgins can be seen cutting the metal, mounting it together and making modifications as he went along to devise the most functional end result.
At the top of the metal frame is a motor connected to a slip ring that can deliver power to the LED strip while it spins so there’s no concern of wires getting tangled. A bearing is at the base of the triangle frame to provide support while it rotates. A Raspberry Pi 4 drives the operation along with a step down converter going from 12V to 5V and a fan for the motor. A magnet is attached to the top of the triangle frame that passes by a hall-effect sensor so the Pi knows exactly when a full rotation has been achieved.