This Clever DIY Laser Projector Works at Distances Exceeding 90 Feet

If you've ever seen the kind of laser show with projected animations, like the famous one projected onto Stone Mountain in Georgia, then you've experienced persistence of vision (PoV). Those shows don't use conventional movie projects that expose the entire frame at once, but rather one or more laser beams moving very quickly to create the illusion of solid lines. Traditional laser projectors rely on mirror galvanometers, which are tiny mirrors that pan and tilt at ridiculous speeds to direct the laser beam. But Ben took a different approach for his DIY laser projector by using an old hard drive.

Disclaimer: don't fool around with lasers if you don't know what you're doing. It is easy to blind yourself or others, and even to start fires.

Instead of reflecting the laser beam off of a single mirror galvanometer that could move the beam around in the X and Y axes on the projection surface, Ben used several mirrors mounted to a single spinning hub. Each mirror sits at a slightly different angle, so the first mirror might reflect the beam up at a 10-degree angle, the last mirror tilts the beam down at a 10-degree angle, and the mirrors in-between tilt the beam at regular intervals from one extreme to the other. As the hub spins, the beam reflects off of the mirrors to project several horizontal lines on the projection surface.

By modulating the laser beam at a high speed, Ben can create patterns in the horizontal lines. A stack of horizontal line patterns creates a complete 2D image, just like a monochrome CRT (cathode-ray tube) monitor. To make that all come together, Ben just needed a way to spin the hub at a precise speed, and modulate the laser quickly and sync it up with the hub's rotational speed.

Ben used an Arduino Nano development board to control everything. It receives the text to display from a smartphone via a Bluetooth module. The mirrors attach to a 3D-printed hub spun by a hard drive motor and the Arduino monitors its speed using an infrared break beam sensor. The Arduino also modulates a powerful laser diode using a MOSFET to achieve the rapid switching necessary for this to work. Timing was important, because if the system ran too slow then the PoV effect would be lost, but too fast and the Arduino wouldn't be able to keep up.

In the end, of course, Ben was successful and the result is very impressive. The laser is powerful enough that Ben had no trouble projecting text onto a fence in his backyard that was 90 feet away from the projector.