The researchers built a laser projector from an old hard drive

Rotary hard drives are phasing out most consumer computers in favor of faster technologies such as solid-state drives and their various interfaces. But there are millions of them still in circulation and will eventually be taken out of service - so what do we do with them? If you have one that would otherwise go in the trash, they can be turned into some other interesting device, like this laser text projector.

Even the slowest drives can spin at around 5,000 RPM, perfect for such applications. The device works by mounting twelve mirrors, each at a slightly different Angle, on a drum spun by a motor in the driver. Reflecting the laser light off the rotating drum creates a projection of 12 horizontal lines. The length of each line can be controlled by quickly turning the laser on and off according to the mirror it is pointing at.

Because of the persistence of vision, this allows you to display text on a laser-projected surface. At such high speeds, it took [Ben] Ben Make Everything quite a bit of iteration to get it into a usable space. From sensors that are too slow, to lasers that aren't bright enough, to 3D printing that isn't precise enough, he goes through his build design and process in great detail.

After solving all the problems, including building its own constant current laser power supply and burning some laser diodes in the process, [Ben] has a laser projector capable of displaying readable text over great distances, which is also portable and runs on a 12 V power supply. He also noted some areas of possible improvement, such as unbalanced 3D-printed parts that cause a bit of wobble, and the Arduino controller not being fast enough to hold more text. But it's still an impressive project, similar to the two-mirror version we saw some time ago, but also with the ability to display text.

Source: Laser Net