Hard Drive Motor Turned into a Rotary Encoder

If you’ve ever taken apart a hard drive (HDD), you know there’s a bounty of useful bits inside, including powerful magnets, a read/write arm, and a motor that spins the platters to access the correct data. After noticing how smoothly this motor works, YouTuber “GreatScott!” decided that this type of motion would be much more pleasing than the soft stops on encoders that you would normally buy for electronics projects.

While lesser hackers might attempt to find a way to stuff an encoder into the spindle assembly, GreatScott! instead tested the output leads, and even disassembled a sacrificial spindle assembly in order to figure out that it works in almost the same manner as a brushless DC motor. With this information in hand, he set up an Arduino Nano to interpret the analog signals coming from the three motor leads, along with a fourth attached to the Nano’s ground.

While this allowed him to correctly read the spindle direction, he decided to complete the project by turning these signals into square waves using two op amps as comparators. With this upgrade, he could use only digital pins on the Arduino to resolve directional information. The project, seen in the video below, looks interesting in and of itself, ending with him spinning a HDD platter as an input. It’s a great intro into how encoders and HDD motors work, and one could take this further to form the basis for other really interesting interfaces!