Hard drive controller

We had a box of hard drives lying around, and I was given them to use in projects. I found a tip online (center of reliable information, I know) that some really old drives (40 mb or less) have stepper motors – I found the smallest drive, at around 850 mb, and opened it. I found no stepper motor, but while staring at the platters, I was struck by the resemblance to a DJ desk. So, I thought, why not turn it into a little DJ desk?

I originally thought of using the existing platter motor as a dynamo – however, I looked it up online, and these motors are very complex to run, as they don’t run off of DC or AC but a specific signal of 3 staggered sine waves. I tried gutting the motor and fitting a motor of my own, but none of mine would fit properly without machining, which I cannot do.

I went online again, and found this tutorial that detailed how to turn a hard disk into a rotary input device. They used it to fast forward through tracks, not to DJ, but the idea was similar. They showed how to reverse engineer the motor and turn it into a useable signal. Since I gutted the first motor, I went and got another drive and opened it. This one was much simpler to open, and had simpler insides.

However, there was an issue – its motor had 3 connections, while the instructions only dealt with 4 connection motors. I looked online, and couldn’t find much reference to the 3 connection one, aside from hints about it missing a hall sensor. So I went and found another one that definitely has 4 connections on the back.

I still need to get some components for it to work – I need a specific circuit that contains “comparators”, to help amplify the generated sine wave and turn it into a square wave (presumably to make it digitizable for the arduino, as opposed to analogue). Hopefully it works!

Sorry for the less than interesting photos.


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