Thursday, August 02, 2012
Unknown
A couple of years ago we built a fun system that would allow DJs to mix music tracks in interesting ways. Our design called for an input device that would allow the DJ to quickly seek through a track and find a specific playback position, and we wanted to be able to do this by spinning a rotary control with a flick of the wrist - much like turntable DJs can spin the record back and forth to do the same.
We found that we had only limited choices for building our device: we first tried to use rotary encoders, but it is not easy to find a cheap encoder that spins smoothly and freely. Another alternative was to buy some audio equipment (like turntables) that spin well and feel good to use - but this seemed both expensive and wasteful for our purposes. Then, while looking for inspiration amongst assorted junk in the lab, we came upon a broken hard disk drive with its case open. We admired the quality of the bearings in the motor that drives the disk plates, enjoyed the fact that even a soft flick would get it spinning for a long time, and wondered whether we could sample an output from it when it was spun by hand, in much the same way that an electric motor, when turned, acts as a dynamo and outputs a voltage.
The answer is yes - and it's a very simple process to turn a hard disk into a rotary input device that has some unique properties. All you'll need is an old hard disk drive, a few op amps, resistors and a programmable microcontroller of some kind.
In this Instructable we'll show the basic principles behind this hack, then provide the schematics and firmware for the HDDJ device (shown below) that we used in our project, and which includes a few extra buttons, lights and a motorized slider for good measure.
We found that we had only limited choices for building our device: we first tried to use rotary encoders, but it is not easy to find a cheap encoder that spins smoothly and freely. Another alternative was to buy some audio equipment (like turntables) that spin well and feel good to use - but this seemed both expensive and wasteful for our purposes. Then, while looking for inspiration amongst assorted junk in the lab, we came upon a broken hard disk drive with its case open. We admired the quality of the bearings in the motor that drives the disk plates, enjoyed the fact that even a soft flick would get it spinning for a long time, and wondered whether we could sample an output from it when it was spun by hand, in much the same way that an electric motor, when turned, acts as a dynamo and outputs a voltage.
The answer is yes - and it's a very simple process to turn a hard disk into a rotary input device that has some unique properties. All you'll need is an old hard disk drive, a few op amps, resistors and a programmable microcontroller of some kind.
In this Instructable we'll show the basic principles behind this hack, then provide the schematics and firmware for the HDDJ device (shown below) that we used in our project, and which includes a few extra buttons, lights and a motorized slider for good measure.
Step 1Crack open a hard disk drive
Old, unwanted or broken hard disk drives (HDDs) are usually free and easy to get hold of. They come in all shapes and sizes, but the most common are the 3.5" HDDs that are used inside desktop PCs. We experimented with a number of different 3.5" HDD models, and found that most are suitable for our purposes (and would guess that smaller, laptop-sized disks would work just as well). The largest variation lies in how easy it is to open the case of some compared to others. Seagate HDDs, which often use plain Phillips screws in the casing, are our favorite.
The first step is to open the drive by removing all the screws that hold the case closed. Often these are torx screws, and you'll need an appropriate screw driver. Sometimes a screw will be hidden behind a label - so if you have trouble opening the case after all the screws seemed to have been removed, poke at the labels to find the culprit. If there is a label saying "Warranty Void if Removed," then, for sure, remove it.
Open the case, and reveal the disk platters in all their untouched glory. Never again will they be so free of fingerprints.
Remove the actuator that holds the read-write head, which stops the platters from spinning around freely. It's up to you how much more you want/need to remove (rule of thumb: anything sharp should go). The only thing that you need to keep attached are the frame, platters and spindle motor.
