Has anyone here built a diy scratch wheel?

[ReggieUK]

Hi all, while I've been messing around building a midifighter classic, I got to thinking about how to tackle making a scratch wheel.

In the past I've made an arcade spinner from a hard drive motor and a ps2 mouse, the hdd motor had a threaded shaft, that stopped just short of the bottom, I drilled that out, put a long bolt in, cut the encoder wheel off one of the mouse rollers, drilled a small hole same diameter as the bolt and threaded it onto the bolt, held in place with a couple of nuts.

I then mounted the ps2 mouse circuit board to the inside of a tub with the encoder wheel lined up to pass through it, so it works exactly the same as one axis on a mouse. This method worked really well for a spinner for arcade games, very accurate but of course there's no way to sense whether the thing is being touched, only when it's being moved.

I saw another method that does similar things, that deals with touch via capacitive sensing, it essentially uses a metal shaft of some description, with a metal grommet slightly wider than the shaft diameter, with a wire attached to the grommet which goes off to your sensor, on the other end, the shaft is attached to a thin metal disc or you can buy sticky backed copper foil, then a sheet of thin plastic on top.

Has anyone tried anything like this themselves, what kind of results did you get?

[Polygon]

I did in virtual dj.
Took apart an old internal CD drive, so that just the motor assembly remained. Mounted that into a heavy duty cardboard box, leaving the spindle outside.
I then took two of those printable CDs (the ones with a white, grainy texture on them), glued them together with the printable surface facing outwards. I printed a very fine line pattern on the bottom cd, and mounted an old laser mouse board under it. I soldered the left mouse click button to another button i placed under the CD assembly, so whenever i would touch the CD, the mouse would click and the laser would start tracking.
Software was all virtualDJ's.

[ReggieUK]

I think the grommet wired to a sensor is a neat idea, pretty sure that's how most of the dj controllers work at least for sensing the platter has been touched.

I'm looking at other methods for the spinner mechanism, rotary encoders look like a good option, not the clicky knob things, the ones they use for sensing motor positions, they're about 40 bucks but some of them can do 1024 pulses per revolution, 5000-1000rpm so they can certainly move fast enough for scratching, I'm just not sure on the kind of resolution you would need?

I've also seen some rotary encoder chips, I think they work by sitting directly underneath whatever is spinning, the spinning thing would have a magnet attached and that would give you your encoder pulses.