Scratchy - HDD discs hacked into pseudo-turntables to alter sound(s) playing through WebAudioAPI on a connected laptop

Hi there !

As said in the title, I'm working on a project that'd be pretty much a dumb controller for a laptop connected

To achieve my goal ( playing normally / in reverse audio & altering the play speed in ~realtime ), I need the following capabilities:

• detect touch on the discs ( presumably done using capacitive sensing )
  
• detect rotation speed & direction of the discs ( ' got my little idea on that, somewhat inspired of our multimeters wheel - more on this in a later post ;p )
  
• rotate the discs at a certain speed & a certain direction - as well as use them as "force feedbacks" ( when the disc is touched, to make exponentially harder turning the disc by hand as it goes far forward/ backward the original "touch position" )
  
  

After digging a little, there seems to be many ways to do the three above steps, but I'd like to design the different parts separately / check their alternatives before having the complete circuit ;)

• on the capacitive touch side of things, I have to test an "RC oscillator + freq comparator" circuit to see if I can rely on that, but I was wondering how hard it'd be to implm a freq comparator in Espruino ( or even write a lib that - as the CapSense lib does for the Arduino - uses a capacitive voltage divider & a touchpad directly connected to one of the uC pins ) ?

• to detect rotation speed & direction while still being able to drive the motors to turn the discs, I plan to use traces on the bottom face of the discs that'd connect to 3 different points of a voltage divider which 'd in turn pass a specific voltage to a uC pin: sensing the 3 different voltages 'd provide info on the direction, while the change rate of the voltage 'd indicate the rotation speed. This being said, it seems we can also use motors as sensors, but gotta digg & test that to know how precise it can be ( .. )

• to drive the motors ( which 'd be steppers I guess, to be able to drive them slowly ) normally, no troubles ( I hope ), but to use them as "force feedback", I'm wondering how to make sure I don't damage them

Lastly, to have sort of a vinyl aspect, I originally planned to use conductive paste on a black non-conductive material & "draw concentric circles by removing matter", but it didn't end up well just while testing with acrylic paint on a copper plate I found in my junk stuff ( there are blobs of paint in places, & the result is not as clean as expected )
I'll have to test with the cutting tool instead of a sharp wood stick to see if it renders better, or even cut in the copper plate & then get it tainted black while preserving touch capability ? ( .. )

Right now, I'm testing my plan to detect rotation speed & dir, starting by using some conductive ink ( & hoping it 'll work as intended ;p )

Last but not least, any hint is very welcome :D

Thanks for the reading ;)