Photodiodes or phototransistors will be much faster than LDRs, and have a smaller window.
Try mounting the LEDs in an opaque block with holes drilled in it and the optical disk flying just a little above it (not touching, so it doesn't get scratched).
Thanks gordon, that's made it easier! I'm trying to think about the best way of making the circuit... it's going to need a way of driving 5 motors with PWM - at this point I'm not sure if those motors will need to be spinning at different speeds or the same - I'm still attempting to work out the relationship between speed/frequency/size etc.
I was hoping there might be some way of having an ADSR on this - but I'm guessing that it'd need 25 seperate ADSRs if all a key does is completes the circuit and lights an LED. I've also looked at the idea of using the LED/photosensor as an opto coupler, which would effectively be an ADSR (or an AD at best). Apparently though, when Mike Walters prototyped that with the melloman, the decay time was around a minute, so he ended up using transistors.
Yeah I was thinking of mounting them just like that, my only concern is the fact that those 3mm holes through the block would need to have a 1mm gap between them - very precise drilling required and I don't have any way of doing it!
plus, typically, the base of a 3mm led means that it isn't going to fit the whole thing inside the little 'tube' that it creates. I'm not sure if the LEDs are going to sit on the underside or overside of the disc yet though.
I've also designed the discs so that they're the excact size of a minidisc, and will fit inside the shell of one. That would protect them and provide ideal storage too, besides looking cool
Nice little recycling aspect there aswell