Just starting this project, which again uses a 2.5" laptop drive.
Last year I made a POV "slot" clock on a HDD platter, inspired by other peoples projects I saw online. Around the same time saw an excellent project on YouTube where someone had made a digital POV clock by spinning a set of digit-shaped windows, in front of a row of LEDs. By illuminating each LED when the appropriate digit was in front of it, a row of digits can be displayed... aka a digital clock (http://www.youtube.com/watch?v=7Qyawcw-ots)
That project used a 3.5" drive and it looked like the digits were actually laser or plasma cut into the metal platter itself. I decided to make an easier version by etching the digits into a piece of FR4 copper clad board to replace the platter. FR4 (the fibreglass PCB backing material) is quite translucent so it should transfer the light nicely from LEDs placed behind it.
So far I just have the platter made. I am using a 2.5" laptop drive and the space behind the platter is very limited, so I will probably place the LEDs on flexible kapton copper-clad sheet and put a row of windows cut in plastic sheet over the top to stop cross-illumination.
I'll spin the disk using the same TDA5144 circuit I used in the previous project but I'm not sure about indexing yet... there is not really space on the platter to cut a slot for a photointerrupter, and a magnet on the disk (for a fixed hall sensor) would need a counterweight and might not fit. I might try an IR reflective sensor here, but need to play with them a bit first as I've not used them before.
Keep ya posted!