Great job on the Hard Drive Clock and thanks for the mention about the clock that I built. "The clock works by removing the top of the hard drive and cutting a slot into the platter. Then lights are mounted underneath and flashed as it spins. By timing it right you can create the illusion of clock hands, color bars or other designs. I have quite a few magnets lying around so my first thought was I could eliminate 2 of the three platters by using a magnet on the top platter and a magnetic sensor to detect it. The one disadvantage to this method is I now have to cover the entire bottom of the drive case in white instead of just one strip of white tape. If everything is flat it works well. If things stick up at weird angles you get shadows."