I am trying to create a simple DIY tachometer using parts to a Radio Shack serial ball mouse I have. The idea is to use the shaft encoder(disk with equi-spaced slots) and the (what seems to be) infrared emiter and reciever to obtain an electric pulse. That is, as the disk spins, the IR signal will repeatidly be broken causing the reciever to see a pulse of IR. My problem is the circuit building. Does anyone have any idea on how to get this project to work? Any help would be great. THanks. Lucas.