Abstract: Apparatus for converting the revolutions of a shaft into pulses including a disc having devices such as slots or reflectors radially spaced around its periphery and light-transmitting and light-receiving fiber optic cables aligned for sensing the devices as the disc rotates. A light source, such as a light-emitting diode, is positioned at the outer end of a light-transmitting cable for providing light, and at least one phototransistor at the outer end of a light-receiving cable converts the light signals into electric pulses. Preferably, the light-transmitting and light-receiving cables are paired, giving successive signals as a slot or reflector is sensed for activating a counting circuit. A single light-transmitting cable is preferably split near the disc to provide two light sources from a single light-emitting diode.