Optical Encoder
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The Optical Encoders typically consist of a rotating and a stationary member. The rotor is usually a metal, glass, or a plastic disc mounted on the encoder shaft. The disc has some kind of optical pattern, which is electronically decoded to generate position information. The rotor disc in absolute optical encoder uses opaque and transparent segments arranged in a gray-code pattern. The stator has corresponding pairs of LEDs and phototransistors arranged so that the LED light shines through the transparent sections of the rotor disc and received by phototransistors on the other side.

Depending upon the shaft position, the phototransistor output is modulated in a gray-code pattern, which can be converted internally to binary or BCD. Typically CMOS, TTL-, PNP-, and NPN-type outputs with 8 or 10-bit Gray-code, binary, or BCD formats are available.