Reflective/Transmissive Encoders
For this talk I'm going to focus on reflective and transmissive encoders which can be fabricated pretty easily, used in a variety of roles, and interfaced with a micro-processor fairly cleanly.
Operation
Both types of encoder depend on a circuit that produces a light (typically infrared) that is either reflected back to the sensor, or blocked from the sensor. The presence and/or absence of light is measured by an electrical circuit which feeds your processor.
Fabrication
Creating a reflective or transmissive encoder consists of printing a regular pattern of light and dark areas on some material and transferring that pattern to the sensor disk. The
Types
These circular encoders can be divided into three types, rate, directional, and absolute. Lets look at each type and get an idea of what they are good for.