A rotary encoder, also called a shaft encoder, is an electro-mechanical device that converts the angular position or motion of a shaft or axle to analog or digital output signals. There are two main types of rotary encoder: absolute and incremental. The output of an absolute encoder indicates the current shaft position, making it an angle transducer. The output of an incremental encoder provides information about the motion of the shaft, which typically is processed elsewhere into information such as position, speed and distance. Rotary encoders are used in a wide range of applications that require monitoring or control, or both, of mechanical systems, including industrial controls, robotics, photographic lenses, computer input devices such as optomechanical mice and trackballs, controlled stress rheometers, and rotating radar platforms. Technologies Mechanical: Also known as conductive encoders. A series of circumferential copper tracks etched onto a PCB is used to encode the information via contact brushes sensing the conductive areas. Mechanical encoders are economical but susceptible to mechanical wear. They are common in human interfaces such as digital multimeters. Optical: This uses a light shining onto a photodiode through slits in a metal or glass disc. Reflective versions also exist. This is one of the most common technologies. Optical encoders are very sensitive to dust. On-Axis Magnetic: This technology typically uses a specially magnetized 2 pole neodymium magnet attached to the motor shaft. Because it can be fixed to the end of the shaft, it can work with motors that only have 1 shaft extending out of the motor body. The accuracy can vary from a few degrees to under 1 degree. Resolutions can be as low as 1 degree or as high as 0.09 degree (4000 CPR, Count per Revolution). Poorly designed internal interpolation can cause output jitter, but this can be overcome with internal sample averaging. Off-Axis Magnetic: This technology typically employs the use of rubber bonded ferrite magnets attached to a metal hub. This offers flexibility in design and low cost for custom applications. Due to the flexibility in many off axis encoder chips they can be programmed to accept any number of pole widths so the chip can be placed in any position required for the application. Magnetic encoders operate in harsh environments where optical encoders would fail to work. Basic types Absolute An absolute encoder maintains position information when power is removed from the encoder. The position of the