Rotary Enc
Reports angular shaft position as quadrature pulses (incremental, requires homing) or absolute serial position word (immediate at power-up), with resolutions from 256 counts/rev (cheap) to 36+ bits (interferential).
Optical: a coded glass disc rotates between an LED and a photodiode array; the photodiode pattern is decoded into Gray code (absolute) or quadrature ABZ (incremental). Magnetic: a multi-pole magnet ring rotates over a Hall-effect or magnetoresistive array; the chip computes angle from the magnetic-vector phase. Multi-turn variants add a battery-backed counter or geared scale to track full revolutions.
In plain terms
Like a clock face viewed through a slit — only one position is visible at any moment, and the chip counts how many positions have passed since the last reset.
Why designers use it
- Servo motor feedback — closing the position loop on every CNC, robot, and printing press.
- Industrial measurement — angle indication on valves, dampers, telescope mounts.
- Computer mice and trackballs (historically) — incremental encoder on the rolling ball converted motion into cursor pixels.
- Joystick and rotary-control inputs — every studio mixing-console knob is a rotary encoder.
Best for
- Servo feedback
- Robotics
- Industrial knobs
Key specifications
- Operating limits: Check the exact manufacturer's datasheet (A family name does not establish voltage, current, temperature or timing limits.)
- Pin assignment: Match the complete part and package code (A similar name or function does not guarantee the same wiring.)
- Mechanical fit: Use the exact package drawing (Check pad layout, dimensions and viewing direction before building.)
When not to use it
- For very low-cost applications where a potentiometer is sufficient — encoders are pricier and need digital decoding.
- Where shaft-speed exceeds the encoder's max RPM rating — pull a high-speed magnetic encoder.
Common mistakes
- Skipping the index pulse (Z) and trying to find home from raw quadrature — without Z, the absolute angle is unknown after power-up.
- Routing encoder wires next to motor power leads — switching transients couple in and the count reads spurious.
Where you will find it
- A Heidenhain ECN 1325 13-bit absolute multi-turn rotary encoder on a Yaskawa Sigma-7 servo motor for an FA Robotics robot's elbow: the encoder's BiSS-C absolute readout means the robot's elbow knows its position the instant power comes up — no calibration cycle.
- A Boston Dynamics Spot's hip joint uses a Renishaw RM44SI on-axis magnetic absolute rotary encoder: the encoder's hollow-shaft format lets cable bundles route through the centre of the joint while delivering 14-bit absolute position to the Spot's gait controller.
- An ATI Industrial Automation Axia80 force-torque sensor uses a Heidenhain RIK6 rotary encoder for the fingertip rotation axis on a Schunk SVH 5-finger gripper: the encoder's 1024 lines/rev resolution lets the gripper turn jar lids precisely around the central axis.
A short history
A rotary encoder converts shaft motion into electrical information. An incremental encoder produces pulses that a counter uses to track motion from a reference; an absolute encoder provides a position code. These approaches support position and speed measurement, but they differ in how the system establishes its position after startup.