In-Depth: How Rotary Encoder Works and Interface It with Arduino

A rotary encoder module converts the angular mechanical position of a shaft into electrical signals that can be processed by an Arduino Uno. Inside the module, a rotating disk with patterned contact points or optical slots interrupts signals as the knob turns, generating two distinct square-wave outputs known as channel A and channel B. By monitoring these two signals using digital input pins, the Arduino can determine both the direction of rotation and the relative speed. Because the outputs are shifted out of phase with one another—a technique called quadrature encoding—the Arduino can check which channel changes state first to decipher whether the shaft is turning clockwise or counter-clockwise. Additionally, many rotary encoder modules include an integrated pushbutton activated by pressing down on the shaft, which closes an internal circuit and pulls a designated pin low. Jumper wires connect the encoder's power, ground, and signal pins directly to the digital and power pins of the Arduino Uno. Through the Arduino IDE, custom firmware continuously polls or listens for state transitions on these input lines, allowing the system to accurately track step-by-step movements, count total revolutions, and register button clicks for interactive control applications.