How to use a rotary encoder

What is a rotary encoder?

A rotary encoder is an electromechanical device that converts the angular position or motion of a rotating shaft into electrical signals. These signals can be processed to determine rotational direction, position, and speed, making rotary encoders a key component in many types of control systems.

Wiring

Different models of rotary encoders will have different colour codes. I am using YUMO E6B2-CWZ3E, the colours referred to below will only apply to this model.

There are four wires:

1. Ground
2. 5V
3. A switch
4. B switch

Getting started

Rotary encoders work using two switches which are operated slightly out of phase, meaning that in one direction switch A then B pulse from LOW to HIGH, and in the other direction switch B then A pulse LOW then HIGH, enabling you to detect both that a pulse happened i.e. that it was rotated, but also in which direction.

Basic Example

In this basic example the encoder outputs the value as a positive or negative number from it's starting position.

#define enc1A_pin 2
#define enc1B_pin 3

boolean enc1A_prev;
boolean enc1B_prev;

long enc1 = 0;
long prev_enc1 = 0;

void setup() {
  pinMode( enc1A_pin, INPUT_PULLUP );
  pinMode( enc1B_pin, INPUT_PULLUP );
  Serial.begin( 9600 );
}

void loop() {
  boolean enc1A = !digitalRead( enc1A_pin );
  boolean enc1B = !digitalRead( enc1B_pin );
  
  if ( enc1A_prev == 0 && enc1A == 1 && enc1B_prev == 1 && enc1B == 1 ) enc1++;
  else if ( enc1A_prev == 1 && enc1A == 1 && enc1B_prev == 0 && enc1B == 1 ) enc1--;
  
  if ( prev_enc1 != enc1 ) {
    Serial.println( enc1 );
  }

  if ( enc1A_prev != enc1A ) enc1A_prev = enc1A;
  if ( enc1B_prev != enc1B ) enc1B_prev = enc1B;
  
  prev_enc1 = enc1;
}