1. Interfacing a Rotary Encoder with an Arduino
Arduino Uno
microcontroller board
Panasonic EVE-KC2F2024B
Rotary encoder

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3. Rotary Encoders
Rotary encoders are used keep track of the rotational position of a knob, like a volume knob on a stereo, or the rotational position of a motor shaft.
Panasonic EVE-KC2F2024B
24 pulses per revolution
6mm diameter flattened output shaft
Output type: quadrature (incremental)
Minimum life: 15,000 rotations
Cost: less than $1 (USD)

4. Encoder Output and Rotational Direction
clockwise rotation of knob
counterclockwise rotation of knob A B
COM B
pin B = ON
pin B = OFF A
pin A = ON
pin A = OFF
When switch A goes ON and B is OFF, then rotation must be clockwise.
When switch A goes ON and B is ON, then rotation must be counterclockwise.
When switch A goes OFF and B is ON, then rotation must be clockwise.
When switch A goes OFF and B is OFF, then rotation must be counterclockwise.
increment rotational counter
decrement rotational counter

5. Inside a Mechanical Rotary Encoder
As the encoder knob is turned, the spring-loaded contacts pass over metal segments that connect to the A, B and COM pins.
Electrical continuity occurs when a contact touches metal, but no continuity occurs when a contact touches the black plastic.
One of the three contacts is always touching COM.
A COM B
electrical continuity
between A and COM
no electrical continuity
between A and COM
spring-loaded electrical contacts

6. Sensor Wiring Rotary encoder Four 10kΩ resistors Two 0.01μF capacitors
This part of the circuit keeps the A, B and COM “switches” from flickering at the beginning or end contact this “debounces” the switches
The encoder is the part in the red box

7. A Simple Sketch
This sketch increments the variable “encoderPos” when the encoder knob is turned clockwise and decrements the variable when the knob is turned counterclockwise.
The sketch uses an “interrupt” to avoid missing any changes in the position of the knob.
The Arduino Uno has two interrupts attached to digital pins 2 and 3; we only use pin 2 as an interrupt here.
volatile int encoderPos = 0; // the value of a volatile variable can change
// in the function called by the interrupt
void setup() {
pinMode(2, INPUT); // encoder pinA is attached to digital pin2
pinMode(3, INPUT); // encoder pinB is attached to digital pin3
attachInterrupt(0, encoder, CHANGE); // interrupt0 maps to pin2
Serial.begin (9600); }
void loop(){ } // main body of the sketch employing the interrupt
void encoder() {
if(digitalRead(2) == digitalRead(3)) // check to see if pins A & B have the same state
{encoderPos--; } // decrement position if A & B are the same
else
{encoderPos++; } // increment position if A & B are not the same
Serial.println(encoderPos, DEC); // send encoderPos to serial monitor

8. Example Application
This implementation shows a knob mounted to the rotary encoder. This hardware includes two LEDS that come on and off as the encoder passes over the contacts. The hardware can be used with the sketch on the previous slide to demonstrate how the encoder works.