Interfacing a Rotary Encoder with an Arduino

Panasonic EVE-KC2F2024B24 pulses per revolution

6mm diameter flattened output shaftoutput type: quadrature (incremental)

minimum life: 15,000 rotationscost: less than $1 (USD)

Arduino Unomicrocontroller board

Interfacing a Rotary Encoder with an Arduino

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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.

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AB

COM

clockwise rotation of knobcounterclockwise rotation of knob

Bpin B = ON

pin B = OFF

Apin 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

Encoder Output and Rotational Direction

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The Guts of a Mechanical Encoder

spring-loaded electrical contacts

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 continuitybetween A and COM

no electrical continuitybetween A and COM

Sensor Wiring (need four 10kΩ resistors and two 0.01F capacitors)

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10kΩ10kΩ10kΩ

10kΩ

the encoder is the part in the red box

this part of the circuit keeps the A, B and COM “switches” from flickering at the beginning or end contact . . . this “debounces” the switches

A Simple Sketch

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volatile int encoderPos = 0; // the value of a volatile variable can change // in the function called by the interruptvoid 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)) // get state of encoder pins A & B encoderPos++; // increment position both are HIGH else encoderPos--; // decrement position if both are LOW Serial.println (encoderPos, DEC); // send encoderPos to serial monitor

• 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.

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Example ApplicationThis 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.