I am working towards debouncing my keyes rotary encoder using the Bounce2 library found here ( https://github.com/thomasfredericks/Bounce2 ).

I believe the problem lies in my code as there isn't much in terms of a circuit. The encoder is connected to my arduino as follows

  • 5V : connected to 5v out on arduino
  • GND : connected to GND
  • SW : connected to pin A1
  • DT : connected to pin 3
  • CLK : connected to pin 2

I am trying to call an ISR from a CLK input. When the ISR is called it should increment or decrement a value based on the direction the encoder was turned. This encoder is tied to an ISR because it will be used for user input and I would like it to remain responsive throughout the sketch.

Previously, I was using millis() to debounce the encoder, but I was still having trouble receiving more than one input from the encoder. I was hoping that this libary would resolve this issue.

The current output of the code I have included never increments/decrements the starting value no matter which direction the encoder is turned. In short, it always outputs 0.

If someone could explain what I am doing wrong that would be wonderful! Then maybe, but just maybe, I can stop beating my head against my desk. :p

Thanks, Kevin

#include <Bounce2.h>

#define sw A1
#define LED_PIN 9
#define clk 2
#define dt 3

int ledState = LOW;
int onOff = LOW;

volatile int virtualPosition = 0;
int lastCount = 0;

// Initiate bounce objects
Bounce debouncerSW = Bounce();
Bounce debouncerROT = Bounce();

void setup() {

  pinMode(sw, INPUT_PULLUP);
  pinMode(clk, INPUT);
  pinMode(dt, INPUT);
  pinMode(LED_PIN, OUTPUT);

  // set up button instace

  // set up rotary encoder instance

  // setup the LED
  digitalWrite(LED_PIN, ledState);

  // attach ISR
  attachInterrupt(digitalPinToInterrupt(clk), isr, LOW);

  Serial.println("Start"); // just to let me know sketch has finished setup

void loop() {


  if ( debouncerSW.fell() ) {
    ledState = !ledState;
    onOff = !onOff;
    digitalWrite(LED_PIN, ledState);

    Serial.print("onOff = ");
  virtualPosition = lastCount;

  Serial.print ("lastCount = ");
  Serial.println (lastCount);

  delay(1000); // for readability / simulates delay time for rest of main sketch
} // end main loop

void isr ()  {

  // Update the Bounce instance :

  if (debouncerROT.fell()) {
    if (digitalRead(dt) == LOW)
      virtualPosition -- ; // Could be -5 or -10
    else {
      virtualPosition ++ ; // Could be +5 or +10

    // Restrict value from 0 to 100
    virtualPosition = min(100, max(0, virtualPosition));
} // end ISR
  • I also want to note that no form of hardware debouncing is in use. The rotary encoder is connected directly to the arduino with no passive components in place. Commented Dec 12, 2016 at 19:18
  • See my answer to How to read RPS for fast rotation with status change method in Arduino?. Also see my comment to other answer there, “Implemented with a state machine, quadrature coding does not need debouncing. Bounce can cause invalid states or extra states, but they cancel out.” In other words, debouncing rotary encoder inputs is a wrongheaded approach. Commented Dec 12, 2016 at 20:11
  • @jwpat7 Thank you! I will take a look! Commented Dec 12, 2016 at 20:37
  • I’ve always found with encoders that hardware denouncing saves me a lot of trouble. All you need is a couple of small caps.
    – Delta_G
    Commented Aug 5, 2020 at 14:19


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