Arduino Debounce with Interrupts

What is debounce?

When using physical devices like buttons or switches, the bouncing effect generates noise, causing multiple unwanted interrupts. Debounce eliminates this noise.

Testing the Bounce

To test the bounce effect, connect Pin 2 to Ground using a wire or button and count the interrupts triggered.

const int intPin = 2;
volatile int ISRCounter = 0;
int counter = 0;

void setup() {
    pinMode(intPin, INPUT_PULLUP);
    Serial.begin(9600);
    attachInterrupt(digitalPinToInterrupt(intPin), debounceCount, FALLING);
}

void loop() {
    if (counter != ISRCounter) {
        counter = ISRCounter;
        Serial.println(counter);
    }
}

void debounceCount() {
    ISRCounter++;
}
            

Eliminating the Bounce

Hardware Debounce

Use a capacitor (1uF) in parallel with the button or switch to filter noise.

Software Debounce

Filter the bounce in code by ignoring interrupts that occur within a certain time threshold.

const int timeThreshold = 150;
const int intPin = 2;
volatile int ISRCounter = 0;
int counter = 0;
long startTime = 0;

void setup() {
    pinMode(intPin, INPUT_PULLUP);
    Serial.begin(9600);
    attachInterrupt(digitalPinToInterrupt(intPin), debounceCount, FALLING);
}

void loop() {
    if (counter != ISRCounter) {
        counter = ISRCounter;
        Serial.println(counter);
    }
}

void debounceCount() {
    if (millis() - startTime > timeThreshold) {
        ISRCounter++;
        startTime = millis();
    }
}