Interruption triggered twice when set to FALLING I have a simple sketch with a button that triggers an interruption set to happen when the button pin goes from HIGH to LOW. It has debouncing so no repetitions happen when the button is pressed, but sometimes when releasing the button the interruption also fires. Why would that be? Shouldn't the debouncing take care of any micro-rising during the release of the button?

volatile int contador = 0;
int n = contador;

long t = 0;
void setup() {    

    pinMode(2, INPUT_PULLUP);
    attachInterrupt( 0, incrementaContador, FALLING);
} 

void loop() {   
    if (n != contador) {
        n = contador;
    }
}

void incrementaContador() {

    if ( millis() &gt; (t + 50) ) {
        contador++ ;
        t = millis();
    }
}


This same code works correctly when set to LOW instead of FALLING.
but sometimes when releasing the button the interruption also fires


Yes, well when you release the button it may also bounce. In other words OFF/ON/OFF so that will count as a press. A capacitor over the switch might be better.

Example: