Ard Interrupt Attach

In this tutorial, you'll learn about Arduino attachInterrupt Not Firing. We cover key concepts, practical examples, and best practices to help you understand and apply this topic effectively.

The Problem

attachInterrupt() is called but the ISR never runs.

Quick Fix

Wrong

attachInterrupt(0, myISR, CHANGE);  // Digital pin 2 on Uno

myISR is never called when pin 2 changes.

Right

int interruptPin = 2;
volatile int counter = 0;

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

void loop() {
  Serial.print("Counter: ");
  Serial.println(counter);
  delay(100);
}

void myISR() {
  counter++;
}

Counter increments each time pin 2 goes from HIGH to LOW.

Prevention

Use digitalPinToInterrupt() instead of hardcoded interrupt numbers. Only specific pins support interrupts (Uno: 2,3; Mega: 2,3,18-21). ISRs must be short and use volatile for shared variables. Avoid Serial.print() in ISRs.

DodaTech engineers apply these same patterns across Doda Browser, DodaZIP, and Durga Antivirus Pro for production IoT reliability.

FAQ