How to Use Interrupts in Arduino: Simple Guide with Examples

Use attachInterrupt() in Arduino to run a function automatically when a specific pin changes state. Define an interrupt service routine (ISR) function and link it to a pin and trigger mode like RISING or FALLING. This lets your Arduino react immediately to events without waiting in the main loop.

Syntax

The basic syntax to use an interrupt in Arduino is:

• attachInterrupt(digitalPinToInterrupt(pin), ISR, mode);

Where:

• pin is the Arduino pin number that supports interrupts.
• ISR is the name of the function to run when the interrupt triggers.
• mode defines when the interrupt triggers: LOW, CHANGE, RISING, or FALLING.

arduino

attachInterrupt(digitalPinToInterrupt(pin), ISR, mode);

Example

This example turns on an LED when a button connected to pin 2 is pressed using an interrupt. The LED is connected to pin 13.

arduino

const int buttonPin = 2;
const int ledPin = 13;
volatile bool ledState = false;

void setup() {
  pinMode(ledPin, OUTPUT);
  pinMode(buttonPin, INPUT_PULLUP);
  attachInterrupt(digitalPinToInterrupt(buttonPin), toggleLED, FALLING);
}

void loop() {
  if (ledState) {
    digitalWrite(ledPin, HIGH);
  } else {
    digitalWrite(ledPin, LOW);
  }
}

void toggleLED() {
  ledState = !ledState;
}

Output

When the button on pin 2 is pressed, the LED on pin 13 toggles ON or OFF immediately.

Common Pitfalls

Common mistakes when using interrupts in Arduino include:

• Using delay() or Serial.print() inside the ISR, which can cause problems because ISRs should be very fast.
• Not declaring variables shared between ISR and main code as volatile, which can cause wrong values.
• Forgetting to use digitalPinToInterrupt() to get the correct interrupt number for the pin.
• Using pins that do not support interrupts.

arduino

/* Wrong way: Using delay inside ISR */
void interruptFunc() {
  delay(100); // Avoid this
}

/* Right way: Keep ISR short and fast */
volatile bool flag = false;
void interruptFunc() {
  flag = true; // Just set a flag
}

Quick Reference

Parameter	Description	Example Values
pin	Pin number that supports interrupts	2, 3 (depends on board)
ISR	Function called when interrupt triggers	void myISR()
mode	When to trigger interrupt	LOW, CHANGE, RISING, FALLING

Key Takeaways

Use attachInterrupt() with digitalPinToInterrupt(pin) to set up interrupts.

Keep interrupt service routines (ISR) short and avoid delay or Serial calls inside them.

Declare variables shared with ISR as volatile to ensure correct behavior.

Only use pins that support interrupts on your Arduino board.

Choose the correct trigger mode (RISING, FALLING, CHANGE, LOW) for your event.