⚡ ESP32 Interrupt Handling – How to Use External Interrupts

In this tutorial, you’ll learn how to use interrupts with ESP32 in Arduino IDE to handle external events like button presses, sensor signals, or pulse inputs — without constantly checking them in loop().

🧠 Principle: What is an Interrupt?

In a microcontroller, an interrupt is like someone tapping your shoulder while you’re doing something important — asking you to quickly deal with a more urgent task.

Let’s imagine this:

You’re washing clothes (main program), when suddenly your phone rings (an interrupt). You pause the washing, answer the phone (interrupt service), then return and continue washing (return from interrupt).

If another more important call comes in while you’re still on the first call, you put the first call on hold to answer the new one. This is nested interrupts, and it relies on interrupt priorities.

📌 Key Concepts:

In polling (no interrupts), your program constantly checks for changes, wasting CPU time. With interrupts, the CPU does other work and only reacts when the event occurs — more efficient, especially for rare or delayed inputs.

For example:
In a button-controlled project, using interrupts means your ESP32 only responds when the button is pressed, rather than checking the button state every cycle.

⚠️ ESP32 supports RISING, FALLING, CHANGE, HIGH, and LOW level trigger modes for GPIO interrupts.

Awesome! Let’s move on to interrupt handling — a super useful and powerful concept when working with microcontrollers like the ESP32.

Here’s the next part of your tutorial series:

📌 Example: Button Triggered LED with Interrupt

Let’s create an example where:

🔧 Circuit Setup

Component GPIO
Button GPIO 14
LED GPIO 27

📟 Arduino Code Example

const int buttonPin = 14;
const int ledPin = 27;

volatile bool ledState = false;

void IRAM_ATTR handleInterrupt() {
  ledState = !ledState;
  digitalWrite(ledPin, ledState);
}

void setup() {
  Serial.begin(115200);
  
  pinMode(ledPin, OUTPUT);
  pinMode(buttonPin, INPUT_PULLUP);  // use internal pull-up

  // Attach interrupt to pin 14, trigger on falling edge (button press)
  attachInterrupt(digitalPinToInterrupt(buttonPin), handleInterrupt, FALLING);

  Serial.println("Interrupt demo started");
}

void loop() {
  // nothing to do here — everything is interrupt-driven!
}

📋 Explanation

Part Meaning
attachInterrupt() Links a GPIO pin to an ISR (interrupt service routine)
digitalPinToInterrupt(pin) Converts a GPIO pin to its interrupt ID
handleInterrupt() This function runs automatically when the pin changes
IRAM_ATTR Required on ESP32 to place the ISR in RAM (for speed)
FALLING Trigger the interrupt on falling edge (high → low)

🧠 Interrupt Modes

Mode Triggered When
RISING LOW → HIGH
FALLING HIGH → LOW
CHANGE Any change (HIGH ↔ LOW)
HIGH Stays HIGH (less common)
LOW Stays LOW (less common)

⚠️ Tips & Warnings

📚 Bonus: Detach an Interrupt

detachInterrupt(digitalPinToInterrupt(buttonPin));

This stops the interrupt from firing (useful for power saving or mode switching).

🧪 Use Cases of Interrupts

📚 References