Interrupt-driven button handling in Arduino - Mini Project: Build & Apply

Interrupt-driven button handling

📖 Scenario: You want to make a simple Arduino project where pressing a button changes the state of an LED immediately, without waiting for the main program loop. This is useful when you want your Arduino to react quickly to button presses.

🎯 Goal: Build an Arduino program that uses an interrupt to detect when a button is pressed and toggles an LED on or off right away.

📋 What You'll Learn

Create a variable to store the LED pin number

Create a variable to store the button pin number

Set up the LED pin as output and the button pin as input with pull-up resistor

Create a volatile variable to hold the LED state

Attach an interrupt to the button pin to detect button presses

Write an interrupt service routine (ISR) to toggle the LED state

In the main loop, set the LED to the current state

Print the LED state to the Serial Monitor when it changes

💡 Why This Matters

🌍 Real World

Interrupt-driven button handling is used in devices where quick response to user input is important, like remote controls, game controllers, or safety switches.

💼 Career

Understanding interrupts and hardware input handling is essential for embedded systems developers, IoT engineers, and anyone working with microcontrollers.

1

Set up LED and button pins

Create two integer variables called ledPin and buttonPin. Set ledPin to 13 and buttonPin to 2. In the setup() function, set ledPin as an output and buttonPin as an input with the internal pull-up resistor enabled.

Arduino

int ledPin = 13;
int buttonPin = 2;

void setup() {
  pinMode(ledPin, OUTPUT);
  pinMode(buttonPin, INPUT_PULLUP);
  // Your code here
}

void loop() {
  // Your code here
}

Need a hint?

Use pinMode to set the pin modes inside setup().

2

Create LED state variable and attach interrupt

Create a volatile bool variable called ledState and initialize it to false. In the setup() function, attach an interrupt to buttonPin using attachInterrupt(digitalPinToInterrupt(buttonPin), toggleLED, FALLING). Define an empty function called toggleLED() that will be the interrupt service routine.

Arduino

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

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

void loop() {
  // Your code here
}

void toggleLED() {
  // Your code here
}

Need a hint?

Use attachInterrupt in setup() and define toggleLED() as the ISR.

3

Toggle LED state inside the interrupt

Inside the toggleLED() function, toggle the value of ledState by setting it to its opposite using ledState = !ledState;. In the loop() function, set the LED output to ledState using digitalWrite(ledPin, ledState ? HIGH : LOW);.

Arduino

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

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

void loop() {
  digitalWrite(ledPin, ledState ? HIGH : LOW);
  // Your code here
}

void toggleLED() {
  ledState = !ledState;
  // Your code here
}

Need a hint?

Toggle ledState inside toggleLED() and update the LED in loop().

4

Print LED state changes to Serial Monitor

In the setup() function, start the serial communication with Serial.begin(9600);. Create a non-volatile boolean variable called lastLedState initialized to false. In the loop() function, check if ledState is different from lastLedState. If yes, print "LED is ON" or "LED is OFF" accordingly using Serial.println(), then update lastLedState to ledState. Keep the LED output code as before.

Arduino

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

void setup() {
  pinMode(ledPin, OUTPUT);
  pinMode(buttonPin, INPUT_PULLUP);
  attachInterrupt(digitalPinToInterrupt(buttonPin), toggleLED, FALLING);
  Serial.begin(9600);
  // Your code here
}

void loop() {
  digitalWrite(ledPin, ledState ? HIGH : LOW);
  if (ledState != lastLedState) {
    if (ledState) {
      Serial.println("LED is ON");
    } else {
      Serial.println("LED is OFF");
    }
    lastLedState = ledState;
  }
  // Your code here
}

void toggleLED() {
  ledState = !ledState;
}

Need a hint?

Use Serial.begin(9600); in setup() and print messages in loop() when the LED state changes.