External interrupts to control an LED

The objective of this project is to use external interrupts to control an LED with a button press. The LED will respond immediately to the button press, thanks to attachInterrupt(), allowing non-blocking, real-time input control. This demonstrates how to use interrupts to prioritize user input without the need for constant polling.

Fundamental Programming Concepts

• External Interrupts (attachInterrupt()): Allows the program to respond immediately to an event (like a button press) without constantly checking the button’s state.
• Digital Input (Button): Reads the state of the button to trigger the interrupt.
• Digital Output (LED): Controls the LED by turning it on or off based on the button press.

Requirement Components

To complete this button-interrupt LED controller using Arduino project, you will need:

• Arduino Uno Board
• LED
• 220Ω Resistor
• Push Button
• 10kΩ Resistor (pull-down)
• Breadboard
• Jumper Wires
• USB Cable (for connecting Arduino to your computer)

Circuit Diagram

Insert your Arduino Button-Interrupt LED Controller Circuit Diagram here to help visualize the setup.

Circuit Connection

How to Connect the Circuit

1. LED: Connect the anode of the LED to Pin 13 and the cathode to GND using a 220Ω resistor.
2. Button: Connect one side of the button to Pin 2 (an interrupt pin) and the other side to GND. Use a 10kΩ pull-down resistor between Pin 2 and GND.
3. Power: Ensure that the Arduino is powered via USB.

Explanation of Circuit

• The button is connected to Pin 2, which is an interrupt-capable pin. When pressed, it triggers an interrupt that will toggle the state of the LED.
• The LED is connected to Pin 13 and will turn on or off depending on the button press, controlled by the interrupt.

Programming Section for external interrupts to control an LED

Arduino Syntax

Arduino Code:

Here’s the Arduino code to control an LED using a button press with external interrupts:

const int ledPin = 13;    // Pin connected to the LED
const int buttonPin = 2;  // Pin connected to the button (interrupt pin)
volatile bool ledState = LOW;  // Volatile variable for LED state
void setup() {
  pinMode(ledPin, OUTPUT);  // Set the LED pin as output
  pinMode(buttonPin, INPUT_PULLUP);  // Set the button pin as input with internal pull-up
  attachInterrupt(digitalPinToInterrupt(buttonPin), toggleLED, FALLING);  // Attach interrupt to the button
}
void loop() {
 // The LED state is controlled by the interrupt, so the main loop is empty
}
// ISR (Interrupt Service Routine) to toggle the LED
void toggleLED() {
  ledState = !ledState;  // Toggle the LED state
  digitalWrite(ledPin, ledState);  // Set the LED based on the new state
}

Steps to Upload Code:

1. Connect your Arduino to your computer using a USB cable.
2. Open the Arduino IDE and select the correct Board and Port.
3. Copy and paste the provided code into a new sketch.
4. Click the Upload button to transfer the code to your Arduino.
5. Press the button to see the LED toggle its state (on/off) in real-time using interrupts.

Check Output

Once the code is uploaded, pressing the button connected to Pin 2 will trigger an interrupt that toggles the LED connected to Pin 13. The LED should turn on and off with each press of the button, responding instantly due to the interrupt.

Troubleshooting Tips

• LED not responding? Ensure the button is correctly connected to Pin 2 (an interrupt pin) and GND.
• Button presses not detected? Check that the attachInterrupt() function is called with the correct pin and that the FALLING mode is used to detect the button press.
• LED flickering? Ensure proper debouncing is applied either through hardware or in the ISR (Interrupt Service Routine).

Further Exploration

• Debounce the Button: Add a software debouncing technique inside the ISR to prevent unwanted multiple triggers from a single press.
• Multiple Interrupts: Experiment with additional interrupt pins to control multiple LEDs or other outputs.
• Advanced Control: Use the interrupt to trigger more complex actions, such as controlling motors or sending signals to other devices.

Note

This project demonstrates how to use external interrupts in Arduino for real-time input handling. By using attachInterrupt(), we can create immediate, non-blocking responses to button presses, making the project more responsive and efficient.

FAQ

Q1: What is an external interrupt, and why use it?
An external interrupt allows the Arduino to immediately respond to an input event, like a button press, without having to constantly check the state of the input. This ensures more efficient and responsive code.

Q2: How does attachInterrupt() work in this project?
The attachInterrupt() function attaches an interrupt to the specified pin. When the button is pressed, it triggers the ISR (Interrupt Service Routine) to toggle the LED.

Q3: Can I debounce the button in this project?
Yes, you can implement debouncing either through software or hardware. In software, you can add a small delay or check the time between interrupts in the ISR to ensure only valid presses are registered.

Q4: Can I use interrupts for multiple buttons?
Yes, you can attach interrupts to multiple pins (depending on your Arduino model) to control more buttons or outputs like LEDs.

Q5: What happens if I don’t use an interrupt for the button?
Without an interrupt, you would have to use a polling method (constantly checking the button’s state in the loop), which could delay the response to the button press or interfere with other parts of the program.