Rising, falling, and change triggers in Arduino - Mini Project: Build & Apply

Rising, falling, and change triggers

📖 Scenario: You are building a simple Arduino project to detect button presses. The button can be pressed down or released, and you want to know when the button is pressed (rising edge), released (falling edge), or changed state (either pressed or released).

🎯 Goal: Create an Arduino sketch that reads a button input and prints messages when the button state rises (goes from LOW to HIGH), falls (goes from HIGH to LOW), or changes state.

📋 What You'll Learn

Use a variable called buttonPin set to pin 2

Use a variable called buttonState to read the current button state

Use a variable called lastButtonState to store the previous button state

Detect rising edge (LOW to HIGH) and print "Button pressed"

Detect falling edge (HIGH to LOW) and print "Button released"

Detect any change in button state and print "Button state changed"

💡 Why This Matters

🌍 Real World

Detecting button presses and releases is common in devices like remote controls, game controllers, and user interfaces.

💼 Career

Understanding how to detect input changes is important for embedded systems programming and hardware interface development.

1

Set up the button input pin

Create an integer variable called buttonPin and set it to 2. In the setup() function, set buttonPin as an input using pinMode(buttonPin, INPUT). Also, start serial communication at 9600 baud with Serial.begin(9600).

Arduino

int buttonPin = 2;

void setup() {
  // Set buttonPin as input
  // Start serial communication
  // Your code here
}

void loop() {
  // Your code here
}

Need a hint?

Use pinMode to set the pin mode and Serial.begin(9600) to start serial communication.

2

Create variables to track button state

Create two integer variables called buttonState and lastButtonState. Initialize lastButtonState to LOW before setup(). In the loop() function, read the current button state from buttonPin using digitalRead(buttonPin) and store it in buttonState.

Arduino

int buttonPin = 2;
int buttonState;
int lastButtonState = LOW;

void setup() {
  pinMode(buttonPin, INPUT);
  Serial.begin(9600);
}

void loop() {
  // Read the button state
  // Your code here
}

Need a hint?

Use digitalRead(buttonPin) to get the current button state.

3

Detect rising, falling, and any change in button state

In the loop() function, use if statements to detect when the button state changes compared to lastButtonState. If buttonState is HIGH and lastButtonState is LOW, print "Button pressed". If buttonState is LOW and lastButtonState is HIGH, print "Button released". If buttonState is different from lastButtonState, print "Button state changed". Finally, update lastButtonState to the current buttonState.

Arduino

int buttonPin = 2;
int buttonState;
int lastButtonState = LOW;

void setup() {
  pinMode(buttonPin, INPUT);
  Serial.begin(9600);
}

void loop() {
  buttonState = digitalRead(buttonPin);
  // Detect rising edge
  // Detect falling edge
  // Detect any change
  // Update lastButtonState
  // Your code here
}

Need a hint?

Compare buttonState and lastButtonState to detect changes and print messages accordingly.

4

Print the button state changes

Add Serial.println statements inside the if blocks to print the exact messages: "Button pressed" for rising edge, "Button released" for falling edge, and "Button state changed" for any change. Run the program and observe the serial monitor output when pressing and releasing the button.

Arduino

int buttonPin = 2;
int buttonState;
int lastButtonState = LOW;

void setup() {
  pinMode(buttonPin, INPUT);
  Serial.begin(9600);
}

void loop() {
  buttonState = digitalRead(buttonPin);

  if (buttonState != lastButtonState) {
    // Print "Button state changed"
    // Print "Button pressed" if rising edge
    // Print "Button released" if falling edge
    // Update lastButtonState
    // Your code here
  }
}

Need a hint?

Press and release the button to see the messages in the serial monitor.