Acquista | Scarica | Come iniziare | Guide | Riferimento | Hardware | FAQ | Dizionario

Learning   Examples | Foundations | Hacking | Links

Examples > Digital I/O

Debounce

This example demonstrates the use of a pushbutton as a switch: each time you press the button, the LED (or whatever) is turned on (if it's off) or off (if on). It also debounces the input, without which pressing the button once would appear to the code as multiple presses. Makes use of the millis() function to keep track of the time when the button is pressed.

Circuit

A push-button on pin 7 and an LED on pin 13.

Code

int inPin = 7;         // the number of the input pin
int outPin = 13;       // the number of the output pin

int state = HIGH;      // the current state of the output pin
int reading;           // the current reading from the input pin
int previous = LOW;    // the previous reading from the input pin

// the follow variables are long's because the time, measured in miliseconds,
// will quickly become a bigger number than can be stored in an int.
long time = 0;         // the last time the output pin was toggled
long debounce = 200;   // the debounce time, increase if the output flickers

void setup()
{
  pinMode(inPin, INPUT);
  pinMode(outPin, OUTPUT);
}

void loop()
{
  reading = digitalRead(inPin);

  // if we just pressed the button (i.e. the input went from LOW to HIGH),
  // and we've waited long enough since the last press to ignore any noise...  
  if (reading == HIGH && previous == LOW && millis() - time > debounce) {
    // ... invert the output
    if (state == HIGH)
      state = LOW;
    else
      state = HIGH;

    // ... and remember when the last button press was
    time = millis();    
  }

  digitalWrite(outPin, state);

  previous = reading;
}