Arduino button debounce with millis()

How the example works

1. 01Use a pull-up input

   On Arduino boards supporting INPUT_PULLUP, connect the normally open pushbutton between digital pin 2 and GND. Pressed is LOW. Confirm your board's pinout before wiring.

2. 02Track the most recent transition

   Every time the raw input changes, reset changedAt to the current millis(). This ensures bouncing delays the decision.

3. 03Count only a stable press

   After the reading holds for 35 ms, update stablePressed. Toggle the LED on entering pressed state, not on release.

4. 04Inspect edge cases

   Test a press with short bounce, a held press, release bounce, a second press, and millis() rollover. Change the interval based on actual switch measurements.

Reference code

Arduino C++. Read the limitations below before using this code with real hardware or network services.

// Reference sketch: button on pin 2 to GND.
const uint8_t buttonPin = 2;
const uint8_t ledPin = LED_BUILTIN;
const unsigned long debounceMs = 35;
bool lastRaw = false;
bool stablePressed = false;
unsigned long changedAt = 0;
bool ledOn = false;

void setup() {
  pinMode(buttonPin, INPUT_PULLUP);
  pinMode(ledPin, OUTPUT);
}

void loop() {
  const unsigned long now = millis();
  const bool rawPressed = digitalRead(buttonPin) == LOW;
  if (rawPressed != lastRaw) changedAt = now;
  if ((unsigned long)(now - changedAt) >= debounceMs &&
      rawPressed != stablePressed) {
    stablePressed = rawPressed;
    if (stablePressed) {
      ledOn = !ledOn;
      digitalWrite(ledPin, ledOn ? HIGH : LOW);
    }
  }
  lastRaw = rawPressed;
}

Test cases to check

• A burst of alternating raw samples shorter than 35 ms produces zero accepted presses.
• One sustained press produces one accepted event, even if it is held for a long time.
• Release bounce does not create another event; the next stable press counts once.
• The unsigned time subtraction handles the normal millis() wraparound pattern.

Official references

• Arduino official debounce example
• Arduino built-in examples