Debounce in Arduino

A press counts once the contacts stop bouncing.

// A press only counts once the contacts stop bouncing.
const int BUTTON_PIN = 2;
const unsigned long SETTLE_MS = 25;
int steadyState = HIGH;
int lastReading = HIGH;
unsigned long lastChange = 0;
void setup() {
  pinMode(BUTTON_PIN, INPUT_PULLUP);
  Serial.begin(9600);
}

void loop() {
  int reading = digitalRead(BUTTON_PIN);
  if (reading != lastReading) lastChange = millis();
  if (millis() - lastChange > SETTLE_MS && reading != steadyState) {
    steadyState = reading;
    if (steadyState == LOW) Serial.println("Pressed");
  }
  lastReading = reading;
}

How it works

1. Every raw change restamps lastChange.
2. Only a reading stable past SETTLE_MS becomes the steady state.
3. The print fires on the clean falling edge alone.

Keywords and builtins used here

• HIGH
• INPUT_PULLUP
• LOW
• Serial
• begin
• const
• digitalRead
• if
• int
• long
• loop
• millis
• pinMode
• println
• setup
• unsigned
• void

The run, in numbers

Lines

20

Characters to type

540

Tokens

119

Three-star pace

60 tpm

At the three-star pace of 60 tokens a minute, this run takes about 119 seconds.

Type this snippet

Step 3 of 3 in Timing, step 12 of 27 in Language basics.

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Debounce in other languages

• JavaScript