Pull-up, pull-down and bounce: wiring a button properly

Three ways to wire a button

The internal resistors

The internal ones are fine for a button close to the board. With long wires or in noisy environments, use a lower external resistor, for example 10 kΩ, which holds the level more firmly.

ESP32: the pins that decide how it boots

At power-on the ESP32 reads the level of five pins (strapping pins) to decide how to start. Each one has an internal resistor that holds it at the right value: a button, or an external pull-up or pull-down on these pins, can change the boot. Choose other pins for buttons.

Bounce

Wiring with the ESP32

The sketch

// Button with the internal pull-up and debounce: counts the presses without counting fake ones.
// The button connects the pin to GND: pressed = LOW. Same sketch for Arduino UNO and ESP32.
#include <Arduino.h>

#ifdef ARDUINO_ARCH_ESP32
const int BUTTON_PIN = 27;     // do not use GPIO 34-39 (no internal pull-up) or the boot pins
#else
const int BUTTON_PIN = 7;
#endif
const unsigned long DEBOUNCE_MS = 50;   // debounce time: increase it if it still counts double

int stableState = HIGH;        // last accepted state
int lastReading = HIGH;        // last raw reading
unsigned long changedAt = 0;
unsigned long presses = 0;

void setup() {
  Serial.begin(115200);
  pinMode(BUTTON_PIN, INPUT_PULLUP);
}

void loop() {
  int reading = digitalRead(BUTTON_PIN);
  if (reading != lastReading) {
    changedAt = millis();              // the contact is still bouncing: start over
    lastReading = reading;
  }
  if (millis() - changedAt > DEBOUNCE_MS && reading != stableState) {
    stableState = reading;             // steady for long enough: it's a real change
    if (stableState == LOW) {
      presses++;
      Serial.print("Presses: ");
      Serial.println(presses);
    }
  }
}

The sketch counts the presses without ever stopping with delay(), so it can do other things in the meantime. If a press is still counted twice, increase DEBOUNCE_MS.

Common mistakes