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Arduino - Button - Debounce

When a button is pressed/released or when a switch is toggled, newbies usually think simply that its state is changed from LOW to HIGH or HIGH to LOW. In practice, it is not exactly like that. Because of the mechanical and physical characteristics, the state of the button (or switch) might be toggled between LOW and HIGH several times. This phenomenon is called chattering. The chattering phenomenon makes a single press that may be read as multiple presses, resulting in a malfunction in some kinds of applications. This tutorial shows how to eliminate this phenomenon (called debounce the input).

Arduino chattering phenomenon

Hardware Required

1×Arduino UNO or Genuino UNO
1×USB 2.0 cable type A/B
1×Push Button
1×(Optional) Panel-mount Push Button
1×Breadboard
1×Jumper Wires
1×(Optional) 9V Power Adapter for Arduino
1×(Recommended) Screw Terminal Block Shield for Arduino Uno
1×(Optional) Transparent Acrylic Enclosure For Arduino Uno

Or you can buy the following sensor kits:

1×DIYables Sensor Kit (30 sensors/displays)
1×DIYables Sensor Kit (18 sensors/displays)
Please note: These are Amazon affiliate links. If you buy the components through these links, We will get a commission at no extra cost to you. We appreciate it.

About Button

If you do not know about button (pinout, how it works, how to program ...), learn about them in the following tutorials:

Wiring Diagram

Arduino Button Wiring Diagram

This image is created using Fritzing. Click to enlarge image

Let's see and compare Arduino code between WITHOUT and WITH debounce and their behaviors.

Reading Button without Debounce

Before learning about debouncing, just see the code without debouncing and its behavior.

Quick Steps

  • Connect Arduino to PC via USB cable
  • Open Arduino IDE, select the right board and port
  • Copy the below code and open with Arduino IDE
/* * Created by ArduinoGetStarted.com * * This example code is in the public domain * * Tutorial page: https://arduinogetstarted.com/tutorials/arduino-button-debounce */ // constants won't change. They're used here to set pin numbers: const int BUTTON_PIN = 7; // the number of the pushbutton pin // Variables will change: int lastState = LOW; // the previous state from the input pin int currentState; // the current reading from the input pin void setup() { // initialize serial communication at 9600 bits per second: Serial.begin(9600); // initialize the pushbutton pin as an pull-up input // the pull-up input pin will be HIGH when the switch is open and LOW when the switch is closed. pinMode(BUTTON_PIN, INPUT_PULLUP); } void loop() { // read the state of the switch/button: currentState = digitalRead(BUTTON_PIN); if(lastState == HIGH && currentState == LOW) Serial.println("The button is pressed"); else if(lastState == LOW && currentState == HIGH) Serial.println("The button is released"); // save the the last state lastState = currentState; }
  • Click Upload button on Arduino IDE to upload code to Arduino
Arduino IDE Upload Code
  • Open Serial Monitor
  • Keep pressing the button several seconds and then release it.
  • See the result on Serial Monitor
COM6
Send
The button is pressed The button is pressed The button is pressed The button is released The button is released
Autoscroll Show timestamp
Clear output
9600 baud  
Newline  

⇒ As you can see, you pressed and released the button just the once. However, Arduino recognizes it as multiple presses and releases.

Reading Button with Debounce

Quick Steps

  • Copy the below code and open with Arduino IDE
/* * Created by ArduinoGetStarted.com * * This example code is in the public domain * * Tutorial page: https://arduinogetstarted.com/tutorials/arduino-button-debounce */ // constants won't change. They're used here to set pin numbers: const int BUTTON_PIN = 7; // the number of the pushbutton pin const int DEBOUNCE_DELAY = 50; // the debounce time; increase if the output flickers // Variables will change: int lastSteadyState = LOW; // the previous steady state from the input pin int lastFlickerableState = LOW; // the previous flickerable state from the input pin int currentState; // the current reading from the input pin // the following variables are unsigned longs because the time, measured in // milliseconds, will quickly become a bigger number than can be stored in an int. unsigned long lastDebounceTime = 0; // the last time the output pin was toggled void setup() { // initialize serial communication at 9600 bits per second: Serial.begin(9600); // initialize the pushbutton pin as an pull-up input // the pull-up input pin will be HIGH when the switch is open and LOW when the switch is closed. pinMode(BUTTON_PIN, INPUT_PULLUP); } void loop() { // read the state of the switch/button: currentState = digitalRead(BUTTON_PIN); // check to see if you just pressed the button // (i.e. the input went from LOW to HIGH), and you've waited long enough // since the last press to ignore any noise: // If the switch/button changed, due to noise or pressing: if (currentState != lastFlickerableState) { // reset the debouncing timer lastDebounceTime = millis(); // save the the last flickerable state lastFlickerableState = currentState; } if ((millis() - lastDebounceTime) > DEBOUNCE_DELAY) { // whatever the reading is at, it's been there for longer than the debounce // delay, so take it as the actual current state: // if the button state has changed: if (lastSteadyState == HIGH && currentState == LOW) Serial.println("The button is pressed"); else if (lastSteadyState == LOW && currentState == HIGH) Serial.println("The button is released"); // save the the last steady state lastSteadyState = currentState; } }
  • Click Upload button on Arduino IDE to upload code to Arduino
  • Open Serial Monitor
  • Keep pressing the button several seconds and then release it.
  • See the result on Serial Monitor
COM6
Send
The button is pressed The button is released
Autoscroll Show timestamp
Clear output
9600 baud  
Newline  

⇒ As you can see, you pressed and released the button just the once. Arduino recognizes it as the single press and release. The chatter is eliminated.

We Made It Simple - Arduino Button Debounce Code with Library

To make it much easier for beginners, especially when using multiple buttons, we created a library, called ezButton. You can learn about ezButton library here.

Arduino Button Debounce Code for A Single Button

/* * Created by ArduinoGetStarted.com * * This example code is in the public domain * * Tutorial page: https://arduinogetstarted.com/tutorials/arduino-button-library * * This example reads the state of a button with debounce and print it to Serial Monitor. */ #include <ezButton.h> ezButton button(7); // create ezButton object that attach to pin 7; void setup() { Serial.begin(9600); button.setDebounceTime(50); // set debounce time to 50 milliseconds } void loop() { button.loop(); // MUST call the loop() function first if(button.isPressed()) Serial.println("The button is pressed"); if(button.isReleased()) Serial.println("The button is released"); }

Arduino Button Debounce Code for A Multiple Buttons

/* * Created by ArduinoGetStarted.com * * This example code is in the public domain * * Tutorial page: https://arduinogetstarted.com/tutorials/arduino-button-debounce */ #include <ezButton.h> ezButton button1(6); // create ezButton object that attach to pin 6; ezButton button2(7); // create ezButton object that attach to pin 7; ezButton button3(8); // create ezButton object that attach to pin 8; void setup() { Serial.begin(9600); button1.setDebounceTime(50); // set debounce time to 50 milliseconds button2.setDebounceTime(50); // set debounce time to 50 milliseconds button3.setDebounceTime(50); // set debounce time to 50 milliseconds } void loop() { button1.loop(); // MUST call the loop() function first button2.loop(); // MUST call the loop() function first button3.loop(); // MUST call the loop() function first if(button1.isPressed()) Serial.println("The button 1 is pressed"); if(button1.isReleased()) Serial.println("The button 1 is released"); if(button2.isPressed()) Serial.println("The button 2 is pressed"); if(button2.isReleased()) Serial.println("The button 2 is released"); if(button3.isPressed()) Serial.println("The button 3 is pressed"); if(button3.isReleased()) Serial.println("The button 3 is released"); }

The wiring diagram for above code:

Arduino Button Library Wiring Diagram

This image is created using Fritzing. Click to enlarge image

Video Tutorial

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Additional Knowledge

  • DEBOUNCE_DELAY value depends on the applications. Different applications may use different values.

Extendability

The debounce method can apply for switch, touch sensor ...

Button on Commercial Products

Most electronic products have a reset button. Additionally, the button also keeps other functionalities in many products.

The Best Arduino Starter Kit

See Also

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