SENSORS/ACTUATORS

INTERNET OF THING (IoT)

ESP32 UNO - Button - Debounce

One tap, five "pressed" messages? Fix it with ESP32 Uno button debounce code that turns every real press into exactly one event. Inside a push button, two metal strips hit each other and spring back for a few milliseconds. The ESP32 Uno form board samples its pins thousands of times per second, so it catches each of those tiny jumps. A short time filter in your Arduino code, written by hand or taken from a library, hides them.

What you will do:

Upload a plain button sketch and count the false events it prints
Build a debounce filter based on the millis() timer
Shrink the same job to a few lines with the ezButton library
Read three buttons at once, each with its own debounce timer

Here is a scope-style view of the noisy edge a single press produces:

Components You Need

1	×	ESP32 Uno-form Board
1	×	USB Cable Type-A to Type-C (for USB-A PC)
1	×	USB Cable Type-C to Type-C (for USB-C PC)
1	×	Breadboard-mount Button with Cap
1	×	Breadboard-mount Button Kit
1	×	Panel-mount Push Button
1	×	Push Button Module
1	×	Breadboard
1	×	Jumper Wires

Or you can buy the following kits:

DIYables Sensor Kit (18 sensors/displays)

Disclosure: Some of the links provided in this section are Amazon affiliate links. We may receive a commission for any purchases made through these links at no additional cost to you.
Additionally, some of these links are for products from our own brand, DIYables .

Button Basics

After this part, you know which page explains the button itself.

Topic	Where to Find It
Button pinout, INPUT_PULLUP and a first sketch	ESP32 Uno - Button
Typical bounce length	About 1 to 20 ms, depending on the button and its age
Pin level with this wiring	HIGH when free, LOW when pushed

Good to know: ESP32 Uno pins run at 3.3V logic. With a button wired to GND and the internal pull-up on, no other voltage ever reaches the pin.

ESP32 Uno Pinout

The printed labels on the Uno headers are not the numbers you type in a sketch. Look up D6, D7 and D8 in this picture to find the GPIO number behind each one.

How to Connect the Button

By the end of this part, one button sits between D7 and GND.

The wiring diagram between ESP32 Uno Button

This image is created using Fritzing. Click to enlarge image

Component Pin	ESP32 Uno Pin
Button leg 1	D7 (GPIO14)
Button leg 2	GND

Good to know: you need no resistor here. The sketches call INPUT_PULLUP, which links GPIO14 to 3.3V inside the chip.

The first two sketches use this exact circuit. Run the raw version first, then the filtered one, and compare the two outputs.

ESP32 Uno Code - Raw Button Read (No Debounce)

This sketch prints a line every time the pin level flips, with no filter at all.

Upload and Test

First time with this board? Set it up with ESP32 Uno - Getting Started before you continue.
Build the circuit by following the wiring table above.
Plug in the USB Type-C cable between the ESP32 Uno and your computer.
Select the board in Arduino IDE: pick ESP32 Dev Module and the COM port of the board (CH340).
Paste the sketch into a new Arduino IDE window.
Click Upload (Upload) and wait until the IDE reports the upload is done.
Start the Serial Monitor and set it to 9600 baud.
Push the button, keep it down for two or three seconds, and let go.
Read the log. Yours may look like this:

Newbiely | Arduino IDE 2.3.8

──

☐

Newbiely.ino

···

8 Serial.println("Hello World!");

Output

Serial Monitor

Message (Enter to send message to 'ESP32 Dev Module' on 'COM15')

New Line

9600 baud

The button is pressed The button is released The button is pressed The button is pressed The button is released The button is released The button is released

Ln 11, Col 1

ESP32 Dev Module on COM15

Pro tip: tap the button with a very light touch. A soft, slow press usually makes the contacts bounce even more, so the extra lines show up more often.

That log came from a single press and a single release. Every line after the first pair is a bounce that the ESP32 Uno read as a real event.

※ NOTE THAT:

No debounce time fits every case. A clicky tactile switch may settle in 10 ms, while a big panel button or a worn one may need far longer, so tune DEBOUNCE_TIME for your own part.

ESP32 Uno Code - Debounced Button with millis()

This sketch only accepts a new level after it has stayed unchanged for 50 ms.

/* * This ESP32 Uno code was developed by newbiely.com * * This ESP32 Uno code is made available for public use without any restriction * * For comprehensive instructions and wiring diagrams, please visit: * https://newbiely.com/tutorials/esp32-uno/esp32-uno-button-debounce */ #define BUTTON_PIN 14 // D7 (GPIO14) on the ESP32 Uno reads the button #define DEBOUNCE_TIME 50 // quiet time in ms; raise it if extra messages show up int last_steady_state = LOW; // last level that stayed stable long enough int last_flickerable_state = LOW; // last raw level, bounces included int current_state; // raw level read in this loop pass unsigned long last_debounce_time = 0; // millis() value of the latest raw change void setup() { // start the Serial Monitor link at 9600 baud Serial.begin(9600); // turn on the built-in pull-up, so the pin idles HIGH pinMode(BUTTON_PIN, INPUT_PULLUP); } void loop() { // get the raw level of the button pin current_state = digitalRead(BUTTON_PIN); // a raw change means a bounce or a real press, so restart the clock if (current_state != last_flickerable_state) { // note the time of this change last_debounce_time = millis(); // remember the new raw level last_flickerable_state = current_state; } if ((millis() - last_debounce_time) > DEBOUNCE_TIME) { // the level has been quiet long enough, so act on a real change if (last_steady_state == HIGH && current_state == LOW) Serial.println("The button is pressed"); else if (last_steady_state == LOW && current_state == HIGH) Serial.println("The button is released"); // store the accepted stable level last_steady_state = current_state; } }

Upload and Test

Load this sketch into the Arduino IDE in place of the old one.
Send it to the board by clicking Upload.
Leave the Serial Monitor open with the same baud rate.
Press and hold the button for a moment, then release it.
Check the log:

Newbiely | Arduino IDE 2.3.8

──

☐

Newbiely.ino

···

8 Serial.println("Hello World!");

Output

Serial Monitor

Message (Enter to send message to 'ESP32 Dev Module' on 'COM15')

New Line

9600 baud

The button is pressed The button is released

Ln 11, Col 1

ESP32 Dev Module on COM15

Pro tip: press the button ten times as fast as you can and count the lines. You should get exactly ten pairs. If some taps go missing, your presses are shorter than 50 ms, so try 30 ms.

One push now gives one "pressed" line, and one release gives one "released" line. The bounce is filtered out.

The Shortcut: ESP32 Uno Button Debounce Code with ezButton

This part gets the same clean result with far less code.

The timer logic above grows long when you copy it for each button. Our ezButton library keeps one timer per button for you. Read the ezButton library guide for all its functions.

Step 1 — Install the library

Open Library Manager in the Arduino IDE, type "ezButton", and click Install on the library by ArduinoGetStarted.com.

Step 2 — Debounce one button

The wiring stays the same: one button from D7 (GPIO14) to GND.

/* * Created by ArduinoGetStarted.com * * This example code is in the public domain * * Tutorial page: https://arduinogetstarted.com/tutorials/arduino-button-library * * ESP32 Uno sketch: the ezButton library filters the bounce on one button * and sends each press and release to the Serial Monitor. */ #include <ezButton.h> ezButton button(14); // one ezButton object on D7 (GPIO14) void setup() { Serial.begin(9600); button.setDebounceTime(50); // ignore changes shorter than 50 ms } void loop() { button.loop(); // let the library sample the pin before any check if(button.isPressed()) Serial.println("The button is pressed"); if(button.isReleased()) Serial.println("The button is released"); }

Code Part	What It Does
ezButton button(14)	Creates a button object on D7 (GPIO14) with the pull-up on
setDebounceTime(50)	Sets the quiet time to 50 ms
button.loop()	Samples the pin and runs the timer, so call it first in every pass
isPressed() / isReleased()	Returns true once for each clean press or release

The output matches the hand-made filter, in about a third of the lines.

Step 3 — Debounce three buttons

Add two more buttons. Each one gets its own pin, its own object and its own timer.

The wiring diagram between ESP32 Uno Button Library

This image is created using Fritzing. Click to enlarge image

Component Pin	ESP32 Uno Pin
Button 1 leg 1	D6 (GPIO27)
Button 2 leg 1	D7 (GPIO14)
Button 3 leg 1	D8 (GPIO12)
Leg 2 of all three buttons	GND

The third button uses D8, which is GPIO12 and one of the boot strapping pins. It must be LOW when the board starts, or the flash gets the wrong voltage and the board will not boot. A button to GND can only pull the pin LOW, so this circuit is safe. Never wire anything to D8 that could pull it HIGH (for example a module output or a pull-up resistor to 3.3V). If the board fails to start or upload, unplug the D8 wire and try again.

/* * This ESP32 Uno code was developed by newbiely.com * * This ESP32 Uno code is made available for public use without any restriction * * For comprehensive instructions and wiring diagrams, please visit: * https://newbiely.com/tutorials/esp32-uno/esp32-uno-button-debounce */ #include <ezButton.h> ezButton button_1(27); // first button on D6 (GPIO27) ezButton button_2(14); // second button on D7 (GPIO14) ezButton button_3(12); // third button on D8 (GPIO12), a strapping pin void setup() { Serial.begin(9600); button_1.setDebounceTime(50); // 50 ms quiet time for the first button button_2.setDebounceTime(50); // 50 ms quiet time for the second button button_3.setDebounceTime(50); // 50 ms quiet time for the third button } void loop() { button_1.loop(); // sample the first button button_2.loop(); // sample the second button button_3.loop(); // sample the third button if(button_1.isPressed()) Serial.println("The button 1 is pressed"); if(button_1.isReleased()) Serial.println("The button 1 is released"); if(button_2.isPressed()) Serial.println("The button 2 is pressed"); if(button_2.isReleased()) Serial.println("The button 2 is released"); if(button_3.isPressed()) Serial.println("The button 3 is pressed"); if(button_3.isReleased()) Serial.println("The button 3 is released"); }

Try pressing button 3, then button 1, then holding button 2 while you tap button 3. Each button reports on its own:

Newbiely | Arduino IDE 2.3.8

──

☐

Newbiely.ino

···

8 Serial.println("Hello World!");

Output

Serial Monitor

Message (Enter to send message to 'ESP32 Dev Module' on 'COM15')

New Line

9600 baud

The button 3 is pressed The button 3 is released The button 1 is pressed The button 1 is released The button 2 is pressed The button 3 is pressed The button 3 is released The button 2 is released

Ln 11, Col 1

ESP32 Dev Module on COM15

Video Tutorial

See the ESP32 Uno build in action in the video below.

Code Explanation

This part shows how the millis() filter decides what is real.

Code Part	What It Does
BUTTON_PIN 14	Points the sketch at D7 (GPIO14)
last_flickerable_state	Holds the newest raw level, bounces included
last_debounce_time = millis()	Restarts the clock on every raw change
millis() - last_debounce_time > DEBOUNCE_TIME	True only after 50 ms with no change
last_steady_state	Holds the accepted level and is compared with the new one to print pressed or released

A bounce keeps resetting the clock, so only the final settled level passes the 50 ms test and gets printed.

ESP32 Uno vs UNO R4 for This Project

Moving this debounce project from the UNO R4 to the ESP32 Uno changes only the pin numbers and the logic level.

Item	Arduino UNO R4	ESP32 Uno
Logic voltage	5V	3.3V
Single button pin in code	7 (D7)	14 (D7)
Three-button pins in code	6, 7, 8	27, 14, 12
D8 at boot	Normal pin	Strapping pin, must stay LOW
Debounce logic and ezButton	Same code	Same code
Arduino IDE board	Arduino UNO R4 WiFi or Minima	ESP32 Dev Module

The buttons go into the same header holes, so the circuit stays the same. Just never pull D8 HIGH at power-on.

Go Wireless: See Button Presses on Your Phone

This part gives you an idea for taking the debounced button beyond the USB cable.

The ESP32 Uno has WiFi and Bluetooth (Classic and BLE) built in. A clean, debounced press is a good event to send to a phone: show the button state on a web page, log each press with a time, or use one button to switch something in a web app. Without debounce, the phone would get a burst of fake events for every tap.

Good to know: web and Bluetooth libraries need loop() to run often. Both debounce methods on this page never call delay(), so they fit well next to a wireless library.

Troubleshooting

Problem	Possible Cause	Solution
No COM port shows up in Arduino IDE	CH340 driver not installed or a charge-only cable	Install the CH340 driver and use a USB cable that carries data
Upload stops at "Failed to connect" or "Waiting for download"	Board did not enter download mode	Hold the BOOT button while the upload starts, then release it
Board will not boot or upload with three buttons wired	Something pulls D8 (GPIO12) HIGH at startup	Make sure button 3 goes to GND only, or unplug the D8 wire while uploading
No lines appear when you press	Button leg not on D7 or not on GND	Put one leg on D7 (GPIO14) and the other on the GND rail
Lines appear with nobody touching the button	Floating pin from a loose jumper	Push the wires in firmly and keep INPUT_PULLUP in pinMode()
Doubled lines even with the debounce sketch	Button bounces longer than 50 ms	Raise DEBOUNCE_TIME or setDebounceTime() to 80 or 100 ms
Quick taps are lost	Debounce time longer than your press	Lower the value to 20 or 30 ms
Sketch uses pins 6, 7 and 8 and nothing works	Old Uno pin numbers left in the code	Use 27, 14 and 12, the GPIO numbers for D6, D7 and D8
Compile error about ezButton.h	Library missing	Install ezButton from Library Manager

FAQ

What is contact bounce in a push button?

It is the short burst of on-off changes that happens when the metal parts inside a button touch or separate. It lasts a few milliseconds, which is too fast for you to notice but slow enough for the ESP32 Uno to read many times.

Can a capacitor debounce the button instead of code?

Yes. A small capacitor (around 100 nF) from the pin to GND smooths the edge. Code is simpler, costs nothing and is easy to tune, so most projects use the software way shown here.

Is the ezButton library better than the millis() sketch?

They use the same idea. The hand-written sketch shows how the timer works. ezButton hides that code, gives one timer per button and adds handy functions like isPressed() and getCount().

Does debouncing slow down my ESP32 Uno sketch?

No. Neither method uses delay(). The code only compares two numbers in each loop pass, so the rest of your sketch keeps running at full speed.

Which GPIO number do I type for D7 on the ESP32 Uno?

Type 14. The ESP32 Uno code uses GPIO numbers, not the Uno labels, so D6 is 27 and D8 is 12. Typing 7 would point at a chip pin that is not on the D7 hole.

Why is D8 a risky pin on this board?

D8 is GPIO12, which the chip reads at boot to set the flash voltage. If it is HIGH at that moment, the board does not start. A button to GND is fine, but a module or resistor that pulls D8 up can stop the board from booting.

Can I wire a button to A2, A3, A4 or A5?

Yes, but these pins (GPIO35, 34, 36, 39) are input only and have no internal pull-up. INPUT_PULLUP does nothing on them, so add a 10k ohm resistor from the pin to 3.3V. The digital header pins avoid that extra part.

Does the UNO R4 debounce code run on the ESP32 Uno unchanged?

The logic does, and ezButton supports both boards. You only change the pin numbers, for example 7 becomes 14. The UNO R4 uses 5V logic, while ESP32 Uno pins take 3.3V only.

Do I need to install a driver for the ESP32 Uno?

Many computers need the CH340 driver, because this board uses a CH340 USB-to-serial chip. If no COM port appears after you plug it in, install the driver and try again.

Can I count how many times the button was pressed?

Yes. With ezButton, call button.setCountMode(COUNT_FALLING) in setup() and read button.getCount() in the loop. Thanks to the debounce, each press adds exactly one.

What if I need more button pins than the Uno headers give?

The ESP32 Uno has a few extra holes near the power header: GPIO32 and GPIO33 (I/O, PWM, analog on ADC1, so they also work while WiFi is on) and GPIO15 (I/O, PWM, analog on ADC2). Add pin headers to those holes and put the bare GPIO number in your sketch. For extra buttons, GPIO32 and GPIO33 are the best choice, since they have internal pull-ups. Two warnings: GPIO15 and GPIO0 (the IO0 pin at the unused Uno NC position) are boot strapping pins, and a wrong connection can stop the board from booting or uploading code, so use GPIO32/33 first. Never use the six holes under the digital header (SD0 to SD3, CMD, CLK = GPIO6 to GPIO11); they are wired to the flash chip and using them crashes the board.

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