SENSORS/ACTUATORS

INTERNET OF THING (IoT)

ESP32 S3 UNO - Keypad 4x4

This ESP32 S3 Uno keypad 4x4 tutorial shows you how to connect a 4x4 matrix keypad to the ESP32 S3 Uno form board and read every key press with Arduino code. You will see each pressed key in the Serial Monitor. Then you will turn the membrane keypad into a simple password lock that checks the code you type.

In this tutorial, you will:

Wire a 4x4 matrix keypad to the ESP32 S3 Uno
Install the DIYables_Keypad library in the Arduino IDE
Read which key is pressed and print it to the Serial Monitor
Check a password entered on the keypad

Hardware Preparation

1	×	ESP32 S3 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	×	Keypad 4x4
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 .

Overview of 4x4 Keypad

A 4x4 keypad is a cheap and easy way to give your project 16 input buttons. The keys are thin membrane switches laid out in a grid of rows and columns, which is called a matrix. Each button in the grid is called a key.

Pinout

The matrix layout means you do not need 16 wires for 16 keys. The keypad has only 8 pins, split into two groups.

Row pins

Four pins connect to the four rows of keys. They are labeled R1, R2, R3 and R4.

Column pins

Four pins connect to the four columns of keys. They are labeled C1, C2, C3 and C4.

When you press a key, it joins one row pin to one column pin. The library scans the rows and columns very fast to find out which pair is joined, and so which key is pressed.

ESP32 S3 Uno Pinout

The image below shows the pinout diagram of the ESP32 S3 Uno form board. Use it to find the Uno header pins D2 to D9 and their GPIO numbers when you wire the keypad.

Wiring Diagram

The keypad uses eight digital pins in a row, from D9 down to D2. Plug the keypad's 8-pin connector into the board with jumper wires as shown below.

This image is created using Fritzing. Click to enlarge image

Keypad Pin	ESP32 S3 Uno Pin
R1	D9 (GPIO46)
R2	D8 (GPIO21)
R3	D7 (GPIO14)
R4	D6 (GPIO3)
C1	D5 (GPIO20)
C2	D4 (GPIO19)
C3	D3 (GPIO17)
C4	D2 (GPIO18)

D9 (GPIO46) and D6 (GPIO3) are boot strapping pins on the ESP32 S3 Uno. The board reads them at power-up to choose its boot mode. A keypad is a passive part, so it is normally safe here. Still, do not hold any key down while you power on, reset or upload. If the board does not boot or the upload fails, unplug the keypad wires from D9 and D6, upload again, and then plug them back in.

ESP32 S3 Uno Code

This sketch sets up the keypad with the DIYables_Keypad library and a 4x4 key map. In the loop, it asks the library for a key. When a key is pressed, the sketch prints that key to the Serial Monitor.

#include <DIYables_Keypad.h> // DIYables_Keypad library const int ROW_NUM = 4; // four rows const int COLUMN_NUM = 4; // four columns char keys[ROW_NUM][COLUMN_NUM] = { {'1','2','3', 'A'}, {'4','5','6', 'B'}, {'7','8','9', 'C'}, {'*','0','#', 'D'} }; byte pin_rows[ROW_NUM] = {46, 21, 14, 3}; // GPIO46 (D9), GPIO21 (D8), GPIO14 (D7), GPIO3 (D6) - connect to the row pinouts of the keypad byte pin_column[COLUMN_NUM] = {20, 19, 17, 18}; // GPIO20 (D5), GPIO19 (D4), GPIO17 (D3), GPIO18 (D2) - connect to the column pinouts of the keypad DIYables_Keypad keypad = DIYables_Keypad( makeKeymap(keys), pin_rows, pin_column, ROW_NUM, COLUMN_NUM ); void setup(){ Serial.begin(9600); delay(1000); Serial.println("Keypad 4x4 example"); } void loop(){ char key = keypad.getKey(); if (key){ Serial.println(key); } }

The two arrays pin_rows and pin_column hold the GPIO numbers, not the D labels. If you wire the keypad to other pins, change only these two lines.

Detailed Instructions

Follow these steps to get the keypad working:

New to the ESP32 S3 Uno? Follow ESP32 S3 Uno - Getting Started first.
Wire it up as shown in the diagram.
Connect the board to your computer with a USB Type-C cable.
Open Arduino IDE, choose the ESP32S3 Dev Module board and the correct COM port.
Open the Library Manager by clicking the Libraries icon on the left side of the Arduino IDE.
Search for the library: type DIYables_Keypad in the search box and find the keypad library by DIYables.io.
Install it by clicking the Install button.

Search for DIYables_Keypad created by DIYables.io and click the Install button.

Newbiely | Arduino IDE 2.3.8

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Library Manager

DIYables_Keypad

All

DIYables_Keypad by DIYables.io

The library is designed for Arduino, ESP32, ESP8266... to use with keypad such as 3x4, 4x4 keypad. It also works with Arduino Uno R4 WiFi/Minima More info

1.0.1

INSTALL

Newbiely.ino

···

1 void setup() {

Output

Serial Monitor

Ln 1, Col 1

ESP32S3 Dev Module on COM15

Copy the code above and paste it into the Arduino IDE.
Upload the code by clicking the Upload button.
Open the Serial Monitor and set the baud rate to 9600.
Press some keys on the keypad and watch the Serial Monitor.

Newbiely | Arduino IDE 2.3.8

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Newbiely.ino

···

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

Output

Serial Monitor

Message (Enter to send message to 'ESP32S3 Dev Module' on 'COM15')

New Line

9600 baud

Keypad 4x4 example 1 2 3 4 A B C * #

Ln 11, Col 1

ESP32S3 Dev Module on COM15

Tip: if a whole row or column of keys does nothing, one wire is loose or in the wrong pin. Check that wire against the wiring table first.

Keypad and Password

Password entry is one of the most popular uses for a keypad. It lets you build a door lock, a safe or an alarm panel. To make it work, you give two keys a special job.

Start key

The "*" key starts a new password. It clears anything typed before.

Enter key

The "#" key ends the password. The sketch then checks what you typed.

All other keys are part of the password. Each time you press a key, the sketch does one of three things:

If the key is "*", it clears the typed password.
If the key is "#", it compares the typed password with the saved one, prints the result, and then clears the typed password.
If the key is anything else, it adds the key to the end of the typed password.

Keypad - Password Code

The saved password in this sketch is "1234A". The sketch builds a String from your key presses and compares it with the saved one when you press "#". You can change the password on the line const String password.

/* * This ESP32 S3 Uno code was developed by newbiely.com * * This ESP32 S3 Uno code is made available for public use without any restriction * * For comprehensive instructions and wiring diagrams, please visit: * https://newbiely.com/tutorials/esp32-s3-uno/esp32-s3-uno-keypad-4x4 */ #include <DIYables_Keypad.h> // DIYables_Keypad library const int ROW_NUM = 4; // four rows const int COLUMN_NUM = 4; // four columns char keys[ROW_NUM][COLUMN_NUM] = { {'1','2','3', 'A'}, {'4','5','6', 'B'}, {'7','8','9', 'C'}, {'*','0','#', 'D'} }; byte pin_rows[ROW_NUM] = {46, 21, 14, 3}; // GPIO46 (D9), GPIO21 (D8), GPIO14 (D7), GPIO3 (D6) - connect to the row pinouts of the keypad byte pin_column[COLUMN_NUM] = {20, 19, 17, 18}; // GPIO20 (D5), GPIO19 (D4), GPIO17 (D3), GPIO18 (D2) - connect to the column pinouts of the keypad DIYables_Keypad keypad = DIYables_Keypad( makeKeymap(keys), pin_rows, pin_column, ROW_NUM, COLUMN_NUM ); const String password = "1234A"; // change your password here String input_password; void setup(){ Serial.begin(9600); Serial.println("Keypad 4x4 password"); input_password.reserve(32); // maximum input characters is 33, change if needed } void loop(){ char key = keypad.getKey(); if (key){ Serial.println(key); if(key == '*') { input_password = ""; // clear input password } else if(key == '#') { if(password == input_password) { Serial.println("password is correct"); // DO YOUR WORK HERE } else { Serial.println("password is incorrect, try again"); } input_password = ""; // clear input password } else { input_password += key; // append new character to input password string } } }

Upload the code above to the ESP32 S3 Uno.
Open the Serial Monitor at 9600 baud.
Type a wrong password: press "1234BC" and then "#".
Type the right password: press "1234A" and then "#".
Check the result in the Serial Monitor.

Newbiely | Arduino IDE 2.3.8

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☐

Newbiely.ino

···

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

Output

Serial Monitor

Message (Enter to send message to 'ESP32S3 Dev Module' on 'COM15')

New Line

9600 baud

Keypad 4x4 password 1 2 3 4 B C # password is incorrect, try again 1 2 3 4 A # password is correct

Ln 11, Col 1

ESP32S3 Dev Module on COM15

Tip: put your own action, like turning on a relay or a servo, under the comment DO YOUR WORK HERE.

Video Tutorial

Watch the video below to see this ESP32 S3 Uno project step by step.

Additional Knowledge

These guides show two common next steps for keypad projects:

FAQ

Does the 4x4 keypad work with the 3.3V pins of the ESP32 S3 Uno?

Yes. The keypad is only a grid of switches, so it has no power pin and no voltage of its own. The ESP32 S3 Uno drives the pins at 3.3V and reads them back, so the keypad is safe to connect directly.

Why does the code use 46, 21, 14, 3 instead of 9, 8, 7, 6?

On the ESP32 S3 Uno, the Uno header labels are not the same as the GPIO numbers. For example, D9 is GPIO46 and D6 is GPIO3. In code you must always write the GPIO number, so the pin arrays use the numbers from the pinout diagram.

Can I use the same keypad library as on the UNO R4?

Yes. The DIYables_Keypad library works on the ESP32 S3 Uno with no change. Only the pin numbers in the code are different.

Can I wire the keypad to other pins?

Yes. Any pin that works as a digital input and output is fine, for example D10 (GPIO10), D11 (GPIO11), D12 (GPIO13) or D13 (GPIO12). Update the pin_rows and pin_column arrays to match your wiring. Avoid D0 and D1, because they are used for the USB serial link.

What if my project needs more pins than the Uno headers give?

The ESP32 S3 Uno has two extra rows of holes with more GPIOs: GPIO15 and GPIO16 (I/O, PWM, analog), GPIO45 and GPIO35 to GPIO42 (I/O, PWM), and GPIO47/GPIO48 (output only, PWM). Solder pin headers to them and write the GPIO number in code. For a keypad, GPIO35 to GPIO42 are a good choice, for example to move the rows off D9 and D6. Do not use GPIO47/GPIO48 for the keypad, because the library needs pins that can also read input. Two warnings: (1) GPIO47/GPIO48 may run at 1.8V instead of 3.3V on some modules (especially ones with "V" in the name, like R8V or R16V), so 3.3V devices can be damaged or act strangely. (2) GPIO0, GPIO3 (D6), GPIO45 and GPIO46 (D9) are boot strapping pins, and a wrong connection can stop the board from booting or uploading code. Use the other extra pins first.

How do I change the password?

Edit the line const String password = "1234A"; and put your own keys between the quotes. Do not use "*" or "#" in the password, because these two keys have special jobs.

Troubleshooting

Problem	Possible Cause	Solution
No COM port shows up in the Arduino IDE	USB driver is missing or the cable is power-only	Install the CP210x or CH340 driver and use a USB data cable
Upload fails or the board does not boot	A key is held down or a wire on D9 (GPIO46) or D6 (GPIO3) disturbs the boot	Release all keys. Unplug the D9 and D6 wires, upload, then plug them back in
Nothing prints when a key is pressed	Wrong baud rate or loose keypad connector	Set the Serial Monitor to 9600 baud and push the jumper wires firmly into the keypad
One whole row or column of keys does not work	One wire is loose or on the wrong pin	Check each wire against the wiring table
The wrong key is printed	Row and column wires are swapped or in reverse order	Make sure R1 goes to D9 and C4 goes to D2 as in the table
Compile error about DIYables_Keypad.h	Library is not installed	Install DIYables_Keypad from the Library Manager
Password is never correct	Extra keys were typed before the password	Press "*" first to clear the input, then type the password and press "#"

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