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Guide to 4×4 Matrix Keypad for Arduino

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Ekostra Electronics

On April 5, 2025

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4×4 Matrix Keypad

16-Button Input Interface for Arduino and Microcontroller Projects

Introduction

The 4×4 matrix keypad is a compact input device with 16 buttons arranged in a grid. Using only 8 pins, it provides an efficient way to add multiple button inputs to Arduino, Raspberry Pi, and other microcontroller projects.

Key Features

⌨️ 16 Buttons

4 rows × 4 columns matrix configuration

🔢 Standard Layout

0-9 digits plus A,B,C,D,*,# symbols

⚡ Low Power

Only draws current during scanning

🔌 Simple Interface

8-pin connection (4 rows + 4 columns)

Technical Specifications

Operating Voltage	1.5V – 24V DC
Contact Resistance	<100mΩ
Insulation Resistance	>100MΩ
Life Expectancy	1,000,000 presses
Dimensions	80mm × 80mm × 10mm (typical)
Button Spacing	19mm × 19mm (standard)

Pin Configuration

Pin	Function	Arduino Connection
1	Row 1	D9
2	Row 2	D8
3	Row 3	D7
4	Row 4	D6
5	Column 1	D5
6	Column 2	D4
7	Column 3	D3
8	Column 4	D2

Note: Pin connections can be customized to any digital pins

Wiring with Arduino

// Basic Connections:
// Row 1 → D9
// Row 2 → D8
// Row 3 → D7
// Row 4 → D6
// Column 1 → D5
// Column 2 → D4
// Column 3 → D3
// Column 4 → D2

// Basic Connections:

// Row 1 → D9

// Row 2 → D8

// Row 3 → D7

// Row 4 → D6

// Column 1 → D5

// Column 2 → D4

// Column 3 → D3

// Column 4 → D2

Important: Always use INPUT_PULLUP mode for columns to avoid floating inputs

Library Setup

Install the Keypad library by Mark Stanley and Alexander Brevig
Include the library in your sketch:

Arduino

#include <Keypad.h>

1

#include <Keypad.h>

Configure the keypad layout:

const byte ROWS = 4;
const byte COLS = 4;
char keys[ROWS][COLS] = {
  {'1','2','3','A'},
  {'4','5','6','B'},
  {'7','8','9','C'},
  {'*','0','#','D'}
};

const byte ROWS = 4;

const byte COLS = 4;

char keys[ROWS][COLS] = {

{'1','2','3','A'},

{'4','5','6','B'},

{'7','8','9','C'},

{'*','0','#','D'}

};

Basic Keypad Example

#include <Keypad.h>

const byte ROWS = 4;
const byte COLS = 4;

char keys[ROWS][COLS] = {
  {'1','2','3','A'},
  {'4','5','6','B'},
  {'7','8','9','C'},
  {'*','0','#','D'}
};

byte rowPins[ROWS] = {9, 8, 7, 6};
byte colPins[COLS] = {5, 4, 3, 2};

Keypad keypad = Keypad(makeKeymap(keys), rowPins, colPins, ROWS, COLS);

void setup() {
  Serial.begin(9600);
}

void loop() {
  char key = keypad.getKey();
  
  if (key) {
    Serial.print("Pressed: ");
    Serial.println(key);
  }
}

#include <Keypad.h>

const byte ROWS = 4;

const byte COLS = 4;

char keys[ROWS][COLS] = {

{'1','2','3','A'},

{'4','5','6','B'},

{'7','8','9','C'},

{'*','0','#','D'}

};

byte rowPins[ROWS] = {9, 8, 7, 6};

byte colPins[COLS] = {5, 4, 3, 2};

Keypad keypad = Keypad(makeKeymap(keys), rowPins, colPins, ROWS, COLS);

void setup() {

Serial.begin(9600);

}

void loop() {

char key = keypad.getKey();

if (key) {

Serial.print("Pressed: ");

Serial.println(key);

}

Advanced Features

Password Entry

// Simple password check
char password[4] = {'1','2','3','4'};
char entered[4];
int pos = 0;

void checkPassword(char key) {
  entered[pos++] = key;
  if(pos == 4) {
    if(strncmp(entered, password, 4) == 0) {
      Serial.println("Access granted!");
    }
    pos = 0;
  }
}

// Simple password check

char password[4] = {'1','2','3','4'};

char entered[4];

int pos = 0;

void checkPassword(char key) {

entered[pos++] = key;

if(pos == 4) {

if(strncmp(entered, password, 4) == 0) {

Serial.println("Access granted!");

}

pos = 0;

}

Keypad Events

// Detect key presses and releases
void loop() {
  if(keypad.getState() == PRESSED) {
    Serial.print("Pressed: ");
    Serial.println(keypad.getKey());
  }
  if(keypad.getState() == RELEASED) {
    Serial.print("Released: ");
    Serial.println(keypad.getKey());
  }
}

// Detect key presses and releases

void loop() {

if(keypad.getState() == PRESSED) {

Serial.print("Pressed: ");

Serial.println(keypad.getKey());

}

if(keypad.getState() == RELEASED) {

Serial.print("Released: ");

Serial.println(keypad.getKey());

}

Multi-key Press

// Detect multiple simultaneous presses
void loop() {
  if(keypad.isPressed('A') && keypad.isPressed('B')) {
    Serial.println("A+B combo pressed!");
  }
}

// Detect multiple simultaneous presses

void loop() {

if(keypad.isPressed('A') && keypad.isPressed('B')) {

Serial.println("A+B combo pressed!");

}

Custom Keymaps

// Special function keys
char keys[ROWS][COLS] = {
  {'F','F','F','F'},
  {'F','F','F','F'},
  {'F','F','F','F'},
  {'R','F','E','F'}
}; // F=Forward, R=Reverse, E=Emergency Stop

// Special function keys

char keys[ROWS][COLS] = {

{'F','F','F','F'},

{'R','F','E','F'}

}; // F=Forward, R=Reverse, E=Emergency Stop

Troubleshooting

No Key Detection

Verify all connections are secure
Check row/column pin assignments
Ensure proper keymap configuration

Ghost Presses

Use INPUT_PULLUP for columns
Add 0.1μF capacitors between rows/cols and GND
Implement software debouncing

Multiple Keys Not Working

Check for short circuits between pins
Verify sufficient power supply
Test with different digital pins

Hotline 24/7

4×4 Matrix Keypad

Introduction

Key Features

⌨️ 16 Buttons

🔢 Standard Layout

⚡ Low Power

🔌 Simple Interface

Technical Specifications

Pin Configuration

Wiring with Arduino

Library Setup

Basic Keypad Example

Advanced Features

Password Entry

Keypad Events

Multi-key Press

Custom Keymaps

Troubleshooting

No Key Detection

Ghost Presses

Multiple Keys Not Working

Project Ideas

Security System

Calculator

Menu System

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