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

Technical Specifications

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

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

Library Setup

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

   #include <Keypad.h>

3. 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'}
   };

    

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);
  }
}

Advanced Features

// 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;
  }
}

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

// 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

Troubleshooting