🔐 4x4 Keypad Password Lock

Secure a virtual lock using a 4x4 membrane keypad and a secret 4-digit code.

📋 Overview

Keypads use a matrix of rows and columns to save pins. A 4x4 keypad (16 buttons) only needs 8 pins. The Keypad library handles the complex scanning logic for you.

What you'll learn: Matrix scanning, including external libraries, and password verification logic.

Estimated time: 45-60 minutes. Difficulty: ⭐⭐⭐ Intermediate.

🧩 Components Needed

Component	Specification	Qty
Arduino Uno R3	5V	1
4x4 Keypad	Membrane type	1
LEDs (Red/Green)	Status indicator	2
Resistors	220Ohm	2

📖 Step-by-Step Tutorial

Install Library

Open Library Manager and install Keypad by Mark Stanley.

Wire Keypad

Connect the 8 pins of the keypad to digital pins 2–9 in order.

Wire LEDs

Green to 10, Red to 11. These show if the code is correct or wrong.

Test Code

Upload the code. Default password is "1234". Press "#" to submit.

💡

Membrane keypads can be tricky to plug into breadboards. Use male-to-male jumper wires to bridge the keypad connector to your breadboard pins.

💻 Arduino Code

keypad_lock.ino

INO

// Keypad Lock : Volt X
#include <Keypad.h>

const byte ROWS = 4, 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);
String pass = "1234", input = "";

void setup() {
  pinMode(10, OUTPUT); // Green
  pinMode(11, OUTPUT); // Red
  Serial.begin(9600);
}

void loop() {
  char key = keypad.getKey();
  if (key) {
    if (key == '#') {
      if (input == pass) {

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