Password Door Lock Using Arduino

SimpleCircuits

Arduino Security Servo

Security Project

Password Door
Lock System

Build a fully functional keypad-controlled door lock with an Arduino UNO, 4×4 keypad, I²C LCD, servo motor, and buzzer. Visual + audio feedback, servo-powered latch, real-time status on display.

4×4 Keypad

I²C LCD

SG90 Servo

5V Powered

6 Max Digits

Finished Build

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Working Principle

How It Works

The system uses a 4-digit password stored in firmware. The user enters digits via the keypad — each keypress shows an asterisk on the LCD. On completion, the Arduino checks the entry and responds immediately with servo movement and audio feedback.

✓ Correct Password

• Buzzer beeps once (300 ms)
• Servo motor rotates to unlock latch
• LCD shows "CORRECT PASSWORD" + "DOOR OPENED"
• D key toggles lock/unlock state

✕ Wrong Password

• Buzzer triple-beeps (200 ms each)
• Servo stays locked at 110°
• LCD shows "WRONG PASSWORD!" + "PLEASE TRY AGAIN"
• Password entry resets automatically

A latch mechanism connected by a steel rod to the servo enables mechanical movement. All system states are reflected on the LCD in real-time.

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Bill of Materials

Components Required

Six key components — all widely available, beginner-friendly, and budget-conscious.

Component	Notes	Buy
Arduino UNO	Main controller	Buy Now
LCD with I2C Module (16×2)	SDA→A4, SCL→A5	Buy Now
4×4 Keypad	Pins 2–9	Buy Now
SG90 Servo Motor	Signal → pin 10	Buy Now
5V Buzzer	Pin 11	Buy Now
Jumper Wires	M-M, M-F set	Buy Now

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Assembly Guide

Step-by-Step Build

Follow these steps in order for a clean, reliable build. Complete wiring details are in the video below.

01

Place the Arduino UNO

Mount on a flat surface or inside a project casing. Ensure full pin access on both sides.

02

Connect the 4×4 Keypad

Row and column pins connect to Arduino digital pins 2 through 9 in order.

03

Wire the LCD with I2C

VCC → 5V, GND → GND, SDA → A4, SCL → A5. I2C address is 0x27 by default.

04

Connect the Servo Motor

Signal wire → pin 10. Power servo from Arduino 5V/GND or an external supply for heavier servos.

05

Connect the Buzzer

Positive terminal → pin 11, negative → GND. Active buzzer recommended.

06

Upload the Code

Open Arduino IDE, paste the code below, select the correct port, and upload.

07

Mount Mechanical Parts

Attach the latch via a steel linkage rod to the servo horn. Align for smooth lock/unlock travel.

08

Power On & Test

Use USB or a 9V adapter. LCD shows welcome message, then prompts for password entry.

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Wiring

Circuit Diagram

Complete wiring and connection details are shown clearly in the tutorial video. Click the diagram to view full resolution.

🎥

Full assembly tutorial above — exact wire positions, I2C address setup, mechanical latch alignment, and live demo of lock/unlock cycles.

Follow the video carefully for exact wire positioning and the mechanical latch configuration.

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Firmware

Arduino Code

Upload this sketch to your UNO. Default password is 0123 — change it inside the Password password = Password("0123"); line.

password_lock.ino — Arduino C++

#include <Servo.h>
#include <LiquidCrystal_I2C.h>
#include <Keypad.h>
#include <Password.h>

#define buzzer 11

Servo servo;
LiquidCrystal_I2C lcd(0x27, 16, 2);

String newPasswordString;
char newPassword[6];
byte a = 5;
bool value = true;

Password password = Password("0123"); // ← Change your password here

byte maxPasswordLength = 6;
byte currentPasswordLength = 0;
const byte ROWS = 4;
const byte COLS = 4;

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

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

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

void setup() {
  Serial.begin(9600);
  pinMode(buzzer, OUTPUT);
  servo.attach(10);
  servo.write(50);
  lcd.init();
  lcd.backlight();
  lcd.setCursor(3, 0);
  lcd.print("WELCOME TO");
  lcd.setCursor(0, 1);
  lcd.print("DOOR LOCK SYSTEM");
  delay(3000);
  lcd.clear();
}

void loop() {
  lcd.setCursor(1, 0);
  lcd.print("ENTER PASSWORD");

  char key = keypad.getKey();
  if (key != NO_KEY) {
    delay(60);
    if (key == 'C') {
      resetPassword();
    } else if (key == 'D') {
      if (value == true) {
        doorlocked();
        value = false;
      } else if (value == false) {
        dooropen();
        value = true;
      }
    } else {
      processNumberKey(key);
    }
  }
}

void processNumberKey(char key) {
  lcd.setCursor(a, 1);
  lcd.print("*");
  a++;
  if (a == 11) a = 5;
  currentPasswordLength++;
  password.append(key);
  if (currentPasswordLength == maxPasswordLength) {
    doorlocked();
    dooropen();
  }
}

void dooropen() {
  if (password.evaluate()) {
    digitalWrite(buzzer, HIGH);
    delay(300);
    digitalWrite(buzzer, LOW);
    servo.write(50);
    delay(100);
    lcd.setCursor(0, 0);
    lcd.print("CORRECT PASSWORD");
    lcd.setCursor(0, 1);
    lcd.print("DOOR OPENED     ");
    delay(2000);
    lcd.clear();
    a = 5;
  } else {
    for (int i = 0; i < 3; i++) {
      digitalWrite(buzzer, HIGH); delay(200);
      digitalWrite(buzzer, LOW);  delay(200);
    }
    lcd.setCursor(0, 0);
    lcd.print("WRONG PASSWORD! ");
    lcd.setCursor(0, 1);
    lcd.print("PLEASE TRY AGAIN");
    delay(2000);
    lcd.clear();
    a = 5;
  }
  resetPassword();
}

void resetPassword() {
  password.reset();
  currentPasswordLength = 0;
  lcd.clear();
  a = 5;
}

void doorlocked() {
  if (password.evaluate()) {
    digitalWrite(buzzer, HIGH);
    delay(300);
    digitalWrite(buzzer, LOW);
    servo.write(110);
    delay(100);
    lcd.setCursor(0, 0);
    lcd.print("CORRECT PASSWORD");
    lcd.setCursor(2, 1);
    lcd.print("DOOR LOCKED     ");
    delay(2000);
    lcd.clear();
    a = 5;
  } else {
    for (int i = 0; i < 3; i++) {
      digitalWrite(buzzer, HIGH); delay(200);
      digitalWrite(buzzer, LOW);  delay(200);
    }
    lcd.setCursor(0, 0);
    lcd.print("WRONG PASSWORD! ");
    lcd.setCursor(0, 1);
    lcd.print("PLEASE TRY AGAIN");
    delay(2000);
    lcd.clear();
    a = 5;
  }
  resetPassword();
}

setup()

Initializes LCD, servo at 50°, buzzer pin, and keypad. Shows 3-second welcome message. Default password: 0123.

loop()

Polls keypad continuously. Displays asterisks for each digit. After max digits, automatically triggers doorlocked → dooropen sequence.

dooropen() / doorlocked()

Evaluates password, moves servo to 50° (open) or 110° (locked), plays appropriate buzzer pattern, updates LCD.

Key	Function
C	Reset / clear current password entry
D	Toggle lock ↔ unlock state (requires correct password)
0–9, A, B, #, *	Password character input (displayed as * on LCD)

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Design Rationale

Why Choose This Design?

A practical balance of security, feedback, and expandability — perfect for learning embedded systems.

🔒

Simple yet Secure

Easy to build but provides a solid layer of basic access control.

🔑

Customizable Password

Change length and value directly in the code — no hardware changes needed.

📺

Visual + Audio Feedback

LCD shows real-time state. Buzzer gives distinct tones for success and failure.

🚪

Mechanical Realism

Servo-powered steel rod latch simulates a real-world door mechanism.

🔄

Expandable

Add GSM, fingerprint sensor, RFID, or Bluetooth for advanced security layers.

💰

Low Cost

All parts under ₹500 combined. Great for students and DIY enthusiasts.

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