In this project, we will build a Smart Door Lock System using Arduino, 4×4 Keypad, Servo Motor, Buzzer, and 16×2 I2C LCD Display. Users can enter a password using the keypad. If the password is correct, the servo motor unlocks the door. If the password is incorrect, the buzzer alerts the user.

This project is perfect for beginners learning:

Arduino
Keypad interfacing
Servo motor control
I2C LCD display
Password-based security systems

Components Required

Component	Quantity
Arduino Uno/Nano	1
4×4 Matrix Keypad	1
SG90 Servo Motor	1
16×2 I2C LCD Display	1
Buzzer	1
Jumper Wires	As required
Breadboard (Optional)	1

Circuit Connections

🔢 Keypad Connections

Keypad Pin	Arduino Pin
R1	9
R2	8
R3	7
R4	6
C1	5
C2	4
C3	3
C4	2

Servo Motor Connections

Servo Wire	Arduino
Red	5V
Brown/Black	GND
Orange/Yellow	Pin 10

Buzzer Connections

Buzzer	Arduino
Positive (+)	Pin 11
Negative (-)	GND

I2C LCD Connections

I2C LCD Pin	Arduino Uno/Nano
VCC	5V
GND	GND
SDA	A4
SCL	A5

Important Notes

Servo Power Issue

Servo motors sometimes draw high current and may not work properly using only USB power.

Symptoms:

Servo jitter
Weak movement
Arduino reset

LCD Not Displaying Text?

If LCD does not display text:

Adjust the blue potentiometer on the I2C module
Try changing I2C address from 0x27 to 0x3F

Required Arduino Libraries

Install these libraries from Arduino IDE Library Manager:

Keypad
Servo
LiquidCrystal_I2C

How the Smart Door Lock Works

LCD displays “Enter Password”
User enters password using keypad and Press # key
If password is correct, LCD shows Access Granted
Servo rotates and unlocks the door
After 5 seconds, door locks automatically
If password is incorrect, LCD displays as “Wrong Password”
Buzzer beeps 3 times, the press * key to clear entered password

Please Note – Default Password is 1234 but You can change it in code

Arduino Code:

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

// ===== LCD =====
LiquidCrystal_I2C lcd(0x27, 16, 2);

// ===== KEYPAD SETTINGS =====
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'}
};

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

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

// ===== SERVO =====
Servo lockServo;
int servoPin = 10;

// ===== BUZZER =====
int buzzerPin = 11;

// ===== PASSWORD =====
String correctPassword = "1234";
String enteredPassword = "";

void setup() {

  Serial.begin(9600);

  // ===== LCD START =====
  lcd.init();
  lcd.backlight();

  lcd.setCursor(0, 0);
  lcd.print("Smart Door Lock");

  lcd.setCursor(0, 1);
  lcd.print("Enter Password");

  // ===== SERVO =====
  lockServo.attach(servoPin);

  // ===== BUZZER =====
  pinMode(buzzerPin, OUTPUT);

  // ===== LOCK POSITION =====
  lockServo.write(0);

  delay(2000);

  lcd.clear();
  lcd.print("Enter Password");
}

void loop() {

  char key = keypad.getKey();

  if (key) {

    Serial.print("Pressed: ");
    Serial.println(key);

    // ===== DISPLAY * =====
    if (key != '#' && key != '*') {

      enteredPassword += key;

      lcd.setCursor(0, 1);

      for (int i = 0; i < enteredPassword.length(); i++) {
        lcd.print("*");
      }
    }

    // ===== CHECK PASSWORD =====
    if (key == '#') {

      lcd.clear();

      if (enteredPassword == correctPassword) {

        Serial.println("Access Granted");

        lcd.setCursor(0, 0);
        lcd.print("Access Granted");

        // Servo unlock
        lockServo.write(90);

        delay(5000);

        // Servo lock
        lockServo.write(0);

        lcd.clear();
        lcd.print("Door Locked");
      }

      else {

        Serial.println("Wrong Password");

        lcd.setCursor(0, 0);
        lcd.print("Wrong Password");

        // Buzzer alert
        for (int i = 0; i < 3; i++) {

          digitalWrite(buzzerPin, HIGH);
          delay(200);

          digitalWrite(buzzerPin, LOW);
          delay(200);
        }
      }

      enteredPassword = "";

      delay(2000);

      lcd.clear();
      lcd.print("Enter Password");
    }

    // ===== CLEAR PASSWORD =====
    if (key == '*') {

      enteredPassword = "";

      lcd.clear();
      lcd.print("Password Cleared");

      delay(1000);

      lcd.clear();
      lcd.print("Enter Password");
    }
  }
}

Future Improvements

You can upgrade this project by adding:

RFID module
Fingerprint sensor
ESP32 WiFi control
Solenoid lock
Mobile app unlock
OTP verification
Emergency exit button

Video Tutorial

You can also watch the complete video tutorial on my YouTube channel for step-by-step explanation and demonstration.

Arduino Smart Door Lock using Keypad, Servo & I2C LCD