Arduino Keypad Password Door Lock System

 1. Introduction

This project explains how to build an Arduino keypad password door lock system using a 4x4 keypad and a servo motor. The door unlocks only when the correct password is entered, making it a simple security system.

---

2. Components

• Arduino Nano /Uno
• 4x4 Keypad
• Servo Motor (SG90)
• Jumper wires
• Breadboard

---

3. Circuit and Connections

Keypad Connections:

R1 → D2
R2 → D3
R3 → D4
R4 → D5
C1 → D6
C2 → D7
C3 → D8
C4 → D9

Servo Motor Connections:
VCC → 5V
GND → GND
Signal → D10

---

4. Circuit Working

When a key is pressed on the keypad, Arduino reads the input and stores it. Once four digits are entered, Arduino compares it with the predefined password.

• If correct → Servo rotates and unlocks the door
• If wrong → No action is taken

After a few seconds, the door locks again automatically.

---

5. Code

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

Servo myServo;

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

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

String password = "1234";
String input = "";

void setup() {
  myServo.attach(10);
  myServo.write(0);
}

void loop() {
  char key = keypad.getKey();

  if (key) {
    input += key;

    if (input.length() == 4) {
      if (input == password) {
        myServo.write(90);
        delay(3000);
        myServo.write(0);
      }
      input = "";
    }
  }
}

---

6. Code Working

• The keypad reads user input
• The entered digits are stored in a string
• When 4 digits are entered, it checks with the stored password
• If matched, servo rotates to unlock
• After delay, it returns to lock position

---

7. Tips

• Use a strong password instead of "1234"
• Add a buzzer for wrong attempts
• Use external power if servo is unstable
• You can add LCD for better display

---

8. Uses

• Home security systems
• Locker systems
• Office access control
• Electronic door locks

---

9. Conclusion

This project demonstrates a simple and effective Arduino-based security system using a keypad and servo motor. It is ideal for beginners and practical applications.