Smart Door Lock System

An Arduino-based smart door lock system that combines RFID card access and a keypad backup password, with real-time status feedback through an LCD display, LED indicators, and a buzzer.

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Overview

This project simulates a dual-authentication smart lock:

• Tap an authorized RFID card to unlock the door, or
• Enter the correct 4-digit password on the keypad as a backup method.

On successful authentication, a servo motor rotates to simulate the door unlocking, the LCD confirms access, the green LED lights up, and a short buzzer tone sounds. On failure, the red LED stays on and the buzzer sounds an error pattern. The door auto-locks again after a few seconds.

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Features

• RFID-based access using the MFRC522 module
• Keypad password backup (4x4 membrane keypad)
• Audio feedback via buzzer (success tone / error pattern)
• Visual status indicators using Red (locked) and Green (unlocked) LEDs
• 16x2 I2C LCD showing live system status (Who goes there?, Enter, mortal!, YOU SHALL NOT PASS!, etc.)
• Servo-driven lock mechanism with automatic re-lock after a timeout
• Serial Monitor debug logging for keypad input and servo actions

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Circuit Diagram

Pin Connections

Component	Device Pin/Wire	Arduino Pin
MFRC522 RFID Reader	SDA (SS)	10
	SCK	13
	MOSI	11
	MISO	12
	RST	9
	GND	GND
	3.3V	3.3V
4x4 Keypad	R1	A1
	R2	A2
	R3	A3
	R4	0 (RX)
	C1	2
	C2	3
	C3	4
	C4	5
16x2 LCD (I2C)	VCC	5V
	GND	GND
	SDA	A4
	SCL	A5
Servo Motor	Signal	6
	VCC	5V
	GND	GND
LEDs & Buzzer	Green LED (+)	7
	Red LED (+)	8
	Buzzer (+)	A0

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Software & Libraries

Install these libraries via the Arduino Library Manager:

• MFRC522 — RFID reader communication
• Keypad — 4x4 matrix keypad input
• LiquidCrystal_I2C — I2C LCD display
• Servo — built into the Arduino core
• SPI / Wire — built into the Arduino core

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Getting Started

Run on Real Hardware

1. Wire the components according to the pin connection tables above.
2. Install the required libraries listed above via the Arduino IDE Library Manager.
3. Select Arduino Uno as your board and the correct COM port.

Setting Your RFID Card UID

byte validUID[4]={0x01,0x02,0x03,0x09};   // Replace with your RFID UID

To use your own card:

1. Upload the sketch and open the Serial Monitor (9600 baud).
2. Scan your card — the UID will be printed.
3. Replace the placeholder bytes in validUID[] with your card's actual UID.

Default Password

The default backup password is 1234, configurable here:

String password="1234";

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How It Works

1. On startup, the LCD displays a welcome message, then switches to the idle "Who goes there?" prompt.
2. The system continuously checks for:
   • A new RFID card tap, or
   • Keypad input.
3. RFID path: if a card is detected, its UID is compared against validUID[]. A match grants access; a mismatch denies it.
4. Keypad path: digits are collected into inputPassword as they're typed. Pressing # submits and compares against the stored password; pressing * clears the current entry.
5. On access granted: the green LED turns on, the red LED turns off, a success tone plays, the servo rotates to 90° (unlocked), and the LCD shows "Enter, mortal!". After 5 seconds, the servo returns to 0° (locked) and the LCD shows "Door Locked".
6. On access denied: the red LED stays on and a 3-beep error pattern plays on the buzzer.

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