How to Build a DIY Smart Lock Using Arduino

Building a DIY smart lock using Arduino is an excellent project for enhancing home security while learning about electronics and programming. This guide will walk you through the process of creating a smart lock that you can control with RFID (Radio Frequency Identification) cards or a keypad. Let’s dive into the step-by-step process.

1. Gather Materials and Tools

You’ll need the following components for the project:

• Arduino Uno: The microcontroller that controls the smart lock.
• Servo Motor: Responsible for physically locking and unlocking the door.
• RFID Module (RC522): For reading RFID tags or cards to control access.
• Keypad (optional): As an alternative input method for unlocking.
• Relay Module: Allows you to control a high-powered lock or solenoid.
• Breadboard and Jumper Wires: For connecting the components.
• Power Supply: Such as a battery pack or USB power for the Arduino.
• Locking Mechanism: You can use a solenoid lock or create a custom locking mechanism using the servo motor.
• Buzzer and LEDs (optional): To provide audio and visual feedback on the lock status.

2. Set Up the RFID Module

• Wiring: Connect the RFID module to the Arduino using jumper wires. The RC522 RFID module usually has the following pins:
  • SDA to pin 10
  • SCK to pin 13
  • MOSI to pin 11
  • MISO to pin 12
  • RST to pin 9
  • GND to ground
  • VCC to 3.3V
• Install RFID Library: Download and install the MFRC522 library from the Arduino IDE library manager. This library will allow the Arduino to interact with the RFID module.

#include <SPI.h>
#include <MFRC522.h>

#define SS_PIN 10
#define RST_PIN 9
MFRC522 rfid(SS_PIN, RST_PIN);

void setup() {
  Serial.begin(9600);
  SPI.begin();
  rfid.PCD_Init();
  Serial.println("Place your card to the reader...");
}

void loop() {
  if (rfid.PICC_IsNewCardPresent() && rfid.PICC_ReadCardSerial()) {
    Serial.print("Card UID: ");
    for (byte i = 0; i < rfid.uid.size; i++) {
      Serial.print(rfid.uid.uidByte[i], HEX);
    }
    Serial.println();
    rfid.PICC_HaltA();
  }
}

3. Control the Lock Mechanism with a Servo Motor

• Wiring: Connect the servo motor to the Arduino.
  • Servo signal pin to digital pin 6
  • VCC to 5V
  • GND to ground
• Code: Use the Servo library to control the motor’s rotation, which will lock or unlock the door based on RFID input.

#include <Servo.h>

Servo myServo;

void setup() {
  myServo.attach(6);  // Attach the servo to pin 6
  myServo.write(90);  // Set the initial position (locked)
}

void unlockDoor() {
  myServo.write(0);  // Rotate servo to unlock position
  delay(5000);       // Keep the door unlocked for 5 seconds
  myServo.write(90); // Return to locked position
}

4. Integrating RFID with the Lock

• After reading the RFID card, compare its UID (Unique Identification Number) with the stored authorized IDs. If it matches, trigger the servo to unlock the door.

void loop() {
  if (rfid.PICC_IsNewCardPresent() && rfid.PICC_ReadCardSerial()) {
    String cardUID = "";
    for (byte i = 0; i < rfid.uid.size; i++) {
      cardUID += String(rfid.uid.uidByte[i], HEX);
    }
    Serial.print("Card UID: ");
    Serial.println(cardUID);

    // Check if the UID matches the authorized card
    if (cardUID == "12ab34cd") {
      Serial.println("Access granted.");
      unlockDoor();
    } else {
      Serial.println("Access denied.");
    }
    rfid.PICC_HaltA();
  }
}

5. Adding a Keypad for Alternative Access

• If you want a backup access method, you can connect a keypad to the Arduino. You’ll need the Keypad library.
• Wiring: Connect the rows and columns of the keypad to the appropriate pins on the Arduino.
• Code: Set up a passcode and add it to the main program.

#include <Keypad.h>

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

Keypad keypad = Keypad(makeKeymap(keys), rowPins, colPins, ROWS, COLS);
String inputCode = "";
String correctCode = "1234";

void loop() {
  char key = keypad.getKey();
  if (key) {
    inputCode += key;
    Serial.println(inputCode);
    if (inputCode.length() == 4) {
      if (inputCode == correctCode) {
        Serial.println("Access granted.");
        unlockDoor();
      } else {
        Serial.println("Access denied.");
      }
      inputCode = "";
    }
  }
}

6. Enhancing the System with LEDs and Buzzers

• LEDs: You can add LEDs to indicate lock status. A green LED for access granted and a red LED for access denied.
• Buzzer: Add a buzzer to sound an alert when access is denied or granted.

int greenLED = 7;
int redLED = 8;
int buzzer = 9;

void setup() {
  pinMode(greenLED, OUTPUT);
  pinMode(redLED, OUTPUT);
  pinMode(buzzer, OUTPUT);
}

void unlockDoor() {
  digitalWrite(greenLED, HIGH); // Turn on green LED
  tone(buzzer, 1000, 200);      // Sound the buzzer
  myServo.write(0);             // Unlock
  delay(5000);
  digitalWrite(greenLED, LOW);
  myServo.write(90);            // Relock
}

7. Testing and Deployment

• Test the smart lock using both the RFID and keypad methods.
• Mount the lock securely on the door with the servo attached to the locking mechanism.

Conclusion

By following this guide, you’ll be able to build a customizable DIY smart lock using Arduino, RFID, and keypad input. With this setup, you can improve your home security and gain practical experience with Arduino-based projects.