Password Based Door Lock System using Arduino is a high-security project where a secure password will act as a door unlocking system. Traditional lock systems using mechanical lock and key mechanisms are being replaced by new advanced techniques of locking systems. These techniques are an integration of mechanical and electronic devices and are highly intelligent. One of the prominent features of these innovative lock systems is high efficiency.

Such an automatic lock system consists of an electronic control assembly, which controls the output load through a password. This output load will be an electric motor to open the security gate.

This system demonstrates a Password-based Door Lock System using Arduino, wherein once the correct code or password is entered, the door is opened, the concerned person is allowed access to the secured area. Again, if another person arrives, it will ask to enter the password. If the password is wrong, then the door would remain closed, it will employ an audible alarm to alert the security services.

The main component in the circuit is Arduino. In this project, a 4×4 Matrix Keypad is used to enter the password and a 16x2 alphanumeric LCD to display the password and final status of the person. The password which is entered is compared with the predefined password.

If the entered password is correct, then the system opens the door by rotating the door electric motor and displays “The password is correct” on LCD.

If the password is wrong, then the door remains closed, and it will employ an audible alarm to alert the security services and displays “The password is incorrect” on LCD.

The link of working project is given below.

https://youtu.be/QdsK_zng5qE

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🛠️ เจาะลึกเบื้องหลังการทำงาน (Deep Dive / Technical Analysis)

Basic button projects use one pin per button. A full numeric keypad has 16 buttons. The High Security Keypad System introduces the concept of structural "Matrix Scanning." By utilizing the <Keypad.h> library, the programmer builds an array that scans rows and columns horizontally and vertically, allowing a massive amount of buttons to be read using minimal Arduino pins.

The Row/Column Sweeping Matrix

A 4x4 Membrane Keypad does not have 16 wires. It has exactly 8 wires (4 Rows, 4 Columns).

1. The C++ code tells the Arduino to apply 5V exclusively to Row 1.
2. It then reads all four Columns (C1, C2, C3, C4). If column 2 is HIGH, the code mathematically deduces: "Row 1 + Col 2 = The Number 2 was pressed!"
3. The Arduino then turns Row 1 OFF, and puts 5V into Row 2. It scans the columns again.
4. It does this continuous, chaotic sweeping sequence 1,000 times a second. It is totally invisible to the human eye!

Password String Concatenation and Comparison

The Arduino must catch multiple key presses and build them into a password.

• You declare a massive char buffer array: char inputPassword[5];.
• As the user types 1-2-3-4, the Arduino slots them into index 0, index 1...
• The Execution Trap: You cannot easily compare two arrays in C++ by just using ==. You must utilize strcmp() (String Compare).

char masterPassword[5] = "890A"; // The secret code
if (strcmp(inputPassword, masterPassword) == 0) { // If the result is 0, they match perfectly!
  UnlockSafeDoor();
} else {
  TriggerRedLEDAlarm();
}

Security Mechanism Components

• Arduino Uno/Nano (Keypads consume massive pin counts, Uno is preferable).
• 4x4 Membrane or Tactile Matrix Keypad (8-pin output).
• 12V Solenoid Deadbolt driven by a 5V relay module to physically actuate the door mechanism!
• A custom Clear() button function (Often assigned to the '*' key) allowing the user to wipe the inputPassword array if they make a typo!