Arduino - Keypad Door Lock

In this tutorial, we learn how to make door lock system with password using keypad and solenoid lock.

When the door is unlocked by a correct password, It keeps the door unlocked for 20 seconds, and then automatically lock the door again. The Arduino code supports multiple passwords.

Hardware Required

1×Arduino UNO or Genuino UNO
1×USB 2.0 cable type A/B
1×Keypad 4x4
1×Solenoid Lock
1×12V Power Adapter
1×DC Power Jack
n×Jumper Wires
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About Keypad and Solenoid Lock

If you do not know about solenoid lock and button (pinout, how it works, how to program ...), learn about them in the following tutorials:

Wiring Diagram

  • Arduino - Door lock with keypad, solenoid lock
  • Arduino, keypad, solenoid lock wiring diagram

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Arduino Code - Door lock system with password using keypad, solenoid lock

/* * Created by * * This example code is in the public domain * * Tutorial page: */ #include <Keypad.h> const int RELAY_PIN = A5; // the Arduino pin, which connects to the IN pin of relay const int ROW_NUM = 4; //four rows const int COLUMN_NUM = 4; //four columns char keys[ROW_NUM][COLUMN_NUM] = { {'1','2','3', 'A'}, {'4','5','6', 'B'}, {'7','8','9', 'C'}, {'*','0','#', 'D'} }; byte pin_rows[ROW_NUM] = {9, 8, 7, 6}; //connect to the row pinouts of the keypad byte pin_column[COLUMN_NUM] = {5, 4, 3, 2}; //connect to the column pinouts of the keypad Keypad keypad = Keypad( makeKeymap(keys), pin_rows, pin_column, ROW_NUM, COLUMN_NUM ); const String password_1 = "1234ABC"; // change your password here const String password_2 = "5642CD"; // change your password here const String password_3 = "4545B"; // change your password here String input_password; void setup(){ Serial.begin(9600); input_password.reserve(32); // maximum input characters is 33, change if needed pinMode(RELAY_PIN, OUTPUT); // initialize pin as an output. digitalWrite(RELAY_PIN, LOW); // lock the door } void loop(){ char key = keypad.getKey(); if (key){ Serial.println(key); if(key == '*') { input_password = ""; // reset the input password } else if(key == '#') { if(input_password == password_1 || input_password == password_2 || input_password == password_3) { Serial.println("password is correct"); digitalWrite(RELAY_PIN, HIGH); // unlock the door for 20 seconds delay(20000); digitalWrite(RELAY_PIN, LOW); // lock the door } else { Serial.println("password is incorrect, try again"); } input_password = ""; // reset the input password } else { input_password += key; // append new character to input password string } } }

Quick Steps

  • Connect Arduino to PC via USB cable
  • Open Arduino IDE, select the right board and port
  • On Arduino IDE, Go to Tools Manage Libraries
  • Arduino add library
  • Search “keypad”, then find the keypad library by Mark Stanley, Alexander Brevig
  • Click Install button to install keypad library.
  • Arduino keypad library
  • Copy the above code and open with Arduino IDE
  • Click Upload button on Arduino IDE to upload code to Arduino
  • In put a wrong password, and then input a correct password
  • See the the lock tongue's state during 20 seconds.


  • In the above code, To make it simple, we used the delay function. It is better to use millis() instead of delay(). See How to use millis() instead of delay()
  • You can add a piezo buzzer to make the beep sound each time keypad is pressed.
  • In the above codes, the door is locked again after 20 seconds. You can replace it by a door sensor. The door is locked when the door sensor detect the door is closed by user.
  • In the above code, the passwords are hard-coded. In the practice, it should be able to add/delete/change passwords dynamically via a special mode. If so, the passwords should be saved on EEPROM memory. The number of passwords can be saved depends on the EEPROM's size. The code will become complicated. If you want to build such system, we provide a coding service. Please feel free to contact us.

Video Tutorial

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