Password Lock With Arduino

Introduction: Password Lock With Arduino

This instructable will show you how to make a pass-code lock system using the Arduino Mega board.
What you will need:
--->one Arduino Mega (the arduino uno or duemilianove does not have enough digital pins for this project)
--->one LCD module
--->one Keypad
--->one Battery pack (or you can use the USB cable and PC power)
--->one 10K Ohm potentiometer
--->four 10K Ohm resistors
---> Breadboard
---> hookup wire

Step 1: Wire the LCD to the Arduino

The LCD module has 16 pins.
First of all, connect pins 1 and 16 of the LCD to the ground rail on the Breadboard
Then connect pins 2 and 15 of the LCD to the +5v rail on the breadboard
Now connect the ground rail(should be blue) of the breadboard to a ground pin on the Arduino; 
Connect the +5v rail of the breadboard(this one is red) to one of the +5v pins on the Arduino board.

Now comes the contrast potentiometer which has to be connected to pin 3 of the LCD.
The potentiometer will have 3 pins. Take the middle pin and connect it to pin 3 of the arduino with hookup wire. Connect the othere two pins one to +5v and the other to GND(ground). The order does not matter.

Now let's do a test: power up the arduino. The LCD should light up. If it does then Great! If the LCD does not light up then turn off the power and check the wires. 

Never change, move, or take out wires from the circuit board when the Arduino is powered up. You may permanently damage the Arduino.

If the light works rotate the potentiometer all the way to the right and all the way to the left until you see 2 rows of black squares. That's the contrast. 

Now take out the power and let's hook up the LCD to the Arduino with the signal wires so we can display something on it.
Ready? Let's go!

Connect the pins as follows:
LCD Pin 4   --> Arduino Pin 2
LCD Pin 5   --> Arduino Pin 3
LCD Pin 6   --> Arduino Pin 4
LCD Pin 11 --> Arduino Pin 9
LCD Pin 12 --> Arduino Pin 10
LCD Pin 13 --> Arduino Pin 11
LCD Pin 14 --> Arduino Pin 12

And that should do it for the LCD circuit.
A test code for the the LCD: temporary.

#include <LiquidCrystal.h>

// initialize the library with the numbers of the interface pins
LiquidCrystal lcd(2,3,4,9,10,11,12);

void setup() {
  // set up the LCD's number of columns and rows:
lcd.begin(16, 2);
// Print a message to the LCD.
lcd.print("hello, world!");

void loop() {
// set the cursor to column 0, line 1
// (note: line 1 is the second row, since counting begins with 0):
lcd.setCursor(0, 1);
// print the number of seconds since reset:

Copy and paste it in an arduino environment window, make sure you have the board and serial port set correct and click UPLOAD after you plug in the usb with the arduino.
You will see the TX and RX led's blinking, that means the code is going to the arduino.
push the reset botton once on the arduino, tune the contrast, and you should see Hello World displayed. 
Congratulations! You've got the LCD working! :)

Step 2: Wire the Keypad to the Arduino

OK. Now that we're done with the LCD and we got it working, it's time to connect the keypad to the arduino. This can be a little tricky depending on what type of keyboard you are using. In my case, I used a 3x4 keypad that I had for some time. 
If you have a keyboard that is made especially for connecting to an arduino, then it's easy. You just look at the datasheet for it and it tells you exactly how to hook it up.
If you have a keypad and you have no datasheet for it then hang on cause I was in the same situation.
Mine had on the back a diagram that shows you which pins are connected together when you press a certain key.
If you don't have that, you will have to use a multimeter and figure out which pins are connected together when you press each key. 
To do that, take your multimeter and set it on continuity(the diode symbol).
Then put the test leads on pins 1 and 2 of the keypad. Now press every key until you get continuity. 
Take paper and a pen and write down the key(ex:1, 2, #) and the two pins(ex: 6[1;2]). 
Do so for every key until you get all of them figured out.
Make a table:

That is what I got.
Whatever you get, if you write down the keys in that order you will see the logic in it.
From my table I can see that the row pins are 1,2,3,4; and the column pins are 5,6,7.

Now plug the pins of the keypad in a breadboard and let's start connecting it.
Connect the pins for rows 2 and 3( in my case pins 2 and 3) to +5v through 10K Ohm resistors. Do the same with the pins for column 1 and 3 pins( in my case pins 5 and 7).

If you have an arduino mega, connect the keypad as follows:
Keypad pin row1--> arduino pin 25
Keypad pin row2--> arduino pin 24
Keypad pin row3--> arduino pin 23
Keypad pin row4--> arduino pin 22
Keypad pin column1 --> arduino pin 28
Keypad pin column2 --> arduino pin 27
Keypad pin column3 --> arduino pin 26

(The arduino uno does not have enough digital pins so it does not fit this project.)

That should do it for the keypad. :) we're one step closer to finish. Hang in there. :) Almost done.

Step 3: Preparations for the Code

Before we put in the final code we have to make some modifications.

o to the link above and download the libraries: keypad and password.
They are two files. take the files and put them in /Arduino/Libraries.

if the download does not work for bizarre reasons, go to:

Step 4: Code

Now it's time for the code.
Make sure you have all the wires in place and connect the USB cable.
Upload the following code to the arduino. Copy and paste it in the arduino window just like last time.

#include <Password.h>
#include <LiquidCrystal.h>
#include <Keypad.h>
LiquidCrystal lcd(2,3,4,9,10,11,12);
Password password = Password( "4321" );
const byte ROWS = 4; // Four rows
const byte COLS = 3; // Three columns
// Define the Keymap
char keys[ROWS][COLS] = {
  {'*','0',' ',}
// Connect keypad ROW0, ROW1, ROW2 and ROW3 to these Arduino pins.
byte rowPins[ROWS] = {25, 24, 23, 22}; //connect to the row pinouts of the keypad
byte colPins[COLS] = {28, 27, 26}; //connect to the column pinouts of the keypad
const int buttonPin = 7;
int buttonState = 0;

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

#define ledPin 13

void setup(){
   pinMode(buttonPin, INPUT);
lcd.begin(16, 2);
digitalWrite(ledPin, LOW); // sets the LED on
keypad.addEventListener(keypadEvent); //add an event listener for this keypad

void loop(){
buttonState = digitalRead(buttonPin);
if (buttonState == HIGH) {

//take care of some special events
void keypadEvent(KeypadEvent eKey){
switch (keypad.getState()){
switch (eKey){
case ' ': guessPassword(); break;

void guessPassword(){
if (password.evaluate()){
digitalWrite(ledPin,HIGH); //activates garaged door relay
digitalWrite(ledPin,LOW); //turns off door relay after .5 sec
lcd.print("VALID PASSWORD "); //
password.reset(); //resets password after correct entry

lcd.print("INVALID PASSWORD ");
password.reset(); //resets password after INCORRECT entry

Give it a test: type 4321 then press #.
You should see the message VALID PASSWORD    Welcome

After that the LED on the arduino board will light up for a short time. you can put a lock, or a solenoid instead of the led and there you have it: The Arduino Passcode lock 

If you have any problems or questions regarding this instructable, feel free to post a comment. I will answer as soon as I can.Also, if you like the project, consider voting it in the following contests:
Thanks for reading this 'till the end and I hope you liked it.



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67 Discussions

you can use a arduino uno with not a lot more work just shift in the keypad and or shift out the lcd
try it sometime
i have my uno driving 644 pins (leds)
2X 20x4 lcd's
2 keypads
and about 10 buttons all over the house

Hey Everyone

I have a question about my project and I'll really appreciate any help you can give,

I'm going to programming a software in order to automatically open up 250 doors with FINGERPRINT SCANNER, I mean I've 250 members in a gym and I want to recognize any of them by their fingerprint and then open their related door wardrobe.
So the question is, I don't know after verifying any individual person and understanding the related door, how can I command to the doors to open?
Let me clarify the sentence, Arduino have 16 pins as output and I've 250 doors to control.
I know it's completely ridiculous to dedicate 250 pins to 250 doors but I don't know how to overcome this problem and reduce the pins number!

Thank you in advance for your attention to this matter.

Many thanks

1 reply

Try using some shift registers. Its either those or another microprocessor(could be an arduino) in serial. You could get 256 pins from 16 bit Serial in Parallel out shift register provided you can make 16 serial connections. I would recommend looking for a controller that uses UART Bus.

I hope you find a solution soon!.

Have a good day.

may i have the schematic diagram of your circuit..,tnx:)

What you used pin 7 for (buttonPin)?

how to change input password with keypad (replace current password with new one), I have this problem and I can't solve it. Can you help me ?

What is buttonpin in th Code..?

What is the recommended resistance for the potentiometer? I'm thprying to make it more compact.

1 reply

i am getting error in the code where am i wrong?? i have a mac.. can some one please post the correct version of this code! i need to submit my assignment

#include <Wire.h>

#include <LiquidCrystal_I2C.h>

#include <Keypad.h>

//constants for LEDs

int greenLED = 12;

int redLED = 13;

//set our code

char* ourCode = "1234";

int currentPosition = 0;

//define the keyboard

const byte rows = 4;

const byte cols = 4;

char keys[rows][cols] = {






byte rowPins[rows]= {11,10,9,8};

byte colPins[cols]= {7,6,5,4};

Keypad keypad = Keypad(makeKeymap(keys), rowPins, colPins, rows, cols);

LiquidCrystal_I2C lcd(0x3F,20,4); // Set the LCD I2C address

#define BACKLIGHT_PIN 13

void setup()


lcd.init(); // initialize the lcd


// Print a message to the LCD.



//setup and turn off both LEDs

pinMode(redLED, OUTPUT);

pinMode(greenLED, OUTPUT);

digitalWrite(redLED, LOW);

digitalWrite(greenLED, LOW);


void loop(){

int l;

char key = keypad.getKey();

if (int(key) != 0) {


lcd.print(" . ");


for(l=0; l<=currentPosition; ++l)





if (key == ourCode[currentPosition])



if (currentPosition == 4)



currentPosition = 0;




void invalidCode()


digitalWrite(redLED, HIGH);





lcd.print("** ACCESS DENIED! **");


lcd.print("** INVALID CODE **");




digitalWrite(redLED, LOW);



void unlockDoor()


digitalWrite(greenLED, HIGH);





lcd.print("** ACCESS GRANTED! **");


lcd.print("** WELCOME **");



//add any code to unlock the door here


digitalWrite(greenLED, LOW);



void displayCodeEntryScreen()




lcd.print("Let's Make It Secret");


lcd.print("Code Project...");


lcd.print("Enter Secret Code:");


void clearScreen()



lcd.print(" ");


lcd.print(" ");


lcd.print(" ");


lcd.print(" ");



1 reply

Did you try to indent your code?


Can i get the Schematic Diagram of this project please ? as i am new to this arduino seystems... Thanks!!1!1!


2 years ago

hi..can i use a tack switches instead of a keypad as an improvised keypad for the password?

Can you help me to do this as a user defined or changeable password lock...

HI.. Iam new here.. I have an idea of getting the passcode from the user. Instead of setting the code in the program is there any way that it can be obtained from the user.. if so can i get the code for it.. Thanks in advance

HI.. Iam new here.. I have an idea of getting the passcode from the user. Instead of setting the code in the program is there any way that it can be obtained from the user.. if so can i get the code for it.. Thanks in advance

Hi ,my fellow friends

I want u all to inform that u can use a 10 K ohm variable resistor instead of key pad.

u can asign a variable for the mapped value of the variable resistor. For example -

int x = analogRead ( 1 );

x = map(x, 0, 1023, 0, 28);

this is for A-Z letter map down. We can use if and else or if statements for value of each map. For example-

if ( x = 0 )


lcd.print ( A);


this will make it support Arduino uno.

note : I am a student of class 7 who is very interested in semiconductor ,ic,

and electronics engineering. if mistakes are any pls write it to me. I am from India.

Nc instructions!!

can you help me with my project .. i already have GSM module can you help me how will i connect it into your device??.. if the passwords denied the person will receive a sms that something is opening the door/device..

they have only 3 trials in the password.. then it will send..

so bad english.. >_<

what type of lock can I put on it and could you give me the code for it, because im just a novice at arduino, kind of