NFC Computer Unlocker





Quit pulling your hair out over incorrect passwords. Using an Arduino Leonardo and Adafruit's NFC shield, you can unlock your computer with an NFC card. The Arduino reads the NFC card's unique identifier and once it receives the correct one, it uses the Arduino Leonardo's keyboard emulation feature to type a password. 

Step 1: Parts Needed

You will need the following parts for this build:
Arduino Leonardo
Adafruit's NFC Shield
NFC Tag (included with shield)
A Small Piece of Hookup Wire
You will optionally need:
More NFC Tags (available from Adafruit)
Tools Needed:
Sharp Knife
Soldering Iron
Wire Cutters and Strippers
Micro USB Cable

Step 2: Hardware

You will need to solder the header pins to the shield and retrace the jumper for this project to work. 
Step One:
Solder the header pins to the shield. The easiest way is to insert the header pins into the Arduino and place the shield on top of the header pins. Solder the header pins on the top of the shield. 
Step Two: 
Cut the jumper between the IRQ pin and Pin 2 using a sharp knife. We need to do this because the NFC shield doesn't communicate with the Arduino Leonardo at Pin 2.  Use a multimeter to check continuity between the two pins. 
Step Three: 
Strip about 1/2" of insulation off of each end of a small piece of wire. Then solder this wire between IRQ and pin 6 on the Arduino. 
Once all of that is done, the NFC shield is ready to communicate with the Arduino. 

Step 3: Software

The software that needs to be uploaded to the Arduino is below. Make sure that you have the Adafruit NFC Library installed. Learn more about that here.

#include <Wire.h>
#include <Adafruit_NFCShield_I2C.h>

#define IRQ 6 // this trace must be cut and rewired!
#define RESET 8

Adafruit_NFCShield_I2C nfc(IRQ, RESET);

//////////////////////////////////// SETUP

void setup() {
  // set up Serial library at 9600 bps
  // find Adafruit RFID/NFC shield

  uint32_t versiondata = nfc.getFirmwareVersion();
  if (! versiondata) {
    Serial.print("Didn't find PN53x board");
    while (1); // halt
  // Got ok data, print it out!
  Serial.print("Found chip PN5"); Serial.println((versiondata>>24) & 0xFF, HEX);
  Serial.print("Firmware ver. "); Serial.print((versiondata>>16) & 0xFF, DEC);
  Serial.print('.'); Serial.println((versiondata>>8) & 0xFF, DEC);
  // configure board to read RFID tags
Keyboard.begin(); //initiate the Keyboard

/////////////////////////////////// LOOP

unsigned digit = 0;

void loop() {
  uint8_t success;
  uint8_t uid[] = { 0, 0, 0, 0, 0, 0, 0 }; // Buffer to store the returned UID
  uint8_t uidLength; // Length of the UID (4 or 7 bytes depending on ISO14443A card type)

  // wait for RFID card to show up!
  Serial.println("Waiting for an ISO14443A Card ...");

  // Wait for an ISO14443A type cards (Mifare, etc.). When one is found
  // 'uid' will be populated with the UID, and uidLength will indicate
  // if the uid is 4 bytes (Mifare Classic) or 7 bytes (Mifare Ultralight)
  success = nfc.readPassiveTargetID(PN532_MIFARE_ISO14443A, uid, &uidLength);

  uint32_t cardidentifier = 0;
  if (success) {
    // Found a card!

    Serial.print("Card detected #");
    // turn the four byte UID of a mifare classic into a single variable #
    cardidentifier = uid[3];
    cardidentifier <<= 8; cardidentifier |= uid[2];
    cardidentifier <<= 8; cardidentifier |= uid[1];
    cardidentifier <<= 8; cardidentifier |= uid[0];

    if (cardidentifier == 606061173) {
              delay(5000); //makes sure the password isn't repeated

Once the code is uploaded, open the serial monitor set at 9600 baud. Place the NFC tag on the shield for a second and then remove it. The serial monitor should say, "Card detected #card number." Copy the unique card number and paste it in the cardidentifier == 606061173 statement in the code. The card number will replace 606061173. Then change the keyboard.write statements to spell out your password one letter at a time. Reupload the code and whenever the NFC tag is placed on the shield it will type your password for you. 

Step 4: 3D Printing

You can optionally 3D print an enclosure to house the Arduino and to mount it onto a desk. The .stl file is on this page. The two screw holes on the case allow a long screw to pass through. This is meant to be mounted underneath a desk. The NFC signal should work as long as the table is thinner than 5cm. 



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    50 Discussions


    4 years ago on Introduction

    I added some simple AES encryption using Davy Landman's AESLib for Arduino; please see my repo here:

    2 replies

    i see, but maybe you should tell that in the instructeable ? :) so people with an uno dont do it, and in the code explain what it should be for uno and leonardo ? :)


    Reply 5 years ago

    Doing this using an arduino UNO is an entirely different matter. The Leonardo is able to act as a HID because of its special AVR chip which combines the actual microprocessor and the processor used for serial communication on an UNO or an Mega (or an 2009, if I am not mistaken). If you have an UNO or Mega available, you can see this second microcontroller for USB communication next to the USB poet. It will have something like Mega8U2 or Mega16U2 written on it. Using such Arduinos as a HID is pony possible by flashing a different firmware onto this chip using something called DFU. This involves cutting a jumper on an UNO R1 and will make your arduino inaccessible for programming until you flash the vanilla firmware onto the chip. Speaking from experience, this is kind of annoying.


    5 years ago on Step 4

    This looks like a nice idea. And it is a great example of the keyboard function of the Leonardo.

    My one concern is that you are storing the password in clear text in the arduino code. If some stole the arduino they'd have your password.

    Have you thought about using the NFC reader as part of a two-factor authentication system? So you would need both the card and a password?

    2 replies

    As far as I know you can't read the code off an Arduino. Also if you 3D print the case it will be bolted to your table :-)

    MihneaVThe Electrodog Show

    Reply 2 years ago

    I think that he meant to say:Someone might steal the arduino,and trigger the kev presses,then in something like notepad,they'll see the password being typed out for them.


    2 years ago

    so the code says uploading then just sits there and never finishes-anyone have that problem?


    3 years ago

    I'm having some problems I hope you can help me with on this project.

    I'm getting this error message.

    Keyboard_NFC_Unlocker:61: error: 'Keyboard' not found. Does your sketch include the line '#include <Keyboard.h>'?

    Keyboard.write('m'); //update with your password!


    exit status 1

    'Keyboard' not found. Does your sketch include the line '#include <Keyboard.h>'?

    Adding #include <keyboard.h> just tells me the file can't be found. Any help would be awesome. Thanks!

    1 reply

    Reply 2 years ago

    Did you ever get answer or figure this out?


    2 years ago

    I have same keyboard error as npro6979

    Can you provide any guidance on how to fix this please?


    3 years ago

    This might be a dumb question, but I don't see how the arduino is connected to the computer after it is programmed? Does the USB have to remain constantly plugged in to work? Or is it programmed to send the password over wifi?

    The reason I asked was, like any nfc card or sticker.... there is an identifier to verify it. Just like the card or sticker, doesn't the phone also have a unique number that we use for payment or file transfer? So in theory the technology should be able to work with few tweaks right? Just was an idea


    Reply 3 years ago on Introduction

    Yes, it should on the condition that the NFC shield mentioned here supports the NFC tech that the phone would emulate. Check this out: