NFC Ring Lock Box




Hi everybody!
Welcome to my first instructable! I apologize in advance for my poor level in English.
In this step-by-step guide I am going to teach you how to build a simple and very cheap NFC Ring Lock Box !

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Step 1: What You'll Need

Ok first, the idea was to create a box locked from the inside. Many different designs were described and easy to make with Instructables but I decided to create mine.

It had to be the cheapest possible and be able to fit in the top of the box. Also to not take too much storage space.

Cheap Box. I used an unfinished wooden box because you can paint and decorate it however you want. There are many wooden boxes here. But it was too expensive for me so I went here.

Inside system lock. Mine.

Switch. Rocker

Battery and its MicroUSB/USB cable. Mine. It has to be a 5V battery that can be charged and deliver power simultaneously.

Arduino Nano and its MiniUSB/USB cable. Very cheap.

Servo SG90. Very cheap.

PN532 Elechouse NFC. Best One

NFC RING to unlock the box. Official

Micro USB Female to USB Female Adapter. Like this one.

And for sure you'll also need some Basics Tools: 3 Hands, Screwdriver, Driller, Soldering kit ...

Step 2: Connect the NFC Reader/writter and the Servo SG90 Motor to the Arduino Nano

If you received the same SERVO as me, the 3 pins are stuck together. You must detach them from themselves before continuing.

Connect the red wire to the 5V of the Arduino Nano.
Connect the black to the ground GND.
Connect the white wire to the Digital 3.

For the PN532 you can read this but I will tell you everything you need to know to make it work ;)
First you need to put your PN532 into the I2C mode.
Solder the 4 pin connector.

VCC connect to 3.3V, ground to ground, and Analog 5/SCL and Analog 4/SDA.

Just look at the picture.

Step 3: Software

First you need to download the software to use the Arduino Nano.
And then the libraries files to put in your Library folder in your Arduino folder.
You can find help here and here.
And finaly download my sketch called "Nairod785" for this project.

The only thing you need to change is this line:

if (ringUid=="47d6b2b62880" || ringUid=="47c9b2b62880"){
change it with the Uid of your NFC tags, NFC Ring...

You can get the Uid of your NFC Ring by running on the Arduino the example sketch in the PN532 folder called ISO14443A_uid.

Note: Each tag, so each side of the ring has a different uid, that's why you must scan both of them and then enter the 2 UID.

Upload the sketch to the Arduino Nano and test it.

Step 4: Prepare the Box

I did some wood burning as you can see.
I used my pen to draw the different shapes and my soldering kit to burn the wood a little.
Drilled 2 holes for the "external interface" : power ON/OFF and micro USB female to charge the battery and to have access to the arduino in case we need to change the sketch or debug the box.
Paint it and it is almost finished!
Fix the internal lock system.

Step 5: Putting It All Together

Look at my diagram, you have to connect everything like this.

After testing the reading distance with the PN532 board, I realized that the wood between the ring and the PN532 was too big, so I had to scratch the wood a little to reduce the wood's thickness.

When everything seems to work, find the good position for the SERVO and then fix/glue everything to the wood.

You can add plexiglas to protect the circuit if you want.

Step 6: Finished

Feel free to comment, ask questions.

I would be pleased to help anyone in need of assistance.

Thanks to:
John McLear and Lokki

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    36 Discussions


    1 year ago

    I'm trying something very similar and your code works great with the NFC module and some NFC badges I have. However, when I tried with an NFC ring I bought on Ebay I could not get it to read. I don't see your ring for sale anymore. Can you provide the specifications of the ring so I can purchase a similar one? Thanks for your time.

    1 reply

    Reply 1 year ago

    Hey check this out
    Of course, you can find it on Google by typing NFC Ring
    You're welcome


    3 years ago

    Very good, I used part of your code to solve my problem.

    Do you know how to use an Android with NFC?

    My NFC tag changes every time i read it.

    I would like to use my phone to unlock a door.


    3 years ago

    Hey! Awesome box! I have and RFID/NFC chip in my hand and it only has one number. I put number in both spots and uploaded the script just fine, but when I scan hand nothing happens. Any clues? Thanks


    3 years ago

    when i try to upload i get this error message back, any suggestions, thanks for whatever help you can offer

    Arduino: 1.6.9 (Windows 10), Board: "Arduino Nano, ATmega328"

    C:\Users\mom\Documents\Arduino\libraries\PN532\PN532.cpp: In member function 'uint8_t PN532::mifareclassic_WriteNDEFURI(uint8_t, uint8_t, const char*)':

    C:\Users\mom\Documents\Arduino\libraries\PN532\PN532.cpp:551:56: warning: narrowing conversion of '(((int)len) + 5)' from 'int' to 'uint8_t {aka unsigned char}' inside { } [-Wnarrowing]

    uint8_t sectorbuffer1[16] = {0x00, 0x00, 0x03, len + 5, 0xD1, 0x01, len + 1, 0x55, uriIdentifier, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00};


    C:\Users\mom\Documents\Arduino\libraries\PN532\PN532.cpp:551:77: warning: narrowing conversion of '(((int)len) + 1)' from 'int' to 'uint8_t {aka unsigned char}' inside { } [-Wnarrowing]

    uint8_t sectorbuffer1[16] = {0x00, 0x00, 0x03, len + 5, 0xD1, 0x01, len + 1, 0x55, uriIdentifier, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00};


    C:\Users\mom\Documents\Arduino\libraries\PN532\snep.cpp: In member function 'int16_t SNEP::read(uint8_t*, uint8_t, uint16_t)':

    C:\Users\mom\Documents\Arduino\libraries\PN532\snep.cpp:82:31: warning: left shift count >= width of type [enabled by default]

    uint32_t length = (buf[2] << 24) + (buf[3] << 16) + (buf[4] << 8) + buf[5];


    C:\Users\mom\Documents\Arduino\libraries\PN532\snep.cpp:82:48: warning: left shift count >= width of type [enabled by default]

    uint32_t length = (buf[2] << 24) + (buf[3] << 16) + (buf[4] << 8) + buf[5];


    C:\Program Files (x86)\Arduino\hardware\tools\avr/bin/avr-ar: unable to rename 'core\core.a'; reason: Permission denied

    exit status 1

    Error compiling for board Arduino Nano.

    Invalid library found in C:\Program Files (x86)\Arduino\libraries\Nairod_files: C:\Program Files (x86)\Arduino\libraries\Nairod_files

    Invalid library found in C:\Program Files (x86)\Arduino\libraries\Nairod_files: C:\Program Files (x86)\Arduino\libraries\Nairod_files


    3 years ago

    Hello friend can i ask after connecting the servo with arduino and pn532 together but when run the ISO14443A uid to get my uid it gives me Error while setting serial port parameters: 9,600 N 8 1 i want to know where is the error thanks


    Reply 3 years ago

    You probably can but I recommend using the new KeyDuino made especially for the NFC ring ;)


    Reply 3 years ago

    Thanks!! but keyduino and pn532 it's not in my country i found this after searching i'm just asking if it's ok
    And i'll use tag instead of ring


    3 years ago

    Friend i have a lockbox it has locked because the battery is low thats why i went to shop to bring the battery but my friend has locked the lockerbox. In side the lockerbox. Ha no battery so i can not open it you know how to open means pless call me in this number 971568629552 because in the locker inside has my friends passports,visa all so i hope u can help me plesss

    1 reply

    Reply 3 years ago

    Call me on Skype as you as you can, my user ID is victus61


    3 years ago

    Cannot upload library. It says "library invalid". How can that be? Any ideas?


    4 years ago on Introduction

    So do you turn on the circuit to activate the reader, or can you leave it on? I imagine the battery wouldn't last long if the arduino is always waiting for the ring. If so, any tips on how to save on battery drain?


    4 years ago on Introduction


    I like your project, it is very interesting. Since you have so much experience with NFC and locks, can you tell me if the whole system can be miniaturized to fit a tube the size of an electric tooth brusk?

    Thank you and don't stop inventing cool ideas.


    1 reply

    Reply 4 years ago

    Hey Joe! Thanks for the compliments, and the answer to your question is: yes for sure! Well actually you need a NFL antenna to read the tag or the ring, and every Antena I saw on the market still big. But you still have a chance with the KeyDuino, check it out on the NFC ring forum. It's a minimalist NFC Ring reader built with arguing and USB!

    If you have more question, Pm me :)


    4 years ago on Introduction


    Very impressive project

    I'm wondering if i can just read/write using this NFC

    because i have exactly the same one you use (the red one) but i couldn't find a single info or a way to do it

    Thanx in advance

    By the way I'm using Arduino mega 2560

    2 replies

    Reply 4 years ago on Introduction

    Of course you can read and write with this module PN532.
    Any arduino will do the job I guess:)
    Download the PN532 Elechouse library


    4 years ago on Introduction


    I am having a bit of a problem with the software. When I found my rings NFC UID it was

    0x4 0x72 0x87 0xBA 0x34 0x35 0x80 - using iso14443a_uid code

    But for your code, you have it as a 12 digit number. which is not the case for my ring apparently. As well, if I wanted to use a UID with Length 4, how would I change the code?

    please and thanks!

    1 reply

    Reply 4 years ago

    Your UID is 47482ba343580
    Just delete the 0x and put the letters in minuscule. :)