Project tutorial
RFID+Relay+RFID Door Lock Code = RFID PC Switch!

RFID+Relay+RFID Door Lock Code = RFID PC Switch! © GPL3+

A simple RFID controlled relay module to turn your PC on/off.

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Components and supplies

A000066 iso both
Arduino UNO & Genuino UNO
RFID Module (Generic)
I used MFRC522.
Relay Module (Generic)
I used a 5v Single Channel Relay Module
826 04
Male/Female Jumper Wires
7 for the RFID module -> Arduino , 3 For the Relay -> Arduino and 2 For the Relay -> Motherboard.

About this project

If you prefer a Video Version.

This project is about adding an optional security feature besides the password on your personal computer.

I've decided to use an RFID + relay door lock code that I have found on Youtube out of curiosity and because I thought, "Hey! They both have the same modules, maybe the code can be the same, too!"

Basically, you need to get the UID's from the RFID cards or tags/keys first using the example codes from the MFRC522 Library (I used DumpInfo) []. Then, add the UID on the code to allow it to activate the relay and turn on the desktop PC.

The relay is enabled by the RFID card and works with delay counts that are just enough for common push button switches. (I used 500ms delay to turn the PC on). And made the RFID key to initiate the shutdown process (Like when you press the power button for about 5 secs and it will turn off.)

Here is the Project File Link:

Just ask questions if you don't get my explanation. This is my first time here! LOL.


Social Media Links To Follow (I mean, if you want to):

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This is really an RFID Door Lock code. I just used it to power my PC on.
 * ----------------------------------------------------------------------------
 * This sketch uses the MFRC522 library ; see
 * for further details and other examples.
 * NOTE: The library file MFRC522.h has a lot of useful info. Please read it.
 * This sketch show a simple locking mechanism using the RC522 RFID module.
 * ----------------------------------------------------------------------------
 * Typical pin layout used:
 * -----------------------------------------------------------------------------------------
 *             MFRC522      Arduino       Arduino   Arduino    Arduino          Arduino
 *             Reader/PCD   Uno           Mega      Nano v3    Leonardo/Micro   Pro Micro
 * Signal      Pin          Pin           Pin       Pin        Pin              Pin
 * -----------------------------------------------------------------------------------------
 * RST/Reset   RST          9             5         D9         RESET/ICSP-5     RST
 * SPI SS      SDA(SS)      10            53        D10        10               10
 * SPI MOSI    MOSI         11 / ICSP-4   51        D11        ICSP-4           16
 * SPI MISO    MISO         12 / ICSP-1   50        D12        ICSP-1           14
 * SPI SCK     SCK          13 / ICSP-3   52        D13        ICSP-3           15
#include <SPI.h>
#include <MFRC522.h>

#define RST_PIN         9           // Configurable, see typical pin layout above
#define SS_PIN          10          // Configurable, see typical pin layout above

MFRC522 mfrc522(SS_PIN, RST_PIN);   // Create MFRC522 instance.

String read_rfid;                   // Add how many you need and don't forget to include the UID.
String ok_rfid_1="e199312d";        // This is for my main RFID Card. aka. The one I will be using to turn on my PC. Can also be used to shut it down if you want to.
String ok_rfid_2="fbecb673";        // This is for the RFID Keyfob. aka. Shutdown Keyfob. Not advisable tho. Just shutdown your PC normally.
int lock = 7;                       // For the Card.
int lock2 = 7;                      // For the Keyfob.
 * Initialize.
void setup() {
    Serial.begin(9600);         // Initialize serial communications with the PC
    while (!Serial);            // Do nothing if no serial port is opened (added for Arduinos based on ATMEGA32U4)
    SPI.begin();                // Init SPI bus
    mfrc522.PCD_Init();         // Init MFRC522 card

    //Choose which lock below:
    pinMode(lock, OUTPUT);
    pinMode(lock2, OUTPUT);
 * Helper routine to dump a byte array as hex values to Serial.
void dump_byte_array(byte *buffer, byte bufferSize) {
    for (byte i = 0; i < bufferSize; i++) {
        read_rfid=read_rfid + String(buffer[i], HEX);

void open_lock() {
  //Use this routine when working with Relays and Solenoids etc.

void close_lock2() {          // You can also just use the card to shutdown your PC. This is just for those moments that you really need to shut it down quickly. 
  //Use this routine when working with Relays and Solenoids etc.
  digitalWrite(lock2, HIGH);

void loop() {

      // Look for new cards
    if ( ! mfrc522.PICC_IsNewCardPresent())

    // Select one of the cards
    if ( ! mfrc522.PICC_ReadCardSerial())

    dump_byte_array(mfrc522.uid.uidByte, mfrc522.uid.size);
    if (read_rfid==ok_rfid_1) {
      //ok, open the door.

    if (read_rfid==ok_rfid_2) {
      //ok, open the door.
    //Add below as many "keys" as you want
    //if (read_rfid==ok_rfid_2) {
      //also ok, open the door
    //  open_lock();
    // else not needed. Anything else is not ok, and will not open the door...


Visual Wiring Diagram
I made this using Photoshop. The wires have various colors to avoid confusion.
Visual diagram 517kceshx2


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