Arduino - RFID/NFC - Relay

In this tutorial, we are going to learn how to use RFID/NFC tag to activate relay using Arduino. You can extend this tutorial by using the relay to control motor, actuator...

Hardware Required

1×Arduino UNO or Genuino UNO
1×USB 2.0 cable type A/B
1×RFID/NFC RC522 Kit (reader + tags)
1×Relay
10×Jumper Wires
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About RFID/NFC RC522 Module and Relay

If you do not know about RFID/NFC RC522 Module and relay (pinout, how it works, how to program ...), learn about them in the following tutorials:

How It Works

  • The UIDs of some RFID/NFC tags are preset in Arduino code
  • User taps an RFID/NFC tag on RFID/NFC reader
  • The reader reads UID from the tag.
  • Arduino gets the UID from the reader
  • Arduino compares the read UID with the predefined UIDs
  • If the UID is matched with one of the predefined UIDs, Arduino activates the relay.

Wiring Diagram

Arduino RFID RC522 relay wiring diagram

Image is developed using Fritzing. Click to enlarge image

Arduino Code - Single RFID/NFC Tag

/* * Created by ArduinoGetStarted.com * * This example code is in the public domain * * Tutorial page: https://arduinogetstarted.com/tutorials/arduino-rfid-nfc-relay */ #include <SPI.h> #include <MFRC522.h> #define SS_PIN 10 #define RST_PIN 9 #define RELAY_PIN A5 // the Arduino pin connects to relay MFRC522 rfid(SS_PIN, RST_PIN); byte authorizedUID[4] = {0xFF, 0xFF, 0xFF, 0xFF}; void setup() { Serial.begin(9600); SPI.begin(); // init SPI bus rfid.PCD_Init(); // init MFRC522 pinMode(RELAY_PIN, OUTPUT); // initialize pin as an output. digitalWrite(RELAY_PIN, LOW); // deactivate the relay Serial.println("Tap RFID/NFC Tag on reader"); } void loop() { if (rfid.PICC_IsNewCardPresent()) { // new tag is available if (rfid.PICC_ReadCardSerial()) { // NUID has been readed MFRC522::PICC_Type piccType = rfid.PICC_GetType(rfid.uid.sak); if (rfid.uid.uidByte[0] == authorizedUID[0] && rfid.uid.uidByte[1] == authorizedUID[1] && rfid.uid.uidByte[2] == authorizedUID[2] && rfid.uid.uidByte[3] == authorizedUID[3] ) { Serial.println("Authorized Tag"); digitalWrite(RELAY_PIN, HIGH); // activate the relay for 2 seconds delay(2000); digitalWrite(RELAY_PIN, LOW); // deactivate the relay } else { Serial.print("Unauthorized Tag with UID:"); for (int i = 0; i < rfid.uid.size; i++) { Serial.print(rfid.uid.uidByte[i] < 0x10 ? " 0" : " "); Serial.print(rfid.uid.uidByte[i], HEX); } Serial.println(); } rfid.PICC_HaltA(); // halt PICC rfid.PCD_StopCrypto1(); // stop encryption on PCD } } }

Quick Steps

Because UID is usually not printed on RFID/NFC tag, The first step we need to do is to find out the tag's UID. This can be done by:

  • Copy the above code and open with Arduino IDE
  • Click Upload button on Arduino IDE to upload code to Arduino
  • Open Serial Monitor
  • Tap an RFID/NFC tag on RFID-RC522 module
  • Get UID on Serial Monitor
  • COM6
    Send
    Tap RFID/NFC tag on reader Unauthorized Tag with UID: 3A C9 6A CB
    Autoscroll Show timestamp
    Clear output
    9600 baud  
    Newline  

After having UID:

  • Update UID in the line 18 of the above code. For example, change byte authorizedUID[4] = {0xFF, 0xFF, 0xFF, 0xFF}; TO byte authorizedUID[4] = {0x3A, 0xC9, 0x6A, 0xCB};
  • Upload the code to Arduino again
  • Tap an RFID/NFC tag on RFID-RC522 module
  • See output on Serial Monitor
  • COM6
    Send
    Tap RFID/NFC tag on reader Authorized Tag
    Autoscroll Show timestamp
    Clear output
    9600 baud  
    Newline  
  • Tap another RFID/NFC tag on RFID-RC522 module
  • See output on Serial Monitor
  • COM6
    Send
    Tap RFID/NFC tag on reader Authorized Tag Unauthorized Tag with UID: BD 1E 1D 00
    Autoscroll Show timestamp
    Clear output
    9600 baud  
    Newline  

※ NOTE THAT:

  • To make it easy to test, The active time is 2 seconds, it should be increased in practical use/demonstration

Arduino Code - Multiple RFID/NFC Tags

We can allow multiple RFID/NFC tags to activate the relay. The below code uses two tags as an example.

/* * Created by ArduinoGetStarted.com * * This example code is in the public domain * * Tutorial page: https://arduinogetstarted.com/tutorials/arduino-rfid-nfc-relay */ #include <SPI.h> #include <MFRC522.h> #define SS_PIN 10 #define RST_PIN 9 #define RELAY_PIN A5 // the Arduino pin connects to relay MFRC522 rfid(SS_PIN, RST_PIN); byte authorizedUID1[4] = {0x3A, 0xC9, 0x6A, 0xCB}; byte authorizedUID2[4] = {0x30, 0x01, 0x8B, 0x15}; void setup() { Serial.begin(9600); SPI.begin(); // init SPI bus rfid.PCD_Init(); // init MFRC522 pinMode(RELAY_PIN, OUTPUT); // initialize pin as an output. digitalWrite(RELAY_PIN, LOW); // deactivate the relay Serial.println("Tap RFID/NFC Tag on reader"); } void loop() { if (rfid.PICC_IsNewCardPresent()) { // new tag is available if (rfid.PICC_ReadCardSerial()) { // NUID has been readed MFRC522::PICC_Type piccType = rfid.PICC_GetType(rfid.uid.sak); if (rfid.uid.uidByte[0] == authorizedUID1[0] && rfid.uid.uidByte[1] == authorizedUID1[1] && rfid.uid.uidByte[2] == authorizedUID1[2] && rfid.uid.uidByte[3] == authorizedUID1[3] ) { Serial.println("Authorized Tag 1"); digitalWrite(RELAY_PIN, HIGH); // activate the relay for 2 seconds delay(2000); digitalWrite(RELAY_PIN, LOW); // deactivate the relay } else if (rfid.uid.uidByte[0] == authorizedUID2[0] && rfid.uid.uidByte[1] == authorizedUID2[1] && rfid.uid.uidByte[2] == authorizedUID2[2] && rfid.uid.uidByte[3] == authorizedUID2[3] ) { Serial.println("Authorized Tag 2"); digitalWrite(RELAY_PIN, HIGH); // activate the relay for 2 seconds delay(2000); digitalWrite(RELAY_PIN, LOW); // deactivate the relay } else { Serial.print("Unauthorized Tag with UID:"); for (int i = 0; i < rfid.uid.size; i++) { Serial.print(rfid.uid.uidByte[i] < 0x10 ? " 0" : " "); Serial.print(rfid.uid.uidByte[i], HEX); } Serial.println(); } rfid.PICC_HaltA(); // halt PICC rfid.PCD_StopCrypto1(); // stop encryption on PCD } } }

Do the similar steps as the above, and then tap one by one tag on RFID-RC522 module. The result on Serial Monitor looks like below:

COM6
Send
Tap RFID/NFC tag on reader Authorized Tag 2 Authorized Tag 1
Autoscroll Show timestamp
Clear output
9600 baud  
Newline  

You can extend the above code for three, four, or more tags.

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