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 (for USB-A PC)
1	×	USB 2.0 cable type C/B (for USB-C PC)
1	×	RFID/NFC RC522 Kit (reader + tags)
1	×	RFID Key Fob
1	×	RFID Card
1	×	Relay
10	×	Jumper Wires
1	×	(Recommended) Screw Terminal Block Shield for Arduino Uno
1	×	(Recommended) Breadboard Shield For Arduino Uno
1	×	(Recommended) Enclosure For Arduino Uno

Or you can buy the following sensor kits:

1	×	DIYables Sensor Kit (30 sensors/displays)
1	×	DIYables Sensor Kit (18 sensors/displays)

Disclosure: Some links in this section are Amazon affiliate links. If you make a purchase through these links, we may earn a commission at no extra cost to you.
Additionally, some links direct to products from our own brand, DIYables.

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

This image is created using Fritzing. Click to enlarge image

To simplify the setup, the pins of the RC522 module are directly connected to the pins of the Arduino. However, this can cause the Arduino to stop working in certain situations, as the output pins of the Arduino supply 5V while the RC522 module's pins are designed to function at 3.3V. It is therefore advisable to regulate the voltage between the Arduino pins and the RC522 module's pins. For additional information, please refer to the Arduino - RFID RC522 tutorial. The following diagram illustrates how to use resistors to regulate 5V to 3.3V:

Arduino RFID RC522 with voltage regulated wiring diagram

This image is created using Fritzing. Click to enlarge image

※ NOTE THAT:

The order of pins can vary according to manufacturers. ALWAYS use the labels printed on the module. The above image shows the pinout of the modules from DIYables manufacturer.

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 5 #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
It need to install MFRC522 library. See Arduino - RFID/NFC RC522 tutorial

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 5 #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.

Video Tutorial

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The Best Arduino Starter Kit

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Arduino - RFID/NFC - Relay

Hardware Required

About RFID/NFC RC522 Module and Relay

How It Works

Wiring Diagram

Arduino Code - Single RFID/NFC Tag

Quick Steps

Arduino Code - Multiple RFID/NFC Tags

Video Tutorial

The Best Arduino Starter Kit

See Also