Connect RFID Module to NodeMCU ESP8266 to Read Key Cards and Control LED

This tutorial covers using NodeMCU ESP8266 with the RFID RC522 module (13.56MHz) to read card UID and use it as a trigger to turn an LED on and off.

Required Components

• NodeMCU ESP8266 V2 (CP2102)
• RFID Reader RC522 with key card
• Micro USB cable for uploading code
• Breadboard 830 points
• Jumper wires (male-male, male-female)
• LED 5mm red with 220 Ohm resistor

Wiring NodeMCU ESP8266 to RFID RC522

Connect the wires between NodeMCU ESP8266 and RFID RC522 module as follows:

NodeMCU ESP8266	RFID RC522
3.3V	3.3V
GND	GND
D7 (GPIO13)	MOSI
D6 (GPIO12)	MISO
D5 (GPIO14)	SCK
D2 (GPIO4)	SDA (SS)
D1 (GPIO5)	RST

Note that we use 3.3V from the board to power the RFID module, which matches the RC522 requirement of 3.3V supply.

Wiring LED to NodeMCU ESP8266

For the LED, connect a 220 Ohm resistor in series with the LED and wire it to the board as follows:

NodeMCU ESP8266	LED Circuit
D0 (GPIO16)	LED anode (through R 220 Ohm)
GND	LED cathode

The resistor limits current to protect the LED from damage.

Installing MFRC522 Library for Arduino IDE

1. Open Arduino IDE
2. Go to Sketch > Include Library > Manage Libraries
3. Search for “MFRC522”
4. Install the MFRC522 library that supports ESP8266

After installation, you can include the library in your code.

Code to Read RFID Card UID

Before writing the LED control code, we need to read the UID of the card you want to use.

#include <SPI.h>
#include <MFRC522.h>

// Define pins connected to RFID
#define SS_PIN 4    // D2
#define RST_PIN 5   // D1

MFRC522 rfid(SS_PIN, RST_PIN);

void setup() {
  Serial.begin(9600);
  SPI.begin();
  rfid.PCD_Init();
  Serial.println("Ready to read RFID card...");
}

void loop() {
  // Check if a card is present
  if (!rfid.PICC_IsNewCardPresent()) {
    return;
  }
  
  // Read card data
  if (!rfid.PICC_ReadCardSerial()) {
    return;
  }
  
  // Print UID to Serial Monitor
  Serial.print("UID: ");
  for (byte i = 0; i < rfid.uid.size; i++) {
    Serial.print(rfid.uid.uidByte[i]);
    Serial.print(" ");
  }
  Serial.println();
  
  rfid.PICC_HaltA();  // Stop reading card temporarily
}

Upload this code to the board, then open Serial Monitor at 9600 baud rate. Tap the key card on the reader and you will see the UID displayed. Write down this UID for the next step.

Code to Control LED with RFID Card

Take the UID from the previous step and insert it into the code to check if the tapped card matches the registered one.

#include <SPI.h>
#include <MFRC522.h>

#define SS_PIN 4    // D2
#define RST_PIN 5   // D1
#define LED_PIN 16  // D0

MFRC522 rfid(SS_PIN, RST_PIN);

// Enter your card's UID here
// *** Replace these values with your card's UID ***
byte authorizedUID[] = {166, 233, 165, 29, 247};
byte uidSize = 5;

bool ledState = false;

void setup() {
  Serial.begin(9600);
  SPI.begin();
  rfid.PCD_Init();
  pinMode(LED_PIN, OUTPUT);
  Serial.println("RFID LED Control Ready");
}

void loop() {
  if (!rfid.PICC_IsNewCardPresent()) {
    return;
  }
  
  if (!rfid.PICC_ReadCardSerial()) {
    return;
  }
  
  // Check if UID matches the registered card
  if (uidSize == rfid.uid.size) {
    bool match = true;
    for (byte i = 0; i < uidSize; i++) {
      if (authorizedUID[i] != rfid.uid.uidByte[i]) {
        match = false;
        break;
      }
    }
    
    if (match) {
      // Valid card -> toggle LED state
      ledState = !ledState;
      digitalWrite(LED_PIN, ledState ? HIGH : LOW);
      Serial.println(ledState ? "LED ON" : "LED OFF");
    } else {
      // Invalid card
      Serial.println("Unauthorized card");
    }
  }
  
  rfid.PICC_HaltA();
  delay(500);  // Delay to prevent repeated reads
}

Upload this code and try tapping the card with the matching UID. The LED will turn on. Tapping another card will not trigger the LED.

Code Adjustments Required

• Line 12: Change authorizedUID values to match your card’s UID
• Line 13: Update uidSize to match your card’s UID length
• To support multiple cards, create a 2D array to store multiple UIDs

Summary

1. Wire RFID RC522 to NodeMCU ESP8266 according to the connection table
2. Install the MFRC522 library
3. Upload the UID reading code to extract your card’s UID
4. Insert the UID into the LED control code
5. Test by tapping the card on the reader. If valid, the LED turns on; if not, nothing happens

Once you understand the principle, you can adapt this to control relays, motors, or other devices instead of an LED.