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Using Smartphont to Read NFD tag

What is NFC?

NFC (Near Field Communication) is a short-range wireless technology that allows two electronic devices to communicate when they are within a few centimeters of each other. It’s most commonly used in contactless payments, digital keycards, smart tags, and tap-to-share features. NFC works by using magnetic field induction and doesn’t require pairing like Bluetooth — just a simple tap is enough to exchange data.

In this tutorial, we are using an iPhone to tap on the NTAG203 to open up a website.

Wiring and Library

We will be using DFRobot PN532 module, please refer to this tutorial. We will be using Adafruit_PN532 library, we have a tutorial on how to install a library here.

Types of Tag

In this tutorial, we are using NTAG203, NTAG215 or NTAG216 should work fine as well. You cannot use MIFARE Classic tag or card.

Code for Writing Data

#include <Wire.h>
#include <Adafruit_PN532.h>

#define SDA_PIN A4
#define SCL_PIN A5

Adafruit_PN532 nfc(SDA_PIN, SCL_PIN);

void setup(void) {
  Serial.begin(115200);
  Serial.println("Starting NFC writer with Adafruit PN532");

  nfc.begin();

  uint32_t versiondata = nfc.getFirmwareVersion();
  if (!versiondata) {
    Serial.println("Didn't find PN53x board");
    while (1);
  }

  nfc.SAMConfig(); // configure board to read RFID
  Serial.println("Waiting for an NFC tag...");
}

void loop(void) {
  uint8_t uid[] = { 0 };
  uint8_t uidLength;

  if (nfc.readPassiveTargetID(PN532_MIFARE_ISO14443A, uid, &uidLength)) {
    Serial.println("Tag detected!");

    const char *url = "youtube.com"; // Keep short due to 144 byte limit & omit the "https://" part
    uint8_t urlPrefix = 0x01; // 0x01 = http://www.

    // Build NDEF URI record
    uint8_t urlLength = strlen(url);
    uint8_t payloadLength = 1 + urlLength; // Prefix + URL

    uint8_t ndef[] = {
      0xD1,  // MB, ME, SR, TNF=0x01 (well-known)
      0x01,  // Type Length = 1
      payloadLength, // Payload Length
      0x55,  // Type = 'U'
      urlPrefix // URL Prefix
    };

    uint8_t messageLength = sizeof(ndef) + urlLength;
    uint8_t totalLength = messageLength + 3; // TLV: 0x03 len + msg + 0xFE

    uint8_t full[totalLength];
    full[0] = 0x03;               // NDEF Message TLV tag
    full[1] = messageLength;      // Length of NDEF message
    memcpy(&full[2], ndef, sizeof(ndef));
    memcpy(&full[2 + sizeof(ndef)], url, urlLength);
    full[totalLength - 1] = 0xFE; // Terminator TLV

    // Write to tag starting at page 4
    int page = 4;
    for (int i = 0; i < totalLength; i += 4) {
      uint8_t buffer[4] = {0x00, 0x00, 0x00, 0x00};
      for (int j = 0; j < 4 && (i + j) < totalLength; j++) {
        buffer[j] = full[i + j];
      }

      if (!nfc.ntag2xx_WritePage(page, buffer)) {
        Serial.print("Failed writing to page ");
        Serial.println(page);
        return;
      }
      page++;
    }

    Serial.println("✅ Wrote NDEF URL to NTAG203 successfully!");
    delay(5000); // prevent immediate re-trigger
  }
}
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