Hi!
I'm working on a NFC-project (Near Field Communication) with the Adafruit PN532 RFID/NFC shield which is on top of my Arduino Mega 2560 R3.
Adafruit PN532: Adafruit PN532 NFC/RFID Controller Shield for Arduino + Extras : ID 789 : $39.95 : Adafruit Industries, Unique & fun DIY electronics and kits
I've been using it to read 2 different Mifare Classic tags which I've added data to through my Android phone. Mainly just a simple word to each card.
What I'm planning to do is to turn on 2 different LEDs based on what card is in front of the NFC-antenna. I'm wondering how to read the data from the serial monitor(or any other way) and use it to ignite them.
The red line is the Hex for the word "bensin" if I'm not entirely mistaken. How can I access/use that information to ignite a LED?
I've been using an example from the Adafruit to get a memorydump from the tags:
#include <Wire.h>
#include <SPI.h>
#include <Adafruit_PN532.h>
// If using the breakout with SPI, define the pins for SPI communication.
#define PN532_SCK (2)
#define PN532_MOSI (3)
#define PN532_SS (4)
#define PN532_MISO (5)
// If using the breakout or shield with I2C, define just the pins connected
// to the IRQ and reset lines. Use the values below (2, 3) for the shield!
#define PN532_IRQ (2)
#define PN532_RESET (3) // Not connected by default on the NFC Shield
//Define pins for LED
int bensin = 51;
int diesel = 53;
// Uncomment just _one_ line below depending on how your breakout or shield
// is connected to the Arduino:
// Use this line for a breakout with a SPI connection:
//Adafruit_PN532 nfc(PN532_SCK, PN532_MISO, PN532_MOSI, PN532_SS);
// Use this line for a breakout with a hardware SPI connection. Note that
// the PN532 SCK, MOSI, and MISO pins need to be connected to the Arduino's
// hardware SPI SCK, MOSI, and MISO pins. On an Arduino Uno these are
// SCK = 13, MOSI = 11, MISO = 12. The SS line can be any digital IO pin.
//Adafruit_PN532 nfc(PN532_SS);
// Or use this line for a breakout or shield with an I2C connection:
Adafruit_PN532 nfc(PN532_IRQ, PN532_RESET);
void setup(void) {
pinMode(bensin, OUTPUT);
pinMode(diesel, OUTPUT);
// has to be fast to dump the entire memory contents!
Serial.begin(115200);
Serial.println("Looking for PN532...");
nfc.begin();
uint32_t versiondata = nfc.getFirmwareVersion();
if (! versiondata) {
Serial.print("Didn't find PN53x board");
while (1); // halt
}
// Got ok data, print it out!
Serial.print("Found chip PN5"); Serial.println((versiondata>>24) & 0xFF, HEX);
Serial.print("Firmware ver. "); Serial.print((versiondata>>16) & 0xFF, DEC);
Serial.print('.'); Serial.println((versiondata>>8) & 0xFF, DEC);
// configure board to read RFID tags
nfc.SAMConfig();
Serial.println("Waiting for an ISO14443A Card ...");
}
void loop(void) {
uint8_t success; // Flag to check if there was an error with the PN532
uint8_t uid[] = { 0, 0, 0, 0, 0, 0, 0 }; // Buffer to store the returned UID
uint8_t uidLength; // Length of the UID (4 or 7 bytes depending on ISO14443A card type)
uint8_t currentblock; // Counter to keep track of which block we're on
bool authenticated = false; // Flag to indicate if the sector is authenticated
uint8_t data[16]; // Array to store block data during reads
// Keyb on NDEF and Mifare Classic should be the same
uint8_t keyuniversal[6] = { 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF };
// Wait for an ISO14443A type cards (Mifare, etc.). When one is found
// 'uid' will be populated with the UID, and uidLength will indicate
// if the uid is 4 bytes (Mifare Classic) or 7 bytes (Mifare Ultralight)
success = nfc.readPassiveTargetID(PN532_MIFARE_ISO14443A, uid, &uidLength);
if (success) {
// Display some basic information about the card
Serial.println("Found an ISO14443A card");
Serial.print(" UID Length: ");Serial.print(uidLength, DEC);Serial.println(" bytes");
Serial.print(" UID Value: ");
nfc.PrintHex(uid, uidLength);
Serial.println("");
if (uidLength == 4)
{
// We probably have a Mifare Classic card ...
Serial.println("Seems to be a Mifare Classic card (4 byte UID)");
// Now we try to go through all 16 sectors (each having 4 blocks)
// authenticating each sector, and then dumping the blocks
for (currentblock = 0; currentblock < 64; currentblock++)
{
// Check if this is a new block so that we can reauthenticate
if (nfc.mifareclassic_IsFirstBlock(currentblock)) authenticated = false;
// If the sector hasn't been authenticated, do so first
if (!authenticated)
{
// Starting of a new sector ... try to to authenticate
Serial.print("------------------------Sector ");Serial.print(currentblock/4, DEC);Serial.println("-------------------------");
if (currentblock == 0)
{
// This will be 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF for Mifare Classic (non-NDEF!)
// or 0xA0 0xA1 0xA2 0xA3 0xA4 0xA5 for NDEF formatted cards using key a,
// but keyb should be the same for both (0xFF 0xFF 0xFF 0xFF 0xFF 0xFF)
success = nfc.mifareclassic_AuthenticateBlock (uid, uidLength, currentblock, 1, keyuniversal);
}
else
{
// This will be 0xFF 0xFF 0xFF 0xFF 0xFF 0xFF for Mifare Classic (non-NDEF!)
// or 0xD3 0xF7 0xD3 0xF7 0xD3 0xF7 for NDEF formatted cards using key a,
// but keyb should be the same for both (0xFF 0xFF 0xFF 0xFF 0xFF 0xFF)
success = nfc.mifareclassic_AuthenticateBlock (uid, uidLength, currentblock, 1, keyuniversal);
}
if (success)
{
authenticated = true;
}
else
{
Serial.println("Authentication error");
}
}
// If we're still not authenticated just skip the block
if (!authenticated)
{
Serial.print("Block ");Serial.print(currentblock, DEC);Serial.println(" unable to authenticate");
}
else
{
// Authenticated ... we should be able to read the block now
// Dump the data into the 'data' array
success = nfc.mifareclassic_ReadDataBlock(currentblock, data);
if (success)
{
// Read successful
Serial.print("Block ");Serial.print(currentblock, DEC);
if (currentblock < 10)
{
Serial.print(" ");
}
else
{
Serial.print(" ");
}
// Dump the raw data
nfc.PrintHexChar(data, 16);
}
else
{
// Oops ... something happened
Serial.print("Block ");Serial.print(currentblock, DEC);
Serial.println(" unable to read this block");
}
}
}
}
else
{
Serial.println("Ooops ... this doesn't seem to be a Mifare Classic card!");
}
}
// Wait a bit before trying again
Serial.println("\n\nSend a character to run the mem dumper again!");
Serial.flush();
while (!Serial.available());
while (Serial.available()) {
Serial.read();
}
Serial.flush();
}
Anyways, this is my first post in here. I'm not very experienced yet, but I'm hoping to become. Really enjoying fiddling with my Mega 
Apologizes in advanced if this is a stupid question, but I'm having trouble finding the solution.