Reading NFC card (PN532) with Arduino Uno

Question

I am trying to detect a RFID card using the NFC-PN532 module and Adafruit_PN532 library.

Initialization code:-

#include <Adafruit_PN532.h>
#include <Wire.h> 
#define SCK (13)
#define MISO (12)
#define MOSI (11)
#define SS (10)
Adafruit_PN532 nfc(SCK, MISO, MOSI, SS);
void setup()
{ 
 Serial.begin(9600);
 Serial.println("Initializing please wait.......");
 delay(3000);
 nfc.begin();
 uint32_t versiondata = nfc.getFirmwareVersion();
 if (! versiondata) 
 {
 Serial.print("Didn't find PN53x board");
 while (1); // halt
 }
 Serial.print("Device Found PN5 Chip"); 
 Serial.println((versiondata>>24) & 0xFF, HEX); 
 Serial.print("Firmware version > "); 
 Serial.print((versiondata>>16) & 0xFF, DEC); 
 Serial.println((versiondata>>8) & 0xFF, DEC);
 nfc.SAMConfig(); //Set to read RFID tags
 Serial.println("Waiting for RFID Card ...");
}

Main loop:-

void loop() 
{
 uint8_t success = 0;
 uint8_t uid[] = { 0, 0, 0, 0, 0, 0, 0 };
 uint8_t uidLength;
 success = nfc.readPassiveTargetID(PN532_MIFARE_ISO14443A, uid, &uidLength);
 if (success) 
 {
 Serial.println("Card Detected!");
 }
 else
 {
 Serial.println("Card Not Detected or Removed!");
 }
}

Whenever i place a valid card on the PN532, Card Detected! is printed on the serial monitor.

However, when i remove the card, Card Not Detected or Removed! does not get printed.

How can i make the program to loop in such a way that it can detect when the card is present/removed?

• Jaromanda X: once you fix this (not sure why it is behaving this way) you wont detect when a card is removed ... you'll detect when a card is not present ... there's a difference :p
• Sandrocottus: @JaromandaX yes, you are right. But then how do i modify the code to detect "card inserted"and "card removed"?
• Jaromanda X: you'd achieve that with code that only prints card removed if this is the first loop after card was present, ... try adding nfc.setPassiveActivationRetries(0x10); to your setup just before nfc.SAMConfig(); - this should stop the code waiting for a card :p

Answer 1

The default behaviour of readPassiveTargetID is to wait "forever" for a card - which is why your code only sees when there is a card present

So, in setup() add nfc.setPassiveActivationRetries(0x10); as follows - comments came from my own code, but I'm sure they were originally in some example or other :p

// Set the max number of retry attempts to read from a card
// This prevents us from waiting forever for a card, which is
// the default behaviour of the PN532.
nfc.setPassiveActivationRetries(0x10);
// configure board to read RFID tags
nfc.SAMConfig();

As for "detecting" removal

void loop() 
{
 static bool wasSuccess = false;
 uint8_t success = 0;
 uint8_t uid[] = { 0, 0, 0, 0, 0, 0, 0 };
 uint8_t uidLength;
 success = nfc.readPassiveTargetID(PN532_MIFARE_ISO14443A, uid, &uidLength);
 if (success) 
 {
 wasSuccess = true;
 Serial.println("Card Detected!");
 }
 else if (wasSuccess)
 {
 wasSuccess = false;
 Serial.println("Card Removed!");
 }
 else
 {
 // you may want to remove this, it will flood the output :p
 Serial.println("Card Not Detected!");
 }
}

• Jaromanda X: @Patrick - including the detection of remove? I ask, because I've been meaning to write some code for my PN532 :p