NFC & logic level problems (pn532)

Other Hardware General Electronics
1

Hi,
I am working on project with Adafruit NFC shield. I'm having problem with accesing NFC shield with IRQ.
Problem is that the interrupt on irq happens after sending commands to pn532 what is pretty normal, but even after sending command and waiting some time the pn532 triggers the IRQ even when the NFC card is not in range...

    //sendACK(); 
    cardToRead = 0;
    Serial.println("IAFC 1");
    delay(100);
    pn532_packetbuffer[0] = 0x4A; /// PN532_COMMAND_INLISTPASSIVETARGET;
    pn532_packetbuffer[1] = 0x01;  // max 1 cards at once (we can set this to 2 later)
    pn532_packetbuffer[2] = 0x00;   ///  PN532_MIFARE_ISO14443A;
    
    Serial.println("IAFC 2");
    delay(100);
    if (!sendCommandCheckAck(pn532_packetbuffer, 3))
      return 0x00; 
      

    delay(100);
    
    Serial.println("IAFC 3");
    delay(100);
 

    attacheInterupt(0,ReadCard,FALLING); 
    return 0x01;
    // Wait for a card to enter the field

after this I do

 attacheInterupt(0,ReadCard,FALLING);

the problem is that interrupt is fired two times, one time it fires without any logical reason and second time when the card gets in range...

What is strange i checked the voltage on the pin used for irq, and I see the non logical Level drop but sometimes I dont see the from card, But both times the interrupt is fired.

Also I am wondering why after sending command for awating card I get sinusinodal voltage level

I hope someone have any idea what is the cause of my problems..