RFID check

Projects Programming
19 
 for (int i=0; i<4; i++)
      if(memcmp(data,tag1,4)==0) tag1_card = true;

You only need to do the memcmp() once.

     if(memcmp(data,tag1,4)==0) tag1_card = true;
        
    if (tag1_card) {
      digitalWrite(6,HIGH);
      delay(500);
      digitalWrite(6,LOW);
      tag1_card=false;
    }

You don't need to set a flag, then immediately afterwards check the flag.