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/*My project is a Library management system using rfid cards. Im trying to generate a code wherein User first scan a book and then the record will be pushed in Issued_Books table in Firebase . Then the user scans his id to ensure that the book will be issued on his/her id. But in my program is scanning only books id. It fails to scan users Id after that. Im a beginner so can anyone guide me? */

//My loop code is as following:

void loop() {


  if ( !mfrc522.PICC_IsNewCardPresent() ) {
    delay(50);
    return;
  }

  if ( !mfrc522.PICC_ReadCardSerial() ) {
    delay(50);
    return;
  }
String book; 

  for ( byte i = 0; i< mfrc522.uid.size; i++ ) {
    Serial.print(mfrc522.uid.uidByte[i] < 0x10 ? " 0" : " ");
    Serial.print(mfrc522.uid.uidByte[i], HEX);
    book.concat(String(mfrc522.uid.uidByte[i] < 0x10 ? " 0" : " "));
    book.concat(String(mfrc522.uid.uidByte[i], HEX));}
    book.toUpperCase();

    Firebase.pushString("Issued_Books/Book_rfid",book);

      Serial.println();

  if ( !mfrc522.PICC_IsNewCardPresent() ) {
    delay(50);
    return;
  }

  if ( !mfrc522.PICC_ReadCardSerial() ) {
    delay(50);
    return;
  }
  String user;

  //Serial.print("Scan your id: ");
    for ( byte i = 0; i< mfrc522.uid.size; i++ ) {
    Serial.print(mfrc522.uid.uidByte[i] < 0x10 ? " 0" : " ");
    Serial.print(mfrc522.uid.uidByte[i], HEX);
    user.concat(String(mfrc522.uid.uidByte[i] < 0x10 ? " 0" : " "));
    user.concat(String(mfrc522.uid.uidByte[i], HEX));}
    user.toUpperCase();
    //Serial.print(F("Card UID: "));
    Firebase.setString("Issued_Books/Book_rfid/user_rfid",user);

    delay(3000);
}
1

also look into sprintf to get hex formatting (I dont have these libraries so I cannot test, this is all written in stackexchange editor, so I might have a typo somewhere)

unsigned long startScanTime;
bool GotBookId = false, GotUserId = false;
void loop() {
GotBookId = false;
GotUserId = false;

  if ( !mfrc522.PICC_IsNewCardPresent() ) {
    delay(50);
    return;
  }

  if ( !mfrc522.PICC_ReadCardSerial() ) {
    delay(50);
    return;
  }
String book; 

  for ( byte i = 0; i< mfrc522.uid.size; i++ ) {
    Serial.print(mfrc522.uid.uidByte[i] < 0x10 ? " 0" : " ");
    Serial.print(mfrc522.uid.uidByte[i], HEX);
    book.concat(String(mfrc522.uid.uidByte[i] < 0x10 ? " 0" : " "));
    book.concat(String(mfrc522.uid.uidByte[i], HEX));
  }
    book.toUpperCase();
    if(book != "")
       GotBookId = true;


    Serial.println("Got Book");

startScanTime = millis(); //timeout look to get user card
  while( !mfrc522.PICC_IsNewCardPresent() && (millis() - startScanTime < SCAN_TIMEOUT) ) {
   //do nothing but wait
  }

  if(!mfrc522.PICC_IsNewCardPresent())
  { //did not get the user id, return from loop
      return;
  }
  if ( !mfrc522.PICC_ReadCardSerial() ) {   
    return; //should never hit this if library works correctly
  }
  String user;

  Serial.print("Scan your id: ");
    for ( byte i = 0; i< mfrc522.uid.size; i++ ) {
    Serial.print(mfrc522.uid.uidByte[i] < 0x10 ? " 0" : " ");
    Serial.print(mfrc522.uid.uidByte[i], HEX);
    user.concat(String(mfrc522.uid.uidByte[i] < 0x10 ? " 0" : " "));
    user.concat(String(mfrc522.uid.uidByte[i], HEX));}
    user.toUpperCase();
    //Serial.print(F("Card UID: "));
    GotUserId = true;




   if(GotBookId && GotUserId){
       Firebase.pushString("Issued_Books/Book_rfid",book);
       Firebase.setString("Issued_Books/Book_rfid/user_rfid",user);
   }
}
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  • Thanks for the reply , but actually even this code is encountering the same problem. After first scan the code eventually pushing same rfid as a 'book' and 'user' in the firebase where I want the user to scan a book whose rfid will be stored in firebase then user will scan his id and an user id will be set for that particular book.
    – Dhiraj
    Mar 8 '19 at 11:34
  • Every book will be issued by a particular user ..so user id should be stored each time differently for that particular book . I mean 1 book rfid will have 1 user rfid. but due to setString(); each time it only updates previous id . Any solution for above problems?
    – Dhiraj
    Mar 8 '19 at 11:41
  • I have not worked with Firebase so I am not familiar with their API, but a 10 second google query lead me to here which cites the update method you should be using instead of the set string firebase.google.com/docs/database/admin/save-data
    – Lev
    Mar 8 '19 at 20:35
  • thanks but Im confused how to do it in firebase arduino. I mean through C Programming
    – Dhiraj
    Mar 11 '19 at 13:25
  • have you tried something like Firebase.setString(String("Issued_Books/Book_rfid/") + String(book) + String("/user_rfid"),user);
    – Lev
    Mar 18 '19 at 19:46

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