Keyboard print UID MFRC522 Arduino Leonardo

Question

I want to print the UID of a card as an HID with the Arduino Leonardo.

Here is the code that I have

void loop() {
if (  mfrc522.PICC_IsNewCardPresent()) {


// Select one of the cards
     if (  mfrc522.PICC_ReadCardSerial()) {



  // Dump debug info about the card; PICC_HaltA() is automatically called
         mfrc522.PICC_DumpToSerial(&(mfrc522.uid));
         Keyboard.print(mfrc522.uid);
    }
  }
}

and this is what the compiler says

note:   no known conversion for argument 1 from 'MFRC522::Uid' to 'const Printable&'
exit status 1

Does anyone know how to do it?

darclander · Accepted Answer · 2021-05-30T13:20:20.760

I believe that the isse you are facing is that you are trying to print a MFRC522::Uid which is a HEX number such as 00 00 00 00 while the keyboard.print() only accepts char, int or string according to: Arduino.cc. I found the following code snippet here. I believe it might resolve your issue. It should write: "Card UID: 00 00 00 00".

Serial.print("Card UID:");    //Dump UID
for (byte i = 0; i < mfrc522.uid.size; i++) {
    Serial.print(mfrc522.uid.uidByte[i] < 0x10 ? " 0" : " ");
    Serial.print(mfrc522.uid.uidByte[i], HEX);
}

NOTE: If you are using Keyboard.print() I believe you need to use Keyboard.begin() in your setup method.

Keyboard print UID MFRC522 Arduino Leonardo

1 Answers1