Arduino converting byte array to String?

Question

I am working on a little RFID project but I am having one tiny problem.

I have a RC522 RFID Module connected to an Arduino UNO and I want to be able to read TAGS and then compare the read ID to a string.

The ID will get stored into a byte array with the size of 4.

For instance...

byte readTAG[4];

will hold...

{ C3, 7D, DF, C7 }

I now want to take this array and convert it into a String such as...

"C37DDFC7"

This way...I could do operations such as

if(readTag == "12345678") {
    // Do something...
}

How would I go about doing this?

Thanks in advance!

Here is my code:

#include <MFRC522.h>
#include <SPI.h>

int RST_PIN = 9;
int SDA_PIN = 10;

byte readCard[4];

MFRC522 mfrc522(SDA_PIN, RST_PIN);

void setup() {
  Serial.begin(9600);
  SPI.begin();
  mfrc522.PCD_Init();
}

void loop() {
  ReadTAG();  

}

// Lese TAG aus und gebe die ID im Serial Monitor aus.
void ReadTAG() {
  // Wenn ein neuer TAG vorhanden ist UND erfolgreich gelesen werden konnte, dann Lese TAG aus.
  if (mfrc522.PICC_IsNewCardPresent() && mfrc522.PICC_ReadCardSerial()) {     
    for (int i = 0; i < 4; i++) { 
     readCard[i] = mfrc522.uid.uidByte[i];
     Serial.print(readCard[i], HEX);       
    }       
    Serial.println();    

    // Wenn der TAG ausgelesen wurde dann stoppe das Lesen da er sonnst das gleiche TAG vielemale ausließt.
    mfrc522.PICC_HaltA();
  }
}

Is there a particular reason why you want to take the extra time to convert and then compare as strings instead of just comparing as bytes? — Ignacio Vazquez-Abrams, Dec 18 '14 at 18:50
Actually there would be no reason...I just haven't figured out how to compare it at all... — Bavilo, Dec 18 '14 at 22:05

score 0 · Answer 1 · answered Dec 18 '14 at 22:08

0

Some things about C/C++ I hate. And some I do not.

#define cmpID(var, b1, b2, b3, b4) \
( \
  var[0] == 0x ## b1 && \
  var[1] == 0x ## b2 && \
  var[2] == 0x ## b3 && \
  var[3] == 0x ## b4 \
)

 ...

if (cmpID(readTag, 12, 34, 56, 78))
{
   ...
}

answered Dec 18 '14 at 22:08

Ignacio Vazquez-Abrams

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Arduino converting byte array to String?

1 Answers1