如何将我的rfid卡的uid存储在字符串中？

Question

我是C ++和arduino的入门者，但这并不能阻止我尝试出色的项目。我有一个arduino mega 2560 v3。我想制作一个简单的rfid扫描仪，这样当扫描正确的卡时，它就会关闭我的电路。这是我的代码，来自我套件中的教程指南，这是Elegoo针对mega 2560提供的最完整的入门套件。

//www.elegoo.com
//2016.12.09

/*
 * --------------------------------------------------------------------------------------------------------------------
 * Example to change UID of changeable MIFARE card.
 * --------------------------------------------------------------------------------------------------------------------
 * This is a MFRC522 library example; for further details and other examples see: https://github.com/miguelbalboa/rfid
 * 
 * This sample shows how to set the UID on a UID changeable MIFARE card.
 * NOTE: for more informations read the README.rst
 * 
 * @author Tom Clement
 * @license Released into the public domain.
 *
 * Typical pin layout used:
 * -----------------------------------------------------------------------------------------
 *             MFRC522      Arduino       Arduino   Arduino    Arduino          Arduino
 *             Reader/PCD   Uno           Mega      Nano v3    Leonardo/Micro   Pro Micro
 * Signal      Pin          Pin           Pin       Pin        Pin              Pin
 * -----------------------------------------------------------------------------------------
 * RST/Reset   RST          9             5         D9         RESET/ICSP-5     RST
 * SPI SS      SDA(SS)      10            53        D10        10               10
 * SPI MOSI    MOSI         11 / ICSP-4   51        D11        ICSP-4           16
 * SPI MISO    MISO         12 / ICSP-1   50        D12        ICSP-1           14
 * SPI SCK     SCK          13 / ICSP-3   52        D13        ICSP-3           15
 */

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

#define RST_PIN   5     // Configurable, see typical pin layout above
#define SS_PIN    53   // Configurable, see typical pin layout above

MFRC522 mfrc522(SS_PIN, RST_PIN);   // Create MFRC522 instance

/* Set your new UID here! */
#define NEW_UID {0xDE, 0xAD, 0xBE, 0xEF}

MFRC522::MIFARE_Key key;

void setup() {
  Serial.begin(9600);  // Initialize serial communications with the PC
  while (!Serial);     // Do nothing if no serial port is opened (added for Arduinos based on ATMEGA32U4)
  SPI.begin();         // Init SPI bus
  mfrc522.PCD_Init();  // Init MFRC522 card
  Serial.println(F("Warning: this example overwrites the UID of your UID changeable card, use with care!"));

  // Prepare key - all keys are set to FFFFFFFFFFFFh at chip delivery from the factory.
  for (byte i = 0; i < 6; i++) {
    key.keyByte[i] = 0xFF;
  }
}

// Setting the UID can be as simple as this:
//void loop() {
//  byte newUid[] = NEW_UID;
//  if ( mfrc522.MIFARE_SetUid(newUid, (byte)4, true) ) {
//    Serial.println("Wrote new UID to card.");
//  }
//  delay(1000);
//}

// But of course this is a more proper approach
void loop() {

  // Look for new cards, and select one if present
  if ( ! mfrc522.PICC_IsNewCardPresent() || ! mfrc522.PICC_ReadCardSerial() ) {
    delay(50);
    return;
  }

  // Now a card is selected. The UID and SAK is in mfrc522.uid.

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

  // Dump PICC type
//  MFRC522::PICC_Type piccType = mfrc522.PICC_GetType(mfrc522.uid.sak);
//  Serial.print(F("PICC type: "));
//  Serial.print(mfrc522.PICC_GetTypeName(piccType));
//  Serial.print(F(" (SAK "));
//  Serial.print(mfrc522.uid.sak);
//  Serial.print(")\r\n");
//  if (  piccType != MFRC522::PICC_TYPE_MIFARE_MINI 
//    &&  piccType != MFRC522::PICC_TYPE_MIFARE_1K
//    &&  piccType != MFRC522::PICC_TYPE_MIFARE_4K) {
//    Serial.println(F("This sample only works with MIFARE Classic cards."));
//    return;
//  }

  // Set new UID
  byte newUid[] = NEW_UID;
  if ( mfrc522.MIFARE_SetUid(newUid, (byte)4, true) ) {
    Serial.println(F("Wrote new UID to card."));
  }

  // Halt PICC and re-select it so DumpToSerial doesn't get confused
  mfrc522.PICC_HaltA();
  if ( ! mfrc522.PICC_IsNewCardPresent() || ! mfrc522.PICC_ReadCardSerial() ) {
    return;
  }

  // Dump the new memory contents
  Serial.println(F("New UID and contents:"));
  mfrc522.PICC_DumpToSerial(&(mfrc522.uid));

  delay(2000);
}

在打印uid的for循环中，我尝试将这一行代码存储在字符串中。 String userid = mfrc522.uid.uidByte[i] < 0x10 ? " 0" : " ";但这没用。

因此，我可以快速使用帮助的快速回顾是，我需要将uid存储在字符串中，具有if语句来确定uid是否会让我通过，以及如何接受uid将关闭电路。我没有特定的电路，但是一旦解决了这个问题，我会做一个。谢谢。如果答案很明显，很抱歉，这是一个愚蠢的问题。同样，如果它有助于更​​轻松地回答我的问题，则可以使用我的uid（例如93 D1 4E 49）作为示例。

Answer 1

尝试这样的事情：

String userid;
for (byte i = 0; i < mfrc522.uid.size; i++) {
  Serial.print(mfrc522.uid.uidByte[i], HEX);
  userid += String(mfrc522.uid.uidByte[i], HEX);
}
Serial.println(userid );

如果这对您没有帮助，我想here是一些解决方案。