How to Use the RC522 RFID Module with Arduino

1#include <SPI.h>
2#include <MFRC522.h>
3
4#define SS_PIN 10
5#define RST_PIN 9
6#define greenLED 8
7#define redLED 7
8
9String UIDlist[4] = {"A3D4F231", "A31F094B", "12AB34CD", "DEADBEEF"};
10bool LEDstate = false;
11
12MFRC522 mfrc522(SS_PIN, RST_PIN);
13
14void setup() {
15  pinMode(greenLED, OUTPUT);
16  pinMode(redLED, OUTPUT);
17  Serial.begin(9600);
18  SPI.begin();
19  mfrc522.PCD_Init();
20  Serial.println("Scan your RFID card...");
21}
22
23void loop() {
24  if (!mfrc522.PICC_IsNewCardPresent()) return;
25  if (!mfrc522.PICC_ReadCardSerial()) return;
26
27  String uidString = "";
28
29  for (byte i = 0; i < mfrc522.uid.size; i++) {
30    if (mfrc522.uid.uidByte[i] < 0x10) {
31      uidString += "0";
32    }
33    uidString += String(mfrc522.uid.uidByte[i], HEX);
34  }
35
36  uidString.toUpperCase();
37  Serial.println(uidString);
38
39  for (int i = 0; i < 4; i++) {
40    if (UIDlist[i] == uidString){
41      LEDstate = true;
42      break;
43    }
44
45    else{
46      LEDstate = false;
47    }
48  }
49
50  if(LEDstate){
51    digitalWrite(greenLED, HIGH);
52    delay(1000);
53    digitalWrite(greenLED, LOW);
54  }
55
56  else{
57    digitalWrite(redLED, HIGH);
58    delay(1000);
59    digitalWrite(redLED, LOW);
60  }
61}