ESP32 RFID RC522 Card Reader (with LCD)
In this project, we will connect the MFRC522-based RC522 RFID module to the ESP32 via SPI and read the card/tag UID. This forms the basis for applications such as door locks, membership systems, and access control. We will display the read UID on an LCD screen; this version does not compare it with an authorized card list. **WARNING:** The RC522 operates only at **3.3V**; supplying 5V will burn out the module!
Video
Circuit Diagram
Source Code
1// ─────────────────────────────────────────
2// BlueGrays · bluegrays.com
3// ESP32 RFID RC522 Card Reader (with LCD)
4// ─────────────────────────────────────────
5// Reads the RC522 RFID module over SPI; the UID of a scanned card is shown
6// in HEX on the 16x2 I2C LCD for 3 s, then the "scan a card" screen
7// returns.
8//
9// Pins:
10// GPIO 5 -> RC522 SDA (SS)
11// GPIO 18 -> RC522 SCK, GPIO 19 -> RC522 MISO, GPIO 23 -> RC522 MOSI
12// GPIO 27 -> RC522 RST
13// GPIO 21 -> LCD SDA, GPIO 22 -> LCD SCL
14// RC522 3.3V -> RC522 3.3V -> 3V3, IRQ is left unconnected
15// LCD VCC -> LCD VCC -> 5V (VIN), all GNDs common
16
17#include <Wire.h>
18#include <LiquidCrystal_I2C.h>
19#include <SPI.h>
20#include <MFRC522.h>
21
22// Pin definitions
23const int RST_PIN = 27; // RC522 RST
24const int SS_PIN = 5; // RC522 SDA (SS)
25
26// SPI pins are the VSPI default
27MFRC522 rfid(SS_PIN, RST_PIN);
28LiquidCrystal_I2C lcd(0x27, 16, 2); // LCD addr 0x27 or 0x3F
29
30unsigned long lastScan = 0; // Last scan time (ms)
31const unsigned long DISPLAY_HOLD = 3000; // UID display time (ms)
32bool showingCard = false; // Is a UID on the screen
33
34// Waiting screen
35void showWaitMessage() {
36 lcd.clear();
37 lcd.setCursor(0, 0);
38 lcd.print("Kart okutun");
39 lcd.setCursor(0, 1);
40 lcd.print("Scan a card");
41}
42
43void setup() {
44 Wire.begin(21, 22); // I2C: SDA=21, SCL=22
45 lcd.init();
46 lcd.backlight();
47
48 // Splash screen 3 s
49 lcd.setCursor(3, 0);
50 lcd.print("BlueGrays");
51 lcd.setCursor(3, 1);
52 lcd.print("RFID v1.0");
53 delay(3000);
54
55 // Start SPI and the RC522
56 SPI.begin();
57 rfid.PCD_Init();
58 delay(50);
59
60 showWaitMessage();
61}
62
63void loop() {
64 // When the time is up, go back to the waiting screen
65 if (showingCard && millis() - lastScan > DISPLAY_HOLD) {
66 showWaitMessage();
67 showingCard = false;
68 }
69
70 // Leave if there is no new card or it cannot be read
71 if (!rfid.PICC_IsNewCardPresent() || !rfid.PICC_ReadCardSerial()) {
72 delay(50);
73 return;
74 }
75
76 // Print the UID in HEX, e.g. 0A:1B:2C:3D
77 lcd.clear();
78 lcd.setCursor(0, 0);
79 lcd.print("Kart UID:");
80 lcd.setCursor(0, 1);
81 for (byte i = 0; i < rfid.uid.size; i++) {
82 if (rfid.uid.uidByte[i] < 0x10) lcd.print("0");
83 lcd.print(rfid.uid.uidByte[i], HEX);
84 // No separator for a 7-byte UID: 14 chars fit the line
85 if (rfid.uid.size <= 5 && i < rfid.uid.size - 1) lcd.print(":");
86 }
87
88 lastScan = millis();
89 showingCard = true;
90
91 // Halt the card and stop encryption
92 rfid.PICC_HaltA();
93 rfid.PCD_StopCrypto1();
94}
95
FAQ
Which pins should I use to connect the RC522 to the ESP32?▾
The ESP32's default SPI pins are used: SCK = GPIO 18, MISO = GPIO 19, MOSI = GPIO 23. Use the pins specified in the code (e.g., 5 and 27) for SDA (SS) and RST; the supply voltage must be 3.3 V.
Do LCD and RFID work at the same time?▾
Yes. Since the LCD uses I2C (GPIO 21/22) and the RC522 uses the SPI bus, they do not interfere with each other; the two separate communication buses operate simultaneously.
Why is the UID 4 bytes on some cards and 7 bytes on others?▾
MIFARE Classic cards typically use a 4-byte UID, while MIFARE Ultralight and NTAG tags use a 7-byte UID. When making a comparison, you should also check the UID length.
Can I add authorized cards without changing the code?▾
Yes, you can write a mod that adds the next card to the list when the "administrator card" is scanned, and you can save the list to permanent storage via Preferences.