RC522 RFID Module: Pinout, Wiring, Arduino & ESP32 Code

The RC522 RC522 NXP RC522 NXP In Stock: 11386 pcs RFID module is a 13.56 MHz contactless reader and writer commonly used with Arduino, ESP32 and other microcontrollers. The name RC522 usually refers to a breakout board built around NXP’s MFRC522 reader IC. Antenna tuning, interface configuration, and component quality may vary between module manufacturers. It creates a radio-frequency field that powers a compatible passive card or tag, reads the tag’s UID and accesses stored memory when the correct authentication key is available. This article explains the RC522 pinout, specifications, supported tags, read/write process, Arduino and ESP32 connections, example code, measured range, common problems and modern NFC alternatives.

Catalog

Figure 1. RC522 RC522 NXP RC522 NXP In Stock: 11386 pcs RFID Module

RC522 RFID Module Pinout

Figure 2. RC522 RC522 NXP RC522 NXP In Stock: 11386 pcs Pinout

Most blue RC522 breakout boards are configured for SPI. The MFRC522 IC also supports I²C and UART but using these interfaces may require board-specific solder-jumper or strap changes. Check the module schematic before attempting an I²C or UART connection.

RC522 RFID Module Specifications

Note: NXP lists MFRC52202HN1 as End of Life and recommends CLRC663 plus for new reader designs.

Reference: NXP Semiconductors, MFRC522 - Standard performance MIFARE and NTAG frontend, Product Data Sheet, Rev. 3.9, 27 April 2016, document number 112139.

What Cards and Tags Can the RC522 Read?

The RC522 RC522 NXP RC522 NXP In Stock: 11386 pcs reads and writes 13.56 MHz ISO/IEC 14443 Type A cards and tags. It works best with MIFARE Classic Mini, 1K and 4K products. The MFRC522 supports these products at the RF level, but available read, write and protection features depend on the tag and software library.

It cannot read 125 kHz tags, ISO/IEC 14443 Type B, FeliCa, ISO/IEC 15693 or UHF tags. Protected cards may allow UID detection but block access to their stored data. The RC522 also does not support normal communication with NFC smartphones.

How the RC522 Reads and Writes RFID Tags

The process begins when the microcontroller tells the RC522 RC522 NXP RC522 NXP In Stock: 11386 pcs to scan for a tag. After a compatible passive tag responds, the reader performs anticollision to separate multiple responses, obtains the tag’s UID and selects one tag for communication.

Figure 3. RC522 Tag Detection, Authentication, and Data Read/Write Process

Before accessing protected memory, the reader authenticates using the correct sector key. A read operation transfers data from the selected block to the microcontroller, while a write operation sends new data to the block and checks whether the tag accepted it. The RC522 then reports whether the operation succeeded or failed.

RC522 Wiring and Setup with Arduino and ESP32

The Arduino Uno and ESP32 communicate with the RC522 RC522 NXP RC522 NXP In Stock: 11386 pcs through SPI, but they use different pins and logic levels. Install the MFRC522 library through Arduino Library Manager before uploading the UID-reading sketch in Section 5.3.

The library is frozen and receives only sporadic maintenance. It supports MIFARE Classic cards, but NTAG and MIFARE Ultralight support is partial. It does not support I²C, UART, MIFARE DESFire authentication, smartphone communication, or card emulation.

RC522 Interfacing with Arduino

The Arduino Uno communicates with the RC522 through SPI. Power the module with 3.3 V and connect both devices to a common ground. Because the Uno produces 5 V GPIO outputs, SDA/SS, SCK, MOSI and RST must pass through a 5 V-tolerant logic buffer powered from 3.3 V. On common RC522 boards, the SDA pin functions as SS or chip select in SPI mode.

Figure 4. Arduino Uno and RC522 SPI Wiring

Arduino Uno and RC522 Connections

A direct MISO connection commonly works, but an upward level shifter provides stricter worst-case compatibility. The Uno’s 3.3 V pin is limited to 50 mA. If the module becomes unstable, use an external regulated 3.3 V supply with its ground connected to the Arduino ground.

RC522 Interfacing with ESP32

The ESP32 and RC522 use 3.3 V logic, so a level shifter is normally unnecessary. RST is connected to GPIO 22, avoiding GPIO 0 because GPIO 0 affects the ESP32 boot mode. These connections apply to the classic ESP32 DevKit; other ESP32 variants may use different SPI pins.

Figure 5. ESP32 and RC522 SPI Connections

ESP32 and RC522 Connections

ESP32-specific settings used by the shared sketch are:

const byte SS_PIN = 5;

const byte RST_PIN = 22;

Serial.begin(115200);

SPI.begin(18, 19, 23, SS_PIN);

Shared RC522 UID-Reading Code

The following sketch automatically selects the pin assignments and SPI initialization for an Arduino Uno or classic ESP32. Open the Serial Monitor at 9600 baud for the Uno or 115200 baud for the ESP32.

#include

#include

#if defined(ARDUINO_ARCH_ESP32)

const byte SS_PIN = 5;

const byte RST_PIN = 22;

const unsigned long SERIAL_BAUD = 115200;

#else

const byte SS_PIN = 10;

const byte RST_PIN = 9;

const unsigned long SERIAL_BAUD = 9600;

#endif

MFRC522 reader(SS_PIN, RST_PIN);

void setup() {

Serial.begin(SERIAL_BAUD);

#if defined(ARDUINO_ARCH_ESP32)

SPI.begin(18, 19, 23, SS_PIN);

#else

SPI.begin();

#endif

reader.PCD_Init();

Serial.println("Place a compatible RFID tag near the reader.");

}

void loop() {

if (!reader.PICC_IsNewCardPresent() ||

!reader.PICC_ReadCardSerial()) {

return;

}

Serial.print("Card UID:");

for (byte i = 0; i < reader.uid.size; i++) {

Serial.print(reader.uid.uidByte[i] < 0x10 ? " 0" : " ");

Serial.print(reader.uid.uidByte[i], HEX);

}

Serial.println();

reader.PICC_HaltA();

delay(500);

}

RC522 Security Limitations

The RC522 is a reader, not a complete security system. A tag’s UID identifies the tag but should not be treated as a secret password because compatible devices may copy or emulate it. Therefore, UID-only systems are unsuitable for payments, secure access control or other applications where impersonation could cause serious harm.

Security also depends on the card technology. MIFARE Classic uses the legacy Crypto1 cipher, which researchers have shown to be vulnerable to practical key-recovery and memory-access attacks. Default keys and keys stored without protection in microcontroller firmware create additional risks. The RC522 is suitable for learning and low-risk identification, but sensitive systems should use a compatible reader and cards with modern mutual authentication, AES encryption, secure messaging and protected key storage, such as appropriate MIFARE DESFire or MIFARE Plus products.

RC522 Read Range: Datasheet Typical Distance and Published Test Results

Datasheet Typical Distance

The NXP MFRC522 datasheet specifies a typical read/write distance of up to 50 mm, depending on antenna size and tuning. This is not a guaranteed range for every RC522 RC522 NXP RC522 NXP In Stock: 11386 pcs module. Tag design, antenna alignment, supply voltage, electrical noise, and nearby metal can affect the actual distance.

Published Test Results

Wijanarko et al. (2025) tested an ESP32-based access-control prototype using an RC522 module and a MIFARE Classic 1K card.

The prototype detected the card at distances from 1 to 5 cm and failed at 6 cm. However, the study did not report repeated trials, numerical success rates, measured response times, or antenna orientation. Therefore, these findings describe this prototype only and should not be presented as a universal RC522 reliability rating.

Reference: Wijanarko, Y., Alfarizal, N., and Pratama, M. R. (2025). “Implementation of an RFID RC522 and IoT-Based Automatic Door Security System in an Electrical Engineering Laboratory.” Indonesian Journal of Artificial Intelligence and Data Mining, 8(2), 478–488.

RC522 Application Examples and Limitations

Attendance-System Application

Tan et al. (2018) developed a university attendance system using an RFID-RC522 RC522 NXP RC522 NXP In Stock: 11386 pcs reader, NodeMCU controller, Wi-Fi, and compatible 13.56 MHz campus cards. Students scanned their cards at the classroom entrance, and a mobile application confirmed that the cloud database received each attendance record. In one classroom test, the reported attendance rate increased from 85% to 98%.

The paper did not state the attendance sample size, test duration, number of class sessions, reading distance, scan time, or card-failure rate. It also lacked a control group and evaluated a wider platform containing mobile, QR-code, and classroom-interaction features. Therefore, the increase cannot be attributed to the RC522 alone.

Reference: Tan, P., Wu, H., Li, P., and Xu, H. (2018). “Teaching Management System with Applications of RFID and IoT Technology.” Education Sciences, 8(1), Article 26. DOI: 10.3390/educsci8010026.

Offline Payment Application

Dewanto et al. (2021) built an offline payment prototype using an Arduino Uno, MFRC522 reader, LCD, and microSD card. It updated electronic-money balances and stored purchases, top-ups, and refunds locally.

A 30-tap test achieved 100% card-detection success at 1–3 cm and 0% at 4 cm. Reader response time at 1–3 cm was 0.1–0.2 seconds. Complete transactions took 1.4–2.0 seconds with sufficient balance, 0.5 seconds with insufficient balance, and 0.3 seconds for unregistered cards.

The paper did not clearly explain how the taps were distributed, how many cards were used, or the variation between measurements. Its stopwatch-based results apply only to the prototype. Card cloning, key recovery, replay attacks, and tamper resistance were not tested, so the system was not validated for production payment use.

Reference: Dewanto, S. A., Munir, M., Wulandari, B., and Alfian, K. (2021). “MFRC522 RFID Technology Implementation for Conventional Merchant with Cashless Payment System.” Journal of Physics: Conference Series, 1737(1), 012012. DOI: 10.1088/1742-6596/1737/1/012012.

Common RC522 Problems and Diagnostic Tests

Problem	Diagnostic test	Solution
Module is not detected	Check for 3.3 V and run PCD_DumpVersionToSerial().	Correct the power, ground, SPI, SS and RST connections.
Tag is not recognized	Test the included 13.56 MHz card close to the antenna.	Use an ISO/IEC 14443A-compatible card. The RC522 RC522 NXP RC522 NXP In Stock: 11386 pcs cannot read 125 kHz tags.
Reading is unstable	Hold the card parallel to the antenna and remove nearby metal.	Use short wires, stable 3.3 V power and proper tag alignment.
Authentication fails	Verify the tag type, sector, block and Key A or Key B.	Use the correct MIFARE Classic sector key.
Data cannot be written	Test an unused data block and read it back.	Check access permissions and avoid block 0 or sector trailers.
Reader stops after one card	Remove and present the card again.	End the session with PICC_HaltA() and PCD_StopCrypto1().
Reader fails when a motor activates	Disconnect the motor or relay and retest.	Use separate power filtering and flyback protection.

RC522 vs PN532, PN7160, and CLRC663 Plus

Device	NFC Modes	Smartphone Support	Host Interface	Supported Standards	Product Status	Recommended Use
MFRC522	Reader/writer only	Limited; no peer-to-peer or card-emulation modes, and the common Arduino library does not support smartphone communication	SPI, I²C or serial UART	ISO/IEC 14443A, MIFARE and NTAG	End of Life; NXP recommends CLRC663 Plus	Existing low-cost Arduino and ESP32 projects using compatible cards or tags
PN532 PN532 NXP In Stock: 10135 pcs	Reader/writer, card emulation and NFCIP-1 peer-to-peer	Yes, when supported by the smartphone operating system and application	SPI, I²C or high-speed UART	ISO/IEC 14443A/B, MIFARE, FeliCa and ISO/IEC 18092	Not Recommended for New Designs; NXP recommends PN7160	Maintaining older NFC projects that require multiple NFC modes
PN7160	All NFC Forum modes: reader/writer, card emulation and active or passive peer-to-peer	Yes; supports reader interaction, card emulation and peer-to-peer, although phone operating systems may restrict P2P	I²C or SPI using NCI 2.0	NFC Forum Tag Types 1–5, ISO/IEC 14443A/B, MIFARE Classic, FeliCa and ISO/IEC 15693	Active	New embedded and IoT products requiring full NFC support; not intended for EMVCo payment compliance
CLRC663 Plus	Multi-protocol reader/writer and ISO/IEC 18092 passive initiator	Limited to reader-side communication with compatible phone card-emulation modes; requires a host protocol stack	SPI, I²C or UART	ISO/IEC 14443A/B, MIFARE, NTAG, FeliCa, ISO/IEC 15693 and ISO/IEC 18000-3 Mode 3	Active; recommended MFRC522 replacement	High-performance access-control, industrial, gaming and multi-protocol reader designs

The PN532 is not recommended for new designs. NXP recommends the PN7160 as its replacement. The PN7160 supports all NFC Forum modes, but peer-to-peer availability still depends on the software stack and smartphone operating system.

Frequently Asked Questions [FAQ]

1. How can duplicate RFID scans be prevented in an attendance system?

Store the last UID and scan time, then ignore repeated scans within a chosen delay. For better control, require the card to leave the RF field before accepting it again.

2. How should RC522 UIDs be stored in a database?

Store the UID length together with every raw byte because UIDs may contain 4, 7 or 10 bytes. Avoid converting them into a normal integer, which can remove leading zeros or exceed the available number size.

3. How much usable memory does a MIFARE Classic 1K card provide?

The card contains 1,024 bytes divided into 16 sectors. After excluding the manufacturer block and sector trailers, approximately 752 bytes remain in normal data blocks.

4. Can the RC522 read and write NDEF records on NTAG tags?

The hardware can communicate with compatible NTAG products, but NDEF handling depends on the software library. The program must understand the NFC Type 2 memory structure, TLV fields and NDEF record format rather than treating the tag as ordinary raw memory.