RFID Modules Explained

RFID Modules Explained

RFID (Radio Frequency Identification) lets you identify a card or tag without contact. In electronics projects, this means building attendance systems, access control doors, library management, and inventory tracking. Three RFID modules dominate the maker market in India — the RC522, PN532, and RDM6300. Here is how each works and which to buy.

The Two Frequencies: 125 kHz vs 13.56 MHz

This is the fundamental split in RFID technology. 125 kHz systems (EM4100/EM4102 cards) are older, read-only, and simpler. The card ID is fixed at manufacture and cannot be changed. Used in older office access systems and parking gates.

13.56 MHz systems (ISO 14443-A/B, ISO 15693) are newer, support read-write operations, encryption, and memory segmentation. Mifare Classic 1K cards (the most common 13.56 MHz card) have 1 KB of writable memory divided into 16 sectors of 4 blocks each.

The RC522 and PN532 work at 13.56 MHz. The RDM6300 works at 125 kHz. They are not interoperable — a Mifare 1K card will not be read by an RDM6300, and an EM4100 card will not be read by an RC522.

RC522 (MFRC522): The Standard Choice

The RC522 uses the NXP MFRC522 chip and operates at 13.56 MHz. It reads and writes Mifare 1K, Mifare 4K, Mifare Ultralight, and NTAG2xx NFC tags. Interface: SPI (up to 10 MHz). Operating voltage: 2.5–3.3 V (not 5V — connect to 3.3V only). Current: ~13 mA during read. Range: 3–5 cm. Price: ₹70–120.

Wiring to ESP32 (SPI):

• SDA (SS) → GPIO 5
• SCK → GPIO 18
• MOSI → GPIO 23
• MISO → GPIO 19
• RST → GPIO 22 (or any free GPIO)
• 3.3V → ESP32 3.3V pin
• GND → GND

Library: MFRC522 by GithubCommunity. Install via Library Manager. The standard "DumpInfo" example sketch reads any Mifare card UID and memory content — run this first to verify your wiring.

Each Mifare 1K card has a unique 4-byte UID (printed on the back in some cases). For attendance/access systems, you typically only need to read and store this UID — no need to write card memory unless you need offline credential storage.

PN532: More Capable, More Expensive

The PN532 NFC controller supports 13.56 MHz RFID/NFC, reads all Mifare variants, and also supports NFC peer-to-peer (reading NFC-enabled Android phones, NFC payment cards). Interface: SPI, I2C, or HSU (high-speed UART) — selectable via solder jumpers on the module. Operating voltage: 3.3V. Price: ₹300–500.

Use the PN532 when you need to read NFC from smartphones (e.g., reading an NFC tag written to a phone), interact with NFC payment cards (for informational purposes, not financial transactions), or need I2C interface to save SPI pins.

For standard Mifare attendance/access projects, the RC522 is more than sufficient at half the price.

RDM6300: 125 kHz Read-Only

The RDM6300 reads EM4100/EM4102 125 kHz cards only. UART output (9600 baud) sends a 14-character ASCII string including card ID when a card is detected. Operating voltage: 5V. Price: ₹150–220. Includes a coil antenna that must be connected externally.

Use this if you have existing 125 kHz EM4100 cards from an older system, or if your application only needs read-only identification and cannot use 13.56 MHz cards. For new projects, the RC522 is a better choice.

Cards and Tags

For RC522 projects, buy Mifare 1K cards (white PVC credit-card size) or Mifare 1K key fobs. Both work identically with the RC522. Cards are more professional for attendance systems; fobs are more practical for keys and access control. Mifare 1K cards cost ₹20–40 each in packs of 5–10. Key fobs cost ₹30–60 each.

Note: Mifare Classic 1K cards have a known security vulnerability (CRYPTO-1 cipher is weak). For access control to secure areas, use Mifare DESFire cards with proper mutual authentication. For student attendance and general maker projects, Mifare 1K is fine.

Practical Applications

• Attendance system: RC522 + ESP32 + DS3231 RTC + Google Sheets API
• Door access control: RC522 + ESP32 + electric door lock relay + authorized UIDs stored in SPIFFS
• Library book tracking: RC522 + Arduino Nano + PC serial interface
• Inventory tagging: RC522 + ESP32 + MQTT + database

Browse RFID modules and Mifare cards at Circuitkar — we stock RC522 modules with cards and key fobs.