RFID Modules

Which RFID module fits your tags, range, and project?

Start with the credential you already have. Existing 125 kHz fobs belong with 125 kHz readers, while existing 13.56 MHz cards and stickers belong with 13.56 MHz readers. A 125 kHz reader such as the RDM6300 125KHz RFID Reader reads TK4100 and EM4200 class tags; 13.56 MHz readers such as the RC522 RFID Reader/Writer over SPI and PN532 NFC/RFID Reader Writer read MIFARE and NTAG class tags. Neither family reads the other.

Then choose by job. RC522 is the cheapest viable 13.56 MHz option for tag-only projects. For phones, extra protocols, or interface flexibility, PN532 is the better nfc rfid module, and PN532 connections over SPI, I2C, or serial matters if you plan to host it from a controller. HF modules normally read at 1–5 cm on small boards. If you want no-code door access, a standalone controller is the right class. If you need 1–10 m range or many tags at once, UHF is the correct product class, not RC522, PN532, or RDM6300.

RC522 vs PN532 vs 125KHz readers: what actually changes the choice

For a rc522 rfid reader project, the split is straightforward: RC522 fits low-cost ISO14443A tag work, PN532 fits phone-facing or multi-protocol 13.56 MHz work, and 125 kHz readers fit existing low-frequency fobs or Wiegand and UART ID systems. RC522 is the roughly $2 budget recommendation. PN532 is commonly about $4–8 more when the extra flexibility matters.

PN532 over I2C is known to lock up on ESP32 because of clock stretching, so HSU or SPI is the safer choice there.

Compatibility checks before you add a module to cart

• Match the tag family exactly. Tags are often sold separately, and a 125 kHz reader will not read 13.56 MHz cards, while a 13.56 MHz mifare rfid card reader will not read TK4100 or EM4200 fobs.
• Check whether your project only reads IDs or also needs writing. The 125KHz read-only RFID key tag uses a TK4100 chip and is read-only. For writable 125 kHz work, you need T5577-class tags; for 13.56 MHz RC522 or PN532 projects, MIFARE and NTAG class tags can store user data.
• If you need a writable 13.56 MHz card, the 13.56MHz RFID IC card with 8Kbit EEPROM is one concrete example, with 100,000 rewrite cycles.
• Confirm voltage before wiring. The SPI RC522 board is restricted to 3.3 V voltage levels.
• Plan mixed-voltage UART carefully. The RDM6300 125KHz UART reader uses 5 V UART TTL, so Raspberry Pi class 3.3 V RX pins need a divider on the reader TX line. If this is your route, RDM6300 serial wiring and tag reading basics shows the usual hookup, and these are common modules for Arduino boards.
• Standard tags detune on metal. For tools, machines, or metal enclosures, use on-metal or ferrite-backed tags.
• Hobby HF readers effectively handle one tag in the field at a time. If you are planning attendance gates or bulk inventory reads, UHF is the right direction instead.

When is a standalone access controller the better buy?

If the job is a door or gate and you do not want to write firmware, a standalone rfid access control module is the better fit than a reader board. The CU-K15-IC10 13.56MHz access controller is a self-contained unit with 255-user storage, 12V DC power, tamper alarm, door monitoring, and memory retention during power loss. The RFID access controller with digital keypad raises capacity to 1000 users, adds touch-key operation, four working modes, a doorbell connection, and is available in 125KHz or 13.56MHz versions.

That is the trade. Standalone controllers can be enrolled and used without programming, but they are closed systems. You give up custom logic, richer logging, and application-level control compared with MCU-hosted readers such as the RC522 SPI reader or PN532 module.

• Choose a standalone controller when you want built-in relay handling, user storage, door monitoring, and keypad fallback without code.
• Choose a standalone keypad unit specifically if users need PIN entry as a backup to cards or fobs.
• Choose a reader module when you need custom behavior, WiFi, database logging, or app logic. In that case the reader only identifies the credential; the lock side still needs a relay module, 12 V strike or maglock hardware, and a power supply. A custom networked build is closer to what an MCU-based smart door lock build involves, often built around ESP8266 boards.

Which tags are commonly paired with these modules?

Tag choice should be as deliberate as reader choice. Match the reader and credential by frequency and protocol family to avoid the usual dead-on-arrival mismatch. MIFARE Classic is still common in RC522 tutorials, but its Crypto1 security is broken, so treat it as a convenience credential rather than a secure one. For phone automation, NTAG213, NTAG215, and NTAG216 are the usual NFC tags, with 144, 504, and 888 bytes of memory respectively.

For 125 kHz controller-style projects, using a 125 kHz Wiegand reader in an Arduino access project matches panel-style wiring.

FAQs on RFID Modules

Glossary

RFID

The umbrella term for several incompatible identification families, so frequency still has to match before a tag will read.

NFC

A 13.56 MHz subset of RFID that matters when phones are part of the project.

MIFARE Classic

A common 13.56 MHz card family that works with RC522, but its Crypto1 security is broken.

NTAG213/215/216

Common phone-readable NFC tags that mainly differ by memory size: 144, 504, and 888 bytes.

Wiegand

A two-wire reader-to-controller interface used in access systems, not a card type and not the same as UART.

UID

The tag identifier used for basic recognition, but not a secret and not enough by itself for real security.

T5577

The writable 125 kHz tag family used when an LF project needs programmable credentials instead of read-only IDs.

On-metal tag

A tag with shielding that keeps it readable on metal surfaces where standard tags usually fail.