Building a Passive RFID Tag Reader

An NFC/RFID reader project using the MFRC522 module and Arduino reads 13.56MHz Mifare cards and tags. The application I built uses it for a tool checkout system in my workshop.

The MFRC522 communicates over SPI. Card detection is interrupt-driven — the IRQ pin goes low when a card enters the field. On detection, the Arduino reads the card UID (4 or 7 bytes) and looks it up in a table stored in EEPROM that maps UIDs to tool names. An LCD displays the last check-out event.

Range is about 3cm with the standard antenna coil. For a tool pegboard where you want to scan cards from 10cm away, a larger antenna coil wound on a credit-card-sized former and matched to 13.56MHz improves range to 8-10cm. The matching network (parallel capacitor to resonate the coil inductance) is critical — measure the coil inductance and calculate the capacitor accordingly.