RC522Hacking

Project RC522Hacking
Status	In progress
Contact	bertrik
Last Update	2015-08-12

Introduction

This page is about the RC-522 mifare reader board.

This board can be found for a rather low price (about E3,-) on ebay, and usually comes packaged with a mifare 1k card and a mifare 1k key fob. It is 'arduino-compatible' in the sense that you interface with it through a SPI connection. It should be able to read all 'mifare' kind of RFID cards.

The problem with this board however, is that in its default configuration only seems to work reliably with the card/key-fob that it was packaged with. It doesn't to work with other mifare cards (e.g. OV-chipkaart).

This project is about modifying this board to make it actually work with other mifare cards.

Investigation

My two main suspicions why this board doesn't quite work, are:

• some software problem, quite a few things can be modified in software (conductance of the driving transistors, sensitivity settings)
• some hardware problem, either using the wrong circuit between the chip and the antenna, or using sub-standard components in the circuit

I've played a lot already with the software settings, but can't seem to make a change that actually improves performance with the non-working mifare cards.

With respect to hardware, I ordered two of these boards, and one of them came with a poorly soldered capacitor (C8). This one actually worked with a mifare light card! Properly soldering the capacitor made it no longer work. It also gave me a chance to measure the capacitor value, it has a value about 220 pF.

Results

TDLR, my most up-to-date fix is:

• replace C8 and C9 with a 100 pF capacitor

This enables reading of all cards I currently own.

References

• NXP MFRC522 datasheet
• NXP application note AN1445, Antenna design guide