I am currently building a simple audio book player for my kids. One part of are RFID chips for every audio book. An RFID-RF522 reader detects them and plays the corresponding audio book.
Connecting the RFID-RC522 board was more difficult than I first thought as most tutorials on the Internet have an incorrect pinout for current Raspberries. Those that are correct lack the interrupt line which causes a high power consumtion.
With this schematic the connection is simple and compact:
It allows to use interrupts which enables to write low power applications. You can find the schematics at fritzing.org.