How to connect multiple RFID readers (RC522) to a RPi?

Question

I'm trying to connect x9 RC522 RFID readers to an RPI.

I'm wondering if it can be done using the standard RPi GPIO pins or if I need some other controller.

Also, it's worth mentioning that it will need to be able to distinguish between the readers, and know which one is providing which data.

And I'm not sure if I use a port expander, something like this, if the data stream will get "tagged" to identify which reader it came from.

Answer 1

did this exact thing using 5x RFID-RFC522 Readers.

You can use the RST Pins to select the reader you want to use. Connect all the other pins in parallel (see schematic below). Just set all the RST pins to low, except the one on the pin you want to use. Set that one to high. Then initialize SPI, read/write, and close SPI again.

I wrote a more detailed explanation here.

This is the schematics and code I made:

Schematic for 2 readers:

Schematic for 4 readers:

Code to run it all (using pimylifeup's MFRC522-Python Library):

import RPi.GPIO as GPIO
from mfrc522 import SimpleMFRC522
import spidev

class NFC():
    def __init__(self, bus=0, device=0, spd=1000000):
        self.reader = SimpleMFRC522()
        self.close()
        self.bus
        self.boards = {}
        
        self.bus = bus
        self.device = device
        self.spd = spd

    def reinit(self):
        self.reader.READER.spi = spidev.SpiDev()
        self.reader.READER.spi.open(self.bus, self.device)
        self.reader.READER.spi.max_speed_hz = self.spd
        self.reader.READER.MFRC522_Init()

    def close(self):
        self.reader.READER.spi.close()

    def addBoard(self, rid, pin):
        self.boards[rid] = pin

    def selectBoard(self, rid):
        if not rid in self.boards:
            print("readerid " + rid + " not found")
            return False

        for loop_id in self.boards:
            GPIO.output(self.boards[loop_id], loop_id == rid)
        return True

    def read(self, rid):
        if not self.selectBoard(rid):
            return None

        self.reinit()
        cid, val = self.reader.read_no_block()
        self.close()

        return val

    def write(self, rid, value):
        if not self.selectBoard(rid):
            return False

        self.reinit()
        self.reader.write_no_block(value)
        self.close()
        return True


if __name__ == "__main__":
    nfc = NFC()
    nfc.addBoard("reader1",5)
    nfc.addBoard("reader2",6)

    data = nfc.read("reader1")
    nfc.write("reader2",data)