How to connect multiple RC522 RFID Reader to Raspberry PI? - raspberry-pi3

Question

I want to know if it is possible to connect multiple RC522 to one Raspberry PI, if yes how do we do it? I read in some articles that with CS(chip select) pin we can control Readers, but the CS pin is not present on RC522 I have.
Can you please help me?

Answer 1

Chip Select (CS) is referred to as SS or NSS in some of the RFC522 documentation, is that the issue? If so, connect your CS0 to NSS on one module, CS1 to the NSS on the other, and you can use both modules on the same SPI bus.
If you need more devices than that, you could switch to the I2C interface. In I2C mode, a number of the pins on the chip become address selects, so you can put a whole bunch of them on the same I2C bus. The data sheet for the chip is always helpful with this sort of information. Section 8.1, "Digital interfaces" may be particularly helpful.
In I2C mode, you have 5 bits of addressing, so you can put up to 32 devices on the bus.

Answer 2

Posted this answer before on the raspberry pi stackexchange.
I'll just repost it here for visibility.
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)