Trying to use two MFRC522 readers with one Raspberry Pi 3

Question

I'm trying to get two MFRC522 readers to work with a Raspberry Pi 3 Model B. I started off using the pi my life up tutorial to get one working and it worked brilliantly. To get the second one going I tried a couple of different repos I found in github but none of them worked. I was sort of able to get both to read but it behaves oddly. The status is always MI_ERR but it will read the card. The other issues I'm seeing are it randomly displays a different uid and it will indicate card 2 is read when I'm putting the tag on card 1. Below is the pin configuration along with my code. Please note that each MFRC522.py was updated to indicate pin 15 or 22 for the NRSTPD. Any help would be greatly appreciated.

Reader 1 3.3v = Pin 1 RST = Pin 15 GND = Pin 9 MISO = Pin 21 MOSI = Pin 19 SCK = Pin 23 SDA = Pin 24

Reader 2 3.3v = Pin 1 RST = Pin 22 GND = Pin 9 MISO = Pin 21 MOSI = Pin 19 SCK = Pin 23 SDA = Pin 24

import RPi.GPIO as GPIO
import MFRC522_Chip2
import MFRC522
import signal

plate1 = [222, 86, 127, 87, 246]
plate2 = [86, 126, 214, 255, 87]

indicator1 = 0
indicator2 = 0

GPIO.setmode(GPIO.BOARD)
GPIO.setwarnings(False)

continue_reading = True

# Capture SIGINT for cleanup when the script is aborted
def end_read(signal,frame):
    global continue_reading
    print "Ctrl+C captured, ending read."
    continue_reading = False
    GPIO.cleanup()

# Hook the SIGINT
signal.signal(signal.SIGINT, end_read)

# Create an object of the class MFRC522
MIFAREReader_Chip2 = MFRC522_Chip2.MFRC522()

# Create an object of the class MFRC522
MIFAREReader = MFRC522.MFRC522()

# Welcome message
print "Welcome to the MFRC522 data read example"
print "Press Ctrl-C to stop."

# This loop keeps checking for chips. If one is near it will get the UID and authenticate
while continue_reading:

    # Scan for chip 1   
    (status,TagType) = MIFAREReader.MFRC522_Request(MIFAREReader.PICC_REQIDL)

    #print (status)

    # If a card is found
    if status == MIFAREReader.MI_OK:
        print ("Card 1 detected")
        # Get the UID of the card
        (status,uid) = MIFAREReader.MFRC522_Anticoll()

        if indicator1 == 1:
            GPIO.setup(12, GPIO.OUT)
            GPIO.output(12, GPIO.LOW)
            print ("!")
        else:
            GPIO.setup(12, GPIO.OUT)
            GPIO.output(12, GPIO.HIGH)

        indicator1 = 0

        print (uid)

        # If we have the UID, continue
        if status == MIFAREReader.MI_OK:
            if uid[:5] == plate1:
                print ("Plate 1 in position")
                indicator1 = 1
            else:
                ("Find plate 1")
                indiator1 = 0

    # Scan for chip 2   
    (status,TagType) = MIFAREReader_Chip2.MFRC522_Request(MIFAREReader_Chip2.PICC_REQIDL)

    #print (status)

    # If a card is found
    if status == MIFAREReader_Chip2.MI_OK:
        print ("Card 2 detected")
        # Get the UID of the card
        (status,uid) = MIFAREReader_Chip2.MFRC522_Anticoll()

        if indicator2 == 1:
            GPIO.setup(16, GPIO.OUT)
            GPIO.output(16, GPIO.LOW)
            print ("?")
        else:
            GPIO.setup(16, GPIO.OUT)
            GPIO.output(16, GPIO.HIGH)

        indicator2 = 0

        print (uid)

        #If we have the UID, continue
        if status == MIFAREReader_Chip2.MI_OK:

            if status == MIFAREReader.MI_ERR:
                if uid[:5] == plate2:
                    print ("Plate 2 in position")
                    indicator2 = 1
                else:
                    print("Find plate 2")
                    indiator2 = 0

Do you set the NSS line so that only one reader IC receives SPI register read/write operations at any time? — Michael Roland

Carol Laila Carol Laila · Accepted Answer · 2019-10-16T16:37:53

Follow these steps:

1. First, the SDA pin must be different for each RFID reader (use pin 24 and 12);

2. In Raspbian "cmd" type: sudo nano /boot/config.txt and add this information dtoverlay = spi1-3cs (this line activates Raspberry pin 12);

3. Use the github MFRC522 library: https://github.com/YongxinLIAO/SmartFactoryRFID.git

4. Create 2 folders for each reader, each folder must have a separate library MFRC522;

5. In the library of each folder, change the RESET pin to 15 and in the other library change the RESET pin to 22;

6. On the "spidev 0.0" line in the MFRC522 library, leave a reader like this and in the other library change to "spidev 1.0";

I advise testing each reader at a time to avoid overlapping errors.

Trying to use two MFRC522 readers with one Raspberry Pi 3

1 Answers