Two RC522 I2C

Projects Networking, Protocols, and Devices
1

Hello,
How can I use two of the RC522 with i2c bus? My library: GitHub

I did try to make a second MFRC522 class and duplicated the code.

So my try:

#include <Wire.h>
#include "MFRC522_I2C.h"

#define RST_PIN 2

MFRC522 mfrc522(0x2B, RST_PIN); 
MFRC522 mfrc522_2(0x28, RST_PIN);

void setup() {
  Serial.begin(115200);           
  Wire.begin();
  mfrc522.PCD_Init();
  mfrc522_2.PCD_Init(); 
  ShowReaderDetails();
  ShowReaderDetails_2();
  Serial.println(F("Scan UID"));
}

void loop() {
if ( ! mfrc522.PICC_IsNewCardPresent() || ! mfrc522.PICC_ReadCardSerial() ) {
    return;
  }
  for (byte i = 0; i < mfrc522.uid.size; i++) {
    Serial.print(mfrc522.uid.uidByte[i], HEX);
  } 
  Serial.println();

if ( ! mfrc522_2.PICC_IsNewCardPresent() || ! mfrc522_2.PICC_ReadCardSerial() ) {
    return;
  }

  for (byte i = 0; i < mfrc522_2.uid.size; i++) {
    Serial.print(mfrc522_2.uid.uidByte[i], HEX);
  } 
  Serial.println();  
}

void ShowReaderDetails() {
  byte v = mfrc522.PCD_ReadRegister(mfrc522.VersionReg);
  Serial.print(F("MFRC522 Software Version: 0x"));
  Serial.print(v, HEX);
  if (v == 0x91)
    Serial.print(F(" = v1.0"));
  else if (v == 0x92)
    Serial.print(F(" = v2.0"));
  else
    Serial.print(F(" (unknown)"));
  Serial.println("");
  if ((v == 0x00) || (v == 0xFF)) {
    Serial.println(F("WARNING: Communication failure, is the MFRC522 properly connected?"));
  }
}

void ShowReaderDetails_2() {
  byte v = mfrc522_2.PCD_ReadRegister(mfrc522_2.VersionReg);
  Serial.print(F("MFRC522 - 2  Software Version: 0x"));
  Serial.print(v, HEX);
  if (v == 0x91)
    Serial.print(F(" = v1.0"));
  else if (v == 0x92)
    Serial.print(F(" = v2.0"));
  else
    Serial.print(F(" (unknown)"));
  Serial.println("");
  if ((v == 0x00) || (v == 0xFF)) {
    Serial.println(F("WARNING: Communication failure, is the MFRC522 - 2  properly connected?"));
  }
}

The UIDs of the first device (0x2B) came up quickly, but the second device (0x28) made no output. Only if I put an nfc card on the first device, then came out an output.

Where is the problem?

2

You must use different RST pins for the two chips otherwise they disturb each other by resetting them to often.

3

I tested it out with different reset pins. But the phenomenon is the same.

4

Did you run an I2C scanner on your hardware setup? Does it see both devices? Otherwise your hardware setup is wrong.