Both HSPI and VSPI pins pulled down. Those pins cannot be used as GPIOs. Even when using a single SPI bus.

[EricRafaelP]

Step 1: Describe your environment

• OS version: Windows 10
• Arduino IDE version: 1.8.16
• MFRC522 Library version: 6599c0f95afdc5e3804940d473803357c2f4e72d from yoprogramo:master
• Arduino device: ESP32
• MFRC522 device: RC522

Step 2: Describe the problem

The library is somehow enabling HSPI in addition to VSPI, thus pulling down pins for both SPI buses. Those pins cannot be pulled up (therefore taking 8 pins to work instead of 4).

Expected Results:

• To be able to use the remaining pins as GPIOs (in this case, as interrupts with pullup configuration.

Relevant Code:

  #include <SPI.h>
#include <MFRC522.h>

#define SS_PIN 5
#define RST_PIN 32
#define RFID_RST          32
#define SPI_MOSI          23
#define SPI_MISO          19
#define SPI_SCK           18
#define RFID_SS           5

#define GREEN_BTN          13
#define RED_BTN           16
#define KEYPAD_INT        33

volatile bool green_button_rise = false;
volatile bool red_button_rise = false;
 
//MFRC522 rfid(RFID_SS, RFID_RST); // Instance of the class
SPIClass RFID_SPI(VSPI);
MFRC522 rfid(RFID_SS, RFID_RST,RFID_SPI);
MFRC522::MIFARE_Key key; 

// Init array that will store new NUID 
byte nuidPICC[4];

void setup() { 
  Serial.begin(115200);
  //SPI.begin(); // Init SPI bus
  RFID_SPI.begin(SPI_SCK,SPI_MISO,SPI_MOSI,RFID_SS);
  rfid.PCD_Init(); // Init MFRC522 

  for (byte i = 0; i < 6; i++) {
    key.keyByte[i] = 0xFF;
  }

  // ********* PIN SETUP ********* 
  pinMode(GREEN_BTN, INPUT_PULLUP);
  attachInterrupt(digitalPinToInterrupt(GREEN_BTN), greenButtonISR, FALLING);
  pinMode(RED_BTN, INPUT_PULLUP);
  attachInterrupt(digitalPinToInterrupt(RED_BTN), redButtonISR, FALLING);
 
}
 
void loop() {

  // Look for new cards
  if ( ! rfid.PICC_IsNewCardPresent())
    return;

  // Verify if the NUID has been read
  if ( ! rfid.PICC_ReadCardSerial())
    return;



 for (byte i = 0; i < 4; i++) {
      nuidPICC[i] = rfid.uid.uidByte[i];
    }
   
  printHex(rfid.uid.uidByte, rfid.uid.size);
    Serial.println();
   rfid.PICC_HaltA();

  
  rfid.PCD_StopCrypto1();

  if(green_button_rise){
        green_button_rise = false;
        Serial.println("Green button pressed");
      }

   if(red_button_rise){
        red_button_rise = false;
        Serial.println("Red button pressed");
      }
  
}



void printHex(byte *buffer, byte bufferSize) {
  for (byte i = 0; i < bufferSize; i++) {
    Serial.print(buffer[i] < 0x10 ? " 0" : " ");
    Serial.print(buffer[i], HEX);
  }
}


// ********* Interrupts *********
void greenButtonISR() {
  green_button_rise = true;
}

void redButtonISR(){
  red_button_rise = true;
}