RFID RC522 works sometimes

Projects Programming
1

I have a 522 module with very simple code to get the ID.

/*
PINOUT:
RC522 MODULE         MEGA
SDA                   D53
SCK                   D52
MOSI                  D51
MISO                  D50
IRQ                   N/A
GND                   GND
RST                   D5
3.3V                 3.3V
*/
/* Include the standard Arduino SPI library */
#include <SPI.h>
/* Include the RFID library */
#include <RFID.h>


/* Define the DIO used for the SDA (SS) and RST (reset) pins. */
#define SDA_DIO 53
#define RESET_DIO 5
/* Create an instance of the RFID library */
RFID RC522(SDA_DIO, RESET_DIO); 

void setup()
{ 
  Serial.begin(9600);
  /* Enable the SPI interface */
  SPI.begin(); 
  /* Initialise the RFID reader */
  RC522.init();
}

void loop()
{
  
  if (RC522.isCard())
  {
    /* If so then get its serial number */
    RC522.readCardSerial();
    Serial.println("Hello kevin");
    
    for(int i=0;i<5;i++)
    {
    Serial.print(RC522.serNum[i],DEC);
    //Serial.print(RC522.serNum[i],HEX); //to print card detail in Hexa Decimal format
    }
    Serial.println();
    Serial.println();
  }
    
  delay(1000);
}

Sometimes it will work for ages then it just stops!

Any ideas? There seems to be lots of discussions on this but no real answers.....

2

Have you got level shifters between the two systems? You need to have them as one works at 3V3 and the other at 5V.

3

So when connecting the RFID module to the Mega hardware SPI I need level shifters?

The on-line sketches I have been looking at don't say that. I know the RFID is 3.3v but the sketches don't specify shifters?

4

So when connecting the RFID module to the Mega hardware SPI I need level shifters?

Yes

The on-line sketches I have been looking at don't say that.

That is because they are written by idiots who haven't got a clue. It might just happen to function if you hold your face right but it is not a reliable design because the voltages involved at each end are not within the specification.
In order to recognise a voltage as a logic one or high, it needs to be greater than 0.7 Vcc. with a Vcc of 5V then this represents 3.5V, and your RFID module only spits out 3.3V. Now it is possible that 3.3V will be recognised as a logic one but it is not guaranteed, so the rule in electronics is always design to the guaranteed levels. Some idiots think they know better that this and think if it works for them it will work for everybody. They are wrong.

Similarly the 5V out of the Arduino is too much for the module and you could get damage of the RFID module.

I know the RFID is 3.3v but the sketches don't specify shifters?

See above.