I'm fairly new to Arduino (and C), but not to embedded electronics and programming.
I'm using an MFRC522 module (the common one) with a Nano, and getting some strange results. They are on a very simple custom PCB I've made (the only parts on it, except for a couple of LEDs on D4 & D5) I'm using SS_PIN on 8, and RST_PIN on 7, which is changed from 10 & 9, because the board will also be using an NRF24L01 module on the SPI bus (not fitted yet).
And I'm using the MFRC522 library. The DumpInfo example in the library works fine, but not the ReadNUID example.
When I bring a tag/card near the reader, the sketch (sometimes) gets some of its output to the serial monitor, but then (always) the board reboots and the startup messages appear again. This happens continuously while the card is near.
I have the RFID IRQ connected to pin D3, and while thinking that may be causing the problem, and trying all sorts of stuff, I found that it wasn't. In the process I did get the sketch to work, and have distilled the fix down to two seemingly superfluous lines of code:-
Added a null if statement at the start of loop:-
if (GotIRQ) {}
and defined a volatile variable for it to test:-
volatile boolean GotIRQ=false;
Doesn't work if it's not volatile. (A clue?)
What Gives? Some dumb newbie mistake?
(I could post the entire code if required, but I've started again from the original source, and only made the 2 changes and 2 additions described above)
Here is the code:-
/*
* --------------------------------------------------------------------------------------------------------------------
* Example sketch/program showing how to read new NUID from a PICC to serial.
* --------------------------------------------------------------------------------------------------------------------
* This is a MFRC522 library example; for further details and other examples see: https://github.com/miguelbalboa/rfid
*
* Example sketch/program showing how to the read data from a PICC (that is: a RFID Tag or Card) using a MFRC522 based RFID
* Reader on the Arduino SPI interface.
*
* When the Arduino and the MFRC522 module are connected (see the pin layout below), load this sketch into Arduino IDE
* then verify/compile and upload it. To see the output: use Tools, Serial Monitor of the IDE (hit Ctrl+Shft+M). When
* you present a PICC (that is: a RFID Tag or Card) at reading distance of the MFRC522 Reader/PCD, the serial output
* will show the type, and the NUID if a new card has been detected. Note: you may see "Timeout in communication" messages
* when removing the PICC from reading distance too early.
*
* @license Released into the public domain.
*
* Typical pin layout used:
* -----------------------------------------------------------------------------------------
* MFRC522 Arduino Arduino Arduino Arduino Arduino
* Reader/PCD Uno Mega Nano v3 Leonardo/Micro Pro Micro
* Signal Pin Pin Pin Pin Pin Pin
* -----------------------------------------------------------------------------------------
* RST/Reset RST 9 5 D9 RESET/ICSP-5 RST
* SPI SS SDA(SS) 10 53 D10 10 10
* SPI MOSI MOSI 11 / ICSP-4 51 D11 ICSP-4 16
* SPI MISO MISO 12 / ICSP-1 50 D12 ICSP-1 14
* SPI SCK SCK 13 / ICSP-3 52 D13 ICSP-3 15
*/
#include <SPI.h>
#include <MFRC522.h>
#define SS_PIN 8 //QQ This changed from 10
#define RST_PIN 7 //QQ This changed from 9
MFRC522 rfid(SS_PIN, RST_PIN); // Instance of the class
MFRC522::MIFARE_Key key;
volatile boolean GotIRQ=false; //QQ needed for null if statement
// Init array that will store new NUID
byte nuidPICC[3];
void setup() {
Serial.begin(9600);
SPI.begin(); // Init SPI bus
rfid.PCD_Init(); // Init MFRC522
for (byte i = 0; i < 6; i++) {
key.keyByte[i] = 0xFF;
}
Serial.println(F("This code scan the MIFARE Classsic NUID."));
Serial.print(F("Using the following key:"));
printHex(key.keyByte, MFRC522::MF_KEY_SIZE);
}
void loop() {
if (GotIRQ) {} //QQ If this is not included, board resets when a RFID tag is detected
// Look for new cards
if ( ! rfid.PICC_IsNewCardPresent())
return;
// Verify if the NUID has been readed
if ( ! rfid.PICC_ReadCardSerial())
return;
Serial.print(F("PICC type: "));
MFRC522::PICC_Type piccType = rfid.PICC_GetType(rfid.uid.sak);
Serial.println(rfid.PICC_GetTypeName(piccType));
// Check is the PICC of Classic MIFARE type
if (piccType != MFRC522::PICC_TYPE_MIFARE_MINI &&
piccType != MFRC522::PICC_TYPE_MIFARE_1K &&
piccType != MFRC522::PICC_TYPE_MIFARE_4K) {
Serial.println(F("Your tag is not of type MIFARE Classic."));
return;
}
if (rfid.uid.uidByte[0] != nuidPICC[0] ||
rfid.uid.uidByte[1] != nuidPICC[1] ||
rfid.uid.uidByte[2] != nuidPICC[2] ||
rfid.uid.uidByte[3] != nuidPICC[3] ) {
Serial.println(F("A new card has been detected."));
// Store NUID into nuidPICC array
for (byte i = 0; i < 4; i++) {
nuidPICC[i] = rfid.uid.uidByte[i];
}
Serial.println(F("The NUID tag is:"));
Serial.print(F("In hex: "));
printHex(rfid.uid.uidByte, rfid.uid.size);
Serial.println();
Serial.print(F("In dec: "));
printDec(rfid.uid.uidByte, rfid.uid.size);
Serial.println();
}
else Serial.println(F("Card read previously."));
// Halt PICC
rfid.PICC_HaltA();
// Stop encryption on PCD
rfid.PCD_StopCrypto1();
}
/**
* Helper routine to dump a byte array as hex values to Serial.
*/
void printHex(byte *buffer, byte bufferSize) {
for (byte i = 0; i < bufferSize; i++) {
Serial.print(buffer[i] < 0x10 ? " 0" : " ");
Serial.print(buffer[i], HEX);
}
}
/**
* Helper routine to dump a byte array as dec values to Serial.
*/
void printDec(byte *buffer, byte bufferSize) {
for (byte i = 0; i < bufferSize; i++) {
Serial.print(buffer[i] < 0x10 ? " 0" : " ");
Serial.print(buffer[i], DEC);
}
}
OK, trying to cut down to a minimal example has proved useful. It seems the problem is caused by the loop that stores the NUID, but not if the superfluous if statement is present. The code is :-
// Cut down version of MFRC522 library ReadNUID example that exhibits strangle
// problem of rebooting the board when a card is near the reader.
// But only if:-
// * the Store NUID loop is included
// and
// * the superfluous "if" statement at start of loop() is NOT present.
// Changes from original example are indicated by comments starting with "//QQ"
// (plus a lot of removed code)
#include <SPI.h>
#include <MFRC522.h>
#define SS_PIN 8 //QQ This changed from 10
#define RST_PIN 7 //QQ This changed from 9
MFRC522 rfid(SS_PIN, RST_PIN); // Instance of the class
MFRC522::MIFARE_Key key;
volatile boolean GotIRQ=false; //QQ needed for null if statement
// Init array that will store new NUID
byte nuidPICC[3];
void setup() {
Serial.begin(9600);
SPI.begin(); // Init SPI bus
rfid.PCD_Init(); // Init MFRC522
for (byte i = 0; i < 6; i++) {
key.keyByte[i] = 0xFF;
}
Serial.println(F("This code scan the MIFARE Classsic NUID."));
}
void loop() {
// if (GotIRQ) {} //QQ If this is not included, board resets when a RFID tag is detected
// Look for new cards
if ( ! rfid.PICC_IsNewCardPresent())
return;
// Verify if the NUID has been readed
if ( ! rfid.PICC_ReadCardSerial())
return;
Serial.print(F("PICC type: "));
MFRC522::PICC_Type piccType = rfid.PICC_GetType(rfid.uid.sak);
Serial.println(rfid.PICC_GetTypeName(piccType));
// Store NUID into nuidPICC array //QQ does not fail if this loop is excluded
for (byte i = 0; i < 4; i++) {
nuidPICC[i] = rfid.uid.uidByte[i];
}
// Halt PICC
rfid.PICC_HaltA();
// Stop encryption on PCD
rfid.PCD_StopCrypto1();
}
