RFID functions and interpreting its data

Projects Programming
1

So after much reading and investigation. I've pretty much realized that using the mfrc522 is beyond me in many ways :sweat_smile:

I have read the specs on it a few times over and I understand the way the sectors, blocks and trailer sections are set up... I have an understanding of how it communicates with a given picc... but still after days and days of agonizing over different examples and trying to write my own small snippets i've identified a few things I still dont understand that can help me move forward:

  1. I still dont understand the type of data that the PCD is transfering to the arduino... what I think is happening is that serial data is filling up the serial buffer as like... hex or asci and waiting there to be read.

  2. I dont know how to check for, read, and use the information using the mfrc522 library... i've read through the library a few times and I just dont understand the explanations of the functions.

  3. I've been assuming that :

mfrc522.PICC_IsNewCardPresent() - checks if a new PICC is present

and

mfrc522.PICC_ReadCardSerial()) - reads the UID

if these are assumptions are true, where is the data from the UID being stored? and what is the best way to interpret and use this data?

in my code I constructed a for loop that first

creates an led animation

then i wanted to used the mfrc522.PICC_IsNewCardPresent() and mfrc522.PICC_ReadCardSerial()) functions but then... I just dont know where that data is going.

what I'd like to do is something like (obviously this me making a kind of pseudo code):

//create a variable called "Key1" and make it equal zero in a for loop. this loop cycles until key1 = 1

for(byte Key1 = 0; Key = 1; +0 ){

Led animation;

check if card present;

if (card is present){
key1 +1;
//if PICC present, return a value of 1 to Key1 and break for loop

}

Read cardUID;
int ReadId = CardUID

If (cardUID = Masterkey) {
Serial.println("you finally freakin did it!");
led animation;
}
}
//and yea the arduino spoke to and from the PCD, and all was right with the land

2

The library has examples. DumpInfo.ino seems to show a very simple application using it.

3

Well yes, the library has examples. Your right about that, but that doesn't answer any of my questions... ive already established that. That is always the first place i check to understand how to use different functions.

the DumpInfo.ino might be an example of the data being interpreted, but it cant tell me what value if any it returns from using the functions i'm asking about, or helping me understand the type of data or how to utilize it.

i dont want to just copy and paste lines of code if I dont understand what its doing or how to really use it correctly...

4

That library is a really bad example of how to write a library. But it is useable.

what I think is happening is that serial data is filling up the serial buffer as like... hex or asci and waiting there to be read.

All the data is in bytes. These bytes are stored inside the chip at certain addresses in the chip.

Hex is just a human way to represent a byte, and ASCII is an interpretation you can apply to a byte.

The bytes from the chip are read normally through an SPI interface. Many of these bytes inside the chip are read from the RFIF token when a new token is presented to the reader.

I dont know how to check for, read, and use the information using the mfrc522 library

As the library simply reads bytes from the chip your best bet at understand it and what these bytes stand for is to get the data sheet for the MFRC522 chip. This contains far more data than you need to know, but there is a section with all the registers and what the bits in each mean. For example there are some bytes that make up the URL.

What the library does is to read some of these bytes and return things like a new token has been detected message.

5

what I think is happening is that serial data is filling up the serial buffer as like... hex or asci and waiting there to be read.

sorry :sweat_smile: i'm interpreting it the best that my brain can muster.

but there is a section with all the registers and what the bits in each mean.

I saw that on the sheet, but I wasn't sure what to really make of it. I know its probably useful if i could figure it out :stuck_out_tongue:

but Update:

mfrc522.PICC_IsNewCardPresent() - definitely does what I thought it did, if i understand correctly... it just returns a true or false value.

... Ive managed to get the led strip to cycle through the way i want, but it happens with any PICC instead of reading the UID and creating case by case events....

I have an example that someone else has done but the code is so visually dense to me that its difficult to make out what is going on. lol if I had my printer up and running, I would consider cutting it into sections and trying to interpret it section by section.... :sweat_smile:
in any case. Thanks for directing me once again.

whats the saying again? ..."everybody gets ONE" lol.

6

lol if I had my printer up and running, I would consider cutting it into sections and trying to interpret it section by section.

We you could do that with a word processor.

I did write a library for this chip that makes a lot more sense. Unfortunately it is written in Python for the third edition of my book Raspberry Pi for dummies so it is probably not much use to you.