MFRC522
by GithubCommunity
This library drives the MFRC522 RFID/NFC reader chip over SPI, handling the register-level commands needed to detect a card, read its unique ID (UID), and read/write data blocks on Mifare Classic and Ultralight cards. `PICC_IsNewCardPresent()` and `PICC_ReadCardSerial()` are the two calls behind virtually every "scan a card" project. The catch that trips people up is the reset pin timing — the RC522 needs a hardware reset pulse via the RST pin before it will respond, which is why `mfrc522.PCD_Init()` must run after `SPI.begin()` in setup, not before. Mifare Classic cards also use per-sector authentication keys (default `FFFFFFFFFFFF`), which trips people up if they try reading a sector that was previously locked with a custom key.
Installation
Arduino IDE — Library Manager
Sketch → Include Library → Manage Libraries → search MFRC522
PlatformIO
lib_deps = miguelbalboa/MFRC522Supported boards
Examples
Read a card UID
The standard pattern behind every RFID access-control or attendance-tracking project.
#include <SPI.h>
#include <MFRC522.h>
#define SS_PIN 10
#define RST_PIN 9
MFRC522 mfrc522(SS_PIN, RST_PIN);
void setup() {
Serial.begin(9600);
SPI.begin();
mfrc522.PCD_Init();
}
void loop() {
if (!mfrc522.PICC_IsNewCardPresent() || !mfrc522.PICC_ReadCardSerial()) return;
Serial.print("UID: ");
for (byte i = 0; i < mfrc522.uid.size; i++) {
Serial.print(mfrc522.uid.uidByte[i], HEX);
Serial.print(" ");
}
Serial.println();
mfrc522.PICC_HaltA();
}