miguelbalboa/rfid

This is an Arduino library for MFRC522 and other RFID RC522 based modules. It allows you to read and write different types of Radio-Frequency IDentification (RFID) cards using an RC522 reader connected via the Serial Peripheral Interface (SPI).

Note on Development Status: The library is in a feature freeze. No new functions or APIs are being added; updates are limited to bug fixes, typos, or documentation. For advanced development, consider using the RFID_MFRC522v2 library.

The MFRC522 library and hardware have the following limitations:

• No Card Simulation: The reader cannot act as a card.
• No Mobile Communication: You cannot communicate with mobile phones using this hardware.
• No Peer-to-Peer: Peer-to-peer communication is not supported.
• Feature Upgrades: If you require NFC or more advanced features, consider using a chip like the PN532.

The library primarily targets Arduino boards. However, it is compatible with the following boards (though you may need to change pins and not all examples will be available):

• Teensy
• ESP8266 (via Arduino IDE board plugin)

Note for Advanced Users: If your microcontroller supports multiple SPI interfaces, this library only uses the default (first) SPI of the Arduino framework.

To use this library, ensure your environment meets the following requirements:

• Arduino IDE: Version 1.6 or newer is required. Older versions are not supported and will cause compiler errors.
• Custom Compilers: If you are using your own compiler instead of the Arduino IDE, you must enable c++11 support.

You can initialize the MFRC522 object using one of three constructors depending on your hardware wiring:

1. Default: Uses default pins.
2. Reset Pin only: Specify only the resetPowerDownPin.
3. Full Configuration: Specify both chipSelectPin and resetPowerDownPin.

After instantiation, you must call PCD_Init() to begin communication with the module.

If the library reports an unknown firmware version (e.g., 0x12), try the following:

1. Initialization Delay: Some boards require more time to stabilize after initialization. Add a small delay immediately after calling PCD_Init():

mfrc522.PCD_Init();
delay(4);

2. Connection/Power: Intermittent reporting of random firmware versions is often caused by poor connections or an unstable power source.
3. Hardware Authenticity: If the firmware version is permanently reported as unknown, the hardware may be a counterfeit or defective.

If your tag or card is not being detected, verify the following:

1. Frequency: Ensure the tag is 13.56 MHz (Mifare Type A). This library does not support 125 kHz animal RFID tags.
2. Type: NFC tokens are not officially supported (though some may work).
3. Distance: The distance between the antenna and the token must be less than 1cm.
4. Security/Protocol: Newer Mifare cards (e.g., DESFire, Ultralight) may fail due to missing authentication requirements. Check the security or protocol documentation for details.
5. Encryption: If you can only read the card UID, the card is likely encrypted (e.g., public transport or university cards). This library cannot bypass such encryption.

If you encounter WARNING: Communication failure, is the MFRC522 properly connected? or receive no input from the reader, check the following:

1. Physical Connections: Verify pin settings in your code against the physical wiring. Check for cold solder joints on the pin headers.
2. Power Supply: Ensure the power supply is stable. Adding a capacitor between 3.3V and GND can help. Most breakouts work at 3.3V; while some are 5V tolerant, SPI communication specifically requires 3.3V. Use a level shifter if necessary.
3. Signal Integrity: SPI is sensitive to long connections and prototyping boards. Use shorter wires and soldered connections where possible.
4. Hardware Defects: Some MFRC522 breakouts may have soldering issues on the board itself.

If you experience timeouts or intermittent tag detection, try these steps:

1. Physical Positioning: Try the other side of the antenna or decrease the distance between the MFRC522 and the tag.
2. Increase Antenna Gain: You can increase the antenna gain using the following method:

mfrc522.PCD_SetAntennaGain(mfrc522.RxGain_max);

3. Power: Ensure you are using a high-quality power supply.
4. Hardware Quality: Low-quality components (common in some inexpensive breakouts) can affect detection. Specifically, some boards may require replacing L1 and L2 inductors with 2.2uH inductors with higher operating current, or replacing C4 and C5 with 33pf capacitors to tune the matching circuit.

The MIFARE Ultralight C chip has 192 bytes of memory, organized into 48 pages of 4 bytes each.

Page Map:

• Pages 0 + 1: Used for the 7-byte UID.
• Page 2: Contains the UID check digit, one byte of manufacturer internal data, and the lock bytes.
• Page 3: OTP (One Time Programmable) bits. Once set to 1, they cannot be reverted to 0.
• Pages 4-39: Read/write pages, unless blocked by lock bytes in Page 2.
• Page 40: Lock bytes.
• Page 41: 16-bit one-way counter.
• Pages 42-43: Authentication configuration.
• Pages 44-47: Authentication key.

The MIFARE Ultralight chip has 64 bytes of memory, organized into 16 pages of 4 bytes each.

Page Map:

• Pages 0 + 1: Used for the 7-byte UID.
• Page 2: Contains the UID check digit, one byte of manufacturer internal data, and the lock bytes.
• Page 3: OTP (One Time Programmable) bits. Once set to 1, they cannot be reverted to 0.
• Pages 4-15: Read/write pages, unless they have been blocked by the lock bytes defined in Page 2.