Door mechanism with RFID

For this project, I used a simple electromagnetic lock and a small wood door to simulate a house entrance.

Some information first:

  • RFID is an acronym for radio-frequency identification.
  • RFID is the contactless exchange of information. And a very big advantage is that the transmitter (tag) needs no own power. It can be passive.
  • These cheap handy transmitters get the needed power from the magnetic field, created by the receiver. Unfortunately the field strength is deceasing inversely proportional to the square. (inverse square law)
  • Only short distances possible.
  • The signals can get through non metallic materials, such as wood or plastic.
  • The well-known RFID chip RC522 works with 13.56 MHz and communicates without encryption. A mikrocontroller talks with the chip over the SPI. (Serial Peripheral interface)


This is the receiver board with the good visible coil on the left side:

Two RFID tags:

You can also use your credit card if the symbol is on it, or an implant.

This is a screenshot of the pins, when nothing is in range:

NSS = Slave Select
MOSI = Master Out / Slave In
SCK = Clock sent by the board. (125 kHz)
MISO = Master In / Slave Out    (Slave sends data to the Master)

If the door is open and you put a tag for 10 sec. to the receiver board, it gets stored.  Not very safe 😉

 Such a door mechanism should have an UPS in real. In case the power grid is down.