For this project, I used a simple electromagnetic lock and a small wood door to simulate a house entrance.
Some information first:
- RFID is a acronym for radio-frequency identification.
- RFID is the contactless exchange of information. And a very big advantage is that the transmitter (tags) needs no own power. It can be passive.
- These cheap handy transmitter get the needed power from the electromagnetic 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.
More is coming soon.