Just thought I’d share (i.e., show off an Arduino based project using all open source software, an rfid reader from ebay, and an xEMi [xEM Tag + Injection Kit].
$57 for the tag and injection kit
$12 for the door latch (ebay)
$8 for the rfid reader.
$20ish for the Arduino (I wire my own using an atmel328). The board is powered by a standard 12vAC bell transformer.
The code to read out the rfid reader is from: https://github.com/monkeyboard/Wiegand-Protocol-Library-for-Arduino
… and I use the standard flash library that comes with the Arduino ide to save the card codes for later lookup. A standard electrical box (like for wall switches, or sockets) is used for the electronics, with a blank cover. I drilled two hols in the blank cover for an, “erase” and an, “remember” code buttons. A couple LED’s provide feedback.