Dorms are magical places that are full of both elation and despair, studious learning and alcohol-fueled mistakes. For most residents, their dorm is the first place they’ve ever lived without their parents. That means they’re free to decorate with Scarface posters, liquor bottles, and milk crate-based furniture. It also means they can integrate new technology that their parents would struggle to adapt to. That’s what California State Polytechnic University student Keavon Chambers did when they created this NFC Door Unlocker.
Like all other dorms on the planet, Cal Poly’s doesn’t allow residents to actually modify anything. That includes the door, or even re-keying the lock. That’s why Chambers’ NFC Door Unlocker doesn’t make any alterations to the door itself, and still allows the lock to be turned with the regular key. However, it does let Chambers unlock the door with the swipe of a simple NFC key card. The system is sensitive enough to work through a bit of air and clothing, which means Chambers doesn’t even have to take the card out of his pocket. The system will also automatically lock the door once it has closed.
To build this, Chambers used a Teensy 3.2 microcontroller development board paired with an Adafruit PN532 NFC reader module and a MIFARE DESFire EV1 NFC keycard. That card was chosen because it has built-in encryption circuitry that prevents would-be burglars from cloning the authentication key. The Teensy 3.2 is placed over the lock inside on a 3D-printed mount, and the NFC reader is outside the door. Chambers says that exposing the NFC reader doesn’t expose the system, as all of the authentication is handled by the Teensy 3.2 inside. A simple hobby servo motor is used to turn the lock when the correct NFC card is detected. The mechanism to turn the lock was specifically designed with a gap so the lock can be operate with a normal key without having to force the servo motor to turn.
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Author: Cameron Coward