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Door Unlocker
Keys are obsolete. Everyone in your college dorm probably uses keys to enter their rooms. Why not be different, and make a home-made alternative authentication system? Now here at MIT the administration actually cares if the door locks or strike plates are modified, so I need a way of locking and unlocking the door without modifying any door components. The solution? Make something to pull the door handle.
History of my door unlocker
The very first version of my door unlocker was made when I was somewhat new to building circuits on my own and when I had no digital circuit experience whatsoever. It was based off a scrap mechanical part I found with a worm gear translation, a string, an aluminum rod to gain leverage on the ultra-high-force Simmons Hall doorknob, and some wonderful RC timing and relays that sent the motor forward, stopped, waited, and reversed the motor in order to pull and release the door handle, thus unlocking the door:
The signal was simply a pulse sent to the circuit by a 486 laptop if the external keyboard mounted on the other side of the door typed the correct password. The second version of my door opener was created when I found an old IBM typewriter. I completely disassembled it and used just the nice stepper motor tracking for the head, which allowed for much more precise control of the distance that the string travelled to pull the doorknob. This was also accompanied by an LCD display, separated from its 33Mhz NEC laptop and mounted through the door, sending the wires through the hole left after unscrewing the provided eyehole:
(back of the door)
(front of the door)
The LCD display permitted people to leave messages as well as enter a dialog box that would allow a password to be entered to unlock the door. The second version of the door opener also used a variety of other entry authentication systems, including using a barcode scanner (where to enter my room you would have to bring a particular brand of EZ Mac and scan the UPC to enter), using magnetic reed sensors positioned strategically behind the door (where you would have to tap the correct sequence at the correct place on the door with a strong magnet), and capacitive (where you just tap your fingers on the doorknob itself in a particular pattern). After moving enough times I just settled for the password system.
The current version
The current version of the door unlocker uses no computers, but rather a PIC16F630 microcontroller attached to a PS/2 keyboard (using my PIC PS/2 keyboard driver) and four IRL520 transistors used to drive each coil of the stepper motor. A string is attached to the sliding head where a typewriter head would have been (it has quite a strong pull!) and is tied to a C-clamp that grasps the door handle. Here are some pictures:
(back of the door)
(all the electronics are in this box)
(the PIC16F630-based circuit inside)
(outside of door with waterproof PS/2 keyboard)
Schematic
Code
A quick-and-dirty program to drive the door unlocker here. When the correct 5 numpad keys are typed in order, it unlocks the door. Uses the PIC PS/2 driver I wrote.
Other home-made door opener ideas at MIT that I have seen done
- Thumbprint scanner
- Touch-sensitive pads disguised as artwork
- Magnetic card reader
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