Inspired by several door-unlocking mechanisms I've seen on hackaday.com, I decided to create one on my own. This one has a two-button interface; one to start and end the password submission, and one to actually tap in the rhythm that is your password. There is also a status light. I was able to build this really cheaply using parts I had scavenged over the past few months. The only things I had to pay for were the microcontroller itself, which was $21 (http://www.pjrc.com/teensy/), and some picture hanging wire which I had from before.
It's lots of fun to tap in the Star Wars Theme or something to enter my room. Now, I don't have to worry about locking myself out of my room again! Plus, it feels good and geeky.
I chose the Teensy because this is my first microcontroller, and I don't have a programmer yet. The Teensy only requires an A-miniB USB cable and free software to install, compatible with Mac/Windows/Linux. Also, it's really easy to upload the hex file; just compile, and press the button on the Teensy.
The cost of this project to me was $21, plus the picture-hanging wire.
Parts from the street came from a coffee percolator (relay, LED, capacitor) and a router (LED, modular jack, power jack, capacitors). Free samples were the 7805 5-volt regulator, buttons and switch. I also found lots of stuff in the "broken parts" box in my EE lab: banana connectors and cable, wire, the sn754410 driver, a four-pin header and resistors. I had an extra laptop charger lying around that I used for power, and an Apple modem cable whose tab was broken.
Other hardware: a wall plate.
I used a hot glue gun, a soldering iron, a needle file and a power drill, which are pretty standard. The most unusual thing I used was a long, flexible grabber tool.