I believe that kids (and not only kids) that have their hands on electronics, wanted at least once in their lives to make an electronic keylock system for their house or room. When i was a kid, i had bought a Smart Kit Keycode lock system, and i had adapted it on the external door of my house. But this door had already the automatic-release mechanism. I only had to find which wires actuate this mechanism and hook the relay of the kit in parallel to this.
Then, i discovered that making a key-code circuit, is simple, very simple. As a matter of fact, so simple, that i designed this very simple key-code circuit, similar to the one from smart-kit but much better (mine had automatic reset operation when wrong code was entered), which took me only a few hours to design. Not to mention the microcontrollers… But why don’t i have a keycode-lock for my apartment’s door? Simple because it is expensive and needs a great mod on the door or frame.
Servo-Actuated Door Keylock Hack with capacitance touch-pad – [Link]
Devices known as electrical key-lock can de found in many versions, but I will demonstrate you another interesting workaround of that device. Specificity of that device is a new way to read more keys using only one input of microcontroller. As you can see I used an analog to digital conversation and with that method I can precise detect which key is pressed. This way of detecting keys can be implemented only with microcontrollers who have an internal A/D converter, and we will use PIC12F675, because we don’t need many ports for reading state of keys.
KeyLock - [Link]