The Door Lock

This is the project that I am proudest of. It is a system that enables someone to lock or unlock the door

a)      from inside, either with the use of a remote control, or with the use of the buttons on the project box next to the door, and

b)      from outside by using the keypad and entering the correct PIN. The servomotor then turns and locks or unlocks the door.

The LED’s on both the inside and outside indicate whether the door is locked or unlocked as well as if the system is in “guest mode” or not, meaning that there is a second PIN working. The LED’s are programmed to turn off 10 seconds after the last activity. The buzzer, is  programmed to make a characteristic “beep” sound when pressing the keys and to make a very disturbing siren noise if the wrong PIN is entered more than 3 times. I decided to build the pass-code protected door-lock, so that I could lock my door without having to carry a key with me. I later decided to implement the remote-control addition in order to be able to lock and unlock the door without having to  get up and go to the door.

The main parts are three: first, is the arduino uno which is at the inside of the door and is responsible for everything that the system does, second the little projects box on the outer side of the door, which has the keypad, some LED’s and the piezoelectric buzzer, and lastly, the servomotor with the key, that is responsible for the locking and unlocking of the door. I had little experience with arduino’s and programming up to then, so it was a bit challenging to finish this project.

In the beginning, the project was just a thought at the back of my head, until I decided to make a rough sketch of the required schematic and I research what would be needed to make something like that. After making a list of the items I would need, I built the core circuit on a breadboard and quickly realized two things: firstly, the speaker was not loud enough and second,  the servomotor would jitter and make noise when stationary. The second problem was easy to solve with the use of a simple transistor, in order to turn the power to the servo off when it is not needed. However, in order to solve the first problem, I created my own amplifier on a small part of a protoboard. After the project worked on the breadboard, I went on to transfer it on my door: one project box on the inside and one on the outside. The servo in front of the lock and the key attached on it. The wires encased in two UTP cables and went over the door in order to avoid any problems. The first version of this project had a few drawbacks; It had no remote control capability, it needed two different power supplies for the servomotor and the arduino and there was some problem with the filter of the of the amplifier used for the sounds, resulting in a somewhat jitterish sound, since the wire was several meters long. The latter was easily fixed by discarding the speaker and using a piezoelectric buzzer instead. The problem with the dual power supply was fixed with the use of a splitter inside the project box. Finally, I decided to upgrade the first version by enabling the use of a remote control. I took the remote control of an old television and hacked a broken DVD player to obtain its infrared receiver. I then analyzed the output of the remote control using an arduino, the infrared receiver I had just taken out of the old DVD player and some code that I wrote. Afterwards, I programmed the arduino microcontroller to recognize the signals of the remote control and installed the IR receiver.

Now, from the remote control I can lock and unlock the door, set it to normal or guest mode (determines which PIN will be used) and set the system on a “mute” mode. The “mute” mode means that the outside controls are isolated and whatever I do from the inside cannot be heard or seen by the buzzer or LED’s on the outside.

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