We had this idea since January but It was the last week when I started the project with Arduino, Bluetooth and Android.
It's been a while since I don't use Arduino, but It wasn't difficult to catch up though, what you can see in the picture is the first version of the circuit for my tests, the board with the HC-05 bluetooth interface.
The Arduino part is not the key here though(it's only used for the prototype), the most important part is the mobile application working with it, and that's where I am spending more time since last week, starting building the Android application.
For this app I am using a SurfaceView with a separate thread for painting and the Bluetooth library. Right now the application is able to handle other bluetooth devices such as the one in the picture and showing it nicely in a canvas when that happens.
My first attempts learning Android weren't fruitful enough because I didn't have a real idea of what to build, this time I will end up with something. :-)
I found really easy to debug the application from the terminal, I thought It was going to be more difficult and I was gonna need Eclipse, but I always avoid big IDEs, they are quite slow.
I am having a lot of fun learning Android! :-)