If you're reading this article you're probably like me: I go through phases where I get so engrossed in a project (which most others would see as trivial), so focused on the goal that sleep and food are afterthoughts, I put my body through a gauntlet to appease some primitive urge of mine to CREATE.
Such was the beginnings of this project. I attended Google I/O 2011 and managed to get my hands on an Android ADK demo board. ADK is the Accessory Development Kit , an Arduino-based interface board whereby you can connect your compatible Android device (2.3.4 and any device from 3.1 onwards) to virtually any hardware and use the phone to control a device, or vice-versa. It's called the Android Open Accessory platform, and it's totally cool.
To introduce the concept to the Google’s keynote speech they produced a regular ball maze toy , familiar to many, which was controlled by a Motorola Xoom tablet. This Instructable is kind of two instructables in one: first, I'll be illustrating the steps required to set up the ADK from scratch and then I'll be reproducing Google's ball maze on a Nexus One phone to demonstrate a simple use of the ADK board (I'll keep the massive bowling-ball version for another Instructable).
So continuing with my story: I grew up with a ball maze, my parents had one as far back as I can remember. A little while after I got home from Google I/O I found the maze at my parents’ house and shortly thereafter I discovered I had everything I needed to make my very own Googley maze controlled by my Nexus One.
[Lights on, cue primitive one-tracked mind]
The goal was set: I had one night to make this from scratch, hardware and software. I'd never written a real-world Android app before (not that this is very real-world yet...), but I was convinced that it couldn't be too hard. I worked from 7pm to about 5am, though I probably could have done it in 2-4 hours if I had an Instructable like this to start with - being my first ever Android project, much of that time was reading!
Only the Nexus One (Gingerbread 2.3.4) has been tested with the code I'm supplying, but it should work with little to no modifications on a stock up-to-date Nexus S and possibly also Android 3.1 tablets. As of writing, I am unaware of any other supported devices or Android versions.
So dig through grandma’s game closet for that old ball maze, grab your Nexus, break out your Google ADK board if you went to Google I/O (or get a compatible one from the suppliers listed here ) and start building!
The idea is relatively simple: monitor the phone’s accelerometer, and translate the three-dimensional acceleration vector (ie. which way is "down") into a coordinates on a two-dimensional plane - one dimension for each servo or axis of rotation on the maze. This is mapped to two absolute positions between 0-255 for positioning the servo arms. These values are passed to the ADK board which acts as the servo controller and controls the tilt on the maze.
In other words, you can now play the ball maze game by using your phone as a remote controller!