I want to determine orientation (pitch, roll and yaw), and ignore other movement. As far as I understand, the best way to do this would be with a 3-axis accelerometer, 3-axis gyroscope and a 3-axis magnetometer. At least, within a reasonable budget and small size. SO that'll take up 9 pins in total - which is more than the number of analogue pins on the duemilanove, but not than on the mega.
I've read that the PMW pins accuracy is effected by the comparison between the clock of the microprocessor and the frequency, hence analogue is the more accurate choice. Does this apply to the arduino at all, though, since all of the data is digitised and exported digitally? Does it all come to the same thing? If so, I'd not be losing accuracy by choosing a PMW capable sensor and buying the cheaper board?
My concern is that the clock isn't especially accurate on the arduino, and wanted to bypass that as a problem. It could be that its plenty accurate enough for what I want, and I'm simply too n00bish to know.
Any advice appreciated, and sorry for the rambling post.