I've done a gravity-based sensor project - a physically small one - that uses an ADXL345 3-axis accelerometer. It works great and yields quick and accurate attitude data in a mostly-stationary environment. I included a pair of momentary switches for mode and data entry, but I want to lose them and use tap/doubletap sensing instead, and I've got that working, mostly.
I can currently sense tap-pause-tap, tap-pause-doubletap, doubletap-pause-tap and doubletap-pause-doubletap - and the no-pause versions of those four commands. I expect I'll be able to extend that to directional taps (top/bottom, left/right, front/back), too, but the logic is getting messy - even using a state machine - and it is too frequently confusing motion for commanding.
Has anyone done or seen a treatise on tap menuing?