You’ve all experienced the power of acoustic resonance when you’ve tapped out a drum beat out on your desk, or knocked on someone’s door. Hard, dense surfaces are great at propagating sound waves, and that can be harnessed for more than just playing music. Ben Hencke’s TapTDOA project is designed to use those acoustics to provide a control interface that can be integrated into just about any device, and at a very low cost.
TapTDOA stands for “Tap Time Difference of Arrival,” and that describes the system well. The project utilizes piezo elements as contact microphones, which can easily pick up the sound waves moving through a hard material. With some calibration, those waves and be filtered and processed to determine exactly where on the surface you’re tapping. It works like a complex form of triangulation, where the precise time differences between the piezo elements detecting a tap is used to calculate the location of the tap.
That detection can be used in two ways, either in conjunction or separately. First, TapTDOA could be used to recognize a pattern of intervals between taps, and the intensity of those taps. Second, it can calculate where on the surface you’re tapping, which is the real magic. Imagine tapping out a pattern between specific areas of your door in order to unlock it. TapTDOA is still being developed, but there is already a lot of work done if you want to start experimenting with it yourself.