A Non-Tactile Pushbutton

[JEC]

As it turns out, I know exactly how I'd design this for you.

A company called QPROX (qprox.com) sells integrated circuits which can be used to design touch-sensitive control surfaces - similar to an iPod control wheel, or the flat panel on your microwave.

The touch sensitive areas can be defined as any shape, and on nearly any non-metallic material.

There is a certain processing latency involved with these chips (typically tens of milliseconds) - but since it's a fixed quantity, you can compensate for it when you take your measurements.

It would then be simple to interface one of these ICs with our regular USB button box engines.

However...

It occurs to me that DirectRT can accept microphone input and record elapsed time between the presentation of a stimulus and reception of a sufficiently loud sound. I wonder if a simple microphone placed in close proximity to the tapping fingers wouldn't solve this problem straight away?