Touchscreen using sound input?

i don't really know if it is actually possible, but i believe that it can be made. How possible is it to make a program that recognizes different sound bouncing 开发者_开发百科from the screen and turn it into a position that will obviously be later fed to the mouse.

I know that it sounds kind of dumb, but lately i've been noticing that a very dull, strong sound is made when touching the screen, and that sound varies when doing so at different positions. Probably the microphone "hears" differently because the screen acts as a drum with the casing. Anyways, what do you think, anyone has any experience programming with sound?

First of all most domestic touch screens work by detecting pressure based on a criss-cross mesh layer underneath the display layer.

However I have seen an example where a touch interface was interrogated onto a pane of glass, it used 4 microphones to determine the corners, when you tapped a certain part of the screen it measures the delay in the sound getting to each microphone, therefore allowing one to triangulate the touch.

This is the methodology you would use, you don't even need to set up the hardware to test it, you could throw up an interface in VB, when you click in a box it sends out a circular wave and just calculate using the times it takes to reach the 4 points where the pointer is.

EDIT

As nikie suggested, drag & drop, or any kind of gestures would be impossible using the microphone method, as the technique needs a wave of sound to detect the input.

http://computer.howstuffworks.com/question7161.htm

I don't know if this will get you far, but you can investigate the techniques used in MIDI drums for returning various nuances of play.