[sdiy] Phototheremin and ultrasonics....

[harrybissell at prodigy.net]

Ultrasonics are not easy to use for this position sensing
application, especially in multiple axis.

There is a minimum distance in most apps... generated by the
amount of time the transducer 'rings' after you transmit a pulse.

You cannot use a fixed frequency because of the potential for destructive
interference from multiple reflective objects... the Polaroid (and similar) systems use a pulse burst of several spaced frequencies so that
one of them is bound to get through...

Multiple axis would be hard, but not insurmountable

Interference from other ultrasonic sources (cymbals, for instance) might
be a big problem

If you choose to use a phase shift type detector (rather than echo ranging)... the wavelength of the ultrasonic system (in air) could be
a limiting factor as well...

That (all) said... I'd consider ultrasonic for one axis control, possibly with the other axis done optically...

H^) harry

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