Rick,

I have been doing some mental calculations to help you:

Sound travels 1130 feet/sec at 75 degrees far. This is a great
place to start.  (The deviation is 1.1 Ft / degree far by the way)

That is 13,560 inches per second.

Using the formula  d = t * 13,560/2 you can figure out the distance
(in inches) from the unit.
d= distance in inches
t= time to ping an object and back

Therefore:
distance to object = time for ping to get there and back times 6780

d=t*6780

A 40Khz sound wave has a wavelength of .33 inches so I am not sure
if you can get much better resolution then .33 inches. Maybe I am
wrong on this - Does anyone else dispute this?

Now remember this is all in the AIR medium.  Water is about 4 times
these numbers as sound travels through liquids at 4,757 ft/sec.
And Steel is around 16,500 Ft/sec.

Interesting subject, Rick. Thanks for instigating it.


John Adams ------- http://pobox.com/~electronics ---------
electronics@pobox.com
Check out the H.W.S Internet Guide to Electronics book as well. Links on my
site