That's the serious limitation of single transducer designs, you have to
wait
for the transducer to settle before making it into a receiver.
> But even when I used two, the cross-talk was enough
> to mess up readings less than 20cm (~8 in). Did you do anything fancy?
Not really, I bunged it together on my breadboard. I recall I initially
had what I thought were crosstalk problems (I'm working without a
scope), it turned out to be the signal was so good, it was reflecting
off the ceiling :-)
I rebuilt that circuit about a month ago, and I had some crosstalk that
was very hard to eliminate, I just did some more decoupling and
filtering, in the end I only had a range of about 1 foot. I couldn't
find the diagrams I made from the original experiment due to a hard
drive crash :-(
Thomas pointed out the danger of vibration, I think that can be
minimised by fitting the transducers in grommets or something similar,
anyway I'll find out when I try the experiment. I should be able to
compensate for crosstalk in software.
I thought about sending discrete pings like before and reading them
through the AD, if the vibration is too much of an issue, then that's
what I'll do. I can hold the return signal in a cap for a few
milliseconds while the interrupt starts an AD conversion. This will
limit the mimimum distance it can work over but that still might be
within range, as I said the original version could range down to about
5cm.
How's the word wrap on the last 3 paragraphs?
Dave Everett.
>
> Robin.
> --
> R.M.O'Leary <robin nospam at acm.org> +44 973 310035 P.O. Box 20, Swansea SA2 8YB, U.K.