Re: [mowbot] A Lurker Says, "Hello".

Dave Everett (Deverett nospam at
Wed, 25 Sep 1996 08:18:07 +1000

robin nospam at wrote:
> Dave Everett <Deverett nospam at> wrote:
> > I did build a sonar system last year that had a range of about 3 metres,
> > but it also had a minimum of about 2 inches. I might do a few experiments
> > with that later on.
> I'm impressed! Most of my experiments were with a single transducer,
> and ring stopped anything less than about 50cm (maybe 40cm with
> stepped gain).

That's the serious limitation of single transducer designs, you have to
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

How's the word wrap on the last 3 paragraphs?

Dave Everett.

> Robin.
> --
> R.M.O'Leary <robin nospam at> +44 973 310035 P.O. Box 20, Swansea SA2 8YB, U.K.