On Tue, 8 Dec 1998, Nigel Orr wrote:

> At 15:06 07/12/98 -0500, you wrote:
>
> Considered ultrasonics?  At that rate, a standard 40kHz ultrasonic link
> might be easier to do?  And you could probably run it from a PIC pin (or
> between 2 pins as push-pull) directly?  At the other end, just detect the
> on-off keyed signal with a pre-amp and rectifier.  This assumes there isn't
> alot of other noise in the water in the same frequency range... what's the
> application?

I'm worried that ultrasonics wont't work, - the application
is a "hoseless" scuba diving decompression computer.  "Hoseless"
because the air pressure hose from the tank to the processor is replaced
by a radio link that broadcasts the tank pressure to your wrist.
But it's not necessarily line-of-sight, and as you mentioned,
there's usually a DSP component when you're talking about acoustics,
which I'd really like to avoid.

There are a couple units out there
that do this already via RF, but they aren't telling
their freq data, of course.  They use low-power intermittent
bursts.  Really low power - one works for several years at
400 hours of use per year on a couple of button cells.

-Will

>
> Our systems could probably manage about 30km underwater at 1200 baud, but
> the DSP cards might be too big for your needs ;-)
>
> Nigel
> --
> Nigel Orr                  Research Associate   O   ______
>         Underwater Acoustics Group,              o / o    \_/(
> Dept of Electrical and Electronic Engineering     (_   <   _ (
>      University of Newcastle Upon Tyne             \______/ \(
>