On Sat, 31 Jan 2004 16:27:07 +0100, "Meindert Sprang"
wrote:

"Larry W4CSC" wrote in message
...

Ethernet requires a router and ethernet hubs to
connect devices.

No it does not. Ethernet over 10base-T (cat5 cable) requires a hub and a
cable to every device. The now almost obsolete thin ether net (10base-2, or
coax) would allow you to run a cable from device to device, using BNC T's at
every device.

The keyword is "obsolete". SOMEONE in an ethernet system has to be in
CONTROL, assigning IPs and controlling the movement of packets. It's
not just a broadcast medium. Again, we have the old problem of ONE
talker and a bunch of listeners, just like NMEA0183.

Of course, it will keep Meindert in work if we have extra boxes to
buy...(c;

USB, on the other hand, WOULD let the GPS talk directly to the chart
plotter.

No. USB works with one master and many slaves. Generally the computer is the
master an all other devices are slave. To make a GPS master, it would
require different USB hardware inside the GPS and quite some computing power
to behave as a USB master.

Same problem I point out with the router or hub scenario. Tons of
wiring to a central control point. Where will all the wires go in the
overloaded boat wireways? Who will act as the controller? Will I
have to buy a $2000 notebook to act as a "hub" for the USB? Not
practical, either financially or physically.

But, USB wouldn't work well in a broadcast situation because
it only allows two devices to talk to each other.

USB is master-slave. So only the master can initiate communications to a
slave, by asking if the slave has something to say. Slave can NEVER talk to
eachother.

Same as NMEA.....one talker many listeners. Same old problems.

NMEA2000 (CAN based) isn't all that bad, the problem is that it is not an
open protocol and you have to pay heavily to get your first NMEA2000
compliant device on the market. Buying the standard documents, test suite,
manufacturet and product ID for the first product costs about $10,000!

Like I have mentioned before, NMEA-0183 could well be upgraded to higher
speeds and a bidirectional bus (RS-485). Something like combining NMEA
(point to point, but RS-422) and Seatalk (broadcast but single wire) into
high speed RS-485. Still cheap to implement.

Wireless, either 802.11-something ethernet or Bluetooth is the best
answer. Wireless uses no wireway space. Instruments can be placed
anywhere you can get DC to them.

If you can get DC to an instrument, you can also get a twisted wire to that
instrument.

Wireless is too unreliable. When I walk away from my Bluetooth multiplexer
with my Palm in hand, I lose conact after one brick wall and 5 meters
distance. Even my WLAN stops at two concrete floors.

I have no problems with my Bluetooth connections at 20 ft. I don't
have any brick or concrete walls in the boat. They are conductive and
absorptive, unlike fiberglass and plastics used in boats. Maybe we'll
just use 802.11b?

So imagine what happens in a metal hull.....

Meindert


Notice my note that this is for PLEASURE YACHTS made of PLASTIC AND
FIBERGLASS. How many boaters in any marina have a steel hull? Here,
I'd say it's around 1%? less?



Larry W4CSC

No, no, Scotty! I said, "Beam me a wrench.", not a WENCH!
Kirk Out.....