Steve,

Actually a mulxtiplexer is designed to compress multiple serial lines into a
single physical proprietary formatted data stream. This single line may be
connected directly to a modem, frame relay or even tunneled on a TCP/IP
connection to a second multiplex whose job is to split the connection back
into distinct serial lines. A typical 4 port multiplexer system would like
like this:

+----------+ +----------+
device 1--| | | |--device1
| | | |
device 2--| |wire/phone | |--device2
| Mux |-------------| Mux |
device 3--| | | |--device3
| | | |
device 4--| | | |--device4
+----------+ +----------+

The point of using a multiplexer is to maintain separate physical
connections between the local and remote sides while only using a single
resource (typically a phone line). Each device maintains its independence
i.e. device 1 on the local side can only talk to device 1 on the remote
side, etc. This is exactly Mr Anderson doesn't want to do.

In fact, in Mr. Anderson's orignal post, he explicitly states that he has a
single broadcaster and multiple receivers. There can be no collisons. The
only question is whether the sum of the current draws of the the receivers
is enough of a current sink to pull down the 5 volt transmitter source.


Steve Lusardi wrote:

Lisa,
NMEA interfaces are slow and bit serial (EIA RS-232). The protocol is very
basic and there is no provision for either addressing or data collisions.
As you stated, your solution is incorrect, the device to use is called a
statmux or statistical multiplexor in general. Specifically, there are
multiplexors available for this purpose that prevent data collisions and
allow orderly sentence broadcast. Contact a qualified nav equipment dealer
for further info. These devices are inexpensive and available.
Steve

"Lisa Collins" wrote in message
...
You can easily make a Tee type of cable that has multiple NEMA outputs.
Generally speaking you are not supposed to do this but we have had
excellent results running 2 devices requiring NEMA data. Most serial
devices do not pull enough current to drop the 5 volt signal
signficantly.

The manufacturer of your radio should be able to tell you which part of
the
stereo plug is ground and which part is NEMA data in.

Lisa
www.ultimatepassage.com

William G. Andersen wrote:

How do I wire my GPS to multiple devices?
I have a Garmin GPS 12 (handheld) mounted on the instrument panel. I
use the Garmin PC/DC cable to get 12 volt power from my utility
lighter, and to connect to a serial connector.
I have a Furuno 1622 radar with a Furuno NMEA cable, to which I added a
serial cable to connect to the Garmin PC cable. That works great:
lat/long, waypoints, course and speed displayed on the radar.
I'm replacing my VHF radio with one that has DSC and NMEA input. The
NMEA
input plug looks like that on a stereo headset cord.
How do I get the GPS wired to that and the radar serial connector?