Wow Lori, this is going to be even longer than you post... I'll do my best, but would not know how to keep it short AND clear. I did not know anything about NMEA when we bought our boat; a little more know but by far too little.
I'll first start to clarify a little.
First about the controller behind your fridge.
As far as I know this is the solutions for the earlier Mahe's, when Simrad's AT10 did not exist yet. It has a Furuno controller behind the fridge. I do not know it's functions except for that it must have an NMEA2000 <-> NMEA 0183
translator. Let's call this "Instruments Mark I". Year 2006/2007
In later models this expensive Furuno module was replaced by the cheap
and simple Simrad AT10. Let's call this "Instruments Mark II", which I have, and Cotemar. This Simrad AT10 is the thing you could not find, of course, you having Mark I instruments. Year 2008/2009.
At this moment there is an NMEA2000 version of the autopilot. Now that this is the case, the whole Furuno equipment
MAY have switched to NMEA2000, removing the need for the Simrad AT10.
This is my speculation; it has to be confirmed by somebody having a 2010 or 2011 Mahe. Let's call this "Instruments Mark III".
In this case it might be difficult to connect NMEA0183 stuff like AIS
or older plotters; or there might be a provision on the new autopilot, like a configurable in/output.
Anyhow, newer AIS equipment
, like the one I just bought, also has USB, avoiding this problem.
I would like to help you, but I do not know the Furuno controller of the Mark I's. You have to help yourself, but maybe my input is useful by translating it to your situation. Maybe make a diagram, and write on all wires which NMEA data is going which way. And study the autopilot manual, your can do a lot of configurations of input and output data. Also on Internet
you can find a lot of information from people who have reverse-engineered the NMEA data (you have to pay a lot of money
to get NMEA specifications).
First let me explain my set-up, see attached diagram. This is the standard diagram from Pochon for the Mark II's, published earlier, with my additions.
There is a 3-position switch. This gives the autopilot 3 options as input:
MIDDLE POSITION is the factory set-up. The autopilot uses the data from the Furuno GP32; including waypoint data. This is now a back-up solution for cases where both my plotter AND PC break down. Uses lowest power, useful for ocean crossings.
LOWER POSITION is what I used in 2008 and 2009. This is based on a Garmin
276C 4-inch plotter with in-built GPS
. Power consumption
is quite low, maybe 200 mA or so. It works very well. The moment I change a waypoint, the autopilot gives 5 beeps and the ship changes course. Nice in heavy rain. This now is also a backup solution; the plotter goes into the oven
in case of lightning
from thunderstorms, together with a hand VHF
UPPER POSITION is new in 2010. It uses an ASUS UL50A series laptop
as plotter with plotter software
and maps. This laptop
uses 0.9A at 12V despite it's big screen
. This is reached by using a low-voltage SU7300 processor and LED backlight.
It also used a Miniplex Lite multiplexer. 4 inputs, a.o. for AIS. Simple, no programming required.
I used 2 inputs of the multiplexer, see the diagram:
- One input for position from the Furuno GP32 GPS
- One input for data coming from NMEA2000, like depth
and STW and wind data. This was connected to the AT10's output on the NMEA0183 side, using the spare wire.
To my regret I was not able to get the waypoint data from the laptop to the autopilot. I succeeded only into getting XTE out of the multiplexer. This is probably due to the plotter software
version number which had bugs. I need to upgrade this plotter software. As a consequence, if I wanted the autopilot to steer to a waypoint, I used the Garmin
276C to generate the waypoint, switch in lower position, and navigated on the laptop for having an overview on the big screen
The 3-position switch and the multiplexer are in the instrument panel. The AIS will also go there.
OK, now about your plan to use the autopilot as multiplexer. I have also considered this, but I have not done so for the following reasons:
- This would require a wire from the AP to the instrument panel, which is not yet there. In my solution the spare wire that you describe could be used...
- More important: I worried about the system becoming confused internally. As an example: position and waypoint data would go from the Furuno GP32 to the autopilot, would be multiplexed there internally with the NMEA2000 data. The waypoint and position data would then go to the multiplexer. But at the same time your PC plotter software would OUTPUT the same data to the multiplexer. This would also go to the autopilot, if you want the autopilot to be able to head
for the waypoint position on your PC screen. This is a loop.
You can think of other possible internal contradictions....
- Third, I don't have this problem since my multiplexer has sufficient inputs
- Problem with my setup is that on the PC I only get data from NMEA2000 and from the GPS, and NOT from the autopilot. There is some useful data that I can now not get on the PC, for instance the true wind speed and direction. These are not made available by the NMEA2000 wind instrument, but are re-calculated by the autopilot.
OK, now to my 2011 plans:
For above reasons I have decided to upgrade my Miniplex Lite to a new version of the Miniplex USB multiplexer. This is is fully SW configurable, NMEA input and output sentences can be enabled / disabled. (And even the multiplexer's SW can be upgraded in case of bugs). This means that IF necessary, I can break loops like I mentioned above by disabling certain outputs.
I got the module in by mail today from this Dutch company. They waited to send it to me until now because only last week there was a new SW version in it that allows SW upgrades by downloading.
Furthermore I have purchased an AIS transponder with built-in antenna
splitter. It's called EasyTRX2-is (internal splitter). It is designed and produced in Germany
. Nice thing is you can set an internal collision
alarm. It will give a strong beep, even when both Garmin plotter and navigation
PC are switched off to reduce power consumption
. This is nice for our future ocean-crossing plans. Also it saves your route
, and of the other ships, on a memory card. Nice for insurance
claims... If you're not dead.
And the plan is to upgrade my PC plotter software and the wiring, with the aim:
- To be able to send waypoint data to the autopilot
- To see AIS both on a separate program, and as overlay on the plotter program
- To get wind data and so on the PC
-The planfor 2012: to get radar
screen and overlay on the laptop....
Are you still with me?
I have a lot of back-ups, both the Furuno GPS and the Garmin mini-plotter for the navigation
PC. The Garmin can even be used in the dinghy
and in cities, it runs 10 hours on internal battery. Also we have a 2nd laptop, used for browsing, emails, pictures and watching DVD's. It also has the full set of navigation SW. But will use 2-3 amps i.s.o. 0.9A.
Please note it is quite complex. There is a lot of puzzling out to do. For instance, the GP32 has a software table which informs the whole system about the compass
variation for the spot where you are..... This is used to define the difference between true and magnetic heading on the autopilot.....
Any suggestions are appreciated. And please correct mistakes
in this explanation.
Also, I still have not figured out how to get the image from a standard radar antenna
displayed on our navigation laptop.
Lori, maybe useful is the following: You were speculating that a certain wire goes from here to there. You can check this by measuring the AC voltages when the system is operating with a digital multimeter. You are then basically measuring the quantity of signal content. Do this for all wires on both sides. If all are about equal the two ends should belong to one cable.... If in doubt, then disconnect on one side and measure again.
And if you get a multiplexer, note that only part of them have optical isolators as is demanded by NMEA0183. Having this is useful to prevent undesired effects, caused by ground loops and interferences.
Also you wrote "would rather stay away from serial
connections unless it would be better in long run". Well, RS232
is serial; RS424 is serial, and is the "physical" layer used by the NMEA0183 protocol, with addition requirements for example optical isolation of inputs and 4800 baud rate. So NMEA0183 is serial as well. The 38.4 Kbaud rate from most AIS transponders is also serial; NMEA2000 is also a serial format.....
I hope this helped. Good luck,