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post #1 of 14 Old 05-30-2008 Thread Starter
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Simrad instruments

Two instrument questions:
1) Does anyone have experience using Simrad instruments, in particular IS20 system? What are your impressions?


2) Are there any NMEA multi/demultiplexers that allow essentially a few NMEA inputs to go in, be multiplexed and then DEmultiplexed into a few outputs? I've seen many to one, but not many to many so far.
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post #2 of 14 Old 05-30-2008
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Quote:
Originally Posted by brak View Post
Two instrument questions:
1) Does anyone have experience using Simrad instruments, in particular IS20 system? What are your impressions?


2) Are there any NMEA multi/demultiplexers that allow essentially a few NMEA inputs to go in, be multiplexed and then DEmultiplexed into a few outputs? I've seen many to one, but not many to many so far.
Hope you get some replies to this Brak. In the Coursemaster thread I've noted that I'd like to fit Simrad to the NWB but that's based purely on how purty they look. I'd also like opinions on how they work. You'll see that Cam has nice things to say about Simrad Auto Pilot.

As for your second question.......I think my brain just melted. I know what NMEA is but as for the rest.........do you mean can you multiple repeat, as in send info from your various cockpit instruments to one repeat at the nav station and another somewhere else ?

Andrew B (Malö 39 Classic)

“Life is a trick, and you get one chance to learn it.”
― Terry Pratchett.
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post #3 of 14 Old 05-30-2008
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You can't really demultiplex a serial signal like NMEA without a computer to control the demuxing, since the signal inputs are effectively identical in format, other than the data.

Besides, why would you want to demux the signals after muxing them in the first place? THe output from the mux has all the combined information and any equipment attached to the output would generally ignore information it doesn't require, so there really isn't a need for demuxing the data stream.

Also, the output stream of an NMEA mux can drive multiple NMEA devices.




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post #4 of 14 Old 05-30-2008 Thread Starter
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Quote:
Originally Posted by sailingdog View Post
You can't really demultiplex a serial signal like NMEA without a computer to control the demuxing, since the signal inputs are effectively identical in format, other than the data.

Besides, why would you want to demux the signals after muxing them in the first place? THe output from the mux has all the combined information and any equipment attached to the output would generally ignore information it doesn't require, so there really isn't a need for demuxing the data stream.

Also, the output stream of an NMEA mux can drive multiple NMEA devices.
Well, by demultiplexing I meant simply connecting multiple listeners to one NMEA output. I am somewhat leery to connect more than one to the wire - while there is no flow control or anything, I still think that they can interfere with each other simply by pulling down the voltage during reception or some such. I guess if there is no other way out of this - then that's ok.

Here is the thing - my current system is Raymarine autopilot (computer and head) using Seatalk among them. Garmin GPS has 2 NMEA in/out ports (i.e. 2 inputs and 2 outputs really).
1 output goes to autopilot
1 output goes to DSC
1 input goes to DSC
1 input goes to depth sounder (broken now)

Ideally, I'd like to replace instruments at minimal cost and complexity (see part two) and have
- Instrument output go to GPS to be displayed (depth/speed/wind etc)
- GPS output to go to instruments, in particular to wind instrument, to get true wind data

At this point I only have 1 free input (from depth sounder) and no free outputs. So, I can do a few things with instruments depending on how they work (native NMEA may be multiplexed, Seatalk requires translator box etc). But I dont have any free outputs - so ideally I'd like to split up output that goes to DSC, for example, to have it go to DSC and instruments instead. Thats where demultiplexing comes in - not really message demultiplexing, simply signal splitting. I guess if I can't find anything, I'll just split the wire and see how that works, but I am a bit leery of that option.
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post #5 of 14 Old 05-30-2008 Thread Starter
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Now, for instruments.

Package of speed/depth/wind by Simrad sells cheaper than comparable package of ST60 instruments from Raymarine. Simrad instruments speak NMEA natively, so I don't need an additional converter box (which is another $300 or so). Simrad uses a combined speed/depth thruhull (solves my other issue), and a single multifunction display for speed/depth (and another one for wind). I can connect NMEA directly to GPS. However, I am not sure if GPS will re-transmit NMEA messages, so wind data probably won't reach the autopilot (unless I use multiplexer)

Raymarine speaks Seatalk, which is nice, but I can only connect that to autopilot and autopilot does not really need this data, except for wind data perhaps to steer to wind. I would need a separate box to pull Seatalk data out into NMEA. Also, Raymarine does not have combined speed/depth sensors (not sure why) and requires separate speed and depth displays (which would mean more holes in my cockpit to install them) - they have combined instrument but it appears to be only a repeater. The only true upside to Raymarine is that instruments would look like my autopilot control head, keeping the style - but that's not too critical

So, that is what I am trying to feel out now - what would be the best approach. It's tough to judge how instruments would work out by the documentation and sales brochure.
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post #6 of 14 Old 05-30-2008
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The NMEA 0183 specification says that up to FOUR listeners can be used on any NMEA output, so what you're asking for doesn't really make much sense.




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post #7 of 14 Old 05-30-2008 Thread Starter
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Quote:
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The NMEA 0183 specification says that up to FOUR listeners can be used on any NMEA output, so what you're asking for doesn't really make much sense.
Well, the problem is - specification is not necessarily what's out there. My datamarine NMEA output cannot be understood by Garmin GPS, even though I can read both using my laptop serial - what does that mean?

I'll try the splitting if this is the only option. In my experience, multiple listeners on a serial connection is a recipe for problems.
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post #8 of 14 Old 05-30-2008
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The Simrad IS20 and IS12 instuments are simnet, and therefor NMEA 2000 compatable. NMEA 2000 is a drop cable to backbone system, if you wire it like a NMEA 2000 network (unlike a SIMNET daisychain network) each device and share data with the other.

I am in the middle of installing a NMEA 2000 Network on our boat.

1. Simrad IS 12 Combi depth/speed.
2. Simrad TP 32 Tillerpilot
3. Garmin GMI 10 Display
4. Lowrance 7300 HD chartplotter
4a. Lowrance puck GPS that came with the Chartplotter, powered by the network

When they are all connected to the NMEA network, the Tilerpilot can use the GPS to go to waypoints, Garmin can diplay depth, speed from either paddle wheel or GPS, and Bearing to waypoiint, etc.

If I add a wind transducer, I can do so with out buying another display, save for calibration issues. If I buy a simrad IS20 transducer, I can display wind date on the Garmin display, but I may have to either borrow a Simrad diplay to caibrate the transducer, if needed, or pay a installer to calibrate it for me.

It all plays nicely together, or at least it should. THe Lowrance connectors mate with the garmin connectors, etc.

Go to Maretron : Marine Electronic Instruments if you want to learn more about NMEA 2000 networking.

NOTE, NMEA 2000 is not the same as NMEA 0183. Compltetly different beasts.

Chris

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Last edited by witzgall; 05-31-2008 at 12:04 AM.
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post #9 of 14 Old 05-31-2008 Thread Starter
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Hmm, this is the question I have I suppose. I read documentation on Simrad site and it seems to refer to both NMEA2000 and NMEA0183. For purposes of connecting instruments among themselves I can use whatever they want. But none of my other instruments support NMEA2000 and I need NMEA0183 to talk to them. Do you know if IS20 instruments support NMEA0183 (by which I mean that they have appropriate inputs and outputs)?
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post #10 of 14 Old 05-31-2008 Thread Starter
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Ok, reading some more, Simrad instruments are all different in the way they work.
IS20 uses NMEA2000 or Simrad analog
IS15 uses old Simnet of some sort and each instrument has one NMEA 0183 input or output (so for input AND output I'd need two instruments at least)
IS12 does not have any NMEA support natively but has special repeater-instrument that does the translation.
IS12 is definitely discontinued and IS15 seems to be discontinued too.

Well, back to Raymarine then.
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