Getting instruments connected to a laptop

[RichardDunstan]

I'm trying to find out more information about linking up instruments to a laptop onboard. I've run out of sources so I thought you might be able to help.

Ideally, I'd like to have the wind, depth and compass/log send information to the computer. The GPS is already tied in which uses up the laptop's only serial port. I'm looking to get an autopilot in the somewhat distant future so I would like to be able to send information from either the compass or wind to it.

I looked this up on the internet and it appears as though I need to use a multiplexer. This combines the feed from the instruments into the single serial port on the computer. It also allows information to be sent to another instrument or, in my case, the autopilot.

I've found three companies that do these multiplexers for NMEA 0183 marine applications. They are:

CruzPro NC20 - http://www.cruzpro.com/nc20.html (US$180)

Noland Engineering N183-41 -http://www.nolandengineering.com/product.html (US$190)

ShipModul MiniPlex-41 - http://www.shipmodul.com/en/index.html (US$200)

Is there anyone out there who has had any real-world experience with any of these products and, if so, can you tell us a little about how you did it? I'm also a little concerned about current draw.

For people who haven't heard about these products, here's a little explanation about each (it's a bit technical):

CruzPro NC20 - http://www.cruzpro.com/nc20.html (US$180)
The CruzPro NC20 NMEA combiner accepts up to 4 (US$180) or 8 (US$250) channels of NMEA (and/or RS232) serial data at 4800 BAUD and combines these signals onto one RS232 compatible output line at either 4800 or 9600 BAUD (selectable).
The NC20 can handle any mix of NMEA and RS232 input signals at 4800 BAUD and multiple units can be daisy-chained for more inputs than 4 or 8 channels.

Noland Engineering N183-41 - http://www.nolandengineering.com/product.html (US$190)
N183-41 Multiplexer - The N183-41 Serial Multiplexer combines up to four NMEA 0183 inputs into a single serial output for connection to a host computer or other NMEA 0183 devices. A Talker port is also provided to allow the computer to send data (waypoints, etc.) to instruments.
They have a good section on explaining NMEA 0183 (http://www.nolandengineering.com/nmeainfo.html) and an excellent section on installation which covers some typical scenarios (http://www.nolandengineering.com/tips.html)

ShipModul MiniPlex-41 - http://www.shipmodul.com/en/index.html (US$200)
MiniPlex-41 - The MiniPlex-41 is a four channel multiplexer, connecting up to four nautical instruments to each other and a PC. Instruments with an NMEA interface can exchange data with other instruments, such as a GPS delivering position information to an auto-pilot. An instrument that delivers data is called a talker, while an instrument that receives data is called a listener. The current NMEA specification provides the possibility to connect one talker to up to four listeners. There is no provision however, to connect more than one talker to one or more listeners. It is thus impossible to connect both a log and a GPS to an auto-pilot or PC. The MiniPlex-41 circumvents this limitation by offering four listener ports, one RS-232 port and two talker ports. Now a system can be built with up to four talkers and up to eight listeners. The PC can also act as a talker/listener, without sacrificing the number of allowed talkers. Incoming data is buffered and retransmitted as complete NMEA sentences to the connected instruments and PC. From the PC, NMEA data can also be sent to the instruments.

Thanks

Rich

 

[Robin2]

You may also wish the instruments and PC to connect to, say, an autopilot or radar. This will mean sharing the data several ways. I think Raymarine has an interface unit for joining everything together.

 

[Guest]

Seems you already know more than most about it !

My question .... sorry - I don't know about the serial bits you quote ..... is there a USB way of doing it ? As its easy to get a USB multi station connector etc ..... And USB is a type of Serial communicator ...... just a thought !

 

[bedouin]

Firstly, yes you do need a multiplexer.

If you are thinking of going for an autohelm then you will probably want to solve the problem at the NMEA level, rather than on the PC, since you'll want to combine NMEA streams from Wind, Compass and GPS into the AH (I know - I'm looking at this at the moment).

What sort of instruments do you have? It is possible that the instrument manufacturer provides a unit that could help as well.

I have no experience of any of the products, but it is in essence a very simple application and so I don't imagine you would have much problem with any of them (I've been thinking about trying to build one myself - I may have a go if I've any spare time this winter). Also I wouldn't worry about current draw - it will be low compared to the instruments themselves.

 

[bedouin]

Re: Seems you already know more than most about it

I don't think you can connect RS232C to USB - but you can buy USB to serial converters fairly cheaply that will do the job.

 

[tome]

I've used the Noland product and it worked fine, coping with various instruments including a 10Hz compass. There will be a slight delay in the data stream, but this can be ignored for most applications.

I don't recall whether the RS232 control port could be used to view NMEA data, so you will probably need an RS422-RS232 converter to link the talker port to a laptop. These are widely available.

RS422 is a differential standard which basically means that the polarities of the two wires swing in opposite directions. RS232 is unipolar with one wire remaining at 0 Volts. It's possible to cheat a little by using 0V and one wire from 422 devices and to drive 232 in this way (most GPS sets do this so they can be connected to a PC) but not if the 422 wires are isolated.

Linking the NMEA to/from instruments is not so straightforward. The autopilot will be ok as they all have NMEA inputs, but some instruments (eg Raymarine) use proprietary data buses and need an expensive data translator/level convertor for NMEA. Simrad IS15 has dual NMEA and Roblink buses so are ok: in fact, they will handle the multiplexing of NMEA data also so if you have spare NMEA ports on your instruments they can be used in place of the Noland/whatever.

 

[johna]

For my interest and understanding could you explain why you want all these instruments linked to the computer and how you intend to use the data. I have the GPS connected for use with the Neptune Planner / plotter and all the other information is available on my chart plotter via SeaTalk. I am not sure why I would need it on the PC. I really am interested to know in case I am missing something.

John Arrowsmith

 

[stefan_r]

USB - someone said you can't do serial thru USB but they may have been wrong....don't really know, try and find a response from me to another user a few months ago on this list somewhere as that gives the technical reasons

PCMCIA - you can get a PC Card from 'Socket' that basically has 1,2,3,4 serial port cables and connectors coming out of it...you can then put all your NMEA inputs into each serial port and have a separate Com Port for each one. This is how I have GPS (Garmin) COM1, RayMarine-Seatalk [thru NMEA converter I got from yachtbits.com] Depth, Log, Speed, SeaTemp (temp not that useful!!!) COM2, and Autopilot COM3, NavText COM4 and still have a spare serial port in the back of the machine for some other bit of kit.

This card is about £200 if I remember right....

Cheers
Stefan



mailto: stefan@athito.com

 

[jacksong]

you can get little cables with some logic in them that plug into usb and present an RS232 port, they were about 30 quid each last time I checked.

J

--
I am not a Frog, I am a free Womble

 

[colvic]

Re: Seems you already know more than most about it

Some of the latest equipment now comes with a USB connector, which in a simlified explanation is just a faster serial connection.

4800 bit transfer rate is very slow, but as mentioned earlier you won't notice it really.

Nautical Data did a software almanac which they now incorporate with Maptech chart plotters which had the instuments you're after on the home page as well as position etc. from the GPS.

After five years of playing and using, it seems to me that luck has a lot to do with what you can source to work with each other. Sure it is by far the cheapest option when up and running, and you could still down load weather charts& faxes and Navtex onto the lap top. Been doing the last three (as well as chart plotter and Garmin 128) via the onboard PC for last four years and really no problems that couldn't be sorted.

Phil;

 

[RichardDunstan]

John,

We have two objectives out of this.

Firstly, we want to be able to collate all the information from our instruments to be able to produce more accurate polar diagrams for performance reasons.

Secondly, we want the instruments to feed into navigation software like MaxSea which can make use of our polar diagrams to give us our optimum course.

We can do this manually, and currently do, but it would give us a competitive advantage to be able to have this update every few minutes rather than every few hours.

The difference between your setup and ours is that you appear to have an expensive instrument package (ie Raymarine). We don't. Your setup has all the things I'm trying to do already done for you. The SeaTalk protocol (like Nexus and FastNet) is a information bus thing that means the instruments talk and listen in an ordered manner. The NMEA protocol doesn't have that bus technology built in yet.

What we are trying to do is to make use of what we currently have (all NMEA compatible) but not the same manufacturer. You could say that we could just spend money on a new instrument package but, on a tight budget, we would rather spend money on things that make the boat go faster like sails.

Rich

 

[RichardDunstan]

Stefan,

There is a USB multiplexer made by ShipModul http://www.shipmodul.com/en/index.html which goes for about US$230.

I hadn't thought about the PCMCIA card. I'll look into that. Thanks.

Do you remember what the make and model of the NMEA convertor was?

Rich

 

[RichardDunstan]

Re: Seems you already know more than most about it

Phil,

I didn't find the information you mentioned but I found a very useful site from there (http://www.maptech.com/support/techsupport/index.cfm) which has a support forum.

It is worth a look as it covers these issue in a fair amount of detail.

Interestly enough, they mention combining NMEA inputs by splicing.

Rich

 

[tome]

Richard

If I understand:

1 You want to record NMEA data over varying wind conditions to quantify boat performance, and to display processed results in polar form for tweaking comparisons

2 You want to input this processed data into your application (MaxSea) so that it can use the performance data in conjunction with real-time NMEA instrument readings in order to calculate and update optimum courses.

3 You want to reduce the process update rate from several hours to several minutes

4 You don't want to spend anything much to achieve this

All feasible, though 4 could be a problem IMHO

 

[RichardDunstan]

All correct apart from 3. We have the boat's polars on laminate so we can quickly refer to them. This gives us our optimum boat speed for a particular wind angle and set of conditions. However, ever few hours on an ocean race, the nav will check the course, calculating the optimum VMG, taking into account the polars.

This process is complex, is easy to make mistakes and only gets done every few hours.

It would be good if we could have that optimum course to steer every 15 minutes.

Your point 4 is the killer though.

Richard

 

[vyv_cox]

PCMCIA

I have a PCMCIA card with two serial ports that I use to receive Weatherfax. I bought it about two years ago after a great deal of difficulty in sourcing it. I was told countless times that I could get one "anywhere" but this proved not to be the case. Eventually my weatherfax dealer found one for me somewhere in Holland, but he is now out of business so sorry, can't help.

 

[kdf]

I would go the multiplexor way - it takes 4 or 8 nmea inputs, adds them together and spits out a single nmea the back end. This means that you can put multi-function displays further down the line and they will be able to get the right data off the cable. Also most muxes have an RS232 output which duplicates the nmea output for connection to a PC.

I don't recommend using the PC as a MUX - if the PC goes down then you've lost the common nmea connection between the instruments.

 

[extravert]

There seems to have been some good information and some mis-information in this thread. During a previous contract I developed software for a well known (but unspecified!) marine instrument manufacturer, so I've got a bit of inside knowledge here. Here follows a short sermon on NMEA-0183...

NMEA-0183 is designed to communicate data between one data source (ie an instrument like your compass) and multiple data sinks (like a display), called talkers and listeners respectively. It's a pretty old standard.

NMEA-0183 runs at 4800 baud, which is slow but reliable. You can't change that, it's fixed in the standard and all instruments/displays use it.

Although NMEA-0183 is a differential standard and RS232 (your PC serial port) is not, you can connect the NMEA-0183 data lines straight to you serial port's RXD and signal ground pins. If you are worried about damaging your PC you can use opto-isolators.

You cannot have multiple talkers all wired into a single listener - splicing in all the wires together won't work. Your listener will receive rubbish.

NMEA-0183 and RS232 are basically the same and compatible. NMEA-0183 and USB are completely different. Both serial but totally incompatible.

If you want to connect multiple talkers (ie instrument) to one listener (ie PC serial port or a multi-display) then you need a multiplexer as the original poster suggested. These are sometimes called concentrators. These have multiple input terminals to connect 1 talker to each, and one output. All the input data is combined into this output.

Some modern displays act as multiplexers/concentrators. For example my Cetrek C-Net 2000 displays (no, I'm not associated with them) each can have 3 inputs from instruments, and then combines all this data onto one output. This may be suitable for the original poster, ie get an extra display thrown in free.

If the data format between your talkers and listeners is incompatible, a multiplexer won't help.

Unfortunately a lot of manufacturers have not stuck rigidly to the standard. This leads to incompatibility between different manufacturers' equipment.

Even if you equipped your PC with multiple serial ports with a PCMCIA card or similar, the chances are that the software on the PC would not be able to read from multiple serial ports. It would probably expect all its data to be combined to come in to a single serial port using a multiplexer/concentrator.

A PC's serial port can act as a single listener and a single talker at the same time. That's because it has a data in pin (RXD) and a data out pin (TXD). Only a single signal ground pin is used.


With regard to a home project playing with NMEA-0183, it is not too difficult for someone who has experience of basic digital electronics and software in a language like C. Unfortunately, the cost of a development system like a microcontroller compiler will probably be prohibitive for many people. In computing terms, NMEA-0183 is old fashioned simple stuff.

When I replaced all my instruments and displays with Cetrek, I kept my old Danaplus mast displays because they were working perfectly and are very expensive to replace. Unfortunately Danaplus used NMEA-1083 version 1.0 and Cetrek use NMEA-0183 version 2.0, different enough to cause problems. I built myself a small micrcontroller (SG Thompson ST-10) based circuit board and wrote a program to translate between version 2.0 and version 1.0. It's installed and still running fine today.

 

[JerryHawkins]

Another product

A company called Actisense (UK based) produce an NMEA data combiner. Have a look at http://www.actisense.com

Cheers,

Jerry

 

[bedouin]

I was thinking of using a PIC chip for this - an entire Dev environment will cost £40, and the finished product could be built for about £10 a shot.

In terms of technical specification NMEA and RS232 are not quite compatible. It's a while since I looked this up but IIRC, the low part of a NMEA pulse (0V) is not technically a low RS232 (I think < -2V) but thousands of people have treated them as identical without coming to grief.

More significantly though, you can drive NMEA at TTL levels without needing full RS232 voltages - which can simplify the ancilliary components.