Cheap pc onboard: is it possible?

[verbumomo]

Thought during boat refurbishing....
As in most cases money matters (more if your not rich and your refurbishing a sailing vessel from zero) and all electronics made for nautical are expensive I thought that there maybe a cheaper solution for pc onboard. Scenario: a laptop, gps/plotter, ais, autopilot and a some other stuff like ssb radio and dsc vhf. The right, usual way would require a multiplexer (like miniplex) connect everything to it and this one, via usb or bt to pc - maybe the ssb directly to the rs232 of pc.
Considering that in a sailing boat (40 feet) distances are not high and that a rs422 ist easily converted to rs232 (wire A to in and B to ground, same for output) and that nmea sentences are sequential and devices ignore sentences they don't use, why not use a cheap pc multiplexer (4 rs232 port to 1 usb)?
The only problem should be the AIS with it's higher speed, but is it a problem? All data go to pc, the navigation program, as a listener, will read all sentences and use them, recombine them and sent to output (don't know if Maxsea, Sail or CNP puts AIS sentences in talking) - I think the problem is for all the devices acting as listener from pc due to high speed of AIS but sentences, even if they are nmea, are sentences like any other data so they can be recombined and filtered by the pc. Maybe I'm wrong, but as long as the pc is on there will be no problems - problems occour when we don't use the pc but only the devices: a gps/plotter, AIS and vhf dsc so there we have the AIS that forwards to gps/plotter and plotter to vhf dsc could be solved with a switch that disconnects from mux and combines in and out (gps out to dsc and ais out to gps in) but if I add an autopilot things become weird as I have to double the gps out...
Any idea? Where am I wrong?
momo
A newbie from Italy

[TeddyDiver]

eeer... a lot of thought.. I'm all ears and wait the experts...
If it works you make a few scetches of wiring

[verbumomo]

More thoughts: with an AIS only top nmea mux models will work properly. Not all gps plotters accept the high data rate, commun ones, like Geonav 7, require a 4800 baud rate, and ais receivers like Nasa can't be set to lower rates - result: a mux with filtering is required when devides become more.
What I want that someone point out is the thoghness of data transmission with pc mux: this devices accept rates up to 200k, 7 times the rate of ais so it won't be a problem for mux and pc as long as the pc works as a listener and devices as talkers - will trobles accour when the pc acts as a talker (to autopilots)? I have to take a sharper look to Maxsea and CNP data handling settings...

[robherc]

I'm NOT an expert on nautical electronic systems, but I AM an expert (well, somewhat...whatever being able to bill $100/hr for consulting makes you) on computers. Therefore, I'm going to take you at your word that the wiring is compatible, and approach this from the computer's end of things.

In the computer, you can process ANY signal that is input to the USB/RS232/IEEE1394/etc. AS LONG AS you write a program that can translate the code, and that "knows what to listen for." I know of programs already in existence that can read nmea GPS input & use it to run an autopilot, so that part should be no problem for you. As far as the AIS, I'm not sure if the software already exists, but with a bit of funding, you can always find a programmer (not me, worry) who can do it.

BIGGEST Caveat: Naval electronics systems are made to be 100% water-tight, computers are NOT. If you don't find a way to completely protect all of your connections, water could get into the network, and possibly cause a malfunction, damage, or even the total destruction of any/all of your equipment. ...just a cautionary thought.

[JotM]

I am not quite sure how well your Dutch is, but it seems to me more people have thought of this.
http://www.pcnautic.nl/index.php?paginaid=5 :

USB-RS232-ATEN
Omvormer van seriële data naar USB geschikt voor RS232, NMEA en AIS
Sluit hiermee u windmeter, GPS, AIS enz. direct aan op uw PC of laptop

USB-RS232-ATEN
Translation of serial data to USB, fit for RS232, NMEA and AIS
Directly connect your wind meter, GPS, AIS, etc. to your PC or laptop

Oh, and they sell a IP65 watertight 1 GHz Intel Celeron based PC too.

Cheers

[robherc]

There you go...problem solved

[Tim B]

Interesting project. I'd like to throw the OpenPilot software into the mix if I may. Whilst it doesn't handle autopilot, it does allow you to connect as many NMEA feeds as you have serial ports.

These can be USB or true serial, depending on how your underlying OS operates. OP can be re-compiled for Linux or windows with differing levels of support for charting, depending on which version of the GDAL library is available.

I would be interested if anyone would like to offer some autopilot code for OpenPilot.

Cheers,

Tim B.

[Jack Daniels Eq]

I am not sure this int more statement than Q&A
Bit sized chunks might be more doable
I am working on a more complex variant
BR>Jack

[TedZ]

Isn't this a subset of the thread "Multi Purpose On-Board Computers?"

And as i said there, any reasonable sized embedded system can do all of the things you require with the processor and the connectivity in a piece of Tupper Ware if you like, maybe 6" x 6" with a snap on lid! I use Rabbit systems and you get more I/O than you could ever use for under $100. The biggest challange is what you want to read the info on. For my taste a terminal is too big and bulky. A small LCD screen would be fine. A lot of software for these devices is in existance. GPS interfaces, serial and parallel reads, LCD drivers etc. Multiplexing is not an issue as embedded systems use a multi-tasking philosophy where each function is assigned to a state (costate with multiple tasks) and they "wake up" as needed by the incoming data stream. Helps to be able to program in C, C+. C++ etc.

Ted

[Jack Daniels Eq]

We know all this - there is a massive difference between breadboard & a standalone system that I would entrust to my 80' 3,500 HP Powerboat.
I am looking for stuff that is already on the ground and can be integrated into a full blown automation yacht system - without breaking the bank or reinventing das wheal
Any practical examples?
BR>Jack

[TedZ]

Originally Posted by Jack Daniels Eq

I am not sure this int more statement than Q&A
Bit sized chunks might be more doable
I am working on a more complex variant
BR>Jack

If you don't want to spend a lot of money and you don't want to develop maybe, because you are not the thread starter, you could outline your requirements. I don't understand your statement quoted here but if i knew what the "complex variant" was i would certainly be happy to give some suggestions of existing equipment.

People who are building data logging hardware and software have a lot of capability. These folks for example, and there are many more.
http://www.windmill.co.uk/logger.html

Ted