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Old 09-05-2012, 07:02   #1
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GPS data feed into OpenCPN

Hi. I am using multiple instances of OpenCPN on one computer to display the GPS positions of a number of small boats in one place - kind of a basic fleet tracking system I guess.

We have a receiving unit that outputs the GPS position strings from each of the boats. This has serial outputs.

I have tested multiple USB-GPS coming into the computer and OpenCPN through a standard USB hub and this works fine.

The "standard" approach would be to use a serial to USB hub such as an Edgeport, but these are very expensive (I would need a 16-way unit!).

Would there be any issue with wiring the outputs from the receiving unit as USB plugs, and then putting them into the standard USB hub? The GPS units are powered on the boats themselves and all we are transmitting is data.

Also, would there be any baud rate issues that you can forsee?

Kind regards
Paul
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Old 09-05-2012, 08:30   #2
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Re: GPS data feed into OpenCPN

...if you mean soldering wires from the serial (db9) output (data out+gnd or signal gnd) from your "receiving unit" directly to a usb jack, I've tried it various ways and it's nogo....
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Old 09-05-2012, 10:35   #3
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Re: GPS data feed into OpenCPN

Paul,
It should be possible (I really haven't tried a config this massive ) to use 16 of something like Green USB to RS232 RS-232 9P DB9 Adapter Converter PDA PC Win 2000 XP Win7 Vista | eBay and say two of New High Speed High Quality 10 Ports Hub USB For PC Laptop | eBay to connect 16 NMEA streams to a pc for less than 50 dollars. Of course it will be totally useless in OpenCPN even if you manage to combine the streams together with VSPE or something like that (in that case you will need to change the prefix in $GPxxx sentences to identify the originating streams) without programming something able to draw 16 boats at the same time... It will be a funny project, no doubt.
And no, don't even try to cut those USB cables and connect the wires directly to RS-232 or RS-422, it simply does not work...

Pavel
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Old 09-05-2012, 12:15   #4
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Re: GPS data feed into OpenCPN

USB is a BUS, not a port, with very high speeds and different protocols for which device on the bus, and type of bus. Some common USB devices are handled by default drivers in the OS, other custom devices may require custom drivers.

So USB is not juts a fancy serial port. You're not the first person to make that assumption.

Quote:
Originally Posted by PNewman View Post
The "standard" approach would be to use a serial to USB hub such as an Edgeport, but these are very expensive (I would need a 16-way unit!).
Serial-to-USB adaptors are very inexpensive ridiculously cheap (I've successfully used this type on a Garmin GPS), as are USB hubs. So you could possibly go that route at low cost.

(on preview, this is the same solution as nohal)
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Old 09-05-2012, 13:42   #5
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Re: GPS data feed into OpenCPN

Lake-Effect is quite right!

The USB to serial adapters should be those that use the Prolific chipset. The drivers are solid and depending on the software can be configured to each have it's own com port. They are pretty cheap for electronics gear. You'll need a powered USB hub.

Frankly, the application would be better served in one program instance and the data output as AIS data. Generic chart software will handle AIS output. AIS shows multiple ships because it is what it's used for.
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Old 09-05-2012, 14:05   #6
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Re: GPS data feed into OpenCPN

(thanks Paul B )

To the OP (Paul N) -

Paul B's suggestion would be optimum - have all boats show up in one OpenCPN instance as AIS data.

Quote:
We have a receiving unit that outputs the GPS position strings from each of the boats. This has serial outputs.
.. do you mean that each boat's position is a separate GPS datastream, on a separate serial connector?

If yes, and you agree with the AIS idea, then it would be possible to produce a custom piece of microcontroller-based hardware to scan all streams, grab each boat's data, then retransmit all positions as AIS data in a single stream.

... budget allowing, of course
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Old 09-05-2012, 14:22   #7
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Re: GPS data feed into OpenCPN

You might not need a microprocessor. You might be able to make an event driven application in software.

You don't have to accept every single update. If you updated once in a while it would be good enough to see ship positions. You just need a list of com ports to poll and you just wait til you get the reading from the one you want (or time out) then wait on the next port. It would be different if it were jet planes at the airport.
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