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  #1  
Old 01-02-2011
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Using OpenCPN with GX2100/2150 DSC and AIS

I'm starting to get seriously excited about pulling AIS data into OpenCPN from a SH GX2100 VHF/AIS radio. But I am trying to figure out how to send GPS data back to the radio for DSC coordinates if I hit the distress button.

OpenCPN 2.3 has a clearly written configuration tab for the AIS. No problem there - just select your COM port. I expect this is a one-way communication (AIS signal from GX2100 to netbook), so you're only using "half" of the COM port's full duplex capability.

On the GPS tab I have "GARMIN" selected on the NMEA data source, since the Netbook is tethered with an Oregon 400c handheld. I was hoping that OpenCPN could pass through the GPS's NMEA sentences, and that appears to be the case, because there is an "Autopilot Output Port" that I could use to send the sentences to the radio for DSC. In other words, rather than send it to Autopilot, I could send it to DSC instead (or split it to go to both). Since this is also a one-way communication, I was hoping I could use the "other half" of the COM port's duplex. That way I only need one USB-Serial (or hopefully Bluetooth-Serial) adaptor. But OpenCPN will not allow me to select the same COM port as I elected for AIS.

Has anyone figured a way around this? Since my Garmin only has a mini-USB connector, it really is not suitable for conversion to NMEA serial which could then be fed to multiple devices. I was thinking the direct USB connection to the Netbook would be cleanest, then feed it out from OpenCPN. But maybe someone knows of a different program that can run in the background on the Netbook and send the Garmin's NMEA sentences independently of OpenCPN?

More specifically to OpenCPN, it seems that the documentation never even mentions sending or receiving DSC data. Is this something that they overlooked?
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Formerly posted as "RhythmDoctor"
1998 Catalina 250WK Take Five (at Anchorage Marina, Essington, on the Delaware River)
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Last edited by TakeFive; 01-03-2011 at 12:28 PM.
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Old 01-03-2011
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Hello,

I don't think you can do what you want to. AFAIK, the reason is that the AIS port runs at 38.4K baud and the DSC port runs at 4800 (or maybe 9600?) baud.

You will need two serial ports, 1 at 38.4 to receive the AIS data from the SH radio and another at 4800 baud to send the GPS position data from the computer to the SH radio.

The serial ports can be real or virtual. If virtual, you will need two USB connections.

Good luck,
Barry
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Old 01-03-2011
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Quote:
Originally Posted by BarryL View Post
Hello,

I don't think you can do what you want to. AFAIK, the reason is that the AIS port runs at 38.4K baud and the DSC port runs at 4800 (or maybe 9600?) baud.

You will need two serial ports, 1 at 38.4 to receive the AIS data from the SH radio and another at 4800 baud to send the GPS position data from the computer to the SH radio.

The serial ports can be real or virtual. If virtual, you will need two USB connections.

Good luck,
Barry
Thanks for the reminder about baud rate differences. The newly announced GX2150 addresses this by allowing you to set AIS and DSC outputs to the same baud rate. There's another thread where they are saying that this allows the AIS and bidirectional DSC communications to go over a single port. In other words, GPS coordinates go out to the radio, and both AIS and DSC sentences go from the radio to the chart plotter or netbook (in the case of OpenCPN). But the main challenge seems to be configuring OpenCPN to allow both GPS out and AIS in via the same COM port. I still have more to learn, but it looks like there might be serial port emulator software that can duplicate COMx port to COMy, thus tricking the software into thinking the AIS is coming in on a different port. I'm going to need to get the GX2150 hardware first and start to experiment with it to see if if works.

This is only a major issue if I try to do Bluetooth from radio to netbook, because the serial to Bluetooth adapters are so expensive ($50-100 per port) that I would want to minimize the number of COM ports. If I instead make a hardwire connection I can afford to split things up over multiple COM ports because serial to USB connectors are very inexpensive (<$10) and I can use a hub to aggregate them all into one USB wire going to the cockpit. (Yes, I plan to mount my netbook in the cockpit, since I'm a daysailor who picks my conditions carefully. I sailed all season last year without a drop of water getting into the cockpit.)
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Formerly posted as "RhythmDoctor"
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1991 15' Trophy (Lake Wallenpaupack)
1985 14' Phantom (Lake Wallenpaupack)

Last edited by TakeFive; 01-03-2011 at 03:50 PM.
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Old 01-04-2011
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It is always comforting to see I am not alone with this problem. Sine it is OpenCPN I assume you are running Linux and therefore GPSD. I think the newer versions now support multiple devices (and AIS by the way), so you could fire up an additional utility to send out the GPS data to the tracking radio. We intend to do this and retire our Brookhouse multiplexer but it hasn't come to fruition yet. First order of business is to subscribe to the GPSD developer's forum to get up to speed. Google is your friend, GPSD.
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