Aaron and I are in the process of installing an AIS receiver on my little C-Dory. I’ll have more details once I have something substantial to report. Today, though, I wanted to mention the major difficulty owners of Raymarine C-series and E-series multi-function displays will encounter: There’s only one NMEA port on the back of the unit!
If you’re already using this port, connecting the input from the AIS receiver will be a challenge. On my boat, that port supplies GPS data to the DSC VHF radio. Now that I’ve solved my VHF MMSI issue, I’m not willing to simply leave the VHF disconnected from a source of location data. What to do?
I’ve considered several implementation schemes that might work. Here are the most promising, from most expensive to least expensive:
- For about $300, I could purchase an NMEA multiplexer, a kind of “fork” for NMEA data that can support different NMEA baud rates for each accessory. It gathers all incoming data and combines it into a single stream (at high baud rate) for the C-80, and sends outgoing data at appropriate baud rates for each listener.
- For about $100, I could buy a separate GPS receiver and connect it to my VHF. This liberates the VHF radio from the C-series entirely, freeing up the single NMEA port for AIS data. It also means that I have a backup source of GPS location data; the VHF serves as the only display for these raw coordinates, but some backup is better than no backup!
- For almost free, I could split the cable coming out of the single NMEA port in the back of my C-80, connecting the output to the VHF and the input to the AIS receiver. That is, I COULD do this if Raymarine allowed the user to set the baud rate for the incoming (AIS: 38,400 baud) and outgoing (DSC VHF: 4800 baud) NMEA streams independently. Unfortunately, they don’t allow this, and my VHF can only listen at 4800 baud! So this option isn’t an option at all
Right now, I’m very strongly favoring the $100 option. At this point, I can’t imagine that I would need to plug anything else into my C-80, so I can’t justify a $300 NMEA multiplexer. That may change. If it does, the $100 GPS may still have a role as a backup unit, or it can be repurposed somewhere else.
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First of all, thanks for a great blog.
Even if I’m more race oriented, many of the integration issues are exacly the same. As we see an increasing number of gadgets that send (instruments, laptop, GPS, AIS, …) and recieve (instruments, laptop, vhf, autopilot, …) NMEA, sooner or later you need some kind of multiplexor.
We use the ShipModule http://www.shipmodul.com/en/index.html which works great.
Shame, shame, shame on you! The author of a beautiful electronics blog saying “there will never be another (piece of electronics gear) for me!” Of course there will. And it will want to live wherever you put that $100 GPS, AND THE SCREW HOLES WON’T MATCH UP….
Quick, go with the multiplexor! Something new and excitingly NMEA is just around the corner!
Ha! Sandy, you’re certainly right, but like I said, I can always cross that “oops-I-need-a-multiplexer” bridge when I come to it. And frankly, I’ve lost GPS fix on each of my last two outtings…some new devilry to contend with…so the idea of a backup GPS is getting more attractive all the time!
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