Custom NMEA Sentences-convert HDG in HDM

[Madden]

Hi everyone! Let's see how knowledgeable the group is about NMEA tweak and twist stuff!

I'm in the middle of a complicated NMEA network installation. Very old B&G wind/speed/log,new vrspermarine xb8000 AIS,new simrad AC12 autopilot.

The only fluxgate compass I have is simrad's FC40. It sends HDG as NMEA0183. I want a heading sent to my B&G so that I can calculate TWD and opp tacks and all that.

B&G ONLY recognizes the obsolete HDM NMEA input sentence.

Can I use OpenCPN to configure a custom HDM output sentence? Or can I do it somehow else?

Thanks for the ideas!

[Paul Elliott]

NavMonPc will optionally send HDG and HDM messages, when possible, based on whatever inputs it has. Look under "Options/NMEA Options". You will need a serial port (or two), and will need to configure the router ("Options / NMEA Routing") to send the "Calculated" outputs to the serial port. By default the calculated messages are only routed to the Virtual serial ports and the TCP/IP server.

If you want, to reduce your computer's workload I can help you configure NavMonPc to minimize some of the other stuff it does.

[Madden]

Hi Paul!

Thanks for the suggestion... I managed to install Navmon and it's reading all the NMEA data I get from my Shipmodul Multiplex-Lite device via USB on COM5. Including my NMEA0183 HDG reading from my fluxgate compass.

I can imagine, on the NMEA Monitor "Serial A >>" and "Serial A <<" values are what is being sent and received from and to Serial A.

Under "NMEA Options - Internally-generated NMEA Sources" I have HDM set to ON. On "NMEA Routing" I configured for the row "Source: Serial A" the column "Serial A: Send".

I get the following info on the NMEA monitor:

Serial A << $IIHDM,307.,*5B
Serial A >> $IIHDM,307.,*5B

However, it doesn't show up on my B&G display :/

Any troubleshooting ideas?

[Paul Elliott]

You should configure the router to send "Calculated" to SerialA. It's OK if it also sends to Vports, etc.

Do not set the SerialA source to send to SerialA, unless you want to echo everything you receive back out the transmit wire (but perhaps you do in this case).

Where is that "Serial A << $IIHDM,307.,*5B" coming from? This is an input to SerialA, and I don't like that trailing decimal point, or the fact that there is no "M" as the last parameter.

The default NavMonPc generated HDM message looks like this when seen on the NMEA monitor:
Serial A >> $NMHDM,000.0,M*21

As a test, kill all the inputs to NavMonPc, by disconnecting the serial cable, or by setting the NMEA router to ignore SerialA inputs. Then, enable manual heading input (options / General Options / Manual HDG Entry). Any value is OK, I used 000.

What do you see for the SerialA output (look at the NMEA monitor)? If you connect SerialA to your B&G display, is HDM being recognized?