NMEA interconnection

[Durcott]

Hi Folks,

I'm trying to get a KVH AutoComp compass talking to a Simrad RADAR display.

The compass output is 'single ended' - 1 signal wire and a reference ground wire, whereas the Simrad's input looks like a more standard two wire NMEA A/B differential input.

Now - I need to analyse the output from the compass to see what sentences it is actually putting out, but are there any 'gotchas' in trying to fire a single ended sender into a differential input?

Thanks

Jeff Adams

 

[tome]

We use the KVH C100 compass, which outputs $HCHDM sentences at up to 10Hz. You should have no problems connecting it to the Simrad radar. The 'normal' NMEA input is an opto isolator and not a true differential input

Cheers
Tom

 

[AngusMcDoon]

To see what's being sent, you can whack NMEA straight into a RS232 serial port on a PC (not USB though). Use Hyperterm or any serial terminal app to read from the serial port, all flow control off, 4800 baud, 8 data bit, no parity.

You will need to connect the NMEA ground to serial ground (pin 7), and NMEA signal to serial RxD (pin 3).

Google will tell all.

 

[Durcott]

Thanks,

you anticipated my next question /forums/images/graemlins/smile.gif

Jeff

 

[tome]

Those connections are for the older 25 way serial ports. Use pin 2 signal & pin 5 ground

 

[AngusMcDoon]

Oops!

NMEA to RS232 guff

See section 5.

 

[pau1gray]

You may also find that the KVH has an ouput at 9600 Baud instead of 4800 so play around with the terminal

 

[tome]

True enough, though the default is 4800 unless you've played around with it already

 

[Durcott]

Ah-Ha!

It's one of THOSE standards /forums/images/graemlins/crazy.gif

That might explain why the NAV display 'blinks' but doesn't show any data.

I'll look into that.

Jeff

 

[hightech]

The simrad Radars have an NMEA reader built in for diagnostics etc. Switch the set off and then press and hold the range up and MOB buttons then press the power button. hold the range up and MOB until the unit beeps for the second time, thne let go. You should then see two banks of data, NMEA1 port and NMEA2 port, from this you can work out what is getting into the unit.

 

[Durcott]

Thanks for that /forums/images/graemlins/cool.gif

Jeff