Interfacing NMEA Data to Computer

[bobfnbw]

Actually from what I know about charts in general and electronic ones in specific is that all charts are suspect.
Many are left over from the old days of sailing, and are not to be trusted in any way, unless you are using a mark 1 eyeball, a compass and good piloting. That is one thing I learned long ago, and still is revelent today, no matter how you navigate. The days of using electronic charts to pilot without your own piloting skills is not here yet, even with gps accurate to 1 meter. The simple truth is that no chart can be trusted in total.
I did download open cpn today. Wan't real thrilled with it, but then I only played with it for a hour, with one large area chart of the gulf of mexico. But it is a step in the right direction. And I appreciate anyone that puts that kind of work into a program and then not charge for it.
But as it stands now its now what I was looking for. I wouldn't mind paying for a good program, but haven't found the one I wanted yet. But I will play with opencpn some more.
And I have read the opncpn thread as well here on cruising forum.
Thanks for all that are helping me understand this. I appreciate your time.
Bob

[ess105]

I'm trying to do a similar hookup but failing miserably. I have enabled the NMEA output in the ST60 Graphic unit. I have created a cable from my ST60 graphic NMEA output to a DB9 RS232 connector connecting the + to pin 3 and the - to pin 5. I am using hyperterminal to look at the data on my PC and all I get is garbage at 4800,8,N,1. If I connect my garmin handheld into the same RS232 to USB adapter I see sensible strings.

Any thoughts? I suspect it's the cable I made up but can't be sure.

[rustypirate]

I believe that I read somewhere that Raymarine units talk at the higher baud rates like AIS units do.

You may need to have a seperate com port configured for the raymarine gear with a higher baud rate.

[oprlid]

Originally Posted by ess105

I have created a cable from my ST60 graphic NMEA output to a DB9 RS232 connector connecting the + to pin 3 and the - to pin 5.

On a PC 9-pin RS232 connector, pin 2 is RxD - that's where the PC reads the data.

Pin3 is TxD - that's where the PC will send it's data to another device.

You want your PC to receive data comming from the ST60. So NMEA-Out + has to go to Pin 2 on the 9-pin sub-d plug.

Regards
Frank

[goboatingnow]

note that 0183 signals are TTL level and some rs232 hardware cant handle the low input levels

[hellosailor]

ess-
I don't think I've ever made up a custom serial cable that was right the first time. On the DB9 type, pins 2 and 3 are your data pair and pin 5 is typically a common ground, which may or may not be separate from other grounds.
The problem is that pins 2 and 3 are described as "TxD" and "RxD" and those descriptions ARE WORSE THAN USELESS because they are relative terms and the descriptions are REVERSED depending on which side of the cable you are working on.
For instance, the "TxD" line from a GPS is the line on which the GPS is "Talking". From the GPS maker's point of view, that is TxD. Now if you go to plug that into an autopilot--you are going to plug it into the RxD connection, because the autopilot is LISTENING for that talker on that wire. TxD always becomes RxD, and RxD always becomes TxD, when all you have is a simple one-to-one connection.
In more complicated setups, where there may be several "talkers" and one "listener", or vice versa, how you wire things up may change.

Bottom line? Tx and Rx (as they are also commonly called) should be on pins 2 and 3, and if it doesn't work, one of the most common problems is that you've just got these backwards. Me, sometimes I get boat brains and wire the DB9 up backwards anyway. I find that it really really helps to use a loupe, make sure of which pins are #2 and #3, and then MARK THEM with a paint or magic marker, before even thinking about soldering them. It is very easy to rotate the DB9 shell in your hand, and wind up with the pins connected wrong.

[ess105]

Typo in my first message. My + from the ST60 was in fact connected to pin 2 (not 3 as I originally typed). The - was wired to pin 5 as stated. I do see traffic from the unit but it's garbage. I have tried all the different baud rates and it changes the garbage being received as expected. The garbage being seen comes in bursts just as one would expect data to come from the unit. The garbage stops when I switch off the nav instruments. So I think it's talking and I think the wiring is roughly right or I wouldn't see anything.

What I am seeing could be explained by goboatingnow's explanation. ie I am seeing something but not enough to obtain fidelity. I would rather it's something else though.

[W32PAMELA]

Connect your DC ground to pin 5, ST60 + to pin 2 and ST60 - to pin 3 and give it a try.