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Old 15-03-2009, 15:28   #1
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Laptop USB link to NMEA on S1 Autopilot

I have a Garmin GPS
Smartpilot ST6002+ Controller
S1 Smartpilot Computer

the GPS is connected to the ST6002+ Conmtroller via the NMEA connection
The Controller receives the relevant route and track data to provide the additional info on BTW/DTW/XTE/COG/SOG

The ST6002 Controller is connected to the S1 Smartpilot Computer via Seatalk as per the setup diagram

I wish to take the data from the S1 Computer and connect it to my laptop to run my maxsea program

The laptop has Maxsea10.3 installed and works when connected directly to the GPS via USB connection. I have installed the Garmin PC Serial to USB driver to enable this to work.. It all functions correctly

However, when i attach one end of a USB cable (bare wires green to NMEA Out -, White to NMEA out +) and then plug it into the laptop, the laptop does not recognise the connection and there is no feed to maxsea.

Please can you advise what connections i should be making to take a feed from the NMEA out on the S1 Computer and to be able to connect to my laptop so that I may run maxsea from the data from the autopilot.

I believe i need to add in a serial to usb adaptor at somepoint (though i though the serial to USB driver would have done this).

Adding in the serial to usb adaptor is no problem..but how do I wire the NMEA Out +/- connections to a Serial 9 pin adaptor if this is what needs to be done



Thankyou
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Old 15-03-2009, 15:37   #2
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make sure Garmin Gps is out putting NMEA data not Garmin data which is usual default setting
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Old 15-03-2009, 15:51   #3
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Yes, you will need a USB to serial port adapter. Wire a female DB9 so that NMEA+ from the autopilot goes to pin 2 of the D9 and wire the NMEA- to pin 5 of the DB9. Make sure all the drivers need for the USB to serial port adapter are installed and the adapter is working properly. Plug the DB9 previously wired into the adapter. Start Maxsea and configure it for the serial port the USB to serial adapter is using. The serial port should be set to 4800 baud, 8N&1.

Good luck.
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Old 15-03-2009, 15:54   #4
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If you are not expecting Maxsea to control the autopilot, you may split the nmea output of the garmin to the laptop directly. This will let the Garmin control the autopilot. If you want Maxsea to control the autopilot, you should put the laptop between the gps and the autopilot.

NMEA talkers can be heard by three listeners. You just connect each of the listeners' IN+ to the Garmin's OUT+ and wire all the grounds together. An NMEA listener can't distinguish between two talkers, they run together and make no sense.
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Old 15-03-2009, 18:01   #5
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Originally Posted by rodney_k View Post
Yes, you will need a USB to serial port adapter. Wire a female DB9 so that NMEA+ from the autopilot goes to pin 2 of the D9 and wire the NMEA- to pin 5 of the DB9.
I suggest that you do not wire NMEA- to pin 5 (ground) of the DB9 connector. Instead, connect pin 5 to the ground connection of the autopilot, which is probably the NMEA pair shield.

NMEA- is usually an actively driven signal, so unless it is a fully-isolated floating output you will be shorting out the signal.
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Old 15-03-2009, 18:28   #6
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Either way would probably work. Paul's suggestion is the best practice. Some NMEA talkers & listeners are single ended, and some are true differential inputs & outputs.
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Old 16-03-2009, 10:34   #7
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Thanks for that so far

just a couple of points to clear up my confusion

as I say to get the gps to work directly with my laptop i plug it in to the USB port (the cable attaches to the etrex and has a usb male adaptor on the other end) so there is no physical usb to serial adaptor. Instead I have installed the garmin usb to serial driver. thsi works fine

therefore why does it notwork when i wire oned end of a usb cable to the nmea out on the smartpilot computer and plug in the usb male end into the laptop? I would have thought the usb to serial driver acted as a virtual replacement for the physical usb to serial adaptor you say i need?

the second question stems from Raymarines response to the same post i put here there answer as follows:
The pilot will NOT send this information out. You will need to "T" the NMEA from the GPS and go to both pilot and laptop.
This seems to contradict the commisioning guide for the manual which states that the S1 nmea outputs BWC, GGL, HDG, HDM, HDT, VTG sentences. Surely, if this information is received by the ST6002+ controller which is connected to the S1 computer by seatalk, it should be able to output this information via its NMEA out?

Thanks for your answers
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Old 16-03-2009, 13:05   #8
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The Garmin GPS is a "native" USB device. The Garmin usb to serial driver software makes the Garmin native USB look like a serial port to your Maxsea software.

Connecting the NMEA balanced output directly to the USB port will not work because of a variety of reasons. Here are a couple:

* While usb & nmea are balanced two wire differential systems, the logic levels are different... USB is 2.8v high, and 0.3 volts low. For NMEA, the voltages on the + line are + and - 5 volts. When output + is at +5 V, output - is at 0 V, and vice versa. This is the unipolar NMEA operation. In bipolar mode 5 V are used. Bipolar mode output is + at 5v, - at -5v, and vice versa.

* USB has a minimum speed of 10kbps, your S1 computer's NMEA out is at 4800 bps.

A USB to serial adapter translates levels and speeds to match your laptop's USB port. I have had good luck with Keyspan 19HS adapters.

I don't have experience with S1 autopilot computers but I do have a type 300 autopilot computer aboard my boat. It will repeat GPS signals that are input on the computer's NMEA input. Mine will output XTE, BWC, GLL, HDG, HDM, HDT, HSC, & VTG if the information is available from Seatalk or the NMEA input. Bear in mind that the NMEA sentences will begin with $II if coming from the autopilot. I don't know if Maxsea "cares" about the $II header.

Note: Your setup will not allow Maxsea to control the autopilot.
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Old 16-03-2009, 13:26   #9
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MaxSea needs certain information (GLL most importantly) that is not sent out by the ST controller. It has to hear that from the GPS directly.

GLL - lattitude and longitude numbers
GSA - general satellite data
GSV - detailed satellite data
RMB - recemmended navigation data

These are some other important NMEA words that are output from you Etrex but are not passed thru the controller.
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Old 16-03-2009, 14:02   #10
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Originally Posted by sandy daugherty View Post
MaxSea needs certain information (GLL most importantly) that is not sent out by the ST controller. It has to hear that from the GPS directly.

GLL - lattitude and longitude numbers
GSA - general satellite data
GSV - detailed satellite data
RMB - recemmended navigation data

These are some other important NMEA words that are output from you Etrex but are not passed thru the controller.
Let's be clear here, I cannot speak to the S1 autopilot course computer, but the type 300 WILL REPEAT the GLL sentence if the GLL sentence is available from either the Seatalk side or the course computer's NMEA input. The difference is that the GLL sentence from the course computer's NMEA output will be $IIGLL, while the GLL sentences from the GPS have the header $GPGLL.

The question is whether or not Maxsea will accept the $II vs the $GP. I'm running Coastal Explorer 2.x on my laptop and CE does just fine with $IIGLL or $GPGLL only.
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