Can anyone help with GPS data?

[robp]

I know that this has been aired several times before but I can't find the answers with a search.

I'm trying to get data out of my Valsat 2008 (MLR), into my laptop which has Neptune plotting software. I've connected (I think) as per details provided by Neptune and enabled GPS in the Plotter Programme but get no data. I'm pretty sure the problem lies in the actual connection to the serial port. The suggestion is to connect GPS to PC data to pin 2, PC to GPS data to pin 3 and "signal ground" to pin 5. (Plus connecting 7 & 8 together and 1, 4 & 6 together). The GPS however has Data out + & -, Data in + & - and of course 12 V + & -. Should I common the three -ve's externally?

NMEA 0183 is already selected on the GPS and it talks to the Pilot etc.

Any help gratefully received.

Rob

 

[Trevor_swfyc]

All I will say is keep the data -ve and the 12volts -ve separate. Also if you do not get any data is the baud rate set correct, and the programme may have to be set to recieve data on com 1.
Good luck
Trevor

 

[robp]

Thanks Trevor. Com 1 is selected within the programme and it only has GPS ports for Garmin 1.5, Other v 1.5 or Magellan V2.1 GSA. All are 4800 Baud.

A colleague said he couldn't get data on his Yeoman until he "grounded" the data -ve. Must admit to being nervous about that.

 

[johna]

I use my Garmin 120 with Neptune and have no problems. Have you spoken or e-mailed Les Empage, creater of Neptune, you will find him most helpful. I purchased a lead from him to connect the Garmin to the Laptop. Contact Les through Neptune web site or direct.

I am sold on the Neptune Planner / Plotter as I believe it requires the right mixture of paper charts and electronic planning and plotting; but I accept that you do need a laptop for the plotting.

I have just acquired a new (to me) boat with Garmin 120 and Raytheon chart plotter using C-Map so I have the problem of what to use. The Garmin gives me route and track without chart data, the Plotter gives me everything except the planning facility and Neptune gives me the planning function, route, track and a coastline. I also want to add radar. What a headache.

 

[Guest]

I think the problem is that you are dealing with two different serial interface standards. The PC uses RS232 which signals both positive and negative of the common ground while the fact that you have a Data+ and Data- output from the GPS suggests that it is using a differential signal such as RS422 where one line goes from 0 volt to +5 volt and the other changes from +5 volt to 0 volt at the same time. This should be given in the GPS manual.

You can get converter units that plug into the PC that will convert RS422 to RS232 from firms such as Maplin.

Hope this helps.

John

 

[robp]

Yes he called me last night after I had left a message. What service! Jaubury seems to have it right. I now have something else to try tonight. Use 0 Volt line as signal ground and try data -ve to try and get +ve going data relative to ground. Other wise a little box of tricks.

Look forward to that nice big screen with everything connected?

Thanks

Rob

 

[robp]

Thanks Jon. Yes, the Neptune guy (Les?) called me and explained that. I'll try and fudge it tonight or buy/build a differential receiver. I'm comfortable with electronics but glaze over when it comes to digital. Started to learn though!

 

[jfkal]

It should work without a converter. Make sure the speed is set correctly 4800 bps and the number of stop bits. are you getting nothing or garbage?

 

[robp]

Getting nothing. Speed set to 4800. Stop bits? Can't find any other configuration menus. MLR mentioned "correct sentences" too. Any further enlightenment would be most welcome.

I'm trying the re-wire tonight.

Thanks for your suggestion.

Rob

 

[HaraldS]

I think all the usggestions have been right, so good luck on your next try.
A few hints here to help troubleshooting.

Start simple: Take GPS data out - and connect to pin 5 of your PC
Take GPS data out+ and connect to pin 2 of your PC.

Don't connect anything else.

The connections tieing 1,4,6 shouldn't hurt, but are probably not needed.
Same for the 7,8.

If your programm doesn't revceive GPS data with that simple setup. Try a terminal program. You will probably find something under Start-Menue->programs->accessories->communications->hyperterminal.

Set it up to your com port and baud 4800, data bits 8, stop bits1, flow control none.

You should be getting GPS records printed on your screen, they al start with $ sign and will probably be something like $GPGAA or $GPRMC or the like.

If that works your nav program might not be set up right, maybe wrong port.

If that doesn't work, also hyper term may be pointed to the wrong port.

If port and everything seems right and it is still not working, take the GPS off and connect pin 2 and 3, start hypertem again and see if you get echoed what you type. If it works your PC and its setup are right and you will need to see why the GPS isn't sending as expected.

If you get to that point, let's 'talk again'.

If the echoing doesn't work, you will need to figure out what setup on the PC might be wrong.


if you get it all to work, only then connect the reberse path from PC to GPS, you will only need it to upload routes and waypoints.

If making that connection leads to the previous part failing, we'll need to do some checks on your gps interface.

don't connect any DC ground between the two at this point.


good luck!

 

[robp]

Many thanks for this Harald. I'm printing it and taking with me now. I'll let you know.

BR

Rob

 

[jfkal]

Sure.

Below is the soldering info.
Check the COM X number set in your PC whether it matches the settings in the program. Else if you senf me your e-mail address I forward you a small monitor program which helps you to make sure the data arrives at the PC. Helps to find out whether the problem is the PC program or the GPS.

Have fun

**************************************************************************
GPS Cable
**************************************************************************
A GPS interface cable can be made from just a few parts at Radio Shack.
1. 9 pin female DB9 connector and plactic hood.
2. Any length of three or four conductor cable.

Procedure:
Solder the ends of the cable to pins 2, 3, 5 on the female DB9
connector.

The wire soldered to Pin 2 of the connector should be attached
to the wire sending data out (NMEA 0183 data out) of the GPS.

The wire soldered to Pin 3 of the connector should be attached
to the wire sending data into the GPS. This is optional. It
is only necessary if you wish to up-load way points to the GPS.
(A feature not supported by all GPS systems.)

The wire soldered to pin 5 of the connector is the gound
connection and should attached to the ground/common output of
the gps.

Make sure you put the GPS unit in NMEA 0183 data output mode

Refer to your GPS unit for the data output wires & Colors

Pin 1 2 5
o o o o o
View of solder side of the
6 o o o o 9 DB9F connector

 

[robp]

Re: Got it going and..

Due to the differential output on the GPS, it works with Pin 2 connected to data out -ve and pin 5 connected to 0 Volts on GPS. (As per Les from Neptune). Connecting pin 3 to data in
-ve doesn't appear to work. Connecting pin 3 to data in +ve causes GPS to shut down or not receive. Les suggests I might need a differential driver for this. Harald, you suspected something like that might happen?

Thanks JFCAL for your confirmation of pin connections.

Many thanks to all for your help, I've been avoiding all this stuff in the past but can't any longer!

How helpful Neptune (Les Empage) is too. I have no connection (pun intended) with the company but his after sales help is superb.

Rob

 

[HaraldS]

Re: Got it going and..

The results you describe confirm the suspicion that the power source for the differntial drivers isn't galvanically isolated from the regular ground.
For that reason -ve of the GPS will appear to toggle between about +/- 3V, which just barely satisfies the RS232 input requirement on the PC-port pin2, which is speced to be between +/-5V to +/-15V, but most seem to start working at around +/- 2.5V.
To get a more reliable signal, I had suggeted you also use the opposite differntial signal +ve, by connecting +ve to PC-pin 5, and -ve as you have it to pin 2. That would have given you twice the voltage, but we can't do this because of the appearnt power source issue. (I'm saying this presuming your +ve out is just open and not tied to ground).
But there is still a fair chance to get the other direction working: If you connect -ve in of the GPS to pin 3 of the PC, like you already did, and then connect the +ve in of the GPS with ground (0 Volt), it shoudl start working.

 

[rogerm]

For lots of further background into this area (NMEA 0183) try looking at:-http://vancouver-webpages.com/peter

And/or try a web search on "NMEA 0183".
Roger

 

[robp]

Re: Got it going and..

I'll try that. But I did start sweating a bit last night when the GPS started reading 00º00' etc. Can connecting +ve of data in to 0V cause any problem?

 

[HaraldS]

Re: Got it going and..

Rob, connecting a differntial input to 0V should never be a problem.
What can damage a differential receiver is moving one or both of the inputs out of what is called the common mode range.

These receivers only receive the differnce between the two inputs and don't react to input relative to ground as long as things are in that range. To make them receive a signal relative to ground, one end needs to be tied to ground. The inputs are symmetric and should behave the same, except that you receive ones instead of zeroes and vice versa if they are switched.

Since RS232 sens ones as a negative signal, and that is also the idle state, the -inputs will give the right translation.

As you found out it is relatively safe to connect an RS422 sender to an RS232 input. It will most likley work, while not with a great noice imunity and not on long cables.

The other way is trickier. The RS232 output of your laptop, will likely toggle between -8V and +8V, relative to ground. But I have seen some laptops only do 5-7V. While more is better when connecting RS232 to RS232, it makes things worse when trying to drive an RS422 input.

The common mode range of a high quality RS422 receiver circuit is between -7and +12V, yours could be less tolerant and may already be hosed.

Your RS232 output pin, will be around -7V in idle state, and that is already too much for the input. What worries me is the asymetric behaviour you get, depending which input you connect to the PC pin 3. It could mean that something is already broken. But it could be that they are just slightly differnt in common mode tolerance.

From the behaviour you see, it seems that when you connect +ve input with PC pin 3, the ciruit is driven out of range and internally shorts so that the internal supply voltage breaks down, same seems to supply some parts of the GPS receiver and that is why it going crazy.

So grounding any input is no problem, but putting mor ethan 5V either way on it relative to ground is risky.

Since your -ve seemed more tolerant you may be lucky. Safer would be to clip the input with a Zener diode of about 4V (between ground and -ve) and then a resistor of 3k in line with the wire from -ve to pin 3 of the PC.

Off sourse an RS232 to RS422 adaoter is always a better solution.

It keeps amazing me how many hours of time go into troubleshooting this NMEA stuff, it's really old technology. My favorite on boats would be fibre-optic, as one wouldn't have to worry about ground loops and electrolysis and all the other signal stuff you are just going through.

Wishing you good luck.
Harald

 

[robp]

Re: Got it going and..

Thanks for such a comprehensive explanation Harald. Yes I understand it now. Think I'll wait for the cct diagram for the line driver or RS232/RS422 and do it properly. Not the end of the world not to upload waypoints or routes right now. But the convenience of having the boat position on the plotter speeds things up considerably.

Thanks again

Rob