Com Port Ground

[GWB]

I just connected up my laptop to the output of my Furuno GP36 so as to receive nav data from the Furuno and run Seaclear on the laptop. It works fantastic for a while and then starts producing Egyptian hieroglyphics (I can look at the input using hyperterminal) I verified that it is not the output from the Furuno by checking the GPS data on my vhf (this recieves the same input from the Furuno)

Sooo, the problem is either noise (and I turned off everything around it - makes no difference) or its some kind of ground/common problem. The common/ground is connected to pin 5 on the pc com port... and the only other wires connected to the com port are tx and rx.

Anyone else experienced this kind of problem?

Thanks for any input

[SariTimur]

I have had this with some other high speed nav data on computers where the RS232 ground alone was not good enough. I was told by the supplier of that equipment to connect the shield to a ground on the computer. They suggested the screw that connects to the DB9 connector on the computer side. When I did this it worked. Once we started using laptops with USB to DB9 connectors problem didn't exist so I guess there the ground was looped through already or the newer laptops were better against noise. Never found out but it would be worth trying in you case not to hard to give it a whirl. It is interesting though that hyperterminal doesn't see a problem.

Cheers

[richardhula]

Try strapping the -ve signal lead (pin 5 on db9) to battery negative/ground. This is the most common solution for such problems giving the +ve signal a firm reference.

Probably easiest to do this where lead joins Furuno GPS.

[GWB]

Thanks - I'll give it a whirl Richard. Sari - I did try tying ground/batt negative to the computer case and that did not work. Hyperterminal is the device showing the weird characters... sometimes. Other times the characters are as they should be - that is strings of english characters and numbers

[osirissail]

There is "freeware" that will display the output of your GPS on your computer - VisualGPSâ„¢
This is a good way to confirm that the GPS output is really getting into the computer. You can open the programs NMEA sentence window and watch the actual GPS sentences being downloaded to your computer. It also has current position and accuracy windows plus more to see how the GPS if performing.
- - With any new installation of a computer navigation program I also install the Visual GPS program to be sure that the GPS is "talking" to the computer before trying to "install/activate" the GPS in the navigation program.
- - One limitation is that you can only utilize one program that will be using the GPS at a time. You cannot run the navigation program and a GPS utility program at the same time - at least not on any computer I have used.
- - There is an old time problem that affects Windows operating systems and GPS's - and that is that the operating system can think that the GPS signal is a "mouse" signal and it causes strange things to happen especially with the cursor. The work-around was to start the computer without the GPS turned on or plugged in and also the navigation program - and then turn on or plug in the GPS to the computer. It was also common that once the navigation program was shut down that other programs with "comm" port provisions would go weird if the GPS was still turned on.

[richardhula]

Originally Posted by osirissail

One limitation is that you can only utilize one program that will be using the GPS at a time. You cannot run the navigation program and a GPS utility program at the same time - at least not on any computer I have used.

By itself true, but there are many utility programs available that will echo or distribute the GPS signal on your PC to several of other programs simultaneously via virtual COM ports.

Google NavMonPC (free) or GpsGate.

[SailFastTri]

Pin 1 is for chassis ground. Pin 5 is signal ground (in a DB-9 connector). Generally no harm if you tie them together.

[SailFastTri]

Originally Posted by richardhula

Try strapping the -ve signal lead (pin 5 on db9) to battery negative/ground. This is the most common solution for such problems giving the +ve signal a firm reference.

Probably easiest to do this where lead joins Furuno GPS.

GPS will generally use Pins 2 (transmit), 3 (receive)and ground (pins 5 and 1) on a db9 connector.

The serial port on the PC should be set for 8, N, 1 (8 bits, no parity, 1 stop bit) and data rate matters. The issue in the original question could be caused by mismatched data rate.