Gemini 105M - Connecting Chart Navigator Pro to the Garmin 492/498 to Transfer Routes

Since I have a newer computer, it does not have a DB9 RS232 Connector on the laptop. Therefore, I purchased a USB to DB-9 RS-232 interface from Radio Shack. Since we are cruising, I’m not able to get things shipped to me as easily as if I were at a house so I picked this one up at Radio Shack. I hoped the interface would work and it did. However, when you connect the cable up to the USB port for the first time, you must also be connected to the internet so the computer can search for drivers. (I’m using VISTA so the drivers aren’t on the CD.) My computer found the right driver after a while and installed it for me.

Next you must connect the DB9 – RS232 up to the Garmin. You will need to buy a connector, shell and enough wire to accomplish the job. In my case, I picked it all up from Radio Shack. Since you need three conductors, I used their 24 gauge 2 conductor with shielding ground audio cable. I then used the two insulated connectors for the signals and the shield for the third wire since it was ground. Just a bit of theory here, RS232 bases its signal off of ground. A “one” in data is at 5v (actually above 3.8v if remember correctly) and a “zero” is at 0 (less than .8) volts. It simply changes between these voltages at the right speed (baud) and that is how it transmits and receives data. However, you must connect the right pins to the right wires on the Garmin. (Note: The new Garmin’s have switched to a newer data transmission technology so if you have a newer GPS than the 492/498, this may not work for you.)

Once I assembled the parts, I then ran the cable with enough spare length so I could sit at the salon table and transfer the data to the Garmin 492. I connected the cable as follows:
DB9 Connector - RS-232
Pin 3 – TxD to the brown wire on the Garmin which is the receive wire for the Garmin
Pin 2 – RxD to the blue wire on the Garmin which is the transmit wire for the Garmin – My blue wire was already connected to the autohelm so I had to splice into it.
Pin 5 – to Ground – Since the 492 is using RS232, you need to connect the ground wire to the same place you connected the Garmin power’s ground. I connected another wire onto the outside braid, soldered it, and then ran that wire to the ground. That way it was insulated in case it came in contact with something it shouldn’t.

Now that you have the data cable run, you also have to make sure everything talks at the same speed and in the same language. Garmin uses a proprietary “sentence” structure to transfer the routes. This is one of the reasons I purchased Chart Navigator Pro, they can talk Garmin sentences.

If you are like me and are using your Garmin to also talk to your autohelm, ST4000 in my case. You will have to change the settings in the Garmin before it will understand the information from the Chart Navigator Pro. (Just remember to change it back when you want to have the autohelm driven by the Garmin.)

You have to change settings on your Garmin in the System menu and specifically the Comm tab.
1) Change the baud rate from 4800 to 38400 on the GPS
2) Change the Serial to Garmin Data Transfer

Next you must configure a port on your computer.
1) Under Tools/options for Chart Navigator Pro, choose the instruments tab and after you plug in your USB to RS232 interface, you can then manually configure the port for Garmin and set the baud to 38400.
2) To send a route, right click on the route and then click on Garmin

The route should transfer and you will find it under Routes in the Garmin with a truncated name.

It may sound complicated but it really isn’t with the info above. Figuring all this out on the otherhand took awhile.

We have now taken to calling our Autohelm HAL. We hope the computer, GPS, and autohelm won’t take over while we are out at sea and decide to stay there.

Don’t forget, when you are ready to go back to using the GPS with the autohelm, change the settings back to
NEMA in and out
4800 baud

The next time you want to transfer a route, you shouldn’t have to touch the settings in Chart Navigator Pro because those settings shouldn’t change. Of course you will have to change the Garmin.

I hope this helps and let me know if something is confusing.

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Jim and Deb's Adventures