Gemini 105M - Connecting the Garmin 492/498 to the ST4000 Autohelm
One of the things I wanted was to have the Garmin 492 talk to our autohelm so it would automatically correct for crosstrack errors. This became apparent that it would be very helpful on one of our crossings and especially at night. It was actually very easy once it was figured out.
Basically, the ST4000 can receive information in NMEA sentences which is an industry standard. It also is required that the sentences are send at 4800 "baud." Therefore there are two steps you must do. Set up the GPS and wire it to the autohelm.
Wiring - Basically, all you have to do is to connect the blue wire from the Garmin to the + of NMEA in on your autohelm and then connect the - of NMEA in on your auto helm to ground.
Specifically, you must remove your autohelm and find some little push on connectors. They are smaller than the ones you typically can get. The picture below shows you where the wires are connected.
The blue wire is from the GPS. The brown wire IS NOT from the GPS. It is simply a brown wire I had that I could use to connect the - side to Ground.
Reinstall the autohelm and now you get to setup the GPS.
On the System menu, choose the Comm tab and set up the Serial to NMEA In / NMEA Out and the Baud Rate to 4800. After you do this, click on the NMEA Setup to get to the next screen.
When the Garmin comes configured it has many more of these NMEA Output Sentences checked. I unchecked everything except for the ones you see in the picture above. 3 of them.
On the Garmin, push the Nav button and choose the route you are going to use. Then you will get a purple line showing up on your map screen. Next, push the -10 and +10 on the autohelm at the exact same time. The autohelm with think a bit and then beep. When it beeps, you must then acknowledge it by pushing -10 and +10 another time. By the way, on the autohelm screen, you can see what it is doing. You can read how much you are off course, the distance to the next waypoint, and some other data. When you get to the next waypoint, the autohelm will beep again and you must acknowledge the new course action by again pushing -10 and +10 at the same time. I think you are supposed to look around before you acknowledge so the Autohelm doesn't run into something. We have now begun calling our autohelm HAL and hope it doesn't take over our ship.
I hope this helps and let me know if something is confusing.
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