Auto Pilot

[PlantBob]

Hi, due to disabilities, I’m am having a custom pontoon built. What I would like to do is build an auto pilot system that works like this:

the pontoon is manually driven from point a to point b
While this is happening, a GPS must be recording and storing the points
Now, when I want to get back to point A from B, the GPS must be read and sent to my steering system(can be designed to work with whatever I come up with here or another forum)
While moving back to point A, the GPS must be monitored to make sure the boat is in correct path.

What Microchip parts would I need?

[kellyseye]

Most 'normal' GPS receivers won't have the positional accuracy to do as you wish. You would need 'centimetric' GPS which costs $1,000's.

[ScaleRobotics]

But if you are using your pontoon at a lake, it might work out ok. A GPS with WAAS has accuracy within 10 feet in the USA.

[mackrackit]

You may want to look at this setup
http://www.picbasic.co.uk/forum/content.php?r=450-Amicus18-with-GPS-Shield


Accuracy
Position 7 meters CEP (90%) horizontal, SA
Explanation
http://gpsinformation.net/main/errors.htm

It will find the dock but will not park.

[ScaleRobotics]

The Amicus platform is very nice. For a gps, a shield might be overkill for just 3 or 4 connections. These are a bit smaller, have WAAS capability, don't require a separate antenna, and are cheaper. They are 3.6v. http://www.sparkfun.com/products/10702

[kellyseye]

WAAS not withstanding you're still looking at an 'error' greater than the width (or length) of the vessel - the difference between docking and missing altogether. GPS will get you in the general area but you would need to go 'manual' or use a more 'local' reference system to get the docking capability.

[mackrackit]

An external antenna is nice for when the unit is inside a structure such as a cabin. Not sure about the cost difference either when one is a "raw" component and the other is ready to use. But it was just a suggestion.

[timmers]

Given the complexity of driving steering servos, pid control filter setups and all the other tweaks required with the potential cost of an ooops moment... buy a marine autopilot that has a warranty / come back!
Raymarine do a good system which can track a gps route from a standard nmea interface. Most gps systems (not all) have a breadcrumb trail to return you to the start.

As a skipper, I can confirm that they do a very good job, providing you programme the gps correctly!