I am in the process of upgrading a remote controlled vehicle to bring in some kind of intelligence to reach a programmed spot and return back to base. To startwith, the destination will be reached in a straight line from base.

Before I proceed some details of the vehicle :

It is a modified 35 hp tractor with following replacements :

Clutch and Brake : Hydraulic cylinders
Steering : Stepper drive
Gas pedal : DC Motor + pulley and wire link.
Start and Stop engine : Relays

All the above are in control by an 89c52rd2 powered by the vehicle 12V battery. Comunication with the vehicle is with a 12 channel 433MHz remote unit meant for overhead cranes. The signals from the hand held unit are recieved by the vehicle mounted reciever. These are then synthesised into vehicle controls. The setup is working fine the last six months.

The new proposal :

The range with the current setup is just about 100 m. In order to increase this and also try out navigatiopn capabilities I have been asked to provide a facility whereby the user enters a destination co-ordinate onto the tractor mounted control unit. Once started the tractor should reach that point and return back to base using GPS.

The help I want:

I am generally aware of the GPS modules that are used with notebook PCs with USB interface. But how about modules that interface with MCUs ? A search in this forum threw up a link to a UK based company - but the link is dead - maybe some temporary problem.

I would like to hear from someone who has done a similiar navigation project and the pitfalls therein. Aspects on the output data from such GPS modules, the possible accuracy that I can get ( I need +/- 10m)are other concerns.

Thanks for your time.

Raghu