Anders,

Although not exactly what you wanted (it's hard to find links to
PIC-based lawnmower control), I happen to have a few links for PIC-based
model airplane speed controls. Their focus is on speed control rather
than position. Covers issues like electronic braking as well, which you
may need else "dead dog rover". The last one is a 16F84 design.

PIC 16C73       http://professionals.com/~cmcmanis/robotics/servo.html
PIC12C509N   http://home.HiWAAY.net/~mjn/
PIC16F84        http://members.magnet.at/users/avg/motor_controller.html

Charlie

>  Subject: DC Motor Control
>    Date: Fri, 28 May 1999 10:33:03 +0200
>    From:  Anders Wallberg
>
> Hello, I am relatively new to PICs and need some directions.
> Trying to do DC motor control with PIC16F84
> I have 2 DC motors with tacho (0 - 50 Hz) ( driving 1 wheel each of a robotic
application
> (lawnmower!)) that I want to control. The main focus is  position but a big sp
eed error can cause
> big position errors in the end!
> The load can differ a lot between motors so some speed control is needed.
>
> if possible some ramp-up and ramp-down and synchronization between motors is a
 wish.
>
> Its OK to split functions up on different PICs
> We want to give "commands" on serial to the motorcontrol (i.e., go 5000 tacho
pulses fwd)
>
> we use L6203 fullbridge drivers and PWM , so far.
>
> We want Preferable to use the PIC Basic Pro compiler.
>
> PLS. help with hints and URL to projects like this.
>
> ( We been checking out the motormind B from Parallax and we don't think that i
s enough, maybe with a
> PIC "front end" handling sync and ramp-up/down)
>