How to decide the LDR 's (Photocell) external resistance ?

Pcedison,
This sounds like an interesting project. I hope that you are still tracking this thread. I have an old style (huge) satellite dish that I want to turn into a parabolic reflector for a water heater. I need a solar tracker to run the motor on the dish. What was your plan? Please keep us posted as you make progress. Thanks, MT.