This lesson is to get you using the analog to digital converter on the ATMega328.  A must read for background information is a guide from parallax (page 41)

http://www.parallax.com/dl/docs/books/edu/BAADv1.3.pdf

The code for this example can be found here

http://www.arduino.cc/en/Tutorial/Potentiometer

If you just finished lesson 3, you can improvise and change the speed of the cylon eyes based on the potentiometer reading.  Ion executed this example nicely, code can be found on our google code page here

 http://code.google.com/p/rbots/source/browse/trunk/StarterKit/Lesson4_Potentiometer2CylonEyes/Lesson4_Potentiometer2CylonEyes.pde

pota2dcyloneyes.mp4

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Parts List:

10k potentiometer