Spaghetti was my very first robot, which was a Line following robot using a LM393 Dual Comparator. How it operates, is that the light is reflected off the surface off the floor and bounces up into a pair of photocells, which then is sent into the comparators, which will only output the highest value resistance. It is a very simple circuit, that requires somewhat a lot of wiring. I really enjoyed building it, it was very fun and I suggest getting the book: "
Robot Building for Beginners" by David Cook, which really got me inspired to continue my passion with robotics, so I owe a lot to him.
Here are some pictures!