Well last weekend i finished up a little project using a few photo-resistors and two four transistors in two darlington pairs. The result was a simple circuit that changed motor direction by light levels. It worked fairly well on a nine volt battery and would avoid the shadows cast by an object and the object itsef, but a problem developed in the power dropped across the power switchimg transitor and the unit would over heat and until the components cooled down only one turning direction would work.
This cicuit was really just a study in designing one "nerve" for the main robot design, but it told me alot about imporvements to do to increase the sensitivity of the cells and response time. I know that there are many other IC units that can be used in place of transistors, but I really like the durability and recovery properties of transitors. IC's are great but they have a great limitation when exsposed to high heat or electromagnetic interferance.
Some of the systems I worked on in the Navy really took this lesson home. The main room all of our equipment needed quite a large AC system. If it ever went out the bays would get hot enough to give you a good burn. After the heat went down, the only equipment to survive without great need for repairs, was the stuff built off of old 1960's and 70's designs. Everything using mostly IC circuitry would be dead or near dying. Course, not that I don't love IC's, I just think we shouldn't depend upon them for all applications, same with transistors and such.