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Later in this chapter, I’ll show you a general way to implement such FSMs. The NXT Turtle in Chapter 6, as well as JohnNXT in Chapter 8, use this technique to feature autonomous behaviors. Finally, you’ll learn an elegant implementation of a particular kind of FSM—decision tables. Finite State Machines in Brief Let me introduce a bit of the theory behind FSMs. I promise I’ll be brief; however, some definition is needed here for you to understand what you’ll put in practice later. A finite state machine or finite state automaton (plural automata) is a model of behavior composed of a finite number of internal states (or simply states), the transitions between these states, the set of events that can occur, and actions performed.

In your program, you use only the main task. Remember that you’ll have to put a task named main in every NXC program you’ll write. This task is the first one to be executed when the program is run, so you must put it inside all the actions you want your robot to do. Here, you set the input port to 4 to manage the Ultrasonic Sensor using this code: CHAPTER 2 ■ QUASIMODO SetSensorLowspeed(IN_4); You start an infinite loop (at least, until the batteries run out, the automatic NXT poweroff feature turns it off, or you just stop the program), inside of which you can make the robot do whatever you want.

After learning some more theory in Chapter 3, you’ll be able to build and program a scale-sized replica of the imperial AT-ST in Chapter 4: the All Terrain Scout Transport walker from the Star Wars saga. 45 CHAPTER 3 ■■■ Finite State Machines M ost simple robots don’t show much interesting behavior. Usually, a sequential program flow regulates their actions: the robot walks until it sees an obstacle, it backs up and turns, and then starts walking forward again in a loop. What do you do if you desire more interesting behavior?