Page 123 - Hacking Roomba

104 Part I — Interfacing

You can test this out with the roombacomm.Waggle test program.

By far the most interesting curve the Roomba does is the expanding spiral, usually when it first
starts up. You can implement a spiral by keeping a fixed velocity and incrementing the radius
value over time. In the example program Spiral.java, you can see one way to go about this.
Listing 5-5 shows the important parts of Spiral.java.

Listing 5-5: Important Parts of Spiral.java

int radius = 10;
int radius_inc = 20;
int pausetime = 500;
int speed = 250;
while( !done ) {
roombacomm.drive(speed,radius);
radius += radius_inc;
roombacomm.pause(pausetime);
}

An initial radius is defined that is then incremented by radius_inc amount every
pausetime milliseconds.Try modifying Spiral.java to choose different values for those three
numbers. With the numbers in the listing, Roomba spirals out, but if you choose a large initial
radius and a negative radius_inc, the Roomba would spiral inward.

Real-Time Driving

The problem with the distance-based methods is the pause() method in them that causes
your program to wait (or block). Although it is paused, it can’t do anything else, such as check
for user input or read the Roomba’s sensors. A refinement you could add to RoombaComm
would be to implement a way to drive a certain distance without blocking the code. One way
to do this might be to put all Roomba control code in one thread and sensor reading or user-
interface checking in another thread.
However, if you want to drive your Roomba in real time, you don’t necessarily need to drive
specific distances or angles. By using the simplest methods like goForward(), spinLeft(),
and spinRight(), coupled with stop(), you can create a program to drive the Roomba
from your computer.
In Java the easiest way to respond to single key presses is to write a GUI program. Java makes it
quite easy to build GUI programs with buttons and windows and such. The toolkit one gener-
ally uses to make GUI Java programs is called Swing and is part of Java. Normally these Swing
GUI elements handle mouse clicks and key presses for you, but you can override that function-
ality and have your own program listen to key presses. This is done by making your code’s class
implement a KeyListener and having a method called keyPressed().