Page 137 - The Definitive Guide to Building Java Robots

Preston_5564C04.fm Page 118 Wednesday, October 5, 2005 7:22 AM

118 CHAPTER 4 ■ SENSORS

' north east
IF east = 1 AND north = 1THEN
headingD = 45
ENDIF

' north west
IF west = 1 AND north = 1 THEN
headingD = 315
ENDIF
' south west
IF west = 1 AND south = 1 THEN
headingD = 225
ENDIF

' south east
IF east = 1 AND south = 1 THEN
headingD = 135
ENDIF

SEROUT 16,16468,[DEC headingD]
GOTO main

■Note Make sure you have the directive for PBASIC 2.5 at the top of your Stamp program, otherwise you’ll
get compile errors on the if-then statements.

Next, I need to create a corresponding Java class that communicates with our compasses.
However, before I discuss this class, I’d like to show you a class diagram of how these sensors
relate to the classes in Chapter 2 (see Figure 4-10).
The CompassStamp class has four constants and one field. The constants are the actual
bytes that correspond to the Compass.bs2 in Example 4-1. Since they’re all unique, I can also
use them to enumerate the compasses in the class. The instance field, compass, I set defaulted
to the Devantech compass. This will be used in the class as the command sent to the BASIC
Stamp and used to determine the delay time for getting the reading.
This class has four public methods. The first two, setCompass() and getCompass(), set and
get the values for the compass reading. The other two getHeading() methods return the compass
heading as an int.
In getHeading(), first I create the byte[] that calls the parent execute() method. Then, because
the command string will return a string of tilde-delimited (~) integers, I parse and convert that
to an int so it can be returned. This method also uses the private method getCompassDelay()
because, depending on the current compass, the delay time to get the reading differs.