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Preston_5564C03.fm Page 82 Wednesday, October 5, 2005 7:21 AM

82 CHAPTER 3 ■ MOTION

The difference seen in the following class is that the interface is the actual format of the
command string in the method createCmd(). Also, because we’re used to dealing with servo
positions between 0–255, I left this in rather than requiring the worker program to keep track of
pulse widths between 750 and 2250 milliseconds.
The two fields in the class are cmds—a StringBuffer and a Boolean—to provide status to
any class using this object. Because the timing is determined by the LM32, I choose to use a
timer to signal the class for state change (busy=false). This is done via the setBusy() method
where a single task is set to be run at a specified time in the future (now + milliseconds in future).
The constructor calls the super constructor with the JSerialPort, and sets the maxPins field
to 32. The move() method converts the StringBuffer to a byte[] before sending out the serial
port via the Controller, execute method.

■Note I could have put in a parameter here for a delay in the call to execute(), but I wanted to show you
another way to do the same thing without tying up resources during a move.

The construction of the serial command has the following syntax:

"#" + channel (0-31)
+ "P" + pulsewidth (750-1500milliseconds)
+ "S" + speed(milliseconds for move)
You can string up to 32 commands together before you have to terminate it by appending
the following:
"T" + time for total move(milliseconds) + "\r"

The pulsewidth is the time in milliseconds that I have simplified via the getPw() method.
It will return a pulsewidth ranging from 750 to 1500 from a byte between 0 and 255.
Finally, the test program uses only two servos and moves them to positions 100 and 200,
respectively, during a 1-second timeframe. (See Example 3-12.)

Example 3-12. LM32.java

package com.scottpreston.javarobot.chapter3;

import java.util.Date;
import java.util.Timer;
import java.util.TimerTask;

import com.scottpreston.javarobot.chapter2.JSerialPort;
import com.scottpreston.javarobot.chapter2.SingleSerialPort;
import com.scottpreston.javarobot.chapter2.Utils;