Arduino + Java

Forum 2005-2010 (read only) Software Interfacing
1

Hi all,

I am trying to capture and analyze my arduino's output in java. Seeing as I am running windows, I have decided to use the RXTX library to access the serial port in Java. I am very close to successfully receiving data, however I am having a small problem.

Here is my code:

import gnu.io.CommPort;
import gnu.io.CommPortIdentifier;
import gnu.io.SerialPort;

import java.io.FileDescriptor;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;

import java.nio.ByteBuffer;

public class SerialTest {
      
      // Set up and connect to the serial port
      public void connect(String portName) throws Exception {
            CommPortIdentifier portIdentifier = CommPortIdentifier.getPortIdentifier(portName);
            if(portIdentifier.isCurrentlyOwned()) {
                  System.out.println("Error: Port is currently in use");
            }
            else {
                  CommPort commPort = portIdentifier.open(this.getClass().getName(), 2000);
                  
                  if(commPort instanceof SerialPort) 
                  {
                        SerialPort serialPort = (SerialPort)commPort;
                        serialPort.setSerialPortParams(9600, SerialPort.DATABITS_8, SerialPort.STOPBITS_1, SerialPort.PARITY_NONE);
                        
                        InputStream in = serialPort.getInputStream();
                        
                        (new Thread(new SerialReader(in))).start(); // begin reading the serial port
                  }
                  
                  else
                        System.out.println("Error: Only serial ports are handled.");
            }
            
      }
      
      
      // facilitates the reading of the serial port
      public static class SerialReader implements Runnable {
            
            public SerialReader(InputStream in)
            {
                  this.in = in;
            }
            
            public void run() {
                  byte[] buffer = new byte[1024];
                  int len = -1;
                  try
                  {
                        while( (len = this.in.read(buffer)) > -1 ) {
                              System.out.println( (new String(buffer, 0, len)) ); // convert the byte data to a string
                        }
                  } catch(IOException e) {
                        e.printStackTrace();
                  }
            }
            
            private InputStream in;
      }
      
      public static void main(String [] args) {
            SerialTest tst = new SerialTest();
            
            try
            {
                  tst.connect("COM3");
            } catch(Exception e) {
                  e.printStackTrace();      
            }
            
      }
}

Here is the resulting output:

533
531
532

5
32
532
531

5
33
532
533

5
33
532
533
5
3
2
533
533
5
3
2
532
532
53
2

533
533
53
3

533
532
53
4

532
533
532



532
531
532



532
532
531



533
533
532



533
532
533



532
532
533

5
32
532
533

5
32
532
532

5
34
530
533
5
3
3
532
533
5
3
2
532
531
53
2

533
532
53
2

534
532
53
3

533
532
533



532
533
531



532
532
531



532
532
534



532
534
531



533
533
533

5
33
532
533

5
32
532
532

5
32
532
534
5
3
2
533
533
5
3
2
533
532
53
3

532
533
53
3

532
531
53
3

533
532
533



531
533
532



533
533
532



532
532
531



532
533
531



533
532
533

5
32
532
533

5
32
532
532

5
33
532
532
5
3
3
532
532
5
3
3
533
532
53
2

532
532
53
3

533
533
53

Where as the actual output (according to hyperterminal) should be something similar to:

533
532
533
533
532
533
531
...

Does anyone have any idea why the byte buffer is being converted so incorrectly? Also, is there a way to have the arduino write integers to the serial port as opposed to ASCII strings? Any help on this is greatly appreciated!

2

Oops ignore this first question, I figured out that the error was little more than a print formatting problem... Which brings me to a second problem:

I need to be able to parse these values to integers. At the moment, the data from the serial port is coming in chunks of multiple numbers. For example, in each iteration of the read loop, the byte array is populated with something similar to the following:

533
532
53

This wouldnt be a problem if I didnt need to analyze the data in real time, however that is not the case. Does anyone know a way to either have the arduino output actual numbers to the COM port or at the very least a way to have it format the output strings so that they are strings of individual numbers and not "chunks?"

3

Try adding some magic code, or define some structure,
for example:

1 byte magic_code + value in 3 bytes
0xEE, 0x00, 0x00, 0xFF

to receive a 255 integer

4

Is this on the java end? And do you mean, separating out the serial port output into groups of 3 bytes and popping a 4th 0xFF on to get an integer?

5

this is on both sides, you can not relay on the serial transmission itself.

What I say is to implement a known structure to receive, so you always get the complete "data" packet, 0xEE in this case only helps to syncronize your serial communication, but you can use other ways, even a flexible one like:

0xFF, 0x00, N data bytes, 0xFF, 0xFF

6

Ohh, I understand. Ill give it a try, thanks for the help!