In this tutorial I am going to show how-to communicate a Java program with an Arduino board through the serial port.

Getting started

Before start, be sure you have installed Java JDK correctly. You can read this blog to do it. Once this is done, check the Java compiler version.

$ javac -version
javac 1.8.0_171

Installing jRXTX library

I work with jRXTX. This library is native in Ubuntu and you have to install following these steps:

Install the library from repositories.

$ sudo apt install librxtx-java

This will install the correct native library in /usr/lib/jni and the jar library in /usr/share/java

$ ls /usr/lib/jni
librxtxI2C-2.2pre1.so 
librxtxRaw-2.2pre1.so 
librxtxSerial-2.2pre1.so
librxtxI2C.so 
librxtxRaw.so 
librxtxSerial.so
librxtxParallel-2.2pre1.so 
librxtxRS485-2.2pre1.so
librxtxParallel.so 
librxtxRS485.so

$ ls /usr/share/java
. . . 
RXTXcomm-2.2pre2.jar
RXTXcomm.jar
. . .

The serial ports /dev/tty* are only accessible to members belonging to groups dialout and tty. You therefore have to add your user to those groups

$ sudo adduser <user> dialout
$ sudo adduser <user> tty

Afterwards you have to reboot your computer in in order for the group changes to become active.

Configure Eclipse

In order to use the library jRXTX on Eclipse IDE. You have to add it to user library.

Now, ensure add the user library to the Java project.

The Java program

I used the same java program showed in rxtx example page to test the library.

package serial;

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

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

public class TwoWaySerialCom {
    public TwoWaySerialCom() {
        super();
    }

    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();
                OutputStream out = serialPort.getOutputStream();

                (new Thread(new SerialReader(in))).start();
                (new Thread(new SerialWriter(out))).start();

            } else {
                System.out.println("Error: Only serial ports are handled by this example.");
            }
        }
    }

    /** */
    public static class SerialReader implements Runnable {
        InputStream in;

        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.print(new String(buffer, 0, len));
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }

    /** */
    public static class SerialWriter implements Runnable {
        OutputStream out;

        public SerialWriter(OutputStream out) {
            this.out = out;
        }

        public void run() {
            try {
                int c = 0;
                while ((c = System.in.read()) > -1) {
                    this.out.write(c);
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }

    public static void main(String[] args) {
        try {
            (new TwoWaySerialCom()).connect("/dev/ttyACM0");
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

Arduino program

I created a basic arduino program to respond a string received by serial port.

/**
 * Arduino serial test
 * Author: Rodrigo Tufino <rtufino@ups.edu.ec>
 * Date: 26-06-2018
 */
void setup() {
  Serial.begin(9600);
  Serial.println("Serial Echo Device");
  delay(1000);
}

void loop() {
  delay(100);
  if (Serial.available() > 0) {
    String dato = Serial.readString();
    Serial.println(dato);
  }
}

Test

$ java serial.TwoWaySerialCom

Serial Echo Device
Hello
Hello

how are you?
how are you?

Working in Microsoft® Windows®

You need two files to use this library on Microsoft Windows:

• rxtxSerial.dll
• rxtx-2.2pre2.jar

You have to copy the rxtxSerial.dll file to system folder C:\winsows\system32. The rxtx-2.2pre2.jar file is the library to add to Java’s project. You can download these archives from here.

 

Esta obra está bajo una Licencia Creative Commons Atribución-NoComercial 4.0 Internacional.