Control an Arduino with Java

Question

I am looking to turn an LED on and off with a Java program. I did the project in C# in roughly 5 minutes, but it seems to be somewhat more challenging in Java. I had the Arduino wait for a 1 or 0 to be written to the COM port and would change the LED based on that. The code I am using for the Arduino is as follows.

int LedPin = 13;
char data;

void setup()
{
    Serial.begin(9600);
    pinMode( LedPin , OUTPUT );
}

void loop()
{
    data = Serial.read();
    if (Serial.available() > 0)
    {
        if(data == '1' )
        {
            digitalWrite(LedPin,HIGH);
        }
        else if(data == '0' )
        {
            digitalWrite(LedPin,LOW);
        }
    }
    else
        if (Serial.available()<0)
        {
            digitalWrite(LedPin,HIGH);
            delay(500);
            digitalWrite(LedPin,LOW);
            delay(500);
        }
}

How would I do this with a Java application?

Answer 1

You can use the JArduino (Java-Arduino) library, which provides a Java API to control your Arduino using serial port (using a USB cable, or wireless devices behaving as serial ports from a software point of view), UDP (via an ethernet shield). All the code related to communication between Java and Arduino is managed internally by the library.

Here is a Java sample to blink an LED:

public class Blink extends JArduino {

public Blink(String port) {
    super(port);
}

@Override
protected void setup() {
    // initialize the digital pin as an output.
    // Pin 13 has an LED connected on most Arduino boards:
    pinMode(DigitalPin.PIN_12, PinMode.OUTPUT);
}

@Override
protected void loop() {
    // set the LED on
    digitalWrite(DigitalPin.PIN_12, DigitalState.HIGH);
    delay(1000); // wait for a second
    // set the LED off
    digitalWrite(DigitalPin.PIN_12, DigitalState.LOW);
    delay(1000); // wait for a second
}

public static void main(String[] args) {
    String serialPort;
    if (args.length == 1) {
        serialPort = args[0];
    } else {
        serialPort = Serial4JArduino.selectSerialPort();
    }
    JArduino arduino = new Blink(serialPort);
    arduino.runArduinoProcess();
}
}

JArduino is available at: JArduino

Answer 2

You can easily build Arduino programs in Java, thanks to the excellent HaikuVM.

Here is an example:

import static processing.hardware.arduino.cores.arduino.Arduino.*;

public class Blink {
    static byte ledPin = 13;            // LED connected to digital pin 13

    public static void setup() {
        pinMode(ledPin, OUTPUT);        // sets the digital pin as output
    }

    public static void loop()           // run over and over again
    {
        digitalWrite(ledPin, HIGH);     // sets the LED on
        delay(500);                    // waits for a second
        digitalWrite(ledPin, LOW);      // sets the LED off
        delay(500);                    // waits for a second
    }
}

Answer 3

In order to communicate with a comm port in Java, you need some implementation of the Java Communications API. I can attest to RXTX, I have used it before to communicate with an Arduino.

Once you have your Java Communications implementation, it becomes fairly simple to communicate with an Arduino:

CommPort arduino = getArduinoPort();
arduino.getOutputStream().write(1);

public CommPort getArduinoPort() {
    Enumeration ports = CommPortIdentifier.getPortIdentifiers();
    while(ports.hasMoreElements()) {
        CommPortIdentifier identifier = (CommPortIdentifier) ports.nextElement();
        if(isArduino(identifier)) {
            return identifier.open(getClass().getName(), 2000); // 2 second timeout
        }
    }
    return null;
}

public boolean isArduino(CommPortIdentifier identifier) {
    // if you know the name of the port ahead of time you can
    // compare it here with identifier.getName(), otherwise
    // you can interface with the user like the Arduino IDE's
    // serial monitor
}

The RXTX website also has other examples [2] which you might find useful.