Serial Com Java to Arduino with ServoMotors [duplicate]

Question

Im doing my thesis right now, Arduino Automatic Telescope. And im stuck at a problem cant control my servo motors from my Java program, LED light for debugging works but my motors dont move.

void loop() {
  if (Serial.available() > 0) {
    // Turn on LED when receiving data
    digitalWrite(ledPin, HIGH);
    
    // Read the incoming data
    String receivedData = Serial.readStringUntil('\n');
    int position = receivedData.toInt();
    
    // Move servos
    altitude.write(position);
    azimuth.write(position);
    delay(1000);
    
    // Return to zero
    altitude.write(0);
    azimuth.write(0);
    
    // Turn off LED when done processing
    digitalWrite(ledPin, LOW);
  }
}

Java code

public static void main(String[] args) {

       SerialPort arduinoPort = SerialPort.getCommPort("COM4");

       if(arduinoPort.openPort()){
        System.out.println("Port opened successfully");
       }else{
        System.out.println("Port couldnt be opened");
        return;
       }

       //Configure Port
       arduinoPort.setComPortParameters(9600, 8, SerialPort.ONE_STOP_BIT, SerialPort.NO_PARITY);
       arduinoPort.setComPortTimeouts(SerialPort.TIMEOUT_READ_BLOCKING, 1000, 0);


       sendIntToArduino(arduinoPort,90);
       // Add delay to ensure data is sent
        try {
            Thread.sleep(2000);  // Wait 2 seconds
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

       arduinoPort.closePort();
    }

    public static void sendIntToArduino(SerialPort port, int degrees) {
        // Convert to string with newline
        String command = degrees + "\n";
        byte[] buffer = command.getBytes();
        
        port.writeBytes(buffer, buffer.length);
        System.out.println("Data was SENT: " + degrees);
    }

Manually everything works fine all cables are correctly connected. I think the problem is the data type im sending my data. If you got any advices im all ears.

When I open my serial monitor and type 90. Both motors move 90degrees and back to 0 like my arduino sketch. — SeUz75
– SeUz75, Commented Apr 24 at 11:05
After some debugging my java sends this data Port opened successfully Data was SENT: [B@448139f0 Data was : 574810 Which is correct. Seems like the line Serial.available>0 never is true :/ — SeUz75
– SeUz75, Commented Apr 24 at 12:05
I haven't done any Arduino programming in a while, but worth trying: in the Java code, add a delay between opening the port and sending the string. — 001
– 001, Commented Apr 24 at 13:33
Bellow I have answered my question after a week of thinking about it. — SeUz75
– SeUz75, Commented Apr 30 at 18:23

Vijay · Accepted Answer · 2025-04-24 18:33:45Z

0

When you open the serial port, Arduino resets, so any data sent immediately can be lost. Adding a delay ensures the board is ready to receive input.

Update your Java code w/ below:

if (arduinoPort.openPort()) {
    System.out.println("Port opened successfully");

    // Add this delay to wait for Arduino reset to complete
    try {
        Thread.sleep(2000);  // Wait 2 seconds
    } catch (InterruptedException e) {
        e.printStackTrace();
    }

    sendIntToArduino(arduinoPort, 90);
} else {
    System.out.println("Port couldn't be opened");
}

answered Apr 24 at 18:33

Vijay

4404 silver badges4 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

SeUz75 Apr 30 at 18:18

So i've come to the conclution that the fist serial read that my java program does is almost 100% WRONG every time. Even adding delay isnt fixing it but I kept them. So what I did was my arduino is SENDING me gps data every 1sec. And the MOST IMPORTANT it to have a cycle which READS AGAIN 2 or 3 times the serialWrite of the Arduino ! And the outcome is this Data received from arduino is : 42. Data received from arduino is : 42.135398,24.745300 Data received from arduino is : 42.135398,24.745300 And this is how I solved this problem. Hope if anybody has the same problem will see my solution

Collectives™ on Stack Overflow

Serial Com Java to Arduino with ServoMotors [duplicate]

1 Answer 1

1 Comment

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Linked

Related