Arduino having trouble getting serial data

Question

For a school project, I'm currently trying to build a vending machine. The brain of the opperation would be my laptop, using an arduino to control the hardware.

I am using the following code to trigger a vend:

public class App {
    public App() {

    }

    public static void main(String[] args) {
        System.out.println("Hoi!");
        SerialPort comPort = SerialPort.getCommPorts()[0];
        comPort.openPort();
        comPort.setComPortTimeouts(SerialPort.TIMEOUT_READ_SEMI_BLOCKING, 0, 0);
        InputStream in = comPort.getInputStream();
        OutputStream out = comPort.getOutputStream();

        try {
            out.write('g');
        } catch (Exception e) {
            e.printStackTrace();
        }
        try {
            Thread.sleep(100);
        } catch (InterruptedException ex) {
            Thread.currentThread().interrupt();
        }
    }
}

And the following code to in the arduino:

#include <Stepper.h>

const int stepsPerRev = 2048;
Stepper motor1(stepsPerRev, 8, 9, 10, 11);
char derp;
void setup() {
 Serial.begin(9600);
 Serial.println("Start");
  motor1.setSpeed(6);
}

void loop() {
  if (Serial.available() > 0) {
    derp = Serial.read();
  }
  else {
    derp = 'k';
  }
  if(derp == 'g'){
    motor1.step(stepsPerRev);
  }
  delay(100);
}

Unfortunately, this does not seem to work. When I place the out.write in a while(true) block, it does seem to work. But this triggers an infinite amount of vends.

Any ideas how I could do this better?

gooper20 gooper20 · Accepted Answer · 2020-06-04T14:32:53

I found my own answer.

The Arduino resets automatically when a serial port is opened. This means that the Java program needs to wait a few seconds before trying to write to the serial port.

Arduino having trouble getting serial data

1 Answers