Using Processing to find the value of a knob and send it through a serial port

Processing Electronics (Arduino, etc.)
1

hey i’m pretty new to processing and I was wondering if I could take a knob constantly get the value of it and send the value of the knob through the serial port. I have tried it and all I’ve gotten is this error

Jul 07, 2020 2:32:42 PM controlP5.ControlBroadcaster printMethodError
SEVERE: An error occured while forwarding a Controller event, please check your code at knobValue
java.lang.reflect.InvocationTargetException
at sun.reflect.GeneratedMethodAccessor5.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at controlP5.ControlBroadcaster.invokeMethod(Unknown Source)
at controlP5.ControlBroadcaster.callTarget(Unknown Source)
at controlP5.ControlBroadcaster.broadcast(Unknown Source)
at controlP5.Controller.broadcast(Unknown Source)
at controlP5.Knob.setInternalValue(Unknown Source)
at controlP5.Knob.updateInternalEvents(Unknown Source)
at controlP5.Knob.updateInternalEvents(Unknown Source)
at controlP5.ControllerGroup.drawControllers(Unknown Source)
at controlP5.ControllerGroup.draw(Unknown Source)
at controlP5.ControlWindow.draw(Unknown Source)
at controlP5.ControlWindow.draw(Unknown Source)
at sun.reflect.GeneratedMethodAccessor3.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at processing.core.PApplet$RegisteredMethods.handle(PApplet.java:1436)
at processing.core.PApplet$RegisteredMethods.handle(PApplet.java:1429)
at processing.core.PApplet.handleMethods(PApplet.java:1628)
at processing.core.PApplet.handleDraw(PApplet.java:2495)
at processing.awt.PSurfaceAWT$12.callDraw(PSurfaceAWT.java:1547)
at processing.core.PSurfaceNone$AnimationThread.run(PSurfaceNone.java:313)
Caused by: java.lang.NullPointerException
at test.knobValue(test.java:59)
… 23 more

and I know that whats messing it up is this line of code

port.write(theValue);

here is my full script:

import controlP5.*;
import processing.serial.*;

Serial port;
ControlP5 cp5;

void setup() {
  size(700,400);
  smooth();
  noStroke();
  
  cp5 = new ControlP5(this);
                     
          cp5.addKnob("knobValue")
               .setRange(0,255)
               .setValue(220)
               .setPosition(100,210)
               .setRadius(50)
               .setNumberOfTickMarks(10)
               .setTickMarkLength(4)
               .snapToTickMarks(true)
               .setColorForeground(color(255))
               .setColorBackground(color(0, 160, 100))
               .setColorActive(color(255,255,0))
               .setDragDirection(Knob.HORIZONTAL)
               ;
}

void draw() {

}


void knobValue(int theValue) {
    port.write(theValue);
}
1 Like
2

Hi @processingHax You haven’t opened the port. “myPort = new Serial(…” I suggest you see the serial examples, File, Examples, Libraries, Serial, SimpleWrite. Get that sending serial values, then merge it with your ControlP5 sketch.

1 Like
3

oh thanks so much I got it working now

1 Like