diff --git a/src/main/java/de/neemann/digital/draw/elements/VisualElement.java b/src/main/java/de/neemann/digital/draw/elements/VisualElement.java
index fa8d44d99..7b326bcbe 100644
--- a/src/main/java/de/neemann/digital/draw/elements/VisualElement.java
+++ b/src/main/java/de/neemann/digital/draw/elements/VisualElement.java
@@ -333,7 +333,7 @@ public class VisualElement implements Drawable, Movable, AttributeListener {
             interactor = null;
             resetShape();
         } else
-            interactor = getShape().applyStateMonitor(ioState, null);
+            interactor = getShape().applyStateMonitor(ioState);
     }
 
     /**
@@ -344,13 +344,10 @@ public class VisualElement implements Drawable, Movable, AttributeListener {
      * @param pos            the position
      * @param posInComponent position in CircuitComponent
      * @param modelSync      used to access the running model
-     * @return true if model is changed
      */
-    public boolean elementClicked(CircuitComponent cc, Point pos, Vector posInComponent, SyncAccess modelSync) {
+    public void elementClicked(CircuitComponent cc, Point pos, Vector posInComponent, SyncAccess modelSync) {
         if (interactor != null)
-            return interactor.clicked(cc, pos, ioState, element, modelSync);
-        else
-            return false;
+            interactor.clicked(cc, pos, ioState, element, modelSync);
     }
 
     /**
@@ -361,13 +358,10 @@ public class VisualElement implements Drawable, Movable, AttributeListener {
      * @param pos            the position
      * @param posInComponent position in CircuitComponent
      * @param modelSync      used to access the running model
-     * @return true if model is changed
      */
-    public boolean elementPressed(CircuitComponent cc, Point pos, Vector posInComponent, SyncAccess modelSync) {
+    public void elementPressed(CircuitComponent cc, Point pos, Vector posInComponent, SyncAccess modelSync) {
         if (interactor != null)
-            return interactor.pressed(cc, pos, ioState, element, modelSync);
-        else
-            return false;
+            interactor.pressed(cc, pos, ioState, element, modelSync);
     }
 
     /**
@@ -378,13 +372,10 @@ public class VisualElement implements Drawable, Movable, AttributeListener {
      * @param pos            the position
      * @param posInComponent position in CircuitComponent
      * @param modelSync      used to access the running model
-     * @return true if model is changed
      */
-    public boolean elementReleased(CircuitComponent cc, Point pos, Vector posInComponent, SyncAccess modelSync) {
+    public void elementReleased(CircuitComponent cc, Point pos, Vector posInComponent, SyncAccess modelSync) {
         if (interactor != null)
-            return interactor.released(cc, pos, ioState, element, modelSync);
-        else
-            return false;
+            interactor.released(cc, pos, ioState, element, modelSync);
     }
 
     /**
@@ -395,13 +386,10 @@ public class VisualElement implements Drawable, Movable, AttributeListener {
      * @param pos            the position
      * @param posInComponent position in CircuitComponent
      * @param modelSync      used to access the running model
-     * @return true if model is changed
      */
-    public boolean elementDragged(CircuitComponent cc, Point pos, Vector posInComponent, SyncAccess modelSync) {
+    public void elementDragged(CircuitComponent cc, Point pos, Vector posInComponent, SyncAccess modelSync) {
         if (interactor != null)
-            return interactor.dragged(cc, pos, posInComponent, getTransform(), ioState, element, modelSync);
-        else
-            return false;
+            interactor.dragged(cc, pos, posInComponent, getTransform(), ioState, element, modelSync);
     }
 
 
diff --git a/src/main/java/de/neemann/digital/draw/shapes/AsyncClockShape.java b/src/main/java/de/neemann/digital/draw/shapes/AsyncClockShape.java
index 7abc19954..579dc4129 100644
--- a/src/main/java/de/neemann/digital/draw/shapes/AsyncClockShape.java
+++ b/src/main/java/de/neemann/digital/draw/shapes/AsyncClockShape.java
@@ -5,7 +5,6 @@
  */
 package de.neemann.digital.draw.shapes;
 
-import de.neemann.digital.core.Observer;
 import de.neemann.digital.core.element.ElementAttributes;
 import de.neemann.digital.core.element.PinDescriptions;
 import de.neemann.digital.draw.elements.IOState;
@@ -43,7 +42,7 @@ public class AsyncClockShape implements Shape {
     }
 
     @Override
-    public InteractorInterface applyStateMonitor(IOState ioState, Observer guiObserver) {
+    public InteractorInterface applyStateMonitor(IOState ioState) {
         return null;
     }
 
diff --git a/src/main/java/de/neemann/digital/draw/shapes/BitSelShape.java b/src/main/java/de/neemann/digital/draw/shapes/BitSelShape.java
index 4b2ce4a4b..6bffe3fc0 100644
--- a/src/main/java/de/neemann/digital/draw/shapes/BitSelShape.java
+++ b/src/main/java/de/neemann/digital/draw/shapes/BitSelShape.java
@@ -5,7 +5,6 @@
  */
 package de.neemann.digital.draw.shapes;
 
-import de.neemann.digital.core.Observer;
 import de.neemann.digital.core.element.ElementAttributes;
 import de.neemann.digital.core.element.Keys;
 import de.neemann.digital.core.element.PinDescriptions;
@@ -50,7 +49,7 @@ public class BitSelShape implements Shape {
     }
 
     @Override
-    public Interactor applyStateMonitor(IOState ioState, Observer guiObserver) {
+    public Interactor applyStateMonitor(IOState ioState) {
         return null;
     }
 
diff --git a/src/main/java/de/neemann/digital/draw/shapes/BreakShape.java b/src/main/java/de/neemann/digital/draw/shapes/BreakShape.java
index a02553c9c..cbb9e4d63 100644
--- a/src/main/java/de/neemann/digital/draw/shapes/BreakShape.java
+++ b/src/main/java/de/neemann/digital/draw/shapes/BreakShape.java
@@ -5,7 +5,6 @@
  */
 package de.neemann.digital.draw.shapes;
 
-import de.neemann.digital.core.Observer;
 import de.neemann.digital.core.element.ElementAttributes;
 import de.neemann.digital.core.element.Keys;
 import de.neemann.digital.core.element.PinDescriptions;
@@ -51,7 +50,7 @@ public class BreakShape implements Shape {
     }
 
     @Override
-    public Interactor applyStateMonitor(IOState ioState, Observer guiObserver) {
+    public Interactor applyStateMonitor(IOState ioState) {
         return null;
     }
 
diff --git a/src/main/java/de/neemann/digital/draw/shapes/BusSplitterShape.java b/src/main/java/de/neemann/digital/draw/shapes/BusSplitterShape.java
index 88d8e851a..83ce61c7f 100644
--- a/src/main/java/de/neemann/digital/draw/shapes/BusSplitterShape.java
+++ b/src/main/java/de/neemann/digital/draw/shapes/BusSplitterShape.java
@@ -6,7 +6,6 @@
 package de.neemann.digital.draw.shapes;
 
 import de.neemann.digital.core.BitsException;
-import de.neemann.digital.core.Observer;
 import de.neemann.digital.core.element.ElementAttributes;
 import de.neemann.digital.core.element.Keys;
 import de.neemann.digital.core.element.PinDescriptions;
@@ -56,7 +55,7 @@ public class BusSplitterShape implements Shape {
     }
 
     @Override
-    public Interactor applyStateMonitor(IOState ioState, Observer guiObserver) {
+    public Interactor applyStateMonitor(IOState ioState) {
         return null;
     }
 
diff --git a/src/main/java/de/neemann/digital/draw/shapes/ButtonLEDShape.java b/src/main/java/de/neemann/digital/draw/shapes/ButtonLEDShape.java
index 91aa6cc47..2dd6d0d04 100644
--- a/src/main/java/de/neemann/digital/draw/shapes/ButtonLEDShape.java
+++ b/src/main/java/de/neemann/digital/draw/shapes/ButtonLEDShape.java
@@ -6,7 +6,6 @@
 package de.neemann.digital.draw.shapes;
 
 import de.neemann.digital.core.ObservableValue;
-import de.neemann.digital.core.Observer;
 import de.neemann.digital.core.Value;
 import de.neemann.digital.core.element.ElementAttributes;
 import de.neemann.digital.core.element.Keys;
@@ -56,10 +55,10 @@ public class ButtonLEDShape extends ButtonShape {
     }
 
     @Override
-    public InteractorInterface applyStateMonitor(IOState ioState, Observer guiObserver) {
+    public InteractorInterface applyStateMonitor(IOState ioState) {
         inputValue = ioState.getInput(0);
         button = (ButtonLED) ioState.getElement();
-        return super.applyStateMonitor(ioState, guiObserver);
+        return super.applyStateMonitor(ioState);
     }
 
     @Override
diff --git a/src/main/java/de/neemann/digital/draw/shapes/ButtonShape.java b/src/main/java/de/neemann/digital/draw/shapes/ButtonShape.java
index 7ec0b88e3..373605702 100644
--- a/src/main/java/de/neemann/digital/draw/shapes/ButtonShape.java
+++ b/src/main/java/de/neemann/digital/draw/shapes/ButtonShape.java
@@ -5,7 +5,6 @@
  */
 package de.neemann.digital.draw.shapes;
 
-import de.neemann.digital.core.Observer;
 import de.neemann.digital.core.SyncAccess;
 import de.neemann.digital.core.element.Element;
 import de.neemann.digital.core.element.ElementAttributes;
@@ -51,30 +50,25 @@ public class ButtonShape implements Shape {
     }
 
     @Override
-    public InteractorInterface applyStateMonitor(IOState ioState, Observer guiObserver) {
+    public InteractorInterface applyStateMonitor(IOState ioState) {
         this.button = (Button) ioState.getElement();
-        ioState.getOutput(0).addObserverToValue(guiObserver);
         return new InteractorInterface() {
             @Override
-            public boolean clicked(CircuitComponent cc, Point pos, IOState ioState, Element element, SyncAccess modelSync) {
-                return false;
+            public void clicked(CircuitComponent cc, Point pos, IOState ioState, Element element, SyncAccess modelSync) {
             }
 
             @Override
-            public boolean pressed(CircuitComponent cc, Point pos, IOState ioState, Element element, SyncAccess modelSync) {
+            public void pressed(CircuitComponent cc, Point pos, IOState ioState, Element element, SyncAccess modelSync) {
                 modelSync.modify(() -> button.setPressed(true));
-                return true;
             }
 
             @Override
-            public boolean released(CircuitComponent cc, Point pos, IOState ioState, Element element, SyncAccess modelSync) {
+            public void released(CircuitComponent cc, Point pos, IOState ioState, Element element, SyncAccess modelSync) {
                 modelSync.modify(() -> button.setPressed(false));
-                return true;
             }
 
             @Override
-            public boolean dragged(CircuitComponent cc, Point posOnScreen, Vector pos, Transform trans, IOState ioState, Element element, SyncAccess modelSync) {
-                return false;
+            public void dragged(CircuitComponent cc, Point posOnScreen, Vector pos, Transform trans, IOState ioState, Element element, SyncAccess modelSync) {
             }
         };
     }
diff --git a/src/main/java/de/neemann/digital/draw/shapes/ClockShape.java b/src/main/java/de/neemann/digital/draw/shapes/ClockShape.java
index 0334f42d9..835ce91a6 100644
--- a/src/main/java/de/neemann/digital/draw/shapes/ClockShape.java
+++ b/src/main/java/de/neemann/digital/draw/shapes/ClockShape.java
@@ -6,7 +6,6 @@
 package de.neemann.digital.draw.shapes;
 
 import de.neemann.digital.core.ObservableValue;
-import de.neemann.digital.core.Observer;
 import de.neemann.digital.core.SyncAccess;
 import de.neemann.digital.core.element.Element;
 import de.neemann.digital.core.element.ElementAttributes;
@@ -56,17 +55,13 @@ public class ClockShape implements Shape {
     }
 
     @Override
-    public Interactor applyStateMonitor(IOState ioState, Observer guiObserver) {
-        ioState.getOutput(0).addObserverToValue(guiObserver); // necessary to replot wires also if component itself does not depend on state
+    public Interactor applyStateMonitor(IOState ioState) {
         return new Interactor() {
             @Override
-            public boolean clicked(CircuitComponent cc, Point pos, IOState ioState, Element element, SyncAccess modelSync) {
+            public void clicked(CircuitComponent cc, Point pos, IOState ioState, Element element, SyncAccess modelSync) {
                 ObservableValue value = ioState.getOutput(0);
-                if (value.getBits() == 1) {
+                if (value.getBits() == 1)
                     modelSync.modify(() -> value.setValue(1 - value.getValue()));
-                    return true;
-                }
-                return false;
             }
         };
     }
diff --git a/src/main/java/de/neemann/digital/draw/shapes/ConstShape.java b/src/main/java/de/neemann/digital/draw/shapes/ConstShape.java
index 5c0c540f7..65255cba1 100644
--- a/src/main/java/de/neemann/digital/draw/shapes/ConstShape.java
+++ b/src/main/java/de/neemann/digital/draw/shapes/ConstShape.java
@@ -5,7 +5,6 @@
  */
 package de.neemann.digital.draw.shapes;
 
-import de.neemann.digital.core.Observer;
 import de.neemann.digital.core.Value;
 import de.neemann.digital.core.element.ElementAttributes;
 import de.neemann.digital.core.element.Keys;
@@ -47,7 +46,7 @@ public class ConstShape implements Shape {
     }
 
     @Override
-    public Interactor applyStateMonitor(IOState ioState, Observer guiObserver) {
+    public Interactor applyStateMonitor(IOState ioState) {
         return null;
     }
 
diff --git a/src/main/java/de/neemann/digital/draw/shapes/DILShape.java b/src/main/java/de/neemann/digital/draw/shapes/DILShape.java
index 89fdc7fbe..8a077bb9c 100644
--- a/src/main/java/de/neemann/digital/draw/shapes/DILShape.java
+++ b/src/main/java/de/neemann/digital/draw/shapes/DILShape.java
@@ -5,7 +5,6 @@
  */
 package de.neemann.digital.draw.shapes;
 
-import de.neemann.digital.core.Observer;
 import de.neemann.digital.core.element.ElementAttributes;
 import de.neemann.digital.core.element.Keys;
 import de.neemann.digital.core.element.PinDescription;
@@ -66,7 +65,7 @@ public class DILShape implements Shape {
     }
 
     @Override
-    public InteractorInterface applyStateMonitor(IOState ioState, Observer guiObserver) {
+    public InteractorInterface applyStateMonitor(IOState ioState) {
         return null;
     }
 
diff --git a/src/main/java/de/neemann/digital/draw/shapes/DataShape.java b/src/main/java/de/neemann/digital/draw/shapes/DataShape.java
index a0d183cfe..e051b5dac 100644
--- a/src/main/java/de/neemann/digital/draw/shapes/DataShape.java
+++ b/src/main/java/de/neemann/digital/draw/shapes/DataShape.java
@@ -6,7 +6,6 @@
 package de.neemann.digital.draw.shapes;
 
 import de.neemann.digital.core.Model;
-import de.neemann.digital.core.Observer;
 import de.neemann.digital.core.Signal;
 import de.neemann.digital.core.element.ElementAttributes;
 import de.neemann.digital.core.element.Keys;
@@ -54,7 +53,7 @@ public class DataShape implements Shape {
     }
 
     @Override
-    public Interactor applyStateMonitor(IOState ioState, Observer guiObserver) {
+    public Interactor applyStateMonitor(IOState ioState) {
         return null;
     }
 
diff --git a/src/main/java/de/neemann/digital/draw/shapes/DelayShape.java b/src/main/java/de/neemann/digital/draw/shapes/DelayShape.java
index 0097c1979..0e2dfe4b3 100644
--- a/src/main/java/de/neemann/digital/draw/shapes/DelayShape.java
+++ b/src/main/java/de/neemann/digital/draw/shapes/DelayShape.java
@@ -5,7 +5,6 @@
  */
 package de.neemann.digital.draw.shapes;
 
-import de.neemann.digital.core.Observer;
 import de.neemann.digital.draw.elements.IOState;
 import de.neemann.digital.draw.elements.Pin;
 import de.neemann.digital.draw.elements.Pins;
@@ -39,7 +38,7 @@ public class DelayShape implements Shape {
     }
 
     @Override
-    public Interactor applyStateMonitor(IOState ioState, Observer guiObserver) {
+    public Interactor applyStateMonitor(IOState ioState) {
         return null;
     }
 
diff --git a/src/main/java/de/neemann/digital/draw/shapes/DemuxerShape.java b/src/main/java/de/neemann/digital/draw/shapes/DemuxerShape.java
index 0e7dd86db..8317dfeab 100644
--- a/src/main/java/de/neemann/digital/draw/shapes/DemuxerShape.java
+++ b/src/main/java/de/neemann/digital/draw/shapes/DemuxerShape.java
@@ -5,7 +5,6 @@
  */
 package de.neemann.digital.draw.shapes;
 
-import de.neemann.digital.core.Observer;
 import de.neemann.digital.core.element.ElementAttributes;
 import de.neemann.digital.core.element.Keys;
 import de.neemann.digital.core.element.PinDescriptions;
@@ -63,7 +62,7 @@ public class DemuxerShape implements Shape {
     }
 
     @Override
-    public Interactor applyStateMonitor(IOState ioState, Observer guiObserver) {
+    public Interactor applyStateMonitor(IOState ioState) {
         return null;
     }
 
diff --git a/src/main/java/de/neemann/digital/draw/shapes/DiodeBackwardShape.java b/src/main/java/de/neemann/digital/draw/shapes/DiodeBackwardShape.java
index 4c91bf718..3a4ba52de 100644
--- a/src/main/java/de/neemann/digital/draw/shapes/DiodeBackwardShape.java
+++ b/src/main/java/de/neemann/digital/draw/shapes/DiodeBackwardShape.java
@@ -5,7 +5,6 @@
  */
 package de.neemann.digital.draw.shapes;
 
-import de.neemann.digital.core.Observer;
 import de.neemann.digital.core.element.ElementAttributes;
 import de.neemann.digital.core.element.Keys;
 import de.neemann.digital.core.element.PinDescriptions;
@@ -50,7 +49,7 @@ public class DiodeBackwardShape implements Shape {
     }
 
     @Override
-    public InteractorInterface applyStateMonitor(IOState ioState, Observer guiObserver) {
+    public InteractorInterface applyStateMonitor(IOState ioState) {
         return null;
     }
 
diff --git a/src/main/java/de/neemann/digital/draw/shapes/DiodeForewardShape.java b/src/main/java/de/neemann/digital/draw/shapes/DiodeForewardShape.java
index 64820dba7..3c6f78938 100644
--- a/src/main/java/de/neemann/digital/draw/shapes/DiodeForewardShape.java
+++ b/src/main/java/de/neemann/digital/draw/shapes/DiodeForewardShape.java
@@ -5,7 +5,6 @@
  */
 package de.neemann.digital.draw.shapes;
 
-import de.neemann.digital.core.Observer;
 import de.neemann.digital.core.element.ElementAttributes;
 import de.neemann.digital.core.element.Keys;
 import de.neemann.digital.core.element.PinDescriptions;
@@ -50,7 +49,7 @@ public class DiodeForewardShape implements Shape {
     }
 
     @Override
-    public InteractorInterface applyStateMonitor(IOState ioState, Observer guiObserver) {
+    public InteractorInterface applyStateMonitor(IOState ioState) {
         return null;
     }
 
diff --git a/src/main/java/de/neemann/digital/draw/shapes/DiodeShape.java b/src/main/java/de/neemann/digital/draw/shapes/DiodeShape.java
index ba900a9c9..6358bde75 100644
--- a/src/main/java/de/neemann/digital/draw/shapes/DiodeShape.java
+++ b/src/main/java/de/neemann/digital/draw/shapes/DiodeShape.java
@@ -5,7 +5,6 @@
  */
 package de.neemann.digital.draw.shapes;
 
-import de.neemann.digital.core.Observer;
 import de.neemann.digital.core.element.ElementAttributes;
 import de.neemann.digital.core.element.Keys;
 import de.neemann.digital.core.element.PinDescriptions;
@@ -48,7 +47,7 @@ public class DiodeShape implements Shape {
     }
 
     @Override
-    public InteractorInterface applyStateMonitor(IOState ioState, Observer guiObserver) {
+    public InteractorInterface applyStateMonitor(IOState ioState) {
         return null;
     }
 
diff --git a/src/main/java/de/neemann/digital/draw/shapes/DipSwitchShape.java b/src/main/java/de/neemann/digital/draw/shapes/DipSwitchShape.java
index 8c16c0039..eff56cd92 100644
--- a/src/main/java/de/neemann/digital/draw/shapes/DipSwitchShape.java
+++ b/src/main/java/de/neemann/digital/draw/shapes/DipSwitchShape.java
@@ -6,7 +6,6 @@
 package de.neemann.digital.draw.shapes;
 
 import de.neemann.digital.core.ObservableValue;
-import de.neemann.digital.core.Observer;
 import de.neemann.digital.core.SyncAccess;
 import de.neemann.digital.core.Value;
 import de.neemann.digital.core.element.Element;
@@ -75,15 +74,13 @@ public class DipSwitchShape implements Shape {
     }
 
     @Override
-    public Interactor applyStateMonitor(IOState ioState, Observer guiObserver) {
+    public Interactor applyStateMonitor(IOState ioState) {
         this.ioState = ioState;
-        ioState.getOutput(0).addObserverToValue(guiObserver);
         return new Interactor() {
             @Override
-            public boolean clicked(CircuitComponent cc, Point pos, IOState ioState, Element element, SyncAccess modelSync) {
+            public void clicked(CircuitComponent cc, Point pos, IOState ioState, Element element, SyncAccess modelSync) {
                 ObservableValue value = ioState.getOutput(0);
                 modelSync.modify(() -> value.setValue(1 - value.getValue()));
-                return true;
             }
         };
     }
diff --git a/src/main/java/de/neemann/digital/draw/shapes/DriverShape.java b/src/main/java/de/neemann/digital/draw/shapes/DriverShape.java
index 22e9de8ed..fff2018ef 100644
--- a/src/main/java/de/neemann/digital/draw/shapes/DriverShape.java
+++ b/src/main/java/de/neemann/digital/draw/shapes/DriverShape.java
@@ -5,7 +5,6 @@
  */
 package de.neemann.digital.draw.shapes;
 
-import de.neemann.digital.core.Observer;
 import de.neemann.digital.core.element.ElementAttributes;
 import de.neemann.digital.core.element.Keys;
 import de.neemann.digital.core.element.PinDescriptions;
@@ -68,7 +67,7 @@ public class DriverShape implements Shape {
     }
 
     @Override
-    public Interactor applyStateMonitor(IOState ioState, Observer guiObserver) {
+    public Interactor applyStateMonitor(IOState ioState) {
         return null;
     }
 
diff --git a/src/main/java/de/neemann/digital/draw/shapes/FETShape.java b/src/main/java/de/neemann/digital/draw/shapes/FETShape.java
index 77b2fe765..f74a26058 100644
--- a/src/main/java/de/neemann/digital/draw/shapes/FETShape.java
+++ b/src/main/java/de/neemann/digital/draw/shapes/FETShape.java
@@ -5,7 +5,6 @@
  */
 package de.neemann.digital.draw.shapes;
 
-import de.neemann.digital.core.Observer;
 import de.neemann.digital.core.element.ElementAttributes;
 import de.neemann.digital.core.element.PinDescriptions;
 import de.neemann.digital.core.switching.NFET;
@@ -49,9 +48,8 @@ public abstract class FETShape implements Shape {
     }
 
     @Override
-    public InteractorInterface applyStateMonitor(IOState ioState, Observer guiObserver) {
+    public InteractorInterface applyStateMonitor(IOState ioState) {
         fet = (NFET) ioState.getElement();
-        ioState.getInput(0).addObserverToValue(guiObserver);
         return null;
     }
 
diff --git a/src/main/java/de/neemann/digital/draw/shapes/FuseShape.java b/src/main/java/de/neemann/digital/draw/shapes/FuseShape.java
index 3da53c87f..3eb5d1518 100644
--- a/src/main/java/de/neemann/digital/draw/shapes/FuseShape.java
+++ b/src/main/java/de/neemann/digital/draw/shapes/FuseShape.java
@@ -5,7 +5,6 @@
  */
 package de.neemann.digital.draw.shapes;
 
-import de.neemann.digital.core.Observer;
 import de.neemann.digital.core.element.ElementAttributes;
 import de.neemann.digital.core.element.Keys;
 import de.neemann.digital.core.element.PinDescriptions;
@@ -63,7 +62,7 @@ public class FuseShape implements Shape {
     }
 
     @Override
-    public InteractorInterface applyStateMonitor(IOState ioState, Observer guiObserver) {
+    public InteractorInterface applyStateMonitor(IOState ioState) {
         return null;
     }
 
diff --git a/src/main/java/de/neemann/digital/draw/shapes/GenericShape.java b/src/main/java/de/neemann/digital/draw/shapes/GenericShape.java
index b69e82e69..6f529ed6b 100644
--- a/src/main/java/de/neemann/digital/draw/shapes/GenericShape.java
+++ b/src/main/java/de/neemann/digital/draw/shapes/GenericShape.java
@@ -5,7 +5,6 @@
  */
 package de.neemann.digital.draw.shapes;
 
-import de.neemann.digital.core.Observer;
 import de.neemann.digital.core.element.PinDescriptions;
 import de.neemann.digital.draw.elements.IOState;
 import de.neemann.digital.draw.elements.Pin;
@@ -195,7 +194,7 @@ public class GenericShape implements Shape {
     }
 
     @Override
-    public Interactor applyStateMonitor(IOState ioState, Observer guiObserver) {
+    public Interactor applyStateMonitor(IOState ioState) {
         return null;
     }
 
diff --git a/src/main/java/de/neemann/digital/draw/shapes/GroundShape.java b/src/main/java/de/neemann/digital/draw/shapes/GroundShape.java
index 4df746785..3ec1a3d31 100644
--- a/src/main/java/de/neemann/digital/draw/shapes/GroundShape.java
+++ b/src/main/java/de/neemann/digital/draw/shapes/GroundShape.java
@@ -5,7 +5,6 @@
  */
 package de.neemann.digital.draw.shapes;
 
-import de.neemann.digital.core.Observer;
 import de.neemann.digital.core.element.ElementAttributes;
 import de.neemann.digital.core.element.PinDescriptions;
 import de.neemann.digital.draw.elements.IOState;
@@ -41,7 +40,7 @@ public class GroundShape implements Shape {
     }
 
     @Override
-    public Interactor applyStateMonitor(IOState ioState, Observer guiObserver) {
+    public Interactor applyStateMonitor(IOState ioState) {
         return null;
     }
 
diff --git a/src/main/java/de/neemann/digital/draw/shapes/InputShape.java b/src/main/java/de/neemann/digital/draw/shapes/InputShape.java
index aea2c98b7..08ef0f4dc 100644
--- a/src/main/java/de/neemann/digital/draw/shapes/InputShape.java
+++ b/src/main/java/de/neemann/digital/draw/shapes/InputShape.java
@@ -82,9 +82,8 @@ public class InputShape implements Shape {
     }
 
     @Override
-    public Interactor applyStateMonitor(IOState ioState, Observer guiObserver) {
+    public Interactor applyStateMonitor(IOState ioState) {
         this.ioState = ioState;
-        ioState.getOutput(0).addObserverToValue(guiObserver);
         return new InputInteractor();
     }
 
@@ -148,7 +147,7 @@ public class InputShape implements Shape {
         private long lastValueSet;
 
         @Override
-        public boolean clicked(CircuitComponent cc, Point pos, IOState ioState, Element element, SyncAccess modelSync) {
+        public void clicked(CircuitComponent cc, Point pos, IOState ioState, Element element, SyncAccess modelSync) {
             ObservableValue value = ioState.getOutput(0);
             if (bits == 1) {
                 modelSync.modify(() -> {
@@ -163,7 +162,6 @@ public class InputShape implements Shape {
                     } else
                         value.setValue(1 - value.getValue());
                 });
-                return true;
             } else {
                 if (dialog == null || !dialog.isVisible()) {
                     Model model = ((In) element).getModel();
@@ -172,18 +170,16 @@ public class InputShape implements Shape {
                 } else
                     dialog.requestFocus();
 
-                return false;
             }
         }
 
         @Override
-        public boolean pressed(CircuitComponent cc, Point pos, IOState ioState, Element element, SyncAccess modelSync) {
+        public void pressed(CircuitComponent cc, Point pos, IOState ioState, Element element, SyncAccess modelSync) {
             isDrag = false;
-            return false;
         }
 
         @Override
-        public boolean dragged(CircuitComponent cc, Point posOnScreen, Vector pos, Transform transform, IOState ioState, Element element, SyncAccess modelSync) {
+        public void dragged(CircuitComponent cc, Point posOnScreen, Vector pos, Transform transform, IOState ioState, Element element, SyncAccess modelSync) {
             ObservableValue value = ioState.getOutput(0);
             if (bits > 1 && !value.isHighZ()) {
                 if (!isDrag) {
@@ -198,11 +194,9 @@ public class InputShape implements Shape {
                     if (val != lastValueSet) {
                         modelSync.modify(() -> value.setValue(val));
                         lastValueSet = val;
-                        return true;
                     }
                 }
             }
-            return false;
         }
     }
 }
diff --git a/src/main/java/de/neemann/digital/draw/shapes/Interactor.java b/src/main/java/de/neemann/digital/draw/shapes/Interactor.java
index 942b758aa..ece8bb521 100644
--- a/src/main/java/de/neemann/digital/draw/shapes/Interactor.java
+++ b/src/main/java/de/neemann/digital/draw/shapes/Interactor.java
@@ -23,17 +23,14 @@ import java.awt.*;
 public abstract class Interactor implements InteractorInterface {
 
     @Override
-    public boolean pressed(CircuitComponent cc, Point pos, IOState ioState, Element element, SyncAccess modelSync) {
-        return false;
+    public void pressed(CircuitComponent cc, Point pos, IOState ioState, Element element, SyncAccess modelSync) {
     }
 
     @Override
-    public boolean released(CircuitComponent cc, Point pos, IOState ioState, Element element, SyncAccess modelSync) {
-        return false;
+    public void released(CircuitComponent cc, Point pos, IOState ioState, Element element, SyncAccess modelSync) {
     }
 
     @Override
-    public boolean dragged(CircuitComponent cc, Point posOnScreen, Vector pos, Transform transform, IOState ioState, Element element, SyncAccess modelSync) {
-        return false;
+    public void dragged(CircuitComponent cc, Point posOnScreen, Vector pos, Transform transform, IOState ioState, Element element, SyncAccess modelSync) {
     }
 }
diff --git a/src/main/java/de/neemann/digital/draw/shapes/InteractorInterface.java b/src/main/java/de/neemann/digital/draw/shapes/InteractorInterface.java
index df2641498..8cf245641 100644
--- a/src/main/java/de/neemann/digital/draw/shapes/InteractorInterface.java
+++ b/src/main/java/de/neemann/digital/draw/shapes/InteractorInterface.java
@@ -30,9 +30,8 @@ public interface InteractorInterface {
      * @param ioState   the state of the element
      * @param element   the element which is clicked
      * @param modelSync used to sync model access
-     * @return true if model is changed
      */
-    boolean clicked(CircuitComponent cc, Point pos, IOState ioState, Element element, SyncAccess modelSync);
+    void clicked(CircuitComponent cc, Point pos, IOState ioState, Element element, SyncAccess modelSync);
 
     /**
      * Called if mouse is pressed on running model
@@ -42,9 +41,8 @@ public interface InteractorInterface {
      * @param ioState   the state of the element
      * @param element   the element on which the mouse is pressed
      * @param modelSync used to sync model access
-     * @return true if model is changed
      */
-    boolean pressed(CircuitComponent cc, Point pos, IOState ioState, Element element, SyncAccess modelSync);
+    void pressed(CircuitComponent cc, Point pos, IOState ioState, Element element, SyncAccess modelSync);
 
     /**
      * Called if mouse is released on running model
@@ -54,9 +52,8 @@ public interface InteractorInterface {
      * @param ioState   the state of the element
      * @param element   the element on which the mouse is released
      * @param modelSync used to sync model access
-     * @return true if model is changed
      */
-    boolean released(CircuitComponent cc, Point pos, IOState ioState, Element element, SyncAccess modelSync);
+    void released(CircuitComponent cc, Point pos, IOState ioState, Element element, SyncAccess modelSync);
 
     /**
      * Called if mouse is dragged on running model
@@ -68,8 +65,7 @@ public interface InteractorInterface {
      * @param ioState     the state of the element
      * @param element     the element on which the mouse is dragged
      * @param modelSync   used to sync model access
-     * @return true if model is changed
      */
-    boolean dragged(CircuitComponent cc, Point posOnScreen, Vector pos, Transform transform, IOState ioState, Element element, SyncAccess modelSync);
+    void dragged(CircuitComponent cc, Point posOnScreen, Vector pos, Transform transform, IOState ioState, Element element, SyncAccess modelSync);
 
 }
diff --git a/src/main/java/de/neemann/digital/draw/shapes/LEDShape.java b/src/main/java/de/neemann/digital/draw/shapes/LEDShape.java
index cd7b0c672..9f5252a23 100644
--- a/src/main/java/de/neemann/digital/draw/shapes/LEDShape.java
+++ b/src/main/java/de/neemann/digital/draw/shapes/LEDShape.java
@@ -5,7 +5,6 @@
  */
 package de.neemann.digital.draw.shapes;
 
-import de.neemann.digital.core.Observer;
 import de.neemann.digital.core.Value;
 import de.neemann.digital.core.element.ElementAttributes;
 import de.neemann.digital.core.element.Keys;
@@ -53,9 +52,8 @@ public class LEDShape implements Shape {
     }
 
     @Override
-    public Interactor applyStateMonitor(IOState ioState, Observer guiObserver) {
+    public Interactor applyStateMonitor(IOState ioState) {
         this.ioState = ioState;
-        ioState.getInput(0).addObserverToValue(guiObserver);
         return null;
     }
 
diff --git a/src/main/java/de/neemann/digital/draw/shapes/LayoutShape.java b/src/main/java/de/neemann/digital/draw/shapes/LayoutShape.java
index d1e7dd9e6..b29164c70 100644
--- a/src/main/java/de/neemann/digital/draw/shapes/LayoutShape.java
+++ b/src/main/java/de/neemann/digital/draw/shapes/LayoutShape.java
@@ -6,7 +6,6 @@
 package de.neemann.digital.draw.shapes;
 
 import de.neemann.digital.core.NodeException;
-import de.neemann.digital.core.Observer;
 import de.neemann.digital.core.element.ElementAttributes;
 import de.neemann.digital.core.element.Keys;
 import de.neemann.digital.core.element.PinDescription;
@@ -131,7 +130,7 @@ public class LayoutShape implements Shape {
     }
 
     @Override
-    public InteractorInterface applyStateMonitor(IOState ioState, Observer guiObserver) {
+    public InteractorInterface applyStateMonitor(IOState ioState) {
         return null;
     }
 
diff --git a/src/main/java/de/neemann/digital/draw/shapes/LightBulbShape.java b/src/main/java/de/neemann/digital/draw/shapes/LightBulbShape.java
index 7e1307694..dc517f72b 100644
--- a/src/main/java/de/neemann/digital/draw/shapes/LightBulbShape.java
+++ b/src/main/java/de/neemann/digital/draw/shapes/LightBulbShape.java
@@ -6,7 +6,6 @@
 package de.neemann.digital.draw.shapes;
 
 import de.neemann.digital.core.ObservableValue;
-import de.neemann.digital.core.Observer;
 import de.neemann.digital.core.Value;
 import de.neemann.digital.core.element.ElementAttributes;
 import de.neemann.digital.core.element.Keys;
@@ -54,9 +53,9 @@ public class LightBulbShape implements Shape {
     }
 
     @Override
-    public InteractorInterface applyStateMonitor(IOState ioState, Observer guiObserver) {
-        aValue = ioState.getInput(0).addObserverToValue(guiObserver);
-        bValue = ioState.getInput(1).addObserverToValue(guiObserver);
+    public InteractorInterface applyStateMonitor(IOState ioState) {
+        aValue = ioState.getInput(0);
+        bValue = ioState.getInput(1);
         return null;
     }
 
diff --git a/src/main/java/de/neemann/digital/draw/shapes/MissingShape.java b/src/main/java/de/neemann/digital/draw/shapes/MissingShape.java
index 5e5d298d0..75adf4550 100644
--- a/src/main/java/de/neemann/digital/draw/shapes/MissingShape.java
+++ b/src/main/java/de/neemann/digital/draw/shapes/MissingShape.java
@@ -5,7 +5,6 @@
  */
 package de.neemann.digital.draw.shapes;
 
-import de.neemann.digital.core.Observer;
 import de.neemann.digital.draw.elements.IOState;
 import de.neemann.digital.draw.elements.Pins;
 import de.neemann.digital.draw.graphics.Graphic;
@@ -40,7 +39,7 @@ public class MissingShape implements Shape {
     }
 
     @Override
-    public Interactor applyStateMonitor(IOState ioState, Observer guiObserver) {
+    public Interactor applyStateMonitor(IOState ioState) {
         return null;
     }
 
diff --git a/src/main/java/de/neemann/digital/draw/shapes/MuxerShape.java b/src/main/java/de/neemann/digital/draw/shapes/MuxerShape.java
index c77fc1c90..862263f3f 100644
--- a/src/main/java/de/neemann/digital/draw/shapes/MuxerShape.java
+++ b/src/main/java/de/neemann/digital/draw/shapes/MuxerShape.java
@@ -5,7 +5,6 @@
  */
 package de.neemann.digital.draw.shapes;
 
-import de.neemann.digital.core.Observer;
 import de.neemann.digital.core.element.ElementAttributes;
 import de.neemann.digital.core.element.Keys;
 import de.neemann.digital.core.element.PinDescriptions;
@@ -58,7 +57,7 @@ public class MuxerShape implements Shape {
     }
 
     @Override
-    public Interactor applyStateMonitor(IOState ioState, Observer guiObserver) {
+    public Interactor applyStateMonitor(IOState ioState) {
         return null;
     }
 
diff --git a/src/main/java/de/neemann/digital/draw/shapes/OutputShape.java b/src/main/java/de/neemann/digital/draw/shapes/OutputShape.java
index d2ffd9df1..6a4730ba2 100644
--- a/src/main/java/de/neemann/digital/draw/shapes/OutputShape.java
+++ b/src/main/java/de/neemann/digital/draw/shapes/OutputShape.java
@@ -5,7 +5,6 @@
  */
 package de.neemann.digital.draw.shapes;
 
-import de.neemann.digital.core.Observer;
 import de.neemann.digital.core.Value;
 import de.neemann.digital.core.element.ElementAttributes;
 import de.neemann.digital.core.element.Keys;
@@ -70,9 +69,8 @@ public class OutputShape implements Shape {
     }
 
     @Override
-    public Interactor applyStateMonitor(IOState ioState, Observer guiObserver) {
+    public Interactor applyStateMonitor(IOState ioState) {
         this.ioState = ioState;
-        ioState.getInput(0).addObserverToValue(guiObserver);
         return null;
     }
 
diff --git a/src/main/java/de/neemann/digital/draw/shapes/PinControlShape.java b/src/main/java/de/neemann/digital/draw/shapes/PinControlShape.java
index 35c4851ec..afa86dd3f 100644
--- a/src/main/java/de/neemann/digital/draw/shapes/PinControlShape.java
+++ b/src/main/java/de/neemann/digital/draw/shapes/PinControlShape.java
@@ -5,7 +5,6 @@
  */
 package de.neemann.digital.draw.shapes;
 
-import de.neemann.digital.core.Observer;
 import de.neemann.digital.core.element.ElementAttributes;
 import de.neemann.digital.core.element.PinDescriptions;
 import de.neemann.digital.draw.elements.IOState;
@@ -48,7 +47,7 @@ public class PinControlShape implements Shape {
     }
 
     @Override
-    public InteractorInterface applyStateMonitor(IOState ioState, Observer guiObserver) {
+    public InteractorInterface applyStateMonitor(IOState ioState) {
         return null;
     }
 
diff --git a/src/main/java/de/neemann/digital/draw/shapes/PolarityAwareLEDShape.java b/src/main/java/de/neemann/digital/draw/shapes/PolarityAwareLEDShape.java
index d91b5eca9..1e6637dc5 100644
--- a/src/main/java/de/neemann/digital/draw/shapes/PolarityAwareLEDShape.java
+++ b/src/main/java/de/neemann/digital/draw/shapes/PolarityAwareLEDShape.java
@@ -6,7 +6,6 @@
 package de.neemann.digital.draw.shapes;
 
 import de.neemann.digital.core.ObservableValue;
-import de.neemann.digital.core.Observer;
 import de.neemann.digital.core.Value;
 import de.neemann.digital.core.element.ElementAttributes;
 import de.neemann.digital.core.element.Keys;
@@ -60,9 +59,9 @@ public class PolarityAwareLEDShape implements Shape {
     }
 
     @Override
-    public InteractorInterface applyStateMonitor(IOState ioState, Observer guiObserver) {
-        aValue = ioState.getInput(0).addObserverToValue(guiObserver);
-        cValue = ioState.getInput(1).addObserverToValue(guiObserver);
+    public InteractorInterface applyStateMonitor(IOState ioState) {
+        aValue = ioState.getInput(0);
+        cValue = ioState.getInput(1);
         return null;
     }
 
diff --git a/src/main/java/de/neemann/digital/draw/shapes/ProbeShape.java b/src/main/java/de/neemann/digital/draw/shapes/ProbeShape.java
index f8b6dc379..d286f830e 100644
--- a/src/main/java/de/neemann/digital/draw/shapes/ProbeShape.java
+++ b/src/main/java/de/neemann/digital/draw/shapes/ProbeShape.java
@@ -7,7 +7,6 @@ package de.neemann.digital.draw.shapes;
 
 import de.neemann.digital.core.IntFormat;
 import de.neemann.digital.core.ObservableValue;
-import de.neemann.digital.core.Observer;
 import de.neemann.digital.core.Value;
 import de.neemann.digital.core.element.ElementAttributes;
 import de.neemann.digital.core.element.Keys;
@@ -52,9 +51,8 @@ public class ProbeShape implements Shape {
     }
 
     @Override
-    public Interactor applyStateMonitor(IOState ioState, Observer guiObserver) {
+    public Interactor applyStateMonitor(IOState ioState) {
         inValue = ioState.getInput(0);
-        inValue.addObserverToValue(guiObserver);
         return null;
     }
 
diff --git a/src/main/java/de/neemann/digital/draw/shapes/PullDownShape.java b/src/main/java/de/neemann/digital/draw/shapes/PullDownShape.java
index 48ca58e3c..864215769 100644
--- a/src/main/java/de/neemann/digital/draw/shapes/PullDownShape.java
+++ b/src/main/java/de/neemann/digital/draw/shapes/PullDownShape.java
@@ -5,7 +5,6 @@
  */
 package de.neemann.digital.draw.shapes;
 
-import de.neemann.digital.core.Observer;
 import de.neemann.digital.core.element.ElementAttributes;
 import de.neemann.digital.core.element.PinDescriptions;
 import de.neemann.digital.draw.elements.IOState;
@@ -52,7 +51,7 @@ public class PullDownShape implements Shape {
     }
 
     @Override
-    public InteractorInterface applyStateMonitor(IOState ioState, Observer guiObserver) {
+    public InteractorInterface applyStateMonitor(IOState ioState) {
         return null;
     }
 
diff --git a/src/main/java/de/neemann/digital/draw/shapes/PullUpShape.java b/src/main/java/de/neemann/digital/draw/shapes/PullUpShape.java
index 7f1538668..b6c7d5279 100644
--- a/src/main/java/de/neemann/digital/draw/shapes/PullUpShape.java
+++ b/src/main/java/de/neemann/digital/draw/shapes/PullUpShape.java
@@ -5,7 +5,6 @@
  */
 package de.neemann.digital.draw.shapes;
 
-import de.neemann.digital.core.Observer;
 import de.neemann.digital.core.element.ElementAttributes;
 import de.neemann.digital.core.element.PinDescriptions;
 import de.neemann.digital.draw.elements.IOState;
@@ -46,7 +45,7 @@ public class PullUpShape implements Shape {
     }
 
     @Override
-    public InteractorInterface applyStateMonitor(IOState ioState, Observer guiObserver) {
+    public InteractorInterface applyStateMonitor(IOState ioState) {
         return null;
     }
 
diff --git a/src/main/java/de/neemann/digital/draw/shapes/RAMShape.java b/src/main/java/de/neemann/digital/draw/shapes/RAMShape.java
index 1bfa5db62..31a20bde9 100644
--- a/src/main/java/de/neemann/digital/draw/shapes/RAMShape.java
+++ b/src/main/java/de/neemann/digital/draw/shapes/RAMShape.java
@@ -7,7 +7,6 @@ package de.neemann.digital.draw.shapes;
 
 import de.neemann.digital.core.Model;
 import de.neemann.digital.core.NodeException;
-import de.neemann.digital.core.Observer;
 import de.neemann.digital.core.SyncAccess;
 import de.neemann.digital.core.element.*;
 import de.neemann.digital.core.memory.DataField;
@@ -66,17 +65,16 @@ public class RAMShape extends GenericShape {
     }
 
     @Override
-    public Interactor applyStateMonitor(IOState ioState, Observer guiObserver) {
+    public Interactor applyStateMonitor(IOState ioState) {
         return new Interactor() {
             @Override
-            public boolean clicked(CircuitComponent cc, Point pos, IOState ioState, Element element, SyncAccess modelSync) {
+            public void clicked(CircuitComponent cc, Point pos, IOState ioState, Element element, SyncAccess modelSync) {
                 if (element instanceof RAMInterface) {
                     RAMInterface ram = (RAMInterface) element;
                     DataField dataField = ram.getMemory();
                     DataEditor dataEditor = new DataEditor(cc, dataField, dataBits, addrBits, true, modelSync, ram.getIntFormat());
                     dataEditor.showDialog(dialogTitle, model);
                 }
-                return false;
             }
         };
     }
diff --git a/src/main/java/de/neemann/digital/draw/shapes/RGBLEDShape.java b/src/main/java/de/neemann/digital/draw/shapes/RGBLEDShape.java
index cc067d0aa..78a30ccb9 100644
--- a/src/main/java/de/neemann/digital/draw/shapes/RGBLEDShape.java
+++ b/src/main/java/de/neemann/digital/draw/shapes/RGBLEDShape.java
@@ -6,7 +6,6 @@
 package de.neemann.digital.draw.shapes;
 
 import de.neemann.digital.core.Bits;
-import de.neemann.digital.core.Observer;
 import de.neemann.digital.core.element.ElementAttributes;
 import de.neemann.digital.core.element.Keys;
 import de.neemann.digital.core.element.PinDescriptions;
@@ -60,11 +59,8 @@ public class RGBLEDShape implements Shape {
     }
 
     @Override
-    public Interactor applyStateMonitor(IOState ioState, Observer guiObserver) {
+    public Interactor applyStateMonitor(IOState ioState) {
         this.ioState = ioState;
-        ioState.getInput(0).addObserverToValue(guiObserver);
-        ioState.getInput(1).addObserverToValue(guiObserver);
-        ioState.getInput(2).addObserverToValue(guiObserver);
         return null;
     }
 
diff --git a/src/main/java/de/neemann/digital/draw/shapes/RectShape.java b/src/main/java/de/neemann/digital/draw/shapes/RectShape.java
index 200a51e73..d35c7210a 100644
--- a/src/main/java/de/neemann/digital/draw/shapes/RectShape.java
+++ b/src/main/java/de/neemann/digital/draw/shapes/RectShape.java
@@ -5,7 +5,6 @@
  */
 package de.neemann.digital.draw.shapes;
 
-import de.neemann.digital.core.Observer;
 import de.neemann.digital.core.element.ElementAttributes;
 import de.neemann.digital.core.element.Keys;
 import de.neemann.digital.core.element.PinDescriptions;
@@ -58,7 +57,7 @@ public class RectShape implements Shape {
     }
 
     @Override
-    public Interactor applyStateMonitor(IOState ioState, Observer guiObserver) {
+    public Interactor applyStateMonitor(IOState ioState) {
         return null;
     }
 
diff --git a/src/main/java/de/neemann/digital/draw/shapes/RelayDTShape.java b/src/main/java/de/neemann/digital/draw/shapes/RelayDTShape.java
index 6a1b201ab..36c786962 100644
--- a/src/main/java/de/neemann/digital/draw/shapes/RelayDTShape.java
+++ b/src/main/java/de/neemann/digital/draw/shapes/RelayDTShape.java
@@ -5,7 +5,6 @@
  */
 package de.neemann.digital.draw.shapes;
 
-import de.neemann.digital.core.Observer;
 import de.neemann.digital.core.element.ElementAttributes;
 import de.neemann.digital.core.element.Keys;
 import de.neemann.digital.core.element.PinDescriptions;
@@ -63,10 +62,8 @@ public class RelayDTShape implements Shape {
     }
 
     @Override
-    public InteractorInterface applyStateMonitor(IOState ioState, Observer guiObserver) {
+    public InteractorInterface applyStateMonitor(IOState ioState) {
         relay = (RelayDT) ioState.getElement();
-        ioState.getInput(0).addObserverToValue(guiObserver);
-        ioState.getInput(1).addObserverToValue(guiObserver);
         return null;
     }
 
diff --git a/src/main/java/de/neemann/digital/draw/shapes/RelayShape.java b/src/main/java/de/neemann/digital/draw/shapes/RelayShape.java
index 5032738d6..681ada9c1 100644
--- a/src/main/java/de/neemann/digital/draw/shapes/RelayShape.java
+++ b/src/main/java/de/neemann/digital/draw/shapes/RelayShape.java
@@ -5,7 +5,6 @@
  */
 package de.neemann.digital.draw.shapes;
 
-import de.neemann.digital.core.Observer;
 import de.neemann.digital.core.element.ElementAttributes;
 import de.neemann.digital.core.element.Keys;
 import de.neemann.digital.core.element.PinDescriptions;
@@ -65,10 +64,8 @@ public class RelayShape implements Shape {
     }
 
     @Override
-    public InteractorInterface applyStateMonitor(IOState ioState, Observer guiObserver) {
+    public InteractorInterface applyStateMonitor(IOState ioState) {
         relay = (Relay) ioState.getElement();
-        ioState.getInput(0).addObserverToValue(guiObserver);
-        ioState.getInput(1).addObserverToValue(guiObserver);
         return null;
     }
 
diff --git a/src/main/java/de/neemann/digital/draw/shapes/ResetShape.java b/src/main/java/de/neemann/digital/draw/shapes/ResetShape.java
index 98dd68b88..85d4396eb 100644
--- a/src/main/java/de/neemann/digital/draw/shapes/ResetShape.java
+++ b/src/main/java/de/neemann/digital/draw/shapes/ResetShape.java
@@ -5,7 +5,6 @@
  */
 package de.neemann.digital.draw.shapes;
 
-import de.neemann.digital.core.Observer;
 import de.neemann.digital.core.element.ElementAttributes;
 import de.neemann.digital.core.element.Keys;
 import de.neemann.digital.core.element.PinDescriptions;
@@ -45,7 +44,7 @@ public class ResetShape implements Shape {
     }
 
     @Override
-    public Interactor applyStateMonitor(IOState ioState, Observer guiObserver) {
+    public Interactor applyStateMonitor(IOState ioState) {
         //ioState.getOutput(0).addObserverToValue(guiObserver);
         return null;
     }
diff --git a/src/main/java/de/neemann/digital/draw/shapes/RotEncoderShape.java b/src/main/java/de/neemann/digital/draw/shapes/RotEncoderShape.java
index 4d07b3005..141308135 100644
--- a/src/main/java/de/neemann/digital/draw/shapes/RotEncoderShape.java
+++ b/src/main/java/de/neemann/digital/draw/shapes/RotEncoderShape.java
@@ -5,7 +5,6 @@
  */
 package de.neemann.digital.draw.shapes;
 
-import de.neemann.digital.core.Observer;
 import de.neemann.digital.core.SyncAccess;
 import de.neemann.digital.core.element.Element;
 import de.neemann.digital.core.element.ElementAttributes;
@@ -54,31 +53,27 @@ public class RotEncoderShape implements Shape {
     }
 
     @Override
-    public InteractorInterface applyStateMonitor(IOState ioState, Observer guiObserver) {
-        ioState.getOutput(0).addObserverToValue(guiObserver);
+    public InteractorInterface applyStateMonitor(IOState ioState) {
         return new InteractorInterface() {
 
             private int initialState;
             private boolean initial;
 
             @Override
-            public boolean clicked(CircuitComponent cc, Point pos, IOState ioState, Element element, SyncAccess modelSync) {
-                return false;
+            public void clicked(CircuitComponent cc, Point pos, IOState ioState, Element element, SyncAccess modelSync) {
             }
 
             @Override
-            public boolean pressed(CircuitComponent cc, Point pos, IOState ioState, Element element, SyncAccess modelSync) {
+            public void pressed(CircuitComponent cc, Point pos, IOState ioState, Element element, SyncAccess modelSync) {
                 initial = true;
-                return false;
             }
 
             @Override
-            public boolean released(CircuitComponent cc, Point pos, IOState ioState, Element element, SyncAccess modelSync) {
-                return false;
+            public void released(CircuitComponent cc, Point pos, IOState ioState, Element element, SyncAccess modelSync) {
             }
 
             @Override
-            public boolean dragged(CircuitComponent cc, Point posOnScreen, Vector pos, Transform trans, IOState ioState, Element element, SyncAccess modelSync) {
+            public void dragged(CircuitComponent cc, Point posOnScreen, Vector pos, Transform trans, IOState ioState, Element element, SyncAccess modelSync) {
                 if (ioState != null) {
                     Vector p = pos.sub(trans.transform(CENTER));
                     final int dist = p.x * p.x + p.y * p.y;
@@ -97,13 +92,11 @@ public class RotEncoderShape implements Shape {
                                     ioState.getOutput(0).setBool(a);
                                     ioState.getOutput(1).setBool(b);
                                 });
-                                return true;
                             }
                         }
                     } else
                         initial = true;
                 }
-                return false;
             }
         };
     }
diff --git a/src/main/java/de/neemann/digital/draw/shapes/SevenSegHexShape.java b/src/main/java/de/neemann/digital/draw/shapes/SevenSegHexShape.java
index 23fdbe7b6..4fe101736 100644
--- a/src/main/java/de/neemann/digital/draw/shapes/SevenSegHexShape.java
+++ b/src/main/java/de/neemann/digital/draw/shapes/SevenSegHexShape.java
@@ -5,7 +5,6 @@
  */
 package de.neemann.digital.draw.shapes;
 
-import de.neemann.digital.core.Observer;
 import de.neemann.digital.core.Value;
 import de.neemann.digital.core.element.ElementAttributes;
 import de.neemann.digital.core.element.PinDescriptions;
@@ -72,10 +71,8 @@ public class SevenSegHexShape extends SevenShape {
     }
 
     @Override
-    public Interactor applyStateMonitor(IOState ioState, Observer guiObserver) {
+    public Interactor applyStateMonitor(IOState ioState) {
         this.ioState = ioState;
-        ioState.getInput(0).addObserverToValue(guiObserver);
-        ioState.getInput(1).addObserverToValue(guiObserver);
         return null;
     }
 }
diff --git a/src/main/java/de/neemann/digital/draw/shapes/SevenSegShape.java b/src/main/java/de/neemann/digital/draw/shapes/SevenSegShape.java
index b4a436c2e..8d91fba47 100644
--- a/src/main/java/de/neemann/digital/draw/shapes/SevenSegShape.java
+++ b/src/main/java/de/neemann/digital/draw/shapes/SevenSegShape.java
@@ -5,9 +5,7 @@
  */
 package de.neemann.digital.draw.shapes;
 
-import de.neemann.digital.core.ObservableValue;
 import de.neemann.digital.core.ObservableValues;
-import de.neemann.digital.core.Observer;
 import de.neemann.digital.core.Value;
 import de.neemann.digital.core.element.ElementAttributes;
 import de.neemann.digital.core.element.Keys;
@@ -72,10 +70,8 @@ public class SevenSegShape extends SevenShape {
     }
 
     @Override
-    public Interactor applyStateMonitor(IOState ioState, Observer guiObserver) {
+    public Interactor applyStateMonitor(IOState ioState) {
         inputValues = ioState.getInputs();
-        for (ObservableValue o : inputValues)
-            o.addObserverToValue(guiObserver);
         return null;
     }
 
diff --git a/src/main/java/de/neemann/digital/draw/shapes/Shape.java b/src/main/java/de/neemann/digital/draw/shapes/Shape.java
index 5561139f0..d19f36108 100644
--- a/src/main/java/de/neemann/digital/draw/shapes/Shape.java
+++ b/src/main/java/de/neemann/digital/draw/shapes/Shape.java
@@ -6,7 +6,6 @@
 package de.neemann.digital.draw.shapes;
 
 import de.neemann.digital.core.Model;
-import de.neemann.digital.core.Observer;
 import de.neemann.digital.draw.elements.IOState;
 import de.neemann.digital.draw.elements.Pins;
 import de.neemann.digital.draw.model.ModelCreator;
@@ -29,20 +28,15 @@ public interface Shape extends Drawable, ObservableValueReader {
 
     /**
      * This method call connects the created model element to the shape which represents the model node.
-     * If the look of the shape depends on an inputs state, the shape has to register the guiObserver
-     * to all of the inputs ObservableValues it depends on.
      * To access the actual state while drawing, the Shape needs to store the IOState or the needed inputs
      * in a member variable.
      * If the shape returns an interactor, this interactors clicked method is called if the
      * shape is clicked in running mode. If the shape is not interactive simply return null.
      *
-     * @param ioState     the state of the element, never null
-     * @param guiObserver can be used to update the GUI by calling hasChanged, Is maybe null.
-     *                    If the shape depends on a signal value, you can add this observer to
-     *                    the signal. In this case a repaint is initiated, if the signal changes.
+     * @param ioState the state of the element, never null
      * @return The interactor which is used to interact with the shape while the simulation runs.
      */
-    InteractorInterface applyStateMonitor(IOState ioState, Observer guiObserver);
+    InteractorInterface applyStateMonitor(IOState ioState);
 
     /**
      * Allows the shape to make its drawing dependent of the model by registering a Observer to the model.
diff --git a/src/main/java/de/neemann/digital/draw/shapes/SixteenShape.java b/src/main/java/de/neemann/digital/draw/shapes/SixteenShape.java
index ff4103935..4c4181b59 100644
--- a/src/main/java/de/neemann/digital/draw/shapes/SixteenShape.java
+++ b/src/main/java/de/neemann/digital/draw/shapes/SixteenShape.java
@@ -6,7 +6,6 @@
 package de.neemann.digital.draw.shapes;
 
 import de.neemann.digital.core.ObservableValue;
-import de.neemann.digital.core.Observer;
 import de.neemann.digital.core.Value;
 import de.neemann.digital.core.element.ElementAttributes;
 import de.neemann.digital.core.element.Keys;
@@ -80,9 +79,9 @@ public class SixteenShape implements Shape {
     }
 
     @Override
-    public InteractorInterface applyStateMonitor(IOState ioState, Observer guiObserver) {
-        input = ioState.getInput(0).addObserverToValue(guiObserver);
-        dp = ioState.getInput(1).addObserverToValue(guiObserver);
+    public InteractorInterface applyStateMonitor(IOState ioState) {
+        input = ioState.getInput(0);
+        dp = ioState.getInput(1);
         return null;
     }
 
diff --git a/src/main/java/de/neemann/digital/draw/shapes/SplitterShape.java b/src/main/java/de/neemann/digital/draw/shapes/SplitterShape.java
index c293eabfd..345149e79 100644
--- a/src/main/java/de/neemann/digital/draw/shapes/SplitterShape.java
+++ b/src/main/java/de/neemann/digital/draw/shapes/SplitterShape.java
@@ -6,7 +6,6 @@
 package de.neemann.digital.draw.shapes;
 
 import de.neemann.digital.core.BitsException;
-import de.neemann.digital.core.Observer;
 import de.neemann.digital.core.element.ElementAttributes;
 import de.neemann.digital.core.element.Keys;
 import de.neemann.digital.core.element.PinDescriptions;
@@ -56,7 +55,7 @@ public class SplitterShape implements Shape {
     }
 
     @Override
-    public Interactor applyStateMonitor(IOState ioState, Observer guiObserver) {
+    public Interactor applyStateMonitor(IOState ioState) {
         return null;
     }
 
diff --git a/src/main/java/de/neemann/digital/draw/shapes/StepperMotorShape.java b/src/main/java/de/neemann/digital/draw/shapes/StepperMotorShape.java
index ec5ba1996..8610d6a52 100644
--- a/src/main/java/de/neemann/digital/draw/shapes/StepperMotorShape.java
+++ b/src/main/java/de/neemann/digital/draw/shapes/StepperMotorShape.java
@@ -5,7 +5,6 @@
  */
 package de.neemann.digital.draw.shapes;
 
-import de.neemann.digital.core.Observer;
 import de.neemann.digital.core.element.ElementAttributes;
 import de.neemann.digital.core.element.PinDescriptions;
 import de.neemann.digital.core.io.StepperMotorUnipolar;
@@ -57,9 +56,7 @@ public class StepperMotorShape implements Shape {
     }
 
     @Override
-    public InteractorInterface applyStateMonitor(IOState ioState, Observer guiObserver) {
-        for (int i = 0; i < 4; i++)
-            ioState.getInput(i).addObserver(guiObserver);
+    public InteractorInterface applyStateMonitor(IOState ioState) {
         motor = (StepperMotorUnipolar) ioState.getElement();
         return null;
     }
diff --git a/src/main/java/de/neemann/digital/draw/shapes/SwitchDTShape.java b/src/main/java/de/neemann/digital/draw/shapes/SwitchDTShape.java
index c988a832e..32f1de793 100644
--- a/src/main/java/de/neemann/digital/draw/shapes/SwitchDTShape.java
+++ b/src/main/java/de/neemann/digital/draw/shapes/SwitchDTShape.java
@@ -5,7 +5,6 @@
  */
 package de.neemann.digital.draw.shapes;
 
-import de.neemann.digital.core.Observer;
 import de.neemann.digital.core.SyncAccess;
 import de.neemann.digital.core.element.Element;
 import de.neemann.digital.core.element.ElementAttributes;
@@ -64,15 +63,13 @@ public class SwitchDTShape implements Shape {
     }
 
     @Override
-    public InteractorInterface applyStateMonitor(IOState ioState, Observer guiObserver) {
+    public InteractorInterface applyStateMonitor(IOState ioState) {
         return new Interactor() {
             @Override
-            public boolean clicked(CircuitComponent cc, Point pos, IOState ioState, Element element, SyncAccess modelSync) {
+            public void clicked(CircuitComponent cc, Point pos, IOState ioState, Element element, SyncAccess modelSync) {
                 closed = !closed;
-                if (ioState != null) {
+                if (ioState != null)
                     modelSync.modify(() -> ((SwitchDT) element).setClosed(closed));
-                }
-                return true;
             }
         };
     }
diff --git a/src/main/java/de/neemann/digital/draw/shapes/SwitchShape.java b/src/main/java/de/neemann/digital/draw/shapes/SwitchShape.java
index 2c13b2398..59141c15c 100644
--- a/src/main/java/de/neemann/digital/draw/shapes/SwitchShape.java
+++ b/src/main/java/de/neemann/digital/draw/shapes/SwitchShape.java
@@ -5,7 +5,6 @@
  */
 package de.neemann.digital.draw.shapes;
 
-import de.neemann.digital.core.Observer;
 import de.neemann.digital.core.SyncAccess;
 import de.neemann.digital.core.element.Element;
 import de.neemann.digital.core.element.ElementAttributes;
@@ -63,15 +62,13 @@ public class SwitchShape implements Shape {
     }
 
     @Override
-    public InteractorInterface applyStateMonitor(IOState ioState, Observer guiObserver) {
+    public InteractorInterface applyStateMonitor(IOState ioState) {
         return new Interactor() {
             @Override
-            public boolean clicked(CircuitComponent cc, Point pos, IOState ioState, Element element, SyncAccess modelSync) {
+            public void clicked(CircuitComponent cc, Point pos, IOState ioState, Element element, SyncAccess modelSync) {
                 closed = !closed;
-                if (ioState != null) {
+                if (ioState != null)
                     modelSync.modify(() -> ((Switch) element).setClosed(closed));
-                }
-                return true;
             }
         };
     }
diff --git a/src/main/java/de/neemann/digital/draw/shapes/TestCaseShape.java b/src/main/java/de/neemann/digital/draw/shapes/TestCaseShape.java
index 4d91bacdd..d5366d69f 100644
--- a/src/main/java/de/neemann/digital/draw/shapes/TestCaseShape.java
+++ b/src/main/java/de/neemann/digital/draw/shapes/TestCaseShape.java
@@ -5,7 +5,6 @@
  */
 package de.neemann.digital.draw.shapes;
 
-import de.neemann.digital.core.Observer;
 import de.neemann.digital.core.element.ElementAttributes;
 import de.neemann.digital.core.element.PinDescriptions;
 import de.neemann.digital.draw.elements.IOState;
@@ -43,7 +42,7 @@ public class TestCaseShape implements Shape {
     }
 
     @Override
-    public InteractorInterface applyStateMonitor(IOState ioState, Observer guiObserver) {
+    public InteractorInterface applyStateMonitor(IOState ioState) {
         return null;
     }
 
diff --git a/src/main/java/de/neemann/digital/draw/shapes/TextShape.java b/src/main/java/de/neemann/digital/draw/shapes/TextShape.java
index 680496f06..217f2c224 100644
--- a/src/main/java/de/neemann/digital/draw/shapes/TextShape.java
+++ b/src/main/java/de/neemann/digital/draw/shapes/TextShape.java
@@ -5,7 +5,6 @@
  */
 package de.neemann.digital.draw.shapes;
 
-import de.neemann.digital.core.Observer;
 import de.neemann.digital.core.element.ElementAttributes;
 import de.neemann.digital.core.element.Keys;
 import de.neemann.digital.core.element.PinDescriptions;
@@ -57,7 +56,7 @@ public class TextShape implements Shape {
     }
 
     @Override
-    public Interactor applyStateMonitor(IOState ioState, Observer guiObserver) {
+    public Interactor applyStateMonitor(IOState ioState) {
         return null;
     }
 
diff --git a/src/main/java/de/neemann/digital/draw/shapes/TransGateShape.java b/src/main/java/de/neemann/digital/draw/shapes/TransGateShape.java
index 69bfc325c..1c2a9a819 100644
--- a/src/main/java/de/neemann/digital/draw/shapes/TransGateShape.java
+++ b/src/main/java/de/neemann/digital/draw/shapes/TransGateShape.java
@@ -5,7 +5,6 @@
  */
 package de.neemann.digital.draw.shapes;
 
-import de.neemann.digital.core.Observer;
 import de.neemann.digital.core.element.ElementAttributes;
 import de.neemann.digital.core.element.PinDescriptions;
 import de.neemann.digital.core.switching.TransGate;
@@ -65,7 +64,7 @@ public class TransGateShape implements Shape {
     }
 
     @Override
-    public InteractorInterface applyStateMonitor(IOState ioState, Observer guiObserver) {
+    public InteractorInterface applyStateMonitor(IOState ioState) {
         transGate = (TransGate) ioState.getElement();
         return null;
     }
diff --git a/src/main/java/de/neemann/digital/draw/shapes/TunnelShape.java b/src/main/java/de/neemann/digital/draw/shapes/TunnelShape.java
index 48a3d3f01..8c24f0bd1 100644
--- a/src/main/java/de/neemann/digital/draw/shapes/TunnelShape.java
+++ b/src/main/java/de/neemann/digital/draw/shapes/TunnelShape.java
@@ -5,7 +5,6 @@
  */
 package de.neemann.digital.draw.shapes;
 
-import de.neemann.digital.core.Observer;
 import de.neemann.digital.core.element.ElementAttributes;
 import de.neemann.digital.core.element.Keys;
 import de.neemann.digital.core.element.PinDescription;
@@ -46,7 +45,7 @@ public class TunnelShape implements Shape {
     }
 
     @Override
-    public InteractorInterface applyStateMonitor(IOState ioState, Observer guiObserver) {
+    public InteractorInterface applyStateMonitor(IOState ioState) {
         return null;
     }
 
diff --git a/src/main/java/de/neemann/digital/draw/shapes/VDDShape.java b/src/main/java/de/neemann/digital/draw/shapes/VDDShape.java
index 61fca8303..230ac2409 100644
--- a/src/main/java/de/neemann/digital/draw/shapes/VDDShape.java
+++ b/src/main/java/de/neemann/digital/draw/shapes/VDDShape.java
@@ -5,7 +5,6 @@
  */
 package de.neemann.digital.draw.shapes;
 
-import de.neemann.digital.core.Observer;
 import de.neemann.digital.core.element.ElementAttributes;
 import de.neemann.digital.core.element.PinDescriptions;
 import de.neemann.digital.draw.elements.IOState;
@@ -43,7 +42,7 @@ public class VDDShape implements Shape {
     }
 
     @Override
-    public Interactor applyStateMonitor(IOState ioState, Observer guiObserver) {
+    public Interactor applyStateMonitor(IOState ioState) {
         return null;
     }
 
diff --git a/src/main/java/de/neemann/digital/draw/shapes/custom/CustomShape.java b/src/main/java/de/neemann/digital/draw/shapes/custom/CustomShape.java
index c7176b054..04aa85996 100644
--- a/src/main/java/de/neemann/digital/draw/shapes/custom/CustomShape.java
+++ b/src/main/java/de/neemann/digital/draw/shapes/custom/CustomShape.java
@@ -5,7 +5,6 @@
  */
 package de.neemann.digital.draw.shapes.custom;
 
-import de.neemann.digital.core.Observer;
 import de.neemann.digital.core.element.PinDescription;
 import de.neemann.digital.core.element.PinDescriptions;
 import de.neemann.digital.draw.elements.IOState;
@@ -61,7 +60,7 @@ public class CustomShape implements Shape {
     }
 
     @Override
-    public InteractorInterface applyStateMonitor(IOState ioState, Observer guiObserver) {
+    public InteractorInterface applyStateMonitor(IOState ioState) {
         return null;
     }
 
diff --git a/src/main/java/de/neemann/digital/draw/shapes/ieee/IEEEGenericShape.java b/src/main/java/de/neemann/digital/draw/shapes/ieee/IEEEGenericShape.java
index 6377acc19..0c64d0e96 100644
--- a/src/main/java/de/neemann/digital/draw/shapes/ieee/IEEEGenericShape.java
+++ b/src/main/java/de/neemann/digital/draw/shapes/ieee/IEEEGenericShape.java
@@ -5,7 +5,6 @@
  */
 package de.neemann.digital.draw.shapes.ieee;
 
-import de.neemann.digital.core.Observer;
 import de.neemann.digital.core.element.ElementAttributes;
 import de.neemann.digital.core.element.Keys;
 import de.neemann.digital.core.element.PinDescriptions;
@@ -57,7 +56,7 @@ public abstract class IEEEGenericShape implements Shape {
     }
 
     @Override
-    public InteractorInterface applyStateMonitor(IOState ioState, Observer guiObserver) {
+    public InteractorInterface applyStateMonitor(IOState ioState) {
         return null;
     }
 
diff --git a/src/main/java/de/neemann/digital/draw/shapes/ieee/IEEENotShape.java b/src/main/java/de/neemann/digital/draw/shapes/ieee/IEEENotShape.java
index c4cfa7171..9fda1fdab 100644
--- a/src/main/java/de/neemann/digital/draw/shapes/ieee/IEEENotShape.java
+++ b/src/main/java/de/neemann/digital/draw/shapes/ieee/IEEENotShape.java
@@ -5,7 +5,6 @@
  */
 package de.neemann.digital.draw.shapes.ieee;
 
-import de.neemann.digital.core.Observer;
 import de.neemann.digital.core.element.ElementAttributes;
 import de.neemann.digital.core.element.Keys;
 import de.neemann.digital.core.element.PinDescriptions;
@@ -58,7 +57,7 @@ public class IEEENotShape implements Shape {
     }
 
     @Override
-    public Interactor applyStateMonitor(IOState ioState, Observer guiObserver) {
+    public Interactor applyStateMonitor(IOState ioState) {
         return null;
     }
 
diff --git a/src/test/java/de/neemann/digital/draw/shapes/SevenSegShapeTest.java b/src/test/java/de/neemann/digital/draw/shapes/SevenSegShapeTest.java
index b79a47dad..71d61b6ca 100644
--- a/src/test/java/de/neemann/digital/draw/shapes/SevenSegShapeTest.java
+++ b/src/test/java/de/neemann/digital/draw/shapes/SevenSegShapeTest.java
@@ -34,7 +34,7 @@ public class SevenSegShapeTest extends TestCase {
         PinDescriptions inputs = new PinDescriptions(observableValues);
         SevenSegShape ss = new SevenSegShape(attr, inputs, new PinDescriptions());
         IOState state = new IOState(observableValues, null, null);
-        ss.applyStateMonitor(state, null);
+        ss.applyStateMonitor(state);
 
         checkValue(false, ss, 0, a, 0, 1, cc, 0, 1);
         checkValue(false, ss, 0, a, 0, 1, cc, 1, 1);
@@ -95,7 +95,7 @@ public class SevenSegShapeTest extends TestCase {
         PinDescriptions inputs = new PinDescriptions(observableValues);
         SevenSegShape ss = new SevenSegShape(attr, inputs, new PinDescriptions());
         IOState state = new IOState(observableValues, null, null);
-        ss.applyStateMonitor(state, null);
+        ss.applyStateMonitor(state);
 
         checkValue(false, ss, 0, a, 0, 1, cc, 0, 1);
         checkValue(false, ss, 0, a, 0, 1, cc, 1, 1);