Creating Graphical User Interfaces

Programming the Slider and Edit Text Components

This GUI employs a useful combination of components in its design. Each slider is coupled to an edit text component so that:

• The edit text displays the current value of the slider.
• The user can enter a value into the edit text box and cause the slider to update to that value.
• Both components update the appropriate model parameters when activated by the user.

Slider Callback

The GUI uses two sliders to specify block gains since these components enable the selection of continuous values within a specified range. When a user changes the slider value, the callback executes the following steps:

• Calls model_open to ensure that the Simulink model is open so that simulation parameters can be set.
• Gets the new slider value.
• Sets the value of the Current value edit text component to match the slider.
• Sets the appropriate block parameter to the new value (set_param).

Here is the callback for the Proportional (Kf) slider.

• function KfValueSlider_Callback(hObject, eventdata, handles)
  % Ensure model is open
  model_open(handles)
  % Get the new value for the Kf Gain from the slider
  NewVal = get(hObject, 'Value');
  % Set the value of the KfCurrentValue to the new value set by 
  slider
  set(handles.KfCurrentValue,'String',NewVal)
  % Set the Gain parameter of the Kf Gain Block to the new value
  set_param('f14/Controller/Gain','Gain',num2str(NewVal))
  

Note that, while a slider returns a number and the edit text requires a string, uicontrols automatically convert the values to the correct type.

The callback for the Integral (Ki) slider follows a similar approach.

Current Value Edit Text Callback

The edit text box enables users to type in a value for the respective parameter. When the user clicks on another component in the GUI after typing into the text box, the edit text callback executes the following steps:

• Calls model_open to ensure that the Simulink model is open so that it can set simulation parameters.
• Converts the string returned by the edit box String property to a double (str2double).
• Checks whether the value entered by the user is within the range of the slider:

• If the value is out of range, the edit text String property is set to the value of the slider (rejecting the number typed in by the user).

  If the value is in range, the slider Value property is updated to the new value.

• Sets the appropriate block parameter to the new value (set_param).

Here is the callback for the Kf Current value text box.

• function KfCurrentValue_Callback(hObject, eventdata, handles)
  % Ensure model is open
  model_open(handles)
  % Get the new value for the Kf Gain
  NewStrVal = get(hObject, 'String');
  NewVal = str2double(NewStrVal);
  % Check that the entered value falls within the allowable range
  if  isempty(NewVal) | (NewVal< -5) | (NewVal>0),
      % Revert to last value, as indicated by KfValueSlider
      OldVal = get(handles.KfValueSlider,'Value');
      set(hObject, 'String',OldVal)
  else, % Use new Kf value
      % Set the value of the KfValueSlider to the new value
      set(handles.KfValueSlider,'Value',NewVal)
      % Set the Gain parameter of the Kf Gain Block to the new value
      set_param('f14/Controller/Gain','Gain',NewStrVal)
  end
  

The callback for the Ki Current value follows a similar approach.

Running the GUI

Running the Simulation from the GUI