MATLAB SIMULINK 7 - GRAPHICAL USER INTERFACE Instrukcja Użytkownika Pobierz pdf (Strona 273)

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UI That Accepts Parameters and Generates Plots

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In this figure, the two plots reflect the last successful set of inputs, f1 = 31.41, f2

= 120, and t = [1 2 3 4 5 7 9]. The time vector [1 2 6 4 5 7 9] appears

highlighted so that you can enter a new, valid, value. The highlighting results from

executing the command uicontrol(hObject) in the preceding code listing.

Plot Push Button Behavior

When you click the Plot button, the plot_button_Callback performs three basic

tasks: it gets input from the edit text components, calculates data, and creates the two

plots.

Get Input

The first task for the plot_button_Callback is to read the input values. This involves:

• Reading the current values in the three edit text boxes using the handles structure

to access the edit text handles.

• Converting the two frequency values (f1 and f2) from strings to doubles using

str2double.

• Evaluating the time string using eval to produce a vector t, which the callback used

to evaluate the mathematical expression.

The following code shows how the plot_button_Callback obtains the input:

% Get user input

f1 = str2double(get(handles.f1_input,'String'));

f2 = str2double(get(handles.f2_input,'String'));

t = eval(get(handles.t_input,'String'));

Calculate Data

After constructing the string input parameters to numeric form and assigning

them to local variables, the next step is to calculate data for the two graphs. The

plot_button_Callback computes the time domain data using an expression of sines:

x = sin(2*pi*f1*t) + sin(2*pi*f2*t);

The callback computes the frequency domain data as the Fourier transform of the time

domain data:

y = fft(x,512);

For an explanation of this computation, see the fft function.

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