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In this section, build a simple periodic signal generation system in hybrid mode to set the stage for the chapters that follow. This system involves generating a periodic signal in textual mode and displaying it in graphical mode. Modify the shape of the signal (sine, square, triangle or sawtooth) as well as its frequency and amplitude by using appropriate front panel controls. The block diagram and front panel of this system using a LabVIEW MathScript node are shown in [link] and [link] , respectively. The front panel includes the following three controls:
Waveform type – Select the shape of the input waveform as either sine, square, triangular or sawtooth waves.
Amplitude – Control the amplitude of the input waveform.
Frequency – Control the frequency of the input waveform.
To build the block diagram, first write a .m file code to generate four types of waveforms using the .m file functions
sin ,
square and
sawtooth . To change the amplitude and frequency of the waveforms, use two controls named Amplitude (A) and Frequency (f). Waveform Type (w) is another input controlled by the
Enum Control for selecting the waveform type. With this control, one can select from multiple inputs. Create an Enum Control from the front panel by invoking
Controls
→
Modern
→
Ring&Enum
→
Enum . Right-click on the
Enum Control to select
properties and the
edit item tab to choose different items as shown in
[link] . After inserting each item, the digital display shows the corresponding number value for that item, which is the output of the
Enum Control .
Finally, display the waveforms with a Waveform Graph (Controls → Express → Waveform Graph) and a Build Waveform function (Function → Programming → Waveform → Build Waveform) .
Write a .m file code to add all the numbers corresponding to the even indices of an array. For instance, if the array x is specified as x = [1, 3, 5, 10], then 13 (= 3+10) should be returned. Use the program to find the sum of all even integers from 1 to 1000. Run your code using the LabVIEW MathScript interactive window. Also, redo the code where x is the input vector and y is the sum of all the numbers corresponding to the even indices of x.
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2. Explain what the following .m file does:
L=length(x);
for j=1:L
if x(j)<0
x(j)=-x(j);
end
end
Rewrite this program without using a
for loop.
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3. Write a .m file code that implements the following hard-limiting function:
For , use 1000 random numbers generated via the function rand.
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4. Build a hybrid VI to generate two sinusoid signals with the frequencies f1 Hz and f2 Hz and the amplitudes A1 and A2, based on a sampling frequency of 8000 Hz with the number of samples being 256. Set the frequency ranges from 100 to 400 Hz and set the amplitude ranges from 20 to 200. Generate a third signal with the frequency f3 = (mod (lcm (f1, f2), 400) + 100) Hz, where mod and lcm denote the modulus and least common multiple operation, respectively, and the amplitude A3 is the sum of the amplitudes A1 and A2. Use the same sampling frequency and number of samples as specified for the first two signals. Display all the signals using the legend on the same waveform graph and label them accordingly.
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