Sinusoidal Signal Generator

Question

Hi everyone,
I want to make a program in LabView, in which the output from the VI will be of the type Analogue Waveform and be capable of being displayed on an appropriate Waveform Graph. The Analogue waveform will represent a continuously adjustable sinusoidal function.
The inputs to the VI will perform the following functions:
1) Set the frequency (1Hz to 1KHz). Default 1 Hz.
2) Set the Phase Shift (-180 to 180). Default 0.
3) Set the Amplitude (0 to 20). Default 1.
4) Set the Offset (-5 to 5). Default 0.
5) Set the number of samples per cycle (20 to 1000). Default 100.
6) Set the number of waves (1 to 50). Default 1
7) Set the start time t0. Default 0.
I want to use Sine trig function.
I would greatly appreciate any advice or hint that would help me doing this program.
Thank you,
pontios
[email protected]

Answer 1

OK. So you need help, but YOU have to write the program.
Let's do that in several steps.
1/ analyse the example program given. It is a rather poor triangular curve generator. I say poor because it only generates the max and min points, and the rest is simply interpolated. There should be additionnal points in between, if the plot has to be generated using an IO card for instance.
The only reusable things here are :
1a/ the idea of using a loop that runs the proper number of times to generate an array of Y data
1b/ the setup of the waveform from the Y array.
2/ the only thing to be done is therefore to generate a table of Y values that correspond to the equation y = amplitude . sin(t/(2.PI.frequency) + phase)+ offset
That should be straight forward, using the basic math functions. If not, I'm afraid that you'll have to do some personnal preliminar work. There are a number of tutorials available around. See for instance http://cnx.rice.edu/content/col10241/latest/
The only tricky part here is to generate the t values.
There are two possible solution :
2a/generate one t value and calculate the corresponding y. Put everything in the loop to generate the Y array
2b/ generate an array of t values, and calculate the corresponding Y array.
Solution b is better because it allows to replace easily the function, without being obliged to dig into the diagram. And since the mathematical functions in LabVIEW are mostly polymorphics (they accept either single values as input as well as arrays...), it is as easy to calculate the sin of the t array.
Accordingly, you should use the loop to create a t array. Remove the stuff inside the loop, use delta t time (required in the build waveform) and multiply it by the loop index. That's all.
Hope this helps. Good luck
CC
Chilly Charly    (aka CC)
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