Waveform Generation - what would you do?

[Ram8]

Heyy all,

Case 1 - Function Node subVI

Everything is straightforward, you just need to call this subvi in the main loop

Case 2 - Select subVI

The same thing but with Select. The 'i' will be passed from a 'for' loop in the main vi where this subvi is called.

So my question is which case would you use? I feel like case A is concise and easier for error checks.

Also, is there another efficient way to do this? Advice appreciated! Cheers and hope you have/had a great day!

[GerdW · Accepted solution]

Hi Ram,

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@Ram8 wrote:

So my question is which case would you use? I feel like case A is concise and easier for error checks.

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None of them…

It seems you create a "waveform" (better: an array of samples) by appending 4 ramps.

Why not use the ramp function (4 times) and a simple BuildArray node?

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@Ram8 wrote:

Also, is there another efficient way to do this? 

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As said before: LabVIEW comes with several basic waveform generation functions: use them!

LabVIEW also knows about a waveform datatype, that consists of more than just an array of samples. Use the correct wording for your questions!

Also generic advice: ask for WHAT you want to achieve, don't ask HOW you intend to achieve your goal!

You will get much better help when you describe your requirements (like "I need a waveform of ramp up, hold, ramp down, hold") instead of "should I use a formula node or some select nodes"!

[Ram8]

Hi GerdW,

Thanks! Still new to this world, I will look into the waveform functions.

If it was a random case of if else statements, which approach would you suggest?

Regards,

Ram.

[GerdW]

Hi Ram,

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@Ram8 wrote:

a random case of if else statements

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"if then else" is never random, you have to apply known limits…

Please provide better descriptions of your requirements!

Again: explain the WHAT, but not the HOW!

(What about a simple statemachine, that can append "waveform" parts (like ramp and sine), based on a list of parameters?)

[Ram8]

Hi,

I would like to build an asymmetrical triangular waveform. 

Since the size of the samples is  a variable, I am unsure on the use a case structure.

There are min and max limits to the waveform as well.

The following C code was used to:

double asym_tri(int i, int size, double lo, double hi)
{
	double value;
	if (i < size / 16) {
		value = 16.0 * i / size;
	} else if (i < size / 2) {
		value = (8.0 / 7.0) - (16.0 / 7.0 * i / size);
	} else if (i < size * 9.0 / 16) {
		value = -16.0 * (i - (size / 2)) / size;
	} else {
		value = -(8.0 / 7.0) + (16.0 / 7.0 * (i - (size / 2)) / size);
	}

	return value * (hi - lo) / 2 + (hi + lo) / 2;
}

This is a snippet of me using Ramp Pattern.vi. Could you help me achieve the C code?

The subvi is basically: value * (hi - lo) / 2 + (hi + lo) / 2;

What I wanna achieve is: (I have taken 4096 as sample size here, this can change)

But what I get now is:

I want the waveform as an array, because this value will populate another 3rd party function call.

Lemme know if you need more info.

Regards,

Ram. 

(Extra info: I am able to achieve the waveform using Select and Function Node, but want to optimize to LabVIEW's potential)

[Ram8]

Sorry,

My max and min was intertwined.

But still the limits are as high as 160 and low as -80

But waveform is starting to look like what is needed.

[santo_13]

---

@Ram8 wrote:

Hi,

I would like to build an asymmetrical triangular waveform. 

Since the size of the samples is  a variable, I am unsure on the use a case structure.

There are min and max limits to the waveform as well.

The following C code was used to:

double asym_tri(int i, int size, double lo, double hi)
{
	double value;
	if (i < size / 16) {
		value = 16.0 * i / size;
	} else if (i < size / 2) {
		value = (8.0 / 7.0) - (16.0 / 7.0 * i / size);
	} else if (i < size * 9.0 / 16) {
		value = -16.0 * (i - (size / 2)) / size;
	} else {
		value = -(8.0 / 7.0) + (16.0 / 7.0 * (i - (size / 2)) / size);
	}

	return value * (hi - lo) / 2 + (hi + lo) / 2;
}

This is a snippet of me using Ramp Pattern.vi. Could you help me achieve the C code?

The subvi is basically: value * (hi - lo) / 2 + (hi + lo) / 2;

What I wanna achieve is: (I have taken 4096 as sample size here, this can change)

But what I get now is:

I want the waveform as an array, because this value will populate another 3rd party function call.

Lemme know if you need more info.

Regards,

Ram. 

(Extra info: I am able to achieve the waveform using Select and Function Node, but want to optimize to LabVIEW's potential)

---

What is the source of this C implementation? is this based on any other formula? what is the significance of those constants in the implementation?

[GerdW]

Hi Ram,

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@Ram8 wrote:

But still the limits are as high as 160 and low as -80

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So it boils down to (adjust numbers as needed):

1. ramp 0 to 160 in 256 samples
2. ramp 160 to 0 (?) in 1792 samples
3. ramp 0 to -80 in 256 samples
4. ramp -80 to 0 in 1792 samples

Possible solution:

• You need a FOR loop with the Ramp function inside.
• Provide an input as array, with start, end and NumOfSamples for each row.
• Use a concatenating output tunnel to create your array of samples from each ramp part…

[GerdW]

Hi Ram,

my suggestion as image:

I used an array of clusters to hold your ramp parameters…

[BertMcMahan]

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@GerdW wrote:

Hi Ram,

my suggestion as image:

I used an array of clusters to hold your ramp parameters…

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If the ramps are guaranteed to be contiguous then you can skip the "start/end" and just have "target" and "samples". (You'd need to provide a starting point though.)