topic Re: convert square wave to sinc wave in LabVIEW

convert square wave to sinc wave

keni — Tue, 20 Jul 2010 14:04:38 GMT

Can anyone please show me how to convert square wave to sinc wave?

Re: convert square wave to sinc wave

tbob — Tue, 20 Jul 2010 15:37:01 GMT

What is generating the square wave? Is it by code or by an external instrument? What will generate the sine wave, code or instrument? What kind of hardware is involved?

Re: convert square wave to sinc wave

smercurio_fc — Tue, 20 Jul 2010 15:56:39 GMT

Sinc function

Aargh! I hate it when I press the wrong button... Taking the fourier transform of a square wave gives you a sinc function.

Re: convert square wave to sinc wave

tbob — Tue, 20 Jul 2010 15:56:11 GMT

Sine, sinc, OMG, I need glasses.

Re: convert square wave to sinc wave

keni — Tue, 20 Jul 2010 16:38:46 GMT

Thank you guys. I am just using LabView to generate square wave and convert it to the sinc (sync).

Is there any function that will convert pulse into ECG ( Electro Cardio Gram) signal in labview?

Re: convert square wave to sinc wave

tbob — Tue, 20 Jul 2010 16:41:50 GMT

No, you will have to write your own. Search this forum for ECG. I remember seeing several posts about it.

Once your code is somewhat written, we can help with problems you might have.

Re: convert square wave to sinc wave

keni — Tue, 20 Jul 2010 17:11:01 GMT

Thank you again. I have been given a simple project of converting square wave to look like ECG signal.

What I am thinking is adding sine wave to first 1/4 cycle, adding triangle wave to 2/3 cycle, and adding sine wave to rest 1/4 cycle. Do you think it's possible? How do I go about doing this?

Re: convert square wave to sinc wave

smercurio_fc — Tue, 20 Jul 2010 18:10:54 GMT

While it's possible to do what you're describing, I don't think the results will be all that satisfactory. An ECG signal is a bit more complicated than that. You're probably going to be better off looking (i.e. Google) to see if you can find an ECG waveform simulator/generator.

Re: convert square wave to sinc wave

tbob — Tue, 20 Jul 2010 18:18:10 GMT

Use the wave generator funtions found in palette Signal Processing - Waveform Generation. There are sine and triangle waveform generating functions there. You can set the number of samples and sample rate such that it would generate a partial waveform. Then you use Get Waveform Components to get the Y values, concat the values, then use Build Waveform to build it back to a waveform. You will get a back to back output. In the following example, I used a sine and square wave because a sine and triangle were too close in appearance and you could not readily see the effect.

As Smercurio says, I don't think this is a very good representation of an EKG signal. That signal has P, QRS, and T waves. There is no sine wave. The waves are like triangle waves, so just put DC waveforms (0 amplitude square wave) ahead of and in between triangle waves for P, QRS, and T, followed by DC.

Re: convert square wave to sinc wave

Steve.J — Tue, 20 Jul 2010 19:22:05 GMT

There is an ECG simulator module in the NI Biomedical Starter Kit. You can find more information about this free download by visiting our Biomedical User Group located at www.ni.com/biomedusers

Steve

Re: convert square wave to sinc wave

tbob — Tue, 20 Jul 2010 22:12:07 GMT

This vi will produce sort of an EKG signal:

Re: convert square wave to sinc wave

keni — Wed, 21 Jul 2010 14:16:48 GMT

hello tbob,

Thank you for the file, but I couldn't open it. I have 8.6 version. Can you repost the file?

sim

Re: convert square wave to sinc wave

tbob — Wed, 21 Jul 2010 17:23:30 GMT

In 8.6

Re: convert square wave to sinc wave

keni — Thu, 22 Jul 2010 13:53:36 GMT

Thank you tbob

Re: convert square wave to sinc wave

keni — Thu, 22 Jul 2010 16:49:38 GMT

Hello tbob,

That is really neat EKG signal. I am fairly new to the LabView. They are using some sort of blood flow pump genrator,which generates pulse ( which is square wave). They are using square wave with 4.65V (amplitude) 0.5 (offset) and 920 ms (cycle) to generate square wave. Your square waves are set to generate dc at the beginning, between and end. I don't know much about filters to filter the high frequencies to change it to dc. Can you guide me what i can do?

Re: convert square wave to sinc wave

smercurio_fc — Thu, 22 Jul 2010 17:02:15 GMT

@keni wrote:

Your square waves are set to generate dc at the beginning, between and end.

The square waves in tbob's example do not generate DC at the beginning, between, or end. They have a DC offset (set to 1).You can change this offset (as well as the offsets of the other waveform pieces) by simply changing the constants wired to the "offset" inputs.

I don't know much about filters to filter the high frequencies to change it to dc. Can you guide me what i can do?

This question does not make much sense. What are you trying to filter, and what do you mean by changing it to DC? I don't think you're using the terminology correctly.

P.S. Have you tried the NI Biomedical Startup Kit, as suggested earlier?

Re: convert square wave to sinc wave

keni — Thu, 22 Jul 2010 19:29:05 GMT

But whenever I try to see the waveform from square generator separately, it just graphs a straight dc line. I don't see any squares (pulses). And whenever I put in my specifications it gives me squares (pulses). Am i doing something wrong? and they (school) won't let me download Biomed kit.

Re: convert square wave to sinc wave

smercurio_fc — Thu, 22 Jul 2010 20:00:03 GMT

I have no idea if you're doing something wrong because I have no clue what you're doing. What square generator are you talking about? What specifications are you talking about? The VI that tbob created does not rely on any square wave input. Please provide the code you are creating.

Re: convert square wave to sinc wave

keni — Thu, 22 Jul 2010 20:42:27 GMT

We are using a blood flow pump simulator, which generates square wave of 920 millseconds per cycle and 4.65 volts pick. These square waves need to be converted to the EKG signal or at least look a like. We got everything set up except the big part, converting square waves to EKG signal.

Re: convert square wave to sinc wave

smercurio_fc — Thu, 22 Jul 2010 21:10:06 GMT

@keni wrote:

4.65 volts pick.

That's "peak", not pick. If you remove the for-loop you will get one pulse. This pulse is 240 msec long. You can adjust each of the parameters to set the wavelength duration to match your 920 milliseconds. This is done by adjusting the various parameters, such as the sampling frequency of the number of samples in the clusters. For example, if you change sampling frequency for the cluster that generates the "DC start and end" from 1000 to 500 you double the length of the flat line before and after the pulse, and end up with a pulse that's a total of 500 msec long. It's really not that difficult. Just change one parameter at a time and see what happens.