NChan NSamp number of samples

[Neil_Helsel]

Hey guys.

I am currently using DAQmx Digital 1D Wfm NChan NSamp to collect data from a velocity gate. Right now it runs for a certain number of samples (basically time based on sample rate), but I want to see if I can give the user an option to end the data aquisition early, as if to say they got the data they needed and didn't want to wait any longer.

Is there any way to do it by changing the input to the number of samples terminal with some sort of boolean stop?

Thanks. 

[crossrulz]

If you setup your task to be Continuous Samples, then you can tell the DAQmx Read to read fewer samples.  Put that in a FOR loop so that you will have a maximum number of samples that you will take and use the conditional terminal to stop your loop early.  You will just need to do some combining of your waveforms.

[Neil_Helsel]

So within the for loop, I put a boolean control?

I'm sorry I'm having a little trouble following, because it seems to me that DAQmx will have to wait for the number of sample terminal before it starts collecting data. Could you include a snippet to clarify?

[crossrulz]

Something like this.

[Neil_Helsel]

Very nice. The only problem I'm running into now is that it looks like it gets rid of the previous data every iteration. When I change the output of the loop to indexing it changes the data type from a 1D array of digital waveform to a 2D array of digital waveform and the rest of my code is based on that 1D array.

[Taki1999]

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@Neil_Helsel wrote:

Very nice. The only problem I'm running into now is that it looks like it gets rid of the previous data every iteration. When I change the output of the loop to indexing it changes the data type from a 1D array of digital waveform to a 2D array of digital waveform and the rest of my code is based on that 1D array.

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This is the combining waveform part that crossrulz mentioned earlier.

[crossrulz]

Here, I added the appending of the waveforms.

[Hooovahh]

Just keep in mind this data will grow and grow and grow.  crossrulz put in a stop after 100 interations, but if this number is too big, or you use a while loop data will continue to grow, and eventually Windows will run out of memory, and LabVIEW will throw an error.

A lot of times I will either log to disk, or if the array gets too big, use array subset (or the waveform function that does the same thing) to ensure it doesn't grow beyond some large upper limit.