topic Re: stopping a loop in LabVIEW

stopping a loop

sbz — Wed, 19 May 2010 23:45:14 GMT

Hi,

How do I stop a while loop that collects data from a home made instrument. I don't know how many bytes of data it is collecting. I want to repeat this loop n times but have to stop it after each cycle. Your help is appreciated.

thanks

sbz

Re: stopping a loop

JÞB — Thu, 20 May 2010 00:06:17 GMT

While loop. you stop them on a condition. what type of condition do you want to stop on?

Message Edited by Jeff Bohrer on 05-19-2010 07:06 PM

Re: stopping a loop

sbz — Thu, 20 May 2010 00:20:19 GMT

after collecting data i want to stop it but it's not a constant data coming back(each time might change) so i need sth to listen to it when data collection stops. Can't find any UDP listen function.

Re: stopping a loop

tbob — Thu, 20 May 2010 16:30:07 GMT

You are not explaining yourself very well. Does your data come back in a burst, then no more data comes? You could use a timer to stop after a certain time with no data being received. Start timer. If data is receive, reset timer. If no data, check timer. Do this until timer expires, then stop the loop.

Re: stopping a loop

Verne_D — Thu, 20 May 2010 17:27:49 GMT

Hi sbz,

UDP is not a protocol that "listens" in the sense that it will wait until bits appear or uses any handshaking. For that type of scheme you may have to move to TCP. I'm not sure a bit confused if the issue you're encountering involves network communication or loop condition. Please let us know how we can help.

Re: stopping a loop

zola_the_gorgon — Thu, 20 May 2010 17:48:06 GMT

Hi sbz,

If I understand you correctly, you want to pause at the end of each iteration to check that data has come in on a UDP port.

I am by no means an expert on this, but Labview does have some UDP functionality which might be what you need. The UDP Read function will wait for data until a specified timeout.

To find the UDP functions, go to Functions->Data Communication->Protocols->UDP or on the Functions palette, search for UDP.

These pages have more information:

http://zone.ni.com/devzone/cda/tut/p/id/4950

http://zone.ni.com/reference/en-XX/help/371361B-01/TOC28.htm

Hope this helps.

Re: stopping a loop

sbz — Thu, 20 May 2010 17:54:50 GMT

Thanks to all for replying. The data comes in burst and then stops. I have to press the stop button manually and then the next iteration will start. I don't want it to be manually.

thanks

sbz

Re: stopping a loop

tbob — Thu, 20 May 2010 18:11:50 GMT

Use a timer as I had described in my earlier post. After 1 or 2 seconds of no data, stop the loop. Do you need sample code to do this? Can you try to code something yourself?

Re: stopping a loop

sbz — Thu, 20 May 2010 18:14:21 GMT

I've never used a timer. will try to figure it out.

thanks

Re: stopping a loop

tbob — Thu, 20 May 2010 18:40:16 GMT

Here is an example:

Re: stopping a loop

sbz — Fri, 21 May 2010 00:35:41 GMT

Hi tbob,

I tried to make it as ur example shows but it doesnt work since the string stops at some point but is not empty.

thanks again

sbz

Re: stopping a loop

tbob — Fri, 21 May 2010 15:59:34 GMT

What do you mean by "the string stops at some point but is not empty". This doesn't make any sense. Also, I used a string array just as an example. It isn't a direct substitute for your code. I don't know how you are acquiring data. I don't know what your data is. You have to figure out how to tell when your data ends and use parts of my code to implement stopping the loop. Whatever method you use to read the data, what happens when there is no more data? Do you get some type of termination character? Give me more information.

Re: stopping a loop

sbz — Sat, 22 May 2010 00:23:18 GMT

thanks tbob I figured it out. Now I have a loop that each iteration collects data in a text file and the next iteration ads the data to the bottom of the the previous data.

Is there any way that I could save the data of each iteration in a column next to the previous one instead of all in a long column? I tried the write to spread sheet but had no luck yet.

thanks for your help

sbz

Re: stopping a loop

TCPlomp — Sat, 22 May 2010 11:51:36 GMT

The problems with a column is that you have to interleave your data at every run.

Perhaps you can store your data in a row per time (use a 'tab' as a delimeter and append a CRLF).

After finishing the loop, read the whole file, transpose the array and resave.

Ton