Triggering with a DAQ board--how do I pull data out of startBackground and tell MATLAB to take a few more samples?

조회 수: 11 (최근 30일)
Good afternoon,
I'm having some trouble updating some old NI interfacing code (for a PCI-6115) to the new session based interface in 2011b.
Here's the basic idea: I'd like to run my DAQ board like an oscilloscope, so I set it to passively scan, wait until my signal passes some threshold value, and then record a sample for X length of time (or NUMBEROFSAMPLES number of samples).
I've read through http://www.mathworks.com/products/daq/demos.html?file=/products/demos/shipping/daq/demo_compactdaq_background_acquisition.html and that's given me the basic idea of what needs to be done, but I'm still having trouble getting my code to work properly.
Here's my code %Initial routines for creating the daq session and initializing the channels (device = daq.createSession('ni'), etc.) % thresh = 2; % 2V threshhold value
device.NotifyWhenDataAvailableExceeds = NUMBEROFSAMPLES;
lh = device.addlistener('DataAvailable', @(src, event) stopwhenpassthresh(src, event, thresh));
device.IsContinuous = true;
device.startBackground;
function stopwhenpassthresh(src, event, thresh)
if any(event.Data > thresh)
disp('Triggered')
src.stop;
end
end
Some questions that I have: - How do I pull event.Data and event.TimeStamps out from the stopwhenpassthresh function into something I can process? - If it was at all possible, I'd like to be able to tell my code that when we pass the threshhold value, it should take one extra run of data (and then I can lop off the extra data afterwards). It'd also be nice if I could get a bit more control over the pre-trigger data as well.
Thank you for your help, Paul

채택된 답변

Chirag Gupta
Chirag Gupta 2011년 12월 21일
This may be of help! I proposed 3 different methods, chose whats best in your case: http://www.mathworks.com/matlabcentral/answers/6258-thread-subject-nidaq-continuous-and-background-acquisition
  댓글 수: 1
Paul
Paul 2011년 12월 21일
As best I can tell, this works! I'm using Walter's approach of a circular array (so I don't overload any memory) so I'm using a global counter as well. It's kind of a kludge (still awaiting input from Mathworks about 2012a's trigger routines) but until things go horribly wrong, I'm happy with it. Thanks!

댓글을 달려면 로그인하십시오.

추가 답변 (1개)

Walter Roberson
Walter Roberson 2011년 12월 20일
Use the same data sharing techniques as for graphic callbacks; see http://matlab.wikia.com/wiki/FAQ#How_can_I_share_data_between_callback_functions_in_my_GUI.3F
  댓글 수: 7
Paul
Paul 2011년 12월 20일
Argh. Oh well, is the routine I wrote above what you had in mind?

댓글을 달려면 로그인하십시오.

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by