Well, there are a number of problems, even discounting anything in your subVIs causing trouble.
Your while loop(s) are sucking up every nanosecond of CPU time, not letting anything from the outside get in. Putting a delay of even 1 ms will help that, and may let you get your stop button press noticed. At the moment, your loop will refresh when you write to the serial port, read from the serial port, read the DAQ, or refresh your graph, whichever takes the longest time.
There is no reason that your Intensity and Voltage readings should be synchronized. They are coming from two different sources, each with their own timing characteristics.
You write to the serial port and then read immediately (perhaps even before you write, since there is nothing to ensure that the write happens first), without even checking to see if there are any bytes available. This can easily cause a "delay" in your data, since the data present at the port may (will almost certainly) be the result of one or more commands you sent out in previous iterations of the loop. An error wire going through these (and other functions) will help make things sequential (and let you know where things go wrong).
And lastly (at least from a quick look), you've got a lot of indicators which are refreshed every run-through, particularly your chart, which would have to be completely rewritten on each iteration. You just might not even be able to get 10 Hz speed on even just a constant FP refresh.
Good luck,
Cameron
To err is human, but to really foul it up requires a computer.
The optimist believes we are in the best of all possible worlds - the pessimist fears this is true.
Profanity is the one language all programmers know best.
An expert is someone who has made all the possible mistakes.
To learn something about LabVIEW at no extra cost, work the online LabVIEW tutorial(s):
LabVIEW Unit 1 - Getting Started</ a>
Learn to Use LabVIEW with MyDAQ</ a>
