Dual Channel Timer

[Josh_D]

Dear Labview Community

This is my very first Labview project, since Uni many years ago!  I have tried to get my head around designing a four channel timing system, but can't seem to work it out.  Please could anyone offer an help or advice...or general criticism to what I'm doing stupidly!

I want all four timers to start at the same time, this will eventually be from a physical switch connected to a DAQ, however for simulation purposes I'm using a Start button for now.  I want each of the timers to stop independently of each other, again I want to use four stop buttons to simulate this, as I will eventually add beam break sensors or something similar.  I have modified a vi I found online that I think might work, however I cannot seem to separate the stat/stop button.

I have only added two timers for now, as I thought it would be easy enough to add more once I had the logic figured out.

Any help or advice would be greatly appreciated

Thanks

Josh

[GerdW]

Hi Josh,

some suggestions:

- use shift registers to hold start/stop time for each timer

- you only need one loop to handle all those timers

- usually you should use an array to store same data (to allow easier code scaling)

- use AutoCleanup from time to time

- try to minimize usage of local variables

- event structure is great for UI interaction, but requires a little more effort when you want to handle DAQmx inputs with it…

[Bob_Schor]

More comments:

• Use LabVIEW's Principle of Data Flow to specify the order of execution.  You almost never need to use a Sequence Structure!
• The best way to serialize functions is to always use the Error Line (it helps locate run-time Errors, as well!).
• Were you hoping to use "software timers" that utilize LabVIEW's PC-based Timing functions?  I presume you know that these require "busy-wait" loops to detect when the time is up -- if you don't ask, you won't know.
• On the other hand, if you have a hardware timer, you can put it in a loop running in parallel with other code and have it generate a "software interrupt" (a User Event, for example) when the timer expires, taking essentially no CPU time while waiting.
• Listen to GerdW's advice!

Bob Schor

[Josh_D]

Thank you GerdW and Bob for taking the time to reply. I hugely appreciate any and all advice and tips you have.

I'm slowly digesting the information that you have suggested, I really hadn't though that it would be so difficult to implement a timer in Labview!  I've tried using a shift register, to output the 'initial time' to feed it back into the subtraction operator to create a time = 0; this isn't quite working as expected, I really need it to be a one-shot operation otherwise the time will just follow the loop.

Thanks for the tip on the AutoCleanup, this does help somewhat even if it can be a little over zealous.  I have moved everything into one loop, and simplified the number of variables as suggested - it certainly looks a lot cleaner...

I was planning on using a software timer, simply because I wasn't aware of a hardware timer.  I don't think it will matter too much whichever way is implemented as the old PC will just be running the timers and nothing else at the same time? I have a NI-USB6002 module that I will start adding external switches once I have it working. Busy-wait loops? No, I wasn't aware of that either..

It looks like I have a LOT of reading to do, Labview is quite a learning curve even for simple tasks it seems.

Thanks Again

Josh

[GerdW]

Hi Josh,

you really should take those Training resource to learn LabVIEW!

Just to give an idea:

(All buttons set to latching switch mode…)

[mcduff]

Attached is an old timer that I made a while ago. There is a bit Rube-Goldberg, but it works. It uses an event structure that can easily be modified to include DAQmx events, that can serve as a hardware trigger.

mcduff