How do I modify complete pwm example to make the frequency dynamic just like the duty cycle?

[invasion2121]

I successfully downloaded and compiled "daqmx_pwm_examples.zip"

from http://www.ni.com/white-paper/2991/en

and executed it in LabView.  I know it works because the oscilloscope correctly displays a pulse waveform with the desired frequency and duty cycle. 

I noticed while the program is running, if I decide to change the duty cycle it dynamically updates the pulse wave form on the oscilloscope.  However, if I change the frequency while the program is running it does not update in the oscilloscope. 

I think the reason is because the duty cycle is hooked into a "shift register" whereas the frequency is not. 

I have attempted to hook up the frequency into a shift register as well, and I was wondering if i could get some advise with regards to simplying or correcting my back panel wiring diagram shown here:

http://i.stack.imgur.com/j6tdP.jpg

I would greatly appreciate all / any advise.

Thanks.

[nathand]

You only need one instance of DAQmx Write; it has inputs for both Frequency and Duty Cycle. Delete the additional one. Add an OR on the case structure condition - you want to execute the write if the Duty Cycle has changed, OR if the Frequency has changed.

[invasion2121]

Hi Nathand -

I have updated my wiring diagram based off of your suggestion: http://i.stack.imgur.com/p9g4u.jpg

Is this what you were referring to?

If not, could you please comment?

Thanks.

[nathand]

I think that's the right wiring, but it's hard to tell since you show the false case where nothing happens. You could clean it up a bit by removing excessive wire bends and keeping wires running left to right.

No need to upload to a third-party image hosting site, the image hosting on this forum works fine and you can upload directly. Even better would be to attach your VI instead of a screenshot.

[invasion2121]

HI Nathand -

I have uploaded the VI as well as an image of the back panel.

Please let me know what your thought are.

[nathand · Accepted solution]

Still some ugly wires (particularly the error wire that loops back under the case structure) but the logic looks fine. I'm not really sure what you're asking - are you still having a problem with it, or does it work as you expect? Did you test it?

[invasion2121]

Hi Nathand -

I just tested it right now and it works perfecrtly using the diagram below:

.

I cleaned it up using the "Cleanup Diagram" button.  I uploaded the VI as well in case anybody else needs it.

Thanks for your help.