Reading a PWM and determining pulse width using a digital input pin on a NI 9425 DAQ

[JPISU]

Hello!

I have been experimenting with LabVIEW for about a week now and have run into a brick wall.  I have found a fairly effective way of reading a PWM signal through an analog input and determining the pulse width.  However, it is becoming necessary for this project to do this same thing using a digital input.  I've been playing with this for about a day now and am not making much headway.

For reference, I will be using a 9524 device

Any ideas?

[GerdW]

Hi JPISU,

and what's your problem?

Before you used some kind of AI: took a signal, checked for threshold value to determine PWM pulse, calc the length of the pulse.

Now you could: use a DI to take a signal, check for TRUE to determine the PWM pulse, calc the length of the pulse...

Maybe you need some additional hardware to connect the former analog signal to your digital input?

[JPISU]

That's what I'm hoping to do, actually!  I am trying to think of a way to do it that does not require a counter as my DAQ device does not have one!  I can determine when there is a rising and falling edge, but I am having trouble with the timing in the middle.  Essentially, I haven't been able to calculate the duty cycle.  I understand, mathematically, how it should work (at least I think I do ) but am having difficulty implementing it in LabVIEW.  I've been searching other forums and most provide solutions using a counter.

Thanks!

[JPISU]

Allow me to correct - I thought I was able to detect the rising/falling edge, but I don't have confidence in it.

[amezam]

Hello JPISU,

It is not possible to do PWM at high frequencies using digital lines because the timing used for that has limitations. Check the KB Software-Timed PWM Using a Digital Output Line, it gives examples on how to do it, but you need to have in mind that there might a certain delay.

Best Regards,

[JPISU]

amezam,

Would you reccommend just sticking to an analog input?

[GerdW]

Hi JPISU,

"I thought I was able to detect the rising/falling edge, but I don't have confidence in it."

When you don't have confidence you should do some software testing...

Btw. do you use a cDAQ chassis or a cRIO?

@amezam:

I don't see the connection between outputting a PWM on a DO line and detecting edges of a DI signal?

[JPISU]

Gerd W.

I am not going to need to send a PWM from LabVIEW in my final application.  I will be reading the PWM signal off a board I am testing.  I am concerned with reading this signal (coming off the DUT) into LabVIEW via a DI terminal and then determining pulse width.  

Jane

[JPISU]

Sorry for omitting this - we use a CDAQ chassis.

[JPISU]

Also, if it is helpful at all, I've attached two vi's.  One, functions just as I need it to - but it doesn't involve data aquisition.  The second should be similar to the first, but is non functional - I keep getting an error that my amplitude is zero.

Any thoughts?