Dynamic duty ratio update in every cycle in PWM

Question

Hi All,
I am a LabVIEW newbie working on generating PWM signal. I have to generate a PWM signal such that its duty ratio and in effect the pulse width should change in every cycle based on the values stored in an excel sheet. I have downloaded a ni example and trying to modify it but not with much success. I am using NI PCI 6132 and BNC 2110 in my setup.
I have read examples about generating PWM based on dynamic duty ratio by manual control using 1,2 counters but have not found anything which updates the duty ratio in every cycle.
For an example I am attaching a csv file containing 4 duty ratio values and the vi. My aim is to generate 4 pulses with the duty ratio stored in the csv file and then stop the execution of the program. For the starters I am keeping the frequency as 1 Hz. I know the vi is not proper and I am working on it, but I thought to get some suggestions in the meanwhile.
Thank you very much for your help.
Solved!
Go to Solution.
Attachments:
retriggerable_pwm.vi ‏32 KB
dutyratio.csv ‏1 KB

Answer 1

The 6132 counters can't do what you are asking.  Using this hardware you would need to build the appropriate digital output array based on your desired times and use a buffered digital output task:
Newer STC3-based hardware (e.g. PCIe-6320) is capable of buffered counter outputs:
There are a few downsides to using the digital output method that may or not be an issue for your application:
1.  It requires a much larger buffer (1 byte per sample compared to 8 bytes per period).  If you need high timing resolution and need to output a long sequence of pulses you might not be able to write the entire buffer at once.
2.  More data needs to be streamed across the bus (also 1 byte per sample compared to 8 bytes per period).  Might be an issue if you are running concurrently with other streaming applications.
3.  Less timing resolution (10 MHz max output frequency on the 6132 compared to 100 MHz counter output timebase on an X Series).
Best Regards,
John Passiak
Attachments:
DigOutputArray.vi ‏26 KB