Changing Duty Cycle from a PID controller output

[junekers]

Hello everyone,

My goal is to be able to change the duty cycle of a PWM signal using the output from a PID controller.

I am working with this example provided by NI:

Change Duty Cycle on a Continuous Pulse Train of NI-DAQmx Task 

This example works as was intended, I am able to change the duty cycle from the front panel. The problems begin when I substitute the Duty Cycle Control for the output of the PID controller. 

How can I adapt this code so that the Duty Cycle is changed according to the PID output instead of the Duty Cycle Control as it is now? My guess is that the problem lies with the Event Cases. I have tried changing the Duty Cycle Control to an indicator and wiring it to the PID output and then that to the input at Create Channel vi but no success.

Thanks,

Junekers

[altenbach]

You probably want to attach the actual VI, because it is very difficult to debug a picture. (e.g. what's in the timeout case? Are there other events?)

(Events are primarily for user interactions.)

[junekers]

Thanks for your response. I have attached the VI to the original post. 

[Kevin_Price · Accepted solution]

Sticking with a single loop for now to illustrate most simply, you'd need to change to a polling structure instead of being event-based.

Here's a bare outline.  Your real PID function will need inputs (of course).  You'll most likely want to set a different loop rate via the Wait timer.  But the main idea is to update the task's duty cycle if and only if the desired duty cycle coming from the PID calculation changes.

-Kevin P

[junekers]

Thank you very much Kevin_Price. This works wonderfully with a small caveat. The initial value coming out of the PID controller needs to match the initial value for Duty Cycle. I will try to post a follow up solution for posterity.