PWM duty cycle varying issue on LabVIEW

[VikashKumar23]

Hi,

I have attached two vi files. 

1. FanControllerPWM

2. PWMControl

In FanControllerPWM.vi file I have created a channel that generates PWM and a knob to vary the PWM .Using an external oscilloscope I can able to see the variation in frequency according to the variation in the PWM.

In PWMControl.vi file I have called the FanControllerPWM as subvi and I created a knob to vary the PWM frequency. 

When I try to vary the frequency on the knob on the PWMControl vi the PWM frequency remains the same and doesn't vary.

But I can able to vary it from FanControllerPWM vi. 

can I please know why? what am I missing here ?

[GerdW · Accepted solution]

Hi Vikash,

what am I missing here ?

You missed the basic paradigm of LabVIEW: THINK DATAFLOW!

Explaining DATAFLOW: In PWMControl you read the current value of your knob and then you call FanController using this value. The subVI uses this value - and you wonder about it's usage? As PWMControl has finished its task it does not care about your try to change the knob value later on…

Possible solutions:

- run both VIs in parallel and use a queue/notifier to set the PWM value in your FanController! (basically a producer-consumer scheme)

- get rid of PWMControl and use only FanController…