Continuous Sine Generation with Instantaneous Adaption - Memory Overflow

[RomyS]

Hello all

I want to develop a LabVIEW script that outputs a sine and whose amplitude can be changed while running without big delays. The frequency of the sine wave is 10Hz. Currently I am using the example "Voltage (non-regeneration) - Continuous Output.vi" where I can generate a single waveform that is 0.1s long. I added a 100ms wait function to the while loop to pause before running the next sine. Like this I can ensure that the while loop does not write to many sine profile into the buffer and I am able to adapt the amplitude without much delay. However, including a static wait function means that the buffer can run a little behind since the wait time is not exactly the same as the buffer time. Since I want to run the VI for a long time and possibly include a feedback loop, this inaccuracy is not ideal. If I increase or decrease the wait time in the while loop I get a memory underflow or overflow error. 

Ideally I want to append a new adapted sine wave to the previous one, right before the buffer is finished. How can this be done? I suspect that the buffer time needs to be linked to the wait time of the while loop.  

Some keyfigures:

Used example: Voltage (non-regeneration) - Continuous Output.vi

Labview: 2020
NImax Device Driver: 20.7

Chassis: NI cDAQ-9189

IO Module: NI 9269

Thank you in advance

[Bob_Schor]

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@RomyS wrote:

Ideally I want to append a new adapted sine wave to the previous one, right before the buffer is finished. How can this be done?

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I'm tempted to say "Not easily!".  If you want to change (just) the amplitude of the waveform, you could do that by using one D/A channel to generate the waveform and a second one to drive an amplifier's Gain control to set the Amplitude (if this signal is also a (lower frequency, offset) sinusoid, you'd have FM (Frequency Modulation).  Similarly, if you wanted to adjust the mean of the waveform, use the second D/A to generate the offset voltage and use a summing circuit to add the sinusoid and the "bias" signal.

Almost anything else (it seems to me) almost requires point-by-point processing of the output waveform.  Faulty Programming Gets Annoying! (abbreviated FPGA).

I apologize for the bad Pun.

Bob Schor