variable rate waveform generation

[WM_John_Weeks]

With NI-DAQmx and C or C++ is it possible to generate a continuous analog waveform, and change the sample rate on the fly? I presume that it is, since there are two examples on the NI site:

http://zone.ni.com/devzone/cda/epd/p/id/4773
http://zone.ni.com/devzone/cda/epd/p/id/4775

These examples are for C# and Visual Basic, and a quick look didn't suggest to me how to do it in C or C++.

Thanks for any enlightenment!

[Kenn_N]

John,

Thank you for contacting National Instruments.  These examples do exhibit the functionality you need.  There are some examples that generate a continuous output to the analog output.  You acn use these to start with and add the functionality you need.  The basic idea is to create an array of the values you need to generate the sine wave frequency you need.  The sample clock actually stays the same, but it is used to determine deltaT, which is used in the calculation of the sine wave array.  The second example you reference creates this array with this line of code.

rVal(i) = amplitude * Math.Sin((2.0 * Math.PI) * frequency * (i * deltaT))

This will have to be adapted to C, but the concept is the same, and it creates enough samples to fill the onboard buffer.  Then they write it to the buffer while the task is running.

Hope this helps.

Regards,

[WM_John_Weeks]

OK- thanks for the info. All that C# and Visual Basic looks really different and I really didn't want to take a lot of time learning a language I'm not going to use!

It turns out I have understood the problem- the title of those examples suggests that it might be possible to change the clock.

Again, Thank you!

[Kenn_N]

John,

No problem.  I can see the confusion in the title.  Let us know if you are in need of any more help.  Thanks.

Regards,

[Tom_W_[DE]]

Hi John-

FYI, it is also possible to change the AO Sample Clock rate on the fly.  You can use the DAQmxSetSampClkRate(TaskHandle taskHandle, float64 data); property to accomplish this while an AO task is running. Keep in mind that this will not work for an AI task.

Hopefully this helps-

[WM_John_Weeks]

Thanks, Tom. I missed that one.