How to output a pulse train pattern, i.e., not uniformly spaced in time?

[DanK123]

An example of the pulse train pattern I need is:
(12490 low, 10 high) repeat 6 times plus (9290 low, 10 high) plus (3190 low, 10 high).

Can this be done with a PXI 6608? If not, what card/s do I need?

[JustinBritten]

Greetings,

The generation of each individual pattern is fairly simple as you can specify the raw counts for the pattern. You have the option of specifying frequency and duty cycle or raw counts of delay and pulse edges. You can simply specify 12490 delay edges and 10 pulse edges.

In order to change your pulse train you have two options. First, you could just perform finite pulse train generation instead of continuous. You would setup each pattern as an individual train. This would mean there would be a pause between each individual train as you would be reconfiguring the hardware. Your second option, if you wish to perform continuous pulse train generation, is to change the frequency on the fly. For more information on how to perform th
is operation, please see the following Knowledge Base article.

How Do I Change The Frequency Output Of My Pulse Train On The Fly?
http://digital.ni.com/public.nsf/websearch/7B1B0427C39FE33086256CEE00752133?OpenDocument

The best boards for this operation would be our NI-TIO Counter/Timer hardware. This includes the NI 660x series. You can use either the 6601, 6602, or 6608 in both PCI or PXI format. You may want to look at each of these boards to evaluate which is best for your application.

Counter/Timer Hardware Comparison
http://volt.ni.com/niwc/products/counter_timer.jsp?node=4553&node=4529

Regards,
Justin Britten

Applications Engineer
National Instruments

[DanK123]

"How Do I Change The Frequency Output Of My Pulse Train On The Fly?" addresses two frequency states only, not a third. I have three states, or three different values for delay edges.

The latency introduced by a software solution introduces an unacceptable error. This makes either option above somewhat unsuitable.

What I really need is a counter solution that has an input buffer set up as a repeating ring.

Thanks,
Dan

[Tiano]

Hi there, I would like to know how fast can the finite pulse train reconfigure the hardware?

[Peio]

Hi,

I'm also interested by this problem. Can I garantee a continuous single pattern generation without latency while modifying frequency of each pulse train?

In my application (with the maximum rate offered by the PXI 6608) I have to provide a very wide number of pulse trains. Unfortunately, I can't accept a random latency, BUT, if it's constant, I could deduce it in my frequency computation. How can I quantify this delay? 

The PXI 6608 card on slot 2 doesn't have buffer onboard. Can I directly use the buffer of the PXI 6534 on slot 3?

Thanks

[JoeFriedchicken]

Hi Peio,

Did you read the KnowledgeBase Justin linked to? [1] It points to a DAQmx example called "PWM-Counter Output.vi", and if you look at the counter task, it can be modified to update the output frequency and duty cycle while the VI is running. With these modifications, the latency between changes will be one period of the current output waveform.

[1] How Do I Change The Frequency Output Of My Pulse Train On The Fly?
http://digital.ni.com/public.nsf/websearch/7B1B0427C39FE33086256CEE00752133?OpenDocument