Timing sub-millisecond events with USB6009

[Michael_78]

Hi All,

With a 6009 I dropped a Boolean write function in a while loop with no timing and toggled the output each iteration, the frequency I saw was 1kHz.  I used this for clocking an SPI bus.  This was like a snail for SPI but it worked as a low cost solution.  To drive a RC servo with the exact spec. Required here I had to upgrade to a USB device with a counter output.  This way I could get very high precision control over the servo.

Hope this helps,

All the best

Michael.

[NIquist]

I'm curious to what speed you could push a 6009 with a real-time OS but, as has been noted previously, WinDOZE is totally non-deterministic and would rather log-in to Redmond to check for updates than control your DAQ hardware.  One milli-second is the best resolution you can hope for and that's only when all conditions are just right.

[Coq_Rouge]

@VitusTreatise I think you will need a micro-controller for such a task. It could be a very interesting course in instrumentation. That combined Labview with micro-controllers. Also a tip. Then I teach Labview. I have banned all use of any of the Express or assistant flim-filam. I want my students to learn Labview.

[VitusTreatise]

Thanks to all that have replied, your input has helped re-orient my thinking about Labview quite a bit.

From the teaching standpoint, we start with microcontrollers but the students have no background in them and most can barely program at all, so it's a struggle. We wind up doing a few very basic things. The university has a huge investment in Labview, so thought we'd add that to the course and it's great, the students take to it, but the hardware cost is quite large for a class of 20 to use anything other than the lowest end equipment. Hence the 6009, which is still quite nice, but with a $50 microcontroller and gcc you can make servos do their thing pretty easily. I was pre-disposed to think you could extract the same performance from something costing 4 times as much, but alas.

On the bright side I've also discovered this forum, which is fantastic. You people are great.

[NIquist]

Keep in mind that it's not really the 6009 that has the limitation in your case.  I have very fast DAQs here but would never try to use them for a tight servo loop with a Windows OS.  The USB-6251 can collect quickly but it still can't overcome the latency of the OS for servo feedback applications.  For a nice, tight servo loop you need a Real-Time OS or dedicated hardware.  I do agree with you though... We ARE great.

[GregFreeman]

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@VitusTreatise wrote:

Thanks to all that have replied, your input has helped re-orient my thinking about Labview quite a bit.

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Well I have to commend you on not only your open mindedness(real word?) but the fact that you took in everything here without complaining that somethings not working when it "should". Instead, you worked to understand the responses you were getting. I have seen many a new LabVIEW programmer come to the forum and do an online version of stomping and leave the room because things don't work as they "should", which only puts them back at square one, rather than trying to understand why they are limited.