how to control a ttl output from a USB 6501

[DrTig]

I appologize in advance for my ignorance. I am trying to find a simple solution for controling the frequency of a TTL output from my laptop through a NI USB-6501 to a laser device I use in my research.  I have no previous experience with labview, can anyone point me in the right direction?

[smercurio_fc]

The USB-6501 is, I believe, a software-timed device. This means that in order to create a varying signal you have to do it in a loop in software. This also means that unless you are running on a real-time OS, you will not be able to get precise timing. You did not indicate what kind of resolution and accuracy you needed for your output, so it's unclear whether you will be able to do it with a "regular" OS and the 6501.

As for examples, there are tons of examples that are installed with DAQmx. You did not indicate what software you were trying to use. If you are using LabVIEW, just open the Example Finder (Help -> Find Examples).

[DrTig]

thanks for the quick feedback.  I am running windows 7 OS and ideally I want to be able to pulse that laser at frequencies up to 100 Hz, which would require a resolution in the 1ms range.  This is to try and mimic physiological spike trains that have an intrinsic jitter and so complete precision is not absolute requirement.  If you think the USB-6501 is suboptimal for this purpose could you suggest an NI card that would work better?

[smercurio_fc]

The issue isn't so much the 6501 but the fact that it's software-timed. I'm not up to speed on all of the USB offerings, so I'm not sure if any of the USB-based devices can do hardware timing. Your best bet would be to contact NI sales and they can help you. Do you have any other equipment available, like a function generator?

[Thør]

If you're looking for a speed of about 1ms and precision isn't all that important, then your device might be able to accomplish something similar to what you may be looking for.  Without an onboard clock, you won't be able to output a desired frequency, but you'll be able to output a waveform that is roughly the frequency you want.  Check the examples in the LabVIEW example finder under Hardware Input/Output >> DAQmx >> Analog Generation >> Voltage >> Cont Gen Voltage Wfm-Int Clk-Variable Rate.vi.  This should show you what's involved in generating an analog output.  I hope this helps a little bit.

[DrTig]

Hey Kyle,

Thanks for the suggestion.  I will definately check that out.  Theoretically the output doesn't have to be digital, just mimic a TTL pulse to trigger the laser.  I will let you know how I get on.  I was serious about m igmnorance on this issue so I might come back with some really dumb questions. Thanks again, it's appreciated.