Using NI 9205 module, external trigger into the PFI0 input.

[IronMikeT]

I'm trying to put my external trigger into the PFI0 digital input.   When I connect up my hardware clock, it loads down my signal.  After putting a DC meter on the PFI0 line, open ckt, I see 1.85vDC just sitting there.   I have tried 2 different modules, and they show the same thing.   I am only looking at 1 chan input on AI1, and it is just a 5 volt level.

[hdellere]

Hey Mike,

Could you elaborate a bit on what you're seeing? What do you mean when you say hooking up the clock loads down your signal? How is this module configured currently? Is the AI1 line reading 5V a separate issue?

[IronMikeT]

Sure.  My clock is just a simple 5 vDC timer ckt I made, running about 3.3hz.  When I apply the signal to the PFI0 input, the amplitude goes down a little, and the frequency decreases to 2.65hz.  It doesn't really matter what I have connected to the module, as I have 1.85vDC on the PFI0 input, just sitting there with nothing else going on.  I tried 2 different modules, and the same voltage is there.  Do I need some kind of pull-down resistor on this line?   The AI1 line is just my input signal.  When my ckt is powered, it just sits at 1.00vDC, then goes to 5v when a trigger comes in.  It is not a digital signal, but I am just keeping the voltage levels up to 5v.   My goal is to monitor the AI1 line for 150mS interrupts, or state change from 1 to 5 vDC.  I was thinking I could use a hardware clock, and OR the signals, to produce an interrupt.  I do not want to record data unless the signal changes.

thanks for your help,

Mike

[hdellere]

So for clarification, it sounds like you have a trigger signal on the AI line that you want to use for triggering acquisition on the PFI0 line is that correct?

[IronMikeT]

No, my actual signal is on the A1 line.  I put my external clock into the PFI0 input.   That is supposed to be a digital input.  I can pull that line up in my VI, for clock source.   Just that I have 1.85vDC sitting there, on the PFI0 input.  With nothing else going on.

[anson.kunjappy]

When you are seeing 1.85V, is this an expected value? If it is not, what are you expecting to see.

Also, have you seen this tutorial on ni.com for DAQmx triggering:

NI-DAQmx Data Acquisition Triggering Techniques Using LabVIEW

Anson K

Applications Engineer

National Instruments

[IronMikeT]

No, it is not expected.   Since it is a digital input, it should be 0, until I put my hardware clock into it.  Thus that voltage drags my clock signal down.

I looked at your tutorial.  Certainly some good info there.  I am likely in a digital post-trigger situation.   But I only want to record data, when my input is high for 150mS (min).  Thus I have a clock that is high/low for 150mS, and I was thinking of comparing my input to the fixed clock.

Mike

[TyVo]

Hello Mike,

Would you be opposed to using software timing control when the analog input is acquiring? If using the clock is causing a problem with your voltages you could use some LabVIEW timing instead. Or perhaps the clock signal is required for your circuit? To me it seems like using a timed loop would be easier than triggering off a clock signal.

[IronMikeT]

No, not opposed at all.  Just that I read that hardware timing is much more stable and accurate than software.   I Know there are many ways to do my task in LabView.   Another idea I am considering, is to put the external clock in another input of the 9205.   Then just compare the signals.

[hdellere]

Mike,

Concerning the floating voltage on PFI0, the open circuit behavior of those lines are not spec'd. Without setting a digital task running on that line, the voltage can act unpredictably. As far as comparing the signals to do measurement after 150ms, I think that the signal comparison method is a good option for your application!