DAQ connections for an analog TTL sample clock

[hexagram]

Thanks Kevin! Your explanation of the P.i.j input helped us tremendously. However, we are finding that the PFI lines are still not able to be used as triggers or sample clocks. Also, when we start a digital input task using the port and lines that match the PFI line we connected, we only have an on/off green light, when we try to plot the input as a waveform (as opposed to single sampled), it cites an error "Selected lines do not support buffered operations", however, the PFI still show up on the drag down menu for the sample clock. How can we see them as a waveform and use them as a sample clock and trigger?

Thanks,

[Kevin_Price · Accepted solution]

I jumped in before without absorbing the context of the whole thread.  Here are a few things to know or try.

1. The DI task you use to "peek" at the PFI lines MUST use single sample software timing.  The pins that support PFI functionality do NOT support buffered hardware-timed DIO, and vice versa.

2. Go to "Help->Find Examples..." and select "Counter - Count Edges.vi"   Configure it to count edges on your PFI pins and run it.  If your count increases, you're getting the clock and/or trigger signal.  The problem must be the way you're configuring the AI task.

3. Have you verified that clock and trigger are TTL signals (0-5V logic levels, fast transitions)?

4. Post your actual code -- help us help you.

-Kevin P

[hexagram]

Hi Kevin,

Thank you for all of your help! Your suggestions have been tremendously beneficial to us and we are incredibly grateful. We started the start counter as you suggested, and we noticed that the numbers were indeed increasing for both our trigger and sample clock PFI lines, which means (as you said) that the problem must be with the AI task.

I can't imagine what we are doing wrong with the AI task, however. I've illustrated how we configured the task in the image "configuration.png". We open daq assistant on labview, we select analog input, then voltage, we then select ai0 and ai1 (which is what we have wired our photodiodes to), and then we set the inputs to be RSE and set our sample rate, samples to read, etc. as shown. Other than that we don't change it at all.

Interestingly, we notice that when we run the task using no trigger and an internal sample clock (i.e. not utilizing our PFI lines at all) we see the data as we would expect to in an oscilloscope (refer to "Data without PFI lines trigger.png"). This seems to indicate to me that the wires are connected properly, since we are indeed seeing signals at the right frequency. In addition, the DAQ task is picking up the signals just fine.

Once we use the PFI line we have configured as a trigger, again the signal data can be seen, in correspondence to this trigger. (DatawithTriggerOnly.png).

However, when we try to use PFI3 as a start trigger (for temporal synchronization) and PFI 2 as a sample clock (for data acquisition), we get an error (ErrorwithTriggerandSampleClock.png).

So it seems that our issues only arise when the sample clock PFI line is configured. What we want to do is only have the daq card acquire points at the precise moments that the sample clock signal arrives. The data we have shown is indeed the signal, but we only really want to acquire at the peaks, not the entire signal.

Do you have any suggestions? I don't exactly have much code to post since we are just using the DAQ assistant module in our labview block diagram and nothing else (for now)

Thanks

[hexagram]

Hi Kevin,

I believe that due to your suggestions (and looking over our wiring) we have managed to solve our problem and are now well on our way to acquiring data. Thank you for all of your help!