Software retriggerable pulsing?

[phiellaep]

Hi all, this is my first post. Like most people I am requesting help with something! Sorry!

I am trying to implement TTL control of a device using LabVIEW and my 6052e PXI.

The control is pretty simple, and completely TTL. It's just 4 pins for setting the new switch status, then a 5th pin to be pulsed (high to low) to initiate the switching.

My VI for this (attached) does work. However, it works slowly. I can't get it to update at more than 5 Hz, and I have identified the hold-up as being the Start and Stop for the pulse. Without this, the loop runs very fast indeed.

Clearly, I am not retriggering the pulse efficiently by Starting and Stopping it every iteration, and there must be a better way of doing it. However, having looked at the 'Retriggerable pulse' example VIs, it seems I would need to use a hardware trigger to start the pulsing.

Ideally, what I want is to set up the pulsing channel, and for it to pulse only when I request it. But without using a hardware trigger! Surely this can be done? If not, why? And if so, how?

Many thanks for any advice.

Philip

[asbo]

You didn't attach your VI

[phiellaep]

You didn't attach your VI

Argh! I must not have clicked 'attach'. I will add it when I get back into the office. Thank you!

[phiellaep]

Here is my VI. It is basically a repeating sequence, but the hold-up lies with the start-stop of the pulse in every iteration.

Switch_1x2.vi

[Mellroth]

...The control is pretty simple, and completely TTL. It's just 4 pins for setting the new switch status, then a 5th pin to be pulsed (high to low) to initiate the switching....

Maybe I misunderstand what you are trying to do, but why are you using a counter output to do the switching? Why not use a digital output instead?

/J

[phiellaep]

Do you mean one of the Digital I/O lines?

To specify a 15 us pulse I need to use proper pulse generation, the default pin for which is CTR0.

What I wanted to do was set up the pulse channel, and have it triggered whenever, for example, a boolean variable went HIGH.

What it seems I will have to do (although I not sure why) is use a Digital I/O channel to gate the trigger (PFI9) to start the 15 us pulse. So I'm having to physically wire a Digital I/O line to PFI9 to gate the pulse, which seems daft - why can't I just do it in software?

[Mellroth]

To specify a 15 us pulse I need to use proper pulse generation, the default pin for which is CTR0.

As I said, I might miss some part of your problem and I do missed the fact you had to generate a pulse with 15us width.

If you want to have the pulse generation restarted a bit more efficiently you could try committing the pulse settings to the board before starting the task. I don't know if this will give you the loop rates you need, but it should be more efficient than the current solution (if your hardware support it).

/J

[phiellaep]

OK, thanks.

What I have now is one Digital I/O output physically wired directly to the gate input, which when it goes high starts the retriggerable pulse. It does work, and fast, but it seems a little silly. Possibly this is the best way however.

If anyone has any other ideas I'd be happy to hear them.

Thanks again.

[Maci]

DAQ0.viHello All, I have a similar trigger issue, if someone can help, please. I want to acquire one second worth of (acceleration) data at the signal provided by a digital input., set to trigger on the rising edge. Here is what I have (see attachment), and it is not triggering. Thank you

Maci

DAQ0.vi

OK, thanks.

What I have now is one Digital I/O output physically wired directly to the gate input, which when it goes high starts the retriggerable pulse. It does work, and fast, but it seems a little silly. Possibly this is the best way however.

If anyone has any other ideas I'd be happy to hear them.

Thanks again.