I have a slight dilemma...

[snowman13]

Ok, so I am having major issues. I have spent several hours attempting this, seemingly simple problem...
This is what I am trying to do:

I am trying to create a program that receives a square wave synch input at 40khz. From here, I am trying to detect the beginnning of the positive flat portion of the square wave. From here, I need a for loop that recognizes the beginning of the positive flat portion, then outputs a short pulse at this point.

However, there is a trick.... I need the first output pulse to be right at the beginning, then the second output pulse to be output at about 1/4 of the way through the positive portion of the square wave, then the third to be about 1/2 way through... and so on and so on.

Any help would be great. I know there is something that I missing big time. Because I really should be able to do this in about 10 minutes.

Message Edited by snowman13 on 01-05-2007 09:17 PM

[snowman13]

PS - I am trying to create a song that responds to certain voltage impulses... Such as by lights or something else...

[Ben]

Hi Snowman,

Could you provide a timing diagram defining the output pulses realative to the sync?

We do much better with pictures!

What kind of hardware are you using?

Ben

Message Edited by Ben on 01-06-2007 11:48 AM

[snowman13]

Of course! Here is a really rough sketch of what I am trying to accomplish. Any ideas or suggestions would be great!

[snowman13]

PS -

I am using a PCI slot DAQ and just then standard TI switch board interface card to talk to the DAQ for the inputs and outputs.

Message Edited by snowman13 on 01-07-2007 12:50 AM

[tbd]

Hi snowman,

      Your project seems to require a triggered output, either Analog, or Digital (DO or Counter).  If your board is capable of a waveform output (Analog or Digital) you might be able to use a triggered waveform output.  Not all DO/AO boards are capable of waveform output, but many of the cheaper boards still include Counters - exactly which board are you using?

Note: your original posts suggests using a loop to monitor the analog input to catch rising-edges.  This could work with a much slower input frequency, but at 40KHz input-signal, LabVIEW won't be able to execute fast enough to keep-up!

Cheers.

Message Edited by tbd on 01-07-2007 01:29 AM

[snowman13]

Yes, my board is capable of waveform output. I managed to get a hold of the DAQ as a loaner and free of charge! I got a hold of my regional NI rep, and showed him it... His reponse was, "Whoever lended that to you is crazy!" So I am assuming it is one of the higher model boards. Someone also suggested to me, a sort of infinite PLL. Is that plausible at 40khz?

[tbd]

Hi Snowman,

      I don't know how to apply a Phase-Locked-Loop to this!  A very simple solution might be to wire your 40KHz signal to a Counter Gate input, and use the "Generate Retriggerable Pulse (DAQ-STC).vi" to generate an output pulse of desired delay/duration for every rising-edge of the input (see HELP\Find Examples.)  But you'll need DAQ-STC Counters for that and...

... we still don't know what DAQ board we're working with.   Try using "Get DAQ Device Information.VI" (\NI Measurements\Data Acquisition\Config & Cal) with Info.Type = "Device Name", or pull the board and look at it!

Cheers!

[snowman13]

Ha, I am sorry. Got side tracked... Its a PCI-6259.

[tbd]

Hi Snowman,

      There are two good DAQmx/M-series synchronization articles here and here.  I think your input/output signal synchronization might be implimented simply.  See the attached VI which creates a timing-defined pulse with Analog trigger source (your 40KHz signal.)  I don't have any hardware to test this with, but it's very similar to the "Gen Dig Pulse-Retriggerable.vi" from the DAQmx examples. (examples are good...)

I didn't find/see any examples of how to use the on-board PLL which seems to be used (exclusively?) by internal processes for synchronizing internal and external timebases - if you come across instructions for exploiting the PLL, please post back!

Cheers.

Message Edited by tbd on 01-09-2007 01:40 AM