Control Design Toolkit - version 2.0

[Ryan_V[DE]]

Sidney,

    Would a TTL signal (0-5V) suffice for the amplitude of this binary signal? If so, I would recommend using one of your M Series counters to perform PWM output, only instead of changing the duty cycle, you would change the frequency. There is a great Dev Zone article which describes this process. One thing to note is that DAQmx will throw an error if you try to update the counter output frequency or duty cycle more than once per period. To avoid this, I would use the DAQmx Channel Property "Counter Output->General Properties->More->Advanced->Ready For New Value." By waiting until this property is true, your software will be able to control the pulse width or frequency of each ouput pulse. If you frequency is too high, however, your software will not be able to update these properties fast enough and you will output several cycles of identical pulses.

    If a TTL signal does not work, you will have to generate an analog output signal on-the-fly and stream it to the analog ouptput buffer of your DAQ card. Please have a look at the "Cont Gen Voltage Wfm-Int Clk-Non Regeneration.vi" example located in the LabVIEW Example Finder (Help->Find Examples) on how to stream a waveform to your device.

Hope this helps,

[Sidney Nogueira]

Ryan

Thank you very much, sending me this way to do my block diagram in LabVIEW 7.1 and DAQmx PCI 6221.

I am goint to try to do this.

Regards.

Sidney Nogueira

[Sidney Nogueira]

Please I am not understanding why I configure the x - axis ( time ) between 0  to 15 seconds ( for example ) into one Waveform Chart, and when I run the program this values changes with big numbers differents than that I used according above described.

I am using the LabVIEW 7.1, one DAQmx model PCI 6221 and my diagram is only one DAQ Assistant reading the nine channel ( AI9 ), where the range in y - axis is voltage  configureted from 0 to 10 Vcc, and acquiring data contiinuously with 500 samples at 1000 Hz.

I used one while Loop and 100 ms for each iteration. To stop I have one button.

Sidney Nogueira

[Travis_M.]

Hello Sidney,

Thank you for posting to the NI Discussion Forums.  I apologize, but I do not quite understand the question you are asking.  It sounds to me like you have a waveform chart, and are typing in a time interval of 15 seconds in the X axis, and when you run your program the axis changes its time scale.  If this is the case, I suspect that the problem lies in the X-Axis auto-scaling.  Have you configured the axis to auto-scale the x-axis?  You can set this option by right-clicking on the chart and choosing “properties” (see below).

 

I hope this helps!  Please let us know if you have any additional questions.

Message Edited by Travis M. on 07-11-2006 02:06 PM