Reading a PWM and determining pulse width using a digital input pin on a NI 9425 DAQ

Hello!
I have been experimenting with LabVIEW for about a week now and have run into a brick wall. I have found a fairly effective way of reading a PWM signal through an analog input and determining the pulse width. However, it is becoming necessary for this project to do this same thing using a digital input. I've been playing with this for about a day now and am not making much headway.
For reference, I will be using a 9524 device
Any ideas?

Also, if it is helpful at all, I've attached two vi's. One, functions just as I need it to - but it doesn't involve data aquisition. The second should be similar to the first, but is non functional - I keep getting an error that my amplitude is zero.
Any thoughts?
Attachments:
DigitalEdgeDetectionKnown.vi ‏47 KB
DigitalEdgeDetectionRead.vi ‏148 KB

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How to generate and output 3 TTL square waveforms with different pulse widths using counters of NI 6034E

Hello
I just have a few questions.
I am using the NI 6034E DAQ board in order to
generate simultaneouly 3 different TTL digital signals, with different
pulse width, and output these TTL signals to an external circuit that I
am using for this application.
The following pattern of the TTL pulses will look like this:
01010101 01010101
00110011 00110011
00001111 00001111
From
what I understand, I have to use the 2 counters, Ctr0 and Ctr1, to
generate the TTL pulses that I desire, because the DIO lines are
software timed only and I will not be able to produce a deterministic
output period using these DIO lines. Am I correct?    Also, do I have
to use a separate counter to generate a separate TTL digital pulse. I
need 3 different TTL pulses and there are only 2 counters for this DAQ
device. The three generated TTL signals will be feed to an external
circuit. Concerning the hardware connections for my application, I
assume that the generated TTL signals will be output from
GPCTR0_OUT(pin 2) for counter 0 and GPCTR1_OUT(pin 40) for counter 1
of the NI 6034E. Is this correct? Is there any way that these TTL
signals can be output from three DIO lines(DIO0...2).
Here is some code that I plan to use in order to do this:
#include <NIDAQmx.h>
static TaskHandle gTaskHandle = 0;
DAQmxCreateTask ("", &gTaskHandle);
DAQmxCreateCOPulseChanTime (gTaskHandle, "Dev1/ctr0", "", DAQmx_Val_Seconds, DAQmx_Val_Low, 1.0, 2.0, 2.0);
DAQmxCreateCOPulseChanTime (gTaskHandle, "Dev1/ctr1", "", DAQmx_Val_Seconds, DAQmx_Val_Low, 3.0, 4.0, 4.0);
DAQmxCreateCOPulseChanTime (gTaskHandle, "?????", "", DAQmx_Val_Seconds, DAQmx_Val_Low, 7.0, 8.0, 8.0);
DAQmxCfgImplicitTiming (gTaskHandle, DAQmx_Val_FiniteSamps, 5);
DAQmxStartTask (gTaskHandle);
DAQmxWaitUntilTaskDone(gTaskHandle)
DAQmxErrChk DAQmxStopTask(gTaskHandle)
DAQmxErrChk DAQmxClearTask(gTaskHandle)
I believe this code should generate the 3 TTL square waveforms that I want for my application.
Please provide me with some feedback. It would greatly be appreciated.
Thank You

Hi,
The NI 6034E is a multifuntion DAQ device, this means you have:
(2) counters
(8) DIO lines (software timed)
(16) AI, single ended
(0) Analog Output
You have a couple choices here:
   1. Software timed digital output of all three signals, max 1khz loop rate, non-deterministic.
   2. Hardware timed digital output of 2 signals, max 20Mhz.
   3. Hardware timed digital output of 2 signals and software timed digital output of 1 signal.
   4. Find another NI MIO board such as the NI 6251. This board will do 10Mhz pattern generation for (8) DIO lines.
For the hardware connection, you are correct, the output for the counters will be taken from pin 2 & pin 40. Here's the pinout for the NI 6034E for reference:
The output of the Counters can be routed to some of the PFI's or to the RTSI connector. You can see this in MAX
Message Edited by Matthew W on 11-19-2007 01:24 PM
Attachments:
2007-11-19_131609.jpg ‏61 KB
2007-11-19_132435.jpg ‏86 KB

How does Pulse Params Vi determine pulse width

I need to know how the PulseParams vi calculate pulse width, rise/fall time? Is it based on the standard 10/90 method or something else? How does it determine what is a "valid" pulse? What is the "Delay" parameter and how do you use it?

Hello Lancer,
The following is taken from LabVIEW Help under Pulse Parameters:
X is the input sequence. X must meet the following conditions:
� The number of samples in X must be greater than or equal to 3.
� X should have a rising edge, a plateau, and a falling edge.
� The expected peak noise amplitude must be less than 50% of the expected amplitude.
If the number of samples in X is less than 3, the VI sets all the pulse parameters to NaN and returns an error. If X does not contain a rising edge, plateau, and falling edge, the VI analyzes the data, assigns values to as many pulse parameters as it can identify, and sets parameters it cannot identify to NaN. The VI does not report this condition as an error.
Note X can be a positive- or negative-going pulse. A histogram is used to determine top and base. If the difference between top and base is negative, the pulse is considered negative-going with a negative amplitude.
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Note If the data is noisy, you can apply a median filter to the data before passing it to the Pulse Parameters VI. Refer to Noisy Pulse Analyzed with a Median Filter for more information about analysis with a median filter.
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amplitude = overshoot = undershoot = delay = duration = 0.
top = base = c.
risetime = falltime = slew rate = NaN.
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risetime is the time required to rise from 10% amplitude to 90% amplitude on the rising edge of the pulse.
top is the line that best represents the values when the pulse is active, high, or on. For a negative-going pulse, top is less than base and results in a negative amplitude. For a positive-going pulse, top is larger than base and results in a positive amplitude.
amplitude is the difference between top and base.
base is the line that best represents the values when the pulse is inactive, low, or off and is the level closest to zero. For a negative-going pulse, base is larger than top and results in a negative amplitude. For a positive-going pulse, base is less than top and results in a positive amplitude.
undershoot is the difference between the baseline and the minimum value in the pulse.
error returns any error or warning from the VI. You can wire error to the Error Cluster From Error Code VI to convert the error code or warning into an error cluster.
falltime is the time required to fall from 90% amplitude to 10% amplitude on the falling edge of the pulse.
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delay is the difference between the time origin and the time at which 50% amplitude occurs on the rising edge of the pulse.
Pulse Parameters Details
Note The Cycle Average and RMS, Transition Measurements, Pulse Measurements, and Amplitude and Levels VIs provide more measurements than the Pulse Parameters VI, and you can configure each of those VIs.
The waveform-related parameters are slew rate, overshoot, topline (top), amplitude, baseline (base), and undershoot. If y-axis units are volts, then slew rate has units of volts per sample. The time-related parameters are risetime, falltime, duration (width), and delay and are expressed in units of samples.
Note The VI assumes the input pulse or pulse train has a bimodal, or two-state, distribution. Any input other than a bimodal input can lead to inconsistent results.
The Pulse Parameters VI uses the following steps to calculate the output parameters.
1. Find the maximum and minimum values in the input sequence X.
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3. Determine the upper and lower modes to establish the top and base values.
4. Find the overshoot, amplitude, and undershoot from top, base, maximum, and minimum values.
5. Scans X and determines the slew rate, risetime, falltime, duration, and delay.
The Pulse Parameters VI interpolates duration and delay to obtain a more accurate result not only of duration and delay but also of slew rate, risetime, and falltime.
If X contains a train of pulses, the Pulse Parameters VI uses the train to determine overshoot, top, amplitude, base, and undershoot but uses only the first pulse in the train to establish slew rate, risetime, falltime, duration, and delay.
Note Because pulses commonly occur in the negative direction, the Pulse Parameters VI can discriminate between positive and negative pulses and can analyze the X sequence correctly. You do not need to preprocess the sequence before analyzing it.
If none of these suggestions help, or if I�m not correctly understanding your issue, please post the software and versions you are using, the applicable portions of your code, and any other information that may help, and I�ll be happy to look further into it.
Have a nice day!
Robert M
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Robert Mortensen
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Found by myself (google search!) at:
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Reading a PWM and determining pulse width using a digital input pin on a NI 9425 DAQ

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