Frequency each pulse on sound card

[rudex]

" I am trying enters a square sign (of encoder), the sound card filters the waves of high frequency and therefore he lacks labview information to show the perfect sign. But I believe that it is not necessary, that the sign is perfect to calculate the frequency of each pulse. Is it this way?. I alone want to know the frequency of each pulse. I don't care amplitude.
I have tried to calculate the frequency of each pulse. I have recorded the sign and once saved. I have tried to calculate counting the pulses, with the option ' indices', subtracting at the 2º -1º, 3º-2º,... .
but this is not accurate because the sample rate is to 44100 hz and I use signs from 50 hz to 10khz. To high frequency it counts very few points, to 10 khz it co
unts 4 and this is not accurate.
Is there some form of calculating it more accurate?. What vi's can I use?.
Thank you!."

[chutla]

Greetings, Rudex:

For all but the most crucial measurements the sine wave is fine...Just make sure you set your thresholds closely. There are many good nodes in the WAveform toolbox for doing this. Look especially at the "extract single tone" vi.

Good luck

[mikeporter]

Well, if I understand what you're saying. You are trying to read the frequency of a squarewave coming from an encoder. The problem with doing this with a DAQ card is (to put it simply) the required Nyquist samplng rate. Think for a moment, what is the frequency content of a squarewave? The fundamental (which is what you want) and a theoretically infinite number of harmonics. To adequately sample a squarewave and correctly represent the vertical edges would require an infinitely high sample rate.

If what you need is to measure the squarewave repetition rate, doing it with a DAQ card (or sound card) is the wrong way to do it. What you need is to do a pulse width measurement using a counter.

Mike...

[rudex]

Hi!, I have tried to use "extract single tone information" but I don't use it well. It doesn't give me the frequency of each pulse, only gives me few same values. Could anybody say me how use it?.
I have kept the sign with "Write To Spreadsheet File.vi." I open it and I want the frequency of each pulse comes out in a array.
can you explain to me?.
About the counter is other option. If you want , tell me more...
thanks you.

[mikeporter]

Checkout the examples that ship with LV for pulse width measurements and you should find what you need.

Mike...