Can I convert an analog input to digital?

[lord_ed]

Hello.

I am working with an PCI 6221 and Labview 7.1. I have an analog input signal (ai0) and I want to measure the frequency of this signal through counter 0. The problem is that the counter only accept digital signals.

Can I make this?

1.- Enter this analog signal through ai0.

2.- Convert this to digital (ADC).

3.- Save this values in a file.

4.- Take out this digital signal trhough an DIO.

5.- Enter this digital signal to the counter source and measure the frequency of the signal.

Thanks.

[Dennis_Knutson]

There's Rube Goldberg thread for software but this qualifies for a new Rube Goldberg hardware thread. Instead of all of the complicated loops you seems to want to jump through, why don't you at least try to measure the analog frequency with one of the included functions in LabVIEW. Try Extract Single Tone.

[JaimeC]

Hi,

I do not really believe that will work, counters are for digital signals, I do not really know which is the frequency u ar trying to get. But as Denis says the best and easy think will be just making an analog input measurement and using any of the processing vi's that LabVIEW has to analyze that frequency.

Regards,

[lord_ed]

Well, I think that the best solution is to put an external Schmitt Trigger to convert the analog signal  to a digital and after enter this signal to the counter.

I think that the counter is faster than the labview program.

Thank you.

[JaimeC]

Yeah,

Of course counter is much faster than the analog input and with labview code, I do not know how fast is your signal. The 6221 goes to a maximum of 250 KS/s and taking in consideration a good signal acquisition (10 S per period of your input signal) then the maximum frequency input signal to acquire ok will be around 25KHz, at the maximum following Nyquist requirements it would be 125kHz.

If your frequency is much faster what I would suggest is what you say. You can make an easy external circuitry with a HIgh BW frequency Operational Amplifier that compares to the half of your signal level and comes into saturation (high amplifier) to +5 / 0 Volts. That way you can convert the analog signal to a digital one TTL accepted for the counter.