VCO in Labview

[woutert]

What is the best way to make a VCO (voltage controlled oscilator) in Labview with a PCMCIA "NI DAQCard-6062E (12-bit, 500 kS/s)NI DAQCard-6062E (12-bit, 500 kS/s)" card?

A sinewave with a frequency from 0 to 100 Hz should be created, with shocks in the generated waveform.

I tried it but every 20 seconds there is a mysterious drop in frequency I can't explain.

[JorisV]

Hi, Please try the following VI that ships with LabVIEW 7.1. Go to Find Examples -->Hardware Input and Output-->Daqmx --> Analog generation --> Voltage --> Cont Gen Voltage Wfm-Int Clk.vi That's a good example to do continuous waveform generation and it goes bit lower level than the Express VIs. Check if you still have the same issues. Regards. JorisV

[woutert]

Sorry, I had miss interpreted my VI functionality.

My sinewave generation seems to work fine.

It was my tone detection vi that reported frequency shifts at regular intervals.

I had also problems with the tone detection vi when I used a square wave from a generator.

What are the pitfalls when using the tone detection vi?

Is it only for sine waves? Trangular waves, or square waves?

Can a DC voltage put probems for the algoritm?

ps: I used 2 pc's one to generate, the other to measure.

[JorisV]

Hi, This function uses a FFT function when you go lower level. Since square waves are a combination of multiple Sine waves, you will get different result than when you use a single tone Sine wave. Fourier Analysis is based on the concept that real world signals can be approximated by a sum of sinusoids, each at a different frequency. That's why the amplitude, for example, is never exactly the same as the original one that you define with the signal generator. Just give it a try by inserting the Square signal from the Simulate signal Vi into the Tone measurements VI. It's basic FFT math. Regards. JV