Greetings!
As I understand it, you're trying to get around the low frequency limitation of the soundcard by using some sort of voltage to frequency conversion. (An alternative to this is with a chopper, used to create a pulse-width modulated stream) Both are possible to decode quite easily in Labview, however you will still need an outboard chopper or V to F converter. There are several good voltage to frequency converter chips out there, or if you're fairly good at analog design, you can build one with a pair of 555 op amps. (There used to be some great 555 cookbooks available from Radio Shack, or you can check the web.
Another alternative, not for the faint of heart, is to actually bypass a coupling capacitor or two on your soundcard. I've actual
ly done this, but it takes a while to find out where to do this, and it may not work on every card. If you're not using the microphone input, there is usually only one coupling capacitor in the path, and jumpering that with a wire will make your card work right down to DC. There's always more than one way to skin a cat
🙂 Good luck!
Eric
Eric P. Nichols
P.O. Box 56235
North Pole, AK 99705
