Data acquisition through sound card

[yatang]

Hello everyone,

I want to measure an analog square wave through laptop sound card.

The period of the square wave is 13.4ms, amplitude is 7V(period and amplitude are confirmed with oscilloscope).

However, the data acquired by sound card were incorrect. The period of the acquired square wave was 7ms, amplitude was 1V.

I know the amplitude will be normalized to 1V by sound card, but I don't know why the period was much smaller. I guess this problem is caused by the high input voltage(as 7V may exceed the input range), but I'm not sure.

Could anyone give me some hints? Thank you so much!

[GerdW]

Hi yatang,

I know the amplitude will be normalized to 1V by sound card, but I don't know why the period was much smaller. I guess this problem is caused by the high input voltage(as 7V may exceed the input range), but I'm not sure.

When you know your soundcard will only work with voltage levels upto ~1V why do you try to read amplitudes of 7V?

Some thoughts:

- For testing you rshould use a signal with 1V pk-pk amplitude and no offset. Use a reasonable signal frequency of ~500Hz and a standard sample rate of either 44100Hz or 48kHz…

- How did you determine the period of your signal? Did you obey Nyquist?

- Soundcards often use condensators to avoid DC signals at input and output, can they influence the measurement of your signal?