I generated a PWM from Arduino and everything is fine, all was left was to filter the signal to obtain the sine wave, but to my surprise, I didn't have to... which I find wierd.

I use soundcard Oscilloscope to read the signal using the input micro jack of the computer.

Here is the circuit enter image description here

And here is the sine wave read

enter image description here

Did I forget something, or there is some hidden filter in the soundcard?

I appreciate your help, thanks.

  • \$\begingroup\$ You magically filtered out all the values of your design in the question. \$\endgroup\$ – Sunnyskyguy EE75 Jan 22 at 3:04
  • 1
    \$\begingroup\$ What is the PWM frequency? The sound card will have a filter at the input to the A-to-D converter to avoid aliasing. en.wikipedia.org/wiki/Anti-aliasing_filter \$\endgroup\$ – bigjosh Jan 22 at 3:29
  • \$\begingroup\$ It could be that the soundcard's resolution is so low, that the parasitic resistances and capacitors along the way simply cause a pole inbetween the switching frequency and the waveform (which looks ~35Hz -- is that what you had encoded?). \$\endgroup\$ – a concerned citizen Jan 22 at 6:27
  • \$\begingroup\$ bigjosh 62,5kHz, I think like you said there is a filter to filter the audible frequencies. Thanks. <br><br> A concerned citizen Yes, I encoded a sine wave with frequency 35Hz, can you elaborate more on your comment, I didn't understand it well. Thanks. \$\endgroup\$ – Ahmed Amrani Jan 22 at 16:45

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