I know this can be a pretty beginner question, but I manage to design a good low pass filter (3rd order, 2kHz) that has a good frequency response. The major problem is that the signal has a ~100uV amplitude and still has to pass through a highpass to lose all the DC. What should I do? I guess a 1000x amplifier wouldn't be a nice idea for a low budget project... On Thu, Dec 3, 2009 at 10:07 AM, Vasile Surducan wrote: > In analog will be quite complicated because you need 3 bandpass > filter. The good news is that frequency are far away one from each > other so you will not need a very sharpen filter (meaning higest > order). One solution might be the variable transconductance amplifier > where you can move the central frequency of the filter with a DC > signal. > > What probably is not cristal clear, is that even with FFT you need an > antialising filter in front of your A2D, else you'll see a lot of > frequencies generated by Nyquist. > > Vasile > > On 12/2/09, Bruno L. Albrecht wrote: > > Yeah, I thought a lot about doing it all in some microcontroller, with > FFTs > > and Goertzel et al, but I'm trying to do it all in analog electronics. > > > > On Wed, Dec 2, 2009 at 6:05 PM, Marcel Birthelmer > > wrote: > > > > > On Wed, Dec 2, 2009 at 9:01 PM, andrew kelley > > > wrote: > > > > Use a discrete fourier transform. > > > > > > > > http://www.dspguide.com > > > > http://www.dattalo.com/technical/theory/dtmf.html > > > > http://en.wikipedia.org/wiki/Discrete_Fourier_transform > > > > http://en.wikipedia.org/wiki/Discrete-time_Fourier_transform > > > > > > > > Andrew > > > > > > If you're only looking for a single frequency, you don't have to do > > > the full spectrum DFT... you can just calculate the frequency > > > components in question. > > > -- > > > http://www.piclist.com PIC/SX FAQ & list archive > > > View/change your membership options at > > > http://mailman.mit.edu/mailman/listinfo/piclist > > > > > -- > > http://www.piclist.com PIC/SX FAQ & list archive > > View/change your membership options at > > http://mailman.mit.edu/mailman/listinfo/piclist > > > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist