Re: Low.pass filter

Hi Damian,

Did you try a twin-T notch filter? An RC low pass filter is not really 
that sharp. May these articles will help you:

http://www.g3ynh.info/circuits/Bob_Batey/LB-5.pdf
http://fourier.eng.hmc.edu/e84/lectures/ActiveFilters/node4.html

Hope this helps a bit,

Leo.





Damián Filo schreef op 2018-01-31 16:58:
> Hello everybody.
> 
> As I am finishing up my project of customizing EEG-SMT I encountered
> some things I can't seem to understand about the OpenEEG. One of those
> things is the 3rd order besselworth filter which I cannot successfully
> reverse-engineer in several Bessel filter calculators. Every time when
> I enter the provided values of cutoff frequency, order... I get really
> different values of the parts used. It is really important to me,  I'd
> like to set it to 49Hz cutoff because of european electric network of
> 50Hz. That's why I get too much 50Hz ripple. I will share the
> schematics, board and electrode designs, but at first I need to
> understand the filter. Is there someone, who will be able to explain
> the value selection and formulas used for this filter? I'd be really
> thankful. I spent hours maybe days figuring it out, but I can't seem
> to understand it. I used multiple calculators, but this one looks the
> best: http://www.beis.de/Elektronik/Filter/ActiveLPFilter.html [1]
> 
> Thank you in advance.
> 
> --
> 
> Damián Filo
> 
> Links:
> ------
> [1] http://www.beis.de/Elektronik/Filter/ActiveLPFilter.html
> 
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