Re: Low.pass filter

Hi Damian,

I looked at the schematic on your link:
https://imgur.com/a/MzSs2

I noticed it's only a part of the original schematics.  What puzzled me, 
was the text saying: The 3rd pole is located on the digital part. And 
after some calculations on your schematic, I remembered suddenly that in 
the old diagrams, (I have them somewhere but dont know where) that there 
was a rc filter located on the digital pcb.

So if you input some of the values into your link at
http://www.beis.de/Elektronik/Filter/ActiveLPFilter.html

  it wont work, because only r44,r46,c57,c59 are essential for the low 
frequency cutoff, (in this part of the diagram) that happens to be 
around 152Hz. And r50 and c61 are for a cutoff frequency of 1590Hz. So I 
suppose that the fc of 59Hz could be a mistake and it should be 
around150Hz or 159Hz, maybe a typo. The gain is about r50/r48=12.2 Also 
strange is the name: Besselworth. Never heard of that one. I suppose 
it's a mix of a Besselfilter and Butterworth filter.
I saw that Stefan Jung also responded and I agree that a notch filter 
isn't always a good option.

Hope this will dod for now.
Leo.







Damián Filo schreef op 2018-02-01 12:54:
> Thank you for your reply, but as I am using the original
> filter/amplifier design it would be really time consuming to modify it
> to another type of filter. I just need to get to understand what have
> been used
>  in the original design. The original design is here:
> https://imgur.com/a/MzSs2 [6]
> 
> If you would be able to point me to the right direction I'd be really
> grateful.
> 
> 2018-02-01 11:38 GMT+01:00 salsero <[email protected]>:
> 
>> 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 [4]
>> http://fourier.eng.hmc.edu/e84/lectures/ActiveFilters/node4.html
>> [5]
>> 
>> 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] [1]
>>> 
>>> Thank you in advance.
>>> 
>>> --
>>> 
>>> Damián Filo
>>> 
>>> Links:
>>> ------
>>> [1] http://www.beis.de/Elektronik/Filter/ActiveLPFilter.html [1]
>>> 
>>> 
>> 
> ------------------------------------------------------------------------------
>>> Check out the vibrant tech community on one of the world's most
>>> engaging tech sites, Slashdot.org! http://sdm.link/slashdot [2]
>>> 
>>> _______________________________________________
>>> Openeeg-list mailing list
>>> [email protected]
>>> https://lists.sourceforge.net/lists/listinfo/openeeg-list [3]
>>> Go to the above address to change your
>>> subscription options, e.g unsubscribe.
>> 
>> 
> ------------------------------------------------------------------------------
>> Check out the vibrant tech community on one of the world's most
>> engaging tech sites, Slashdot.org! http://sdm.link/slashdot [2]
>> _______________________________________________
>> Openeeg-list mailing list
>> [email protected]
>> https://lists.sourceforge.net/lists/listinfo/openeeg-list [3]
>> Go to the above address to change your
>> subscription options, e.g unsubscribe.
> 
> --
> 
> Damián Filo
> 
> Links:
> ------
> [1] http://www.beis.de/Elektronik/Filter/ActiveLPFilter.html
> [2] http://sdm.link/slashdot
> [3] https://lists.sourceforge.net/lists/listinfo/openeeg-list
> [4] http://www.g3ynh.info/circuits/Bob_Batey/LB-5.pdf
> [5] http://fourier.eng.hmc.edu/e84/lectures/ActiveFilters/node4.html
> [6] https://imgur.com/a/MzSs2
> 
> ------------------------------------------------------------------------------
> Check out the vibrant tech community on one of the world's most
> engaging tech sites, Slashdot.org! http://sdm.link/slashdot
> 
> _______________________________________________
> Openeeg-list mailing list
> [email protected]
> https://lists.sourceforge.net/lists/listinfo/openeeg-list
> Go to the above address to change your
> subscription options, e.g unsubscribe.


------------------------------------------------------------------------------
Check out the vibrant tech community on one of the world's most
engaging tech sites, Slashdot.org! http://sdm.link/slashdot
_______________________________________________
Openeeg-list mailing list
[email protected]
https://lists.sourceforge.net/lists/listinfo/openeeg-list
Go to the above address to change your
subscription options, e.g unsubscribe.