Re: Low.pass filter
Damián Filo <[email protected]> Fri, 2 Feb 2018 17:13:47 +0100
| Newsgroups | gmane.comp.science.openeeg.general |
|---|---|
| Message-ID | <CALPZnbEsDEzDnESfqP=5G0BhsOfu5ULBL=zte7i9bn_ruhTC7g@mail.gmail.com> |
Of course I am sorry, here is the digital part low pass filter: https://imgur.com/a/GcopG And yes either there is a typo, that the cutoff frequency should be higher or (lower robability) the choice of parts is wrong. I am aware, that the filter is not ideal, but either mistake, I want it to be fixed. The Besselworth filter also puzzled me, I was not sure what to look for, because I couldn't find it anywhere on the internet. I'd like to correct that too. Thank you for your time. 2018-02-01 16:04 GMT+01:00 salsero <[email protected]>: > 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. > -- Damián Filo ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, Slashdot.org! http://sdm.link/slashdot