Re: Openeeg-list Digest, Vol 133, Issue 1

At first, let me thank you for your e-mail.
About the filter, I agree it would probably be the best, if I leave it as
is. But I am facing another problem. After connecting the drl to the body I
get 0 signal, nothing. What could cause it? Should I add the third trimmer
for the drl? Is there any difference between INA114 and INA128 that I used
that would be causing it? Currently I don't have my EEG with me, on Monday
I would be able to show you.
But if you don't have much time, wouldn't there be someone, who will be
able to help me?
Again, thank you.
And as I said, as soon as I will finish the EEG, I will share everything,
even documentation in slovak language.

2018-02-01 13:55 GMT+01:00 Stefan Jung <[email protected]>:

> Hi Dami
>
> I have no time to check the design and look at calculations, but I would
> recommend that you stay with the original filter design for the following
> reasons.
>
> 1. No filter is a brick wall.  A 3rd order filter is really not very
> sharp, so if you choose a 49.5 Hz cut-off, your 50Hz mains noise will only
> see a bit more than 3db reduction, which will not help you.
>
> 2. If you reduce the cutoff point as you intend, your filter pass-band
> will be negatively effected.  I.e. your higher frequency EEG signal will
> start to be attenuated and your processed data will be inaccurate.  No EEG
> amplifier has a perfectly flat transfer function, simply because filters
> are far from ideal.  High order filters produce all sorts of phase delay
> and other problems and are thus also not a solution (not to mention the
> cost).  We all need to accept we live in an in-perfect world.  You should
> not act in a way to further compromise the accuracy for reasons that are
> not that important.
>
> 3. From all my readings about neurofeedback, I have learned that everyone
> has 50 or 60Hz interference and that most people use it to judge their
> electrode conductivity.  If they have high 50/60 Hz, they know that their
> electrode is not well seated, or the electrolyte has started to dry out, or
> whatever.  If the mains is fairly suppressed, they know the electrode
> contact is sound.  There will always be some mains hum, and they simply
> learn to ignore it.
>
> 4. I think the original design team spend many 100s of hours analysing the
> filter response and carefully considered where best to position the
> -3db filter cut-off point.
>
> I KNOW you want to understand the design.  And that is good.  You should
> find discussions and explanations in old openeeg forum messages.  This msg
> will not help you with the filter analysis, but I just want to make you
> aware that the openEEG design does not need to be changed for EU mains.  In
> fact, the design team was mainly from Europe.   Joerge, one of the original
> team members, later made certain modifications regarding safety, leakage,
> etc. to pass/qualify EU medical grade standards for a commercial spinoff
> for a student start-up (based in Berlin, if I remember correctly).
>
> Regards
> Stefan
>
> On Thu, Feb 1, 2018 at 2:02 PM, <openeeg-list-request@lists.
> sourceforge.net> wrote:
>
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>> Today's Topics:
>>
>>    1. Low.pass filter (Dami?n Filo)
>>    2. Re: Low.pass filter (salsero)
>>    3. Re: Low.pass filter (Dami?n Filo)
>>
>>
>> ----------------------------------------------------------------------
>>
>> Message: 1
>> Date: Wed, 31 Jan 2018 16:58:39 +0100
>> From: Dami?n Filo <[email protected]>
>> To: "Discussion of EEG hardware, software, training protocols, NFB
>>         theory - for developers and users."
>>         <[email protected]>
>> Subject: [Openeeg-list] Low.pass filter
>> Message-ID:
>>         <CALPZnbFYtf2_D0XqJArAUOJ-tGUENbKi0258N05DkWj2Q_0cyA@mail.
>> gmail.com>
>> Content-Type: text/plain; charset="utf-8"
>>
>> 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
>>
>> Thank you in advance.
>> --
>> Dami?n Filo
>> -------------- next part --------------
>> An HTML attachment was scrubbed...
>>
>> ------------------------------
>>
>> Message: 2
>> Date: Thu, 01 Feb 2018 11:38:58 +0100
>> From: salsero <[email protected]>
>> To: "Discussion of EEG hardware, software, training protocols, NFB
>>         theory - for developers and users."
>>         <[email protected]>
>> Subject: Re: [Openeeg-list] Low.pass filter
>> Message-ID: <[email protected]>
>> Content-Type: text/plain; charset=UTF-8; format=flowed
>>
>>
>> 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.
>>
>>
>>
>>
>>
>> Dami?n 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.
>> >
>> > --
>> >
>> > Dami?n Filo
>> >
>> > Links:
>> > ------
>> > [1] http://www.beis.de/Elektronik/Filter/ActiveLPFilter.html
>> >
>> > ------------------------------------------------------------
>> ------------------
>> > 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
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>> > Go to the above address to change your
>> > subscription options, e.g unsubscribe.
>>
>>
>>
>>
>>
>>
>> ------------------------------
>>
>> Message: 3
>> Date: Thu, 1 Feb 2018 12:54:03 +0100
>> From: Dami?n Filo <[email protected]>
>> To: "Discussion of EEG hardware, software, training protocols, NFB
>>         theory - for developers and users."
>>         <[email protected]>
>> Subject: Re: [Openeeg-list] Low.pass filter
>> Message-ID:
>>         <CALPZnbF9AUmUqFrGx6+c8+sXufd2yvTp=XyLDpKDLmDOWPfRpw@mail.
>> gmail.com>
>> Content-Type: text/plain; charset="utf-8"
>>
>> 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
>>
>> 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
>> > http://fourier.eng.hmc.edu/e84/lectures/ActiveFilters/node4.html
>> >
>> > Hope this helps a bit,
>> >
>> > Leo.
>> >
>> >
>> >
>> >
>> >
>> > Dami?n 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.
>> >>
>> >> --
>> >>
>> >> Dami?n Filo
>> >>
>> >> Links:
>> >> ------
>> >> [1] http://www.beis.de/Elektronik/Filter/ActiveLPFilter.html
>> >>
>> >> ------------------------------------------------------------
>> >> ------------------
>> >> Check out the vibrant tech community on one of the world's most
>> >> engaging tech sites, Slashdot.org! http://sdm.link/slashdot
>> >>
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>> >
>> >
>> >
>> > ------------------------------------------------------------
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>>
>>
>> --
>> Dami?n Filo
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-- 
Damián Filo

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