From: Joerg Hansmann (info_at_jhansmann.de)
Date: 2001-08-15 00:21:42
Hi Vladimir,
----- Original Message -----
From: Vladimir.K <gogol101_at_yahoo.com>
To: <buildcheapeeg_at_yahoogroups.com>
Sent: Tuesday, August 14, 2001 2:17 PM
Subject: [buildcheapeeg] Re: How to build cheap EEG Walkman
...
> I know that shield drivers and right leg driver are better but
> I haven't seen board design
Yes. There is some work to do with the pcb-layout and
no tested prototype exists, at least non that is working
(Sajith has tried to build one)
> and gameportEEG looks like somethink
> what , I hope, will be able build. ( even I don't like DC-DC
> convertor.)
You can operate the amplifier from +-4.5 V batteries instead.
> > > - add Schmitt Trigger based on NE555 , clean up input signal
> > Bandpass filtering ? Or FFT ?
>
> I havent seen many brains pattern, I'v saw only simple paterns like
> this:
>
> *
> * *
> * **
> *--------*-------*
> * *
> * *
> * *
>
> where you can see "main" wave. So I thought, for simplicity, we don't
> need FFT.
Not all EEG-waves look simple (except if you meditate and produce
large coherent alpha)
> And we cannot cut off frequencies 4-8 Hz.
> All design is mentions as hardware.
>
...
> > What algorithm/method do you want to use for frequency
> multiplication ?
> >
> Am talking about somethink what I realy don't understand. I don't know
> if it's possible.
I am asking, because my current algorithm is not so very good.
To implement it in a walkman like device , a signal-processor
would be needed.
...
> > > so we can train encreasing or decreasing brain waves.
> >
> > That reminds a little bit of the "flexyx " method of Len Ochs.
> > However he did not use the full spectrum but only one predominant
> > frequency.
> >
>
> I pleased that idea is vital when somebody else realized it.
> But flexyx don't have EEG Walkman.
That is true.
> > > - put input frequency also to light googles
> >
> > BTW. it is rather easy to connect LED-goggles to the COM-port.
>
> We don't have COM-port. Devices are portable - as walkman.
Here a signal processor would be helpful also.
...
> > > - add Schmitt Trigger based on NE555 , clean up input signal
> > > and square output signal ( we are interesting only for dominant
> > > frequency )
Squaring the signal after the FFT will show dominant frequencies.
But squaring _before_ FFT or LM567 will only produce a DC-offset
and double the frequencies
because (sin(alpha))^2 = 0.5*(1-cos(2*alpha))
BTW. this could be another way to transform the whole
EEG-spectrum into the audio-band: e.g. 7 squaring stages
with 1st order HP-filters between to remove DC would transform
any input frequency by multiplying it with 128 (2^7).
...
> Question is how quickly you change state f.e. from 20 - 15. I tought
> that tone is reward. But it could be 1 s.
In my EEG-feedback sessions I have the impression, that
changes can occur in fractions of a second.
Regards,
Joerg
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