From: Jim Meissner (jpmeissner_at_mindspring.com)
Date: 2002-01-23 21:01:38
Dear Fil:
There are DC coupled sound cards that will cover the frequency range without having to do frequencies shifting. Even normal ( cheap ) cards have goodresponse down to 10 Hz and usable response to 1 Hz. How would that be useful? You still have to analyze and display the pertinent data.
Jim Peters ( on this group ) is at this time working on the idea you presented about frequency shifting. He is very excited about it. If he is successful, that method only solves the simplest of problems.
What you have not addressed is how to amplify the microvolt signals up to the 100 millivolt range in the presence of 220 volts AC and other interference. Also the patient/experimenter must be protected from electrocution by a properly designed opto isolator circuit that can stand off 5,000 volts and have less than 10 micro amps of leakage. Once you have done that the rest is simple and inexpensive.
Juergen P. (Jim) Meissner
Check out my Website at www.MeissnerResearch.com
Read about the benefits of the Brain State Synchronizer sounds for improving your life and health.
----- Original Message -----
From: Fil Laborde
To: buildcheapeeg_at_yahoogroups.com
Sent: Wednesday, January 23, 2002 1:27 PM
Subject: RE: [buildcheapeeg] Digest Number 286
Hi guys & girls, let me introduce myself,... I'm new to the group, but I'm
very interested in biofeedback, since it seems the logical next step to
altered-state training which is such an important concept in
hypnosis/NLP/related fields. I'm 26, male and from Toronto, Canada.
I did computer engineering at school, and did some VHDL/digital design
stuff. Studied some DSP (digital signal processing) at school too. Right now
I'm really out of all of this, doing web stuff, so I'm going to be more of a
passive viewer than anything else.
Here's my question........ we want a simple to build, good quality results,
and cheap EEG system right?
Every computer comes with a soundcard, they're cheap, allow incredible
sampling rates, and all have at least 2 channels (ie stereo). If they are
fed a signal in the right frequency range, of strong enough magntitude, all
soundcards can handle all the signal processing needs.
>From your schematics, it looks like you're trying to rebuild all the
functionality the soundcard offers? Wouldn't it be simpler to build an
analog EEG interface which would frequency-shift (and amplify) the 0-40Hz
signals up to 400Hz, preserving the phase, and use the soundcard's
functionality to do the rest? This would make the software much easier to
design as well. Most of the filtering could be done digitally on the
resulting signal which allows for much steeper cutoff curves (ie bandpass
from 400Hz-440Hz since this is where the signal would be frequency-shifted
to)?
Are there technical reasons we cannot do the frequency-shift and preserve
signal quality? How would we go about measuring whether we accurately
frequency-shifted the signal?
BTW impressive work on the design guys, I was amazed by the work put into
teh schematic.
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This archive was generated by hypermail 2.1.4 : 2002-07-27 12:28:37 BST