jean.rintoul at gmail.com
Sat Mar 28 12:05:47 PDT 2009
Here are some completely useless to the task at hand, but potentially
interesting left-field ideas for measuring brainwaves.
The antenna noise problem sounds like a big one, but what if the antenna
like properties could be used for good instead of evil?
a faraday cage?
That would be the ultimate in non-invasive comfort, and... a brain theremin?
Also, Hitachi claim to have made the first Optical Topography unit to
measure blood volume changes. This is taking a completely different
approach. Pulse Oximetry is a tried and true reliable technology however.
On Sat, Mar 28, 2009 at 11:02 AM, Mitch Altman <maltman23 at hotmail.com>wrote:
> Noise is everywhere in our crazy modern world (electrical, social,
> psychic, etc., etc. -- and of course, TV, which is all of the above -- but I
> Sensors act as antennas for all sorts of noise, 60Hz from the AC power all
> around us being particularly strong. The signals from our brains running
> down wires from a passive electrode are on the order of 10 microvolts, which
> is way (WAY) lower amplitude than the noise the wires pick up. To deal with
> the noise that the wires pick up as an antenna, the analog board of the
> OpenEEG has a "Differential Input" on the it's first input stage (which is a
> high-gain, low-noise op-amp). It works quite well.
> But if the signal from the electrode were amplified at the source (like,
> putting an amp at the electrode, right next to your head), then the analog
> board would not have to get rid of so much noise, since the amount of noise
> compared to the amount of useful signal is a much better ratio (this is
> called Signal-To-Noise Ratio -- the higher number for this, the better).
> This is the idea behind the active electrodes. But designing and using the
> high-gain, low-noise amplifiers required for these active electrodes is not
> easy. As stated earlier, me and Tracy tried building and using
> "Pedro's Active Electrodes" from the OpenEEG project website. But we got
> lots of other interesting noise that would oscillate at a very low (about
> 0.02Hz, as a guess). We never did figure out what was going wrong with
> them. Some people, including Pedro, have great results with them, and
> others have problems like me and Tracy had. There's probably issues that
> are beyond my expertise in analog design (which is not my realm).
> Creating a Bluetooth interface would also theoretically get rid of the
> issue of noise picked up on the wires, since it gets rid of the wires. But
> then we have some similar problems to the active electrodes: of creating an
> amplifier at the electrode (and this signal would go to the Bluetooth
> transmitter). Probably a non-trivial problem to solve. But it would be a
> way cool way to use an EEG, without wires hanging off of your head.
> > Date: Sat, 28 Mar 2009 10:19:19 -0700
> > From: rachel at xtreme.com
> > To: kinetical at comcast.net
> > Subject: Re: [EEG] wireless?
> > CC: eeg at lists.noisebridge.net
> > Huh, I had the impression that the noise source was local radiation
> > being picked up by the wires, which were acting as antennas. So I guess
> > removing the wires would reduce that, at the cost of adding more local
> > radiation sources. What about the wires to the sensors though, or am I
> > completely wrong about the sources of noise?
> > Rachel
> > Tracy Jacobs wrote:
> > > Hi,
> > >
> > > Thanks to everyone who came to the meeting last night, I'm really
> > > excited about the group. After everyone went home I was talking to
> > > Michael Kan, who had some interesting ideas about engineering the EEG.
> > > I encouraged him to join us next time. He suggested we make the
> > > connection between the EEG and the computer wireless, using a bluetooth
> > > device, to reduce noise and also to ensure safety by having the
> > > completely separate from one another. I don't have any bluetooth
> > > device, but if any of you do, bring it along next time. I will bring a
> > > box for the circuit boards.
> > >
> > > Tracy
> > > _______________________________________________
> > > EEG mailing list
> > > EEG at lists.noisebridge.net
> > > https://www.noisebridge.net/mailman/listinfo/eeg
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