EEG active electrode design

dh <[email protected]> Thu, 30 May 2013 09:11:25 +0800 (CST)

Newsgroups	gmane.comp.science.openeeg.general
Message-ID	<[email protected]>

Hi,everyone
I am from hongkong. In the pass few weeks, I build a signal channel EEG headset with silver pin active electrode, the performance is good (see the attachment).
But I got a problem now, sometime the output is nothing (see the attachment "signal5.jpg"),
after 3 days testing, I guess the silver pins I used is not pure enough but I am not sure.
Any help?
Buy the way which ESD surpressor are you using on the active electrode?
Feel free to call if any one have questions about the EEG board.
Many thanks,
Dong

At 2013-05-30 07:37:42,"Niels Samuels" <[email protected]> wrote:
Hi,

Here's an example (screenshot attached) of a signal I get with Electric Guru, using one channel on the forehead and holding the DRL. I use a battery powered laptop. That is the only way for me to get a usable clean enough signal.

On Wed, May 29, 2013 at 11:44 AM, Alexandre Dubreucq <[email protected]> wrote:

Hi,

I've tried using medical EEG-designed gel (conductive electrolyte gel) on the electrodes, but apart from getting a nice haircut I saw exactly no change in the signal.

I think the problem is that there is a lot of noise in the signal, because what I get is far from a normal EEG graph (or maybe it is my brain...).

Niels, can you tell me which software gave you the best results? Could you by any chance share with me the kind of signal you get (for example with a screenshot or a data file) with your EEG-SMT device?

Regards,

Alex

Le 28 mai 2013 16:24, "Charles Z Henry" <[email protected]> a écrit :

Hi all

I was debugging my EEG-SMT this weekend also. The impedance seems to be the issue. By shorting out the DRL and the electrodes I get a perfectly flat signal.

I also tried putting the EEG on a cantaloupe. The impedance was low enough that the signals stabilized and started making noisy little orbits around 0, but I really had to hold the electrodes tightly.

One thing that I didn't like: once you lose the signal and re-establish the connection, it takes about 10 seconds for the signal to stabilize again. I am hoping to use the EEG-SMT for live performances, and it may be disrupting it takes too long to re-estabilsh connection. However, I don't know what to do about it yet. Probably the best thing is not to lose connection in the first place.

I'm still thinking about how to modify the electrodes. I think it would be useful to add sponges+electrolyte solution to keep the impedance low. Anybody else thinking about modifying the electrodes now?

Chuck

On Mon, May 27, 2013 at 6:10 PM, Niels Samuels <[email protected]> wrote:
Hi Alexandre,

I've managed to get a good signal with the device but only with all four (if using both channels) of the active electrodes on the forehead using a "fairly tight" headband and holding the DRL in my hand or stuck under the headband as well. Also I can only work with the device using a laptop running on the battery (no mains) and using a high quality usb cable. I'm then able to obtain a signal with fairly low mains interference.

Hope this helps.

Kind Regards,

Niels

On Mon, May 27, 2013 at 9:27 PM, Alexandre Dubreucq <[email protected]> wrote:
Hello everyone,

I got myself a OLIMEX EEG-SMT device, and i can't get it to work
properly : the signal is very messy, and if i take off one electrode,
nothing changes on the signal in the software (using brain bay or
elecguru for example).

Has someone already managed to have some results using OLIMEX EEG-SMT
? If yes, how did u fix the electrodes on your head ?

Thanks

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signal4.jpg (image/jpeg, 11.7 KB) - not displayed

signal5.jpg (image/jpeg, 7.4 KB) - not displayed