From: <so...@pk...> - 2007-03-29 13:19:56
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Hi Ray, I don't have a ModularEEG, but I'll answer what I can. I've built something similar. > Which brings me to the first question: Which type of electrodes > would be recommended? Passive or active? And if the passive > electrodes will suffice, are the homemade ones, such as the > sponge-and-salt-water-ones, > really good, or should I purchase some silver electrodes from an > electrode store? Any recommendations from anyone with > experience in this area would be appreciated very much. I haven't used active. I've used passive. I figured active electrodes were one more circuit complication to worry about that isn't necessary. Some might argue for them, but like you, in the begining I was really slowed down by all the "extras". It's not enought just to have an EEG amp; you need cables, electrodes, paste, software.... I wanted to eliminate anything that wasn't necessary. I can always add more later. > Second question: If I go with the passive electrodes, then I will > need > to use the paste with which to attach them to the skin. Is this paste > something special (I realize that it has high conductivity, of course) > that I will have to send away for, or is there a substitute which works > well and is more readily available? I haven't used sponge electrodes, and I haven't tried to make homemade paste. I have AgCl discs from the Electrode Store. I bought a bag of 100 for $47.50 (including shipping). I then divided them up amoung several people on this list for my cost ($.475/electode) plus my shipping to them (84 cents to Europe!). I have about 8 left for myself. I have aranged the AgCl electrodes somewhat like this: http://openeeg.sourceforge.net/doc/gallery/electrode-howto/ I have also used pure silver. I used tin snips to cut off a tiny corner of a silver bar, hammered it flat, and soldered a wire to it. This works as well as the AgCl electrodes. You need paste (or something) between the electrode and the skin. I've only used the paste, so I can't compare it to anything else, but I would recommend it. I bought an 8oz jar of Ten20 paste off the web for $10. I just Googled around till I found the best price. It really is paste. You put a glob of it on the electrode, and then the electrode will just stick in place. That's what you want, a column of paste between the electrode and the skin. CLEAN skin. If you don't clean the site first, or you are sweating, your signals go all over the map. This is really imperitive, and what took me the longest to get all figured out. > Third question: In the website, when I looked at the photographs of the > eeg device, found in the section labeled "Nelo's Electrodes," I noticed > that there was what appeared to be an audio jack in the rear of the > chassis, next to the serial connector. What is that for? I'd guess that is his power supply connection. > And the same is true of the > two black knobs, seen on the right side of the front view. Are they > potentiometers which he added, for some reason? He probably put the gain adjust pots (P202, P203) on the chassis. You don't have to box it all up before you try it out. I haven't put mine in a box yet. When I get everthing working just the way I want, then I might put it in a box. For me, this is not a necessary step. Here's me measuring with an unboxed unit. http://www.pkfamily.com/users/solson/eeg/firsteeg.jpg The only thing I do differently now than in the picture is the electrodes. In the picture I have a ECG electrode on my head that I took out of an emergency room (it's all I had at the time). > Fourth question: (Okay, five questions in one) What does the > programming cable do? Do I still need one, if I have purchased the two > pre-assembled pc boards from Olimex? Where does it connect? > And, finally, how do you use it? I don't see anything about the > programming cable, on the outside of the eeg device, in the > pictures...nothing going into the box or coming out of it, that says > "Programming Cable." I have to guess that this is for programming the ATMEL processor. I understand that the OLIMEX boards have the processors pre-programmed, so you shouldn't need this. > The last questions (about the programming cable) are the ones which I feel > really lost about. Please help, someone!! > --Ray Cole Hope these comments helped. Scott O |