Building an EEG at home with the OpenEEG project DIY electrodes

Overview

This is my design for a DIY saline based electrode set. I chose the saline approach because it is more convenient than using conventional electrodes. Conventional electrodes require a conductive paste which can be expensive, time consuming and messy.

Commercial electrodes are made from precious metals because they conduct well and do not react (ie. rust). I'm hoping the saline approach will counter any impedance gained from using inexpensive metals.

This is an ongoing experiment. Once I have some comparative data I will be able to tell you how well they work. They are sensitive enough to measure ocular (eye) movements which is a good start.

There is one design flaw however. The small screws in the coax plugs rust.

Parts list

The electrodes

The electrodes are made from coax connectors and ear plugs (sponge). The pin assembly inside the plug is removable and is clamped onto the end of the cable with a screw. The pin is inserted into a hole in the back of the sponge. You can use something like a bamboo skewer to prepare the hole. The plug is then reassembled through the head band (see picture at top of page). The sponge is pre-soaked for at least a day in a saline solution. I also use one of these for my DRL (driven right leg).

The cabling

Initially I considered using audio jacks to connect my cables to the eeg but decided against it because they are easy to snap (especially when somebody walks away while still wearing the electrodes). Instead I opted to use a 5 pin din connector. I split the cable progressively down from 5 pair to a single core for each electrode. I was careful to continue the shielding and used heat shrink and tape to insulate the soldered joins.

The head band

The head band is a wide black plastic ladies hair band purchased from a chemist. I did not own a drill bit large enough to fit the coax plugs so I used the biggest bit on hand and filed the rest out with a circular rasp. It is important to remember that the head band rests a good 3cm (1/2 inch) away from the scalp when the electrodes are inserted. Take this into consideration when choosing where to drill your holes. I used the standard international 10/20 system positions. The driven right leg is placed in the middle of the scalp (CZ).

The saline solution

The saline is prepared by mixing a whole heap of table salt and water (I don't know how much is optimum, but more is better than less). It is best to use distilled water if you can.

User contributed comments and advice

If you have questions please do not post them here. That is what the mailing lists are for.

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Is this safe? Connecting the human to a non-medical quality PSU would surely represent a huge risk? Uh?

Also, how about the poor LF response of non-silver electrodes? The lower end of the required bandwidth is 0.1Hz

I doubt a low frequecy filter setting of .1 Hz is necessary for an at home EEG system, unless of course you are trying to resolve the localization of a brain abcess hardly an at home utility.

I find your approach interesting and am currious of your results. Do not be too hasty to disregard any noise, some of the noise might be viable signals (just ampliphy them more). Have you started making any type of database, to record and map the signals, to see if you can reproduce certain patterns? might come in handy for a thought recognition db. Just an ideal.

WHERE DO THE ACTUAL CIRCUIT DRAWING OF THIS EEG

WHERE DO I OBTAIN OR DOWNLOAD A COPY OF THE ACTUAL CIRCUIT DRAWING FROM

man read the freaking page fro mhomesite, it wil tell you all, alan ponderoni


this site is really nice, it has limited info but still more than the NOT ANY informations found on goggle. once i strt this project i hope to contribute something.


peace

I only have a yahoo mail accunt so I can not communicate with olimex. Does anyone have
their address or another way of getting
in touch with them. I live in the US.

Jim

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