OpenEEG

Other EEG and Biofeedback Devices

David Stasuk — Thu, 12 Jun 2008 00:39:10 Z

EEG

Mind Mirror
Bio Semi
EPICS
Brain Master
Monolith EEG? ( MonolithEEG ) by Reiner Münch is a nice EEG based on the Open EEG? (see also the
headset electrodes )
Programmable Chip EEG
The Experimental Portable EEG/EMG Amplifier

Bio Feedback

IBVA

Others

Neuro Phone
Brain State Synchronizer

’’See also the Wiki Node list of related projects.’‘

Sources of Noise

David Stasuk — Thu, 12 Jun 2008 00:28:34 Z

Stecker, MM., Bush, WW., (2001). Interference from cellular phones and the EEG. American Journal of Electroneurodiagnostic Technology, 41 (2) : 156-163.

Abstract:
Despite the high frequencies used in cellular communications, cell phones can cause significant interference in the clinical EEG when they are used within six feet of the electroencephalograph and especially when they are within one foot of the amplifier. The artifact probably appears when the signal is of such high intensity that it is processed nonlinearly by the electroencephalograph. Nonlinearities lead to the appearance of low-frequency components in the output that can appear on the EEG. This is very dependent on the amplitude of the signal. Although a previous study suggested that cellular artifact was present both near the electrodes and near the input box, we found uniformly that artifact was maximal when the cellular phone was next to the amplifiers/amplifier inputs rather than the electrodes. One reason for this is that the cable capacitance causes attenuation of very high-frequency signals in the long electrode cables often used in EEG recordings. Another reason for higher-amplitude noise levels when the cell phone was closer to the amplifiers is that high frequency signals may enter the electroencephalograph through pathways other than the electrode wires themselves.

Literature

David Stasuk — Thu, 12 Jun 2008 00:27:29 Z

Papers

David Stasuk — Fri, 30 May 2008 22:13:45 Z

http://openeeg.sourceforge.net/doc/links.html

NORMATIVE EEG DATABASES AND EEG BIOFEEDBACK

Practical Issues Concerning EEG Biofeedback

Cleaning Electrodes & Other Cleaning Tips

David Stasuk — Sat, 19 Apr 2008 13:32:45 Z

CLEANING ELECTRODES

Immediately after removing the electrode, wash out the gel or cream using distilled or deionized water. A plastic wash bottle with spray tip is very suitable. Never use tap water. A cotton swab can be used to remove the main bulk of the gel or cream. Soak the electrode in a mild saline solution or distilled or deionized water until the next application. Your lab or hospital may have normal saline solution available in prepared bottles. Do not let the old gel or cream dry or harden the cavity.

OTHER CLEANING TIPS

If electrodes are used only occasionally, a brown coating may form over the sensing element. This can be removed by wiping with a mild ammonium hydroxide solution or by lightly abrading with a very thin strip of 200 mesh emery cloth. Electrodes will turn black if continuously exposed to bright light. The finely divided silver in the electrode pellet oxidizes to silver oxide (black) much like a photographic negative. The electrode will perform normally even when the appearance is almost jet black. Cleaning by abrasion to remove the oxide layer is appropriate, however. Store electrodes not in use in a dark drawer or a closed opaque box. Electrodes can be permanently damaged or poisoned when only small amounts of bromide, sulfide and some other metal ions are present. Do not expose the electrodes to tap water, EEG pastes containing abrasive clays, miscellaneous soap solutions or abrasive cleaners.

STERILIZATION

Silver/silver chloride electrodes may be sterilized using the low temperature peroxide sterilization method. This utilizes the STERRAD 100 Sterilizer from Advanced Sterilization Products, a Johnson and Johnson Company.

Electrodes

David Stasuk — Sat, 19 Apr 2008 13:29:11 Z

Electrodes are the contacts from the EEG device to the head (brain).

http://openeeg.sourceforge.net/doc/hw/electrodes/

PassiveElectrodes
ActiveElectrodes
ElectrodeAttachment
ElectrodePlacement
ElectrodeCaps
Cleaning Electrodes & Other Cleaning Tips

Rechloriding & Storing Ag/AgCl Electrodes

http://www.grasstechnologies.com/knowledgebase/sterile7.html

An interesting SMT digitizing electrode design: IMPROVING SIGNAL QUALITY AND TEST RELIABILITY IN EEG
MEASUREMENTS USING INTEGRATED HIGH-DENSITY
SURFACE-MOUNT ELECTRONICS

An interesting paper about accurately recording very low frequency EEG with special electrodes. DC-stable electrode-skin interface for human EEG recordings

What do people think about putting ferrite filters around our electrode cables to suppress H.F. noise, like they do for DC power supplies? I think some of the professional companies are already doing this.

Maybe we can also point the way here to a few well designed hopefully cheap electrodes for sale:

Hair-Mount EEG electrode
spring-clips like a barrette to the root of hair strands .

I’ve just found this one it looks quite nice but not too cheap :
GEREONICS EEG ELECTRODES
Here is a desciption:
Gereonics silver/silver chloride (Ag/Ag Cl?) electrodes are made from very finely powdered high purity silver and silver chloride. They are mixed in a specific ratio and compacted into the electrode body at very high pressures. The resulting pellet is relatively thick (0.7 to 1.0mm) and never needs to be rechloridized, because it is a homogenous mixture. This is unlike electrodeposited Ag/Ag Cl? which is very thin and needs renewal after multiple uses. The only American standard for electrodes is ANSI EC-2 for “Pregelled EEG Disposable Electrodes.” The electrical performance requirements, test procedures and test circuity are set forth in this standard. Specific electrical tests are AC Impedance, DC Offset Voltage, Combined Offset Instability and Internal Noise, Defibrillation Overload Recovery and Bias Current Tolerance. Gereonics electrodes test very significantly better than the specifications for each of these tests. All Gereonics electrodes are 100% tested for Continuity and DC Offset Voltage.

Rechloriding & Storing Ag/Ag Cl Electrodes

David Stasuk — Sat, 19 Apr 2008 13:05:26 Z

Rechloriding & Storing Ag/AgCl Electrodes

Introduction

The Silver/Silver Chloride electrode has been shown to possess superior characteristics to that of unchlorided silver electrodes when used for recording low level AC and DC potentials. Chlorided silver electrodes present less low frequency “noise” than either gold or silver electrodes. The Grass Silver/Silver Chloride electrodes are constructed of pure silver and then chlorided to provide the stability and low noise characteristics. The chloriding process changes the shiny silver appearance to the dark gray color.

It should also be noted that the silver-silver chloride electrode is photo sensitive, changing it’s potential slightly when exposed to light. Therefore, if these electrodes are used during photic stimulation studies, they may need to be shaded or covered to prevent light artifact.

Since the chloriding process deposits chloride ions on the silver surface, care must be taken during handling and storage to avoid scratching or abrading the electrode surface, which will remove part of the chloride surface. If this happens, it is possible to rechloride the electrode.

Rechloriding the Electrode

1. Thoroughly clean the silver surface electrodes of tarnish and dirt. Scouring powder or silver cleaner may be used.
2. Place the electrode in an opaque non-metallic container with 5% salt (Na Cl?) solution.
3. Connect the electrode to be chlorided in the (+) positive terminal of a 1.5 volt battery and the other electrode to the (-) negative terminal. Use a 100 ohm resister in series with the electrode.
4. The chloriding electrode darkens, while the other bubbles. Continue until the darkened surface is evenly coated.

Storing the Ag/Ag Cl? Electrodes

To preserve the chlorided surface when not in use, it is recommended that the electrodes be stored in a salt solution, such as a sterile saline solution. If desired, it is possible to add 0.1% Zepherin Chloride as an anti-bacterial agent.

Related Info

David Stasuk — Sat, 19 Apr 2008 06:32:19 Z

This page is for generating a knowledge base for EEG and Neurofeedback related information.

Frequency spectrum of normal EEG:

Hard questions unanswered from the mailing list

David Stasuk — Fri, 18 Apr 2008 08:58:36 Z

The mailing list seems to answer easy questions pretty well, but some of the more involved questions seem to go without answers a lot.

This is likely because the ones who really have the background to answer them seem to answer questions only infrequently. Understandable given the length of time the project has been running and the very limited bandwidth of the real experts.

I’d like to propose this page as a place where people with questions that have gone a while without an answer can place them, so that when the experts do get time to answer questions they don’t have to wade through all the chaff on the mailing list.

I would propose it work as follows:

The poster of the question who feels it has not been answered adds their question to this page.

Anyone who feels the list of hard questions hasn’t been looked at for a while may remind the mailing list and send a link.

When an answer to a question is made, send it to the list. Either the original poster, the answerer, or anyone who feels so inspired may move the question to a sister page of “answered hard questions” that can be created when the first one is done. (removing it from this page, and summarizing any intermediary discussion, of course)

—————————————————
Questions:

1)
It was posted quite a while back on the mailing list the procedure to chloride some raw silver to create a silver/silver chloride electrode surface for better signals.

If someone could find this in the mailing list and post it here. Thanks.

2)
What do people think about putting ferrite filters around our electrode cables to suppress H.F. noise, like they do for DC power supplies? I think some of the professional companies are already doing this.

3)
Would it be beneficial to connect the electrode cable shielding to the DRL, instead of to VGRD? and would this improve DRL stability? it would be similar to the cable guarding concept except instead of driving the cables with with the eeg signals, you would be driving them with your body ground offset.

4)
Joe Street’s active electrodes use batteries, I very much like this idea but am wondering how many hours he gets out of the batteries before he has to change them? Also as the batteries get lower will the signals just start to get progressively distorted or will they just cut out? How will I know when to change them?

Home Page

David Stasuk — Fri, 18 Apr 2008 08:23:14 Z

OpenEEG Wiki

Welcome to the OpenEEG Wiki. Because of spam this Wiki had to be password protected. The password has been posted in the mailing list. Please go here to edit anything on this Wiki. This Wiki is read only.

This Wiki is running Instiki.

Literature

Software

Hardware

Other EEG and Biofeedback Devices

User Projects, Tutorials and Web Pages

AboutOpenEEG

Sessions (Experiences and reports of Neurofeedback sessions.)

Hard questions unanswered from the mailing list

How to Edit this Wiki

Recently Revised (Requires password)

Operational Amplifier

David Stasuk — Fri, 18 Apr 2008 06:42:42 Z

For general information about operational amplifiers in general, see Wikibooks: Electronics:Op-Amps

We should list all the most important characteristics of the OpAmps here.

-Low voltage drift
-Low Bandwidth (we only want to amplify under 100Hz)
-Ultra high input Impedance
-Pica Amp Input Bias Current?
-A very slow slew rate? (maybe if there is a slow slew rate it would help in not amplifying High frequency signals)
-very low input offset voltage

My main question is what is the most important characteristic here?

I AM NO EXPERT, somebody please correct me if I am wrong about what I am talking about or improve upon what I am saying.

——————————————————————————

In particular, we’ve been using the INA114P, an “instrumentation amplifier” which includes 3 op-amps. The INA114P is the most expensive electronic part on the “modular EEG” board. (I think it’s even more expensive than the microcontroller).

We also use a few TLC277P op-amps.

New Design Guide for Instrumentation Amplifiers
http://www.futurlec.com/News/Analog/Design_Guide.shtml
A Designers Guide to Instrumentation Amplifiers – Second Edition, authored by senior design engineers Lewis Counts, design fellow and vice president of the Linear Products group, and Charles Kitchin, hardware applications engineer.
So, um, how exactly do I get a copy of this design guide ?

Electronic Parts

Anonymous Coward — Sat, 01 Mar 2008 17:23:28 Z

If you come across any electronic parts that may be interesting to the OpenEEG community, please add them here.

Microcontroller

Serial RS-232

USB

Analog to Digital Converter

Digital to Analog Converter

Operational Amplifier

Hardware

Anonymous Coward — Sat, 01 Mar 2008 17:21:22 Z

OpenEEG Hardware (Original OpenEEG hardware page)

HardwareReleaseProcess

ElectronicParts

AlternativeHardware

SoundCardEEG

LTC2449

Anonymous Coward — Sat, 01 Mar 2008 16:55:17 Z

The LTC2449 allows you to multiplex not only the ADC, but the amplifier as well.

8 channels
24 Bit
8 kHz sampling rate / 4 kHz multiplexing rate

http://www.linear.com/pc/productDetail.do?navId=H0,C1,C1155,C1001,C1152,P2474

Ralph Hilton suggested it:
http://sourceforge.net/mailarchive/message.php?msg_id=10364712

I have recently been working on a new GSR meter and came across a datasheet for a new chip which opens up the possibility of a considerable cutting in the cost of a multi channel EEG board. The device is an 8 channel ADC which allows the use of an external amplifier which it multiplexes. This means that instead of requiring multiple nalog boards a single board could handle 8 differential channels at a cost of maybe $50. Given the 24 bit resolution the amplifier need only be here to provide the necessary high impedance input. ven adding separate input buffers on each channel would only add $30. The chip is an LTC2449 available from http://www.linear.com and the suggested amplifier is an LT1368. A very low noise regulator is equired such as an LT1236. I don”t have the time to invest in the project at the moment but thought I’d post the data should anyone be interested in pursuing it. I can provide working C code (Atmel AVR) for interfacing an LTC2440 which is a single channel ery similar chip. It would just need a minor change for hannel selection.

Case Cabling

Anonymous Coward — Sat, 01 Mar 2008 16:34:25 Z

Open EEG? Case and Cabling

This document assumes that you have pre-assembled PCBs, and documents how they are placed in a case.

Required Parts

The case covering the analog boards should be made from a ferrous (magnetic material) because the biggest source of interference is the 50/60 Hz power line hum which is a form of magnetically induced interference. Aluminum cases are useless for shielding this type of interference. The cables could be and any metal shielded coaxial cable.

The following parts can all be obtained from an electronics store (except the warning)

A print copy of the OpenEEG WARNING Document .
Small metal case with internal dimensions of 100mm x 80mm x 20mm (this will contain the analogue PCB)
Large plastic case with internal dimensions of 130mm x 100mm x 120mm (the 130mm x 100mm needs to allow for the externals of the small metal case, and the 120mm allows for the small metal case + the mounting of 3 digital boards, in case you want to expand to that size someday, although these directions do not cover it). The case will probably need to be a little bigger to accomodate the internal side of the sockets, and the battery
A 9-pin serial cable (typically female on the end that plugs into the PC, male on the other end)
9-pin d-sub Serial socket (female, to plug into the above cable) and some wire (to connect it to the digital board)
34-pin IDC cable (PCB-to-PCB cable) (Someone said that this can be made by cutting a floppy drive cable down to size)
9V battery (not powerpack) and 9V battery clip
Some wire to cable up the electrodes (including DRL). I’m unsure what’s best here (certainly shielded), but I’ll try to find out [TODO]
3 [TODO: Type] sockets (to be mounted on the outside of the case for the electrodes)
Pinhead female sockets (see FAQ for details about pinheads, but note that you need sockets, whereas “plugs” are pictured in the FAQ):

Pins	Pieces
2	3
3	3

Preparing the Parts

Case

Metal case

Fit the cases with: [TODO: find out how the links go out through the metal case]

Plastic case

Fit the case with:

The 9-pin, d-sub Serial socket
The [TODO: Type] sockets for the electrodes and the DRL
Mounting points for the PCBs

Cabling

Hook the 9-pin Serial socket into the 3-pin Pinhead connector (using some wire). Hook the pins in the order RXD, TXD, GND1, so that the Serial pins of those names can be connected to the digital board pins of those names
Hook the 9V battery clip into a 2-pin pinhead socket
Hook the remaining two 3-pin pinheads to the [TODO: Type] sockets (for electrodes)
Hook one 2-pin pinhead to the remaining [TODO: Type] socket (for the DRL)
You have a 2-pin pinhead left for the Calibration hookup [TODO]

Joerg Hansmann posted some good instructions for assembling IDC ribbon cables. I
copied-and-pasted those instructions to the electronics wiki

(This document originally copied from http://openeeg.sourceforge.net/doc/SimpleEEG/CaseCabling.html )