Re: [buildcheapeeg] I published current design at SourceForge

From: Doug Sutherland (
Date: 2001-11-29 21:35:18

Hi guys,

Jim just mentioned that he has a working EEG, and we've
been talking about that and other low-cost EEGs over on
the MIND-L list at yahoo. I've been looking at as many
plans/schematics as I can find. I too am keep on the
idea of low cost EEG. So far I have looked into the

1) I have the brainmaster build specification, which
are based on the 68HC11EVBU eval board, AD620
instrumnetation amps, and OP90 op-amps. This is
an interesting schematics, but the 68HC11EVBU
boards are not easy to find. There used to be
firmware and software for this that was freely
available, but that doesn't appear to be public
anymore. The frequency response for the homebrew
brainmaster EEG is 1.7-34 Hz, sampling rate is
120 Hz, and CMRR is around 100 dB.

2) The old HAL-4 design in no longer available,
but it was pretty severely limited with band
width of 4-20 Hz and sampling rate of 64 Hz.

3) Jim has achieved results far superior to all
other low-cost EEGs I have seen, band width
is 0.1-100 HZ with sampling at 120 Hz. This
is better than all of the low-cost EEGs I
have seen including commercial ones like
WaveRider, Brainmaster, POD, etc.

4) I found some really interesting specs on the
biosemi web site. There is a schematics for
an EEG that uses just 3 op-amps, 6 resistors,
and 2 capacitors per channel. This design
yields band width of 0.2-40 Hz and has a
CMRR of 136 dB.

5) The 555-timer based design is interesting, but
my concern is that timing/interrupts are a big
issue (must be DOS only to disable interrupts).
I am wondering what the band width of this
design is (frequency response in Hz) and what
the CMRR looks like. Anybody know?

I like the idea of a low-cost EEG, but there is a
line somewhere where real usability becomes an
issue. There is some useful data at 1-2Hz and
also around 40Hz. The only low-cost designs that
I'm aware of that can deal with those ranges are
the Biosemi design above and Jim's design which
is based on 68HC11 with just op-amps for the
imput stages. I too am planning a low-cost EEG.
I definitely want better frequency response than
WaveRider and Brainmaster based on 68HC11EVBU.
I'd like to push the sampling rates and ADC
resolution a bit higher too if possible. I
found this page interesting, it describes the
IFCN clinical standards:

For acquisition and storage of EEG data “IFCN Standards”
recommend a minimum sampling rate of the analog to digital
conversion (ADC) of 200 samples/second (Nuwer et al 1998).
This rate allows to analyze frequencies up to 100 Hz, as
the maximal allowed frequency of the input signal (the
Nyquist frequency) should be the half of sampling rate. If
the signal is sampled at too low rate, aliasing
(falsification of the signal) may occur with unpredictable
errors in the digital waveform compared to the original
one. Prior to sampling an anti-aliasing low-pass filter
must be used. ADC should be done at a resolution of at
least 12 bits in order for the EEG to be resolved down to
0.5 µV. Whenever possible, the low-pass filter should be
set to 0.16 Hz or less for recording. Routine use of higher
settings of this frequency for recording are discouraged,
as they should be reserved for specific or difficult
clinical recordings only. A 50-60 Hz notch filter should
be available, but not routinely used. Interchannel cross-
talk must be less than 1%, i.e., 40 dB down or better.

I'm not sure close one can get to the above with a
low-cost design, but my goal is to get as close to
that within reason while keeping the parts cost low.
I've been collecting a bunch of info on biofeedback
and neurofeedback, here's my collection of links
below, some of the tech info is very useful.

-- Doug

Electroencephalograph (EEG) Schematics
Amplifiers for bioelectric events: a design with a minimal number of
A Low-Noise, Low Power Multichannel Amplifier Design
Brainmaster EEG Build Schematics
EEG preamp, anti alias filter and isolation circuit
Two-channel data logger for quantitative EEG recording while driving
The OpenEEG Project
ComADC Serial EEG Schematics
Design of a multi-purpose biofeedback machine
How to Build a Lie Detector, Brain Wave Monitor and Other Secret
Parapsychological Electronics Projects
HAL-4 Home Page
HAL-4 Manual

HAL-4 Usenet Newsgroup

Electrocardiogram (ECG) Schematics
Scientific American: Home is where the ECG is
Texas Instruments ECG Schematic
ECG Amplifier with Right Leg Drive

Lego Mindstorms ECG Sensor
Heartbeat Transducer Schematic
ChipCenter Question: Heart Monitor
EKG Happy

Electromyrograph (EMG) Schematics

Self Contained Electromyograph

Galvanic Skin Response (GSR) Schematics
E-Meter GSR Meter Schematics
Huidmeter GSR Schematics
Lego Mindstorms Galvanic Skin Response Sensor
Lie Detector Circuit (GSR)
Simple Lie Detector (GSR)

Respiration Monitor Schematics
Venthesizer Respiration Monitor

Electrotherapy Schematics
Cranial Electrotherapy Stimulator
Muscular Bio-Stimulator
Transcutaneous Electrical Neural Stimulator
Electromagnetic Field Measurement Circuits

Other Miscellaneous Schematics
Digital Step Pedometer Schematic
Float Tank Construction Plans

Parts for Biopotential Measurements
Analog Devices AD620 Instrumentation Amplifier
Burr-Brown INA121 Instrumentation Amplifier
Burr-Brown INA322 Instrumentation Amplifier
Burr-Brown INA331 Instrumentation Amplifier
Burr-Brown INA126 Instrumentation Amplifier
Burr-Brown INA155 Instrumentation Amplifier
Burr-Brown INA156 Instrumentation Amplifier
Burr-Brown INA2126 Instrumentation Amplifier
Vernier Instrumentation Amplifier
Vernier Sensor Interfaces
AnyWear Sensor Interfaces
Prairie Digital Data Acquisition Modules
Thermochron Temperature Logging iButton
PicoTech PC Based Oscilloscopes

Low Cost Neurofeedback Systems
Aleph1 EEG Analyser FM515
Neurotrader Used EEG Equipment

Biofeedback Sensors and Monitors
Neuromedical Supplies Online Catalog
QuickCap EEG Positioning System
Biosemi Active Electrodes
Vernier EKG Sensor
Vernier Exercise Heart Rate Monitor
Vernier Respiration Monitor Belt
Double Differential Surface EMG Pre-amplifier

Wearable Polysomnograph
SmartShirt Sensors
VivoMetrics LifeShirt
Medical Shoe: Biofeedback Shoe Inlay
FitSense Speedometer
ProActive Heart Monitors

Biopotential Measurements Theory Articles
Amplifying, Digitizing, and Recording the EEG
Principles of Electricity and EEG Data Acquisition
The Measurement, Interpretation, and Use of EEG Frequency Bands
Biofeedback from EEG frequency bands
EEG Recording
Acquisition and Signal Analysis in Pharmaco-Electroencephalography
A Guide to Electrode Selection, Location, and Application for EEG
Scalp electrode impedance, infection risk, and EEG data quality
Real Time Holter Monitoring of Biomedical Signals
High Quality Recording of Bioelectric Events: Interference Reduction
The Isolation Mode Rejection Ratio in Bioelectric Amplifiers
Low-cost Active Electrode Improves the Resolution in Biopotential
Lightpowered Active Sensor System with integrated Signalprocessing
Patient Isolation in Multichannel Bioelectric Recordings by Digital
through a Single Optical Fiber
The configuration of the power supply in multichannel battery-powered
for biopotential recordings
A wireless infrared link for a 16-channel EEG telemetry system

Case Study of an Intelligent ECG Monitor
Ground-Free ECG Recording with Two Electrodes
The Galvanic Skin Response (GSR) Meter
Instrumentation Amplifier Designer's Guide

Grounding for High Speed Systems
Resources for Sensors, Measurements, Instrumentation and related

Digital Signal Processing Theory Articles
The Scientist and Engineer's Guide to Digital Signal Processing
An Introduction to Fourier Theory
A Tutorial on Fast Fourier Transforms
The FFT Demystified
Fast Fourier Transforms
FFT Convolution
FFTW C Subroutine
Public Domain FFT Code
The Wavelet Tutorial
Amara's Wavelet Page
Recursive Filtering
MathTools Java Filtering
Filtering Classes and Functions
Signal Processing Information Base
Some general concepts of signal treatment applied to Clinical
Window-Synced Filter for EEG Spectral Analysis
Quadrature Filtering for Real-Time EEG Feedback
Fast Fourier Spectral Analysis of Human Emotions

Biofeedback and Neurofeedback Related Articles
What is Biofeedback?
EEG Biofeedback FAQ
EEG Biofeedback General FAQ
EEG Biofeedback Myths
EEG Manual
Quantitative EEG and Neurotherapy Fact Sheet
Practical Issues Concerning EEG Biofeedback
Functional Map of the Brain
The Scientific Basis of Neurofeedback Training
A Study of Recent Advances in Electroencephalography

Biofeedback for Meditative States
A similarity approach to the analysis of brain wave patterns
Research on Sensing Human Affect
Controlling Computers with EEG Signals
Input/Data Acquisition System Design for Human Computer Interfacing
On Designing a Brain-Computer Interface
A brain-computer interface for playing "Pong"
Hands-Free Computer Access For The Severely Disabled
EEG Biofeedback for Attention Deficit Disorder
EEG Biofeedback: A New Treatment Option For ADD/ADHD
Neurofeedback for ADD/ADHD and Learning Disabilities
Patient-Directed Neurofeedback For ADHD
ADD/ADHD Biofeedback Home Training

Neurofeedback and Substance Abuse Theory
ECG Library

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