Re: CurrentStatus, Re: question about safety testing
----- Original Message -----
From: Dhiya Mehdi <mehdi@...>
Sent: Thursday, January 04, 2001 4:03 AM
Subject: [buildcheapeeg] CurrentStatus
> Can you please give a summary of current status of eeg unit. Also,
> can we build this unit and where to get the latest design and software.
The latest _tested_ design is on the egroups buildcheapeeg server in the
It features 2 channels at about 40Hz bandwidth,
and less than 1 uV noise. Sampling rate is 256 Hz.
However it is not conforming with IEC601-1.
Some better design is under currently development.
The files are:
contains schematics and pcb-layout(160*100mm, single sided) in eagle-format.
(a free eagle demo version to view and print these files can be downloaded
contains c-sources and rom-file of the firmware for the AT90S4433 on the
Compiling the c-sources is optional and can be done with AVRGCC.
The rom-file can be flashed in the AT90S4433 with a freeware tool SP12
and a programmer-cable.
At the moment the only software on PC-side is "electric guru" from Rob Sacks.
However it is neither freeware nor shareware.
For experimental purposes I have written some basic routines for RS232 communication
with the RS232EEG and decoding the data stream. The language is C/C++ and the compiler
is djgpp (a DOS protected mode GNU-C compiler) and some libraries ("allegro" for
multichannel sound and graphics, "dzcomm" for RS232 under allegro).
> Dhiya Mehdi
> To unsubscribe from this group, send an email to:
----- Original Message -----
From: Max Kargl <max.kargl@...>
Sent: Wednesday, January 17, 2001 10:35 PM
Subject: [buildcheapeeg] Re: question about safety testing
> Note:the first part of this message is kept in german,
> as no project-related things are mentioned.
> Hi Jörg,
> 1) da ich jetzt endlich etwas Zeit finde, möchte ich gern an den
> Nachbau der EEG-Schaltung gehen.Dazu hätte ich folgende Fragen:
> a) welches der vorliegenden(Egroups ?) Designs empfiehlst Du?
Die oben genannten files der buildcheap-egroup.
> b) hast Du EINE günstige Bezugsquelle für ALLE Komponenten, vor
> Allem aber für INA114 (von Deutschland nach Östereich pflegt
> bis zu 40 DM Versandkosten zu berechnen!)?
Ist ja uebel teuer...
Ich habe einen Grossteil der Komponenten bei RS-Components
bestellt. Die muestten eigentlich auch nach Oestereich liefern.
> c) muß für die In-Circuit-Programmierung des Controllers das
> Design modifiziert werden,
Nein. Das ist bereits alles fertig vorgesehen.
Es wird die SP12-Programmer software benoetigt
(SP12 for Dos/Windows) und
ein Programmierkabel (lade ich gleich noch auf den e-groups server)
> welche Software ist verwendbar?
> d) Ist PC-seitig(Windows95,98,NT,Linux) schon irgendeine
> Software(Dll) vorhanden ?
> 2) Cheap Electrodes:
> As my grandfather bought a PCE-Trainer (standalone
> biofeedback-device,measuring ultra slow (brain) potentials)with a
> set of headband electrodes included,which I was told on request
> also used
> for EEG-measurements, it showed up that these are very simple made:
> the set consists of a 5cm rubber band which can be adjusted to fit
> any headsize.There are four 4 polished steel (nirosta) electrodes
> attached which are made of simple PRYM Snap-Buttons.On the
> outside the unshielded electrode cables which are bundled into
> a (bajonett-locked) 5 pin Din-Plug,can be clipped in.
> The set costs about 100 $ and can be easily rebuilt for about 5$.
> The electrode placement (for the purpose of ULP-measurement)
> is as follows 2 (GND)dorsal,distance about 10 cm at height of eyes,
> 2 ventral,same distance,at temple-height.
> I guess for the EEG-Amplifier the AGND electrodes would be
> to the ears (with clips).
No. VREF/2 would be correct.
> Contact to the skin is established by applying saltless
> (.Would it make sense to solder sheet silver to the electrode
> surfaces (and after that,chloriding them) for better results ?
> (.By the way,the cheap one-way electrode set (3M) of the same
> distributor is ment for EKG usage only.
> (.Also by the way- As the units case is sealed with superglue,
> I won't be able to take an analyzing glimpse at the circuit
> for the time it is under warranty (6 months), although I am
> to learn some secrets of DC-measurement.
> 3) This point has also been discussed (but not answered) in the
> brainmaster newsgroup:
> Have you ever thought of using the pc's soundcard
> as high quality (16 Bit !) AD-converter ?
> I can imagine several obstacles:
> (a optical insulation would have to deal with analogue signals.
That can be done with 2 optoisolators (one as reference) and a feedback loop
to linearize the response of the optoisolator.
> (b don't know how much aditional noise will be produced.
> (c input decoupling of the soundcard could cut off low frequencies.
A simple time multiplex encoding could be used, realized with a counter
and a analog multiplexer. The multiplexer would scan through some
reference voltages (e.g. AGND, VREF) and then through the channel
; a sync signature:
; the eeg-channel data framed by reference voltages:
this pattern of 16 voltages would be repeated e.g. 256 times per second.
However the output of the soundcard would have to be decoded
by software. The minimum sample-frequency for easy decoding
should be minimum 4 times the data rate(256Hz*16 Voltages),
that is 16384 Hz.
> (d As far as I understand (most?) SCs have a minimum
> adjustable sample frequency of about 8kHz,
> so maybe one would have to take only samples of the sample.
With the method mentioned above that would be no problem.
> (e the only DLL I know offers only a call which can not
> execute in the background.There exist several
> programs(shareware), which utilize the soundcard as realtime-
> oscilloscope but without sourcecode...
> I guess one would need some DMA-Coding(of which I have no idea)
> (f I don't think MS-DirectSound supports the required tasks.
Why not ? AFAIK direct sound can sample into a buffer and tells you
when it is full. Then the buffers are switched and you can analyse the