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Re: CurrentStatus, Re: question about safety testing

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  • Joerg Hansmann
    Hi, ... From: Dhiya Mehdi To: Sent: Thursday, January 04, 2001 4:03 AM Subject: [buildcheapeeg]
    Message 1 of 1 , Jan 21, 2001

      ----- Original Message -----
      From: Dhiya Mehdi <mehdi@...>
      To: <buildcheapeeg@egroups.com>
      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
      file area.
      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
      from www.cadsoft.de)

      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:
      > buildcheapeeg-unsubscribe@egroups.com

      ----- Original Message -----
      From: Max Kargl <max.kargl@...>
      To: <buildcheapeeg@egroups.com>
      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
      > man
      > 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
      > Board-
      > 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
      > rudimentäre
      > Software(Dll) vorhanden ?

      siehe oben

      > 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
      > was
      > 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
      > attached
      > to the ears (with clips).

      No. VREF/2 would be correct.

      > Contact to the skin is established by applying saltless
      > electrode-gel.
      > (.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
      > eager
      > 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 ?

      Yes. ;-)

      > 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
      buffer contents.

      Regards ,

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