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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
      Hi,

      ----- 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:
      rs232eeg_eagle_brd_sch_001021beta.zip
      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)

      rs232eeg_firmware_c-sources_010105.zip
      contains c-sources and rom-file of the firmware for the AT90S4433 on the
      RS232EEG-board.
      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
      http://www.xs4all.nl/~sbolt/e-spider_prog.html#programmer
      (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.

      None.

      > (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
      outputs.
      e.g.

      ; a sync signature:
      AGND
      VREF
      AGND
      VREF
      ; the eeg-channel data framed by reference voltages:
      CH1
      AGND
      CH2
      VREF
      CH3
      AGND
      CH4
      VREF
      CH5
      AGND
      CH4
      VREF

      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 ,

      Joerg
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