From: sleeper75se (sleeper75se_at_yahoo.se)
Date: 2001-12-17 06:59:21
--- In buildcheapeeg_at_yahoogroups.com, "dremelz" <dremelz_at_yahoo.com> wrote:
Hi Jeff, welcome to the group!
> Hi,
> Well, I have a raging sinus infection and my wife and two kids (son
> 4yrs old and daughter 6yrs old) have gone on to church without me.
> So, there is an opportunity of making this extended post this
morning!
Sorry to hear that, but its great you see positives where there's
negatives!
Your post brings up many interesting topics, but due to time and space
restraints (! :-) I will only reply on a couple of those. No doubt,
others in the group will respond on other parts.
> While on the subject of electrodes, the more recent brainmasters
> appear to use .060" (1.5mm) Shrouded Rib-Loc Tip Plugs mounted
> through the chassis.
Hmm, have you any idea what other makers are using? If we choose a
connector that is common, we can keep costs down... (though it's easy
to solder whatever connector you fancy)
> Being able to run for 8 hours with the BrainMaster makes it easy to
> use the EEG for several sessions before having to recharge the
> battery. The BM is able to run this long due to the low power
usage
> of the microprocessor that was chosen, the Motorola HC11 which, in
> circuit, only uses 30-50 milliamps of power (this is now almost
What's being used now, a microcontroller from Atmel, draws some 10 mA
at 7 MHz, so we have every opportunity to be better than the BM.
Quick estimate: suppose the design draws 40 millamps (that is not a
wild guess, the actual figure is probably lower.) and we use four
1.5V batteries with 18000mAh capacity. (Duracell long lasting LR20/D,
costs $3 apiece). We could run our little gizmo for 450 hours
straight for only 3 cents/hour. Wouldn't that be neat? :-)
> Joerg's design using the 6N139 allows for lower power consumption
and
> the 6N139 provides a high degree of isolation. In addition, it is
> hard to go wrong with choosing a serial interface design even
though
> it may not be "cool" technology.
I agree, serial port + optocoupler is ideal for our purposes. There
is one problem here: We don't know if 6N139 is good enough for IEC
601 (medical safety) certification. It has not been tested, as
required, with 5000V during 10 seconds (or has it?!). Reading one of
the certificates
(http://www.fairchildsemi.com/ms/SC/SC_C1027742.pdf), one sees that
is does withstand 3000V for one minute, perhaps that is sufficient.
Hospitals use these devices 24h a day, while home users can choose to
turn them off if there's a lightning storm.
> Regarding the above topic. It is easy for me to waltz into this
> group and make these sweeping observations/suggestions; however, I
> recognize that I have contributed nothing. I have not done the
work,
> interacted, compromised, etc. This project started on the back of
> Joerg's design and he has patiently endured all the debate, second-
> guessing, etc. Thank you Joerg. I have enjoyed having the
> opportunity to learn from what you have done. Now, having said
that,
> as a newbie (don't you just love it when a newbie raises a ruckus--
> can't newbies get away with allot!) I am going to drop the battery
> power bomb in your lap!
I have to confess I've done my share of waltzing... so I second you:
Thanks Joerg!
> I am currently ready to etch the Brain Tuner board. However, after
> continuing research, I am beginning to suspect what Jim Meissner
> wrote over in the Mind-l mailing list, i.e. :
>
> >The original BT5 by Bob Beck was "loosely" based on some
research
[snip]
> > the power to get the effect. Ultimately it just became a very
> > painful shock machine. My impression is that they were burning
> > out some of their neural circuits and becoming desensitized.
>
> Any comments?
Yes, one comment: Ouch! There has to be better ways.
> I am also curious if anyone is interested in contrasting the
OPENEEG
> amplifier pros/cons with Brainmaster pros/cons (i.e., w/the newer
> SuperInput). I know that Joerg's design (thank you Joerg!) has
high
Yes, I am. According to Jim Meissner, the impedances can rise to a
megaohm during deep mediation, which would cause a significant drop
in amplifier gain if the input impedance is 10Mohm. However, that was
for a gifted medium, I believe. I'm just trying to learn to
meditate...
> impedance in a middle stage and he has explained that it gives the
> benefit of high common-mode rejection and it also has an active
> shield and right leg electrode driver. So, both the Brainmaster
and
> the OpenEEG have good CMRR, but how does an unsophisticated high
> impedence input (i.e., Brainmaster) compare to a lower impedance
> sophisticated input (i.e., with active shield and leg driver). The
> subsequent stage(s) might also need consideration to be able to
fully
> comprehend how the systems compare in totality. I am an electronics
> novice with limited understanding. It would help if someone could
> just boil it all down to what it means practically.
> Such as BM's claim that dry electrodes can be used with their
product
> (is that really a practical claim?).
A lot of my knowledge in this area comes from Biosemi.
They make a short statement here:
http://www.biosemi.com/faq/without_paste.htm
They boil it down to this: No.
Comparing other features: The shield driver helps improve signal
quality and (again according to Biosemi) the right leg driver makes
it superior in suppressing common mode signals.
Basically the OpenEEG design should be better than the old BM design.
It does not beat the new super-input's impedance, but if that has any
practical implications... I don't know.
> I am really curious to know what amps and design they are using.
They are most likely just using a simple $3 instrumentation amplifier
without the highpass-filter stage Joerg designed. Benefit: High
impedance. Drawback: Can be dangerous if the amplifier fails. The
brainmaster is, as I understand it, originally a hobby/research-
project. Since they wanted to keep costs down, they did it the cheap
and simple way. Now, a few years later, we can do it better, but
still cheap and simple.
> Also, perhaps I can contribute in a small way here; however, I move
> rather slow in my hobbies with two little kids in the house!
You can at least give us ideas! :-)
Be well,
Andreas
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