From: Jim Meissner (jpmeissner_at_mindspring.com)
Date: 2002-01-18 05:29:37
Dear Moritz:
I know you addressed this to Andreas, but I have taken an interest in getting this project moving so I am putting in my two cents worth.
> Your design looks pretty cool. But I think you left some of the problems
> (the ones why the modulareeg isn't ready for use yet) unaddressed.
> These are, from my point of view:
> - optoisolation
> - power supply (battery ? DCDC ?)
> - INA-amplifier failure protection for the user (input connected to supply)
You must not be following the traffic here. A lot, if not all of this has been addressed.
For your information, I built a brain monitor and used it for 10 years doing altered consciousness research for my Brian State Synchronizer project. I have listed some of the schematics and source code and actual brain wave data on my website www.MeissnerResearch. Take a look at the input stage protection and the opto isolator.
Optoisolation: I have seen this subject batted around for weeks, maybe months.
I have put in my two cents and attempted to find a consensus to get some forward movement. The design that Andreas has come up with, addresses all the issues very well. The design is not the cheapest, but it should work without a lot of fussing. Later during the redesign, cost cutting can be looked at. My priority would be to get something that works first. His designwill work at 112 K Baud using an optical fiber transmitter and separate receiver coupled with 2 inches of fiber optic. This should easily pass the 5,000 volt breakdown and leakage requirement.
Power Supply: Joerg and I have been talking about this. My statement was that all the low cost EEG machines that I know, use batteries. Joerg stated that he did not like batteries. My suggestion is to use batteries unlessJoerg can find a "safe" DC/DC inverter. I am providing some help to him in that quest. I have used safe isolated power supplies in the past, but they were not cheap. Rather than to hold up the project, there should be a choice, batteries - or - isolated power supply. Andreas is using batteries.That could change depending on what Joerg finds.
INA amplifier failure: I am not convinced that this is a "real" problem. I would be interested to hear why you think it is. I can think of several solutions if they were to be needed.
Take a look at my input stage. If you protect the amplifier from ESD it isnot likely to fail in the mode that you are stating. In 10 years I have not seen this type of failure. Even if it did fail, at 6 volts there is no danger to the patient. I know that Joerg has spent a lot of time working on this. If you put in a large resistor to limit the current, the noise goes up. Andreas and I talked about this quite a bit and during his searchinghe found a wonderful INA amp from Linear Technology that has built in ESD protection diodes. With the additions of a small external resistor the ampwill be safe from any anticipated ESD.
I think Andreas should be applauded for the fine work he is doing! I am very impressed with his fast turn around and up dating of schematics and a great looking PC board layout.
Juergen P. (Jim) Meissner
Check out my Website at www.MeissnerResearch.com
Read about the benefits of the Brain State Synchronizer sounds for improving your life and health.
----- Original Message -----
From: Moritz von Buttlar
To: buildcheapeeg_at_yahoogroups.com
Sent: Thursday, January 17, 2002 11:19 PM
Subject: Re: [buildcheapeeg] New schematic and layout
Hi Andreas !
Your design looks pretty cool. But I think you left some of the problems
(the ones why the modulareeg isn't ready for use yet) unaddressed.
These are, from my point of view:
- optoisolation
- power supply (battery ? DCDC ?)
- INA-amplifier failure protection for the user (input connected to supply)
Joerg's working first design, the RS232EEG, has better security features as
far as I can see.
Also, your design is quite expensive in comparison and more difficult to
build for the electronics novice.
But I like the small size very much :)
Maybe we could make a 3-Stage-modular-design consisting of the following
stages:
- analog amplifier
- adc and uC
- communication/power supply/isolation
Then we could design various modules which can be combined like everybody
wants:
Andreas tiny amplifiers with modularEEG adc/uC and somebody elses IrDA
interface
What do you think ?
Moritz
---------------------------------------------------
Moritz von Buttlar
Flash uC/DSP Development http://www.baltic-microsolutions.de
Free EEG Design http://openeeg.sf.net
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This archive was generated by hypermail 2.1.4 : 2002-07-27 12:28:36 BST