From: Jim Meissner (jpmeissner_at_mindspring.com)
Date: 2002-01-09 22:10:00
Dear Joerg:
> Check this out with the chief engineer Joerg Hansmann.
> I do not feel as a chief engineer at all, for this position
> I simply do not have enough experience and knowledge nor
> the required leading qualities ...
Sorry, but you are listed as the chief engineer on the webpage! Get used to it.
Please read the note I sent to Andreas about the offset question. If the offset is really 60 mv and not 60 microvolts, then you should not mix electrodes! The diff. amp should cancel the offsets of similar electrodes.
The original BrainMaster solved this by using 10 nf capacitors between the electrode and the diff amp. with 10 meg to ground. The Mind Mirror is alsoAC coupled.
This would also solve your fear of diff amp failure and putting power supply voltage to the head. I do not share your fear on this issue. Even 12 volts on the electrodes is hardly noticeable. ( you still need the opto isolation for the 10 micro amp leakage spec )
> Electrode offsets can easily result when combining different electrodes
> (my electrode supplyer LAZINA told me, that some people really
> combine different types) or when the Chloride skin of AgCl type
> electrodes wears off.
My memory of this goes back 15 years and is not too clear. I thought you are supposed to re-chlorinate the electrodes every night!
> Some electrode experts here, who know about electrode offsets ?
You have a good question! I do not have the answer. I built my own electrodes, but I am not an expert. I was just too cheap to buy these expensive medical things. I stole the Mind Mirror electrode idea. They used nickel plated buttons with conductive paste mounted in a female snap ( same as on a 9 volt transistor battery clip ). After a few cleanings they are brass buttons. I didn't know I was supposed to have offset problems.
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: Joerg Hansmann
To: buildcheapeeg_at_yahoogroups.com
Sent: Wednesday, January 09, 2002 11:54 AM
Subject: Re: [buildcheapeeg] New input stage
Hi all,
----- Original Message -----
From: Jim Meissner <jpmeissner_at_mindspring.com>
To: <buildcheapeeg_at_yahoogroups.com>
Sent: Wednesday, January 09, 2002 1:31 PM
Subject: Re: [buildcheapeeg] New input stage
...
> Check this out with the chief engineer Joerg Hansmann.
I do not feel as a chief engineer at all, for this position
I simply do not have enough experience and knowledge nor
the required leading qualities ...
[many important points snipped due to a lack of time]
...
> Opinion: The U1 gain could be set much higher and U3 lower.
> Also U1 has half the noise at a G = 100 vs. G = 10.
For low noise high gain in the first stage is good, but not for
electrode DC offsets. (saturation of the input stage)
Therefore I have used INA114 with G=10 (according to the application
example in the INA114 datasheet for an ECG monitor ).
At gain=10, the INA114 seems to be superior to the lt1167.
Electrode offsets can easily result when combining different electrodes
(my electrode supplyer LAZINA told me, that some people really
combine different types) or when the Chloride skin of AgCl type
electrodes wears off.
I have assumed that 100mV DC electrode offset should be handled by the input
stage. But maybe I was overly cautious.
Some electrode experts here, who know about electrode offsets ?
Regards,
Joerg
Yahoo! Groups Sponsor
ADVERTISEMENT
To unsubscribe from this group, send an email to:
buildcheapeeg-unsubscribe_at_egroups.com
Your use of Yahoo! Groups is subject to the Yahoo! Terms of Service.
This archive was generated by hypermail 2.1.4 : 2002-07-27 12:28:36 BST