From: Joerg Hansmann (info_at_jhansmann.de)
Date: 2001-05-28 15:47:17
Hi,
----- Original Message -----
From: Sajith Goonesekera <sajith_at_magix.com.sg>
To: <buildcheapeeg_at_yahoogroups.com>
Sent: Monday, May 28, 2001 2:13 AM
Subject: Re: [buildcheapeeg] Help
...
> I have divide the 5V into half using two 2.2k and get 2.5V
> My Vref/2 is 2.5V
That is ok.
> > There have been a few inconsistencies: I have mixed up TLC272 and
> > OPA2350.
> > TLC272 can be used for all op-amps.
>
> I have used TLC277 instead of TLC272 (I believe it is better than TLC272)
I will take look at the datasheet.
...
> I want to connect it to my brain and measure the singles. How do I do that.
The RS232EEGanalog03 schematic does not provide any optical
isolation (isolation would be done on the digital board by optoisolators
and by using batteries).
So if you power the circuit with a laboratory power supply
and / or connect an oscilloscope ground to AGND or vref/2
you will have _no_ protection against isolation failures or PE-failures.
In worst case if you connect yourself via electrode to the amplifier
this might result in killing yourself.
So be very careful !
A workaround for laboratory testing could be to power the oscilloscope
with an isolation transformer and to use batteries for the amplifier.
If you want to measure real brainwaves, you need EEG-electrodes
(and conductive gel) that give sufficiently low impedance (<10kOhms).
Basically you connect a part of the body that is relatively far away from
where you want to get the signals (e.g. Right leg or right hand ) to R_LEG.
Then you choose the referecence potential (often right and left earlobes connected
together) and connecet it to CH1- and CH2-.
Finally you choose two points of interest from the 10/20 map (e.g. O1, O2) and
connect them to CH1+ and CH2+.
To minimize interference you should use shielded cables for Ch1 and ch2 and
connect the shield single sided to the appropriate shield driver output.
Make sure, that the shield driver outputs _never_ get in contact with
ch2+, ch2-, ch1+, ch1- .
Regards
Joerg
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