From: Joerg Hansmann (info_at_jhansmann.de)
Date: 2001-05-28 00:34:49
Hi,
----- Original Message -----
From: Sajith Goonesekera <sajith_at_magix.com.sg>
To: <buildcheapeeg_at_yahoogroups.com>
Sent: Sunday, May 27, 2001 5:53 PM
Subject: [buildcheapeeg] Help
> Hi
>
> I have build the EEG circuit.(only the analog part)
Congratulations !
Did you make a pcb ? (If yes, please post the the *.sch and *.brd file for review)
Or did you use manual wiring ?
> Do I need a proper Prob to capture the EEG signal
You can make basic tests by using the calibration voltage output pad4 and pad1.
However the calibration voltage is produced by the AT90S4433.
To simulate this signal you only need to connect TTL (0..5V) 10Hz source
to X1 pin 2.
Connect ch1+ and ch1- to pad4 and pad1. Do the same with ch2+ and ch2-.
You should now get a 0.4Vpp rectangle-wave signal (some distorsions due to
butterworth filter) with a DC component of Vref/2 (2V) at ADIN0 and ADIN1.
If you get other AC voltages, you should adjust the gain of each channel with P1 and
P2.
For further tests see attached *.sch file.
The part designations are according to :
http://www.biosemi.com/publications/artikel3.htm
> My ref Voltage is 2.5V is it ok
Were did you measure it and how did you generate it ?
Normally Vref/2 is generated on the digital board and should be 2V.
Vref is 4 V.
> (I have build "rs232eeg03analog.sch")
There have been a few inconsistencies: I have mixed up TLC272 and
OPA2350.
TLC272 can be used for all op-amps.
OPA2350 has lower noise , higher gain*bw and has true rail to rail. But I suppose
that it is more expensive and harder to obtain than TLC272. For 10 bit resolution
it is not really necessary.
...
----- Original Message -----
From: Sajith Goonesekera <sajith_at_magix.com.sg>
To: <buildcheapeeg_at_yahoogroups.com>
Sent: Sunday, May 27, 2001 7:06 PM
Subject: Re: [buildcheapeeg] Help
...
> Any body know the purpase of Right Leg Drive (RLD)
It is to reduce Vcm (see http://www.biosemi.com/publications/artikel3.htm )
and thereby to enhance common mode rejection.
Regards
Joerg
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