Re: Active Electrodes

Hey, 



All electrode cables, active or passive, are to be shielded, I thought. 

----- Original Message -----
From: "tonio112003" <[email protected]> 
To: [email protected] 
Sent: Thursday, January 3, 2013 9:24:30 AM 
Subject: [Openeeg-list] Active Electrodes 

Hi! 
I work in the lab of the university with 
2 different ModularEEG (Olimex) with 6 
Channels (6 electrodes) and one common 
DRL electrode (I use BCI2000 software 
to work with the measured signals). 
One of them works fine with passive 
electrodes and XLR-sockets so we started 
to build another one with active 
electrodes so we could compare them. 

What we did with the stereo plug 3.5mm 
of the active electrode (Olimex), was 
connecting the point to +5V, the middle 
part to ground( and the last part to 
get the signal. 
We did so because that was what we 
interpreted from the documentation in 
the website 
https://www.olimex.com/Products/EEG/Electrodes/EEG-AE/, 
I am not sure yet if was correctly done. 
The +5V and the ground come from a 
external power source. The last part 
of the plug is directly connected 
to the pin +(positive) or -(negative) 
of every channel. 
Every Channel has 3 pins, the middle 
pin (let´s call it Ground/Shield Pin) is 
intended to connect the shield of the cable. 
We use that pin with the EEG with passive 
electrodes but we don´t use it at all 
for the one with active electrodes. 
That´s because I read that the active 
electrodes don´t use shield. 

Active Electrodes: Is it correct the 
connection we made for the active electrodes? 

Ground/Shield Pin: For our EEG  with 
passive electrodes, we connect the 
shield of the cable of the electrodes 
with the Ground/Shield Pin in the board. 
But, that pin is not connected to anything 
in the analog board neither connected 
with other Ground/Shield Pins. Every 
Ground/Shield Pin is in the air. 
Should we connect all the 
Ground/Shield Pins together and 
connect a cable to real 0V ground? 


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