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eye movement amplification

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raviram87

New Member
hello people...

am working on a biomedical project that delas with the amplification of signals generated by eye movements... To record these signals we position electrodes at various points on the user.. (diagram is attached below)...

as u can see in the diagram there is a reference electrode on the forehead... i use a AD620 instrumentation amplifier.... i connected this reference electrode to pin #5 (reference pin) of AD620.... this amplifier is then followed by low pass and high pass filters....

I supply power from a DC power supply unit that has +12, -12 and 0 points... certain points in the filter need to be connected to the ground... should i connect them to 0 point in my DC supply??? i often expereience a minor shock when i use the system.... pls help me...
 

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  • eogelec.JPG
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raviram87

New Member
i do sir.... infact i even isolated the power supply ground and the reference electrode... but still am not getting favourable results...

my system consists initially of AD620... this pin number 5 has been connected to reference pin.... this is followed by a 4th order low pass and high pass bessel filter (active).... i have used sallen-key topology for this...

some points in this filter have to be connected to the ground... these points were connected to the 0 point in my DC supply, which is not connected to the reference electrode at all....
 

raviram87

New Member
if u see the attachment below.... one electrode on the head (below the ear) has been connected to the ground....

if u see the schematic, some points (say the first low pass filter) have been also been connected to the ground....

how do i differentiate between these two grounds? i cannot short them....
 

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  • eyemouse2.gif
    eyemouse2.gif
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Hero999

Banned
I haven't studied your circuit in great depth.

Howver I asseme, that the problem is your circuit is applying up to 24V to a very sensitive part of the body.

Are you amplifying just the AC signals or do you want DC?

Get some op-amps that will run on as lower voltage as you possibly can and (assuming it's just AC you're talking about) fit some AC coupling capacitors to the input pins.

I'm sure I've told you this before but it might have been someone else.
 

Hero999

Banned
Lol, that's got to be fake. :D
 
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