On 26/01/2011 13:40, V G wrote:
> Honest question here. At what point did I say I'm going to directly
> hook up electrodes from my computer to my chest hmm?
you would not want 12V battery connecting direct to chest electrodes.

your "earth" needs isolated from PC.

Something with electrodes needs total isolation (more than 400v) with=20
known low leakage current and its battery or other power source unable=20
to supply current to the electrodes.

Any Website advice using ordinary opamps, non-intrinsic medical standard=20
isolation etc wants to be taken with a pinch of salt.

Googling
    isolated Instrumentation amplifier Analog Devices application note
first 4 hits gives
http://www.analog.com/static/imported-files/tutorials/MT-061.pdf

http://www.analog.com/static/imported-files/tutorials/MT-071.pdf
first page
ANALOG ISOLATION TECHNIQUES

There are many applications where it is desirable, or even essential,=20
for a sensor to have no direct
("galvanic") electrical connection with the system to which it is=20
supplying data. This might be in
order to avoid the possibility of dangerous voltages or currents from=20
one half of the system doing
damage in the other, or to break an intractable ground loop. Such a=20
system is said to be
"isolated", and the arrangement that passes a signal without galvanic=20
connections is known as an
isolation barrier.

The protection of an isolation barrier works in both directions, and may=20
be needed in either, or
even in both. The obvious application is where a sensor may accidentally=20
encounter high
voltages, and the system it is driving must be protected. Or a sensor=20
may need to be isolated from
accidental high voltages arising downstream, in  order to protect its=20
environment: examples
include the need to prevent the ignition of explosive gases by sparks at=20
sensors and the protection
from electric shock of patients whose ECG, EEG or EMG is being monitored.


http://www.analog.com/en/amplifiers-and-comparators/instrumentation-amplifi=
ers/products/index.html

http://www.analog.com/en/circuits-from-the-lab/CN0067/vc.html

I'm sure ADI has a COMPLETE reliable application note that does exactly=20
what you want. Instead of a random person on Internet who obviously has=20
no clue about ECG, EEG or EMG applications or good designs for low=20
frequency high common mode and isolation.





--=20
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist
.