[SOLVED] EEG using my laptop sound card

hello everyone
i am planning to make an EEG for my graduation project "control based on brain computer interface" (for example controlling a wheelchair using brain waves)so as i was doing my research i found that i can use my PC sound card as interface with PC instead of using A/D and RS232 i guess but i'm not sure how it works but i didn't understand how it works and if it is possible to do it?and if anyone have any site that provide an explanation for how it works i'll be very grateful
EEG:!:

The first problem you will discover is that most sound cards have not just AC coupling but actually highpass filters on the inputs that will not alow "brainwave" frequencies into the sound card.

The solution to this problem is actually very old when DC amplifiers were incredably unstable.

What you do is "modulate a carrier" with the low frequency waveform.

Or more correctly you rapidly sample with a "chopper gate" and then pass the resulting AM signal into the sound card. If you use two "choper" waveforms at the same frequency but 90degrees apart you gain some very real advantages.

Go google for "chopper stabalised amplifier" and have a look at the Linux "Software defined radio" project it will give you a wealth of information for the first part of the project (ie electrodes to DSP output) it's then up to you to do the quite difficult task of sorting through the various "learned journals" on the various type and parts of the human brain wave.