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martindinov / hackathon

Where we will store all our hackathon-related code and files.
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Integration of EEG with DC stimulation #6

Open nmdanr2b opened 9 years ago

nmdanr2b commented 9 years ago

a) pass filter on the TSK sensor that will cut off DC (everything below 0.01 Hz?) b) automatic marking of DC on/off in saved (and presented?) data c) ask OpenBCI team whether DC filtering is already implemented in their kit d) ... ?

nmdanr2b commented 9 years ago

On the high pass filter (http://hyperphysics.phy-astr.gsu.edu/hbase/electric/filcap.html#c3): We can either do a small pass filter for both bipolar (TSK) and unipolar (OpenBCI) versions with a switch to change from one to the other, or have a separate unipolar and bipolar pass filters (which simplifies the matter).

Unipolar filter is simply plugged into OpenBCI pin (or any other amp, this is simply matter of a connector).

Bipolar filter is connected to electrodes placed on the subjects head (small crocs should do the job) with sufficiently long and well-isolated wires. From the other side, it is connected to TSK sensor (sticky electrodes that come with it can be used so that we don't have to wield to the sensor itself). This setup, apart from allowing to filter DC, solves two problems:

I'm not entirely sure whether the bipolar pass filter will consist of two filters for each polarity, but most likely it will be the case.

karnival commented 9 years ago

If we're going for the hardware filtering approach, here's how to get the appropriate pot/cap values, for anyone unfamiliar with circuit theory.

f_c = 1/(2 * pi * R * C)

Set f_c = 0.01, because we don't want to lose a lot of stuff above that.

=> RC = 1 / (2 * pi \ 0.1) = 1.6

Current chosen combination: R = 1M, C = 1uF; giving f_c = 0.16 Hz