Re: Looking someone to build a modularEEG

Hi Stephanie

About the 4 versus 8 electrode operation.  Let us get the terminology
correct, for otherwise everyone is confused.

The SMT-EEG is a 2-channel bipolar amplfier.  You would typically use 5
electrodes with it.  2 electrodes for channel 1, 2 for channel 2 and 1
electrode for DRL.

Having said that, however, you could (and one mostly does) link the two
reference electrodes together.  That means you use one electrode connected
to BOTH the CH1- and CH2- inputs.  For that, one would need a simple jumper
cable.  In this instance, you would use a total of 4 electrodes to obtain
2-channel data.

ModEEG can be build with 2, 4 or 6 channels.  If you had a 4-channel modEEG
you could use up to 9 electrodes.  But again, one would likely link some,
or all, reference channels together, thus reducing the amount of
electrodes, site preparations, wires, etc.

I am not sure if the Olimex Admin that replied to your Q in that Olimex
forum is absolutely correct.  My concern is using multiple USB devices (in
this case 2 or more SMT-EEGs) with the same VID and PID tags.  VID = Vendor
ID and PID = Product ID.  These refer to the USB device differentiation.
Also, the Admin should at least have mentioned that in the case of multiple
device usage, you would connect all DRL channels together to one single DRL
electrode.  Again, you would need special jumper- or daisy-chain cables.

If I have some time I will take up the VID/PID issue with Olimex on there
forum.  I am not 100% convinced that it will work - at least
out-of-the-box.  If you re-program the FTDI chip so that each SMT-EEG has
it's own PID, then yes, then I don't see a problem.

I personally would not consider connecting more than 2 SMT-EEG devices to
one PC.  If you want to do NFB, 2 channels are normally enough.  If you
want to do BCI, well then you would want to have as many channels as
possible, at least 8, I would say.  Because 8+ channel amplifiers are
humungusly expensive, I can understand the temptation of using 4, 5 or more
SMT-EEGs... But so many channels should be monopolar anyway.  Bipolar amps
become a huge cable mess, with that many channels.

Regards
Stefan

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