Asymmetric channel noise

Winslow_StrongWinslow_Strong
edited May 2016 in Hardware
I have an 8-channel and 16-channel V3 32-bit OBCI system.  In both systems, when I look at raw signal picked up without anything attached to any pins, and without any filtering, I consistently see channels 5-8 or 6-8 and 14-16 in the 16-channel system as obviously picking up more of the ambient EMF than the other channels.  The highest amplitudes are always either channel 8, channel 16, or both.  I've reproduced this many times, and its independent of orientation or placement of the OBCI on my desk.  I tried to reproduce the issue in the OBCI processing GUI, but couldn't get all the signals on the screen after removing the bandpass and notch filters, and even after rescaling the axis.  

I uploaded some screenshots taken when OBCI is outputting via LSL (i.e. http://docs.openbci.com/software/06-labstreaminglayer ): http://imgur.com/a/gNAqn
The channels are in order: 1-8 or 1-16.  

Wondering if anyone else is seeing this?  Wondering if I should be worried that something is wrong with these boards?  Things look very symmetric when I filter e.g. to alpha bandpass. 

Comments

  • biomurphbiomurph Brooklyn, NY
    @Winslow_Strong
    If you are seeing something when there is nothing connected to the inputs, we can't have any idea what is going on. the board is sensitive to sub-microvolt potentials, and we don't recommend taking an unconnected input signal for anything other than that.
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