Getting Started: Confused about SRB and N1P pins

chesswebchessweb
edited October 2014 in Cyton
In Learning -> Getting Started -> Hardware Setup it says "... Connect your electrodes to the OpenBCI board: one to the SRB pin, one to the N1P pin ...".

Looking at the board, I find the labels SRB and N1P, but for each label there are *two* separate header pins.

Checking the schematics, however, there is not just one SRB pin, but two independent pins labeled SRB1 and SRB2. The same goes for N1P, in the schematics there are two input pins labeled 1N and 1P.

So I'm confused, what does it mean to connect electrodes to SRB and N1P? Which header contact do I pick for SRB (SRB1 or SRB2) and N1P (1N or 1P)?

Comments

  • chipaudettechipaudette
    edited November 2014
    Great questions.  The documentation is still being worked on, so hopefully it can be clarified moving forward.

    Which pins to use is entirely dependent upon the software running on the OpenBCI board.  As of right now (but it could change at any point), one should use the "N" inputs (1N, 2N, etc) along with SRB2 as the reference.  In terms of the double row of pins, these would all be the lower [corrected 2014-11-20] pins.  

    The upper [corrected 2014-11-20] pins are all of the "P" inputs along with SRB1.

    Again, this could be easily changed via the open source software on the OpenBCI board.  So, keep an eye out for updated documentation!

    Chip
  • chesswebchessweb
    edited October 2014
    Thanks, Chip. That helps indeed. But here is another one you might be able to help me with. It concerns the bias signal generation on the OpenBCI V1, V2 and V3 boards. I'm going to start another thread for that.
  • adminadmin
    edited November 2014
    The SRB1 and SRB2 pins are connected to the internal multiplexer that provides complex switching between the input pins of the ADS1299, internal test signals, and the ADCs. See Figure 19 of the datasheet. 

    The SRB2 pin has the option to be open or closed to any INDIVIDUAL channel's P input. That is done by setting or clearing bit 3 in the individual channel's CHnSET register. 

    The SRB1 pin has the option to be open or closed to ALL channel's N inputs. SRB1 connects to ALL N inputs, or to none of them by setting or clearing bit 5 in the MISC1 register. 

    Note that SRB1 is a either/or switch. When closed, the N input is DISCONNECTED from the input pin. When open, the input is available on it's respective pins.

    In general: 

    * If you use the P inputs for your electrodes, you have the option to connect all of the N inputs together and use SRB1 as a reference electrode.

    * If you use the N inputs for your electrodes, you have the option to connect some or all of the P inputs together and use SRB2 as reference for those channels you select.

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