Self noise / unconnected input pins / quantifying noise

antigeinusantigeinus
edited March 2015 in Hardware
Hi Everyone,

Does anyone ever experiance self noise from OpenBCI board?

Recently my OpenBCI board has self noise on almost all channel when none of the electrode were connected. I can see my board is still reacting to outside world by touching the electrode pins, but the problem is I can't get any useful result from it since all the channel is constantly reciving noise (data?) and the noise (data?) from nowhere never gone weak.

Does anyone get this happened on your board too? Is there anyway I can re-calibrate or reset and board so it will go back normal? 

Thank you so much for your reply
-Yen
    

Comments

  • chipaudettechipaudette
    edited March 2015
    Hi Yen,

    With no electrodes connected you *should* see large amounts of noise.  This is true for any EEG system.  Without being connected to your body, the unconnected pins on the OpenBCI board act like little antennas.  They will pick up all sorts of interesting things, such as the static electricity in your hand as you wave your hand by the board.

    If you're concerned about self noise, a better test is to connect an electrode to one of the sense pins (such as IN1N or IN2N or whatever), and electrodes to the SRB2 pin and the Bias pin.  Touch all three electrodes together (preferably using the EEG gel) and set it down on the table.  Make sure that the wires to the electrodes are completely still.  Start the OpenBCI GUI and watch the data.  In a properly working system, this should make the signal in the OpenBCI GUI get very very quiet.  

    Chip
  • antigeinusantigeinus
    Thank you Chip for your explanation! I will go have a try.
  • wjcroftwjcroft Mount Shasta, CA
    edited March 2015
    @chipaudette has a great blog post on this same subject,


  • biomurphbiomurph Brooklyn, NY
    The OpenBCI is built on Texas Instruments ADS1299 IC, which has a very complex switching multiplexer on the inputs. That means that you can connect the inputs internally to different test signals. We access some of these potential connections in our command set.
    See this DOCs page
    under Test Signal Commands.

    With the OpenBCI GUI running, press the '0' (zero) key any time, and all channels will be connected to the AGND (0V) via the internal muxer. The raw EEG data is being stored in a file while our GUI is running, so you can graph it to your hearts content after your test. We have done short and long internal noise tests, and this is the method we use.
  • antigeinusantigeinus
    awesome information! thank you sir
  • antigeinusantigeinus
    chipaudette 
    thank you for the reply once again
    I followed your instruction and connect all three IN2N, SRB2 and Bias together.

    and this is what I have, do you think it looks normal? or is there anything I should check out on channel 3? 

    I tried with the '0' method and the result seems correct.

  • antigeinusantigeinus
    Solved!

    My friend Mohit point out to me that I didn't follow the instruction correctly therefore I see the "noise"

    Connecting the Pieces:   The picture below shows all the connections to the OpenBCI board assuming three players.  On the lower left, we've got three pairs of wires (one pair for each player) *****plugged into the "P" and "N" inputs***** (<-- this is the part I missed!)of three different channels.  Then, in the upper-left, you see three wires plugged into three of the four new Bias pins.  

    Everything seems normal after I connect electrode correctly. Thank you everyone for tolerant me raising up a totally irrelevant question.

    -Yen 
Sign In or Register to comment.

© Vanilla Keystone Theme 2026