Noise at 30Hz when electrodes are not attached

nicewenhuinicewenhui hongkong
edited August 2019 in Cyton
H i,  


I have a huge amount of 30 Hz constant noise when nothing is connected to Cyton -8 channels. 

image
(Image 1. nothing connected)

Besides, when I shorted “input 8” to “SRB", and  then I shorted "SRB" to analog ground, the "self-noise" can not be measured. There is still some 30Hz noise. It's the same to channel 7 and channe 6.

image
(Image 2. short "input 8")

Any ideas on how to solve this?

Thanks for any response.

Comments

  • wjcroftwjcroft Mount Shasta, CA
    Wenhui, hi.

    You should not be using AGND for any connections. 'Bias' is your ground connection. 

    In some high noise environments, unconnected channel pins can produce noise, although this seems like a lot.

    All connections to channels and SRB2, should be made on the pins closest to the board surface. These are the IN1N through IN8N pins. Leave the IN*P pins alone.

    A recommended test is to take a glob of paste or alligator clips and connect one or more channel pins together with SRB2 and Bias. This should eliminate any noise and measure close to zero microvolts.

    A next test would be to run the Cyton tutorial steps, and see if your alpha and other brainwaves look ok. Have you done that? Is this the first use of a new board, or have you had this board for a while and used it in the past with good results?

    Regards,

    William

  • wjcroftwjcroft Mount Shasta, CA
    On closer inspection, the noise is not at 30 hz, but a bit above that. Actually near the 31 hz frequency used for impedance measurement. Is this a new board?

    It's possible the firmware is confused. And is trying to inject the 31 hz. Or the ADS1299 is functioning strangely.

    If this is indeed a brand new board, and the Cyton tutorial steps are not working for you, then it sounds like a malfunctioning board. Send an email to contact at openbci.com and ask how to proceed.

    William
  • nicewenhuinicewenhui hongkong
    Dear William,

    Thank you very much for your reply!

    Sorry for the confusion earlier, I actually connected the BIAS, SRB2 and the Ch8 together, all the pins used are the ones close to the board.

    It's not a new board, we used it for nearly two years, and it worked well before. It suddenly behaved like this one day.

    I also think it is the problem with the ADS1299, I wonder if there is any way to reset the hardware to factory settings.

    Best,
    Wenhui
  • wjcroftwjcroft Mount Shasta, CA
    Wenhui, thanks.

    If the board worked well before, it's possible that the firmware flash memory has glitched and is now activating the 31 Hz current injection. (Normally used only for the impedance measurement function, manually activated by mousing on the 'ohm' symbols near each channel. But in your case seems to be 'always on'.)

    Follow the instructions on this page to reload your firmware on the PIC32 processor on the mainboard. Your RFduino firmware (mainboard and dongle) look to be working fine.


    William

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