Issue with periodical abnormal signal on channel N1P

edited May 2018 in Cyton
So I am using a Cyton (v3-32) using the latest firmware, and although I can get signals on most channels, I have a weird periodic abnormal signal on channel N1P (see image or link). This seems to be periodical (every 1000ms), is present even when the electrodes are removed, and is seen across both Mac and PCs running the OpenBCI_GUI (latest version). There is no cross grounding from any of the solder joints, and probing with a meter shows that the signal is real, and is not coming from any other channel. Has anyone else observed this? and if so, how do I get rid of it?

Comments

  • wjcroftwjcroft Mount Shasta, CA
    Aaron, hi.

    What happens when you go through the steps of the Cyton tutorial? Are you using all the pins CLOSEST to the mainboard?


    The ADS1299 chip pins are labeled (in the data sheet) as IN1N through IN8N (closest to board), and IN1P through IN8P (pins farthest from board). You should be using the SRB2 and Bias pins, also closest to board.

    When you say "probing with a meter shows that the signal is real", can you elaborate?

    Regards,

    William

  • Yes I am using all the pins that are closest to the main board (sorry I meant to type IN1N not IN1P). And by probing I mean I used an oscilloscope to look at the signal (compared to the ground) - so its not a OpenBCI_GUI issue, it appears to be a issue with the board (or the programming on the board).
  • wjcroftwjcroft Mount Shasta, CA
    When you follow the Cyton tutorial steps (link above), do you get all the results expected?
  • Yes, when running the tutorial, I get the expected results in all channels except IN1N - which only shows the 1000ms periodic signal. 
  • wjcroftwjcroft Mount Shasta, CA
    Can you send an email to contact at openbci.com and ask for assistance? This sounds to me like some kind of hardware glitch, I don't think firmware could cause a false signal to be injected onto an input pin. Describe your scope test in the email. I'll mention Joel Murphy @biomurph and Support @openbci, so they get a notification of this thread. But do send the email to support.

  • Will do!
  • biomurphbiomurph Brooklyn, NY
    @aaronjoh

    When you say that you are probing with an o'scope, please tell us where exactly you are probing?

    If you are probing the input pins (1N and 1P) and you are seeing the same signal, then could it be that the signal is coming from outside the board?

    If you can take a good picture of the top and bottom of your Cyton, that would help to see if anything is grossly out of whack with the hardware.
    Also, can you tell us when you purchased your system?
  • I checked to make sure there wasn’t a problem with the input circuit - the transient voltage suppressor and RC filter. I also put the scope on the 1N and 1P pins. 

    Photos of the board are:

    I purchased the system in Jan'2017 (Cyton+Daisy) - we have mainly been using the ganglion boards since that time (building experience with 4 channels), but started to try and use the Cyton in March of this year - and noticed the issue. 
  • biomurphbiomurph Brooklyn, NY
    Well, the board photos look good. I am not sure what the issue is, but if you are seeing the same signal aberation with the oscope, then I would imagine it is coming into the system and not part of the system.
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