Help with 50 Hz noise bursts

FarfalkFarfalk
edited March 2018 in General Discussion
Hi!

I've been using the Cyton board for a while with no problem whatsoever. Recently I've been trying to use some dry electrodes (the well-known FRI long spiked ones) to record alpha waves / low frequency SSVEPs. I use a gold cup electrode fixed to my ear lobe with electrode cream as ground, a dry electrode in FP1 as reference and a dry electrode in O1 as signal source; all pins apart from the first are turned off and SRB2 is used as reference.

Here comes the issue: sometimes, for prolonged (but not easily reproducible!) time periods, sudden high intensity "50 Hz bursts" can be seen in my recordings.
Follows an image:
image
Here I'm using OpenViBE, but the problem can be seen in OpenBCI_GUI as well. I implemented a 50Hz Notch filter coupled with a 2 Hz - 70 Hz bandpass filter.

There are no devices running around me, apart from my battery powered laptop (not connected to AC).

An additional note: of course it's not a 50Hz-only noise - actually its components range from 50 to about 60 Hz, with some sparse low frequency harmonics as well. If a better spectral definition is needed, tell and I'll provide.

Any ideas on how to solve this?

Thanks for any response.

Luca

(I may have posted this twice due to a browser hiccup. Sorry!)

Comments

  • wjcroftwjcroft Mount Shasta, CA
    Luca, hi.

    Do the noise bursts seem to come at a steady repetition rate? That is, the 'silent' time seems to be relatively constant, as shown in your diagram. Or are they more randomly spaced. A fixed spacing would suggest some type of environmental noise broadcaster.

    Do you have any cell towers in your neighborhood?

    You mention you just started using dry electrodes. Does this noise go away when using gold cups with paste?

    Regards,

    William

  • lopezst1lopezst1 United States
    I am also noticing this in my data. These bursts come at infrequent intervals and have occurred in different rooms throughout the house. Any ideas as to why?
  • wjcroftwjcroft Mount Shasta, CA
    Lopez, hi.

    Generally dry contact electrode systems are more susceptible to these effects, than those using electrolytes. Are you using a dry system? 

    Another factor with the newer 5mm dry combs from FRI, is that the tips wear out faster than the original 2mm combs. In other words, if you look at the tips, you may see that the gray AgCl coating has worn down, and you only see the silver plate below. Or even the base plastic below the silver. Check the status of your electrodes.

    Regards,
  • alwayswearshatsalwayswearshats
    Are you using a Wifi Shield or the RFDuino dongle?

    Wondering if this might have to do with the intermittent noise bursts observed when using the Wifi shield.
Sign In or Register to comment.

© Vanilla Keystone Theme 2026