how to remove scalar factor from text file generated from GUI

hrodriguezhrodriguez Lima
in Cyton

Hi,
I´m trying to analyze data generated from Cyton Daysi hardware (16 channels) in a text file. According to documentation, this hardware implements a gaining factor (24x) by default which is "included" in microVolt value in text file, which has highest values in microVolts like following:

Any clue to manage data without scaling so I can get the real microVolt values. Documentation mentioned a 0.02235 microVolts per count value. How can I apply to data to get real microVolts in session ? Tried band-pass filtering (1-55) but values keep high at delta band.

Thanks in advanced,

Regards,

Hernan

Comments

  • wjcroftwjcroft Mount Shasta, CA

    Hi,

    A bandpass filter (blocking below .5 Hz) should remove the DC offset you are seeing. All filters have both the cutoff / limits, and a term which controls how sharp the filter is. Which is called 'order' or 'poles' or 'taps'. It is possible your filter is not sharp enough and is still picking up the DC offset. There are also different filter types besides Butterworth,

    https://www.google.com/search?q=comparing+DSP+filter+types+butterworth+bessel+elliptic+etc

    https://openbci.com/forum/index.php?p=/discussion/201/large-millivolt-data-values-fbeeg-full-band-eeg

    William

  • hrodriguezhrodriguez Lima

    Great! Thanks William, I will update my code.

  • retiututretiutut Louisiana, USA
    edited July 2025

    I'd like to clarify this for anyone else that comes across this thread. The scalar that happens in BrainFlow code actually offsets the physical Programmable Gain Amplifier (PGA). This exists for each channel in the ADS1299 to help us optimize the Signal to Noise Ratio (SNR).

    Let's say we have an electrode that picks up 1 microvolt in one sample.

    The PGA then multiplies this by 24 (if set this way) so that we can get a "louder" (and hopefully "better") signal that can be digitized.

    We then send this magnified value to the PC.

    Finally, we divide this value by 24 to get..... the original value of 1 microvolt that came from the electrode!

    All of the above happens before the data is saved to file

    The GUI and BrainFlow always save the raw, unfiltered data, to file. This gives users the freedom to apply other filters during playback or analysis.

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