Negative VRMS value from ADC channels

Johnny · September 2020

I'm using the Cyton board to detect the EEG signal. In my experiments, I found sometimes a negative uVrms value would come up from some channels. Usually, it happens on channel 8. This negative uVrms value always close to 0 and within -20uVrms. I'm not sure if this negative value is normal behavier and if it's corret. Did you guys encounter this phenomenon? How do you deal with it?
Thanks.

retiutut · September 2020

Try the latest release of the GUI, v5.0.1. This can be found at https://www.openbci.com/downloads .

Hope this helps,
RW

retiutut · September 2020

Not sure how this would be possible with 5.0.1. Here is the code used to get Root Mean Square:

//compute the standard deviation
float std(float[] data) {
    //calc mean
    float ave = mean(data);

    //calc sum of squares relative to mean
    float val = 0;
    for (int i=0; i < data.length; i++) {
        val += pow(data[i]-ave,2);
    }

    // divide by n to make it the average
    val /= data.length;

    //take square-root and return the standard
    return (float)Math.sqrt(val);
}

https://mathworld.wolfram.com/Root-Mean-Square.html

Negative VRMS value from ADC channels

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