large EEG sample data amplitudes, how to process data stream
fnngn
china
Using Cyton Daisy Board, data is transmitted to the host computer via wifi, the sampling rate is 250hz, and the absolute value of the data I collected is between 15000 and 50000. The first question: If I multiply it by the 0.02235 scale factor as stated in the document, then my value is between 335 and 1117uv, but EEG signals are generally between 0 and 100uv. The second question: If I do not multiply it by the 0.02235 scale factor and directly pass the raw data through a 5~50hz filter, then the absolute value of the data is mostly between 0 and 100, but this time there is no multiplication of the scale factor, is this correct? The third question: If the raw data is multiplied by 0.02235 and then passed through a 5~50hz filter, the absolute value of the data obtained is between 0.05 and 0.5, which seems too small.
So how should the data be processed? I hope someone can help me, thank you very much
Comments
Hi Huchenbo,
Are you sure you are using Wifi Shield? Those systems have not been sold for some years. The normal Cyton radio link is via a form of Bluetooth, not Wifi. The raw data is always in microvolts, no multiplying by scale factor.
Beware because there are some Chinese firms selling supposed 'clones' of the Cyton / Wifi Shield, but these are generally unreliable.
You just need to filter out the frequencies below .5 Hz, which are considered the 'DC offset' in DC couple amps like the ADS1299. Your 5-50 Hz bandpass is fine.
https://openbci.com/forum/index.php?p=/discussion/201/large-millivolt-data-values-fbeeg-full-band-eeg
William
Hi William,
I have the same question. I wonder how to process those data in colomn 2-17, like -80000. This could not be the mv so I wonder what should I do to the numbers.
@SimpleRain, did you read my previous comment and link? You just apply a bandpass or highpass filter, such the DC offset, below .5 Hz disappears.
@wjrcoft. Hi, William, thanks for the reply. I did read your comment, what confused was how to build relationship between the values and voltage. As you mentioned, you think a value like -80000 should be some kind of signal below .5 Hz, so I wonder how do you convert from -80000 to .5Hz. I am doing my work on Jupyter notebook so I might not be able to use tools in apps like LSL.
https://www.google.com/search?q=example+of+applying+bandpass+filter+in+jupyter+notebook