General Questions regarding Gel free cap and Cyton Daisy

Shyamal

Hi, I have some question that might help us in our experiments, it would be really helpful if anyone can answer them.

(1) When using Gel free cap and Cyton Daisy, along with brainflow, which gain value should be set? the default seems to be 24.
(2) with the same settings, what should be the maximum impedance values for conducting research experiments that are suitable for creating large dataset and publications.
(3) When comparing the OpenBCI devices to other devices, is it a good practice to match the same gain values regardless of using semi-dry electrodes (wireless device like cyton) vs wet electrodes (wired device)?
(4) Is there any other things that I should consider? the overall goal is to compare the results of wireless device vs wired device data and produce a large dataset for machine learning application.

Thanks!

wjcroft

@Shyamal said:
...
(1) When using Gel free cap and Cyton Daisy, along with brainflow, which gain value should be set? the default seems to be 24.

Default gain is fine for almost all electrodes EXCEPT the Thinkpulse actives. Only they need less gain.

(2) with the same settings, what should be the maximum impedance values for conducting research experiments that are suitable for creating large dataset and publications.

Input impedance of ADS1299 amplifier / ADC chip is 1 gigaohm. This offers excellent performance even when skin impedances are higher than the 'traditional' 5K ohm used in past decades.

http://wwe.eeginfo.com/research/ElectrodeImpedance.pdf

(3) When comparing the OpenBCI devices to other devices, is it a good practice to match the same gain values regardless of using semi-dry electrodes (wireless device like cyton) vs wet electrodes (wired device)?

As mentioned the default gain is fine. Regarding expected impedances with Ultracortex, see:

https://openbci.com/forum/index.php?p=/discussion/comment/13328/#Comment_13328
https://openbci.com/forum/index.php?p=/discussion/2517/expected-impedance-range-with-ultracortex-cyton-resolved

(4) Is there any other things that I should consider? the overall goal is to compare the results of wireless device vs wired device data and produce a large dataset for machine learning application.

As far as I am aware, the distinction between 'wired' and 'wireless' EEG ECG EMG is non existant. The wireless connection does not lose any of the data stream.

Regards,

Shyamal

Thank you for answering the questions. I have two more questions regarding Gelfree BCI Electrode Cap.
(1) Can I use ear clips from an Ultracortex headset, which has dry electrodes, as reference and ground electrodes with a Gelfree BCI Electrode Cap, which has semi-dry electrodes using a saline solution? Are these two types of electrodes compatible for simultaneous use in an EEG setup?

(2) Is it considered a good practice to mix different types of electrodes (e.g., dry electrodes for reference/ground and saline-based electrodes for EEG) in an EEG setup? What potential issues or challenges could arise from using different types of electrodes for reference/ground and EEG electrodes in terms of data quality and accuracy of EEG recordings?

Thanks

wjcroft

@Shyamal said:
...
(1) Can I use ear clips from an Ultracortex headset, which has dry electrodes, as reference and ground electrodes with a Gelfree BCI Electrode Cap, which has semi-dry electrodes using a saline solution? Are these two types of electrodes compatible for simultaneous use in an EEG setup?

Normally with wet based electrodes (gel, paste, or saline), you want to use wet throughout. You COULD use the ear clips if you moistened a small piece of cloth with the saline, and then clipped it between the metal (silver chloride) in the clip, and the ear surface. Then you have identical saline impedance throughout your electrodes.

(2) Is it considered a good practice to mix different types of electrodes (e.g., dry electrodes for reference/ground and saline-based electrodes for EEG) in an EEG setup?

No, already explained that.

What potential issues or challenges could arise from using different types of electrodes for reference/ground and EEG electrodes in terms of data quality and accuracy of EEG recordings?

Skin-electrode impedance differences.