Sampling rate modification on Cyton board
Hi,
First of all, thanks for the development of the whole OpenBCI solution.
I am using a plain CYTON board with the dongle and .txt storage so far.
My sampling rate is 250 Hz but standard practices in EMG require sampling rates of a few kHz. From what I have understood, such sampling rates require the use of SD storage which I can understand. However I do not see where one modifies the sampling rate value on the OpenBCI GUI. Should I change something in the code rather?
Thanks
Jean
Comments
Jean, hi.
I'm uncertain if there is support for higher sd card sample rates, in the default Cyton firmware. This was implemented as a custom user-created option in the DISTANT past, with an earlier firmware version. But it may not be present in current Cyton firmware. As there are limitations in how fast the sd card can be written. You can look through some of those old posts:
https://www.google.com/search?as_q=higher+sample+rate+sd+card&as_sitesearch=openbci.com
This is the SDK command that sets the sample rate, but I believe is relevant to support of the Wifi Shield, which was able to stream at those higher rates:
https://docs.openbci.com/Cyton/CytonSDK/#sample-rate
As far as EMG sample rates, many OpenBCI Cyton (and even Ganglion) users have found success, using the default sample rates. There is some discussion in the EMG research community over minimum sample rates for sophisticated muscle diagnostic purposes. But for more typical muscle activation threshold yes/no detection, 250 Hz is fine.
https://www.google.com/search?q=is+250+Hz+ok+for+emg
https://openbci.com/forum/index.php?p=/discussion/1532/required-sampling-rate-for-emg
William
Hi,
Our lab is considering purchasing the Cyton + Daisy to use for EMG signal acquisition. Our only issue is with the sampling rate. Because we are interested in doing research into different signal processing techniques' effects on EMG, it is important that we are able to sample a large enough bandwidth.
I've seen that the max sampling rate is 250 Hz over Bluetooth, but over WiFi, it can go as high as 16kHz. Is it possible, then, for us to disable Bluetooth, and instead save our data to an SD card sampled at these higher rates? Since the WiFi shield isn't for sale in the shop anymore, it doesn't seem like purchasing that is much of an option for us.
Thanks!
@caden920, hi.
I merged your new thread into this existing thread on the same subject. See previous comments.
Regards, William
Thank you for your quick response. Yes, I had read this thread before posting, but it was still fairly vague, so I was hoping to get some further clarification.
In the docs you link above for the SDK, it says
"IMPORTANT! The Cyton with USB Dongle cannot and will not stream data over 250SPS. Plug in the WiFi Shield to get speeds over 250SPS streaming. You may still write to an SD card though, the firmware will not send EEG data over the Bluetooth radios."
That still reads a little ambiguously to me. Is the SD card writing at the 250 SPS? Or is it writing at whatever speed is set in the software?
I suggest you email (contact at openbci.com), which is customer service. As you can see from the previous links, support for higher sample rates to the sd card WAS implemented, but for a previous firmware version. As far as I am aware, this mod was never integrated into the mainline firmware code. I am unclear myself whether faster sd card writing is currently supported. There are also issues related to sd card buffering / card writing limitations, that would be impacted by higher speeds. The only definitive answer would be determined by testing a running system.
Thank you for the point of contact for me to further address this inquiry.