Does the Wifi Shield help with increasing the offline sampling rate (stored in the SD card)?

HanNguyenHanNguyen Vancouver
in Hardware
According to the OpenBCI website, Cyton board samples data at 250 Hz. So is it possible to increase the sampling rate of Cyton to the SD card? If so, how can I do that? What is its maximum sampling rate? Does the Wifi Shield help with increasing the offline sampling rate? I am thinking of just store the data in the SD card and then analyze it later so the Wifi is not so important to my project.
Thanks.

Comments

  • wjcroftwjcroft Mount Shasta, CA
    Han, hi.

    Yes you can sample faster to the SD card. And to initiate this, apparently the Wifi Shield is required. I know that sounds like a misfeature. My impression is that it is. But that is the state of the current firmware. See this post,


    According to AJ, if using the BLE dongle (only), setting the sample rate higher, then starting and SD card recording will result in the firmware resetting the rate to 250 Hz. This misfeature could probably be fixed with some simple firmware mods. But I'm not sure what other implications the fix would have, in terms of possibly impacting other areas of the Cyton interaction. So it would be best if you do it on your own firmware. I'll open an issue on Github to see if our development engineers have any suggestions.

    So the short answer is, yes, you need a shield if you want to initiate higher sample rate SD card recordings. In terms of max rates, I would say 500 and 1000 are probably supported by the wifi in raw mode, possibly 2000. Most EEG research applications are fine with 500 Hz. Are you doing EEG or EMG?

    Regards,

    William

  • HanNguyenHanNguyen Vancouver
    Thanks a lot, William. I'm doing EEG, and I need the sampling rate to be at least 500 Hz. So after I have he Wifi shield, how do I increase the sampling rate of SD card recordings? I have read the comments in the links you suggested, but the instructions are quite confusing for me. Is there any official instructions written down for this?
    Links I've read:

    Thanks,
    Han
  • wjcroftwjcroft Mount Shasta, CA
    You should be able to do it with the menus of OpenBCI_GUI. See these screen shots,

  • s_artys_arty
    Hi guys,

    Just my two cents.
    I was not able to get seamless data out of the SD card.(even 250Hz) The problem is somewhere in implementation of SD stack. Every so often the SD card takes ~0.3 sec to record the data, which leads to the gap in the log.
    My filters couldn't tolerate that, so I used an external controller to get UART data and store it in the external SD card <- works perfect, there are no gaps.
    Please correct me if I'm wrong.

    William, thank you for all your help here!!!!
    I have one very dumb question: is there any chance I can pretend to be the WiFi Shield and do the same trick to get the data with 1000Hz or 2000Hz ?
    Do you have the interface between Cyton and WiFi shield documented somewhere?

    Thanks,
    Art



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