Sample rate

yjyj France , Bordeaux
in Cyton
Hello,

when I read " up to 16kHz sampling rate " I thought it is exactly what I need to record the (250Hz) "ripples" from the EEG of my mice...

I thus bought the 32 bits board that I tested yesterday...

But which disappointment to notice that it is not planned in the user interface to choose the sample rate, because it seems impossible to go beyond 115kbauds by radio.

Before I (try to) dive into the code I would like to know if anybody knows what would be the maximum flow rate by writing on the card SD?

Thanks,
Yannick.

Comments

  • biomurphbiomurph Brooklyn, NY
    Yannick,
    the PIC32 on the 32bit board runs it's internal clock at 50MHz. It writes to the SD card at 20MHz. I have not done the math on this, but you should be able to greatly increase the sample rate and write the raw data to the SD card. It may also be possible to send down-sampled data over the radio, as the serial.write function is buffered.

    The 3 LSBs of CONFIG1 register on the ADS set the sample rate (page 40 in the Datasheet). I think the best method for testing and benchmarking would be to use the internal signal generator, and test different sample rates with 8 channels only before going with all 16. You can verify the timing in the resulting file on the SD card. If you have a scope, you can watch the SCK pin to monitor the SPI bus.

    Curious, if you are searching for 250Hz signal in your mice, wouldn't 500SPS or 1KSPS suffice?

    Adding the 'select sample rate' functionality to our code and library is a goal of ours. We are here to help.
  • yjyj France , Bordeaux
    Thank you Biomurph,

    Your answer is encouraging I am going to try to dig the question, this device is so nice..., 20 years ago I dreamed to have something like that....

    It is a good idea to maintain the display of the data after under sampling when the raw data rate is higher than 250...

    Curious, if you are searching for 250Hz signal in your mice, wouldn't 500SPS or 1KSPS suffice?
      These
    "ripples" are  short (100ms) bursts the frequency of which
    varies between 100-250Hz, that is why it would be good to have 10
    samples by period to reach a correct precision on their frequency and
    amplitude,... , 2kHz would be perfect...

    In the worst case we can already make a good work by recording the classic EEG...

    thanks,
    Yannick.
    image

    Images -Ripples :

  • eng44eng44
    Hello,

    Could you please let me know which is the maximum sampling frequency in the Cyton board that ensures the reliable transmission of 8 or 16 channels simultaneously?

    I am asking this because I want to record signals (8 or even better 16 channels) up to 250 Hz and send them wirelessly to a computer.

    As a result, I need a sampling frequency of at least 500 SPS.
     
    Thank you in advance.

    Konstantinos
  • wjcroftwjcroft Mount Shasta, CA
    Konstantinos, hi.

    Somehow you added your post to a very old thread from 2015. There have been many threads and posts on sample rate capabilities since that time, for example,


    The Cyton sample rate can be faster going to the onboard SDcard storage. But for transmission to the laptop dongle, rate is limited by Bluetooth to 250 sps with 8 channels and 125 sps 16 channels (Daisy).

    Faster rates are now supported over wifi with AJ's Wifi Shield, see the entire category devoted to this,


    That shield is in beta testing and should be in the OpenBCI store in the coming months. Some older tricks that were prototyped included Bluetooth 2.0/3.0 breakout boards, wired optoisolated usb, etc. See the category link above for some background.

    Regards,

    William

  • eng44eng44
    Hi William,

    Thank you for your prompt reply. The information you gave me is really important for me.

    The Wi-fi product you are describing is really interesting.

    Do you think that the Zigbee protocol could overcome the Bluetooth restrictions and be able to send 8 (or 16) channels with a sampling frequency of 1kSPS?

    Best regards,
    Konstantinos
  • pushtheworldpushtheworld
    @eng44 I wanted to get back in touch with you and let you know a solution for 1kSPS is to use the WiFi shield which can now be purchased from our shop!


    Any questions?
Sign In or Register to comment.

© Vanilla Keystone Theme 2026