Options for Cyton/Daisy Sampling Rate
jctaylor
Canada
Hello,
As I understand things from previous forum posts, the Cyton samples at a fixed 250 Hz +/- a teeny error. If I plug the Daisy in, it drops to 125 Hz +/-.
Yet, on the OpenBCI Shop website, it states "However, if you select the "save data to microSD card" option in the OpenBCI GUI, you can take advantage of the 250 Hz sampling rate." This suggests that there is some way to boost the Cyton+Daisy sampling rate to 250Hz.
I am not using the OpenBCI GUI, as I need to incorporate markers for ERP into my stream. So I am using the Lab Streaming Layer. Is there a way to get the sampling rate up to 250Hz in the LSL. Alternatively, is there a way to use some other software that accepts markers to work at a 250Hz sample rate (and be exportable to EEGLab.
Would love for WifiShield to come back. But in the meantime, what are my options?
Thank you
Jamie
Comments
We just updated this Doc in the last week based on very recent investigation from our Software Team. We are currently developing fixes for Cyton SD card functionality and the WiFi shield (finally!). We realized that what's saved to the SD card with Cyton+Daisy is 250Hz, though it is limited to streaming at 125Hz. This does mean that 1 line of code in GUI v5 is incorrect, where it assumes 125Hz for Cyton+Daisy SD card file playback.
https://github.com/OpenBCI/OpenBCI_GUI/issues/893
This is the most up to date information as of today. We will be releasing more information on this in the near future. If you would like more clarification just ask. Thanks for asking about this! @jctaylor
Take Care,
RW
Jamie, are you sure you need 16 channels for your project?
Using just 8 channels, there are 3 additional 'Aux' channels that can be used markers / triggers. These replace the 3 X Y Z accelerometer channels, when the GUI is configured for digital or analog read mode. Thus all 11 channels are sampling at 250 Hz.
https://docs.openbci.com/Cyton/CytonExternal/
Regards, William
Hi William and RW,
Thank you for your responses!
RW: I'm glad to hear that the WifiShield is back on the planned releases list. I'm not using the GUI, so the code error wasn't really affecting me. EEGlab combined with LabStreamingLayer give me correct readings of 250Hz for Cyton alone and 125Hz for Cyton+Daisy.
William: Right now, I'm just programming an oddball task to check that the systems are working as intended. So I could probably get away with very few channels. However, I'm a psych researcher (albeit on a low budget) and would like for the system's capacity to be over 200 Hz for as many channels I can get. Higher Hz (e.g. through the WifiShield) would be nice, but for now I can live with 200+. So if there's a way to configure software or firmware to send all 16 channels at 250 Hz, that would be desirable.
Thank you, both, for helping me figure out where things stand.
regards
Jamie
p.s. William - I will post a question shortly related to some stuff you've said on the forum in the past, but that your response here may have helped me with.
Understand the need for more channels. But sometimes it is possible to compromise. In this case you can only stream with Daisy at 125Hz. But if you could settle for Cyton mainboard alone with 8 channels plus 3 Aux channels (triggers, markers), those can all stream at 250 Hz.
As Richard pointed out, you can record to SD card, Cyton + Daisy at the full 250 Hz, including the 3 Aux channels. But the Bluetooth streaming protocol limits you to 125 Hz when using Daisy.
@retiutut @wjcroft:
When can we expect a WiFi shield to be ready for sale?
What would be a practical data rate limit? (Not theoretical: smiley:)
Looking forward to hearing from you.
Regards,
Rathin