Timestamp channel unclear behaviour

I have started streaming data (EEG) from a Ganglion using brainflow, and the timestamp channel always has two consecutive values that are the same: [0,0,.5,.5,...] plus some noise.
I was referred to: https://docs.openbci.com/Troubleshooting/FTDI_Fix_Windows/
by Andrey at the brainflow slack, but I don't have the option to change the latency.
I am guessing that I am missing a driver. Can anyone help?
(Using win10)

(I did a quick search in the forum but didn't find anything relevant, sry if I missed)

Comments

  • wjcroftwjcroft Mount Shasta, CA

    Hi Bear,

    No, that is normal. The packet streaming on Ganglion sends two samples per packet, see.

    https://docs.openbci.com/Ganglion/GanglionDataFormat/

    re: FTDI, those notes about adjust the latency are for Cyton users, not Ganglion.

    re: timestamp accuracy. Note that these time values are assigned as the packets are received at your laptop. So depend on the CPU loading, buffering, etc. Thus are only approximate.

    Regards, William

  • Hi, thanks for the reply it cleared my confusion.

    Regarding your last point, that is something I had in mind. Is there a better method for synchronizing data?

  • wjcroftwjcroft Mount Shasta, CA

    Cyton (not Ganglion), has an External Trigger capability, using 3 additional 'Aux' channels.

    https://docs.openbci.com/Cyton/CytonExternal/

    On Ganglion, you could devote one of your 4 channels as a trigger channel. Then use a "voltage divider" (two resistors) to get your trigger channel value into the microvolt range, say 50 microvolts.

    https://www.google.com/search?q=voltage+divider+calculator

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