Trigger sync and SD card on Ganglion
I've checked every post under the Ganglion section of this forum looking for info regarding both trigger synchronization and SD card writing but I still don't understand what can be done. Anyway, here are my questions:
- it seems that there are design issues with respect to SD card writing, as the board sucks (cause it is limited to 4MHz writing speeds?). can I still write on the SD card? how bad is the noise? can I use the board in a lower sampling rate mode to minimize the noise incurred by writing data to the SD card? is there any tutorial for this (for the Ganglion in particular)? or is there any other way (like some cable) to send the EEG data from the board to a PC that does not lose packets (which is the issue with Bluetooth)?
- how can I connect and synchronize external trigger devices? there's a comment from February 2017 (yes, 3 years ago!, https://openbci.com/forum/index.php?p=/discussion/966/external-stimulation-and-digital-trigger) saying a tutorial would be prepared for this but I cannot find it anywhere in your website...
It seems the support for Ganglion boards is way subpar, especially when comparing with the support for the Cyton board... This is a bummer, as 400$ is a lot for a personal purchase and I'm starting to think buying the Ganglion was a waste of my money and I would gladly send it back and pay the difference to get a Cyton board...
Thanks in advance,
Francisco
Comments
Francisco, hi.
Ganglion does not lose packets, if configured correctly.
SD card on Ganglion was abandoned because of limitations in the Simblee CPU architecture. SDcard presence is not promoted in any way for Ganglion. Even though the socket is there.
There are no Aux or extra channels available on Ganglion. The three 16 bit Aux channels on Cyton operate at the full 250 Hz rate. There is no bandwidth for this on the compressed 200 Hz Ganglion stream. You can always use one of the 4 Ganglion channels as your external trigger, using a voltage divider (two resistors), to drop the voltage into say a 20 microvolt range.
Regarding the Cyton purchase, please email OpenBCI directly at contact at openbci.com.
As far as some remarkable BCI using Ganglion, see this video,
https://www.kickstarter.com/projects/bci/make-100-create-your-own-brain-computer-interface
Best regards, William
What configuration steps should I do in order not to lose any packets via bluetooth?
This seems like a good alternative. I would be willing to sacrifice one of the channels for a trigger channel. Can you point me to a link detailing how to do this?
Best, Francisco
All Bluetooth and Wifi can be subject to interference from other devices. Try to position in a room or area not directly adjacent to other sources of microwave emissions. Another way to increase signal strength for the mainboard, is to use a usb extension cable to position the dongle closer to it.
https://www.google.com/search?q=voltage+divider
A voltage divider consists of two resistors that reduce the input voltage to the level you want. If your input trigger source is say in the range of 3.3 to 5 volts, you would want to reduce that to around 30 to 50 microvolts, for connection to a Ganglion input pin. It's also possible (recommended) to employ an optoisolator, to eliminate any potential of the trigger circuit to pose a hazard condition to the subject.
https://docs.openbci.com/docs/02Cyton/CytonExternal#optoisolation
Regards, William
https://github.com/OpenBCI/Documentation/issues/163
Though the Docs mention SD card commands for Ganglion, we are adding more warnings stating that this feature is not available.
Saving to SD card using Ganglion is not possible with the default firmware, and users should not attempt to add this feature, per the information shared by William in this thread.