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Active Electrode Circuit Design

January 27, 2015, 4:34 pm
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Hey, 
Starting a thread here about the best way to go about designing active electrode circuitry. From what I understand, placing an active (op amp or other) device in very close physical proximity to the contact site improves noise reduction and allows for a dry contact between the electrode sensor (gold, silver, Ag-Cl, etc) and the subject scalp.
My basic reference for this is the active electrode circuit published by Olimex


I've used these, and they perform quite well with OpenBCI (5V differential between AVDD and AVSS to power).
The basic shape of the thing has 
TVS and Diode suppression on both ends
Power supply decoupling and zener protection on the V input
Some impedance added to the input and output
High Frequency rejection filter on the op amp

but beyond that, it is just a unity gain follower.
Of course, the specs of the op amp are going to play a very important role:
high impedance inputs
high CMRR
low equivalent input noise at low frequencies

My question is, what about the basic circuit, besides the op amp selection ('tho that could enter this discussion) stands to be improved? Or discarded?


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Can I use the GUI to change the analog chip's sample rate?

August 23, 2017, 1:44 pm
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Hi all,

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Can the GUI be used to change the rate at which the Ganglion's A/D delivers data on its SPI channel? ("Serial1"?)

If so, "Extra Credit":  can the GUI be used to increase that rate to above 200 sa/s?
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My understanding is that:
-- The initial default per-channel sample rate is 200 sa/s.
-- I shouldn't expect the Bluetooth data path to support greater than 200 sa/s.

OK fine.  But what I'm wondering is something like:  
From within the GUI, using the Ganglion firmware as shipped, can I click-click, so that the A/D digital (SPI) output per-channel will be anything faster than 200 sa/s?
And if so, am I correct that there's nothing about the Bluetooth path that will, for example, flag some buffer over-run error and shut down the SPI communication?

(My plan is to ignore data thru the Bluetooth channel, but rather to get data by monitoring the SPI lines -- with all necessary care for patient safety/regulatory concerns).


Thanks! as soon as you're able to reply with what you know or speculate.  
Internally I'm getting some quite reasonable pressure to abandon Ganglion.
I still prefer remaining with Ganglion, but I'm running out of time, travelling after this week.
I have 2-3 other solutions up my sleeve, using Ganglion, but each has downsides and takes time to develop.
I haven't been exploring the GUI myself because a colleague has the Ganglion, but I may retrieve it today/tomorrow.
I'm a software novice, I wouldn't trust my ability to answer by looking at GUI source code.

      -- Bruce P.

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What's an easy way to record events with a high degree of accuracy in terms of timing?

August 23, 2017, 5:04 pm
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I'm a machine learning guy, not an EEG or EE expert by any means, so please bare with me.

I need to record events that happen during the recording of a session with OpenBCI GUI (on Windows/Linux) or possibly with the Python library. That way I can build a training data set, to determine which brainwave patterns correlate with which events. By events I mean things like thinking "yes", "no", blinking, clenching your jaw, etc, etc.

I figure this must be a pretty common task for OpenBCI users, right? Does anyone have a good way of doing this, which they can tell me about? Is the functionality built into the software?

Thanks!
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Is Ten20 electrode paste dog-safe?????

August 23, 2017, 6:22 pm
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OMG OMG OMG. My dog was just licking my forehead like she always does and I remembered that I hadn't cleaned off the electrode paste yet!! Is she going to be OK?

Obviously if she starts throwing up we're going to the animal hospital, but if you know anything about the toxicity of this paste I'd appreciate it.
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Connect STM32 Discovery board with Cyton

August 24, 2017, 2:21 am
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I want to connect my STM32 Discovery Microcontroller board with the Cyton board and I am not sure if we can do it via the SPI pins given for the daisy chain module. I want to extract data from the SD card or stream data directly into my Discovery board via those pins and do some processing on the data. Can I do this arrangement...???

Thanks in advance.


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Ganglion Not Writing to SD card

August 25, 2017, 3:41 am
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Hi there,

I've been trying to get my Ganglion Board to write to SD Card with no success. I've tried updating the firmware with the current version on github (https://github.com/OpenBCI/OpenBCI_Ganglion_Library) combined with the companion SD Card Library (https://github.com/OpenBCI/OpenBCI_Ganglion_SD). I'm using this SD Card (https://www.amazon.co.uk/Transcend-Extreme-Speed-Micro-Memory-Class/dp/B004W63RT4/ref=sr_1_3?ie=UTF8&qid=1503656599&sr=8-3&keywords=transcend+4gb+sd+card). I've been testing sending commands to the board using the nodeJS library (https://github.com/OpenBCI/OpenBCI_NodeJS_Ganglion) and have been able to send commands such as start and stop stream. However, if I send the commands to start and stop writing to the card, the card is empty when I check it.

Any thoughts on this issue would be appreciated!

Thanks,

Nathan 

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who has built the openbci parts? full-BOM/suppliers?

July 21, 2017, 2:46 pm
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I'm a neurology resident trying to build a set of 32bit, daisy, and dongle boards to experiment with. I finally figured out how to get the pcb/gerber files in appropriate format for the board houses and am having then fabbed, but pulling together the full parts list is taking forever (because the BOM on the openbci doc site or that exported from designspark are not complete re details). I basically have combined the 3 boards into one document and am compiling a digikey ID, price, and link for each item. I get that some of the pieces are "custom" and thus this adds some complexity, thus has anyone done the full build and if so can they recommend major electronics supplier part numbers for items such as the specific headers, SDcard, etc? If I can get the full item list together I can then upload to github this along with the gerber files I used (had to mildly modify the designspark files and associated gerber files for the board house). If there is a way to upload files here I can post the spreadsheet I currently have with ~half of the items. Thanks for any recommendations!

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What logic to use in determining where to place the + relative to - electrodes in differential mode?

August 26, 2017, 2:53 pm
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I have a Ganglion with 8 header pins for 4 channels, such that there is one + and one - for differential mode.

I admit, I have trouble wrapping my head around the idea of measuring EEG data differentially rather than as the absolute voltage read in by the sensor, but I believe differential mode is supposed to be a best practice.

That being said, how do I know where to place - relative to where I place + for a given channel? I have 10/20 Brainnet headgear, which color code which holes on the right side of the head correspond to which holes on the left side of the head. Would I place the + on one side and the - in the corresponding positions on the other side? Or would that mean that I'm only reading data for one side of the brain?

If you could help turn my confusion into understanding then I'd be very greatful :)
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Ganglion board now working with python on Linux

March 2, 2017, 5:23 pm
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Hello,

The last few days I worked on the Python repo, and here it is, finally the Ganglion board can be used directly from python. There's a catch: because I have been using the "bluepy" library, it works only on Linux for now.

Still, if you have the right, OS now you can easily use it in you python programs, use the existing plugins to stream in LSL or OSC, etc. Of course the first thing I did was to stream signals to OpenViBE... and it works great, *at last* I can test this nice piece of hardware!


It is possible to switch-on the AUX channels and the impedance check -- in that sense this implementation might be now more advance than the Cyton one :D. I had to make some changes under the hood (e.g. enable automatic discovery for both ganglion and cyton from the "user.py" interface), in theory nothing should break if you have been using the python API before, my apologies if it is the case.

This implementation would not have been as smooth if it were not for the nice NodeJS code out there, thanks @pushtheworld :)

I hope that in the future one could switch from bluepy to another library which runs on Windows and Mac (if any of you knows one....).

As described in the README, you need a recent version of bluepy, which is included in the repo as a submodule. Hence you need to use "git clone --recursive https://github.com/OpenBCI/OpenBCI_Python.git" to get it all. After that run "make" inside the "bluepy/bluepy" folder. Yes, it's a bit hacky at the moment... and it's not over.

During my tests I encountered sever packet drops (15% of data were missing), I had to tune the parameters of my bluetooth dongle. To do type:

sudo echo 9 > /sys/kernel/debug/bluetooth/hci0/conn_min_interval

sudo echo 10 > /sys/kernel/debug/bluetooth/hci0/conn_max_interval


If you survive these steps, please test it and give your feedback, here or, especially if you encounter bugs, on github.

I only tested on my laptop running Ubuntu 16.04, so I'd be eager to know how it goes with other installations.


Enjoy :)
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Medical student here, getting interested in BCI

July 9, 2017, 9:54 am
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As titled, I'm a medical student who recently came across this subject and became interested.

May I know if there are any medical professionals in this field, and what are they doing in general? What are their roles in researching?

What are the big topics / areas of research in this field?

I am aware of invasive VS non-invasive BCI. What are the differences in their current applications / performances?

If I want to do a PhD, what do I need to know? And, where should I go?
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component sourcing - SD card holder & exact component IDs?

August 27, 2017, 1:53 pm
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I could use some help finding a few components, and could help with others looking for the basic components.

I have posted a draft of a bill of materials spreadsheet for the cyton, daisy, and dongle boards here (open ods & xls type formats):
https://github.com/ak1n/V3_Hardware_Design_Files

It has the digikey product ID and link for what I think the appropriate components are (it took me a serious amount of time to compile this)

Highlighted in yellow is the SD-card holder. I am uncertain as to where to get this. Digikey has a bunch of SD-holder components, but I have not yet figured out if they are directly compatible re e.g. size/board requirements. Yes I went to the link recommended by openbci but there are no suppliers. I submitted a request for quote but received no real responses (likely because I put in a small quantity that is not worth it for suppliers there). I stumbled upon this page recommending the next ebay product link:
  http://www.thinkering.de/cms/?p=703
    recommended: http://www.ebay.de/itm/10-Pcs-Micro-SD-TF-Memory-Card-Sockets-Quick-Flip-Connectors-for-PCB-/191687$

Finding a digikey or similar large-supplier ID would be much helpful if anyone knows which are compatible.

Also, highlighted in red are products that didn't have thin film in the info. I.e. I couldn't verify they were the proper type.

Since I'm not an electrical engineer (just a tinkerer), it would be much appreciated if anyone with more electronics knowledge might be able to verify the components in the bill of materials, particularly with respect to helping with an SD card source and re the red-highlighted resistors. This will hopefully also help others not have to spend forever putting together a list verifying the exact components.

Thanks for any input in this regard!
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Have you seen the movie "Listening"?

August 27, 2017, 1:20 pm
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Have you seen the movie "Listening"? If so, what did you think?

image

I'm thinking the 4-channels of my Ganglion has me almost on their level, but to be able to read people's thoughts with a really high level of accuracy I might need to save up for a Cyton board. Incidentally, the movie is on Netflix.
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Stack Exchange proposal for new site on BCI Q&A

August 27, 2017, 2:47 pm
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For those of you familiar with StackOverflow and its sister sites on the Stack Exchange network, I thought you might be interested in this proposal for a BCI Stack Exchange:

https://area51.stackexchange.com/proposals/113408/brain-computer-interfaces?referrer=GUkAb_00B-qrq5QQ5NKU4g2

Please have a look and give it your support if you're interested.

For those who don't know, Stack Exchange is a network of highly structured, gamefied Q&A sites like StackOverflow, which is the world's largest repository of programming knowledge, with millions of active users. The benefit of something like this is having a large community of experts working together across BCI platforms to help answer questions, as well as an easily searched database of prior Q's and A's, with a well-developed voting and reputation system. It absolutely cannot replace the role of a forum, where conversations and free-form discussion take place, however it could be a good addition to the BCI community.
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Basic questions: saving data and data format?

August 7, 2017, 4:44 pm
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Hi there,

I have recently received my Cyton board, so am fairly new to it...

I can't for the life of my find any information regarding recording data and saved data format. 

The OpenBCI GUI has an obvious "Start Streaming Now' button. But I don't see any obvious 'Start Recording Now" button, or see anything about this on the forum.
Does data just record to PC by default when ever the Cyton is streaming data live?

If so, where and what format is the data saved as? 
I see the txt files in my saved folder, e.g. 'OpenBCI-RAW-2017-08-07_20-07-21.txt'.
But surely data is not saved as a txt file?

Ultimately I will be wanting to import saved data into Matlab, but for now, I just want to figure out when, how and where it is saved in the first place.

Thanks in advance!



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Ganglion high pass filter problem

August 28, 2017, 10:59 pm
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Hi!

According to some notions ( please see that for reference: alexandre.barachant.org/blog/2017/03/02/Hands-on-OpenBCI-Ganglion.html ) there is a design flaw, that leads to 2.4Hz high pass filter and strong signal attenuation below 10 Hz. Actually it is not acceptable for correct EEG processing, since it has physiologically important spectrum from 1Hz and up.
So, what are perspectives to resolve this issue in the nearest future?

Best,

Alexei
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Question about Band Power

August 29, 2017, 3:26 am
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Hi there!

I'm using dry electrodes with the ultracortex, and keeping the impedance to less than 5-7 kOhm per site. At what range of uVrms should I set the threshhold to consider the signal an artifact? Can regular brainwaves evoke a band power that exceeds the average to a large degree?

Thanks a lot in advance!
Cheers

Luc
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OpenBCI, LSL, and Matlab 2016b

January 26, 2017, 12:55 pm
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Hi all,

Is anyone else unable to get OpenBCI data into Matlab 2016b?  I'm running OpenBCI_Matlab

https://github.com/OpenBCI/OpenBCI_MATLAB

and can see the stream through the terminal, but picking up the stream in Matlab just leads to "Looking for a device with type='EEG' ..."  I've tried both the master and devel branches of BCILAB as well (as recommended here: https://github.com/sccn/BCILAB/issues/11), and I've checked the StreamInfo() name matches (per the advice given here: http://openbci.com/index.php/forum/#/discussion/761/unable-to-input-openbci-lsl-stream-in-bcilab)

System:
MacBook Pro (Late 2013)
OS X Yosemite (10.10.5)
Matlab 2016b
Cyton board (not daisy-chained)

Thanks,
-Katherine

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Buying Dry / Active Electrodes

August 16, 2014, 10:33 pm
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Could someone recommend some off-the-shelf dry active electrodes for use with OpenBCI? Chip speaks ill of some cheap ones in another thread. Are better ones readily available, even if they cost more?
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Newbie - few questions and what do I need

August 30, 2017, 2:55 am
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Hi All,

I have a bit of background in signal processing and love the idea of home BCI so wanted to get together some equipment to play with.

I have a few questions though

1) Is the ultracortex headset only purpose to hold the sensors in position for easily repeatable results? Do I use the gold cup electrodes?

2) What's the difference between the solid gel and gold cup electrodes? Do they to do the same thing?

3) Could I not purchase a cap (for example) 
or
and just put the electrodes on this?

Thank you,
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Polymer-based dry electrode

August 30, 2017, 6:38 am
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I have seen a couple of papers online regarding research of polymer-based dry electrodes which provide all the benefits of dry over wet (spiky over flat) with the additional benefit of increased comfort when worn (no more spiky metal in the head).

I was wondering if anyone was aware if these were being manufactured yet, a patent is in place from 2012 so its been quite a while since people were playing about with this idea.
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