Soldering 16-Channel OpenBCI Kit
in Cyton
I just started working with the new 16-channel OpenBCI Kit. Before you can use the kit, you need to solder the pin headers so that you can connect the 8-channel daisy module to the 8-channel base module. If you'd like to see my tricks for doing this, feel free to check out the link below.
What tricks have you used to make it easy to solder the headers on?
Chip
Comments
With the SRB* bussed references, you would only need to test SRB2 against each IN*N pin. And then SRB1 against each IN*P pin. (Assuming you use OPENBCI_GUI or other means to change the reference.)
Usually with soldering pins like this, 'less' is 'more'; very little solder is needed. If you have a situation with too much solder, there is a solder sucking tool likely in your lab to remove some of the excess.
Another angle is, you could get one of the JST-PH extender cables, thus not need to unplug from the board very often at all.
http://www.adafruit.com/products/1131
I'm guessing that Joel @biomurph will comment here about the linking of the SRB's between boards.
re: the AGND pin length. Another approach could be: use your solder sucker tool to remove most of the solder from the header socket in that location; then with your diagonal cutters, cut off flush with board. Then apply a bit more solder. OR: remove socket with sucker ENTIRELY from board. Trim pin length then with full access to pin. Then resolder. It may be a good idea to update our assembly tutorial to include trimming the pin before soldering.
re: JST-PH extender plugs / socket. These connectors are very reliable once clicked into place. Quite sturdy and capable of thousands of operations. Wide acceptance in industry. http://www.jst.com/
William
1) purchase the JST extension cord so you don't have to unplug from the main board socket -- and for those who install the main board in the Cortex board holder, have the cord coming out of the holder opening below the board perhaps with the battery pack hanging off the cord (maybe zip-tied to the headset)?
2) the connection from the ear clip electrodes (one for BIAS and one for SRB) *both* need to be connected to those respective inputs on *both* boards?? Because above it mentions there is no direct shared SRB pin and the shared BIAS_INV pin is not the same thing as BIAS. So if I want the ear clip electrodes to be the SRB and BIAS on both boards, it would seem they have to be connected to both boards?
(1) yeah, I mentioned that tip on another thread, it also applies if you use a lithium cell behind the mainboard, and want to recharge it without disassembling. In that case two (shortened) JST extensions allow the mainboard to be unplugged from the lithium; then the lithium connected to the charger.
(2) only the SRB2 pins need the Y cable. The Bias pins do not need a Y, since the 2 Bias pins already have the same signal.
William
1 - good idea! That's a better solution than having it hang out on the cord.
2 - Why are the two BIAS the same? I confirmed with a meter that the BIAS pins and the BIAS_INV thru-hole are not the same node. So wouldn't you want the signal/voltage from (one of) the ear clip electrodes to be attached to the BIAS pins on both boards??
(a short explanation or a link to another thread is fine!)
Thanks
I'm going to assume the comment
"The BIAS_INV connection between the main board and daisy module makes
connection between every channel that has 'include in bias' selected
from the GUI. That pin is not the electrode BIAS output! The BIAS output
is available on both pins labeled BIAS."
means that that somehow the micro and/or A2D chip are in fact connecting the two BIAS nodes on the two boards together, under the proper circumstances.
However if you look at the mainboard and daisy schematics, both ADS1299 have their Bias outputs wired to the respective headers. So only one of these 4 Bias pins needs to be used. See the TI ADS1299 pdf spec sheet for more info on the Bias drive circuitry.
William
So for the case of using two ADS1299's in daisy config, in order to detect 16 channels of EEG data ... why isn't the situation the same for the SRB2 pins on the two boards??
And since it is the case that a Y adapter is needed ... why wouldn't they have made another thru-hole in the main board so that the node could be shared directly with the daughter board??
So I just clipped one of the wires that had the pin socket already crimped (from the kit) and soldered the other end from the main board SRB2 pin, where it sticks out the bottom side.
*In my opinion* - it would still be better to have the SRB(2) pin shared directly in the board stack, perhaps running to a switch where you could enable or disable that link, as needed.
In QEEG and neurofeedback, a common montage is "linked ears", where the left and right earclips are connected via a Y-cable, then plugged into the single reference socket. In this montage, the usual place for Ground (Bias) is somewhere on the midline, For example AFz on the Electro-Cap. The midline location can possibly offer better noise cancellation (inverse mains injection) to reach both sides of the head.
In the case of the daisy, it would be a DOUBLE Y, with the two references first connected via another Y cable, then that goes to the 2nd Y out to the ears. Or obviously the cable could be more like a bus.
William
Interesting idea! Thanks for sharing that. I just assumed that using A1/A2 (either or) as reference and bias was the standard way. But I like the idea of using a midline electrode as the bias, to be physically closer to the 15 electrode signals we're recording & analyzing on the Mark3 headset (F, C/T, P - 7,3,Z,4,8). I guess then, we'd probably want to use FpZ or OZ as the bias? Or perhaps into a Y, again?
Do you suspect increased performance for using both A1 & A2 into a Y, for the reference? Or could we get away with just one earclip on either location?
re: increased performance [for linked ears]. It gives a bit more centralized (non-cortex) location for the reference. It does effect the signal amplitude slightly. This is why the QEEG people use it. But also many neurofeedback protocols with multi-channels recommend linked ears, especially if they have channels on both left and right sides of the head.
But for simple applications, there is no problem with just doing one ear as reference and the other as bias.
Thanks again for all the info in this thread!
The Mark3 headset only has midline locations at FpZ and OZ, beyond the FZ,CZ,PZ locations that we're using for signals. So it would have to be one of those. Hence I was just wondering if tying those two together and then feeding that to the board for the bias, instead of just one midline location, might boost performance in the same sense that tying the ears together and then feeding that to the board for reference, instead of just one ear, apparently does.
If you don't know or if it hasn't really been done, fair enough.
For the Bias wiring you suggest, yes that should work, though I'm unclear it would be a measurable advantage. I've not seen any other montages using two ground connections on the head. But should be fine.
With the Mark IV, other midlines should be available, e.g. AFz, FCz, etc.