snovotill
snovotill
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wtf, where's my 5 minute posting which I just submitted. Let's get serious about our collaboration software folks. I'm done here, bye.,
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I refer above, to the ability to measure electrode to skin contact resistance.
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This is trivial to implement. All that's required is application of a weak AC signal to each electrode through a resistor array via tri-statable CPU output bus pins. A side benefit is the ability to measure GSR. If this has not yet been done it's be…
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At least two other top-notch commercial products use AC to measure GSR in the same way as electrode impedance is measured but the values of the signal injection capacitors are different from what would be used for simple electrode impedance measurem…
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If you use 2.2K on one input and 22K on another input as would often be the case in clinical use then I believe you'll see a huge difference in amplitude between the two channels due to the voltage divider effect of the 1nF capacitors and especia…
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Those are important comments for the EEG technician to know. From a design perspective we do need to minimize the NEED to keep input impedance balanced. If the reference electrode impedance is high while at the same time individual amplifier input i…
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Speaking of montage, to me the holy grail of OpenBCI would be a 24 channel (10/20) Laplacian remontage in firmware. I believe the algorithm is available in OpenVibe. Too bad I'm not a firmware developer \
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Great point and anyone doing such montages aught to make damn sure that the reference electrode(s) specifically, is(are) mounted with the utmost care and lowest possible impedance.
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And although the voltage divider effect will typically show up as a CMRR deficit (depending upon how the test was done) it is important to note that the voltage divider affected uV readings very directly, any time there is an electrode-skin impedanc…
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I suppose for the sake of those who might not have EE mindsets, I should point out the gigantic pink elephant standing among us it this thread. That would be the voltage divider effect between electrode to skin contact impedance (5-50kOhm) and the A…
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Noting that CMMR rejection takes place prior to A->D conversion, we should never see EEG signals as badly contaminated as explained above, because newer equipment is body-mounted rather than chassis grounded. I would propose CMRR becomes importan…
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Hello Joel. Could you please disclose materials and methods used to arrive at the CMRR tabular data presented above? The manufacturer of the chip went to the trouble of providing a high CMRR ratio and yet the tabular data presented above shows a 25d…
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The implication being that perhaps it's some characteristic of the chip. We are getting into undocumented specifications here. This discussion is clearly not cause for alarm, but it could be cause for farther investigation for the purpose of optimiz…
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Well, it's not my intent to point any fingers without knowing and I wonder whether TI apps support might be able to offer an explanation for the discrepancy cited.
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I'm not sure what to make of that spreadsheet. If we look at line 3 vs line 13 we see 28uV and 30uV respectively of CMRR noise. These huge values defy logic and are in direct conflict with the chip specification. It seems to imply that there is some…
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I meant to say ...the "102" contained therein seems to indicate 1nF.