OpenEEG
Alternative Hardware
I don’t know if anybody on the open-eeg mailing list reads Chinese, but I found a Master’s Thesis (Abstract in English) from the Chung Yaun Christian University, that has a schematic for a modular USB 2.0 based multi-channel EEG. You can download the entire thesis here in PDF format. Pages 87 thourgh 90 have schematics for the actual hardware. Maybe it can be used as an alternative hardware design for Open-EEG.
If you don’t want to look through the PDF file, I’ve posted the schematics here:
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(images rotated for easier viewing)
For better quality images check the link to the actual thesis above.
Maybe somebody that has more experience can see if this would be a viable solution for the Open-EEG Project.
Joerg Hansmann’s analysis from the mailing list is below.
- Pros:
- USB2.0 interface (not checked)
- USB powered digital part
- 16 channels
- Synchronous sample and hold for all channels
- Cons:
- Does not meet USB2.0 specification due to lack of power management for USB suspend mode.
- Isolated analog part power supply unclear to me. I suspect extra batteries here.
- Data-Isolation is done via linear optocouplers (1 per channel)
- Signal is always notch filtered
- High gain of the input stage gives low electrode offset voltage handling capability
- Input stage ESD protection completely missing.
- Input stage HF rejection completely missing
- No DRL circuit.
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An easier way to get USB would be to take the output of the Sound Card EEG and send it into an AK5371 (stereo input) or PCM290X series (stereo input/output, and higher quality) all-in-one USB audio chip, then demodulate the same way we are in the Sound Card EEG.
These chips might even have good enough low-frequency response that we could use them in an analog way with the double opto-couple feedback loops shown in this schematic. – Jon