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ADS1299: Resetting ADS1299 after swapping input electrodes

Volbadger
Prodigy 20 points
Part Number: ADS1299

Hi,

I am currently having a problem with my ADS1299 system in which I receive unreadable data after swapping an electrode connected to IN1N with a different style of electrode.  In other words, I connect electrode "A" to IN1N, get good EEG signal, swap electrode "A" with electrode "B", and the signal seems to go to infinite impedance.  However, if I reset the chip, it produces good signal with electrode "B".  My question is, does the ADS1299 set an internal value either through the BIAS drive or its lead-off detection circuit that is particular to the current input, and would be based on the electrode's characteristics?  Please let me know if I need to clarify the question.  Thanks for your help!

-Volbadger

  • 0
    TI__Mastermind 38745 points
    Hello Volbadger,

    There is no way for the ADS1299 to "know" which type of electrode is being used or if there even is an electrode. Is it possible that when you change the electrodes that they inputs are being shocked with ESD? Do you have an ESD protection circuit on the inputs? If the internal ESD protection diodes turn on, you may be required to reset the chip.

    Regards,
    Brian Pisani
  • 0 in reply to Brian Pisani
    Prodigy 20 points
    Hi Brian,

    Thanks for the quick response! There is an ESD protection circuit on the inputs. I may have left important information out earlier. Along with the scenario given above, swapping from "A" to "B", I also tried just unplugging "A" from the input and reattaching it; this went straight back to reading normally. This is what brought up the question about different electrode characteristics, and if the ADS1299 set any internal values based upon say impedance or lead-off detection that needed to be reset. I have a few other ideas around troubleshooting this that deal more with the software and board architecture. Again, thanks for your help!

    -Volbadger
  • 0 in reply to Volbadger
    TI__Mastermind 38745 points
    Volbadger,

    Very strange indeed! The lead-off detection would trigger when electrodes are removed, but that shouldn't cause the device to change state. Once (any) leads are properly connected, the lead-off detection indicators should show that the leads are connected - that should be the only change. Let me know what results you get from troubleshooting.

    Brian