signal has a sudden drop in one channel while recording with Cyton
in Electrodes
I was using the cyton board for ECG monitoring. The ECG signal of a single channel will drop suddenly even if I don't change anything or move the electrode at all. And if I disconnect the electrodes and then connect again, the ECG recording will be back to normal for a while (sometime 1 minute and sometimes 5 minutes), then the signal will disappear again.
It acts as if the two electrodes are connected. Any idea would be appreciated! Thank you!
Comments
Qijia, hi.
This is most likely an intermittent electrode cable or connector. Are you using the self-adhesive electrode dots? The electrodes themselves are less likely the culprit. If the connector is failing it could be either at the electrode end, or the Cyton end. Try completely new cables.
You can also use a multimeter (DVM), to check cable continuity. But since this is an intermittent failure, you may have to wiggle the cable and connectors around while the DVM is connected via clips. Still, the best approach is cable swapping till you find the bad cable.
William
Hi
thanks a lot for the quick reply. I am not sure what do you mean by 'intermittent electrode cable or connector'. I tested the cables and also tried to use different cables. It turns out at channel 5, the phenomenon will happen but not on other channels. What kind of issue could be with this channel? like they will connect themselves ( the two channel inputs）? Thank you!
Great, you did not mention testing the cables in your original post.
You also did not mention this only shows up on one channel.
It still sounds to me, most likely, that there is something PHYSICALLY going on with that channel pin. But since little can go wrong with the channel header pin itself, that leaves me stumped.
A remote possibility is that the ADS1299 channel 5 chip logic is intermittent. But that also sounds unlikely because internal chip failures are usually complete failures that do not behave intermittently. If you have a source of compressed air in your lab / workshop, you might try blowing out all the nooks and crannies of your board, such as the pin areas of the TI ADS1299 chip itself. A remote possibility is that some conductive metal particle has lodged in those areas, resulting in intermittent operation.
I suggest that you email (contact at openbci.com) and give a link to this Forum thread. They may suggest more tests or board replacement. Was this a recent purchase?
William
Thanks for the reply! I'll test what you suggested and if still does not work consistently, I'll email for an exchange. I think we bought it within a year.
It seems that if we only want a 1-channel ECG, 2 electrodes are enough to get the ECG signal. The ground connection is just for mitigating the common noise？ Thx！
I bought a new Cyton board and tested it. I got the same phenomenon. Then I realized that it is not due to the board. After some testing, I found that it is because I did not connect to the ground. Although I am not sure why this is causing the disappearing of the signal. Any idea on this and what is the functionality of the ground in the ECG measuring case besides removing the common noise? Thx！
Best approach is to follow the tutorial, exactly.
https://docs.openbci.com/GettingStarted/Biosensing-Setups/ECGSetup/
Your local environment might have some type of electric field potential phenomena going on. Such that after a period of time, the ADS1299 differential amplifier is 'saturated' and can no longer register the signal. The ground lead in EEG / ECG also has the function of centering the differential amps. When used for ECG, ground is termed DRL "driven right leg", which also injects a counter-mains out of phase signal to reduce mains artifacts.
Why channel 5 is going this, but not other channels, seems odd. But following standard practices / instructions should be a first priority.
William
OK. Thanks for the quick reply!