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I made my own EEG circuit, and have some problems. In the beginning, I did not come across this situation but, suddenly, I started to get these outputs, and I could not find the reason. When I upload my EEG ADC signals to MSP430 it was working like this:

enter image description here

I did not change anything, but now it is giving these signals:

enter image description here

I touched a little bit to my electrodes it became like this but, it came to the same situation:

enter image description here

I have tried to put some DC bias and coupling capacitors, but it did not work, maybe I did not make it properly.

I made it as described in this video.

enter image description here

In my circuit, I used INA121, instrumentation stage, HPF for 0.5 Hz, and LPF for 200 Hz. They are inverting amplifiers. Maybe I could not make proper DC biases or another problem. I am getting 2 inputs as AC signals. Can you advise any solution, DC bias design also can be?

JRE
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Merve Özdaş
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  • Welcome! Please post a full schematic. You you using you MCU’s internal ADC? Are you aware it can’t sample negative voltages? – winny Jul 11 '23 at 19:27
  • Do you mean "upload to" or "sample with"?? Many microcontrollers can't sample negative numbers, and many EEG circuits you'll find therefore add an offset to the signal. – Scott Seidman Jul 11 '23 at 19:51
  • @ScottSeidman it does not need to be in the negative area. the output was like the first plot. between some ADC values like a sinus signal, if I need offset. how can I add? – Merve Özdaş Jul 12 '23 at 10:54

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