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ADS1299: EEG Query

mubeen khalid
Prodigy 155 points
Other Parts Discussed in Thread: ADS1299

Here is my EEG waveform. I am not sure its EEG or noise. Because I am not getting peak amplitude at 10 HZ when eyes are closed. 

I am using differential signal. While using Bias settings. Biasout and BiasINV pins are short and are directly connected to ear electrode. Here are my Register settings.

These signals are from back of the head. Eye blinks are so sharp and clear having different polarities. So can you help what is this thing? according to me its a random noise. We are using 24 electrodes EEG cap.

ADS.WREG(CONFIG1, 0b11010110);
ADS.WREG(CONFIG2, 0xC0);
ADS.WREG(CONFIG3, 0xE6);
ADS.WREG(0x05, 0x00);
ADS.WREG(0x06, 0x81);
ADS.WREG(0x07, 0x81);
ADS.WREG(0x08, 0x81);
ADS.WREG(0x09, 0x81);
ADS.WREG(0x0A, 0x81);
ADS.WREG(0x0B, 0x81);
ADS.WREG(0x0C, 0x81);
ADS.WREG(0x0D, 0xFF);
ADS.WREG(0x0E, 0xFF);
ADS.WREG(0x15, 0x20);

  • 0
    TI__Guru 66386 points

    Hello Mubeen,

    Thanks for your post.

    I would experiment with using a higher gain setting first. Right now, you are only using Gain = 1. Increasing the gain of the internal PGA significantly improves the input-referred noise of the ADS1299, which allows you to resolve smaller amplitude signals.

    Also, are you using an external voltage source for BIASREF? Currently, you have set BIASREF_INT = 0. The BIASREF voltage is needed to set the DC common-mode for the BIAS amplifier and subsequently the body. If you do not have an external BIASREF source, then you should set BIASREF_INT = 1 and use the internal mid-supply voltage.

    Best Regards,

  • 0 in reply to Ryan Andrews
    Prodigy 155 points
    Thank Ryan for your reply really appreciate this. I checked my signals at Gain=24 but result was same. We see a slight change in 10hz frequency on closing eyes. Its mean I am getting EEG but its having so much noise. My BIASREF is ground isn't ok?
    Moreover, I am using 5V unipolar supply.

    Best regards,
  • 0 in reply to mubeen khalid
    TI__Guru 66386 points
    Hello Mubeen,

    With a 5-V unipolar supply, you should be using a mid-supply common-mode voltage for BIASREF, not ground. Try using the internal BIASREF.

    Best Regards,
  • 0 in reply to Ryan Andrews
    Prodigy 155 points
    hey Ryan Thanks for replying. Really appreciate it.

    I have used internal BIASREF. I used BIASOUT pin and connected it to the ear. I am running it on openloop and removed the 1M and 1.5 nCap as suggested in forum to obtain better results, but unfortunately I am not getting any EEG signals from this. :(

    ADS.WREG(CONFIG1, 0b11010110);
    ADS.WREG(CONFIG2, 0xC0);
    ADS.WREG(CONFIG3, 0xEC);
    ADS.WREG(0x05, 0x60);
    ADS.WREG(0x06, 0x81);
    ADS.WREG(0x07, 0x81);
    ADS.WREG(0x08, 0x81);
    ADS.WREG(0x09, 0x81);
    ADS.WREG(0x0A, 0x81);
    ADS.WREG(0x0B, 0x81);
    ADS.WREG(0x0C, 0x81);
    ADS.WREG(0x0D, 0xFF);
    ADS.WREG(0x0E, 0xFF);
    ADS.WREG(0x15, 0x20);

    these are my current register values.