ADS1299: ADS1299 IMPEDANCE CHECK.

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Replies: 5

Views: 57

Part Number: ADS1299

Hi All,

Iam using three ADS1299 in daisy chain mode to acquire 24 Channel EEG. My EEG Recording is all perfect and I want to measure Impedance of electrode of all INP channels. To Achieve this I set the register settings as shown below . My sampling Rate Is 250SPS with 24x gain.

I need to measure Impedance only one time before the EEG Recording starts. To calculate the impedance How many samples or how many seconds of data do I need ?

WREG(CONFIG1, 0b10110110);
WREG(LOFF, 0b00000010); // IMPEDANCE CHECK 6 nA CURRENT // 31.2 HZ CURRENT SIGNAL
WREG(LOFF_SENSP, 0b11111111); // IMPEDANCE CHECK FOR +VE CHANNEL
WREG(LOFF_SENSN, 0b111111111); // IMPEDANCE CHECK FOR -VE CHANNEL
WREG(CONFIG3, 0b11101100);
WREG(BIAS_SENSP, 0b11111111);
WREG(BIAS_SENSN, 0b11111111);
WREG(MISC1, 0b00000000); // open SRB1 Switch

I've externally connected the -ve inputs of all channels to the REF Electrode in my PCB, so SRB1 connection dosen't matter in my case.

I've attached the text file which has the data of the channel . . During this data I had INP electrode at O2, REF at INN & BIAS ELECTRODE attached to the body.

How do I calculate the impedance from the acquired data?eeg24channel2gnd28.txt

5 Replies

  • Can Anyone Help me with this?

  • In reply to Sumit Mourya:

    Hi Sumit,

    Thanks for reaching out and I apologize for the delay in the response.

    Your register configuration seems ok.

    I am working with the team to find out the impedance from the acquired data. 

    I will get back to you by tomorrow.

    Regards

    Praveen

    TI makes no warranties and assumes no liability for applications assistance or customer product design. You are fully responsible for all design decisions and engineering with regard to your products, including decisions relating to application of TI products. By providing technical information, TI does not intend to offer or provide engineering services or advice concerning your designs.

  • In reply to Praveen Aroul:

    Hi Sumit,

    I think it would be better to simplify the test setup to test 1 device at a time (8 channels).

    You could program the same register settings for all 3 devices but turn off the LOFF_SENSP and LOFF_SENSN for the 2 devices.

    Also, you can turn off the BIAS_SENSP and BIAS_SENSN registers for all the 3 devices.

    Can you please confirm if the data you had shared was already converted and processed?

    Can you share the raw data from the ADC (probably hex values)?

    Have you tried DC lead-off detection and see if you are getting constant values?

    After you check DC lead-off and check for constant value, you could use LOFF_FLIP and repeat the same DC lead-off and check for the ADC output codes?

    Please share the raw data for these tests as well.

     

    Regards

    Praveen

    TI makes no warranties and assumes no liability for applications assistance or customer product design. You are fully responsible for all design decisions and engineering with regard to your products, including decisions relating to application of TI products. By providing technical information, TI does not intend to offer or provide engineering services or advice concerning your designs.

  • In reply to Praveen Aroul:

    Hi Praveen,

    Thanks for your suggestions. I turned OFF BIAS_SENSP and BIAS_SENSN for all 3 devices and Turned on LOFF settings for only channel 1 . In daisy chain mode How can I  turn off the LOFF_SENSP and LOFF_SENSN for the 2 devices and keep it on for 1st device. 

    I think in Daisy chain mode register settings & channel settings for 1 ADC channels is same for other 2 devices also. Anyways, I recorded 1st channel data for raw eeg, raw impedance & impedance converted in uv. Attached are all three files. I got different results when I turned off BIAS_SENSP  & BIAS_SENSN.

    Raw EEG data has alpha & eyes blink signal which can be seen after converting data in  microvolts & filtering.

    WREG(CONFIG1, 0b10110110);
    WREG(LOFF, 0b00000010); // IMPEDANCE CHECK 6 nA CURRENT // 31.2 HZ CURRENT SIGNAL
    WREG(LOFF_SENSP, 0b00000001); // IMPEDANCE CHECK FOR +VE CHANNEL
    WREG(CONFIG3, 0b11101100); //for impedance check
    WREG(MISC1, 0b00000000); // open all SRB1 swtiches

    raw eeg data.txteeg impedance raw data.txteeg uv converted impedance data.txt

  • In reply to Sumit Mourya:

    Hi,

    Any help will be appreciated!!