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ADS1294 Respiration data not proper

Arun Kumar27
Intellectual 590 points
Other Parts Discussed in Thread: MSP430BT5190, ADS1294R, ADS1294

Hi,


We are interfacing MSP430BT5190 with ADS1294R using a custom board.

For testing we are using Nettech MiniSim ECG simulator.

We are able to get the ECG data, but unable to get respiration data.

measurement using Internally generated MOD signals ( RESP[1:0] = 10 ), 250SPS, low power mode, 135 degree phase shift, 32KHz modulation clock.

When i collect the data on channel 1, i am getting all zeros.

Any suggestions?

Thanks & regards

Arun

  • 0
    TI__Mastermind 18285 points
    Arun,

    I am moving your post to the correct forum.
  • 0 in reply to Arun Kumar27
    TI__Guru 66816 points

    Hi Arun,

    Thank you for your question. Can you please share some more details about your ADS1294 circuit and the simulator settings you are using for the respiration measurement? A schematic and a list of register settings for the ADS1294R will be helpful for us to get started.

    Have you been able to read any data on Channel 1? Have you tried using another signal source, such as the internal square wave test signal?

    Best Regards,

  • 0 in reply to Ryan Andrews
    Intellectual 590 points

    Hi,

    Please find the circuit for respiration measurement. 

    Following are the register configurations i am using.

    Config1 = 0x46

    Config2 = 0x00

    Config3 = 0x40

    Ch1Set = 0x30      //Gain = 3

    RESP = 0xF6       

    Config4 = 0x20

    And yes i have tried reading channel 1 with internal test, following is the waveform i got. 

    Thanks & regards

    Arun 

  • 0 in reply to Arun Kumar27
    Intellectual 590 points

    Hi,

    The waveform in the above post  is with respiration settings enabled.

    Without any respiration configurations i am getting the following waveform for internal test signal.

    Regards

    Arun 

  • 0 in reply to Arun Kumar27
    TI__Guru 66816 points

    Hi Arun,

    Have you made some progress since your last post?

    I checked your register settings and two things caught my attention. First, you have CONFIG2 = 0x00, meaning the internal test signal is disabled. Are you providing an external signal to the TEST_PACE_OUT pins? Second, you have CONFIG3 = 0x40, meaning the internal reference is powered-down. Are you supplying an external 2.4V reference?

    The respiration modulation clock signal is mostly filtered out in the digital filter (-3dB cutoff = 0.262*fDR), but you might be seeing some of that signal alias into the passband. For quick device evaluation, customers will have this feature disabled in order to measure a clean test signal like in your last post.

    Best Regards,

  • 0 in reply to Ryan Andrews
    Intellectual 590 points

    Hi Ryan,

    Thanks for the reply.

    I made the following changes.

    Config2 = 0x80 (I am giving the external test signal through simulator)

    Config3 = 0xC0

    (Keeping all the other registers same)

    And i am getting the following waveform

    And I am observing that, number of peaks in the above waveform is almost equal to the respiration rate i set in the simulator. (I checked it with multiple runs varying the respiration rate as 15, 30, 60 etc).

    In the document "Respiration Rate Measurement Based on Impedance Pneumography", the respiration wave looks like a sine wave.

    So is there any further processing required for the above wave or am i missing something still?

    Regards

    Arun

  • 0 in reply to Arun Kumar27
    TI__Guru 66816 points
    Hi Arun,

    It looks like you are close to capturing the respiration waveform. As you mentioned, it is generally more sinusoidal than what your image shows. You may be missing data samples. Verify that you are reading data with each /DRDY pulse and that you are able to finish reading the 24-bit STATUS + (4 x 24-bit channel data) before the next /DRDY.

    By the way, CONFIG2 [7] must always equal 0.

    You mentioned that you are driving an external test signal, but it is unclear to me why this is necessary when you are measuring respiration on Channel 1. Regardless, it should not interfere with your measurements if MUX1[2:0] = 000.

    Regards,
  • 0 in reply to Ryan Andrews
    Intellectual 590 points
    Hi Ryan,

    Thanks for the reply.

    The problem was truncation of data while storing it.
    When storing it in the SD Card, the lower most byte was getting truncated. So I was getting a resolution of 16bit only.
    Now I am getting smooth sine curve.

    Regards
    Arun