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Is SINGLE SHOT mode is the Right way to Get ECG signals.

Dinu
Intellectual 335 points
Other Parts Discussed in Thread: ADS1298R, ADS1298

Hi,

Am working on ADS1298R and getting the ECG data through SINGLE SHOT mode (500 SPS). Now am trying to configure the respiration mode also. But am lost. Please Give me suggestions. And is the SINGLE SHOT mode is right way to get the ECG data? What problems it could create? Please help...

  • 0
    TI__Mastermind 38745 points
    Hey Dinesh,

    To configure the device for respiration rate measurement using internally generated modulation and demodulation signals, set bits [7:6] in the RESP register and then configure bits [1:0] of the RESP register to b'10. Channel 1 data will then correspond to data measured using the internal respiration circuitry.

    I would net recommend single shot mode unless your application requires a non-standard or non-continuous collection pattern. Using single shot mode will require that the digital filter be reset with every data point essentially dropping the data rate by a factor of 4. This mode leaves the system more susceptible to aliasing effects, thus requiring more complex analog or digital filtering. Loading on the host processor increases because it must toggle the START pin or send a START command to initiate a new conversion cycle. Unless your system requires that data be collected sporadically, I would high recommend using continuous conversion mode.

    Regards,
    Brian Pisani
  • 0 in reply to Brian Pisani
    Intellectual 335 points

    Thanks Brian,

    I will configure the module, like you suggested and will get back to you.

    Can we get the respiration data, while the module is working in SINGLE SHOT mode?

  • 0 in reply to Dinu
    TI__Mastermind 38745 points
    Hey Dinesh,

    It is possible to get respiration data in single shot mode since the internal modulation circuitry will be running even when the delta-sigma modulator is not.

    Brian
  • 0 in reply to Brian Pisani
    Intellectual 335 points

    Thanks Brian,

    I have tried the Bit changes in Respiration control register as like you advised. But still am getting no response from the module. I have changed the CONFIG 4 registers also, to configure it for Respiration. As we know, from ADS1298R we get the respiration data from channel 1. So is there is any other changes should be done in Channel 1 control register? Or is there is anything we have to do with the Hardware? Thanks in Advance.

  • 0 in reply to Dinu
    TI__Mastermind 38745 points
    Hey Dinesh,

    There are quite a few things you'll have to do in hardware to make an accurate respiration measurement. Refer to the "Respiration" section of the datasheet beginning on page 75. The entire section is worth a read, but I'd like to point out Figure 76 as an example hardware setup for respiration rate measurement. I'd also advise you read this app note to understand the theory behind impedance pneumography, which is how the ADS1298 can make respiration rate measurements: www.ti.com/.../sbaa181.pdf

    Regards,
    Brian Pisani
  • 0 in reply to Brian Pisani
    Intellectual 335 points

    Dear Brian,

    Thanks for your advise and I will look into it. Until now am configuring the ADS 1298R module in SINGLE SHOT mode without the MMB0 board and there is no issues in the ECG waveform data. Since the on board circuitry for Respiration is on the ADS1298R ECDFE board, I hope there will be no issues for Respiration waveform data in SINGLE SHOT mode without the MMB0 board. Is it OK?

  • 0 in reply to Dinu
    TI__Mastermind 38745 points
    Hey Dinesh,

    It should work in theory. As I suggested before, I highly recommend using single shot mode unless there is a real need to do so. Do you need a nonstandard sampling pattern?

    Brian
  • 0 in reply to Brian Pisani
    TI__Mastermind 38745 points
    ... I highly recommend *against using single shot mode...
  • 0 in reply to Brian Pisani
    Intellectual 335 points

    Dear Brian,

    My Host processor doesn't have a interrupt source to check the DRDY pin. And also am not using the MMB0 board.

    For these reasons only am going for Single shot mode and checking for data from ADS1298R module, for every 2 millisec and I have no issues in ECG data. But for Respiration, am getting no response. The channel 1 data has no changes in its output. The Resp register configurations are configured correctly. Can you send me the links for the original datasheet and user guide for ADS1298R to check the hardware.

  • 0 in reply to Dinu
    TI__Mastermind 38745 points
    Hey Dinesh,

    You can receive ECG data without interrupts and without using single shot mode. Even in single shot mode, the DRDY pin is the only indicator that new conversion data is present. You can tell when new data is ready using polling similar to this pseudocode:

    while( 1 ) {
    if( DRDY = 0 ) {
    read SPI data;
    }
    }

    This approach will work when the device is configured in continuous conversion mode.

    How are you attempting to measure respiration? The datasheet and EVM users guide can be found here:
    Datasheet: www.ti.com/.../sbas459j.pdf
    User's Guide: www.ti.com/.../sbau181a.pdf
    For future reference, both documents may be found on the ADS1298R's product page on TI.com.

    Regards,
    Brian Pisani
  • 0 in reply to Brian Pisani
    Intellectual 335 points

    Hi Brian,


    This is how i am attempting to configure respiration in ADS 1298R module.

    H/W Configurations:

    1. Am not using MMB0 board.
    2. In Front end board JP33, pins (5-6) & (7-8) are shorted.
    3. JP36, pins (2-3) are shorted.
    4. JP34 and JP35, pins (1-2) are shorted.

    S/W Configurations:

    1. Single shot mode
    2. Resp. Ctrl Reg : Internal Resp. with Internal Clk, Phase - 112.5 degree, Modulation and Demodulation Enabled.
    3. Channel Ctrl Reg : Normal Operation, PGA = 6, Normal Electrode.
    4. Config 4 : Resp. Freq - 32 KHz, Pulse mode Enable.

    After that i have checked the Channel 1 data for every 2 millisecond by issuing RDATA command and it gives continuous similar data.

    I have checked the Datasheet and User guide and I didn't get what am missing.

  • 0 in reply to Dinu
    TI__Mastermind 38745 points
    Hey Dinesh,

    Do you intend to measure breathing from a patient simulator connected to the inputs or are you intending to use the switched resistor setup that exists on the board? If you want to do the former, change JP34 and JP35 to short pins 2 and 3. If you want to use the on-board switch setup, install the jumper between pins 1 and 2 of JP36.

    Is the ADS1298R configured in SDATAC mode? If not, the data could potentially get corrupted if a DRDY edge were to fall low in the middle of a collection. I again must recommend you collect data from the device synchronously with the DRDY pin (which may be done without interrupts) because of all the timing and aliasing benefits. Even in single shot mode, it is necessary that collections be timed following a DRDY pulse.

    Regards,
    Brian Pisani
  • 0 in reply to Brian Pisani
    Intellectual 335 points

    Dear Brian,

    Thanks for your advise and i will take it. I am intending to check the respiration data from a patient simulator and I have configured it as you suggested. But still no luck.

    Do i have to give an external sq. wave signal in J6, in order to get the resp. data while am measuring it from an simulator? If yes means, what would be the frequency?

    While simulating the resp data with on board sq. wave signal, is the 0.3 Hz sq. wave signal is enough for that?

    Is channel 1 data is the resp. waveform data? If we plot the values from Channel 1 can i get the resp. Waveform?

    Regards,

    Dinesh

  • 0 in reply to Dinu
    TI__Mastermind 38745 points
    Hey Dinesh,

    You should not have to provide a square wave from J6. If pins 1 and 2 are shorted on JP36 (the MSP430 pin and the net titled "MSP") then a square wave with a very low frequency should appear on the MSP net (perhaps probe it to ensure this is the case). In the lower left hand portion of page 63, you can see how that signal will open and close a switch that will change the resistance in the path of the channel 1 inputs slightly which will simulate breathing. For this to work short pins 1 and 2 of JP34 and JP35 such that this circuit is what is providing input to the device rather than ELEC_LA and ELEC_RA.

    Yes, if the device is configured how I have suggested, the output of channel 1 should be a respiration waveform. In the case of the board simulated version, you should expect it to look square. Real breathing tends to look much more sinusoidal. In each case, the frequency should be very low.

    Regards,
    Brian Pisani
  • 0 in reply to Brian Pisani
    Intellectual 335 points

    Hi Brian,

     I have checked the MSP's frequency and it is nearly 0.3Hz. There is an LED D11 glowing. It matches with the signal from MSP. Does it shows the frequency?

  • 0 in reply to Dinu
    TI__Mastermind 38745 points
    Hey Dinesh,

    The simulated respiration should be occurring at that frequency. Are you able to see a square waveform corresponding to the simulated respiration in the output of channel 1?
  • 0 in reply to Brian Pisani
    Intellectual 335 points

    I can see a Waveform but doesn't looks like a square wave. It in a non linear pattern.

  • 0 in reply to Dinu
    TI__Mastermind 38745 points
    Hey Dinesh,

    Can you probe pins 5 and 7 of JP33 to ensure that there is a 32 kHz square wave present (you may have to remove the jumpers momentarily). If there is and you are still unable to get a good waveform, send me a copy of about 3 seconds worth of channel 1 hex data so I can see what the problem might be.

    Regards,
    Brian Pisani
  • 0 in reply to Brian Pisani
    Intellectual 335 points

    Am getting  wave form as shown in the user manual Pg. No: 60. How to ensure that am using 32 Khz square wave in JP33? How to calculate the Respiration rate data using this waveform data?

  • 0 in reply to Dinu
    TI__Mastermind 38745 points
    Hey Dinesh,

    Are you referring to page 43 of the EVM user's guide? That is the respiration waveform. There is no need to check if the modulation waveform is present if you are getting the correct respiration data. If you'd still like to look at it, however, you should connect an oscilloscope to the pins I suggested.

    The respiration rate is simply the frequency of the output waveform that you see. Calculating the period of a digital signal from the data is a topic on its own; one which I do not have much experience with. One method I can think of immediately is high-pass filtering the data to remove the DC component and running a zero-cross timer algorithm to count how many samples occur in one period. From there you can calculate the period in seconds since you know the sample frequency.

    Regards,
    Brian Pisani