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ADS1298: Data converters forum

akhil pendyala
Prodigy 60 points
Part Number: ADS1298
Other Parts Discussed in Thread: MSP430F5659,

Hi ,

I am using ADS1298 in my project to acquire 12 lead ECG and i am interfacing it to MSP430F5659.

1. I got my schematic right.

2. I have completed initialization of ADS1298 and Getting device ID  -  as 92h.

  The problem is when i am trying to read data from ADS1298 using SPI clock of 2Mhz i am getting data from ADS1298. I tried plotting each channel data taking MSB and LSB from received data combined MSB and LSB converted it to equivalent Decimal data and plotted using MS OFFICE EXCEL  but all i am getting is a random waveform nothing looking such as ECG.

Am i  doing any mistake in the process, If so please help me out with how to read correct data from ADS1298 and how to plot it .

Also if possible please send the  flow of how to read data from ADS1298 after configuration.

Thanks in advance.

i am also attaching channel 1 output waveform

  • 0
    TI__Guru 55152 points

    Hi Akhil,

    Thanks for your post and welcome to the forum! 

    You can see the code to voltage conversion FAQ post in my signature to confirm that you're converting correctly. 

    It looks to me like there is a lot of noise in the measurement, are you using the RLD? 

  • 0 in reply to Alexander Smith
    Prodigy 60 points

    Hi 

    Thanks for replying .

    i will see the resource which you mentioned .

    Yeah i was using RLD  same as in ADS1298 ECG FE schematic. Till now i only read data from ADS1298 but i have not handled any noise. If noise was there in measurement how to handle that noise. 

    Best regards,

    Akhil

  • 0 in reply to akhil pendyala
    TI__Guru 55152 points

    Hi Akhil,

    You will need to configure the RLD properly in order to bias the patient and cancel the noise out of the measurement at the PGA. 

    When the RLD is used to bias the patient it shifts both inputs to the same common mode. At the PGA, this common-mode is removed from the measurement as the PGA subtracts the negative channel from the positive channel. This should clean up the measurement significantly. Make sure that the RLD register settings are properly configured.

  • 0 in reply to Alexander Smith
    Prodigy 60 points

    Hi Smith,

    Thanks for replying,

    Now i am getting correct wave forms, but getting noise at V1 to V6 , No noise at L1 and L2 (CH2 and CH3).

    inputs are

    IN1P  - V6  

    IN1N  - WCT

    IN2P - LA

    IN2N - RA

    IN3P - LL

    IN3N- RA

    IN4P - V2

    IN4N - WCT

    IN5P -V3

    IN5N -WCT

    IN6P - V4

    IN6N- WCT

    IN7P - V5

    IN7N- WCT

    IN8P - V1

    IN8N - WCT,

    Running SCLK at 2MHz, In LPM mode at 250SPS. Using internal WCT with 100pF capacitor and configured the registers  WCT1 as 0x0A and WCT2 as 0xDC, RLD_SENSP as 0x06 and RLD_SENSN as 0x02. 

    I have one more doubt, is it necessary to give the test signal at initialization,

    After completing initialization, i am reading the data by giving RDATAC and START commands , am i doing anything wrong?

    Thanks & Regards

    Akhil

  • 0 in reply to akhil pendyala
    TI__Guru 55152 points

    Hi Akhil,

    Great! How much noise are you seeing on the channels? What frequency is the noise?

    I would expect the WCT amplifiers to add some as per the table in the datasheet, but not a lot. 

    Do you have anti-aliasing RC filters on V1-V6? 

    Your register settings look correct and sending the test signal on initialization is not necessary as it only tests the signal chain, does not perform any calibration. 

    All of your digital communication sounds fine. 

  • 0 in reply to Alexander Smith
    Prodigy 60 points

    Hi Alexander Smith

    Thanks for replying.

    Problems were sorted out , Actually the problem was due to  conversion from hex to decimal. With your assurance on register settings we had another look on the whole process and finally we identified the problem.

    Thanks & regards

    Akhil.

  • 0 in reply to akhil pendyala
    TI__Guru 55152 points

    Great to hear! Please let us know if you have more questions. 

    I wish I mentioned it earlier, but for others that find this thread - there is a code to voltage conversion post in the BIOFAQ that can be found in my signature.