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incorrect data acquisition

qing yin80354
Prodigy 30 points

Other Parts Discussed in Thread: ADS1294, CC2530

hi ,

    i'm using  the CC2530 to control ADS1294.when set the MUX as 101  i can get the right results of internal test signal;then i simplely change the   MUX as 000 and give a DC

input ,i can't get the right results.why?what else should be changed?btw,when an input is added to the input pin ,the  results of test signal get larger offset to the real value. 

  • TI__Guru**** 182681 points

    Hi Qing,

    Welcome to our forum!  Can you please tell us what DC level you apply to the ADS1294 device and what output codes you do get?  How is your input connected to the CHp and CHn inputs?  Besides changing the MUX, how are the rest of the registers configured? 

  • in reply to Tom Hendrick
    Prodigy 30 points

    hi Tom,

     Thank you for your reply. I followed the “initial flow at power-up”. The following is my procedure:

    1.       Reset

    2.       set the input short to get the noise ,the results are noise[]

    3.       set internal test signal,   the results are ftest[]                                

           test[]=ftest[] -noise[]={16735511,16735339,16735360,16735371},that is 2mV as set(without connection to the input pin)                        

           test[]=ftest[] -noise[]={16729464,16730041,16729895,16729006},that is 2.2mV-2.3mV(with connection to the input pins, and this will change when the input changes)

    4.       set DC input :   the signal is 20mV DC from signal generator,(+,the red side) is connected to the Lead_LL and grand(the black side) is to Lead_RA,other pins without connection,as follows:

     

    I measured the voltage between IN2P and IN2N,that’s about 12mV.The ad results for this is :4channels output code{16776509,16776514,16776530,16776422}(corresponding input short output code is {8392,16765368,4687,16774322})

    the register value at this time is:  (from address 00h to 19h)

     

     

     

     

  • in reply to qing yin80354
    TI__Guru**** 182681 points

    Hi Qing,

    If I understand correctly, your saying that the internal test signal changes when you apply DC to the inputs, is that correct?  I've tried doing the same thing you describe and I do not see any shift (offset or gain) in the test signal, even with 500mV of offset applied to the input terminals.  When I do the input short, I get voltages ranging from 4.2-4.8uVpp across CH1 to CH4.  You say your input short test codes are {8392,16765368,4687,16774322}, which are quite large - are you running the device in single shot mode or are these numbers an average?  Please also describe the way you determined the values in point 3 above, I see about a 2mV difference between the two sets of data.

    I'm not sure how the setting of the Config2 register above is going to impact your readings, the (0x22) sets the test signal to 'external' and the test frequency bits to 10, which is listed as 'Not used' - I can't configure my board that way at the moment.  Try setting that register to 0x10 and let me know what you see.

  • in reply to Tom Hendrick
    Prodigy 30 points

    Hi Tom,

    If I understand correctly, your saying that the internal test signal changes when you apply DC to the inputs, is that correct? 

    ——Yes！That’s what happened on my board.

    When I do the input short, I get voltages ranging from 4.2-4.8uVpp across CH1 to CH4.  You say your input short test codes are {8392,16765368,4687,16774322}, which are quite large - are you running the device in single shot mode or are these numbers an average? 

    ——In single short mode , but they are almost the same each time . the register configuration :

    Please also describe the way you determined the values in point 3 above, I see about a 2mV difference between the two sets of data.

    ——(16777216-16735511)/8388607*2.4V/6=1.989mV

          (16777216-16729464)/8388607*2.4V/6=2.28mV (Maybe you forgot the gain of 6?)

    I'm not sure how the setting of the Config2 register above is going to impact your readings, the (0x22) sets the test signal to 'external' and the test frequency bits to 10, which is listed as 'Not used' - I can't configure my board that way at the moment.  Try setting that register to 0x10 and let me know what you see.

    ——When I read the test signal code the CONFIG2 is set to 0X10,the following is the register configuration :

          When input DC signal, at the beginning, I configured the CONGIG2 as 0X10,that didn’t work well, so I changed it . The following is 4 channels output codes with CONFIG2 0X10:{16776502, 16776478, 16776542, 16776450}.They are almost the same

    Here is my schematic ADS1294:

     

    For I have been stuck here for more than one week, I’m after the schedule now. My boss urged me .Can you give me some suggestions? How much is the chance that the chip couldn’t work well? If I change a new one, will that help? Thank you very much!

     Best wishes.

    Qing