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The ADS1299EEG-FE daughter - Board with Arduino grounding problem

Vibodha Bandara
Intellectual 260 points
Other Parts Discussed in Thread: ADS1299, TXB0108

Hi all,

I have ADS1299EEG-FE kit and worked fine. Then I separated the  ADS1299EEG-FE daughter-board from MMBO mother board and connected with Arduino Uno ( SCK, Dout, Din, RESET, DRDY are connected with ardunio via   5V-3.3V level shiftier) to control ADS1299 with Arduino. 

The ground line of  ADS1299EEG-FE daughter-board was directly connected with ground line of Uno. 
With this setup I was not able to control the chip correctly. All the register values I read form ADS1299 appeared with crazy values as follows..

 

Then I disconnected the direct connection of two Ground lines of ADS1299 board and Ardiuno Uno and connected them with a 10K resistor .( One side of the resistor is ADS1299 Board Ground and other side is Uno ground).  With this configuration I was able to read the correct register values and read EEG samples as follows. 

But some times the problem happens with is ground configuration also.. I'm very confused with this situation.. please help ..

Thank you

  • 0
    TI__Mastermind 38745 points
    Hello Vibodha,

    There are a number of power supplies required to correctly power the ADS1299. To me it seems like perhaps the power supplies are not quite where they should be so maybe sometimes the device is powered on and sometimes it is not. Could you perhaps probe the ADS1299 supplies (AVDD, AVSS, DVDD) with respect to the EVM board ground? Then could you probe the EVM ground with respect to the Arduino board ground? I'd also check the datasheets of both the level shifter you are using as well as the Arduino board regulator to make sure they are capable of supplying all of the power that will be consumed by the components on the ADS1299 board.

    Regards,
    Brian Pisani
  • 0 in reply to Brian Pisani
    Intellectual 260 points
    Thanks for the response Brian ,
    Here even I separated the daughter-board from MMBO , I used the power supply lines form MMBO mother board . ie J4 connector of the daughter-board was connected with MMBO power connector with connecting wires. So that AVDD, AVSS, DVDD levels are in the recommended values..
    There is

    417 mv drop between Arduino GND and EVM ground ( Without connecting two Ground lines)
    376 mv drop ,, ,, (connecting two Grounds with 10K resistor)
    4 mv drop ,, ,, (connecting two Grounds connected directly)

    I have a Used level sifter with TXB0108 IC

    Regards,
    Vibodha
  • 0 in reply to Vibodha Bandara
    TI__Mastermind 38745 points
    Hi Vibodha,

    I'm sorry it was unclear to me before that you are still using the MMB0 board to power the EVM board. Is the ground on the MMB0 board also connected to the ground on the Arduino board? Is DRDY pulsing on the ADS1299 when you connect the grounds directly? If it's not then the device is probably off. I'd recommend looking at your SPI transactions on an oscilloscope and checking to see where the logic levels are ending up.

    Regards,
    Brian Pisani