accessing ADS1299 SPI from Edison, MISO noise

youssef_har

Hey,

 

I have been working on configuring Edison's SPI bus to control the ADS1299 analog to digital converter chip through the mraa library.

While my program is running, I am monitoring the SPI pins (SCLK, MOSI, MISO, and CS1) and it seems that SCLK, MOSI, and CS1 are working correctly. However, the MISO pin only shows noise.

Is there usually a quick fix for this kind of problems? 

PS: I added a pull up resistor to the MISO terminal but that did not fix the issue.

 

In my program, I am only trying to read ADS1299's register #15, which translates into sending 0x35 - 0x00 - 0x00.

Here is the program that I am running: (Eclipse IDE platform)

 

int main(){

     mraa::Spi* spi;

 

     spi = new mraa::Spi(0);

 

     spi->frequency(4000000);

 

     uint8_t data[] = {0x35,0x00,0x00};

     uint8_t rxBuf[3];

 

     if(spi->transfer(data, rxBuf, 3) == MRAA_SUCCESS){

     printf("Received: %i - %i - %i\n",rxBuf[0],rxBuf[1],rxBuf[2]);

     }

     

     usleep(10000);

 

     delete spi;

 

    return MRAA_SUCCESS;

}

Any help would be appreciated. Thanks,

Youssef

biomurph

Can you tell us about your hardware setup? How do you have the ADS1299 set up? Are you using the TI dev mod?

youssef_har

Hello,

Thanks for the reply. I am using Intel Edison to control ADS1299 via the SPI bus. I connected Edison to the upper card of the ADS1299EEG-FE development kit. I am supplying this card with a 3.3 V as digital input and 5 V as analog input. In addition, I am connecting the CLKSEL, RESET, and PWDN pins to the 3.3V. And I am connecting pins 4, 10, and 18 of J3 to ground. Finally, I made sure I had the correct settings for the JPs. 

My aim is to read 8 input channels, however at this point I am just trying to read 1 ADS1299 register to make sure SPI is working correctly. 

The mraa library automatically controls the CS pin, however since that did not work and I thought it might be the problem, I tried manually controlling this pin while taking care of the delays I need to add in order for certain instructions to fully execute. But that also did not work.

Am I missing something in the hardware? Or maybe some initialisation in software? 

Any help would be appreciated. 

Thanks,

Youssef

biomurph

It sounds like you have the system set up correctly.

Your spi frequency is not too fast.

I am not familiar with the Edison, or the MRAA lib. 

Do you have a way to scope your signal lines?