ADS1299: ads1299. Noise measurement

This RDAC moment

Hello Ildar,

Thank you for your post and welcome to our forum.

The problem you are describing is not very clear. Please try to restate your question. 

If you are having trouble communicating with the ADS1299, you can try the example start-up sequence shown in Figure 67.

Regards,

Hello Ryan, thank you for your answer

i can write and can read a value from the register, it is mean that I have correct connections with ADS1299. Device ID - "0x3E"

Now, I want to check noise (Input shorted) - but receive from all channel - value  - 16776019 (+-1000)- it is not correct, but where can be the problem?

You can see this process in the picture - for all channel - "input shorted"

I set the next resister:

CONFIG3, 0xE0;
CONFIG1, 0x96;
CONFIG2, 0xC0;
0x04, 0x00;
0x0D, 0xFF;
0x0E, 0xFF;
0x0F, 0x00;
0x10, 0x00;
0x11, 0x00;
0x12, 0x00;
0x13, 0x00;
0x14, 0x0F;
0x15, 0x00;
0x16, 0x00;
0x17, 0x00;
CH1SET, 0x09;
CH2SET, 0x09;
CH3SET, 0x09;
CH4SET, 0x09;
CH5SET, 0x09;
CH6SET, 0x09;
CH7SET, 0x09;
CH8SET, 0x09;

My code in STM32 for contimuesly read data:

send_command(RDATAC);

send_command(START);

while 1:{

if (HAL_GPIO_ReadPin(DRDY_GPIO_Port, DRDY_Pin) == GPIO_PIN_RESET){
HAL_GPIO_WritePin(GPIOD, CS_Pin, GPIO_PIN_RESET);
for(int i = 0; i<9; i++){
dataPacket = 0;
for(int j = 0; j<3; j++){
HAL_SPI_TransmitReceive(&hspi3,(uint8_t*)&test,(uint8_t*)&received_Byte,1,0x1000);
dataPacket = (dataPacket<<8) | received_Byte;
}
output[i] = dataPacket;
dataPacket = 0;
}}

//spi settings

hspi3.Init.Direction = SPI_DIRECTION_2LINES;
hspi3.Init.DataSize = SPI_DATASIZE_8BIT;
hspi3.Init.CLKPolarity = SPI_POLARITY_LOW;
hspi3.Init.CLKPhase = SPI_PHASE_2EDGE;
hspi3.Init.NSS = SPI_NSS_SOFT;
hspi3.Init.BaudRatePrescaler = SPI_BAUDRATEPRESCALER_256;   // 250 kHz
hspi3.Init.FirstBit = SPI_FIRSTBIT_MSB;
hspi3.Init.TIMode = SPI_TIMODE_DISABLE;
hspi3.Init.CRCCalculation = SPI_CRCCALCULATION_DISABLE;
hspi3.Init.CRCPolynomial = 10;

I use bipolar voltage

VCAP1 = -1.2V

VCAP2 = 0.001V

VCAP3 = 4.2V

VCAP4=-0.125V

Status bits - 1100 0000 0000 0000 0000 0000‬

Hello Ildar,

We cannot decode the SPI communication from the oscilloscope capture as shown. Also, channel 1 is labeled as "DIN" but I assumed you mean "DOUT" (pin labels are from the ADS1299 perspective).

Are you reading back the register values to confirm they are written correctly?

Note: It is not necessary to close the SRB2 switches for input-short measurements. The PGA input pins will be shorted internally to mid-supply, so you do not want the SRB2 pin voltage contending with this. Please set bit 3 to 0 in all CHnSET registers.

Also, remember that the data output is in binary two's complement. Decimal values will range from -8,388,608 to +8,388,607 (-full-scale to +full-scale).

Regards,

Hello Ryan, thank you for your reply. Yes, it is Dout.

I read all register from ADS1299 and confirmed it. 

I set CHnSET 

CH1SET, 0x01;
CH2SET, 0x01;
CH3SET, 0x01;
CH4SET, 0x01;
CH5SET, 0x01;
CH6SET, 0x01;
CH7SET, 0x01;
CH8SET, 0x01;

But receive the same result (same picture in an oscilloscope). Should be - 0, but i receive  +8,387,607 (-+1000). It looks like the opposite.  Maybe need to replace ADS1299?

VCAP1 = -1.2V

VCAP2 = 0.001V

VCAP3 = 4.2V

VCAP4=-0.125V

Status bits - 1100 0000 0000 0000 0000 0000‬

Ryan, sorry that distract, will you have some advice for us? because our work is stopped. We wait for your answer.

Ildar

Hello Ildar,

I do not see any obvious issues with your setup. Is the reference voltage correct? The voltage difference between VREFP and VREFN should be 4.5 V, and VREFN should be tied to AVSS.

Regards,