REG: ADS1296 output

Hello Brian Pisani,

Thanks for your quick reply.  Sorry for the inconvenience caused.

Here by I have attached the graph please refer the image,

Also attached the circuit schematic for your referral,

SensorBoard.11.pdf

Hello Brian Pisani,

Thanks for the reply.

Here are the below, which I have tried as per your recommendation.

1) Removed the 4V external reference from the board,

2) Enabled the 4V internal reference of the ADS1296 by writing the value 0xE0 in CONFIG3 register.

Now, I have measured the output by changing the input voltage in channel 3 from 80mV to 120mV. I could see the exact output when the gain is set to 1 where as if the gain is set to 12, I am not getting the expected output. Probably my conversion formula used is not right. Here is the conversion formula used,

reference voltage = 4.0;

conversion factor  = reference voltage / (2 ^ 23 - 1);

Output_in_V = { [ channel value ] * (conversion factor) } / gain.

When Gain == 1,

When Gain == 12,

I have also attached the Digital Log for your referral. Please refer Channel 3 for cross verification.ADSlog_gain12.txt

ADSlog_gain12.txt

Not able to find why there is a output variation when the gain parameter is the only change from 1 to 12.

Could you find the problematic area?

Regards,

Nimi

Hello Brian,

Please find the attachment for register settings,

Code used is also attached here,

void AD1296_init(void)
{
	uint8_t data = 0;
	uint8_t RegData[26];	
	
	ADS1296_Data_Stop_Read();

	// Set High resolution mode and  data rate as 8Ksps	
	data = HIGH_RESOLUTION | DAISY_DISABLE | FMOD_64;	
	ADS1296_Register_Write(CONFIG1, 1, &data);
	

	// Enable internal reference
	data = 0xE0;
	ADS1296_Register_Write(CONFIG3, 1, &data);
	
	// No test signal required
	data = 0;
	ADS1296_Register_Write(CONFIG2, 1, &data);

	//Normal input selection
	data = GAIN_12 | NORMAL_INPUT;
	ADS1296_Register_Write(CH1SET, 1, &data);
	ADS1296_Register_Write(CH2SET, 1, &data);
	ADS1296_Register_Write(CH3SET, 1, &data);
	ADS1296_Register_Write(CH4SET, 1, &data);
	ADS1296_Register_Write(CH5SET, 1, &data);
	ADS1296_Register_Write(CH6SET, 1, &data);

	// Read API call initiated as requested by Brian
	ADS1296_Register_Read(0x00, 26, RegData);	
	
	ADS1296_System_Start_Conversion();
	
	ADS1296_Data_Read_Continuous();		
}

void ADS1296_Register_Write(U8 StartAddress, U8 Count, U8* Data)
{
	uint8_t index = 0;
	
	// Global array "ADS1296_WriteRegArray"
	ADS1296_WriteRegArray[0] = WREG | StartAddress;
	ADS1296_WriteRegArray[1] = Count - 1;
	
	for(index = 0; index < Count; index++)
	{
		 ADS1296_WriteRegArray[2+index] = Data[index];
	}
	
	// Low level SPI call.
	spi_master_transfer(ADS1296_WriteRegArray, Count+2, ADS1296_ReadRegArray, Count+2);
}

void ADS1296_Register_Read(U8 StartAddress, U8 Count, U8* Data)
{
	uint8_t index = 0;
	
	ADS1296_WriteRegArray[0] = RREG | StartAddress;
	ADS1296_WriteRegArray[1] = Count - 1;
	
	for (index = 0; index < Count; index++)
	{
		ADS1296_WriteRegArray[2+index] = 0x00;
	}
	
	spi_master_transfer(ADS1296_WriteRegArray, Count+2, ADS1296_ReadRegArray, Count+2);
	
	for (index = 0; index < Count; index++)
	{
		Data[index] = ADS1296_ReadRegArray[2+index];
	}
}

Schematic:-

The input voltage is applied in U798 pin 3 and 4. please find the schematic SensorBoard.pdf

Question:-

1) why there is a change in output signal when the gain is changed from 1 to 12. BTW, when gain is 1, I could see the expected output but when the gain is 12, the output is not the expected one.

Should you require more information, please don`t hesitate to ask.

Please help me to identify the cause.

Hello Brain,

So for I have not seen the Section 7.3 in page no 12. Analog inputs, the full scale differential input voltage range (AINp-AINn) is ±Vref / gain.

Now, Vref in my case is 4V and gain is 12V. In that case, the maximum voltage can be measured by ADS is ±333mV.

Am i correct? Correct me if I am wrong.

Now I set the input variation from 0mV to 220mV. I could see the ADS measuring the same. Please find the below,

Still, the output voltage is not staying constant. Take example at sample 43801 refer graph, i expect the output should stay at 48mV, but it swings between 48mV and zero hence we could see the full area is painted.

As per my expectation, the graph should be like below,

But the same behavior is not happening when the gain is 1. Can you find out where the problem could be?

Regards,

Nimi