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ADS1299: ADS1299 Pin connections

Part Number: ADS1299

I am facing an issue with ADS1299. 

I have programmed ADS1299 channels to internal test signals in CHnSET register. It is showing square wave on Serial Plotter on Arduino IDE, as it should as per the datasheet. 

When I changed the MUX[2:0] value in CHnSET to 000, for external signal routing. I am getting some noise when I place my fingers, I thought it is working fine as human body has some static electrical charge. 
But when I applied a sine wave of 5uV VPP from a function generator, it showed the same waveform as earlier when there was no signal. Shown in the image below. 

I have applied the signal between IN8P and IN8N. BIASOUT pin left open. When BIASOUT pin connected to IN8N, as the datasheet says it is driven ground for voltage reference, the waveform shown by EEG is the same as above, no matter whatever waveform I give as input. 

The registers I have set are as follows: 

  ads_hardReset();         //Hardware reset by RESET pin
  ads_softReset();         // Send reset command
  getDeviceID();             // get device id
  ads_wreg(CONFIG1, 0xD6);  // No Daisy, Osc. Clock output disabled, 250Hz
  ads_wreg(CONFIG2, 0XD5);  // Generate test signal externally 
  ads_wreg(CONFIG3, 0xEC);  // Internal ref buff enabled,bias measurment open
  ads_wreg(CONFIG4, 0X00);  // Continuous conversion mode, Leadoff comparator OFF
  //Only measuring from channel 8    
  ads_wreg(CH1SET, 0xC1);  // POWER DOWN 
  ads_wreg(CH2SET, 0xC1);  // POWER DOWN
  ads_wreg(CH3SET, 0xC1);  // POWER DOWN
  ads_wreg(CH4SET, 0xC1);  // POWER DOWN
  ads_wreg(CH5SET, 0xC1);  // POWER DOWN
  ads_wreg(CH6SET, 0xC1);  // POWER DOWN
  ads_wreg(CH7SET, 0xC1);  // POWER DOWN
  ads_wreg(CH8SET, 0x00);  // init channel with normal eletrode, 1X gain, SRB2 open

  ads_wreg(BIAS_SENSP, 0X80);  //Switch ON for ch8
  ads_wreg(BIAS_SENSN, 0X80);  //Switch ON for ch8 

  ads_wreg(MISC1, 0X20);   //Connect SRB1 to all INxN of channel

  ads_command(_START);     // Start ads conversion
  ads_command(_RDATAC);    // Start continuous conversion mode

//Function used to get data from ADS1299:
global long output[8]=0;
void getADSdata()   
  long dataPacket = 0;
  vspi->beginTransaction(SPISettings(spiClk, MSBFIRST, SPI_MODE1));
  digitalWrite(ADS_CS, LOW); //Low to communicated  

  for(int i = 0; i<3; i++){
     byte dataByte = vspi->transfer(0x00);
     statusData = (dataPacket<<8) | dataByte;
  for(int i = 0; i<8; i++){
    for(int j = 0; j<3; j++){
        byte dataByte = vspi->transfer(0x00);
        dataPacket = (dataPacket<<8) | dataByte;
    output[i] = dataPacket;
    dataPacket = 0;
  digitalWrite(ADS_CS, HIGH);

  Serial.println(output[7]);   //Print Ch8 data and plot. 

For the following situation, I want to ask few questions:

1. Is the code correct while initialising registers? and getting data? 

2. How should I connect IN8P, IN8N, BIASOUT, AGND (if it has to be connected for ground reference), wires to electrodes and gather EEG signals.


  • Hi Lakshay,

    Thanks for the post. Please see my comments below for your questions.

    1. The code looks fine. There is no issue with the signal chain, hardware, and data capture since you are able to get the square wave signals with the internal test signals. However, the waveform attached shows the ADC data output is saturated. Would you please verify that the common-mode signal of the test signal is correct? It may be helpful to use a bigger test signal from your function generator. Please note that the noise performance of the device at PGA Gain = 1 is about 7.59uVpp (DR = 250SPS).

    2. Please refer to Figure 73 in the datasheet for the setup of EEG signal measurement with a single reference electrode. The bias electrode is used to bias the patient to maintain the correct common-mode voltage for the input channels. It also helps to improve the common-mode rejection of the system.