ADS1256: ADS1256 Noise with Arduino

Hello Christopher,

I'm using this breakout board. I will try to re read the datasheet and change those values in the Arduino programming.

I thought about the USB to ISP converter because I own several USB to I2C converters from TI. Still I don't know how to program with this kind of devices, normally I just use software from your web page.

Thanks for your help

Marc

So, I have been trying to change the data rate this morning but it seems like the code either does nothing or breaks the data readout. Also while reading the datasheet I found interesting to change PGA gain which is also not working.

I will explain myself better using the code I have:

I added some lines to edit register 3 (remarked with a big comment), using the table I tried every sample rate, it either does nothing or weird numbers start to appear.

I guess you are well experienced with any issue regarding this chip and code so if you may have a quick solution I will be thankful. In any case I bought ADS1256EVM just to make sure everything will work.

/* ADS1256, datasheet: www.ti.com/.../sbas288j.pdf
  compare: github.com/.../ads12xx.cpp
    connections to Atmega328 (UNO)

    CLK  - pin 13
    DIN  - pin 11 (MOSI)
    DOUT - pin 12 (MISO)
    CS   - pin 10
    DRDY - pin 9
    RESET- pin 8 (or tie HIGH?)
    DVDD - 3V3
    DGND - GND
*/

#define cs 10 // chip select
#define rdy 9 // data ready, input
#define rst 8 // may omit

#define SPISPEED 1250000
// 1700000

#include <SPI.h>
int ledState = LOW;
const long interval = 200;
unsigned long previousMillis = 0;

void setup()
{
  Serial.begin(9600);
  pinMode(A0, OUTPUT);
  pinMode(cs, OUTPUT);
  digitalWrite(cs, LOW); // tied low is also OK.
  pinMode(rdy, INPUT);
  pinMode(rst, OUTPUT);
  digitalWrite(rst, LOW);
  delay(1); // LOW at least 4 clock cycles of onboard clock. 100 microsecons is enough
  digitalWrite(rst, HIGH); // now reset to deafult values

  delay(500);
  SPI.begin(); //start the spi-bus
  delay(500);


  //init

  // digitalWrite(cs, LOW);
  while (digitalRead(rdy)) {}  // wait for ready_line to go low
  SPI.beginTransaction(SPISettings(SPISPEED, MSBFIRST, SPI_MODE1)); // start SPI
  delayMicroseconds(10);

  //Reset to Power-Up Values (FEh)
  SPI.transfer(0xFE);
  delayMicroseconds(100);

  byte status_reg = 0 ;  // address (datasheet p. 30)
  //PGA SETTING
  //1 ±5V
  //2 ±2.5V
  //4 ±1.25V
  //8 ±0.625V
  //16 ±312.5mV
  //32 ±156.25mV
  //64 ±78.125mV
  byte status_data = 0x01; //status: Most Significant Bit First, Auto-Calibration Disabled, Analog Input Buffer Disabled
  SPI.transfer(0x50 | status_reg);
  SPI.transfer(0x00);   // 2nd command byte, write one register only
  SPI.transfer(status_data);   // write the databyte to the register
  delayMicroseconds(10);


  byte adcon_reg = 2; //A/D Control Register (Address 02h)
  byte adcon_data = byte adcon_data = 0b00100110; // 0 01 00 110 => Clock Out Frequency = fCLKIN, Sensor Detect OFF, gain 64
  SPI.transfer(0x50 | adcon_reg);
  SPI.transfer(0x00);   // 2nd command byte, write one register only
  SPI.transfer(adcon_data);   // write the databyte to the register
  delayMicroseconds(10);


/////////////////////////THIS IS SUPOSED TO CHANGE THE DATA RATE!!!!/////////////////////////////////////

  byte drate_reg = 3; //drate
  byte drate_data = 0b00010011; // 5SPS
  SPI.transfer(0x50 | adcon_reg);
  SPI.transfer(0x00);   // 2nd command byte, write one register only
  SPI.transfer(drate_data);   // write the databyte to the register
  delayMicroseconds(10);

  // digitalWrite(cs, HIGH);

  Serial.println("configured, starting");
}


void loop()
{


  unsigned long currentMillis = millis();


  unsigned long adc_val = 0; // store reading

  // digitalWrite(cs, LOW);
  SPI.beginTransaction(SPISettings(SPISPEED, MSBFIRST, SPI_MODE1)); // start SPI
  delayMicroseconds(10);
  //The most efficient way to cycle through the inputs is to
  //change the multiplexer setting (using a WREG command
  //to the multiplexer register MUX) immediately after DRDY
  //goes low. Then, after changing the multiplexer, restart the
  //conversion process by issuing the SYNC and WAKEUP
  //commands, and retrieve the data with the RDATA
  //command.
  while (digitalRead(rdy)) {} ;

  byte channel = 0;
  byte data = (channel << 4) | (1 << 3); //AIN-channel and AINCOM
  SPI.transfer(0x50 | 1); // MUX register
  SPI.transfer(0x00);   // 2nd command byte, write one register only
  SPI.transfer(data);   // write the databyte to the register
  delayMicroseconds(10);

  //SYNC command 1111 1100
  SPI.transfer(0xFC);
  delayMicroseconds(10);

  //WAKEUP 0000 0000
  SPI.transfer(0x00);
  delayMicroseconds(10);

  SPI.transfer(0x01); // Read Data 0000  0001 (01h)
  delayMicroseconds(10);

  adc_val = SPI.transfer(0);
  adc_val <<= 8; //shift to left
  adc_val |= SPI.transfer(0);
  adc_val <<= 8;
  adc_val |= SPI.transfer(0);

  delayMicroseconds(10);

  // digitalWrite(cs, HIGH);
  SPI.endTransaction();

  //The ADS1255/6 output 24 bits of data in Binary Two's
  //Complement format. The LSB has a weight of
  //2VREF/(PGA(223 − 1)). A positive full-scale input produces
  //an output code of 7FFFFFh and the negative full-scale
  //input produces an output code of 800000h.
  if (adc_val > 0x7fffff) { //if MSB == 1
    adc_val = (16777215ul - adc_val) + 1; //do 2's complement
  }
  Serial.println(adc_val);


  // digitalWrite(cs, HIGH);
}

This is the data output in the arduino serial monitor with time stamps when it works at 5sps for example, not even one second has passed and I have multiple readouts.

16:10:04.528 -> 5019
16:10:04.528 -> 4997
16:10:04.528 -> 5016
16:10:04.528 -> 4995
16:10:04.528 -> 5032
16:10:04.528 -> 5041
16:10:04.562 -> 4994
16:10:04.562 -> 5061
16:10:04.562 -> 4992
16:10:04.562 -> 5022
16:10:04.562 -> 5007
16:10:04.596 -> 5026
16:10:04.596 -> 5004
16:10:04.596 -> 5000
16:10:04.596 -> 5024
16:10:04.596 -> 5015
16:10:04.596 -> 5032
16:10:04.630 -> 4992
16:10:04.630 -> 5076
16:10:04.630 -> 5036
16:10:04.630 -> 5020
16:10:04.630 -> 4997
16:10:04.664 -> 5004
16:10:04.664 -> 5038

Hi Marc,

Have you tried reading back the register settings to make sure that they match what your sending? I'd recommend doing this to help verify that the SPI communication is working as expected.

Also, do try looking at the SPI communication and the /DRDY pin on an oscilloscope. It might be that the /DRDY period is changing at the expected period, but that the display data is incorrect.

In the end it looks like most of our noise problems don't come from the ads1256 readout but from our amplifier board.

We will work on that, thanks for your help.

Marc