AD7731 via Arduino SPI

Brendan,

     We tried your suggestion with mixed success. We still don't see the RDY pin go low. I've attached our Arduino code and a screenshot of one section of the output of our logic analyzer. We were able to:

1. Do a reset by writing 32 1's to the ADC.

2. Read the mode register and get the default/power-up value (0x174)

3. Write new mode bytes for continuous read, etc. (see comments in code)

4. Read back the mode bytes and confirm that the write was accomplished

successfully.

Can you see our error or perhaps suggest another test that might be helpful?

Thanks,  George

/*Arduino sketch for AD7731 ADC

This sketch assumes the usual SPI pin assignments found at https://www.arduino.cc/en/Reference/SPI

for the Mega2560:

MOSI = 51

MISO = 50

SCK = 52

SS = 53

*/

#include <SPI.h>

//Set any handy constants and do variable declarations

const  int  adcRDY = 30;  //Monitor pin 30 to see when data is ready for reading

byte mode1, mode2, modedata1, modedata2;        //For mode register bits, mode1 is MSB

void  setup()  {

  pinMode(adcRDY,INPUT);

  pinMode(MISO,INPUT);

  pinMode(MOSI,OUTPUT);

  pinMode(SCK,OUTPUT);

  pinMode(SS,OUTPUT);                   //this is the chip select line, set low to select chip

  pinMode(40,OUTPUT); digitalWrite(40,LOW);    //We're using pin 40 as a trigger for the logic analyzer

  SPI.begin();

  SPI.setBitOrder(MSBFIRST);

  SPI.setDataMode(SPI_MODE3);    //CPOL = 1, CPHA = 0, POL pin on ADC should be HIGH

  SPI.setClockDivider(SPI_CLOCK_DIV16);  //Serial clock frequency is now 1 MHz

  Serial.begin(9600);  //connection to serial monitor for output and debugging

  Serial.println("past setup");

}

void  loop()  {

  digitalWrite(40,HIGH);  //Start the logic analyzer

  digitalWrite(SS,HIGH);  //Set SS HIGH in case it matters

  digitalWrite(SS,LOW);  //Set SS LOW to select chip

  SPI.transfer(0xFF); //hardware reset with 4, 8 byte sets of 1's

  SPI.transfer(0xFF);

  SPI.transfer(0xFF);

  SPI.transfer(0xFF);

  delayMicroseconds(100);  //just in case the chip needs time to settle out

  SPI.transfer(0x12);  //Tell comm register that next operation is read from mode register

  modedata1 = SPI.transfer(0x00);  // Read first byte from the mode register

  modedata2 = SPI.transfer(0x00);  // Read second byte from the mode register

  Serial.println("Default mode register bytes are...");

  Serial.println(modedata1,BIN);  //print out mode data bytes to serial monitor

  Serial.println(modedata2,BIN);  //print out mode data bytes to serial monitor

  mode1=0b00110001;    //MSB   Continuous conversion, unipolar, no digital ports, 24 bit data,

  mode2=0b01110100;    //LSB  Vref=2.5V, 0 - 1.28 V scale, no burnout, fully differential, AIN1(-) AIN2(+)

  SPI.transfer(0x02);  //Tells communications register that next operation is write to mode register.

  SPI.transfer(mode1);  //Tell it to take the reading as described by mode's bits

  SPI.transfer(mode2); 

  Serial.println("New mode register bytes are...");

  SPI.transfer(0x12);  //Tell comm register that next operation is read from mode register

  modedata1 = SPI.transfer(0x00);  // Read first byte from the mode register

  modedata2 = SPI.transfer(0x00);  // Read second byte from the mode register

  Serial.println(modedata1,BIN);  //print out mode data bytes to serial monitor

  Serial.println(modedata2,BIN);  //print out mode data bytes to serial monitor

  delay(1000);  //sit here a while to see if RDY ever goes low

  SPI.transfer(0x30);  //stop continuous conversion

  digitalWrite(40,LOW);  //reset level of logic analyzer trigger to get ready for next sweep

  digitalWrite(SS,HIGH); //deselect chip 

  delay(5000);  //wait 5 s before looping

}

319866a4116221178feca71c97ce4d1b.tiff

Brendan,

     We tried your suggestion with mixed success. We still don't see the RDY pin go low. I've attached our Arduino code and a screenshot of one section of the output of our logic analyzer. We were able to:

1. Do a reset by writing 32 1's to the ADC.

2. Read the mode register and get the default/power-up value (0x174)

3. Write new mode bytes for continuous read, etc. (see comments in code)

4. Read back the mode bytes and confirm that the write was accomplished

successfully.

Can you see our error or perhaps suggest another test that might be helpful?

Thanks,  George

/*Arduino sketch for AD7731 ADC

This sketch assumes the usual SPI pin assignments found at https://www.arduino.cc/en/Reference/SPI

for the Mega2560:

MOSI = 51

MISO = 50

SCK = 52

SS = 53

*/

#include <SPI.h>

//Set any handy constants and do variable declarations

const  int  adcRDY = 30;  //Monitor pin 30 to see when data is ready for reading

byte mode1, mode2, modedata1, modedata2;        //For mode register bits, mode1 is MSB

void  setup()  {

  pinMode(adcRDY,INPUT);

  pinMode(MISO,INPUT);

  pinMode(MOSI,OUTPUT);

  pinMode(SCK,OUTPUT);

  pinMode(SS,OUTPUT);                   //this is the chip select line, set low to select chip

  pinMode(40,OUTPUT); digitalWrite(40,LOW);    //We're using pin 40 as a trigger for the logic analyzer

  SPI.begin();

  SPI.setBitOrder(MSBFIRST);

  SPI.setDataMode(SPI_MODE3);    //CPOL = 1, CPHA = 0, POL pin on ADC should be HIGH

  SPI.setClockDivider(SPI_CLOCK_DIV16);  //Serial clock frequency is now 1 MHz

  Serial.begin(9600);  //connection to serial monitor for output and debugging

  Serial.println("past setup");

}

void  loop()  {

  digitalWrite(40,HIGH);  //Start the logic analyzer

  digitalWrite(SS,HIGH);  //Set SS HIGH in case it matters

  digitalWrite(SS,LOW);  //Set SS LOW to select chip

  SPI.transfer(0xFF); //hardware reset with 4, 8 byte sets of 1's

  SPI.transfer(0xFF);

  SPI.transfer(0xFF);

  SPI.transfer(0xFF);

  delayMicroseconds(100);  //just in case the chip needs time to settle out

  SPI.transfer(0x12);  //Tell comm register that next operation is read from mode register

  modedata1 = SPI.transfer(0x00);  // Read first byte from the mode register

  modedata2 = SPI.transfer(0x00);  // Read second byte from the mode register

  Serial.println("Default mode register bytes are...");

  Serial.println(modedata1,BIN);  //print out mode data bytes to serial monitor

  Serial.println(modedata2,BIN);  //print out mode data bytes to serial monitor

  mode1=0b00110001;    //MSB   Continuous conversion, unipolar, no digital ports, 24 bit data,

  mode2=0b01110100;    //LSB  Vref=2.5V, 0 - 1.28 V scale, no burnout, fully differential, AIN1(-) AIN2(+)

  SPI.transfer(0x02);  //Tells communications register that next operation is write to mode register.

  SPI.transfer(mode1);  //Tell it to take the reading as described by mode's bits

  SPI.transfer(mode2); 

  Serial.println("New mode register bytes are...");

  SPI.transfer(0x12);  //Tell comm register that next operation is read from mode register

  modedata1 = SPI.transfer(0x00);  // Read first byte from the mode register

  modedata2 = SPI.transfer(0x00);  // Read second byte from the mode register

  Serial.println(modedata1,BIN);  //print out mode data bytes to serial monitor

  Serial.println(modedata2,BIN);  //print out mode data bytes to serial monitor

  delay(1000);  //sit here a while to see if RDY ever goes low

  SPI.transfer(0x30);  //stop continuous conversion

  digitalWrite(40,LOW);  //reset level of logic analyzer trigger to get ready for next sweep

  digitalWrite(SS,HIGH); //deselect chip 

  delay(5000);  //wait 5 s before looping

}

319866a4116221178feca71c97ce4d1b.tiff