Problem with AD7856 SPI in Arduino... Help!!

Hi,

Thanks for your question. We are looking into this and will get back to you soon.

Regards,

Karen

Hi,

Apologies for the delayed response. Please note that this part should be allowed 150 ms after power up to perform its calibration before any reading or writing takes place. Can you provide scope shots of the digital signals for us to take a closer look?

Thanks,

Karen

Hi, sorry to don't answering soon but I have many work and I still fight with this ADC. I write this code to drive the ADC:

#include <SPI.h>





uint8_t adcMSB = 0, adcLSB = 0;
unsigned int read_adc;
//uint8_t CtrlRegMSB = B11100001;
//uint8_t CtrlRegLSB = B00010001;
uint8_t CtrlRegMSB = B11100000;
uint8_t CtrlRegLSB = B00010000;
float Vin=0;
float N=3.05194e-4;
void setup()
{

  SPI.begin();
  SPI.setClockDivider(SPI_CLOCK_DIV128);
  SPI.setDataMode(SPI_MODE0);
  SPI.setBitOrder(MSBFIRST);
  pinMode(53,OUTPUT);
  digitalWrite(53,HIGH);
  pinMode(12,OUTPUT);
  digitalWrite(12,HIGH);
  Serial.begin(9600);
  //delay(500);
}


void loop()
{
  digitalWrite(12,LOW);
  delayMicroseconds(1);
  digitalWrite(12,HIGH);
  delayMicroseconds(10);

  digitalWrite(53,LOW);
  SPI.transfer(CtrlRegMSB); 
  SPI.transfer(CtrlRegLSB); 
  digitalWrite(53,HIGH);

  delayMicroseconds(10);

  digitalWrite(53,LOW);
  adcMSB=SPI.transfer(0x00);  
  adcLSB=SPI.transfer(0x00);  
  digitalWrite(53,HIGH);

  delay(100);

  read_adc= word(adcMSB, adcLSB);
  Vin=N*read_adc;
  Serial.print(Vin, DEC);
//  Serial.print("\t");
//  Serial.print(comm,BIN);
  Serial.print("\t");
  Serial.println(read_adc,DEC); 
}

The ADC works one time, one or two seconds, then stops and does not send anything to the master then turns off and turns on the ADC (a kind of reboot), and work again one or two seconds.

The operation is performed with hardware SPI, SPI previously had with software and the device did not stop and I require that the ADC works with hardware SPI speed matters.

I use the external clock in the CLKIN (pin 22) and pin to CONVST.

This is answer of ADC when the AN1 is in 5VDC:

thanks a lot, best regards!

El mensaje fue editado por: José Miguel Hernández I edit because add the answer of ADC

I have a new version, in this version I read and write in ADC via SPI hardware:

but i have problems with interfacing, I have waiting 15 ms and repeat the instruction as a minimum twice to read more than two channelss: this is the new version:

#include <Expander32.h>
#include <SPI.h>

/*
Definitions to work all channels
*/
#define AN1 B11100001
#define AN2 B11110001
#define AN3 B11100101
#define AN4 B11110101
#define AN5 B11101001
#define AN6 B11111001
#define AN7 B11101101
#define AN8 B11111101

Expander32 expander(40, 41); //Enable pins to Expander32SS board

//uint8_t adcMSB1 = 0, adcLSB1 = 0;
//unsigned int read_adc1;

uint8_t RstADCMSB = B01000000;    //this command 
uint8_t RstADCLSB = B00000010;    //reset the spi in ADC
uint8_t CtrlRegMSB = B11100000;    //this command select the chhanel 1
uint8_t CtrlRegLSB = B00010001;    //this commans is the same to all channels
//uint8_t CtrlRegMSB = B11100001;
//uint8_t CtrlRegLSB = B00010001;

//uint8_t StatRegMSB = B11100001;
//uint8_t StatRegLSB = B10010001;

uint16_t AD1=0;
uint16_t AD2=0;
uint16_t AD3=0;
float Vin1=0, Vin2=0, Vin3=0;
float N=3.05194e-4;    //cte to voltaje convertion 5/((2^14)-1)
void setup()
{
  expander.init();        //initialitation of the Expander32SS board
  SPI.begin();
  SPI.setClockDivider(SPI_CLOCK_DIV128);    //Spi to 125kHz
  SPI.setDataMode(SPI_MODE0);                //SPI in mode 0
  SPI.setBitOrder(MSBFIRST);          //send the most significant bit first
  pinMode(53,OUTPUT);
  digitalWrite(53,HIGH);        //Disable the ADC
  pinMode(12,OUTPUT);          
  digitalWrite(12,HIGH);        //PIN to convst ADC
  Serial.begin(9600);
  delay(150);              //Wait for ADC auto calibration
}

void loop()
{
  
  setChannel(AN1);            //What channel read?
  delayMicroseconds(10);    //wait the complete convertion 5us
  AD1 = readChannel();        //read the ADC value
  
//  delayMicroseconds(100);
//

  setChannel(AN2);            //What channel read?
  delayMicroseconds(10);    //wait the complete convertion
  AD2 = readChannel();        //read the ADC value
  
  Vin1=N*AD1;          //Voltaje convertion
  Vin2=N*AD2;          //Voltaje convertion
  
  /*Print the results in serial RS232*/
  Serial.print(Vin1, DEC);
  Serial.print("\t");
  Serial.print(AD1,DEC);
  Serial.print("\t");
  Serial.print(Vin2,DEC);
  Serial.print("\t");
  Serial.println(AD2,DEC); 
  
}

/*
Method to select the channel of ADC
*/
void setChannel(uint8_t channel){
  for (int i=1; i>=0; i--){    // this methos call twice and dont kwon why
  digitalWrite(12,LOW);        //start convertion 
  delayMicroseconds(1);        //
  digitalWrite(12,HIGH);       //
  delayMicroseconds(10);       //Wait a moment
  expander.Spin(16);        //Enable of SPin 16 in Expander32SS board 
  digitalWrite(53,LOW);      //Enable ADC
  SPI.transfer(channel);     //channel to set
  SPI.transfer(CtrlRegLSB);  //Same command all channels
  digitalWrite(53,HIGH);      //Disable ADC
  expander.disable();
  delay(15);                  //Wait 15 ms and dont kwon why
  }
}

/*
Method to read the value of ADC
*/
uint16_t readChannel(void){
  uint16_t out=0;
  uint8_t adcMSB=0;
  uint8_t adcLSB=0;
  for (int i=1; i>=0; i--){    // this methos call twice and dont kwon why
  digitalWrite(12,LOW);        //start convertion 
  delayMicroseconds(1);        //
  digitalWrite(12,HIGH);       //
  delayMicroseconds(10);       //Wait a moment
  expander.Spin(16);        //Enable of SPin 16 in Expander32SS board 
  digitalWrite(53,LOW);      //Enable ADC
  adcMSB=SPI.transfer(0x00);  //send 0x00 to generate clock signal 
  adcLSB=SPI.transfer(0x00);  //send 0x00 to generate clock signal
  digitalWrite(53,HIGH);      //Disable ADC
  expander.disable();
  delay(15);                  //Wait 15 ms and dont kwon why
  }
  out= word(adcMSB, adcLSB);

  return out;
}

With this code the ADC don't stops but and I write to zero un bus spi to read the sample.

best regards!

Hi,

Let me check on this. Meanwhile, if you could provide scope shots of the digital signals (/SYNC, SCLK, DOUT, DIN) together in one cycle, it would help a lot.

Regards,

Karen

thanks, I don't have a scope with four channels only have a two channels I hope  this serves.

Best regards!

Miguel

Hi, Miguel.

Thanks for providing these. Am I correct to assume that SS refers to your /SYNC line? If so, why is this high? This pin is level triggered active low and frames the serial clock for the read and write operations. Also, please check how you are configuring the part. The 1st two bits of MOSI determine which register is addressed, and the subsequent 14 bits of data are written to the addressed register. From the scope shots, the first two bits are 00 which does not address any register. Hence, the next 14 bits are ignored.

Regards,

Karen

Sorry Karen but I don't know what happen with the channel one of the scope but the signals are in negative state i.e. zeros are ones and ones are zeros, I check this in other scope but this don't have screen shoots sorry!

I check the scope and have a incorerct configuration in the channel one, this scope shoots are correct:

SS is connect in SYNC pin.

This is the command in to setChannel() function.

This is the command in to readChannel() function.

This scope shoot is the answer of ADC.

thanks for help me!

Hi, Miguel.

I would just like to clarify, is the MISO line (4th image) the captured ADC result for an input of 5VDC on AIN1? Also, can you check if your channel 2 (for SCK) is also inverted? Note that the AD7856 datasheet states that when a noncontinuous SCLK is used, it should idle high.

Regards,

Karen