ADS1119: Wrong ADC reading

Hi Thanh Dat Le,

Welcome to the E2E forum!  I don't see anything specific to your code that may be an issue.  You say you are applying 2.5V to the input, but what code is being returned by the ADS1119?  It would be better to see the actual code values so can you capture each byte being transmitted prior to calculation?  This helps eliminate a computational error.

It is not clear why you are trying to read more data than the size of the ADC conversion result.  If you suspect that you are getting more data returned make sure that you are using the ADS1119 (16-bit) and not the ADS1219 (24-bit).

The scope shot is helpful, but it is difficult to determine the result.  It would appear to be 0x6F61.  This would appear to be too high for a 2.5V input.  Make sure that your supply voltage is 5V and not 3.3V.  If it is 3.3V the returned value is much closer to 2.5V.

Also make sure that your input source is at the same ground potential as the ADS1119.

Best regards,

Bob B

Hi Bob,

thank you so much for fast response. 

For 2.5V input, the ADC returned 0x7FFF all the time. I tried to config ADC into single shot mode and send START cmd every 1s, same results returned.

Here is screenshot of the communication when I read 2 bytes from the ADC, seems like it matched which I got (0x7FFF). 

I verified the supply voltage 5V, ref voltage 5V and the input 2.5V . All goods and they share the same ground potential. 

I'm not well versed with Arduino, but I believe wire.endtransmission(); defaults to sending a stop bit.  After your RDATA (write 0x10), try using wire.endtransmission(false); to send a repeated start as the datasheet requires.

Ben

Hi Bob, 

thank you for your advice on variable name and data type!

Here are the screen shots of communication when I was writing and reading 0xA7 to/from config register: 

Writing 

Reading

Here is the DRDY pin when I was sending START cmd and followed by READ cmd every 1s:

Everything seems to be alright. I am not sure is there anything wrong here.

Hi Ben, 

I tried to send a repeated start by using wire.endtransmission(false), seems like it doesnt solve the problem.

Thank you for your support !

Hi Thanh Dat Le,

I'm confused by your scope plot for DRDY.  What I see appears to be only one conversion a second.  Maybe you need to zoom in as I cannot tell if the ADC is toggling the DRDY pin during what looks like the low period in the scope plot.  What you should see is DRDY toggling the whole time if the ADC is in continuous conversion mode.

What may be happening is a power issue or perhaps some form of an ESD or transient event that is resetting the ADS1119.  It doesn't appear that you have any analog input protection or input filters.  A transient event can reset the ADS1119 which will also reset the configuration back to default.

Another possibility is something in your code is not functioning as you expect.  Can you attach your sketch as a file for me to review?

Best regards,

Bob B

Hi Bob,

here is the screen shot for DRDY when ADC was put on continuous conversion mode (90SPS).

We expected the DRDY toggle every 1000/90 = 11ms but it seems like the signal is high (no conversion) all the time. 

Do you have any conclusion on this ADS's behaviour?

P/s: I also checked the content of config register every 1s and pretty sure that the ADC was not resetted to default value. 

These devices are dead simple - after a start command, in continuous conversion mode, there's not much that would prevent them from at least toggling DRDY.  As long as RESET isn't being pulled low for some reason, I'm inclined to think the device is damaged.

What happens if you set the MUX to 0b111?  You should get ADC values near zero.

Hi Thanh Dat Le,

I will guess that you are using some form of prototyping system.  Can you send pictures of your setup?  Also, I ask again for the code attached as a file so that I can attempt to replicate.

Best regards,

Bob B

Hi Bob, 

here is the test code and my testing setup: an external Arduino Uno was used to read data from the on board ADC. Analog input signal (2.5V) was generated by a STM32. There is only one ADS1119 connecting to I2C line (pulled up to Vcc with 1K resistor). The reason why we used Arduino to test is we also receive same wrong value (0x7FFF) when reading ADC value using STM32 before.

#include <Wire.h>

void setup() {
  Wire.setClock(100000);
  Wire.begin();
  Serial.begin(115200);

  // checking the I2c device on the line
  byte error, address;
  int nDevices;

  Serial.println("Scanning...");

  nDevices = 0;
  for(address = 1; address < 127; address++ )
  {
    // The i2c_scanner uses the return value of
    // the Write.endTransmisstion to see if
    // a device did acknowledge to the address.
    Wire.beginTransmission(address);
    error = Wire.endTransmission();

    if (error == 0)
    {
      Serial.print("I2C device found at address 0x");
      if (address<16)
        Serial.print("0");
      Serial.print(address,HEX);
      Serial.println("  !");

      nDevices++;
    }
    else if (error==4)
    {
      Serial.print("Unknow error at address 0x");
      if (address<16)
        Serial.print("0");
      Serial.println(address,HEX);
    }    
  }
  if (nDevices == 0)
    Serial.println("No I2C devices found\n");
  else
    Serial.println("done\n");


 // setting up 
   // Reset device by common 0x00 call
  Wire.beginTransmission(0x40);
  Wire.write(0x06);
  Serial.println(Wire.endTransmission());
  delay(500);
  
  // Read the value from the register 0x00 - should return 0 as default
  Wire.beginTransmission(0x40);
  Wire.write(0x20);
  Serial.println(Wire.endTransmission());
  Wire.requestFrom(0x40, 1);
  if (Wire.available() == 1) {
    int value = Wire.read();
    Serial.println(value);
  }
  delay(100);

  // Write a value to the register 0x00 - 0xA7 - 1010 0111 : AIN2AGND, GAIN 0, 20SPS, Cont mode, External ref
  Wire.beginTransmission(0x40);
  Wire.write(0x40);
  Wire.write(0xA7);
  Serial.println(Wire.endTransmission());
  delay(100);

  // Read the value from the register 0x00 - should return 0xA7 = 0d167
  Wire.beginTransmission(0x40);
  Wire.write(0x20);
  Serial.println(Wire.endTransmission());
  Wire.requestFrom(0x40, 1);
  if (Wire.available() == 1) {
    int value = Wire.read();
    Serial.println(value);
  }
  delay(100);

  // Start conversion
  Wire.beginTransmission(0x40);
  Wire.write(0x08);
  Serial.println(Wire.endTransmission());
  delay(1000);

}

void loop() {

// // Start conversion
//   Wire.beginTransmission(0x40);
//   Wire.write(0x08);
//   // Wire.write(0x41);
//   Serial.println(Wire.endTransmission());
//   delay(100);

//Read data by cmd
  uint16_t value;
  // Reading data by cmd
  Wire.beginTransmission(0x40);
  Wire.write(0x10);
  Wire.endTransmission(false);
  Serial.print("Number of bytes requested :"); Serial.println(Wire.requestFrom(0x40, 2));
  Serial.println();
  byte value_1 = Wire.read();
  byte value_2 = Wire.read();

  Serial.print("Byte 0:"); Serial.println(value_1);
  Serial.print("Byte 1:"); Serial.println(value_2);

  value = (value_1 << 8 | value_2);
  if (value > 0x7FFF) 
  {
    value = 0x0;
  }
  //Serial.println(value);
  float voltage = 5.0 * (float(value) / 32767) * 1; 
  Serial.print("Vin :"); Serial.println(voltage);
  Serial.println();

  delay(1000);
}

I think what Bob is asking for is a picture of your actual physical setup.  A camera-phone picture, for instance, of the bench with your devices and connections visible.

It would still be helpful to see what result you get with MUX=0b111

Hi Ben, 

For MUX=0b111, the returned result is constant 0xFFFF (~0), however, the DRDY was not toggling at all so I am not sure that is the true value or not.

Hi Bob, 

I also sent a picture of actual setup to you through direct message, pls check it. Thank you! 

Hi Ben, Bob

it seems like we were provided by a block of clone chips. Thank you so much for helping me these days. 

Well I guess my inclination to think the device was damaged wasn't too far off.

Glad you got it sorted.