ADC128D818 Only reads 0 from Channel Reading Regs

Hi Nathaly,

When you are doing the ch3 and ch4 data reads are you setting the address as shown in Figure 31 in the datasheet? Also, do you have all the Acks and No Acks as shown in that figure?

Mike

Hi Mike, 

  I am not using a repeat start, I am writing the register address and then sending a read command as in Fig 26 + 29, using a stop from master in between. Is this not valid? I don't know how to implement a repeated start, as I am using Arduino's Wire Library. Below is my serial stream and my code for reading. 

Thanks!

int myRead(byte regAddress, int numBytes)
{
  int value =0;
  //Serial.println(" transmitting...");
  Wire.beginTransmission(MYADDRESS);
  Wire.write(regAddress);
  Wire.endTransmission();
  
  Wire.requestFrom(MYADDRESS, numBytes);
  
  while(!Wire.available() )
  {
    //wait till read is done
  };
 // Serial.println(" reading...");
  if (numBytes == 2)
  {
    value = Wire.read() << 8;
    value |= Wire.read();
  }
  else
  value = Wire.read();
  
  return value;
}

Hello Mike!

  Ive been busy with exams, but I am back and tried your suggestion. I only write (0x03) to the config register, but I am still getting readings of 0. I look into the status register a few times to get some clues, and I reset it at the very beginning just in case:

-clear interrupt bit (write (0x08 to Addr00)

-setup all my configurations

-check interrupt status Addr01 ( --> get 0000 0000)

-start conversion (write 0x03 to Addr0)

-check interrupt status right after starting  (  --> get 1000 0000)

-read all configuration registers  ( they all have what I intended)

-read channels (--> get 0)

-read interrupt status (--> get 1000 1111) meaning all my channels have gone below or above the limits of 0-5

   I am using the internal reference of 2.56V, so my analog input range should be between 0 and 2.56v correct? I am in differential mode, and IN1-IN0 is designed to be between 0-2.56, however IN1 on its own may go beyond that voltage. Can this have something to do with it? However, I am only using 4 pins (2 differential inputs) but I am getting limit interrupts for ALL, so not sure what could cause that.

Thanks for looking into this, I appreciate your help!

UPDATE !
The analog inputs to the ADC come from an instrumentation amplifier (INA2331) so I tried feeding the inputs directly from a voltage divider an input of 1.4 v ( according to datasheet that should result in a digital encoding of 2240). I got some readings! But the reading in decimal is -30800 and ALL interrupt bits are up. How could I read such a high number? the first byte read is MSB, correct?, are there 4 bits I should ignore to convert a 16 bit data into 12 bit?

As soon as I use the amp outputs as ADC inputs,  I read 0. I am using the reference to the amplifier (~2.5v) as half a differential input, and the output of the amplifier as the other half. Is there a problem by using the same voltage line for amp-reference and adc-input?

Hi Nathaly,

You are correct that VIN needs to be less than the reference. It actually needs to be 3LSB/2 less than the reference. See page 15 in the datasheet. The inputs can be above that but the difference needs to be less.
The input shouldn't care where the voltage is coming from, it is only interested in what the voltage is. When you have the amplifier connected check that you have the expected voltages at the input pins of the ADC. Is there any noise or spikes on the voltages of the input pins?
Are you using the internal reference? An experiment is that you could try using an external reference and set the reference voltage to 5V, just to see what kind of results that gives you

Mike

So I figured that the value im reading is two bytes (==16 bits) but the ADC only outputs a 12 bit value. So I get my final value and mask it with 0FFF. The values are not crazy but they're way off what they should be [ d=(delta_Vin/Vref)*4096 ]

I tried inputting a value straight from a power supply, with either internal or external 5v reference, and even on different channels. I am getting values but they still don't make sense.  So I used a sample arduino code for this adc from github and both my code and this code get the same value. This makes me thing theres something wrong with the circuit or chip.

For example, if I am in single ended mode,  Input from power supply =1.8v,  

with internal 2.56v reference, I should get 2880 encoding , but I get: 1488 (dec)

with external 5v reference,  I should get 1474 encoding. but I get: 3216

*If it makes a difference my interrupt register still reads 255, and ch7 temperature reading is between 1920 and 2048.

Thanks, and happy holidays!

~Nathaly

Hoooorrraaaaay!!!!

 Hi Mike, Happy new year and all that jazz. Turns out I was misinterpreting the bits all along. I masked the lower 4 bits as you suggested and to keep the higher bits I divided the value by 16 and stored in an integer. 

Thanks so much for your help, I got my circuit working now! :)