trying to understand the AD7124

[Bastiaan]

Hi guys, girls,

I was wondering if you could share a light on the following AD7124. at the example code, I need to change it to read RTC and thermocouple channels. but how to read it is different to the CN0391 evaluation board. i have attached 2 images 1 for the cn0391 schematic and the other the CN0381.

the link to the pdf:
https://www.analog.com/media/en/technical-documentation/data-sheets/ad7124-8.pdf

the procedure to communicate with the CN0391 and CN381 is kinda identical.


//measuring RTC
A typical procedure for reading the RTD is as follows:
1.Reset the ADC.
2.Select the power mode.
3.Set the CHANNEL_0 register analog input to AIN1/AIN2. Assign Setup 0 to this channel. Configure Setup 0 to have a gain of 16 and select the reference source REFIN2(±). Select the filter type and set the output data rate.
4.Program the excitation currents to 500 μA and output thecurrents on the AIN0 and AIN3 pins.
5.Wait until RDY goes low. Read the conversion value.
6.Repeat Step 4.

//measuring Thermocouple
1.Reset the ADC.
2.Select the power mode.
3.Set the CHANNEL_0 register analog input to AIN0/AIN1. Assign Setup 0 to this channel. Configure Setup 0 to have a gain of 128 and select the reference source to REFIN1(±). Select the filter type and set the output data rate.
4.Set the CHANNEL_1 register analog input to AIN2/AIN3. Assign Setup 0 to this channel (both channels use the same setup).
5.Set the CHANNEL_2 register analog input to AIN4/AIN5. Assign Setup 1 to this channel. Configure Setup 1 to have a gain of 1 and select the reference source REFIN2(±). Select the filter type and set the output data rate.
6.Program the excitation current and output the current on the AIN4 pin.
7.Enable both CHANNEL_0 and CHANNEL_1. Enable the DATA_STATUS bit to identify the channel from which the conversion originated. The ADC automatically sequences through these channels.
8.Wait until RDY goes low. Read the conversion value.
9.Repeat Step 8 until the temperature is to be read (every 10 conversions of the pressure sensor readings, for example). 10.Disable CHANNEL_0 and CHANNEL_1. Enable CHANNEL_2. 11.Wait until RDY goes low. Read the conversion.12.Repeat Step 6 to Step 10.

so i require to make 4 functions which read RTD, TC1,TC1 and TC2.
and give them the channel parameters, voltage references, currents etc. I got that.

things I dont understand:

• how do I enable both channels 0 and 1 at the same time?.
• how do I program the excitation current?
• what I dont understand is the until ready and how to active it

I have attached the ad7124 with out any tweaking for convenience.

/*
  CN-0381 Thermometer (AD7124)
  Completely Integrated 4-Wire RTD Measurement System Using a AD7124
  See http://www.analog.com/media/en/reference-design-documentation/reference-designs/CN0381.pdf
  Prints out the RTD temperature and resistor measured at pins AIN2(+)/AIN3(-)
  for schematic see Figure 1., p.2 of CN-0381, e.g. :
  CN-0381 RTD Thermometer
  23.143,108.910
  23.143,108.910
  For more on AD7124, see
  http://www.analog.com/media/en/technical-documentation/data-sheets/AD7124-4.pdf
  The circuit:
  - AD7124 connected on the MOSI, MISO, SCK and /SS pins (pin 10)
  - LED active in low state connected to pin 9.
  created 2018
  by epsilonrt https://github.com/epsilonrt
  This example code is in the public domain.
  https://github.com/epsilonrt/ad7124/tree/master/examples
*/
#include <ad7124.h>

using namespace Ad7124;

/* constants ================================================================ */
const int ledPin = LED_BUILTIN;
const int ssPin = 10;

// Mathematical constants
const double Gain = 16;
const double Rf = 5.11E3;
const long Zero = 1L << 23;
const long FullScale = 1L << 24;

/* public variables ========================================================= */
Ad7124Chip adc;

/* internal public functions ================================================ */

// -----------------------------------------------------------------------------
void setup() {
  int ret;
  long value;

  pinMode (ledPin, OUTPUT);
  digitalWrite (ledPin, 1); // clear the LED

  //Initialize serial and wait for port to open:
  Serial.begin (38400);
  while (!Serial) {
    ; // wait for serial port to connect. Needed for native USB port only
  }

  // prints title with ending line break
  Serial.println ("RTD Thermometer");

  // Initializes the AD7124 device, the pin /CS is pin 10 (/SS)
  adc.begin (ssPin);

  // Setting the configuration 0:
  // - use of the REFIN1(+)/REFIN1(-) reference
  // - gain of 16 for a bipolar measurement
  // - digital filter Sync4 FS=384
  adc.setConfig (0, RefIn1, Pga16, true);
  adc.setConfigFilter (0, Sinc4Filter, 384);

  // Setting channel 0 with config 0 using pins AIN2(+)/AIN3(-)
  adc.setChannel (0, 0, AIN2Input, AIN3Input);

  // Configuring ADC in Full Power Mode (Fastest)
  ret = adc.setAdcControl (StandbyMode, FullPower, true);
  if (ret < 0) {

    Serial.println ("Unable to setting up ADC");
  }
}

// -----------------------------------------------------------------------------
void loop() {
  long value;

  // detect an open wire circuit (no RTD connected) or a short-circuit
  adc.setConfig (0, RefInternal, Pga1, true, Burnout4uA);
  value = adc.read (0);

  if (value >= (FullScale - 10))  {

    // A near full-scale reading can mean that the front-end sensor is open circuit.
    adc.setConfig (0, RefInternal, Pga1, true, BurnoutOff);
    Serial.println ("OPENED");
  }
  else {

    // Setting the configuration 0 for measuring
    adc.setConfig (0, RefIn1, Pga16, true);
    // Program the excitation currents to 500 μA and output the currents on the AIN0
    adc.setCurrentSource (0, IoutCh0, Current500uA);

    // Measuring on Channel 0 in Single Conversion Mode
    digitalWrite (ledPin, 0);
    value = adc.read (0);
    digitalWrite (ledPin, 1);

    // Program the excitation currents to Off
    adc.setCurrentSource (0, IoutCh0, CurrentOff);

    if (value >= 0) {
      double r, t = 0;

      // See Equation (1), p.4 of CN-0381
      r = ((value - Zero) * Rf) / (Zero * Gain);

      // See Equation (2), p.4 of CN-0381
      t = (r - 100.0) / 0.385;

      // Print results
      Serial.print (t, 3);
      Serial.print (",");
      Serial.println (r, 3);
    }
    else {

      Serial.println ("FAIL");
    }
  }
}
/* ========================================================================== */

thanks for looking into this.