Update INA228.cpp

[markliquid1]

updated getShuntVoltage() to allow reading of negative currents

[RobTillaart]

Please have a look at PR #7, there is similar work in progress

[RobTillaart]

If I understand correctly this should allow the small negative range over the bus (and thus negative current for shunt)?

Datasheet 7.3.1 The supported common-mode voltage range at the input pins is –0.3 V to +85 V, which makes the device well suited for both high-side and low-side current measurements.

Next weekend I hope to have time to get hands on with hardware.

[RobTillaart]

Have checked the data sheet and your code is an improvement however with minor points see above.

float INA228::getShuntVoltage() 
{
  //  datasheet P25
  float LSB = 312.5e-9;  //  312.5 nV
  uint16_t config = _readRegister(INA228_CONFIG, 2);
  if (config & 0x0010)   //  ADCRANGE
  {
    LSB = 78.125e-9;     //  78.125 nV
  }

  //  remove reserved bits.
  int32_t value = _readRegister(INA228_SHUNT_VOLTAGE, 3) >> 4;
  if (value & 0x00800000) 
  {
    value |= 0xFF000000;
  }
  return value * LSB;
}

• renamed scale to LSB,
• gave LSB the value as defined in the datasheet instead of scaling in return command
• adjusted the mask for ADCRANGE
• adjusted the mask for the SIGN bit test.

Please give it a try, thanks.

[RobTillaart]

@markliquid1 better use this

float INA228::getShuntVoltage() 
{
  //  datasheet P25
  float LSB = 312.5e-9;  //  312.5 nV
  if (getADCRange() == 1) 
  {
    LSB = 78.125e-9;     //  78.125 nV
  }

  //  remove reserved bits.
  int32_t value = _readRegister(INA228_SHUNT_VOLTAGE, 3) >> 4;
  //  handle negative values
  if (value & 0x00800000) 
  {
    value |= 0xFF000000;
  }
  return value * LSB;
}

[markliquid1]

Thanks, I'll give it a try today. I'm new to programming, so mainly submitted this request as a way to point out the issue with negative current measurement. The code I proposed was inspired by the Adafruit library for the INA228, and did seem to work, but certainly was not the cleanest way to do it, and not consistent with the rest of your library.

[RobTillaart]

Then I will include it in my current develop branch which I'm working on. There is still work todo before the library is functional complete.

Thanks for the clarification

Will close this as a PR. If you have more remarks, please open an issue per topic.

[markliquid1]

Ok, I wasn't yet aware of the "Issue" functionality of github, so I will use that in the future. Thanks for all your open source work on Arduino libraries. I have benefited greatly as I learn, including this INA228. I look forward to your updates.

[RobTillaart]

Included getShuntVoltage() into my develop branch,

Thanks again for pointing out the negative values!