I have a pressure sensor that signals via current and draws between 4 and 20 mA: https://www.amazon.com/gp/product/B093ZNL53C
Using the Arduino library (https://github.com/adafruit/Adafruit_INA219/blob/master/Adafruit_INA219.h#L169), most configurations are in the range from 400 mA to 2 A, and I am trying to get a better fidelity.
I see the datasheet and the library walks you through a 8 step process: https://github.com/adafruit/Adafruit_INA219/blob/master/Adafruit_INA219.cpp#L300, but I am unable to get the setting optimized for exactly what I am looking for.
This was my attempt and I would appreciate any guidance:
void Adafruit_INA219::setCalibration_32V_20mA() {
// By default we use a pretty huge range for the input voltage,
// which probably isn't the most appropriate choice for system
// that don't use a lot of power. But all of the calculations
// are shown below if you want to change the settings. You will
// also need to change any relevant register settings, such as
// setting the VBUS_MAX to 16V instead of 32V, etc.
// VBUS_MAX = 32V (Assumes 32V, can also be set to 16V)
// VSHUNT_MAX = 0.04 (Assumes Gain 8, 320mV, can also be 0.16, 0.08, 0.04)
// RSHUNT = 0.1 (Resistor value in ohms)
// 1. Determine max possible current
// MaxPossible_I = VSHUNT_MAX / RSHUNT
// MaxPossible_I = .4A // kevin saye modification
// 2. Determine max expected current
// MaxExpected_I = .012A // kevin saye modification
// 3. Calculate possible range of LSBs (Min = 15-bit, Max = 12-bit)
// MinimumLSB = MaxExpected_I/32767
// MinimumLSB = 0.000000366 // kevin saye modification
// MaximumLSB = MaxExpected_I/4096
// MaximumLSB = 0.000002629 // kevin saye modification
// 4. Choose an LSB between the min and max values
// (Preferrably a roundish number close to MinLSB)
// CurrentLSB = 0.0000004 // kevin saye modification
// 5. Compute the calibration register
// Cal = trunc (0.04096 / (Current_LSB * RSHUNT))
// Cal = 4096 (0x1000)
ina219_calValue = 1240000; // kevin saye modification
// 6. Calculate the power LSB
// PowerLSB = 20 * CurrentLSB
// PowerLSB = 0.000008 (.008mW per bit) // kevin saye modification
// 7. Compute the maximum current and shunt voltage values before overflow
//
// Max_Current = Current_LSB * 32767
// Max_Current = .032767A before overflow // kevin saye modification
//
// If Max_Current > Max_Possible_I then
// Max_Current_Before_Overflow = MaxPossible_I
// Else
// Max_Current_Before_Overflow = Max_Current .032767A // kevin saye modification
// End If
//
// Max_ShuntVoltage = Max_Current_Before_Overflow * RSHUNT
// Max_ShuntVoltage = .0032767V
//
// If Max_ShuntVoltage >= VSHUNT_MAX
// Max_ShuntVoltage_Before_Overflow = VSHUNT_MAX
// Else
// Max_ShuntVoltage_Before_Overflow = Max_ShuntVoltage .0032767V // kevin saye modification
// End If
// 8. Compute the Maximum Power
// MaximumPower = Max_Current_Before_Overflow * VBUS_MAX
// MaximumPower = .0032767 * 32V
// MaximumPower = 0.1048544W // kevin saye modification
// Set multipliers to convert raw current/power values
// ina219_currentDivider_mA = 10; // Current LSB = 100uA per bit (1000/100 = 10)
ina219_currentDivider_mA = 2500; // Current LSB = 400pA per bit (1,000,000/400 = 10) //0.0000004 // kevin saye modification
//ina219_powerMultiplier_mW = 2; // Power LSB = 1mW per bit (2/1)
ina219_powerMultiplier_mW = 250; // Power LSB = .008mW per bit (2/.008) // kevin saye modification
// Set Calibration register to 'Cal' calculated above
Adafruit_BusIO_Register calibration_reg =
Adafruit_BusIO_Register(i2c_dev, INA219_REG_CALIBRATION, 2, MSBFIRST);
calibration_reg.write(ina219_calValue, 2);
// Set Config register to take into account the settings above
uint16_t config = INA219_CONFIG_BVOLTAGERANGE_32V |
INA219_CONFIG_GAIN_1_40MV | INA219_CONFIG_BADCRES_12BIT_128S_69MS |
INA219_CONFIG_SADCRES_12BIT_128S_69MS |
INA219_CONFIG_MODE_SANDBVOLT_CONTINUOUS;
Adafruit_BusIO_Register config_reg =
Adafruit_BusIO_Register(i2c_dev, INA219_REG_CONFIG, 2, MSBFIRST);
_success = config_reg.write(config, 2);
}
