OpenPlotter I2C 3.x.x - INA219 settings

[Sailoog]

I have edited the title of this thread to be more explicit.

In older posts I have recommended to add these settings:

set_calibration_32V_2A
       """Configures to INA219 to be able to measure up to 32V and 2A of current. Counter
       overflow occurs at 3.2A.
       .. note:: These calculations assume a 0.1 shunt ohm resistor is present
       """
set_calibration_32V_1A
       """Configures to INA219 to be able to measure up to 32V and 1A of current. Counter overflow
       occurs at 1.3A.
       .. note:: These calculations assume a 0.1 ohm shunt resistor is present"""

set_calibration_16V_400mA
       """Configures to INA219 to be able to measure up to 16V and 400mA of current. Counter
       overflow occurs at 1.6A.
       .. note:: These calculations assume a 0.1 ohm shunt resistor is present"""
    
set_calibration_16V_5A
       """Configures to INA219 to be able to measure up to 16V and 5000mA of current. Counter
       overflow occurs at 8.0A.
       .. note:: These calculations assume a 0.02 ohm shunt resistor is present"""

But after a deeper analysis of the code I can se that those pre-configured "calibration" settings seem just the most usual or expected uses of the module but there could be many more possible uses.

Those pre-configured uses are the combination of different values of these constants:

bus_voltage_range
gain
bus_adc_resolution
shunt_adc_resolution
mode

We could expose these constants and its fixed values as "sensor settings" in openplotter but we would also need to expose these private variables:

_current_lsb
_cal_value
_power_lsb

and here comes the problem because calculating these private variables is really complex for normal users. Here is an example of calculating them for "set_calibration_16V_5A"

       """Configures to INA219 to be able to measure up to 16V and 5000mA of current. Counter
       overflow occurs at 8.0A.

       .. note:: These calculations assume a 0.02 ohm shunt resistor is present"""
       # Calibration which uses the highest precision for
       # current measurement (0.1mA), at the expense of
       # only supporting 16V at 5000mA max.

       # VBUS_MAX = 16V
       # VSHUNT_MAX = 0.16          (Assumes Gain 3, 160mV)
       # RSHUNT = 0.02              (Resistor value in ohms)

       # 1. Determine max possible current
       # MaxPossible_I = VSHUNT_MAX / RSHUNT
       # MaxPossible_I = 8.0A

       # 2. Determine max expected current
       # MaxExpected_I = 5.0A

       # 3. Calculate possible range of LSBs (Min = 15-bit, Max = 12-bit)
       # MinimumLSB = MaxExpected_I/32767
       # MinimumLSB = 0.0001529              (uA per bit)
       # MaximumLSB = MaxExpected_I/4096
       # MaximumLSB = 0.0012207              (uA per bit)

       # 4. Choose an LSB between the min and max values
       #    (Preferrably a roundish number close to MinLSB)
       # CurrentLSB = 0.00016 (uA per bit)
       self._current_lsb = 0.1524  # in milliamps

       # 5. Compute the calibration register
       # Cal = trunc (0.04096 / (Current_LSB * RSHUNT))
       # Cal = 13434 (0x347a)

       self._cal_value = 13434

       # 6. Calculate the power LSB
       # PowerLSB = 20 * CurrentLSB
       # PowerLSB = 0.003 (3.048mW per bit)
       self._power_lsb = 0.003048

We could do that but we would need a good documentation or at least values for all these variables for our own pre-configured settings.

This is the result of the html tool to calculate them in your example:


but that result is for arduino and we should make sure those settings are the same as the python settings:

_cal_value
_current_lsb
_power_lsb

bus_voltage_range
gain
bus_adc_resolution
shunt_adc_resolution
mode

Does this all make sense to you?