INA219.py

# -*- coding: utf-8 -*-
"""
    Python class to manage Texas Instruments INA219 Current/Power Monitor.
    https://www.ti.com/product/INA219

    Waveshare UPS HAT (B) for Raspberry Pi.
    https://www.waveshare.com/wiki/UPS_HAT_(B)

    Requires 'smbus' module for I2C/SMBus interface.

"""

import smbus

# Config Register (R/W)
_REG_CONFIG                 = 0x00
# SHUNT VOLTAGE REGISTER (R)
_REG_SHUNTVOLTAGE           = 0x01

# BUS VOLTAGE REGISTER (R)
_REG_BUSVOLTAGE             = 0x02

# POWER REGISTER (R)
_REG_POWER                  = 0x03

# CURRENT REGISTER (R)
_REG_CURRENT                = 0x04

# CALIBRATION REGISTER (R/W)
_REG_CALIBRATION            = 0x05

class BusVoltageRange:
    """Constants for ``bus_voltage_range``"""
    RANGE_16V               = 0x00      # set bus voltage range to 16V
    RANGE_32V               = 0x01      # set bus voltage range to 32V (default)

class Gain:
    """Constants for ``gain``"""
    DIV_1_40MV              = 0x00      # shunt prog. gain set to  1, 40 mV range
    DIV_2_80MV              = 0x01      # shunt prog. gain set to /2, 80 mV range
    DIV_4_160MV             = 0x02      # shunt prog. gain set to /4, 160 mV range
    DIV_8_320MV             = 0x03      # shunt prog. gain set to /8, 320 mV range

class ADCResolution:
    """Constants for ``bus_adc_resolution`` or ``shunt_adc_resolution``"""
    ADCRES_9BIT_1S          = 0x00      #  9bit,   1 sample,     84us
    ADCRES_10BIT_1S         = 0x01      # 10bit,   1 sample,    148us
    ADCRES_11BIT_1S         = 0x02      # 11 bit,  1 sample,    276us
    ADCRES_12BIT_1S         = 0x03      # 12 bit,  1 sample,    532us
    ADCRES_12BIT_2S         = 0x09      # 12 bit,  2 samples,  1.06ms
    ADCRES_12BIT_4S         = 0x0A      # 12 bit,  4 samples,  2.13ms
    ADCRES_12BIT_8S         = 0x0B      # 12bit,   8 samples,  4.26ms
    ADCRES_12BIT_16S        = 0x0C      # 12bit,  16 samples,  8.51ms
    ADCRES_12BIT_32S        = 0x0D      # 12bit,  32 samples, 17.02ms
    ADCRES_12BIT_64S        = 0x0E      # 12bit,  64 samples, 34.05ms
    ADCRES_12BIT_128S       = 0x0F      # 12bit, 128 samples, 68.10ms

class Mode:
    """Constants for ``mode``"""
    POWERDOW                = 0x00      # power down
    SVOLT_TRIGGERED         = 0x01      # shunt voltage triggered
    BVOLT_TRIGGERED         = 0x02      # bus voltage triggered
    SANDBVOLT_TRIGGERED     = 0x03      # shunt and bus voltage triggered
    ADCOFF                  = 0x04      # ADC off
    SVOLT_CONTINUOUS        = 0x05      # shunt voltage continuous
    BVOLT_CONTINUOUS        = 0x06      # bus voltage continuous
    SANDBVOLT_CONTINUOUS    = 0x07      # shunt and bus voltage continuous


class INA219:
    def __init__(self, i2c_bus=1, addr=0x40):
        self.bus = smbus.SMBus(i2c_bus);
        self.addr = addr

        # Set chip to known config values to start
        self._cal_value = 0
        self._current_lsb = 0
        self._power_lsb = 0
        self.set_calibration_32V_2A()

    def read(self,address):
        data = self.bus.read_i2c_block_data(self.addr, address, 2)
        return ((data[0] * 256 ) + data[1])

    def write(self,address,data):
        temp = [0,0]
        temp[1] = data & 0xFF
        temp[0] =(data & 0xFF00) >> 8
        self.bus.write_i2c_block_data(self.addr,address,temp)

    def set_calibration_32V_2A(self):
        """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
        """
        # 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 = 0.32          (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 = 3.2A

        # 2. Determine max expected current
        # MaxExpected_I = 2.0A

        # 3. Calculate possible range of LSBs (Min = 15-bit, Max = 12-bit)
        # MinimumLSB = MaxExpected_I/32767
        # MinimumLSB = 0.000061              (61uA per bit)
        # MaximumLSB = MaxExpected_I/4096
        # MaximumLSB = 0,000488              (488uA per bit)

        # 4. Choose an LSB between the min and max values
        #    (Preferrably a roundish number close to MinLSB)
        # CurrentLSB = 0.0001 (100uA per bit)
        self._current_lsb = .1  # Current LSB = 100uA per bit

        # 5. Compute the calibration register
        # Cal = trunc (0.04096 / (Current_LSB * RSHUNT))
        # Cal = 4096 (0x1000)

        self._cal_value = 4096

        # 6. Calculate the power LSB
        # PowerLSB = 20 * CurrentLSB
        # PowerLSB = 0.002 (2mW per bit)
        self._power_lsb = .002  # Power LSB = 2mW per bit

        # 7. Compute the maximum current and shunt voltage values before overflow
        #
        # Max_Current = Current_LSB * 32767
        # Max_Current = 3.2767A before overflow
        #
        # If Max_Current > Max_Possible_I then
        #    Max_Current_Before_Overflow = MaxPossible_I
        # Else
        #    Max_Current_Before_Overflow = Max_Current
        # End If
        #
        # Max_ShuntVoltage = Max_Current_Before_Overflow * RSHUNT
        # Max_ShuntVoltage = 0.32V
        #
        # If Max_ShuntVoltage >= VSHUNT_MAX
        #    Max_ShuntVoltage_Before_Overflow = VSHUNT_MAX
        # Else
        #    Max_ShuntVoltage_Before_Overflow = Max_ShuntVoltage
        # End If

        # 8. Compute the Maximum Power
        # MaximumPower = Max_Current_Before_Overflow * VBUS_MAX
        # MaximumPower = 3.2 * 32V
        # MaximumPower = 102.4W

        # Set Calibration register to 'Cal' calculated above
        self.write(_REG_CALIBRATION,self._cal_value)

        # Set Config register to take into account the settings above
        self.bus_voltage_range = BusVoltageRange.RANGE_32V
        self.gain = Gain.DIV_8_320MV
        self.bus_adc_resolution = ADCResolution.ADCRES_12BIT_32S
        self.shunt_adc_resolution = ADCResolution.ADCRES_12BIT_32S
        self.mode = Mode.SANDBVOLT_CONTINUOUS
        self.config = self.bus_voltage_range << 13 | \
                      self.gain << 11 | \
                      self.bus_adc_resolution << 7 | \
                      self.shunt_adc_resolution << 3 | \
                      self.mode
        self.write(_REG_CONFIG,self.config)

    def getShuntVoltage_mV(self):
        self.write(_REG_CALIBRATION,self._cal_value)
        value = self.read(_REG_SHUNTVOLTAGE)
        if value > 32767:
            value -= 65535
        return value * 0.01

    def getBusVoltage_V(self):
        self.write(_REG_CALIBRATION,self._cal_value)
        self.read(_REG_BUSVOLTAGE)
        return (self.read(_REG_BUSVOLTAGE) >> 3) * 0.004

    def getCurrent_mA(self):
        value = self.read(_REG_CURRENT)
        if value > 32767:
            value -= 65535
        return value * self._current_lsb

    def getPower_W(self):
        self.write(_REG_CALIBRATION,self._cal_value)
        value = self.read(_REG_POWER)
        if value > 32767:
            value -= 65535
        return value * self._power_lsb