ina219 — Digital wattmeter

The INA219 is a digital wattmeter from Texas Instruments. The INA219 sensor measures direct current, voltage and power from the circuit to which it is connected.

In a direct current circuit, electrical power delivered to an electrical load (measured in watts) is the arithmetic product of the current flowing through the load (measured in amperes) and the voltage across the load’s terminals (measured in volts).

To measure the current, a low value resistor is placed in series with the load, and the voltage across the resistor’s terminal is measured. By applying Ohm’s Law, the current can be derived (current I = voltage V / resistance R).

See also:

• https://en.wikipedia.org/wiki/Voltmeter,

• https://en.wikipedia.org/wiki/Ammeter and

• https://en.wikipedia.org/wiki/Ohm%27s_law

The INA219 sensor is commonly mounted on a breakout board equipped with terminals to attach the load and a power supply, and a shunt resistor used to measure current flowing through the load.

The interface with the Kookaberry is the I2C serial communications bus. I2C stands for Inter-Integrated-Circuit Communications (IIC or I2C). See https://en.wikipedia.org/wiki/I%C2%B2C for more detail.

There are four wires in the I2C interface, being:

• Vcc power at +3.3 volts DC

• Gnd ground (or negative) for signal and power at 0 volts

• SCL being the serial clock signal for communications timing

• SDA being the serial data signal which conveys the digital data being communicated

When using a INA219 circuit board it is important that these signals are connected to the correct Pins on the Kookaberry.

The data-sheet for the INA219 may be obtained from this website: https://www.ti.com/product/INA219

Class INA219

Example Usage:

# Find any INA219 sensors and display its data
import time, fonts
from machine import SoftI2C, Pin
from kooka import display

display.setfont(fonts.mono6x7)

valid_adx = [0x40, 0x41, 0x44, 0x45] # The range of valid INA219 I2C addresses
i2c_bus = SoftI2C(scl=Pin('P3A')',sda=Pin('P3B'))
sensors = i2c_bus.scan() # Search the I2C bus for devices
found = False
for adx in sensors:
    if adx in valid_adx:
        ina219 = INA219(i2c_bus, addr=adx)  # Note it will use the last sensor found
        found = True
        print('Found INA219 at ', hex(adx))

if not found:
    print('No x INA219')    # Edit this line
    raise SystemExit

# measure and display loop
while True: # the loop runs forever
    display.fill(0) # Clear the display
    display.print("PSU V:{:6.3f} V".format(ina219.supply_voltage))
    display.print("Shunt V:{:9.6f} V".format(ina219.shunt_voltage))
    display.print("Load V:{:6.3f} V".format(ina219.bus_voltage))
    display.print("Current:{:9.6f} mA".format(ina219.current))
    display.print("Power:{:9.6f} mW".format(ina219.power))
    display.show()
    time.sleep(5)

INA219 Constructor

class ina219.INA219(i2c, addr=0x40, rshunt=0.01, maxamps=None, voltage_range=INA219.RANGE_32V, gain=INA219.GAIN_AUTO, bus_adc=INA219.ADC_12BIT, shunt_adc=INA219.ADC_12BIT)

Creates an INA219 object on the pre-defined I2C bus with default address 0x40.

i2c should be a machine.SoftI2C object.

addr is the I2C device address, one of (0x40, 0x41, 0x44, 0x45). The address is set with hardware on the I2C sensor.

rshunt is the value of the shunt resistor in the sensor (optional, defaults to 0.01 ohms).

maxamps is the maximum expected current in amps (optional).

voltage_range is the full-scale voltage range. This is either 16V or 32V represented by one of the following constants:

INA219.RANGE_16V

INA219.RANGE_32V(default)

gain is the gain which controls the maximum range of the shunt voltage represented by one of the following constants:

INA219.GAIN_1_40MV

INA219.GAIN_2_80MV

INA219.GAIN_4_160MV

INA219.GAIN_8_320MV

INA219.GAIN_AUTO(default)

bus_adc is the bus ADC resolution (9, 10, 11, or 12-bit) or the setting of the number of samples used when averaging results represented by one of the following constants:

INA219.ADC_9BIT

INA219.ADC_10BIT

INA219.ADC_11BIT

INA219.ADC_12BIT(default)

INA219.ADC_2SAMP

INA219.ADC_4SAMP

INA219.ADC_8SAMP

INA219.ADC_16SAMP

INA219.ADC_32SAMP

INA219.ADC_64SAMP

INA219.ADC_128SAMP

shunt_adc is the shunt ADC resolution (9, 10, 11, or 12-bit) or the setting of the number of samples used when averaging results represented by one of the following constants:

INA219.ADC_9BIT

INA219.ADC_10BIT

INA219.ADC_11BIT

INA219.ADC_12BIT(default)

INA219.ADC_2SAMP

INA219.ADC_4SAMP

INA219.ADC_8SAMP

INA219.ADC_16SAMP

INA219.ADC_32SAMP

INA219.ADC_64SAMP

INA219.ADC_128SAMP

INA219 Properties

The INA219 class presents all of its measurements as properties:

property INA219.bus_voltage

Returns the bus voltage in volts as a floating point number

property INA219.shunt_voltage

Returns the shunt voltage in volts as a floating point number.

A DeviceRangeError exception is thrown if current overflow occurs.

property INA219.supply_voltage

Returns the bus supply voltage in volts as a floating point number. This is the sum of the bus_voltage + shunt_voltage.

A DeviceRangeError exception is thrown if current overflow occurs.

property INA219.current

Returns the bus current in amps as a floating point number.

A DeviceRangeError exception is thrown if current overflow occurs.

property INA219.power

Returns the bus power in watts as a floating point number.

A DeviceRangeError exception is thrown if current overflow occurs.

property INA219.current_overflow

Returns a boolean according to whether or not the sensor has detected current overflow. If True, the current and power values will be invalid.

INA219 Methods

INA219.sleep()

Puts the INA219 sensor into power-down mode.

INA219.wake()

Wakes the INA219 from a power-down mode. It incorporates the 40 micro-second delay required for the sensor to wake.

INA219.reset()

Resets the INA219 sensor to its default configuration. That is:

• rshunt 0.01 ohms

• voltage_range 32 volts

• bus_adc 12-bit resolution

• shunt_adc 12-bit resolution