Measure DC Power with an INA219 and Arduino Uno R3

Specs

PGA Gain & Range

The PGA configuration sets the gain and Full-Scale Range (FSR) of voltage across the shunt resistor. The PGA gain settings in the table below can be found in Table 4 of the INA219 Datasheet.

Resolution & Sampling

The ADC resolution settings adjust the number of ADC bits or number of samples used when averaging results for the Bus Voltage Register and Shunt Voltage Register. Higher ADC resolution or sampling requires longer conversion times. The ADC resolution settings in the table below can be found in Table 5 of the INA219 Datasheet.

Chip Versions

The INA219 IC comes in a SOIC-8 (3.91mm x 4.90mm) or SOT-23 (1.63mm x 2.90mm) package. There are two versions of the INA219 chip: A and B. The A version has a ±1% total max current measurement error over the entire operating temperature range and the B version has a ±0.5% total max current measurement error over the entire operating temperature range, but the overall functionality is otherwise the same. The markings on the chip indicate whether its the A or B version.

Adafruit INA219 Module

The Adafruit board comes with a 6-pin header and a 3.5mm terminal plug for the load. On each side of the board are STEMMA QTSTEMMA QT ('cutie') connectors are Adafruit's name for 4-pin JST SH connectors with 1.0mm pitch. These connectors were implemented on Adafruit boards to make it easy to plug-n-play various sensors and devices without soldering and wiring. The STEMMA QT (JST SH) are a smaller connector than the STEMMA (JST PH) that do not fit on smaller boards. STEMMA QT is cross-compatible with SparkFun Qwiic connectors. connectors for supplying power VCC to the INA219 chip and the two I2C lines (SCLSerial Clock (SCL) is the output clock signal line from the master device. Also referred to as SCK, SCLK, or CLK. and SDASerial Data Line ). Adafruit provides an Overview of the board and an Arduino library on GitHub for communicating with the device over I2C.

On the back of the board are A0 and A1 solder jumpers that can be bridged with solder to change the I2C address to the list below.

• Default = 0x40
• A0 soldered = 0x41
• A1 soldered = 0x44
• A0 and A1 soldered = 0x45

There is also an LED jumper that can be cut to disable the board's power LED if you want to reduce power consumption.

Generic INA219 Module

The Generic INA219 modules are similar to the Adafruit module, with the same functionality, except they do not include the STEMMA QT connectors for I2C and the onboard power LED. A couple other minor differences are the power pin is labeled VCC instead of VIN and the I2C solder jumpers are on the front of the board instead of the back of the board.

Adafruit_INA219 Library

The Adafruit_INA219 library was created by Adafruit for their INA219 module, although the library also works with generic modules. This library can be installed by the Arduino IDE Library Manager and is also available on GitHub. It offers an easy to use interface with pre-calculated calibration options, function calls to read measurement registers, and a power down function. A list of functions available in the Adafruit library are provided below.

Adafruit_INA219 ina219(I2C_Address):

Class constructor to set the I2C address. The default is 0x40.

void begin(void):

Initializes I2C communication address and Wire library with the Adafruit_INA219 device.

void setCalibration_32V_2A():

Highest range setting with a maximum bus voltage of 32V and maximum current of 2A. Uses a PGA gain of 1/8 that has an FSR of 320mV across the shunt resistor. The current LSBThe Least Significant Bit (LSB) in a binary number is the bit that represents the smallest place value carrying the lowest weight. It is also sometimes referred to as the low-order bit or right-most bit due to the convention in positional notation of writing less significant digits further to the right. is 100μA/bit and the power LSB is 2mW/bit. Counter overflow occurs at 3.2767A.

void setCalibration_32V_1A():

Uses a maximum bus voltage of 32V and a slightly lower maximum current of 1A range with higher precision on amps. Uses a PGA gain of 1/8 that has an FSR of 320mV across the shunt resistor. The current LSB is 40μA/bit and the power LSB is 800μW/bit. Counter overflow occurs at 1.31068A.

void setCalibration_16V_400mA():

Uses a lower 16V maximum bus voltage and 400mA maximum current range with higher precision on volts and amps. Uses a PGA gain of 1 that has an FSR of 40mV across the shunt resistor. The current LSB is 50μA/bit and the power LSB is 1mW/bit. Counter overflow occurs at 1.63835A.

float getBusVoltage_V():

Reads the bus voltage in Volts. The bus voltage is across the load: V_IN- - GND.

float getShuntVoltage_mV():

Reads the shunt voltage in millivolts.

float getCurrent_mA():

Reads the current through the load in milliamps.

float getPower_mW():

Reads the load power in milliWatts.

void powerSave(bool on):

Sets power save mode by powering down the INA219. Input argument is a boolean value, where True sets the power same mode on and False turns it off.

The Arduino code sketch provided below reads voltage, current, and power from the INA219 over I2C at a sampling rate of 1 second. The load current is expected to be around 50mA, so the calibration is configured to the lowest setting to maximize the resolution: 16V bus voltage and 400mA current range. The output is printed to the serial monitor on the Arduino IDEIntegrated Development Environment (IDE) is a software application that helps develop software code efficiently. over the USB port.

The output of the measurements from a 5V source through a 0.1Ω shunt and 100Ω load resistor is provided below.

INA219_WE Library

The INA219_WE library was created by Wolfgang Ewald to provide more functionality and control over the INA219. This library can be installed by the Arduino IDE Library Manager and is also available on GitHub. GitHub. Wolfgang Ewald also wrote an https://wolles-elektronikkiste.de/en/ina219-current-and-power-sensor on this library with more details on how it works. A list of functions available in the INA219_WE library are provided below.

INA219_WE INA219_WE(I2C_ADDRESS):

Class constructor to sets the I2C address. If no address is provided INA219_WE(), it sets default I2C address to 0x40.

bool init():

Ensures that the INA219 is reset and then activated with the default values for ADC mode, measurement mode, PGA gain, and bus voltage range. To change these basic settings, you can run the setADCMode(), setMeasureMode(), setPGain(), and setBusRange() functions before the init() call in the setup. If init() returns False, then the INA219 was unable to reset most likely due to the I2C not being connected.

bool reset_INA219():

Writes to the configuration register to reset the INA219.

void setCorrectionFactor(float corr):

Applies a correction factor to the current values if they differ from values measured by calibrated measuring instruments such as a multimeter. The factor is the quotient of the "correct" and the INA219 value.

void setShuntVoltOffset_mV(float offs):

Some INA219 modules tend to show shunt voltage offsets. Although no current is flowing through the load, the output has a small shunt voltage and current. With setShuntVoltOffset() you can correct this by passing the shunt voltage in millivolts, that is measured without current, as parameter to the function.

void setADCMode(mode):

ADC mode for shunt and bus voltage conversion, where BIT_MODE_X are single measurements with X bit resolution and SAMPLE_MODE_X is the mean value from X measurements.

• BIT_MODE_9:
  9-Bit Resolution and 84µs conversion time
• BIT_MODE_10:
  10-Bit Resolution and 148µs conversion time
• BIT_MODE_11:
  11-Bit Resolution and 276µs conversion time
• BIT_MODE_12 (Default):
  12-Bit Resolution and 532µs conversion time
• SAMPLE_MODE_2:
  Mean Value 2 samples and 1.06ms conversion time
• SAMPLE_MODE_4:
  Mean Value 4 samples and 2.13ms conversion time
• SAMPLE_MODE_8:
  Mean Value 8 samples and 4.26ms conversion time
• SAMPLE_MODE_16:
  Mean Value 16 samples and 8.51ms conversion time
• SAMPLE_MODE_32:
  Mean Value 32 samples and 17.02ms conversion time
• SAMPLE_MODE_64:
  Mean Value 54 samples and 34.05ms conversion time
• SAMPLE_MODE_128:
  Mean Value 128 samples and 68.10ms conversion time

void setMeasureMode(mode):

• CONTINUOUS(Default):
  Makes measurements continuously.
• TRIGGERED:
  Single-Shot measurements made "on request" where the function startSingleMeasurement() starts the measurement. The output takes place only when the measurement is completed.
• ADC_OFF:
  Switches the ADC off to save power
• POWER_DOWN:
  Turns the INA219 off. Better to use the powerDown() function, which backs up the content of the configuration register before switching off the INA219.

void setPGain(gain):

Sets the PGA gain and FSR across the shunt resistor.

• PG_40:
  Gain = 1, FSR = 40mV
• PG_80:
  Gain = 1/2, FSR = 80mV
• PG_160:
  Gain = 1/4, FSR = 160mV
• PG_320:
  Gain = 1/8, FSR = 320mV

void setBusRange(range):

Bus voltage range

• BRNG_16:
  16V
• BRNG_32(Default):
  32V

float getBusVoltage_V():

Reads the bus voltage in Volts. The bus voltage is across the load: V_IN- - GND.

float getShuntVoltage_mV():

Reads the shunt voltage in millivolts.

float getCurrent_mA():

Reads the current through the load in milliamps.

float getPower():

Reads the load power in milliWatts.

bool getOverflow():

Checks whether one of the data registers is overflowed. Returns True if there is overflow and False if there is no overflow. If overflow occurs, select a higher PGAIN.

void powerDown():

Backs up the content of the configuration register before switching off the INA219.

void powerUp():

Writes back the copy of the configuration register. This writing process awakens the INA219 and ensures that the INA219 returns to the previously selected mode.

The Arduino code sketch provided below reads voltage, current, and power from the INA219 over I2C at a sampling rate of 1 second. The load current is expected to be around 50mA, so the calibration is configured to the lowest setting to maximize the resolution: 16V bus voltage and 400mA current range. The output is printed to the serial monitor on the Arduino IDEIntegrated Development Environment (IDE) is a software application that helps develop software code efficiently. over the USB port.

The output of the measurements from a 5V source through a 0.1Ω shunt and 100Ω load resistor is provided below.