INA239

October 20, 2025 · View on GitHub

INA239

Arduino library for the INA239, SPI, 16 bit, voltage, current and power sensor.

Description

Experimental

This library controls the INA239, a device that measures voltage, current, power, and temperature.

The library is not tested with hardware yet, feedback welcome.

The library is written to be able to use the faster SPI interface which might be needed (faster than I2C which is used by many other INA devices.).

The INA239 sensor uses a 16 bit ADC.

An important difference with the well known INA226 is that the INA239 works up to 85 Volts, which is more than twice the 36 volt of the INA226. The INA239 has a build in temperature sensor (±1°C) to be used for monitoring and temperature compensation.

The INA239 also provides an ALERT line, to generate an interrupt in case a predefined threshold has been met. This can be an under- or over-voltage, temperature or power limit. The library does not handle these interrupts.

The code is based upon my INA228 library which uses the same registers (plus 3 more) and has a I2C interface. The 239 uses 16 bit where the 228 uses a 20 bit ADC. This means most constants in the formulas are slightly different.

==> USE WITH CARE

Feedback as always is welcome.

Update 0.2.0

In 0.2.0 a bug was fixed in software SPI, so all 0.1.x versions are now obsolete (although HW SPI did work).

Details

The INA239 is a voltage, current and power measurement device. A few important data, Read the datasheet for the details, Section 7, Page 12++.

description	value	notes
bus voltage	85 Volt	unclear for how long.
ADC	16 bit
alert timing	75 µs.

No breakout boards are known.

Calibrating

Note the power and the current are not meaningful without calibrating the sensor. Also the values are not meaningful if there is no shunt connected.

Schema LOW SIDE

         GND                           VCC
          |                             |
          |                             |
          |            +----[ LOAD ]----+
          |            |                |
          |            |                |
      /-------------------------------------\
      |  VIN-         VIN+             VBUS |
      |                                     |
      |                                     |
      |          INA239 BREAKOUT            |
      |                                     |
      |                                     |
      \-------------------------------------/

Not tested with hardware, feedback welcome.

Schema HIGH SIDE

         GND                          VCC
          |                            |
          |                            |
          +---[ LOAD ]---+        +----+
                         |        |    |
                         |        |    |
      /-------------------------------------\
      |                 VIN-     VIN+  VBUS |
      |                                     |
      |                                     |
      |          INA239 BREAKOUT            |
      |                                     |
      |                                     |
      \-------------------------------------/

Not tested with hardware, feedback welcome.

Special characters

Ω == Ohm = ALT-234 (Windows)
µ == micro = ALT-0181 (Windows)
° == degree = ALT-0176 (Windows)
± == plus minus = ALT-0177 (Windows)

https://www.ti.com/product/INA239#tech-docs
https://www.ti.com/product/INA239#params
https://www.ti.com/document-viewer/INA239/datasheet
https://github.com/RobTillaart/INA219 26 Volt, I2C, 12 bit
https://github.com/RobTillaart/INA226 36 Volt, I2C, 16 bit
https://github.com/RobTillaart/INA228 85 Volt, I2C, 20 bit
https://github.com/RobTillaart/INA236 48 Volt, I2C, 16 bit
https://github.com/RobTillaart/INA239 85 Volt, SPI, 16 bit
https://github.com/RobTillaart/INA3221_RT 26 Volt, I2C, 13 bits (3 channel)
https://www.adafruit.com/product/5832
https://www.mateksys.com/?portfolio=i2c-ina-bm
https://github.com/RobTillaart/printHelpers (for scientific notation)

Performance

Run INA239_performance.ino sketch to get a first indication. Numbers below are based upon tests with no board.

Time in micros, SPI speed in MHz.

SPI	function	time	notes
1.0	getBusVoltage	56	100%
1.0	getShuntVoltage	100
1.0	getCurrent	52
1.0	getPower	68
1.0	getTemperature	52
			other functions similar gain.
2.0	getBusVoltage	44
4.0	getBusVoltage	40
8.0	getBusVoltage	32

Most non core functions are as fast as getTemperature()

Interface

#include "INA239.h"

Constructor

INA239(uint8_t select, SPI_CLASS * mySPI = &SPI) Constructor HARDWARE SPI
INA239(uint8_t select, uint8_t dataIn, uint8_t dataOut, uint8_t clock) Constructor SOFTWARE SPI
bool begin() initializes the class.

BUS VOLTAGE

Main function + wrappers.

float getBusVoltage() idem. Returns value in volts. Max 85 Volt. This value is always positive.
float getBusVolt()
float getBusMilliVolt()
float getBusMicroVolt()

SHUNT VOLTAGE

float getShuntVoltage() idem, Returns value in volts. Note the value can be positive or negative as the INA239 is bidirectional.
float getShuntVolt()
float getShuntMilliVolt()
float getShuntMicroVolt()

SHUNT CURRENT

float getCurrent() returns the current through the shunt in Ampere. Note this value can be positive or negative as the INA239 is bidirectional.
float getAmpere() idem
float getMilliAmpere() idem
float getMicroAmpere() idem

TEMPERATURE

float getTemperature() returns the temperature in Celsius.

POWER

float getPower() returns the current x BusVoltage in Watt.
float getWatt() idem
float getMilliWatt() idem
float getMicroWatt() idem
float getKiloWatt() idem

Configuration

Read datasheet for details, section 7.6.1.1, page xx

void reset() Resets the device, be aware that you need to calibrate the sensor (shunt register) again ==> call setMaxCurrentShunt() and more.
void setConversionDelay(uint8_t steps) Conversion delay in 0..255 steps of 2 ms
uint8_t getConversionDelay() return set value.
bool setADCRange(bool flag) flag = false => 164 mV, true => 41 mV Since 0.2.1 setADCRange() calls setMaxCurrentShunt() to update the internal LSB values. Returns false on failure of setMaxCurrentShunt().
bool getADCRange() return set value.

TODO: examples to show the effect of the ADC configuration.

ADC mode

Read datasheet for details, section 7.6.1.2, page xx++

bool setMode(uint8_t mode = INA239_MODE_CONT_TEMP_BUS_SHUNT) default all on.
uint8_t getMode() return set value.

MODE	value	notes
INA239_MODE_SHUTDOWN	0x00	See 0x08.
INA239_MODE_TRIG_BUS	0x01
INA239_MODE_TRIG_SHUNT	0x02
INA239_MODE_TRIG_BUS_SHUNT	0x03
INA239_MODE_TRIG_TEMP	0x04
INA239_MODE_TRIG_TEMP_BUS	0x05
INA239_MODE_TRIG_TEMP_SHUNT	0x06
INA239_MODE_TRIG_TEMP_BUS_SHUNT	0x07
INA239_MODE_SHUTDOWN2	0x08	There are two shutdowns.
INA239_MODE_CONT_BUS	0x09
INA239_MODE_CONT_SHUNT	0x0A
INA239_MODE_CONT_BUS_SHUNT	0x0B
INA239_MODE_CONT_TEMP	0x0C
INA239_MODE_CONT_TEMP_BUS	0x0D
INA239_MODE_CONT_TEMP_SHUNT	0x0E
INA239_MODE_CONT_TEMP_BUS_SHUNT	0x0F

ADC conversion time

bool setBusVoltageConversionTime(uint8_t bvct = INA226_1052_us)
uint8_t getBusVoltageConversionTime() return set value.
bool setShuntVoltageConversionTime(uint8_t svct = INA226_1052_us)
uint8_t getShuntVoltageConversionTime() return set value.
bool setTemperatureConversionTime(uint8_t tct = INA226_1052_us)
uint8_t getTemperatureConversionTime() return set value.

TIMING	value	notes
INA239_50_us	0
INA239_84_us	1
INA239_150_us	2
INA239_280_us	3
INA239_540_us	4
INA239_1052_us	5
INA239_2074_us	6
INA239_4120_us	7

bool setAverage(uint8_t avg = INA239_1_SAMPLE)
uint8_t getAverage() return set value.

AVERAGE	value	notes
INA239_1_SAMPLE	0
INA239_4_SAMPLES	1
INA239_16_SAMPLES	2
INA239_64_SAMPLES	3
INA239_128_SAMPLES	4
INA239_256_SAMPLES	5
INA239_512_SAMPLES	6
INA239_1024_SAMPLES	7

Shunt Calibration

To elaborate, read datasheet for details.

Note: setMaxCurrentShunt() must be called to calibrate your sensor. Otherwise several functions will return zero or incorrect data.

int setMaxCurrentShunt(float maxCurrent, float shunt) The maxCurrent depends on breakout used, See section above. The shunt should be 0.0001 Ω and up.
- returns 0 if OK.
- returns -2 if shunt < 0.0001 Ohm.
bool isCalibrated() is valid calibration value. The currentLSB > 0.
float getMaxCurrent() return set value.
float getShunt() return set value.
float getCurrentLSB() return actual currenLSB. 0.0 means not calibrated.
float getCurrentLSB_mA() returns the LSB in milliAmpere.
float getCurrentLSB_uA() returns the LSB in microAmpere.

Diagnose alert

Read datasheet for details, section 7.6.1.12, page xx++.

void setDiagnoseAlert(uint16_t flags) set all flags as bit mask.
uint16_t getDiagnoseAlert() return all flags as bit mask.

INA239.h has an enum for the bit fields.

void setDiagnoseAlertBit(uint8_t bit) set individual bit.
void clearDiagnoseAlertBit(uint8_t bit) clear individual bit.
uint16_t getDiagnoseAlertBit(uint8_t bit) return individual bit.

Threshold and Limits

Read datasheet for details, section 7.3.7, page xx++

Note: the implementation of this part is rather minimalistic and might be changed / extended in the future. Currently it are just wrappers around the registers.