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INA238

Arduino library for the INA238 power sensor.

Description

Experimental

This library controls the INA238, a device that measures voltage, current, power and temperature.

The library implements a derived INA237 class which is compatible but less precise.

The INA238 sensor differs from the better known INA228. Most important difference is that the INA238 has a 16 bit ADC. This means it is slightly faster than the 20 bit INA228, but less precise. Furthermore the INA238 has no energy and no charge register. Finally there is no configurable temperature compensation.

The INA238 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 the interrupts. The alert / limits part of the library's API still needs a redesign.

The library is limited tested with hardware (RP2040).

==> USE WITH CARE

Feedback as always is welcome.

Details

The INA238 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.

One breakout board is known. https://www.adafruit.com/product/6349 Not tested.

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 |
      |                                     |
      |                                     |
      |          INA238 BREAKOUT            |
      |                                     |
      |                                     |
      \-------------------------------------/

TODO Test

Schema HIGH SIDE

         GND                          VCC
          |                            |
          |                            |
          +---[ LOAD ]---+        +----+
                         |        |    |
                         |        |    |
      /-------------------------------------\
      |                 VIN-     VIN+  VBUS |
      |                                     |
      |                                     |
      |          INA238 BREAKOUT            |
      |                                     |
      |                                     |
      \-------------------------------------/

Tested - see #2

Special characters

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

Related

I2C

Address

The sensor can have 16 different I2C addresses, which depends on how the A0 and A1 address lines are connected to the SCL, SDA, GND and VCC pins.

See table - from datasheet table 7-2, page 19.

A1 A0 Addr HEX A1 A0 Addr HEX
GND GND 64 0x40 SDA GND 72 0x48
GND VCC 65 0x41 SDA VCC 73 0x49
GND SDA 66 0x42 SDA SDA 74 0x4A
GND SCL 67 0x43 SDA SCL 75 0x4B
VCC GND 68 0x44 SCL GND 76 0x4C
VCC VCC 69 0x45 SCL VCC 77 0x4D
VCC SDA 70 0x46 SCL SDA 78 0x4E
VCC SCL 71 0x47 SCL SCL 79 0x4F

Note this might differ per breakout board.

Performance

Run INA238_performance.ino sketch to get a first indication of your board used. Numbers below are based upon tests with RP2040 (see issue #2).

Time in micros, I2C speed in kHz.

I2C function time notes
100 getBusVoltage 620 100%
100 getShuntVoltage 590 95%
100 getCurrent 583 94%
100 getPower 728 117%
100 getTemperature 601 97%
other functions similar gain.
200 getBusVoltage 350 56%
400 getBusVoltage 237 38%
800 getBusVoltage 167 27%

Most non core functions are as fast as getTemperature()

I2C multiplexing

Sometimes you need to control more devices than possible with the default address range the device provides. This is possible with an I2C multiplexer e.g. TCA9548 which creates up to eight channels (think of it as I2C subnets) which can use the complete address range of the device.

Drawback of using a multiplexer is that it takes more administration in your code e.g. which device is on which channel. This will slow down the access, which must be taken into account when deciding which devices are on which channel. Also note that switching between channels will slow down other devices too if they are behind the multiplexer.

Interface

#include "INA238.h"

Constructor

  • INA238(const uint8_t address, TwoWire *wire = Wire) Constructor to set the address and optional Wire interface.
  • bool begin() initializes the class. Returns true if the INA238 address is on the I2C bus.
    • Note: one needs to set Wire.begin() before calling begin().
    • Note: call setMaxCurrentShunt(maxCurrent, shunt) to calibrate your INA238
  • bool isConnected() returns true if the INA238 address is on the I2C bus.
  • uint8_t getAddress() returns the address set in the constructor.
  • bool setAddress(uint8_t newAddress) sets a new I2C address (see #4). returns true if the new address is on the I2C bus.

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 INA238 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 INA238 is bidirectional.
  • float getAmpere()
  • float getMilliAmpere()
  • float getMicroAmpere()

POWER

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

TEMPERATURE

  • float getTemperature() returns the temperature in Celsius.

Configuration

Read datasheet for details, section 7.6.1.2, page 21++

  • 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.
  • void setADCRange(bool flag) flag = false => ~163.84 mV, true => ~40.96 mV
  • bool getADCRange() return set value.

ADC mode

Read datasheet for details, section 7.6.1.2, page 22++

  • bool setMode(uint8_t mode = INA238_MODE_CONT_TEMP_BUS_SHUNT) default all on.
  • uint8_t getMode() return set value.
MODE value notes
INA238_MODE_SHUTDOWN 0x00 See 0x08.
INA238_MODE_TRIG_BUS 0x01
INA238_MODE_TRIG_SHUNT 0x02
INA238_MODE_TRIG_BUS_SHUNT 0x03
INA238_MODE_TRIG_TEMP 0x04
INA238_MODE_TRIG_TEMP_BUS 0x05
INA238_MODE_TRIG_TEMP_SHUNT 0x06
INA238_MODE_TRIG_TEMP_BUS_SHUNT 0x07
INA238_MODE_SHUTDOWN2 0x08 There are two shutdowns.
INA238_MODE_CONT_BUS 0x09
INA238_MODE_CONT_SHUNT 0x0A
INA238_MODE_CONT_BUS_SHUNT 0x0B
INA238_MODE_CONT_TEMP 0x0C
INA238_MODE_CONT_TEMP_BUS 0x0D
INA238_MODE_CONT_TEMP_SHUNT 0x0E
INA238_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
INA238_50_us 0
INA238_84_us 1
INA238_150_us 2
INA238_280_us 3
INA238_540_us 4
INA238_1052_us 5
INA238_2074_us 6
INA238_4120_us 7

ADC Average

  • bool setAverage(uint8_t avg = INA238_1_SAMPLE)
  • uint8_t getAverage() return set value.
AVERAGE value notes
INA238_1_SAMPLE 0
INA238_4_SAMPLES 1
INA238_16_SAMPLES 2
INA238_64_SAMPLES 3
INA238_128_SAMPLES 4
INA238_256_SAMPLES 5
INA238_512_SAMPLES 6
INA238_1024_SAMPLES 7

Shunt Calibration

To elaborate, read datasheet for details, section 7.6.1.3, page 23

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. ( Mateksys == 0.0002 Ω )
    • returns -3 if maxCurrent < 0.0.
  • 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.

Diagnose alert

Read datasheet for details, section 7.6.1.9, page 24++.

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

INA238.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 7.3.6, page 16++

Note: the implementation of this part is rather minimalistic and might be changed / extended in the future. Idem see my INA228 library.

Shunt

  • void setOverCurrentLimit(uint32_t milliamp)
  • float getOverCurrentLimit_mA()
  • void setShuntOvervoltageTH(uint16_t threshold)
  • uint16_t getShuntOvervoltageTH()
  • void setShuntUndervoltageTH(uint16_t threshold)
  • uint16_t getShuntUndervoltageTH()

Bus

  • void setBusOvervoltageTH(uint16_t threshold)
  • uint16_t getBusOvervoltageTH()
  • void setBusUndervoltageTH(uint16_t threshold)
  • uint16_t getBusUndervoltageTH()

Temperature

  • void setTemperatureOverLimitTH(uint16_t threshold)
  • uint16_t getTemperatureOverLimitTH()

Power

  • void setPowerOverLimitTH(uint16_t threshold)
  • uint16_t getPowerOverLimitTH()

Manufacturer and ID

  • bool getManufacturer() Returns 0x5449, can be used to check right sensor. Note 0x5449 == TI in ASCII.
  • uint16_t getDieID() Returns 0x238, can be used to check right sensor. (INA237 will return 0x237).
  • uint16_t getRevision() Returns revision, probably 0x01.

Future

Must

  • update documentation.
  • test and verify with hardware
  • keep sync INA228 where possible.
  • fix TODO's in code + readme.md

Should

  • how to detect nothing connected?
    • vshunt > maxVShunt (new variable)
    • current > maxCurrent
  • examples
    • example to show the effect of the ADC configuration.
  • improve error handling (INA228)
    • constants/enum

Could

  • improve API thresholds and limits (INA228)
  • improve API use bitmasks for diagnostics (INA228)
  • write examples, (please share yours).
  • improve unit tests
  • clean up magic numbers in the code?

Won't

  • cache registers for performance
    • first get library working / tested.
    • reset should reread all cached values...

Support

If you appreciate my libraries, you can support the development and maintenance. Improve the quality of the libraries by providing issues and Pull Requests, or donate through PayPal or GitHub sponsors.

Thank you,

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Arduino library for the INA238 power sensor.

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0.1.3 release Latest
Apr 14, 2026
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