fix #49, math setMaxCurrentShunt() (#50)

- fix #49, precision math setMaxCurrentShunt() in INA226.cpp
- changed max shunt voltage to 81.9 mV (0.02 under datasheet limit)
- changed INA226_MINIMAL_SHUNT_OHM
- update comments in INA226.h
- add INA_comparison_table.md
- updated readme.md

CHANGELOG.md

@@ -6,6 +6,14 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/)
 and this project adheres to [Semantic Versioning](http://semver.org/).
 
 
+## [0.6.1] - 2025-01-27
+- fix #49, precision math setMaxCurrentShunt() in INA226.cpp
+- changed max shunt voltage to 81.9 mV (0.02 under datasheet limit)
+- changed INA226_MINIMAL_SHUNT_OHM
+- update comments in INA226.h
+- add INA_comparison_table.md
+- updated readme.md
+
 ## [0.6.0] - 2024-05-27
 - Fix #47, calibration register is 15 bit, not 16 bit.
 - minor edits
@@ -42,7 +50,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 - update readme.md
 
 ## [0.5.1] - 2023-12-10
-- reimplementation of **setMaxCurrentShunt()**, 
+- reimplementation of **setMaxCurrentShunt()**,
   - thanks to tileiar
 - update readme.md
 - minor edits
@@ -95,7 +103,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 - fix #11 normalize
 - fix #13 simplify sign handling shunt and current
 - add releaseNotes.md
-- **reset()** also resets the calibration (current_lsb, maxCurrent and shunt), 
+- **reset()** also resets the calibration (current_lsb, maxCurrent and shunt),
 thereby forcing the user to redo the calibration call with **setMaxCurrentShunt()**.
 - fixes issue #11 => a factor 10 bug in current_lsb.
 - some edits in readme.md.
@@ -104,19 +112,19 @@ thereby forcing the user to redo the calibration call with **setMaxCurrentShunt(
 ----
 
 ## [0.1.6] - 2021-12-20
-- update library.json, 
-- license, 
+- update library.json,
+- license,
 - minor edits
 
 ## [0.1.5] - 2021-11-05
-- update build-CI, 
+- update build-CI,
 - add badges in readme.md
 - fix address in constructor
 
-## [0.1.4] - 2021-08-07  
+## [0.1.4] - 2021-08-07
 - fix getCurrent()
 
-## [0.1.3] - 2021-06-22  
+## [0.1.3] - 2021-06-22
 - add getCurrentLSB_uA()
 - improve examples
 - fix for calibration
@@ -127,11 +135,11 @@ thereby forcing the user to redo the calibration call with **setMaxCurrentShunt(
 - add getShunt()
 - add getMaxCurrent()
 
-## [0.1.1] - 2021-06-21  
+## [0.1.1] - 2021-06-21
 - improved calibration
 - added functions
 
-## [0.1.0] - 2021-05-18  
+## [0.1.0] - 2021-05-18
 - initial version
 
 

INA226.cpp

@@ -1,6 +1,6 @@
 //    FILE: INA226.cpp
 //  AUTHOR: Rob Tillaart
-// VERSION: 0.6.0
+// VERSION: 0.6.1
 //    DATE: 2021-05-18
 // PURPOSE: Arduino library for INA226 power sensor
 //     URL: https://github.com/RobTillaart/INA226
@@ -205,12 +205,14 @@ int INA226::setMaxCurrentShunt(float maxCurrent, float shunt, bool normalize)
 
   //  #define printdebug true
 
-  //  fix #16 - datasheet 6.5 Electrical Characteristics
+  //  fix #16 - datasheet 6.5 Electrical Characteristics: 81.92 mV
   //            rounded value to 80 mV
+  //  fix #49 - changed to 81.90 mV to have parameters (0.8, 0.1) working
+  //            81.90 == datasheet limit - 0.02 mV to catch math overflow
   float shuntVoltage = maxCurrent * shunt;
-  if (shuntVoltage > 0.080)         return INA226_ERR_SHUNTVOLTAGE_HIGH;
-  if (maxCurrent < 0.001)           return INA226_ERR_MAXCURRENT_LOW;
-  if (shunt < INA226_MINIMAL_SHUNT) return INA226_ERR_SHUNT_LOW;
+  if (shuntVoltage > 0.08190)           return INA226_ERR_SHUNTVOLTAGE_HIGH;
+  if (maxCurrent < 0.001)               return INA226_ERR_MAXCURRENT_LOW;
+  if (shunt < INA226_MINIMAL_SHUNT_OHM) return INA226_ERR_SHUNT_LOW;
 
   _current_LSB = maxCurrent * 3.0517578125e-5;      //  maxCurrent / 32768;
 

INA226.h

@@ -1,7 +1,7 @@
 #pragma once
 //    FILE: INA226.h
 //  AUTHOR: Rob Tillaart
-// VERSION: 0.6.0
+// VERSION: 0.6.1
 //    DATE: 2021-05-18
 // PURPOSE: Arduino library for INA226 power sensor
 //     URL: https://github.com/RobTillaart/INA226
@@ -13,7 +13,7 @@
 #include "Wire.h"
 
 
-#define INA226_LIB_VERSION              "0.6.0"
+#define INA226_LIB_VERSION              "0.6.1"
 
 
 //  set by setAlertRegister
@@ -41,7 +41,7 @@
 #define INA226_ERR_NORMALIZE_FAILED       0x8003
 
 //  See issue #26
-#define INA226_MINIMAL_SHUNT              0.001
+#define INA226_MINIMAL_SHUNT_OHM          0.001
 
 #define INA226_MAX_WAIT_MS                600   //  millis
 
@@ -116,10 +116,12 @@ class INA226
 
 
   //  Calibration
-  //  mandatory to set these!
-  //  shunt * maxCurrent < 81 mV
-  //  maxCurrent >= 0.001
-  //  shunt      >= 0.001
+  //  mandatory to set these values!
+  //  datasheet limit == 81.92 mV;
+  //    to prevent math overflow 0.02 mV is subtracted.
+  //  shunt * maxCurrent <= 81.9 mV otherwise returns INA226_ERR_SHUNTVOLTAGE_HIGH
+  //  maxCurrent >= 0.001           otherwise returns INA226_ERR_MAXCURRENT_LOW
+  //  shunt      >= 0.001           otherwise returns INA226_ERR_SHUNT_LOW
   int      setMaxCurrentShunt(float maxCurrent = 20.0, float shunt = 0.002, bool normalize = true);
   bool     isCalibrated()     { return _current_LSB != 0.0; };
 

INA_comparison_table.md

@@ -0,0 +1,22 @@
+
+## Comparison table INA sensors
+
+Comparison of my INA2xx libraries
+
+
+|                   |  219  |  226  |  228  |  229  |  236  |  239  | 3221  |
+|:------------------|:-----:|:-----:|:-----:|:-----:|:-----:|:-----:|:-----:|
+|  bits             |  12   |  16   |  20   |  20   |  16   |  16   |  13   |
+|  Max Voltage      |  26   |  36   |  85   |  85   |  48   |  85   |  26   |
+|  Communication    |  I2C  |  I2C  |  I2C  |  SPI  |  I2C  |  SPI  |  I2C  |
+|  Channels         |   1   |   1   |   1   |   1   |   1   |   1   |   3   |
+|                   |       |       |       |       |       |       |       |
+|  getBusVoltage    |   Y   |   Y   |   Y   |   Y   |   Y   |   Y   |   Y   |
+|  getShuntVoltage  |   Y   |   Y   |   Y   |   Y   |   Y   |   Y   |   Y   |
+|  getCurrent       |   Y   |   Y   |   Y   |   Y   |   Y   |   Y   |   Y   |
+|  getPower         |   Y   |   Y   |   Y   |   Y   |   Y   |   Y   |   Y   |
+|  getTemperature   |   -   |   -   |   Y   |   Y   |   -   |   Y   |   -   |
+|  getEnergy        |   -   |   -   |   Y   |   Y   |   -   |   -   |   -   |
+|  getCharge        |   -   |   -   |   Y   |   Y   |   -   |   -   |   -   |
+
+

LICENSE

@@ -1,6 +1,6 @@
 MIT License
 
-Copyright (c) 2021-2024 Rob Tillaart
+Copyright (c) 2021-2025 Rob Tillaart
 
 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal

README.md

@@ -26,14 +26,14 @@ Read datasheet for details.
 The INA226 is a voltage, current and power measurement device. 
 A few important maxima, see datasheet, chapter 6.
 
-|  description  |  max  |  unit  | notes |
-|:--------------|------:|-------:|:------|
-| bus voltage   |  36   | Volt   | unclear for how long.
-| shunt voltage |  80   | mVolt  |
-| current       |  20   | Ampere | 
+|  description    |   max  |   unit   |  notes  |
+|:----------------|-------:|---------:|:--------|
+|  bus voltage    |  36    |    Volt  |  unclear for how long.
+|  shunt voltage  |  81.9  |   mVolt  |  datasheet 81.92 mV
+|  current        |  20    |  Ampere  |
 
 
-#### 0.5.0 Breaking change
+### 0.5.0 Breaking change
 
 Version 0.5.0 introduced a breaking change.
 You cannot set the pins in **begin()** any more.
@@ -42,25 +42,32 @@ The user has to call **Wire.begin()** and can optionally set the Wire pins
 before calling **begin()**.
 
 
-#### Special characters
+### Special characters
 
 - Ω == Ohm = ALT-234 (Windows)
 - µ == micro = ALT-0181 (Windows)
 
 
-#### Related
+### Related
 
 - https://www.ti.com/product/INA226#tech-docs
 - https://www.ti.com/product/INA226#params
 - https://www.ti.com/document-viewer/INA226/datasheet
-- https://github.com/RobTillaart/INA219
-- https://github.com/RobTillaart/INA226
-- https://github.com/RobTillaart/INA236
+- 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/INA229  85 Volt, SPI, 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)
 
 
 ## I2C
 
-#### Address
+### Address
 
 The sensor can have 16 different I2C addresses, 
 which depends on how the A0 and A1 address lines 
@@ -88,7 +95,7 @@ See table - from datasheet table 2, page 18.
 |  SCL  |  SCL  |   79   |  0x4F  |
 
 
-#### Performance
+### Performance
 
 To be elaborated, example sketch available.
 
@@ -137,7 +144,7 @@ Also see #30 for another typical deviation problem.
 ```
 
 
-#### Constructor
+### Constructor
 
 - **INA226(const uint8_t address, TwoWire \*wire = Wire)** Constructor to set 
 the address and optional Wire interface.
@@ -148,7 +155,7 @@ Note: one needs to set **Wire.begin()** before calling **begin()**.
 - **uint8_t getAddress()** returns the address set in the constructor.
 
 
-#### Core Functions
+### Core Functions
 
 Note the power and the current are not meaningful without calibrating the sensor.
 Also the value is not meaningful if there is no shunt connected.
@@ -179,7 +186,7 @@ Helper functions for the micro scale.
 - **float getPower_uW()** idem, in microWatt.
 
 
-#### Configuration
+### Configuration
 
 **Note:**
 The internal conversions runs in the background in the device.
@@ -248,7 +255,7 @@ Note: times are typical, check datasheet for operational range.
 Note: total conversion time can take up to 1024 \* 8.3 ms ~ 10 seconds.
 
 
-#### Calibration
+### Calibration
 
 See datasheet.
 
@@ -257,7 +264,7 @@ Calibration is mandatory to get **getCurrent()** and **getPower()** to work.
 - **int setMaxCurrentShunt(float ampere = 20.0, float ohm = 0.002, bool normalize = true)** 
 set the calibration register based upon the shunt and the max Ampere. 
 From these two values the current_LSB is derived, the steps of the ADC when measuring current.
-Returns Error code, see below.
+Returns Error code, see below. See #49 about math rounding errors.
 - **bool isCalibrated()** returns true if CurrentLSB has been calculated by **setMaxCurrentShunt()**.
 Value should not be zero.
 - **float getCurrentLSB()** returns the LSB in Ampere == precision of the calibration.
@@ -269,7 +276,7 @@ Value should not be zero.
 To print these values in scientific notation use https://github.com/RobTillaart/printHelpers 
 
 
-#### About normalization
+### About normalization
 
 **setMaxCurrentShunt()** will round the current_LSB to nearest round value (typical 0.001) by default (normalize == true). 
 - The user **must** check the return value == 0x000, otherwise the calibration register is **not** set.
@@ -283,18 +290,18 @@ normalize flag was set to true.
 See https://github.com/RobTillaart/INA226/pull/29 for details of the discussion.
 
 
-#### Error codes setMaxCurrentShunt
+### Error codes setMaxCurrentShunt
 
 |  descriptive name error        |  value   |  meaning  |
 |:-------------------------------|:--------:|:----------|
 |  INA226_ERR_NONE               |  0x0000  |  OK
-|  INA226_ERR_SHUNTVOLTAGE_HIGH  |  0x8000  |  maxCurrent \* shunt > 80 mV 
+|  INA226_ERR_SHUNTVOLTAGE_HIGH  |  0x8000  |  maxCurrent \* shunt > 81.9 mV
 |  INA226_ERR_MAXCURRENT_LOW     |  0x8001  |  maxCurrent < 0.001
 |  INA226_ERR_SHUNT_LOW          |  0x8002  |  shunt      < 0.001
 |  INA226_ERR_NORMALIZE_FAILED   |  0x8003  |  not possible to normalize.
 
 
-#### Operating mode
+### Operating mode
 
 See datasheet, partially tested.
 
@@ -315,7 +322,7 @@ Descriptive mode functions (convenience wrappers).
 - **bool setModeShuntBusContinuous()** mode 7 - default.
 
 
-#### Alert functions
+### Alert functions
 
 See datasheet, not tested yet.
 
@@ -351,13 +358,13 @@ Returns true if write to register successful.
 The alert line falls when alert is reached.
 
 
-#### Meta information
+### Meta information
 
 - **uint16_t getManufacturerID()** should return 0x5449
 - **uint16_t getDieID()** should return 0x2260
 
 
-#### Debugging
+### Debugging
 
 - **uint16_t getRegister(uint8_t reg)** fetch registers directly, for debugging only.
 

library.json

@@ -15,7 +15,7 @@
     "type": "git",
     "url": "https://github.com/RobTillaart/INA226.git"
   },
-  "version": "0.6.0",
+  "version": "0.6.1",
   "license": "MIT",
   "frameworks": "*",
   "platforms": "*",

library.properties

@@ -1,5 +1,5 @@
 name=INA226
-version=0.6.0
+version=0.6.1
 author=Rob Tillaart <rob.tillaart@gmail.com>
 maintainer=Rob Tillaart <rob.tillaart@gmail.com>
 sentence=Arduino library for INA226 power sensor

test/unit_test_001.cpp

@@ -80,7 +80,7 @@ unittest(test_constants)
   assertEqual(0x8001, INA226_ERR_MAXCURRENT_LOW);
   assertEqual(0x8002, INA226_ERR_SHUNT_LOW);
 
-  assertEqualFloat(0.001, INA226_MINIMAL_SHUNT, 0.0001);
+  assertEqualFloat(0.001, INA226_MINIMAL_SHUNT_OHM, 0.0001);
 }
 
 
@@ -157,9 +157,9 @@ unittest(test_calibration)
   assertEqual(INA226_ERR_NONE, INA.setMaxCurrentShunt(1,  0.05));
   assertEqual(INA226_ERR_NONE, INA.setMaxCurrentShunt(1,  0.080));
 
-  assertEqual(INA226_ERR_SHUNTVOLTAGE_HIGH, INA.setMaxCurrentShunt(80.1, 0.001));
-  assertEqual(INA226_ERR_SHUNTVOLTAGE_HIGH, INA.setMaxCurrentShunt(40.1, 0.002));
-  assertEqual(INA226_ERR_SHUNTVOLTAGE_HIGH, INA.setMaxCurrentShunt(20.1, 0.004));
+  assertEqual(INA226_ERR_SHUNTVOLTAGE_HIGH, INA.setMaxCurrentShunt(82.0, 0.001));
+  assertEqual(INA226_ERR_SHUNTVOLTAGE_HIGH, INA.setMaxCurrentShunt(41.0, 0.002));
+  assertEqual(INA226_ERR_SHUNTVOLTAGE_HIGH, INA.setMaxCurrentShunt(20.5, 0.004));
   assertEqual(INA226_ERR_SHUNTVOLTAGE_HIGH, INA.setMaxCurrentShunt(1.1, 0.080));
 
   assertEqual(INA226_ERR_MAXCURRENT_LOW,    INA.setMaxCurrentShunt(0.0009));