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setMaxCurrentShunt normalization optimized #29

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merged 5 commits into from
Dec 10, 2023
Merged

setMaxCurrentShunt normalization optimized #29

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9d6a5aa
setMaxCurrentShunt
tileiar Nov 1, 2023
accd621
Merge remote-tracking branch 'upstream/master' into SetMaxCurrentShun…
tileiar Dec 8, 2023
98d00b2
normalize optimized (1,2,5) and less greedy autoscale
tileiar Dec 8, 2023
4ed9619
optimized footprint
tileiar Dec 10, 2023
7515b4a
comment 1 and 3 (not 2)
tileiar Dec 10, 2023
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83 changes: 59 additions & 24 deletions INA226.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -182,7 +182,7 @@ int INA226::setMaxCurrentShunt(float maxCurrent, float shunt, bool normalize)

// fix #16 - datasheet 6.5 Electrical Characteristics
// rounded value to 80 mV
float shuntVoltage = abs(maxCurrent * shunt);
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;
Expand All @@ -194,62 +194,97 @@ int INA226::setMaxCurrentShunt(float maxCurrent, float shunt, bool normalize)
Serial.print("normalize:\t");
Serial.println(normalize ? " true":" false");
Serial.print("initial current_LSB:\t");
Serial.print(_current_LSB, 8);
Serial.print(_current_LSB * 1e+6, 1);
Serial.println(" uA / bit");
#endif

uint32_t calib = 0;
uint32_t factor = 1;

// normalize the LSB to a round number
// LSB will increase
if (normalize)
{
calib = round(0.00512 / (_current_LSB * shunt));
_current_LSB = 0.00512 / (calib * shunt);
/* check if maxCurrent (normal) or shunt resistor (due to unusual low resistor values in relation to maxCurrent) determines currentLSB
we have to take the upper value for currentLSB

calculation of currentLSB based on shunt resistor and calibration register limits (2 bytes)
cal = 0.00512 / ( shunt * currentLSB )
cal(max) = 2^16-1
currentLSB(min) = 0.00512 / ( shunt * cal(max) )
currentLSB(min) ~= 0.00512 / ( shunt * 2^16 )
currentLSB(min) ~= 2^9 * 1e-5 / ( shunt * 2^16 )
currentLSB(min) ~= 1e-5 / 2^7 / shunt
currentLSB(min) ~= 7.8125e-8 / shunt
*/
if( 7.8125e-8 / shunt > _current_LSB ) {
// shunt resistor determines currentLSB -> take this a starting point for currentLSB
_current_LSB = 7.8125e-8 / shunt;
}

#ifdef printdebug
Serial.print("Prescale current_LSB:\t");
Serial.print(_current_LSB, 8);
Serial.print(_current_LSB * 1e+6, 1);
Serial.println(" uA / bit");
#endif

// auto scale current_LSB
factor = 1;
while (_current_LSB < 1)
{
_current_LSB *= 10;
factor *= 10;
// normalize _current_LSB to a value of 1, 2 or 5 * 1e-6 to 1e-3
// convert float to int
uint16_t currentLSB_uA = float(_current_LSB * 1e+6);
currentLSB_uA++; // ceil would be more precise, but uses 176 bytes of flash

uint16_t factor = 1; // 1u to 1000u
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uint8_t i = 0; // 1 byte loop reduces footprint
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do{
if( 1*factor >= currentLSB_uA){
_current_LSB = 1*factor * 1e-6;
i=0xFF;
}else if( 2*factor >= currentLSB_uA){
_current_LSB = 2*factor * 1e-6;
i=0xFF;
}else if( 5*factor >= currentLSB_uA){
_current_LSB = 5*factor * 1e-6;
i=0xFF;
}else {
factor *= 10;
i++;
}
}while(i < 4); // 10^4

if(i != 0xFF) {
_current_LSB = 0;
return INA226_ERR_NORMALIZE_FAILED;
}
_current_LSB = 1.0 / factor;

#ifdef printdebug
Serial.print("After scale current_LSB:\t");
Serial.print(_current_LSB * 1e+6, 1);
Serial.println(" uA / bit");
#endif
// done
}

// auto scale calibration
calib = round(0.00512 / (_current_LSB * shunt));
uint32_t calib = round(0.00512 / (_current_LSB * shunt));
while (calib > 65535)
{
_current_LSB *= 10;
calib /= 10;
_current_LSB *= 2;
calib = calib >> 1;
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}
_writeRegister(INA226_CALIBRATION, calib);

_maxCurrent = _current_LSB * 32768;
_shunt = shunt;

#ifdef printdebug
Serial.print("factor:\t");
Serial.println(factor);
Serial.print("Final current_LSB:\t");
Serial.print(_current_LSB, 8);
Serial.print(_current_LSB * 1e+6, 1);
Serial.println(" uA / bit");
Serial.print("Calibration:\t");
Serial.println(calib);
Serial.print("Max current:\t");
Serial.print(_maxCurrent);
Serial.print(_maxCurrent, 3);
Serial.println(" A");
Serial.print("Shunt:\t");
Serial.print(_shunt, 8);
Serial.println(" ohm");
Serial.print(_shunt, 4);
Serial.println(" Ohm");
Serial.print("ShuntV:\t");
Serial.print(shuntVoltage, 4);
Serial.println(" Volt");
Expand Down
5 changes: 2 additions & 3 deletions INA226.h
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Original file line number Diff line number Diff line change
Expand Up @@ -37,12 +37,11 @@
#define INA226_ERR_SHUNTVOLTAGE_HIGH 0x8000
#define INA226_ERR_MAXCURRENT_LOW 0x8001
#define INA226_ERR_SHUNT_LOW 0x8002

#define INA226_ERR_NORMALIZE_FAILED 0x8003

// See issue #26
#define INA226_MINIMAL_SHUNT (0.001)


class INA226
{
public:
Expand Down Expand Up @@ -88,7 +87,7 @@ class INA226
// shunt * maxCurrent < 81 mV
// maxCurrent >= 0.001
// shunt >= 0.001
int setMaxCurrentShunt(float macCurrent = 20.0,
int setMaxCurrentShunt(float maxCurrent = 20.0,
float shunt = 0.002,
bool normalize = true);
bool isCalibrated() { return _current_LSB != 0.0; };
Expand Down
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