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K.Townsend committed May 25, 2012
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322 changes: 322 additions & 0 deletions Adafruit_INA219.cpp
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/**************************************************************************/
/*!
@file Adafruit_INA219.cpp
@author K.Townsend (Adafruit Industries)
@license BSD (see license.txt)
Driver for the INA219 current sensor
This is a library for the Adafruit INA219 breakout
----> https://www.adafruit.com/products/???
Adafruit invests time and resources providing this open source code,
please support Adafruit and open-source hardware by purchasing
products from Adafruit!
@section HISTORY
v1.0 - First release
*/
/**************************************************************************/
#if ARDUINO >= 100
#include "Arduino.h"
#else
#include "WProgram.h"
#endif

#include <Wire.h>

#include "Adafruit_INA219.h"

/**************************************************************************/
/*!
@brief Sends a single command byte over I2C
*/
/**************************************************************************/
void Adafruit_INA219::wireWriteRegister (uint8_t reg, uint16_t value)
{
Wire.beginTransmission(INA219_ADDRESS);
#if ARDUINO >= 100
Wire.write(reg); // Register
Wire.write(value >> 8); // Upper 8-bits
Wire.write(value & 0xFF); // Lower 8-bits
#else
Wire.send(reg); // Register
Wire.send(value >> 8); // Upper 8-bits
Wire.send(value & 0xFF); // Lower 8-bits
#endif
Wire.endTransmission();
}

/**************************************************************************/
/*!
@brief Reads a 16 bit values over I2C
*/
/**************************************************************************/
void Adafruit_INA219::wireReadRegister(uint8_t reg, uint16_t *value)
{
Wire.beginTransmission(INA219_ADDRESS);
#if ARDUINO >= 100
Wire.write(reg); // Register
#else
Wire.send(reg); // Register
#endif
Wire.endTransmission();

Wire.requestFrom(INA219_ADDRESS, 2);
#if ARDUINO >= 100
// Shift values to create properly formed integer
*value = ((Wire.read() << 8) | Wire.read());
#else
// Shift values to create properly formed integer
*value = ((Wire.receive() << 8) | Wire.receive());
#endif
}

/**************************************************************************/
/*!
@brief Configures to INA219 to be able to measure up to 32V and 2A
of current. Each unit of current corresponds to 100uA, and
each unit of power corresponds to 2mW. Counter overflow
occurs at 3.2A.
@note These calculations assume a 0.1 ohm resistor is present
*/
/**************************************************************************/
void Adafruit_INA219::ina219SetCalibration_32V_2A(void)
{
// By default we use a pretty huge range for the input voltage,
// which probably isn't the most appropriate choice for system
// that don't use a lot of power. But all of the calculations
// are shown below if you want to change the settings. You will
// also need to change any relevant register settings, such as
// setting the VBUS_MAX to 16V instead of 32V, etc.

// VBUS_MAX = 32V (Assumes 32V, can also be set to 16V)
// VSHUNT_MAX = 0.32 (Assumes Gain 8, 320mV, can also be 0.16, 0.08, 0.04)
// RSHUNT = 0.1 (Resistor value in ohms)

// 1. Determine max possible current
// MaxPossible_I = VSHUNT_MAX / RSHUNT
// MaxPossible_I = 3.2A

// 2. Determine max expected current
// MaxExpected_I = 2.0A

// 3. Calculate possible range of LSBs (Min = 15-bit, Max = 12-bit)
// MinimumLSB = MaxExpected_I/32767
// MinimumLSB = 0.000061 (61µA per bit)
// MaximumLSB = MaxExpected_I/4096
// MaximumLSB = 0,000488 (488µA per bit)

// 4. Choose an LSB between the min and max values
// (Preferrably a roundish number close to MinLSB)
// CurrentLSB = 0.0001 (100µA per bit)

// 5. Compute the calibration register
// Cal = trunc (0.04096 / (Current_LSB * RSHUNT))
// Cal = 4096 (0x1000)

// 6. Calculate the power LSB
// PowerLSB = 20 * CurrentLSB
// PowerLSB = 0.002 (2mW per bit)

// 7. Compute the maximum current and shunt voltage values before overflow
//
// Max_Current = Current_LSB * 32767
// Max_Current = 3.2767A before overflow
//
// If Max_Current > Max_Possible_I then
// Max_Current_Before_Overflow = MaxPossible_I
// Else
// Max_Current_Before_Overflow = Max_Current
// End If
//
// Max_ShuntVoltage = Max_Current_Before_Overflow * RSHUNT
// Max_ShuntVoltage = 0.32V
//
// If Max_ShuntVoltage >= VSHUNT_MAX
// Max_ShuntVoltage_Before_Overflow = VSHUNT_MAX
// Else
// Max_ShuntVoltage_Before_Overflow = Max_ShuntVoltage
// End If

// 8. Computer the Maximum Power
// MaximumPower = Max_Current_Before_Overflow * VBUS_MAX
// MaximumPower = 3.2 * 32V
// MaximumPower = 102.4W

// Set multipliers to convert raw current/power values
ina219_currentDivider_mA = 10; // Current LSB = 100uA per bit (1000/100 = 10)
ina219_powerDivider_mW = 2; // Power LSB = 1mW per bit (2/1)

// Set Calibration register to 'Cal' calculated above
wireWriteRegister(INA219_REG_CALIBRATION, 0x1000);

// Set Config register to take into account the settings above
uint16_t config = INA219_CONFIG_BVOLTAGERANGE_32V |
INA219_CONFIG_GAIN_8_320MV |
INA219_CONFIG_BADCRES_12BIT |
INA219_CONFIG_SADCRES_12BIT_1S_532US |
INA219_CONFIG_MODE_SANDBVOLT_CONTINUOUS;
wireWriteRegister(INA219_REG_CONFIG, config);
}

/**************************************************************************/
/*!
@brief Configures to INA219 to be able to measure up to 32V and 1A
of current. Each unit of current corresponds to 40uA, and each
unit of power corresponds to 800µW. Counter overflow occurs at
1.3A.
@note These calculations assume a 0.1 ohm resistor is present
*/
/**************************************************************************/
void Adafruit_INA219::ina219SetCalibration_32V_1A(void)
{
// By default we use a pretty huge range for the input voltage,
// which probably isn't the most appropriate choice for system
// that don't use a lot of power. But all of the calculations
// are shown below if you want to change the settings. You will
// also need to change any relevant register settings, such as
// setting the VBUS_MAX to 16V instead of 32V, etc.

// VBUS_MAX = 32V (Assumes 32V, can also be set to 16V)
// VSHUNT_MAX = 0.32 (Assumes Gain 8, 320mV, can also be 0.16, 0.08, 0.04)
// RSHUNT = 0.1 (Resistor value in ohms)

// 1. Determine max possible current
// MaxPossible_I = VSHUNT_MAX / RSHUNT
// MaxPossible_I = 3.2A

// 2. Determine max expected current
// MaxExpected_I = 1.0A

// 3. Calculate possible range of LSBs (Min = 15-bit, Max = 12-bit)
// MinimumLSB = MaxExpected_I/32767
// MinimumLSB = 0.0000305 (30.5µA per bit)
// MaximumLSB = MaxExpected_I/4096
// MaximumLSB = 0.000244 (244µA per bit)

// 4. Choose an LSB between the min and max values
// (Preferrably a roundish number close to MinLSB)
// CurrentLSB = 0.0000400 (40µA per bit)

// 5. Compute the calibration register
// Cal = trunc (0.04096 / (Current_LSB * RSHUNT))
// Cal = 10240 (0x2800)

// 6. Calculate the power LSB
// PowerLSB = 20 * CurrentLSB
// PowerLSB = 0.0008 (800µW per bit)

// 7. Compute the maximum current and shunt voltage values before overflow
//
// Max_Current = Current_LSB * 32767
// Max_Current = 1.31068A before overflow
//
// If Max_Current > Max_Possible_I then
// Max_Current_Before_Overflow = MaxPossible_I
// Else
// Max_Current_Before_Overflow = Max_Current
// End If
//
// ... In this case, we're good though since Max_Current is less than MaxPossible_I
//
// Max_ShuntVoltage = Max_Current_Before_Overflow * RSHUNT
// Max_ShuntVoltage = 0.131068V
//
// If Max_ShuntVoltage >= VSHUNT_MAX
// Max_ShuntVoltage_Before_Overflow = VSHUNT_MAX
// Else
// Max_ShuntVoltage_Before_Overflow = Max_ShuntVoltage
// End If

// 8. Computer the Maximum Power
// MaximumPower = Max_Current_Before_Overflow * VBUS_MAX
// MaximumPower = 1.31068 * 32V
// MaximumPower = 41.94176W

// Set multipliers to convert raw current/power values
ina219_currentDivider_mA = 25; // Current LSB = 40uA per bit (1000/40 = 25)
ina219_powerDivider_mW = 1; // Power LSB = 800µW per bit

// Set Calibration register to 'Cal' calculated above
wireWriteRegister(INA219_REG_CALIBRATION, 0x2800);

// Set Config register to take into account the settings above
uint16_t config = INA219_CONFIG_BVOLTAGERANGE_32V |
INA219_CONFIG_GAIN_8_320MV |
INA219_CONFIG_BADCRES_12BIT |
INA219_CONFIG_SADCRES_12BIT_1S_532US |
INA219_CONFIG_MODE_SANDBVOLT_CONTINUOUS;
wireWriteRegister(INA219_REG_CONFIG, config);
}

/**************************************************************************/
/*!
@brief Instantiates a new INA219 class
*/
/**************************************************************************/
Adafruit_INA219::Adafruit_INA219() {
ina219_currentDivider_mA = 0;
ina219_powerDivider_mW = 0;
}

/**************************************************************************/
/*!
@brief Setups the HW (defaults to 32V and 2A for calibration values)
*/
/**************************************************************************/
void Adafruit_INA219::begin() {
Wire.begin();
// Set chip to known config values to start
ina219SetCalibration_32V_2A();
}

/**************************************************************************/
/*!
@brief Gets the shunt voltage (16-bit signed integer, so +-32767)
*/
/**************************************************************************/
int16_t Adafruit_INA219::getShuntVoltage() {
uint16_t value;
wireReadRegister(INA219_REG_SHUNTVOLTAGE, &value);
return value;
}

/**************************************************************************/
/*!
@brief Gets the shunt voltage (16-bit signed integer, so +-32767)
*/
/**************************************************************************/
int16_t Adafruit_INA219::getBusVoltage() {
uint16_t value;
wireReadRegister(INA219_REG_BUSVOLTAGE, &value);
// Shift to the right 3 to drop CNVR and OVF and then multiply by LSB
return (value >> 3) * 4;
}

/**************************************************************************/
/*!
@brief Gets the raw current value (16-bit signed integer, so +-32767)
*/
/**************************************************************************/
int16_t Adafruit_INA219::getCurrent() {
uint16_t value;
wireReadRegister(INA219_REG_CURRENT, &value);
return value;
}

/**************************************************************************/
/*!
@brief Gets the current value in mA, taking into account the
config settings and current LSB
*/
/**************************************************************************/
int16_t Adafruit_INA219::getCurrent_mA() {
uint16_t value;
wireReadRegister(INA219_REG_CURRENT, &value);
return value / ina219_currentDivider_mA;
}

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