oxullo / adafruit_ina219

INA219 Current Sensor

Adafruit_INA219

INA219 Current Sensor

Calibration and dividers

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.

Calculation example with:

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) MAX_EXPECTED_I = 2 (Our load seeks no more than 2A)

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

2. Determine max expected current MaxExpected_I = MAX_EXPECTED_I

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

4. Choose an LSB between the min and max values (Preferrably a roundish number close to MinLSB) CurrentLSB = 0.0001 (100uA 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. Compute the Maximum Power MaximumPower = Max_Current_Before_Overflow * VBUS_MAX MaximumPower = 3.2 * 32V MaximumPower = 102.4W

Configuration

Take the calibration value computed above (Cal).

Adafruit_INA219 ina219;

void setup()
{
	ina219.begin();
	
	// Sample calibration value computed for 2A over 100mOhm shunt
	ina219.setCalibration(4096);
	
	ina219.setConfiguration(
				INA219_CONFIG_BVOLTAGERANGE_32V |		// Bus voltage range up to 32V
                INA219_CONFIG_GAIN_8_320MV |			// Lower sensitivity (320mV)
                INA219_CONFIG_BADCRES_12BIT |			// Bus ADC resolution
                INA219_CONFIG_SADCRES_12BIT_1S_532US |	// Shunt ADC resolution
                INA219_CONFIG_MODE_SANDBVOLT_CONTINUOUS);	// Free conversion
	
	// Normalisation factors
	// 1mA/LSB / x uA/LSB (1000uA/LSB / 100uA/LSB = 10)
	// 2mW/LSB / x mW/LSB (2mW/LSB / 1mW LSB = 2)
	ina219.setDividers(10, 2);
}

Compatibility

MCU	Tested Works	Doesn't Work	Not Tested	Notes
Atmega328 @ 16MHz	X
Atmega328 @ 12MHz	X
Atmega32u4 @ 16MHz	X
Atmega32u4 @ 8MHz	X
ESP8266	X
Atmega2560 @ 16MHz	X
ATSAM3X8E	X			Use D20/D21.
ATSAM21D	X
ATtiny85 @ 16MHz	X			Use SDA/SCL D0/D2
ATtiny85 @ 8MHz	X			Use SDA/SCL D0/D2

• ATmega328 @ 16MHz : Arduino UNO, Adafruit Pro Trinket 5V, Adafruit Metro 328, Adafruit Metro Mini
• ATmega328 @ 12MHz : Adafruit Pro Trinket 3V
• ATmega32u4 @ 16MHz : Arduino Leonardo, Arduino Micro, Arduino Yun, Teensy 2.0
• ATmega32u4 @ 8MHz : Adafruit Flora, Bluefruit Micro
• ESP8266 : Adafruit Huzzah
• ATmega2560 @ 16MHz : Arduino Mega
• ATSAM3X8E : Arduino Due
• ATSAM21D : Arduino Zero, M0 Pro
• ATtiny85 @ 16MHz : Adafruit Trinket 5V
• ATtiny85 @ 8MHz : Adafruit Gemma, Arduino Gemma, Adafruit Trinket 3V