INA219 I2C

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mongoose-os-libs/ina219-i2c	mgos_ina219.h

A Mongoose library for Texas Instruments' popular I2C current sensor.

Implementation details

The INA219 is a simple I2C device that measures a voltage drop over a shunt resistor, as well as the voltage on the bus. It is able to measure voltage up to 26V (in 4mV increments) on the bus and the voltage drop over the shunt resistor in 10uV increments with a range of 320mV, and is reasonably precise.

Using a 0.1Ohm shunt resistor, the maximum current that can be measured is 3.2A.

API Description

Create an INA219 object using mgos_ina219_create(), set the shunt resistor value using mgos_ina219_set_shunt_resistance(), then call mgos_ina219_get_bus_voltage() to get the bus voltage, call mgos_ina219_get_shunt_voltage() to get the voltage drop over the shunt resistor, and mgos_ina219_get_current() to get the current flowing through the circuit.

Example application

#include "mgos.h"
#include "mgos_config.h"
#include "mgos_ina219.h"

static void ina219_timer_cb(void *user_data) {
  struct mgos_ina219 *sensor = (struct mgos_ina219 *)user_data;
  float bus, shunt, current, res;

  if (!sensor) return;

  mgos_ina219_get_bus_voltage(sensor, &bus);
  mgos_ina219_get_shunt_resistance(sensor, &res);
  mgos_ina219_get_shunt_voltage(sensor, &shunt);
  mgos_ina219_get_current(sensor, &current);
  LOG(LL_INFO, ("Vbus=%.3f V Vshunt=%.0f uV Rshunt=%.3f Ohm Ishunt=%.1f mA",
      bus, shunt*1e6, res, current*1e3));
  }
}

enum mgos_app_init_result mgos_app_init(void) {
  struct mgos_ina219 *sensor;

  sensor = mgos_ina219_create(mgos_i2c_get_global(), mgos_sys_config_get_ina219_i2caddr());
  if (!sensor) {
    LOG(LL_ERROR, ("Could not create INA219 sensor"));
    return false;
  }

  mgos_set_timer(1000, true, ina219_timer_cb, sensor);

  return MGOS_APP_INIT_SUCCESS;
}

Disclaimer

This project is not an official Google project. It is not supported by Google and Google specifically disclaims all warranties as to its quality, merchantability, or fitness for a particular purpose.

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mgos_ina219_create

struct mgos_ina219 *mgos_ina219_create(struct mgos_i2c *i2c, uint8_t i2caddr);

Initialize a INA219 on the I2C bus i2c at address specified in i2caddr parameter (default INA219 is on address 0x40). The sensor will be polled for validity, upon success a new struct mgos_ina219 is allocated and returned. If the device could not be found, NULL is returned.

mgos_ina219_destroy

void mgos_ina219_destroy(struct mgos_ina219 **sensor);

Destroy the data structure associated with a INA219 device. The reference to the pointer of the struct mgos_ina219 has to be provided, and upon successful destruction, its associated memory will be freed and the pointer set to NULL.

mgos_ina219_get_bus_voltage

bool mgos_ina219_get_bus_voltage(struct mgos_ina219 *sensor, float *volts);

Measure the bus voltage on the device. Return the measured voltage in *volts, in units of Volts. Returns true on success and false on failure, in which case *volts is unspecified.

mgos_ina219_get_shunt_voltage

bool mgos_ina219_get_shunt_voltage(struct mgos_ina219 *sensor, float *volts);

Measure the shunt voltage on the device. Return the measured voltage in *volts, in units of Volts. Returns true on success and false on failure, in which case *volts is unspecified.

mgos_ina219_set_shunt_resistance

bool mgos_ina219_set_shunt_resistance(struct mgos_ina219 *sensor, float ohms);

Set the shunt resistor value in units of Ohms. Typical values is ohms=0.100 (which yields a 3.2A range on the current sensor). Returns true on success and false on failure.

mgos_ina219_get_shunt_resistance

bool mgos_ina219_get_shunt_resistance(struct mgos_ina219 *sensor, float *ohms);

Get the shunt resistor value in units of Ohms. Returns true on success and false on failure, in which case *ohms is unspecified.

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