LM75A.cpp

/*
 * \brief I2C LM75A temperature sensor library (implementation)
 *
 * \author Quentin Comte-Gaz <quentin@comte-gaz.com>
 * \date 19 June 2022
 * \license MIT License (contact me if too restrictive)
 * \copyright Copyright (c) 2022 Quentin Comte-Gaz
 * \version 1.3
 */

#include "LM75A.h"
#include <Wire.h>

namespace LM75AConstValues
{

const int LM75A_BASE_ADDRESS = 0x48;

const float LM75A_DEGREES_RESOLUTION = 0.125;

const int LM75A_REG_ADDR_TEMP = 0;
//const int LM75A_REG_ADDR_CONF = 1;  // Not used for now
//const int LM57A_REG_ADDR_THYST = 2; // Not used for now
//const int LM57A_REG_ADDR_TOS = 3;   // Not used for now

}

using namespace LM75AConstValues;

LM75A::LM75A(
  #ifdef USE_TWO_WIRE_FOR_LM75A
  TwoWire* specific_wire,
  #endif
  bool A0_value,
  bool A1_value,
  bool A2_value)
{
  _i2c_device_address = LM75A_BASE_ADDRESS;

  // Update I2C address depending on how the sensor is connected
  if (A0_value)
  {
    _i2c_device_address += 1;
  }

  if (A1_value)
  {
    _i2c_device_address += 2;
  }

  if (A2_value)
  {
    _i2c_device_address += 4;
  }

  // Select Wire (if one I2C range) or TwoWire (if two I2C range)
  #ifdef USE_TWO_WIRE_FOR_LM75A
  _specific_wire = specific_wire;
  #else
  Wire.begin();
  #endif
}

LM75A::LM75A(
  #ifdef USE_TWO_WIRE_FOR_LM75A
  TwoWire* specific_wire,
  #endif
  int address)
{
  _i2c_device_address = address;

  // Select Wire (if one I2C range) or TwoWire (if two I2C range)
  #ifdef USE_TWO_WIRE_FOR_LM75A
  _specific_wire = specific_wire;
  #else
  Wire.begin();
  #endif
}

float LM75A::fahrenheitToDegrees(float temperature_in_fahrenheit)
{
  return ((temperature_in_fahrenheit - 32.0) / 1.8);
}

float LM75A::degreesToFahrenheit(float temperature_in_degrees)
{
  return ((temperature_in_degrees * 1.8) + 32.0);
}

float LM75A::getTemperatureInFahrenheit() const
{
  float temperature_in_degrees = getTemperatureInDegrees();

  if (temperature_in_degrees == INVALID_LM75A_TEMPERATURE)
  {
    return INVALID_LM75A_TEMPERATURE;
  }

  return degreesToFahrenheit(temperature_in_degrees);
}

float LM75A::getTemperatureInDegrees() const
{
  uint16_t real_result = INVALID_LM75A_TEMPERATURE;
  uint16_t i2c_received = 0;

  // Go to temperature data register
  #ifdef USE_TWO_WIRE_FOR_LM75A
  _specific_wire->beginTransmission(_i2c_device_address);
  _specific_wire->write(LM75A_REG_ADDR_TEMP);
  if (_specific_wire->endTransmission())
  {
    // Transmission error
    return real_result;
  }

  // Get content
  if (_specific_wire->requestFrom(_i2c_device_address, 2))
  {
    _specific_wire->readBytes((uint8_t*)&i2c_received, 2);
  }
  else
  {
    // Can't read temperature
    return real_result;
  }
  #else
  Wire.beginTransmission(_i2c_device_address);
  Wire.write(LM75A_REG_ADDR_TEMP);
  if (Wire.endTransmission())
  {
    // Transmission error
    return real_result;
  }

  // Get content
  if (Wire.requestFrom(_i2c_device_address, 2))
  {
    Wire.readBytes((uint8_t*)&i2c_received, 2);
  }
  else
  {
    // Can't read temperature
    return real_result;
  }
  #endif

  // Modify the value (only 11 MSB are relevant if swapped)
  int16_t refactored_value;
  uint8_t* ptr = (uint8_t*)&refactored_value;

  // Swap bytes
  *ptr = *((uint8_t*)&i2c_received + 1);
  *(ptr + 1) = *(uint8_t*)&i2c_received;

  // Shift data (left-aligned)
  refactored_value >>= 5;

  float real_value;
  if (refactored_value & 0x0400)
  {
    // When sign bit is set, set upper unused bits, then 2's complement
    refactored_value |= 0xf800;
    refactored_value = ~refactored_value + 1;
    real_value = (float)refactored_value * (-1) * LM75A_DEGREES_RESOLUTION;
  }
  else
  {
    real_value = (float)refactored_value *  LM75A_DEGREES_RESOLUTION;
  }

  return real_value;
}