Wrong readings for negative temperatures

[loeriver]

As the code uses unsigned int for the temperature readings which are coded as 2's complement signed values, you will get wrong readings if the device is exposed to cold weather (i.e. below 0°C).

I suggest to use some code like this:

int16_t DS3231_Simple::getTemperature()
{
  return (int16_t)(DS3231_Simple::getTemperatureFloat() + 0.5);
}

float DS3231_Simple::getTemperatureFloat()
{
  int16_t temp; 

  rtc_i2c_seek(0x11);
  
  Wire.requestFrom(RTC_ADDRESS,(uint8_t) 2);
  
  temp = Wire.read() << 8;
  temp |= Wire.read();
  
  return(temp/256.);
}

[sleemanj]

While you are correct that this seems to be in error, your proposed solution would drag in floating point, the reason for having getTemperature separately is to be able to avoid that overhead. Umm... I think simply changing the types of the return value and `t` to `int8_t` should fix it, but I don't have time to test and not 100% sure on the fractional representation and rounding when it goes below zero.

[loeriver]

Well, it was just laziness to do it this way (as I needed the floating point value anyway). But I think this should work w/o requiring floating point for the integer value:

int16_t DS3231_Simple::getTemperature()
{
   int16_t temp; 

  rtc_i2c_seek(0x11);
  
  Wire.requestFrom(RTC_ADDRESS,(uint8_t) 2);
  
  temp = Wire.read() << 8;
  temp |= Wire.read();
  
  return((temp + 128) >> 8);
}

A dry run (no DS3231, but a union simulating the 2 registers ) gave the following integer results:

25.5°C: 26°C
19.25°C: 19°C
-18.75°C: -19°C
-25.5°C: -25°C