DS18B20 temperature sensor no "negative values"

[nettylink]

Hi,

I'm using the arduino-motorfocus with N.I.N.A. and have noticed, that negative temperatures are not shown correctly. With negative temperatures always 0.00° are shown.

The current code always returns "0#" on negative temperature readings of the DS18B20.

I've change the following code from:

    byte t_int = (byte)temperature << 1;
    t_int += round(temperature - (byte)temperature);
    Serial.print(t_int, HEX);
    Serial.print('#');

to:

    int t_int = (int) temperature;
    int tmp = (t_int * 2);
    char tempString[8];
    sprintf(tempString, "%04X", (int) tmp);
    Serial.print(tempString);
    Serial.print('#');

I guess there are better solutions, but with this code negative temperatures are shown correctly.

[fehlfarbe]

Thanks! I tested several values and simplified the code a bit :)

[nettylink]

Hi,

thank you very much for the new code. I've also tested a bit more.

When duplicating the temperature as integer, we get a 1 degree resulution.

int16_t t_int = (int16_t)(temperature*2);

When duplicating the temperature as a float, we get a 0.5 degree temp resulution.

float d_temperature = (float)(temperature*2);
int16_t t_int = (int16_t)(d_temperature);

Here are few test values.	temperature (from DS18B20)	tempString (old)	tempString (old as int)	in N.I.N.A. (old)	tempString (new)	tempString (new as int)	in N.I.N.A. (new)
4.49	0008	8	4.00	0008	8	4.00
4.51	0008	8	4.00	0009	9	4.50
-4.49	FFFFFFF8	-8	-4.00	FFFFFFF8	-8	-4.00
-4.51	FFFFFFF8	-8	-4.00	FFFFFFF7	-9	-4.50

[fehlfarbe]

Ok that's weird because the temperature is duplicated as float in the parenthesis and afterwards casted to integer so it should be the same :thinking:

(int16_t)(temperature*2) == (int16_t)((float)(temperature*2))