How to convert the value to the Temperature from Sensor?

Question

I am working on ST Temperature sensor( hts221 ) , I use I2C command communication with sensor. I am new to this...

I have reference the Data sheet for HTS221 , and also get the value from Sensor. But I don't how to convert the value to the actual temperature.

The value get the from the sensor is like the following:

Read HTS221 TEMP_OUT_L: 0x2a value is 0x15
Read HTS221 TEMP_OUT_H: 0x2b value is 0xFF
Read HTS221 T0_degC_x8: 0x32 value is 0xBF
Read HTS221 T1_degC_x8: 0x33 value is 0xBF
Read HTS221 T1/T0 msb: 0x35 value is 0x4
Read HTS221 T0_OUT-3C: 0x3C value is 0x0
Read HTS221 T0_OUT-3D: 0x3D value is 0x0
Read HTS221 T1_OUT-3E: 0x3E value is 0x0
Read HTS221 T1_OUT-3F: 0x3F value is 0x0

The description of temperature register is like the following picture.

And it give the calibration coefficients and the example of temperature conversion like the following picture , but I still understand what it mean.

Does somebody can teach me how to convert the above value to the Temperature from Sensor? I have no idea about this... Thanks in advance.

Answer 1

You need to read the following calibration registers:

T0_degC_x8  (Calibration register 32)
T1_degC_x8  (Calibration register 33)
T1_T0msb    (Calibration register 35)
T0_OUT      (Calibration register 3C and 3D)
T1_OUT      (Calibration register 3E and 3F)

T0_degC_x8 and T1_degC_x8 are 10 bit values, so you need to get the 2 last bits from register 35.

Then it's just simple interpolation to get the measured temperature:

double T_DegC;
double T0_degC = (T0_degC_x8 + (1 << 8) * (T1_T0msb & 0x03)) / 8.0; 
double T1_degC = (T1_degC_x8 + (1 << 6) * (T1_T0msb & 0x0C)) / 8.0; // Value is in 3rd and fourth bit, so we only need to shift this value 6 more bits.
T_DegC = (T0_degC + (T_OUT - T0_OUT) * (T1_degC - T0_degC) / (T1_OUT - T0_OUT)); 

Note:

The register numbering is hexadecimal, so registers 32, 33, and 35 are actually registers 0x32, 0x33, and 0x35.