Read STLM75 - Temperature Sensor

[ezyreach]

Posted on January 19, 2011 at 12:35

Read STLM75 - Temperature Sensor

[brazov22]

Posted on May 17, 2011 at 14:21

Hi,

I think it's 5 right shifted because the choosen resolution of the digital output data is 11-bit. Then it's 3 times right shifted because that resolution correspond to temperature increments of 0.125 °C: /* Offset constants for scale temperature */  #define stts75_span (float)(0.125)    // From [0.5 , 0.25 , 0.125 , 0.0625 ]  #define stts75_offset  (u8)(32)    // From [128 ,  64  ,   32  ,  16    ] /* Convert 2 complements integer value to float in °C */ float stts75_scale_temp(u16 temp) {  float temp_result=0.0;    if(temp>0)  // Positive temperature ?   temp_result=(float)(temp*stts75_span/stts75_offset);  else     // Negative temperature ?   temp_result=(float)(temp*stts75_span/stts75_offset)-256;    if(temp==0)  // Zero ?   temp_result=0.0;    return temp_result; } brazov2

[ezyreach]

Posted on May 17, 2011 at 14:21

@bravoz.ajeje

Thank u very much for ur reply. I got the point that the 5 right shift is done based on the ADC resolution. But i didnt get the point that 3 right shift resolution leads to .125 increase in the temperature. As per the datasheet the increase in temperature is done by 0.5 C and not by .125 C. And moreover how did u fix the offset to be (u8)32? Can you please explain it in bit detail?

[brazov22]

Posted on May 17, 2011 at 14:21

Hi,

sorry, what I said was for STTS75 (I used it): look at page 6 chapter 1.2, you can see that depending on the resolution you choose, you have a certain increment step in temperature, higher bit resolution means lower temperature increment. 3 right shift = 2^(-3) = 0.125 (temperature step) 5 right shift = 2^(5) = 32 (adc resolution 11-bit)

http://www.st.com/internet/com/TECHNICAL_RESOURCES/TECHNICAL_LITERATURE/DATASHEET/CD00153513.pdf

for STLM75 ADC resolution is alway 9-bit, so in this case: 1 right shift = 2^(-1) = 0.5 (temperature step) 7 right shift = 2^(7) = 128 (adc resolution 9-bit) brazov2