How can i convert the temperature using sd_temp_get() to an uint8_t?

RE: How can i convert the temperature using sd_temp_get() to an uint8_t?

Embedded_Engineer — Mon, 07 Sep 2020 06:48:51 GMT

Remember you are getting a 2's complement in your int8_t raw_temp so yes it is for negative values.

If you meant -5 degrees C then it would be raw_temp = 0xFB;

If you did not mean the above then we don't write minus ( - ) with the hex. The most significant bit indicates the sign. You can just compare the raw_temp with -5 and do your logic.

RE: How can i convert the temperature using sd_temp_get() to an uint8_t?

puff — Mon, 11 Feb 2019 13:09:36 GMT

Can't understand, what will be the value for -5C? Will this code work for negative values?

RE: How can i convert the temperature using sd_temp_get() to an uint8_t?

Eirik Nobuki Kosaka — Wed, 20 May 2015 10:26:43 GMT

Thanks! This helped and was able to make it work.

RE: How can i convert the temperature using sd_temp_get() to an uint8_t?

Stefan Birnir Sverrisson — Wed, 20 May 2015 05:01:08 GMT

In addition to Nick's answer, you may need to calibrate the output of the TEMP peripheral. The potential error read on the TEMP peripheral should be pure offset error. You can calibrate the temperature value in software, i.e. if you know the temperature in your room, just add or subtract from the measured value to get the correct value.

RE: How can i convert the temperature using sd_temp_get() to an uint8_t?

Nick Pelis — Tue, 19 May 2015 17:28:19 GMT

The value from sd_temp_get() is in units of 0.25 degrees Celsius (source). This means a value of 4 is 1 degree Celsius, a value of 8 is 2 degrees Celsius, a value of 12 is 3 degrees Celsius, etc.

Assuming you wish to convert the result into a whole number, you would simply divide it by four. I wouldn't worry about any integer overflow as a result of going from a 32 bit to an 8 bit number since the operating range of the nrf514122 is between -25 and 75 degrees C. However, since the temperature can drop below zero, you should use an int8_t instead of a uint8_t.

So your code would look like this:

int32_t raw_temp;
sd_temp_get(&raw_temp);
int8_t temp = raw_temp >> 2;  // divide by 4