Core Module integrated temperature sensor precision


Hi, is it normal the integrated temperature sensor on Core Module returns temperature 2 degrees C above real temperature in the room? All my other instruments agree its ~22C but the core module claims it is 24C. I guess some heat leakage from another component could be blamed?


Also when I read temperature from both humidity tag and core module temperature sensor at the same time the core module temp sensor returns value that is 2C lower than the value returned by humidity sensor.


Hi, if you have loop which is preventing Core Module to sleep, the measurement will be affected by the heat generated by the MCU. By any chance, don’t you have USB stack initialized and USB cable connected?

Regarding the humidity sensor, isn’t it vice versa - I mean that you read temperature from humidity sensor 2C lower, than from the Core Module?


Yes. Sorry. The core temperature sensor returns 2C higher, not lower.

Yes. I have usb stack connected (I export values that way). Here is my code:

I don’t think I am preventing CPU sleep but I don’t know how the usb stack works.


Okay, now it is clear - the USB stack itself prevents the CPU from sleep mode. Because USB stack requires the 48 MHz oscillator running etc. Unfortunately, for the USB application, you cannot get precise temperature sensor reading. You can however you Temperature Tag which is sufficiently distant from the MCU, or you can simply substract a temperature offset. The MCU power consumption and the generated heat is constant. Yep, no kidding - this is dirty, but fairly common practice for many temperature monitoring applications… Another option is going wireless / battery operated - this is where BigClown is the best and in such scenario, the MCU is in the sleep mode vast majority of the time, so it will not affect the reading.


Ok, thank you. I do not need wireless operation so using it just because of this is overkill :slight_smile: But it might warrant a note in core module specs page that the temperature sensor is unreliable under cpu load.

I will just use the temperature provided by humidity tag. That too is slightly higher than expected but I do not have other instruments precise enough to say for sure.


Okay, what is the Humidity Tag revision ?


R3. I guess the latest? I bought it on tuesday :slight_smile:


Yea, that is the latest one, the temperature reading should be very accurate - see SHT20 datasheet for more details.


Thank you. I will take a look.