8 years ago.

Internal temperature from STM32L476

Today I tried using the example for reading the internal temperature sensor in the STM32L476 Discovery demo board by importing this project:

https://developer.mbed.org/teams/ST/code/STM32_ADC_InternalChannels/

However, it appears to give crazy results, and ones that show some strange interaction between ADC channels. For example, in my case in a room that measures 23C the project as given reports the following:

VBat = 4364.5 mV
Internal Temperature = -189.4 degree C
VBat = 4364.5 mV
Internal Temperature = -190.4 degree C
VBat = 4361.3 mV
Internal Temperature = -190.4 degree C
VBat = 4364.5 mV
Internal Temperature = -191.6 degree C

However if I comment out the line 27 where it reads battery voltage I get a very different temperature displayed:

STM32 Internal Channels example
Internal Temperature = 35.0 degree C
Internal Temperature = 45.6 degree C
Internal Temperature = 45.0 degree C
Internal Temperature = 45.3 degree C
Internal Temperature = 44.6 degree C

What is going on here?

I really would expect the temperature to be within a few degrees of reality, and not to be jumping about by what looks like several LSB from reading to reading.

Also what is odd is the example main.cpp is using a few hard-coded constants, and not the data sheet approach (for example section "16.3.31 Temperature sensor" in RM0351, Reference manual, STM32L4x6 advanced ARM-based 32-bit MCUs, DocID024597 Rev 4) to calibration where the expected values for 110C and 30C are given in read-only locations. I'm guessing accessible using code such as:

const uint16_t TS_CAL1 = *(uint16_t *)(0x1FFF75A8);
const uint16_t TS_CAL2 = *(uint16_t *)(0x1FFF75CA);