Support for internal die temperature measurement in some microcontrollers

[mofosyne]

Just a heads up that many microcontrollers have a temperature sensor integrated inside the microcontroller itself.

Typically you would find it attached to the ADC internally or as a separate module.

This would be an easy way for users to gain an extra telemetry in cheap repeater only nodes.

Just be mindful that these sensors on the die itself is not always going to be very accurate unless calibrated and will usually not be exposed to the outside world so is not exactly ambient temperature.

Still if you consider it as the enclosure temperature, you can at least get a general sense of how much heat a device is experiencing over a period of time.

Technical References on internal die temperature options

nRF52840 (Heltek T114, WisBlock etc...)

https://www.mouser.com/datasheet/2/297/nRF52840_OPS_v0.5-1074816.pdf#page=314

26 TEMP — Temperature sensor
The temperature sensor measures die temperature over the temperature range of the device. Linearity
compensation can be implemented if required by the application.
Listed here are the main features for TEMP:
• Temperature range is greater than or equal to operating temperature of the device
• Resolution is 0.25 degrees

Warning

TEMP sensor is restricted when softdevice is active and must be accessed thought it's API. https://docs.nordicsemi.com/bundle/sds_s140/page/SDS/s1xx/sd_resource_reqs/hw_block_interrupt_vector.html

Specifically you should use mpsl_temperature_get() https://docs.nordicsemi.com/bundle/nrfxlib-apis-latest/page/group_mpsl_temp.html

Registers

Registers https://docs.nordicsemi.com/bundle/ps_nrf52840/page/temp.html

ESP32-S3 (T-Deck)

https://www.espressif.com/sites/default/files/documentation/esp32-s3_datasheet_en.pdf#page=59

4.2.2.2 Temperature Sensor
The temperature sensor generates a voltage that varies with temperature. The voltage is internally converted
via an ADC into a digital value.
The temperature sensor has a range of –40 °C to 125 °C. It is designed primarily to sense the temperature
changes inside the chip. The temperature value depends on factors such as microcontroller clock frequency
or I/O load. Generally, the chip’s internal temperature is higher than the ambient temperature

Usage

• API Reference: https://docs.espressif.com/projects/esp-idf/en/stable/esp32c3/api-reference/peripherals/temp_sensor.html
• Example Program: https://github.com/espressif/esp-idf/blob/v5.5.1/examples/peripherals/temperature_sensor/temp_sensor/main/temp_sensor_main.c

[IoTThinks]

This one is interesting.
I have use it before for esp32.

Let me explore how to do this. To see how "hot" is a Esp32s3 repeater under the sun.

[IoTThinks]

I try just now for Heltec v3. I will apply to all esp32. Look quite accurrate.
And I will try for NRF MCU too. They may have the built-in temperature too.

[IoTThinks]

NRF MCUs have the builtin temperature too.

My code works for T-echo Lite.
Let me build for RAK4361.

[IoTThinks]

Testing over the week for esp32 and nrf52.

Very accurate for Heltec v3 outdoor in a solar box.

Up to 54* C at 2pm. Well a hot day in close box.

Down to 24* C at 6am.

My Heltec v3 is on light sleep every 5s so not much heat generated from esp32.

RAK4631 is ok too. As it does not have much load to impact the temperature.

These built-in sensors are even more accurate than the sensor in T1000-e.
T1000-e shows 18* C at room temperature (30* C).

I will make the method name as getMCUTemperature().
Then feed to repeater code as temperature.

You may override it if using BME sensors btw.

[IoTThinks]

This is the PR
#1163