Introduction

The attached example is an adaptation of the standard 'SOC - Thermometer' example which instead of accessing the Si7021 Temperature and Relative Humidity sensor through I2C uses the EFR32's own internal temperature sensor. This sensor is measured during production test and the temperature readout from the ADC at production temperature as well as the Celsius value are given in the device information page. Using these and the millivolts per degrees slope found in the sensor datasheet the current temperature can be calculated according to formula:

T_Celsius = T_Calibration - (ADC_Calibration_Reading - ADC_Current_Reading) * V_Ref / (4096 * Slope)

(For more information, see ADC section of the reference manual of your chosen hardware, e.g. EFR32xG13)

Setting up the project

Start by creating an SoC - Empty sample app for your chosen hardware.

1. In the project menu select new | Silicon Labs appBuilder project.
2. Select Bluetooth SDK and click next
3. Select the latest Bluetooth SDK and click next
4. Select SOC – Empty and click next
5. Enter a name for the project and click next
6. Replace existing app.c with the app.c attached to this article
7. Copy em_adc.c and em_adc.h from the SDK to the project folder if they aren't already in the platform->emlib->inc/src folders.
8. Import the attached gatt.xml file in the GATT Configurator sidebar (.isc file, "Import GATT from .bgproj file"). This will add the Health Thermometer service and Temperature Measurement characteristic and change Device Name to "IntTemp".
9. Press Save and Generate
10. Build and flash

Using the Blue Gecko app you can now read the temperature sampled from the internal temperature sensor.