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BLE Sensor — Real IoT Application

A complete IoT sensor node that reads temperature from an I2C sensor, computes a CRC checksum, and advertises the data over BLE. This example demonstrates how multiple EoS modules work together in a real application.

What it demonstrates

  • BLE initialization, advertising, and data transmission
  • I2C sensor communication (read temperature register)
  • CRC32 checksum computation for data integrity
  • Kernel task creation for periodic sensor sampling
  • GPIO LED toggle for activity indication

Modules used

Module Header Functions
HAL Core eos/hal.h eos_hal_init, eos_gpio_init, eos_gpio_toggle
HAL I2C eos/hal.h eos_i2c_init, eos_i2c_read_reg
HAL BLE eos/hal_extended.h eos_ble_init, eos_ble_advertise_start, eos_ble_send
Kernel eos/kernel.h eos_kernel_init, eos_kernel_start, eos_task_create, eos_task_delay_ms
Crypto eos/crypto.h eos_crc32

Hardware

  • MCU: nRF52840 (or any BLE-capable MCU)
  • Sensor: I2C temperature sensor (TMP102, LM75, or similar) on I2C port 0
  • LED: Connected to pin 13

How to build

# Cross-compile for nRF52
cmake -B build \
  -DCMAKE_TOOLCHAIN_FILE=../../toolchains/arm-none-eabi.cmake \
  -DEOS_PRODUCT=iot
cmake --build build

# Host build (simulated peripherals)
cmake -B build -DEOS_PRODUCT=iot
cmake --build build
./build/ble-sensor

Expected output

[ble-sensor] BLE advertising as 'EoS-Sensor'
[ble-sensor] Sensor task started
[ble-sensor] Starting kernel...
[ble-sensor] TX seq=0 temp=23.50°C crc=0xa1b2c3d4
[ble-sensor] TX seq=1 temp=23.56°C crc=0xe5f6a7b8
...

Data format

The BLE advertisement payload is a sensor_packet_t:

Field Type Description
temperature_x100 int16_t Temperature in 0.01°C units (2350 = 23.50°C)
sequence uint32_t Monotonic packet counter
crc uint32_t CRC32 of the preceding fields