Zephyr BLE Sensor Node

Overview

BLE peripheral on the nRF52840 DK using Zephyr RTOS. Reads a BME280 sensor, exposes data over a custom GATT service, and sleeps aggressively between readings. Demonstrates the Zephyr-specific stack (device tree, Kconfig, BLE GATT) used in IoT firmware roles.

Hardware

Architecture

BME280 (I2C)
    |
    v
[Sensor Thread] --> reads every N seconds --> [BLE GATT Notify]
                                                      |
                                            [Central / Phone App]

Between reads: PM sleep --> system off --> RTC wakeup

Zephyr Concepts

Device Tree

Hardware described in .overlay files rather than #define pin configs scattered in headers. The BME280 is declared as a node on the I2C bus:

/* boards/nrf52840dk_nrf52840.overlay */
&i2c0 {
    bme280@76 {
        compatible = "bosch,bme280";
        reg = <0x76>;
    };
};

At compile time Zephyr generates device handles. No manual I2C address init in main().

Kconfig

prj.conf selects subsystems at build time:

CONFIG_BT=y
CONFIG_BT_PERIPHERAL=y
CONFIG_BT_DEVICE_NAME="SensorNode"
CONFIG_SENSOR=y
CONFIG_BME280=y
CONFIG_PM=y
CONFIG_PM_DEVICE=y

Custom GATT Service

Custom 128-bit UUID service with characteristics for temperature, humidity, and pressure. Notifies connected centrals on each new reading. Connection and disconnection callbacks control the advertising restart.

Power Management

Zephyr PM subsystem puts the SoC into low-power states between readings. Sleep current profiled with the Nordic PPK2 — the goal is sub-10µA average at 1-reading-per-minute.

Build

west build -b nrf52840dk_nrf52840 app
west flash