Sensor Beacon Application

A Zephyr application that broadcasts onboard sensor data (accelerometer, temperature, humidity) and battery voltage information via Bluetooth beacon advertisements, with BLE connection support for runtime configuration via AT commands.

This application is designed to be used with the Atmosic DevTools mobile app to monitor sensor data. It also exposes an AT command interface over BLE GATT for runtime device configuration.

Overview

The sensor_beacon application provides sensor data collection and broadcasting via Bluetooth beacon advertisements, together with BLE connection support and an AT command interface for runtime configuration. It uses dual extended advertising sets: a non-connectable set that continuously broadcasts sensor data, and a connectable set that allows a BLE central to connect, authenticate, and issue AT commands over GATT.

Using with Atmosic DevTools App

The sensor_beacon application is designed to work with the Atmosic DevTools mobile app for monitoring sensor data and controlling wake-up.

Monitoring Sensor Data

  1. Open the Atmosic DevTools app

  2. Navigate to APPLICATIONS → BEACON

  3. The app will start scanning for devices

  4. When your sensor beacon device appears, tap MONITOR

  5. The app will display real-time sensor data from the device

Features

  • Sensor Data Collection: Reads temperature, humidity, and 3-axis accelerometer data

  • Battery Monitoring: Monitors VStore and VBatt voltages

  • Bluetooth Beacon Advertising: Broadcasts sensor data using a standardized beacon format

  • BLE Connection Support: Accepts connections on a second advertising set and provides GATT services for AT command transport

  • AT Command Interface: Runtime configuration of device name, advertising interval, and custom advertising data; settings are persisted to NVS flash

  • Periodic Updates: Configurable interval for sensor data updates

  • Power Management: Supports Zephyr power management

  • Comprehensive Testing: Full Ztest test suite included

Architecture

The application follows a modular design with clear separation of functionalities:

sensor_beacon/
├── src/
│   ├── main.c                 # Application entry point; BLE connection callbacks
│   ├── sensor_beacon.c        # Main application logic and sensor loop
│   ├── sensor_interface.c     # Sensor reading with scaling
│   ├── battery_monitor.c      # Battery voltage monitoring
│   ├── beacon_adv.c           # Dual-set Bluetooth advertising (sensor + connection)
│   ├── beacon_adv_at_cmd.c    # AT command extensions with NVS persistence
│   ├── at_gatt.c              # GATT service for AT command transport (TXRX characteristic)
│   ├── at_cmd_manager.c       # AT command routing and unlock state machine
│   └── sensor_data.c          # Periodic sensor data collection
└── tests/                     # Comprehensive test suite

Dual advertising sets (both started at boot):

  • Set 0 — Non-connectable extended advertising (SID 0). Carries the full sensor beacon payload (Eddystone-URL, Manufacturer Data with sensor readings). Interval: 1–1.2 s normal, 100–150 ms fast.

  • Set 1 — Connectable extended advertising (SID 1). Carries only Flags + Complete Name. Used by a BLE central to connect and interact with the GATT-based AT command interface. Interval: slow (BT_GAP_ADV_SLOW_INT_MIN/MAX).

Configuration

Key configuration options in prj.conf:

  • CONFIG_SENSOR_BEACON_UPDATE_INTERVAL: Update interval in centiseconds (default: 100 = 1s)

  • CONFIG_SENSOR_BEACON_FAST_ADV: Enable fast advertising mode for quick device discovery (default: n)

  • CONFIG_BT_EXT_ADV_MAX_ADV_SET: Number of extended advertising sets (default: 2 — one sensor beacon set, one connectable set)

  • CONFIG_ATM_AT_CMD: Enable AT command framework (default: y)

  • CONFIG_SETTINGS / CONFIG_NVS: Persistent storage for device name and user ad data

Beacon Advertising Intervals

The application supports two advertising modes (selected by Kconfig):

  • Normal Mode (Default): 1-1.2 second intervals for optimal power consumption

  • Fast Mode: 100-150ms intervals for quick device discovery

To enable fast mode, set CONFIG_SENSOR_BEACON_FAST_ADV=y in your configuration.

Sensor Data Format

The application uses a standardized sensor data format for client compatibility:

typedef struct {
    uint16_t temp;      // Temperature (scaled by 256)
    uint16_t humidity;  // Humidity (scaled by 256)
    uint16_t x_axis;    // X-axis acceleration (scaled)
    uint16_t y_axis;    // Y-axis acceleration (scaled)
    uint16_t z_axis;    // Z-axis acceleration (scaled)
    float vstore;       // Storage voltage (volts)
    float vbatt;        // Battery voltage (volts)
} __packed sensor_beacon_data_t;

Beacon Advertisement Structure

The sensor beacon advertising set (Set 0, non-connectable) uses the following payload:

  1. Flags: BT_LE_AD_GENERAL | BT_LE_AD_NO_BREDR

  2. Complete Name: Device name (runtime-configurable via AT+NAME; persisted to NVS)

  3. Service UUID: Eddystone UUID (0xFEAA)

  4. Service Data: Eddystone-URL pointing to atmosic.com

  5. Manufacturer Data: Atmosic Company ID (0x0A24) + sensor data

  6. User Data (optional): Custom TLV element appended when set via AT+ADVDATA

The connectable advertising set (Set 1) carries only:

  1. Flags: BT_LE_AD_GENERAL | BT_LE_AD_NO_BREDR

  2. Complete Name: Device name

AT Command Interface

The sensor_beacon application includes a BLE GATT-based AT command interface that enables runtime configuration of the device over a Bluetooth LE connection. This feature is enabled by default in the production configuration (prj.conf).

Prerequisites

AT command support requires the following Kconfig options (all enabled by default in prj.conf):

  • CONFIG_ATM_AT_CMD=y — AT command core framework

  • CONFIG_ATM_AT_CMD_SET=y — Standard AT command set handlers

  • CONFIG_BT_MAX_CONN=2 — Allows inbound BLE connections for configuration

  • CONFIG_SETTINGS=y / CONFIG_NVS=y — Persistent storage for settings

Note

When CONFIG_BT_MAX_CONN is set to 2, the device advertises as connectable to allow BLE GATT-based configuration in addition to broadcasting beacon data.

GATT Service

AT commands are transported over a custom BLE GATT service. Connect to the sensor beacon device and interact with the TXRX characteristic:

Attribute

Details

Service

custom 128-bit UUID

Characteristic

TXRX (custom 128-bit UUID) Properties: Write + Notify

  • Write the AT command string to the TXRX characteristic to issue a command.

  • Enable notifications on the TXRX characteristic to receive command responses.

Security — Unlock Mechanism

The device starts in a locked state every time a new BLE connection is established. All configuration commands require the device to be unlocked first using AT+UNLOCK.

Lock state lifecycle:

  1. Device powers on or resets → starts locked

  2. New BLE connection established → automatically re-locked

  3. AT+UNLOCK with correct key → unlocked

  4. Configuration commands can now be issued

  5. BLE disconnect or device reset → returns to locked

Supported AT Commands

Command Syntax

AT commands follow the standard format:

AT+<COMMAND>=<parameter>

The AT+ prefix is case-insensitive.

Command Reference

AT+UNLOCK

Unlocks the device for configuration. Must be sent before any other configuration command.

AT+UNLOCK=<key>

Parameter

Description

<key>

Unlock key string (max 31 chars)

Example:

AT+UNLOCK=atm1atm123

Responses:

  • OK — Device unlocked successfully

  • ERROR — Invalid key or authentication failure

Note

The unlock key is atm1atm123. The device is automatically re-locked on each new BLE connection to prevent unauthenticated access.

AT+NAME

Sets the BLE device name. The new name is immediately reflected in the advertisement and persisted to NVS flash so it survives reboot.

AT+NAME=<device name>

Parameter

Description

<device name>

New device name string (1 to 22 characters)

Requires: Device must be unlocked (AT+UNLOCK first).

Example:

AT+NAME=MySensorTag

Responses:

  • OK — Device name updated; advertising restarted with the new name

  • ERROR — Device locked, name empty/too long, or write failure

Note

The default device name is Atmosic Sensor Beacon. The maximum length is set by CONFIG_BT_DEVICE_NAME_MAX (default: 22 characters).

AT+ADVINT

Sets the BLE advertising interval. The new value takes effect immediately and is persisted to NVS flash.

AT+ADVINT=<interval>

Parameter

Description

<interval>

Advertising interval in units of 0.625 ms. Valid range: 400 – 16384 (250 ms to 10.24 s)

Requires: Device must be unlocked (AT+UNLOCK first).

Examples:

AT+ADVINT=400     # 250 ms  (minimum)
AT+ADVINT=1600    # 1 second
AT+ADVINT=3200    # 2 seconds
AT+ADVINT=16384   # 10.24 seconds (maximum)

Responses:

  • OK — Advertising interval updated

  • ERROR — Device locked, value out of range, or write failure

AT+ADVDATA

Sets custom user data to be appended to the beacon advertisement. Data must be in TLV (Type-Length-Value) format and is persisted to NVS flash. Sending this command with empty data clears previously set user data and reverts to sensor-only advertising.

AT+ADVDATA=<tlv data>

Parameter

Description

<tlv data>

Byte array in TLV format. Maximum 27 bytes total. First byte is the length (N); second byte is the type; followed by N−1 payload bytes (maximum 25 bytes of payload).

TLV format layout:

+---------+--------+------------------------------+
| Length  |  Type  |         Payload              |
| (1 byte)|(1 byte)| (Length - 1 bytes, max 25)   |
+---------+--------+------------------------------+

  • Length = number of bytes following it (type byte + payload bytes).

  • Type = application-defined data type identifier.

  • Payload = up to 25 bytes of user-defined data.

Requires: Device must be unlocked (AT+UNLOCK first).

Responses:

  • OK — User data updated; advertising restarted with new payload

  • ERROR — Device locked, invalid TLV format, data too large, or write failure

AT+SYSRESET

Performs a cold system reset of the device.

AT+SYSRESET=<reason>

Parameter

Description

<reason>

Reset reason code (1)

Requires: Device must be unlocked (AT+UNLOCK first).

Example:

AT+SYSRESET=1

Response: The device resets immediately; no response is returned to the client.

Persistent Storage

The following settings survive reboot (saved to NVS flash):

Setting

AT Command

NVS Key

Device name

AT+NAME

sensor_beacon/dev_name

Custom ad data

AT+ADVDATA

sensor_beacon/user_data

Typical Usage Sequence

# 1. Connect to the device over BLE
# 2. Enable GATT notifications on the TXRX characteristic
# 3. Unlock the device
AT+UNLOCK=atm1atm123        → OK

# 4. Change the device name
AT+NAME=MySensorTag         → OK

# 5. Set advertising interval to 2 seconds (3200 × 0.625 ms = 2000 ms)
AT+ADVINT=3200              → OK

# 6. Reset to apply all changes
AT+SYSRESET=1               (device resets; reconnect to verify new settings)

Building and Running

This application is built from openair/applications/sensor_beacon.

Production Build (Default)

Optimized for power consumption, performance, and minimal logging:

west build -p always -b <BOARD> openair/applications/sensor_beacon --sysbuild -T applications.sensor_beacon.atm

Production Build with MCUboot + Serial DFU

Enables MCUboot and supports firmware upgrades over UART:

west build -p always -b <BOARD>@mcuboot openair/applications/sensor_beacon --sysbuild -T applications.sensor_beacon.atm.mcuboot.dfu

Debug Build

Enhanced logging and debugging aids for development:

west build -p always -b <BOARD> openair/applications/sensor_beacon --sysbuild -T applications.sensor_beacon.atm -DFILE_SUFFIX=debug

Example for ATMEVK-3430e-YQN-5:

Production:

west build -p always -b ATMEVK-3430e-YQN-5 openair/applications/sensor_beacon --sysbuild -T applications.sensor_beacon.atm

Debug:

west build -p always -b ATMEVK-3430e-YQN-5 openair/applications/sensor_beacon --sysbuild -T applications.sensor_beacon.atm -DFILE_SUFFIX=debug

Programming

To flash the built images:

west flash --no-rebuild -d build --verify --device <DEVICE_ID> --jlink --fast_load

Example:

west flash --no-rebuild -d build --verify --device 000900066361 --jlink --fast_load

Configuration Differences

The debug and production builds have identical functionality - they differ only in logging verbosity:

Feature

Production Build

Debug Build

Logging Level

Warning/Error only (level 2)

Debug/Verbose (level 4)

ADC Logging

Error level only

Debug level

Sensor Logging

Warning level only

Debug level

Function Names

Not logged

Logged with debug messages

All Other Settings

Identical

Identical

Note

Both configurations maintain the same:

  • Update intervals (1 second)

  • Beacon advertising intervals (1-1.2s normal, 100-150ms fast)

  • Power management settings

  • Stack sizes

  • Watchdog configuration

  • BLE advertising behavior (dual advertising sets)

  • Sensor functionality

Testing

To build and run the test suite:

west build -p always -b <BOARD> openair/applications/sensor_beacon/tests --sysbuild
west flash --no-rebuild -d build --verify --device <DEVICE_ID> --jlink --fast_load

Example:

west build -p always -b ATMEVK-3430e-YQN-5 openair/applications/sensor_beacon/tests --sysbuild
west flash --no-rebuild -d build --verify --device 000900066361 --jlink --fast_load

The test suite includes:

  • Sensor interface validation

  • Battery monitoring tests

  • Beacon advertising tests (dual advertising sets; user data; device name updates)

  • AT command handler tests (unlock, name, interval, advdata, sysreset)

  • Data collection integration tests

  • Scaling factor verification

Power Management

The application supports Zephyr power management:

  • Periodic sensor readings with configurable intervals

  • Automatic sleep between operations

  • Watchdog integration for reliability

LED and Button Functionality

The sensor_beacon application provides platform-specific LED indication and button control functionality to support different hardware configurations.

LED Indications

The application supports three types of LED indications:

  1. Power ON Indication (Tag designs only)

    • Primary LED blinks 3 times at 0.5s interval

    • Shown when device transitions from OFF to ON state via button press

    • Only available when CONFIG_SENSOR_BEACON_BUTTON_POWER_CONTROL is enabled

  2. Power OFF Indication (Tag designs only)

    • Secondary LED blinks 3 times at 0.5s interval

    • Shown when device transitions from ON to OFF state via button press

    • Only available when CONFIG_SENSOR_BEACON_BUTTON_POWER_CONTROL is enabled

  3. Beacon Status Indication (All platforms)

    • Primary LED blinks once for 0.1s

    • Shown every 10 beacon data updates to indicate active beaconing

    • Available on all platforms with LED support

Button Functionality

Button behavior varies by platform configuration:

Tag Designs (Button Power Control Enabled)

When CONFIG_SENSOR_BEACON_BUTTON_POWER_CONTROL is enabled (default for ATMBTCSTAG-3405):

  1. Initial State: Device starts in SoC_off mode when battery is inserted

  2. Turn Device ON: Press button for 2 seconds to bring the device out of soc-off mode

    • Device exits SoC_off mode

    • LED blinks 3 times at 0.5s interval

    • Device starts beaconing

  3. During Beaconing: LED blinks (0.1s on/off) every 10 beacon data updates

  4. Turn Device OFF: Press button for 2 seconds while beaconing

    • LED blinks 3 times at 0.5s interval

    • Device enters SoC_off mode

EVK Boards (Immediate Beaconing Mode)

When CONFIG_SENSOR_BEACON_BUTTON_POWER_CONTROL is disabled (default for EVK boards):

  1. Initial State: Device immediately enters beaconing mode after power on

  2. No ON/OFF Control: Button does not control device power state

  3. During Beaconing: LED blinks (0.1s on/off) every 10 beacon data updates

Supported Boards

The sensor_beacon application has been tested and verified on the following platforms:

ATM34 Platforms

  • ATMBTCSTAG-3405 - ATM34 Tag Reference Design

    • Button power control enabled by default

    • Dual LED support

    • Sensors: ENS210 (Temp/Humidity), LIS3DH (Accelerometer)

    • Optimized for battery-powered operation with SoC_off support

  • ATMEVK-3430e-YQN-5 - ATM34 Evaluation Kit

  • ATMEVK-3405-PBV-5 - ATM34 Evaluation Kit

  • ATMEVK-3405-PQK-5 - ATM34 Evaluation Kit

  • ATMEVK-3405-WQK-5 - ATM34 Evaluation Kit

  • ATMEVK-3405-YBV-5 - ATM34 Evaluation Kit

    • Immediate beaconing mode (no button power control)

    • LED support for beacon status indication

    • Sensors: ENS210 (Temp/Humidity), LIS2DH12 (Accelerometer)

    • Suitable for development and testing

ATM33 Platforms

  • ATMEVK-3330e-QN-6 - ATM33 Evaluation Kit (Planned)

  • ATMEVK-3330e-QN-7 - ATM33 Evaluation Kit (Planned)

    • Immediate beaconing mode (no button power control)

    • LED support for beacon status indication

    • Sensors: ENS210 (Temp/Humidity), LIS2DH12 (Accelerometer)

    • Suitable for development and testing

All supported platforms use the same sensor set for consistent data collection across different hardware configurations.

Compatibility

  • Data Format: Uses standardized sensor beacon data format

  • Advertisement Structure: Standard Bluetooth beacon format with manufacturer data

  • Passive Observers: Compatible with any BLE scanner or beacon monitoring application (Atmosic DevTools, etc.) — no connection required to receive sensor data

  • BLE Centrals: Can connect to the device, authenticate via AT+UNLOCK, and issue configuration commands over the GATT TXRX characteristic

Dependencies

Required Hardware:

  • ENS210 temperature/humidity sensor

  • LIS2DH accelerometer

Ensure that the appropriate jumper (JP25) is installed to enable the sensor subsystem. Refer to the EVK’s user guide for additional details.