Lrima main

iot_obj-sicro-sensor

Authors : LRIMa (Laboratoire de Recherche Informatique de Maisonneuve)

Repo composition

code/
├── actioneur       (esp32 code)
├── broadcaster     (sensor code [nrf52833])
├── central         (python BLE scanning and ALIVEcode integration)
└── central-nrf     (BLE receiver [nrf52840dongle])
schematic/
├── lrima-main/     (Main board KiCad project)
└── lrima-ground/   (Ground board KiCad project)
models/
└── sensor-casing/  (3D CAD models for enclosure)

Physical device

The schematics and PCB were designed using KiCad EDA software There is a protective layer that needs to be applied on the ground part of the pcb to prevent corrosion

Building

Tools needed

• VS Code
• nRF Connect
• nRF Connect VS Code extension
• nRF toolchain v3.2.4
• nRF SDK v3.2.4
• J-Link
• Python 3.8+ (for central application)

Broadcaster

Preparing the environment

Before building the broadcaster program, you must make sure that you changed the CONFIG_BLE_USER_DEFINED_MAC_ADDR and the CONFIG_BLE_USER_DEFINED_NAME so that they are unique. Note that the CONFIG_BLE_USER_DEFINED_NAME must end with a number (ex : 01). If you need mac address, you can use this mac address generator.

Building

The broadcaster uses the sysbuild system from NCS v3.2.4. To build the program for the nrf52833 using the nRF Connect VS Code extension:

1. Open the broadcaster folder in VS Code
2. Use the nRF Connect extension to build using the lrima_greenhouse_nrf52833 board
3. Flash using the extension flashing options

Note: If flashing fails, use the erase and flash option to perform a full erase first.

J-Link setup

Firmware over the air update (DFU)

The board supports over-the-air firmware updates. To prepare an update:

1. Build the application as described above
2. Locate the signed image in the sysbuild app domain: build/broadcaster/zephyr/zephyr.signed.bin
3. Transfer this file to your phone
4. Press and hold button1 until the LED is on, then release
5. You will have up to 60 seconds (configurable via CONFIG_BLE_DFU_ADV_DURATION_SEC) to start the update
6. Use the nRF Connect mobile app to connect to the device (named with your CONFIG_BLE_USER_DEFINED_NAME)
7. Go to the DFU tab and select zephyr.signed.bin
8. Press Upload and monitor the progress

Device Functionality

The broadcaster uses a single BLE advertising workflow. It sends sensor data uplink and then opens a short scan window to receive a downlink sleep update when needed. The user can wake up the device at any time by pressing button1. There is never a connection established, and all communication is done through advertisements and scan responses.

Broadcaster

The broadcaster collects sensor data and transmits it BLE advertisements:

Supported sensors:

• Temperature/Humidity (SHT4X)
• Soil temperature/moisture/conductivity (STCC4)
• CO2 concentration

Transmission behavior:

• Sends data at intervals specified by CONFIG_SENSOR_SLEEP_DURATION_SEC
• Uses BLE advertising for the duration specified in CONFIG_BLE_ADV_DURATION_SEC
• Publishes a 29-byte service payload containing company ID, node ID, sequence, sleep duration, sensor values, and a presence bitmap
• Opens an active scan window after uplink to receive sleep updates sent by the central
• Beacon payload structure is shown below:

Note: The diagram above predates the latest payload format. See the broadcaster documentation for the full 29-byte layout and presence bitmap details.

Central-nrf

The central-nrf firmware runs on the nRF52840 dongle to receive BLE broadcasts from the broadcaster.

Building:

1. Use the nRF Connect VS Code extension to build for nrf52840dongle_nrf52840 board
2. Flash using the nRF Connect for Desktop programmer tools
3. Put the device in DFU mode
4. Flash the build/zephyr/zephyr.hex file

Central (Python Application)

The central application handles BLE scanning, data collection, and integration with ALIVEcode.

Core modules:

• core/storage.py - Persistent data management
• core/payload.py - Sensor data parsing and validation
• core/aliot_sync.py - ALIVEcode cloud integration
• core/downlink_advertiser.py - BlueZ D-Bus advertiser for sleep-time downlink frames
• core/health.py - System health monitoring
• core/config.py - Configuration management

Setup and running:

1. Plug the Central-nrf dongle into a computer or Raspberry Pi

2. Configure the application:

   • Copy config.ini.example to config.ini
   • Set your object_id and auth_token from your ALIVEcode.ca IoT project

3. Install dependencies:

   # For Raspberry Pi 4
   pip install -r requirements_pi4.txt
   
   # For Raspberry Pi 5
   pip install -r requirements_pi5.txt

   (Using a Python virtual environment is recommended)

   dbus-next is required because downlink sleep updates are emitted through BlueZ D-Bus advertising APIs.

4. Run the application:

   python main.py

5. Power on the broadcaster devices

The application will automatically scan for broadcaster devices, collecting sensor data and synchronizing with ALIVEcode. It publishes each node under /doc/<device_index> including /doc/<device_index>/sleep_duration_sec, and uses /doc/sleep_time as the desired target for downlink sleep updates.