BlueNodes

BlueNodes is a Riegel Systems engineering case in the field of embedded & connected systems. The case covers the complete chain from electronics and embedded firmware via a distributed Bluetooth Low Energy network to the mobile application – and thus the left side of the Riegel Systems engineering stack:

From PCB and embedded firmware to wireless networking and mobile software.

Electronics

A custom 4-layer PCB (37.5 × 27 mm) was developed for BlueNodes with double-sided SMD assembly and components down to 0402. The board includes:

• Mains power supply
• Current measurement
• MOSFET power stage
• RF frontend
• Antenna and impedance matching
• Debug and programming interface

The images above show the PCB layout (top and bottom side) and the assembled board from the project.

Embedded

A Nordic nRF52832 serves as the SoC – ARM Cortex-M4, 32-bit, 64 MHz, with an integrated 2.4 GHz transceiver for Bluetooth Low Energy (BLE 5).

The firmware includes, among other things:

• BLE protocol stack
• Distributed rebroadcasting network (mesh)
• Automatic integration of new nodes
• Unique node addressing
• Configurable network separation
• Sensor acquisition and A/D processing
• Switching and dimmer control
• OTA firmware update

Networking

The nodes form a distributed Bluetooth Low Energy network. The mobile app connects to the nearest node; from there messages are forwarded to the remaining nodes of the network via the rebroadcasting mechanism.

Mobile App
    │   BLE
    ▼
Nearest Node
    │
    ├── Node
    │    └── Node
    │
    └── Node
         └── Node

The firmware is based on Nordic nRF OpenMesh and uses the IETF RFC 6206 Trickle algorithm for efficient message distribution. It is a custom rebroadcasting approach – explicitly not the later-standardized Bluetooth mesh standard.

Power & Sensor Engineering

As examples of the project’s hardware depth:

• Current measurement: Infineon TLI4970-D025T5 (coreless magnetic current sensor) for AC/DC current measurement with fast overcurrent detection
• Load switching: Infineon 600 V CoolMOS power transistors with trailing-edge phase-cut control
• Power supply: Non-galvanically isolated buck-converter architecture with 1.8 V and 5 V supply

These components demonstrate engineering competence at the hardware level. This is explicitly not a guide to building or handling mains voltage.

Mobile Application

The associated Android application was developed in Java and handles device management of the network:

• Automatic connection to the nearest BlueNode
• Reachability of further nodes across the network
• Management of nodes and loads
• Structuring the installation by building, floor and room
• Local storage of the structure data in SQLite
• Display of energy consumption statistics
• Integration of new nodes

OTA

Firmware updates can be transferred to the nodes directly from the Android device via OTA-DFU. Connected-device engineering therefore does not end with the first firmware flash: device lifecycle and maintainability are part of the design from the start.

Key takeaway

BlueNodes combines hardware and software into a complete digital product. The case shows that Riegel Systems does not only start at the cloud or the app, but can deliver from its own PCB via embedded firmware and BLE network all the way to the mobile application.

Images: BlueNodes project (codezork/BlueNodes, Apache-2.0).