A modular, Arduino-powered 12V power distribution and control system designed for boats and other off-grid applications.
SmartFuseBox combines fused relays, quick-connect aviation plugs, sensor monitoring, WiFi/BLE/MQTT connectivity, and Arduino-based control into a single 3D-printed enclosure — with a built-in security twist.

I bought a mid-80s boat and wanted to give it a modern electrical upgrade.
The original wiring was dated, messy, and lacked any real security. Since the boat is kept in a marina, theft was also a concern.

SmartFuseBox was born out of the need for:

• Reliable 12V power distribution for navigation lights, bilge pumps, and other onboard systems.
• Quick-connect modularity so I can easily add/remove systems with aviation connectors.
• Integrated monitoring via Arduino sensors (temperature, humidity, light, etc.).
• Basic security through a “poor man’s immobiliser” — the control unit must return a valid 12V feed before the system powers up.

• 8 fused relays for distributing 12V power safely.
• Aviation connectors for quick, reliable connections to onboard systems.
• Linked relays — configure pairs that mirror each other's state.
• Default relay states — individual relays can be set to default-on at boot.
• Immobiliser-style security — the control unit must return a valid 12V feed to enable the system.
• 3D-printed enclosure for a compact, customizable housing.

• DHT11 — temperature and humidity monitoring with failure detection.
• Water level — analog sensor with 15-reading rolling average and corrosion-reduction active pin control.
• Light (LDR) — day/night detection.
• GPS (GY-GPS6MV2) — location, speed, altitude, heading, cumulative distance, and automatic UTC time sync.
• System diagnostics — free memory, CPU usage, WiFi/BT state, SD log size, uptime, and warning count.
• Extensible — add custom local or remote sensors with minimal boilerplate (see Docs/Sensors.md).

• WiFi (AP and Client mode) with a full HTTP REST API for relay control, sensor data, configuration, sound, and warnings.
• Bluetooth BLE — relay control, sensor streaming, and system metrics via BLE characteristics.
• MQTT with Home Assistant auto-discovery — sensors and relays appear as HA entities automatically.
• Serial command protocol for integration with the companion Boat Control Panel (Arduino Mega + Nextion display).

• SD card logging — persistent system logs with configurable SPI speed.
• Warning system — 32-bit bitmask of typed warnings propagated between both controllers.
• RTC support — DS1302 real-time clock with automatic GPS UTC time synchronisation.
• CPU usage and free memory monitoring available via serial, WiFi, and MQTT.

• Nextion touchscreen display for relay switching, sensor readout, and system configuration.
• COLREGS sound signals (H0–H12) via a reserved relay-driven horn.
• Config synchronisation — BCP and SFB automatically stay in sync over the serial link.

Board selection is controlled by a single #define in Local.h.

Two hardware units communicate over a 7-wire serial harness:

The 7-wire harness carries: 12V in, 12V out (immobiliser return), GND, TX (link), RX (link), TX (GPS), RX (GPS).

The firmware is split between two projects that share a common Shared/ library via symlinks:

SmartFuseBox/      ← Fuse box firmware (relays, sensors, WiFi, BLE, MQTT)
BoatControlPanel/  ← Control panel firmware (Nextion display, immobiliser)
Shared/            ← Common command handlers, sensors, config, utilities

The SFB firmware is built around SmartFuseBoxApp, which owns all subsystems and wires them together at startup. Communication uses a text-based serial command protocol (COMMAND:key=value;key=value\n) over two serial ports — one to the BCP and one to a USB debug monitor.

1. Read the setup guide → SETUP.md — covers prerequisites, symlinks, and building.
2. Configure your board → edit Local.h to select your board, set pin numbers, relay count, and enable features such as MQTT_SUPPORT or WIFI_SUPPORT.
3. Flash the SFB sketch → open SmartFuseBox/SmartFuseBox.ino in the Arduino IDE and upload.
4. Configure WiFi → send serial commands (C11:v=1, C13:YourSSID, C14:YourPassword) or use the BCP touchscreen.
5. Connect to Home Assistant → enable MQTT (M0:v=1), set your broker address (M1:192.168.x.x), and enable discovery (M6:v=1). All sensors and relays appear automatically.

• Marine upgrades — modernize older boats with modular, safe wiring and remote monitoring.
• Off-grid projects — camper vans, RVs, or solar-powered cabins needing fused relay control.
• DIY automation — any 12V system that benefits from wireless control and Home Assistant integration.

• Publish STL files for the 3D-printed enclosure.
• Add CAN bus or RS485 support for longer cable runs.
• WebSocket support for real-time bidirectional updates.
• mDNS / Bonjour for automatic device discovery without hardcoded IPs.
• OTA firmware updates via WiFi.

Contributions, ideas, and improvements are welcome!
If you’ve built something similar or adapted SmartFuseBox for your own project, feel free to open an issue or share your setup.

GNU General Public License v3.0 (GPLv3) — see LICENSE for details.