📋 Setup Guide | 📋 Commands | 🔧 Local.h Reference | 🔬 Sensor Reference | 🔩 Bill of Materials

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 → Docs/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.