The Raspberry Pi itself — ports, power, getting online, Bluetooth

What it is

A whole computer, for the price of a decent shackle

A Raspberry Pi is a complete computer on a board about the size of a playing card. No case, no screen, no keyboard — you add those.

The one on Exodus is a Raspberry Pi 5. Everything below is about that model. The older Pi 4 is similar but not identical, so check before you copy a number.

Part	What the Pi 5 has
Processor	Broadcom BCM2712, quad-core 64-bit Arm Cortex-A76 at 2.4 GHz
Memory	1, 2, 4, 8 or 16 GB. Ours has 8 GB, and on a boat that is worth paying for — Signal K alone idles at well over a gigabyte.
Storage	microSD slot (the weak point — more below)
Networking	Gigabit Ethernet, dual-band 802.11ac Wi-Fi, Bluetooth 5.0 / BLE
Video	Two micro-HDMI outputs, each up to 4Kp60
Expansion	40-pin GPIO header, PCIe 2.0 x1, two 4-lane camera/display connectors

Every port, and what it is for

Walking round the board

Port	How many	What goes in it
USB-C (power)	1	Power only. 5 volts. This is the one that matters most and the one people get wrong — see the next section.
USB 3.0 (blue)	2	Fast devices — an SSD, an SDR dongle, a USB hub. Both can run at 5 Gbit/s at the same time.
USB 2.0 (black)	2	Keyboards, GPS pucks, serial adapters. Slower, and perfectly fine for these.
Gigabit Ethernet	1	A network cable. The most reliable way onto the boat's network by a very long way. It also supports PoE+, but only with a separate PoE+ HAT.
micro-HDMI	2	A screen. Note it's micro, so a normal HDMI cable needs an adapter or a micro-to-full cable.
40-pin GPIO header	1	HATs, sensors, relays. 3.3 volt logic — and not 5-volt tolerant. Details in the parts page.
Camera / display (MIPI)	2	Ribbon-cable cameras and small displays.
PCIe 2.0 x1	1	A flat-cable connector for an M.2 SSD via an adapter board. Much faster and much sturdier than an SD card.
microSD	1	The operating system, unless you boot from SSD.
Power button	1	On the board itself. A clean shutdown beats pulling the plug, and on a boat that matters.
RTC battery connector	1	A small backup cell keeps the clock right when the Pi is off. A real-time clock matters more offshore than you'd expect, where there may be no internet to ask the time.

Two ports you'll fill without thinking. The Ethernet and the power. Everything else is optional, and the fewer cables on a boat the fewer things come loose in a seaway.

Power — the part boats get wrong

A Pi wants clean 5 volts. A boat has 12 or 24 and a lot of noise.

The Pi 5 is designed around a 5 volt, 5 amp supply over USB-C with Power Delivery — Raspberry Pi's own is a 27 watt unit.

Why the 5 amps matters

The board itself needs far less than 5 amps. The number is for everything you plug into the USB ports.

Connected to a supply that negotiates 5 volts at 5 amps, the Pi 5 lets its USB ports deliver up to 1.6 amps to your devices.
Connected to anything else, it limits all USB devices to just 600 milliamps.

600 mA between everything is not much. A hard drive, an SDR dongle and a GPS puck together can exceed it, and the symptom is devices that drop out at random and logs that show nothing wrong.

Getting 5 volts from a boat

You can't connect a 12 or 24 volt battery to the Pi. It needs a DC-DC step-down converter — a small box that takes the boat's voltage and gives out a steady 5.

Buy one rated well above what you need. A converter running at its limit gets hot and noisy. Headroom is cheap.
Check it handles your full voltage range. A 12 volt bank charging reads around 14.5 V, and a 24 volt bank near 29. A converter that tops out at 24 is dead on arrival on a 24-volt boat.
A cheap converter will not negotiate Power Delivery. The Pi will then run happily but cap its USB ports at 600 mA and complain on boot. If you are certain the converter really can supply 5 A, the Pi 5 can be told to allow the higher limit with usb_max_current_enable=1 in its config file — but only if you are certain. Forcing it on a supply that can't deliver is how you get random brown-outs.
Fuse it. Close to the battery, sized for the small wire you'll use.
Use a thick, short USB-C lead. A thin cable drops voltage under load, and a Pi that sees a little under 5 volts throttles itself.

How to know it's actually fine

The Pi tells you, if you ask. One command reports whether it has ever seen a low-voltage event since boot:

vcgencmd get_throttled

throttled=0x0 means clean — no under-voltage and no throttling since boot. Anything else means the supply is not good enough, and it is the first thing to look at when the Pi does something strange. Ours read 0x0 the last time we checked.

Power the peripherals separately. On Exodus the USB devices hang off a powered hub with its own supply, so nothing is drawing from the Pi's tiny USB budget. That one change removed a whole category of mystery faults.

Which cables it takes

A short shopping list

For	You need
Power	USB-C lead, short and thick, from a proper 5 V / 5 A supply or converter
Network	Ethernet, Cat5e or Cat6 — either is plenty. How the wires inside are arranged →
Screen	micro-HDMI to HDMI. Not mini, not full-size.
Keyboard / mouse	USB. Or a wireless dongle in one of the two USB 2.0 ports.
Fast storage	USB 3.0 in a blue port, or an M.2 board on the PCIe connector
Anything on NMEA 2000	A CAN HAT, not a cable — the HAT plugs onto the GPIO header and the drop cable plugs into that

Notice what is missing: you do not need a keyboard, mouse or screen to run one. After the first set-up, a Pi on a boat lives in a locker with two cables in it and is reached over the network. That is how it is meant to be used.

Getting it online

Wire first. Wi-Fi if you must.

Ethernet — do this if you possibly can

Plug a cable into the boat's router and the Pi gets an address by itself within seconds. No passwords, no configuration, no radio to drop out. On a boat, where WiFi is fighting a hull full of metal and a lot of other transmitters, a wire is a different class of reliability. Our Pi runs entirely on a cable, and its Wi-Fi radio sits switched off.

Wi-Fi — fine, with caveats

The Pi 5 has dual-band 802.11ac built in. Two things worth knowing:

Prefer 5 GHz where the signal is good — it's faster and, importantly, it stays away from Bluetooth, which lives on the same 2.4 GHz band as the older Wi-Fi.
Set the network up before you need it. The cleanest way is to enter your Wi-Fi name and password in Raspberry Pi Imager's customisation screen when you first write the SD card, so the Pi joins the network the first time it boots, with no screen attached.

First boot with no screen

Write the operating system to the card with Raspberry Pi Imager.
In its customisation settings, set a hostname, a username and password, your Wi-Fi if you're using it, and enable SSH.
Put the card in, power it, and give it a couple of minutes.
Reach it from another computer by its hostname over SSH.

That whole sequence needs no monitor and no keyboard, which is exactly the situation you'll be in when it's bolted behind a panel.

Change the defaults. All of them.

A Pi reachable from a network with a weak or default password is the easiest thing in the world to take over. Set a long unique password, and use SSH keys rather than passwords once it's working.

And do not put it directly on the internet. Reach it from ashore over a private network instead. That page explains how, without opening a single port.

Once it's online

It can see the boat's other devices — the instruments, the router, the radar — and everything else on this site grows from there. A Pi with no network is a very expensive paperweight; a Pi with one is the centre of the boat.

Bluetooth — how it actually works

Convenient, short range, and a little temperamental

The Pi 5 has Bluetooth 5.0 built in, including Bluetooth Low Energy — the low-power flavour that nearly every cheap sensor uses.

Two kinds, and they're different

Classic Bluetooth

The streaming kind. Headphones, speakers, keyboards. A steady two-way connection that stays open. Uses more power.

Bluetooth Low Energy (BLE)

The sensor kind. Tiny bursts of data, then back to sleep for months on a coin cell. Temperature tags, battery monitors, BMS units. This is the one a boat cares about.

How a BLE reading happens

The sensor advertises. It shouts a short message every second or so: "I'm here, and this is my name."
The Pi hears it and either just reads the broadcast, or connects to ask for more.
It asks for a value — a voltage, a temperature — the sensor answers, and the Pi disconnects or waits for the next one.

Many cheap tags never need a connection — they put the reading straight into the broadcast, and the Pi simply listens. That is the most reliable way of all.

What we use it for

The two JK battery management units are read over Bluetooth, and so are the small temperature and humidity tags in the lockers. It was the easier route when the network hub was being unreliable, and it is what we've used since — with the caveats below.

The honest limits

One connection at a time. A BMS will talk to one device. While the Pi is connected, the maker's phone app can't be. You have to choose which of them owns it.
Range is short. Roughly ten metres through open air, much less through a bulkhead, a battery bank or a steel tank. A boat is a Faraday cage with good intentions.
It shares a band with Wi-Fi. On 2.4 GHz they take turns, and both get worse when the other is busy. Another reason to put Wi-Fi on 5 GHz — or just use a cable.
The Linux Bluetooth stack can wedge. Linux uses a program called BlueZ to talk to the radio. Every so often it stops answering and stays that way until something restarts it, and nothing tells you. We run a small watchdog whose only job is to notice and kick it — and if you rely on Bluetooth for anything that matters, you want one too.
One process per device. Trying to read two sensors through one program is asking for trouble. Give each its own.

Use it for convenience, not for safety. A Bluetooth reading that drops out is an annoyance. A bilge alarm that depends on one is a problem. Anything you'd lose sleep over should be on a wire.

The weak points, honestly

Where Pis fail on boats

The SD card

The number one killer. Constant writes wear it out, and a power cut mid-write can corrupt it. Boot from an SSD if you can, keep a spare card with a copy of the working system, and back up regularly.

The power

A noisy or sagging supply causes more strange faults than any software bug. Check throttled before you start blaming the code.

Heat

A Pi 5 runs warm and will slow itself down when hot. In a closed locker on a sunny deck that happens quickly. Give it a heatsink and fan, and some airflow.

Salt air

Bare boards corrode. A case, a dry location, and a spare board in a sealed bag.

The HATs and sensors that go on it → Reaching it from ashore All projects

The Raspberry Pi itself.