Tritium
NMEATouch20
Quick Start Guide — AIS Screen
Before you begin
This guide assumes the firmware has already been flashed to your Guition ESP32-S3 4848S040 unit. If you have not yet flashed the firmware, visit tritium.co.uk/projects/nmea-touch-20 and use the browser flash tool. You will need a USB-C data cable and Chrome or Edge.
Power on the unit
Connect the unit to a 5 V USB-C power supply. On first boot it starts in Access Point (AP) mode — it creates its own WiFi network for configuration.
Connect to the unit's WiFi
On a phone, tablet, or laptop, open WiFi settings and connect to:
SSID: screen1
Password: Epoxy123
Open the configuration page
Open a browser and navigate to http://192.168.7.1. The page is titled Tritium NMEA Display.
Enter your settings
The minimum settings required to get the AIS screen working:
| Setting | What to enter |
|---|---|
| MMSI | Your vessel's 9-digit MMSI number. Without this the unit cannot identify which AIS target is you, so your own boat will appear as a nearby vessel in the list. |
| Low Power | Defaults to true — runs the WiFi radio at reduced power, which is fine for most installations. Set to false for full transmit power if you have range or connection problems. |
| Vessel Network | Your boat WiFi SSID (leave blank to keep the unit as a standalone hotspot) |
| Vessel Password | Your boat WiFi password |
| UDP Port | Port your NMEA data source broadcasts on — typically 2000 or 10110 |
| Time Zone Offset | Your local UTC offset, e.g. +01:00 for BST |
Click Save. The unit restarts and joins your boat WiFi. The AIS screen appears automatically when data is received.
Understanding the AIS screen
The AIS screen shows a table of vessels in reception range, sorted by closest point of approach. Each row is one vessel:
| Column | Meaning |
|---|---|
| Vessel | Ship name as transmitted by the vessel's AIS transponder |
| St | Status icon — ⌂ indicates a vessel saved in your encounter history |
| Az (°) | Azimuth — compass bearing to the vessel from your position |
| CPA (NM) | Closest Point of Approach — nearest distance if both vessels hold course |
| TCPA (Min) | Time to CPA in minutes — blank if the vessel is moving away |
| Cross (NM) | Crossing clearance — how far ahead of the bow (+) or astern of the stern (−) you will pass. Only shown when a crossing is detected. |
Row colours
| Colour | Meaning |
|---|---|
| White | Normal — no immediate concern |
| Amber | CPA/TCPA is active — vessel on a converging course; time to closest approach is known |
| Red | Alarm — crossing clearance is inside your configured threshold |
| Purple | Vessel is turning (ROT detected) — course alteration under way |
| Grey | Stale — no AIS update received within the expected reporting interval |
The Cross column explained
The Cross value tells you how far ahead of the bow or astern of the stern you will pass when your paths cross, in nautical miles.
Positive (+) — you will pass ahead of the vessel's bow. A small positive value (e.g. +0.4 NM) means you will just clear the bow.
Negative (−) — you will pass astern of the vessel's stern. A negative value means the vessel will have crossed ahead of you.
The alarm threshold is set by Cross Ahead and Cross Astern in the configuration page. A row turns red when the crossing clearance is inside either threshold.
Factory reset
The Guition module has no physical reset button. To factory reset, reflash the unit using the flash firmware button on the project page. This restores the firmware and clears all saved configuration, returning the unit to AP mode with the default credentials above.