NMEA 2000 iPad Adapter

flux

Paused because the account is out of ACUs again, so I can’t continue routing or DRC/DFx cleanup.
Accomplished:
  • Placed the 90 × 80 mm prototype board with USB/ESP on the left, isolated CAN/NMEA on the right, J1/J2 at board edges, and ESP32 antenna at the top edge.
  • Applied a 4-layer routing setup and successfully completed one autoroute pass.
  • Found the remaining DRC blocker at the USB ESD array ground, then repositioned/rotated D2 for a cleaner GND escape.
  • Cleared stale routing so the board is ready for a fresh reroute.
Open items:
  • Fresh autoroute is not complete; the run paused due to no ACUs.
  • Current board will show expected airwires because routing was intentionally cleared before the fresh route.
  • Need re-check the router’s reported placement anomaly after ACUs are available.
  • Full DRC/DFx pass is still pending.
  • Generic passives still need production MPNs.
Suggested next steps:
  1. Refill ACUs.
  2. Resume or restart autoroute from the current clean preflight state.
  3. Run full DRC and fix remaining routing/layout issues.
  4. Run DFx/manufacturing review and assign passive MPNs.
Resume autorouting
Inspect placement anomaly
Assign passive MPNs
Run DRC and DFx
U3
U1
J1
D2
GND
C4 P2 - S1 3
R1 P2 - R2 P2
U1 GND - U1 GND
U1 GND - U1 GND
GND
U1 GND - U1 GND
U1 GND - U1 GND
U1 GND - U1 GND
U1 GND - U1 GND
C4 P2 - S1 3
U1 GND - U1 GND
U1 GND - U1 GND
GND
GND
GND
U1 GND - U1 GND
U1 GND - U1 GND
GND
GND
GND
GND
R1 P2 - R2 P2
GND
GND
U1 GND - U1 GND
U1 GND - U1 GND
S1 4 - S2 3
GND
GND
U1 GND - U1 GND
U1 GND - U1 GND
S1 4 - S2 3
U1 GND - U1 GND
GND
GND
U1 GND - U1 GND
U1 GND - U1 GND
GND
U1 GND - U1 GND
U1 GND - U1 GND
U1 GND - U1 GND
U1 GND - U1 GND
U1 GND - U1 GND
U1 GND - U1 GND
U4 -VOUT - U2 GND2
J1 VBUS__1 - U3 VIN
J2 4.1 - J2 4.2
J1 DN1 - J1 DN2
J1 DN1 - J1 DN2
J2 1.1 - J2 1.2
J1 DP1 - J1 DP2
J1 DP1 - J1 DP2
J1 DP1 - J1 DP2
J2 5.1 - J2 5.2
U4 -VOUT - U2 GND2
J2 1.1 - J2 1.2
U1 IO0 - R4 P2
J1 DP1 - J1 DP2
J1 CC2 - R2 P1
J1 DN1 - J1 DN2
U4 +VOUT - U2 VCC2
U2 RXD - U1 IO18
J1 DN1 - J1 DN2
U2 RXD - U1 IO18
J2 4.1 - J2 4.2
U4 -VOUT - U2 GND2
U4 -VOUT - U2 GND2
L1 4 - U2 CANH
U4 -VOUT - U2 GND2
U1 IO0 - R4 P2
U3 VOUT - U1 3V3
J2 5.1 - J2 5.2
U2 TXD - R5 P2
J1 DN1 - J1 DN2
U1 EN - R3 P2
J2 5.1 - J2 5.2
U1 EN - R3 P2
J2 4.1 - J2 4.2
U4 +VOUT - U2 VCC2
L1 4 - U2 CANH
U3 VOUT - U1 3V3
J1 VBUS__1 - U3 VIN
J1 VBUS__1 - U3 VIN
U3 VOUT - U1 3V3
J2 4.1 - J2 4.2
U1 IO0 - R4 P2
U4 -VOUT - U2 GND2
U3 VOUT - U1 3V3
U3 VOUT - U1 3V3
U3 VOUT - U1 3V3
U3 VOUT - U1 3V3
U3 VOUT - U1 3V3
J2 5.1 - J2 5.2
J1 VBUS__1 - U3 VIN
J1 DP1 - J1 DP2
J1 VBUS__1 - U3 VIN
L1 3 - U2 CANL
U1 EN - R3 P2
J1 CC2 - R2 P1
U4 +VOUT - U2 VCC2
J1 CC1 - R1 P1
L1 3 - U2 CANL
U4 -VOUT - U2 GND2
U1 EN - R3 P2
U3 VOUT - U1 3V3
U4 +VOUT - U2 VCC2
J1 CC1 - R1 P1
U2 TXD - R5 P2
J1 VBUS__1 - U3 VIN
J1 VBUS__1 - U3 VIN
L1
C5
Capacitance
100nF
S1
R1
Resistance
5.1kΩ
C7
Capacitance
1µF
C1
Capacitance
10µF
C4
Capacitance
1µF
D1
C2
Capacitance
10µF
R5
Resistance
10kΩ
J2
C8
Capacitance
10µF
R2
Resistance
5.1kΩ
C6
Capacitance
100nF
S2
C3
Capacitance
100nF
R3
Resistance
10kΩ
R4
Resistance
10kΩ
U2
U4

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Project Specification
Project Overview
Status: Draft
USB-powered, isolated, listen-only NMEA 2000/CAN gateway that reads boat network traffic and serves an iPad-friendly Wi-Fi web dashboard.
Intended Use
  • Prototype / validation build for observing NMEA 2000 data on an iPad.
  • Connects to a real NMEA 2000 drop connection as a high-impedance listener.
  • Must avoid disturbing the vessel network during boot, reset, firmware error, or power faults.
What the Device Should Do
  • Receive NMEA 2000 CAN frames at 250 kbps.
  • Decode common public PGNs in firmware and expose data over Wi-Fi.
  • Serve a local web dashboard suitable for iPad Safari.
  • Remain electrically listen-only by default.
Main Features
  • ESP32-S3 Wi-Fi module.
  • Isolated CAN physical interface.
  • Hardware-disabled CAN TX path by default.
  • USB-C 5 V prototype power.
  • NMEA 2000 connector/drop input.
  • No CAN bus termination populated.
  • Status/debug indicators and programming access.
System Architecture
Diagram



  
    
  
  
    
  





















NMEA 2000 Drop
CAN ESD / EMI Protection
Isolated CAN Transceiver
RX-only CAN Path
ESP32-S3 Module
Wi-Fi Access Point / Web Server
iPad Browser Dashboard
USB-C 5 V
3.3 V Regulator
Isolated Bus-Side Supply
Hardware Subsystems
  • NMEA 2000 interface: CAN_H/CAN_L plus bus-side reference; no termination; low-capacitance protection.
  • Isolation: separates USB/ESP32 ground from NMEA 2000 NET-C.
  • Compute / Wi-Fi: ESP32-S3 module using TWAI/CAN listen-only mode.
  • Power: USB-C sink input feeding 3.3 V logic and an isolated CAN-side supply.
  • Safety: TXD default recessive / not fitted or gated, plus firmware listen-only.
Interfaces and Connections
  • USB-C: 5 V power and optional native ESP32-S3 USB programming.
  • NMEA 2000: CAN_H, CAN_L, NET-C bus-side reference, shield strategy; NET-S left unpowered/NC for first prototype.
  • Wi-Fi: iPad connects to local access point or LAN mode.
Power and Runtime Expectations
  • Prototype powered from USB-C 5 V, not NMEA 2000 NET-S.
  • Target current dominated by ESP32 Wi-Fi peaks; design 3.3 V rail for at least 500 mA peak.
  • Future revision may draw from NMEA 2000 NET-S only after protected marine input supply is designed and LEN/current budget is defined.
Power Tree and Power Budget

Table

RailSourceLoadsPreliminary budget
5V_USBUSB-C VBUS3.3 V regulator, isolated CAN-side supply>=700 mA source preferred
3V3LDO/buck from USB 5 VESP32-S3 module, logic250 mA typical, 500 mA peak
ISO_CAN_PWRisolated DC/DC from USB 5 Visolated CAN bus side<100 mA expected
Manufacturing and Assembly Expectations
  • Prototype-first SMD design.
  • Avoid NMEA 2000 certification claims in this revision.
  • Include clear DNI/default-not-fitted markings for any TX enable or termination options.
Firmware-Relevant Hardware Requirements
  • ESP32-S3 TWAI/CAN RX connected to isolated transceiver RXD.
  • CAN TX either not connected, DNI through 0 ohm, or gated off by default.
  • Firmware must configure TWAI listen-only/silent mode at 250 kbps.
  • Web dashboard served over Wi-Fi for iPad.
Physical Design Expectations
  • ESP32 antenna at board edge with copper keepout.
  • Isolation barrier with appropriate clearance between NMEA and USB/logic domains.
  • NMEA connector placement should minimize CAN stub length.
Important Design Decisions
  • First prototype is listen-only and USB-powered.
  • Isolation is included to avoid USB/laptop/charger ground coupling into the vessel network.
  • NMEA 2000 NET-S is not used for power in the first prototype.
  • No 120 ohm bus termination is fitted.
Assumptions
  • User wants Wi-Fi, not BLE.
  • iPad display will be a browser-based dashboard.
  • Initial prototype is for private R&D/prototyping, not certified commercial NMEA 2000 product.
  • Exact connector series/pinout will be finalized before PCB layout.
Change Notes
  • 2026-07-17: User selected listen-only prototype first and Wi-Fi iPad connectivity.

  • Project Overview

  • Intended Use

  • What the Device Should Do

  • Main Features

  • System Architecture

  • Hardware Subsystems

  • Interfaces and Connections

  • Power and Runtime Expectations

  • Power Tree and Power Budget

  • Manufacturing and Assembly Expectations

  • Firmware-Relevant Hardware Requirements

  • Physical Design Expectations

  • Important Design Decisions

  • Assumptions

  • Change Notes

Documents

  • Project Specification

  • Firmware Starter — ESP32-S3 NMEA 2000 Wi-Fi Listener

  • Board Bring-Up Plan — NMEA 2000 WiFi Listener

  • Technical Construction File — NMEA 2000 WiFi Listener

  • Safety Analysis — NMEA 2000 WiFi Listener

  • Preliminary FMEA — NMEA 2000 WiFi Listener

  • Architecture Review Notes — NMEA 2000 WiFi Listener

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