p30obd

ESP32-based Honda OBD live dashboard for B16 / P30-class ECUs (pre-2002 Honda 3-pin DLC K-line). The ESP32 reads the K-line directly, runs a WiFi hotspot, serves a PWA dashboard from flash, and streams live gauges + error codes over WebSocket.

Built on the Honda K-line core from ArduinoHondaOBD (hobd_uni), with the single-board ESP32 + PWA direction developed on softr8/ArduinoHondaOBD. This repo is ESP-only — no ATmega, LCD, Bluetooth, or Torque path.

Data flow

Honda ECU --K-line 9600 8N1--> L9637D --UART2--> ESP32 (firmware/)
                                                   |  WiFi Access Point "P30OBD"
                                                   |  + HTTP :80 (LittleFS PWA)
                                                   |  + WebSocket :81 (~4 Hz JSON)
                                                   v
                                         phone / tablet / laptop
                                         http://192.168.4.1

• K-line reader: FreeRTOS task on core 1, ~250 ms poll of ECU memory rows
• Dashboard: plain HTML/CSS/JS PWA (installable “Add to Home Screen”)
• Stream is read-only (inbound WebSocket messages are ignored)

Repo layout

Path	Role
firmware/	Arduino sketch: K-line + WiFi AP + HTTP + WebSocket
dashboard/	PWA UI + mock WebSocket server for bench dev
tools/deploy.sh	Compile, flash firmware, flash LittleFS dashboard

Required protection / interface

Do not connect the Honda DLC K-line or raw +12V to the ESP32. GPIO is 3.3 V and not 5 V-tolerant. Route K-line through an ST L9637D with logic VCC = 3.3 V. Power the ESP32 from a 12 V → 5 V buck with reverse-polarity and load-dump protection.

flowchart TB
  V12["DLC +12V"]:::pwr
  DI["SS54 diode<br/>(reverse-polarity)"]:::prot
  TV["SMBJ24A TVS<br/>+ 100µF + 100nF"]:::prot
  BK["LM2596 buck<br/>12V → 5V"]:::prot
  VIN["ESP32 5V/VIN"]:::mcu
  KL["DLC K-line ~12V"]:::sig
  LX["L9637D<br/>K-line transceiver<br/>VCC=3V3"]:::prot
  RX["ESP32 GPIO16 (RX2)"]:::mcu
  TX["ESP32 GPIO17 (TX2)"]:::mcu
  ESP["ESP32<br/>WiFi AP + WebSocket :81"]:::mcu
  PH["Phone / PWA"]:::ext

  V12 -->|"fuse 2A"| DI
  DI --> TV
  TV --> BK
  BK -->|"+5V"| VIN
  VIN --> ESP
  TV -->|"+12V protected"| LX
  KL -->|"510Ω"| LX
  LX -->|"RX(8)"| RX
  TX -->|"TX(1)"| LX
  RX --> ESP
  ESP -.->|"ws://192.168.4.1:81"| PH

  classDef pwr fill:#3a1010,stroke:#ff5555,color:#fff;
  classDef sig fill:#10243a,stroke:#55aaff,color:#fff;
  classDef prot fill:#3a2a10,stroke:#ffaa33,color:#fff;
  classDef mcu fill:#14241a,stroke:#55cc88,color:#fff;
  classDef ext fill:#241024,stroke:#cc66cc,color:#fff;

Loading

Plain-text wiring

  HONDA 3-PIN DLC            PROTECTION / L9637D                 ESP32-WROOM
  ---------------            ------------------                  -----------

  +12V o--[FUSE 2A]--+--|>|--+-----------+-----------+--> LM2596 IN
                     |  SS54  |           |           |    LM2596 OUT = 5.0V --> 5V/VIN
                     |(revpol)|         100uF/50V   _|_
                     |        |          + 100nF    /_\ SMBJ24A TVS (to GND)
                     |        +--> +12V_prot --------+--> L9637D VS(6)
  GND  o-------------+------------------ common GND --+--> LM2596 GND, ESP32 GND,
                                                          L9637D GND(4), LI(5)

  K-line o--[510R]--> L9637D K(2)          [12V bus, single-wire half-duplex]

         L9637D VCC(7) <---------------------------- ESP32 3V3   (+100nF to GND)
         L9637D TX(1)  <---------------------------- ESP32 GPIO17 (UART2 TX)
         L9637D RX(8)  ----------------------------> ESP32 GPIO16 (UART2 RX)
         L9637D LO(3) = open    ·    LI(5) = GND

Parts

Part	Value / spec	Role
ST L9637D (SO-8)	VCC tied to 3V3	K-line transceiver, 12V ↔ logic
Resistor	510 Ω 1/4 W	K-line series (K pin ↔ DLC)
Schottky SS54	40 V / 5 A	reverse-polarity
TVS SMBJ24A	24 V standoff, 600 W	load-dump / transient clamp
Cap	100 µF / 50 V	bulk input
Cap ×2	100 nF ceramic	input + VCC decoupling
Buck LM2596 module	set 5.0 V, 40 V max in	12 V → 5 V for the ESP32
Fuse	2 A	DLC +12V feed
ESP32-WROOM dev	—	WiFi AP + WebSocket

Notes:

• Echo: through the transceiver the ESP32’s own 5 request bytes echo on RX; dlcCommand() discards them (#define KLINE_ECHO 1).
• obd_select is hardcoded to 1 (OBD1 / B16/P30). Change the const and reflash for OBD2 — the RPM formula is the only difference.
• Pins: UART2 on GPIO16/17. Avoid strapping pins GPIO0/2/5/12/15 and flash pins GPIO6–11.

Build & flash

Libraries (arduino-cli / Library Manager)

• WebSockets by Markus Sattler
• ESP Async WebServer by ESP32Async
• Async TCP by ESP32Async

One command

tools/deploy.sh [PORT]

Compiles + uploads firmware and builds + flashes the dashboard to LittleFS. PORT is auto-detected if omitted.

Then join WiFi P30OBD (password honda1234 — change in firmware/firmware.ino) and open http://192.168.4.1. Use “Add to Home Screen” for full-screen PWA.

Assumes default 4 MB partition scheme (LittleFS at 0x290000, size 0x160000). Override with FS_OFFSET=… FS_SIZE=… tools/deploy.sh.

Compile only

arduino-cli compile --fqbn esp32:esp32:esp32 firmware

Dashboard (no hardware)

cd dashboard
npm install
npm run mock          # ws://localhost:81
# open index.html?ws=ws://localhost:81

See dashboard/README.md for the JSON schema (integer fields; volt / ign are ×10).

Protocol summary

Honda pre-2002 datalogger over K-line @ 9600 8N1:

1. Wake / init sequence (dlcInit)
2. Read-memory commands with Honda checksum: 0xFF - (sum - 1)
3. Live data as 16-byte rows at addresses 0x00, 0x10, 0x20, 0x30
4. DTCs at row 0x40 → Honda MIL numbers → P-codes in dashboard/dtc-codes.js

Attribution

Original project — kerpz / ArduinoHondaOBD

The Honda K-line protocol core comes from ArduinoHondaOBD by Philip Bordado (kerpz), especially hobd_uni (Arduino UNO: K-line datalogger, LCD, ELM327-over-Bluetooth for Torque).

That work reverse-engineered and documented the pre-2002 Honda DLC path used here: wake/init sequence, read-memory commands, checksum, ECU memory row layout, sensor scaling formulas, and DTC (MIL) decoding. p30obd stands on that core.

• https://github.com/kerpz/ArduinoHondaOBD

This repository

p30obd is a focused ESP32-only product for B16 / P30-class ECUs: firmware, dashboard PWA, deploy script, and hardware docs. It does not replace ArduinoHondaOBD; it continues the ESP path from the fork above on top of kerpz’s hobd_uni protocol core.