ESP32 MicroSquirt I/O box

DIY clone of the official MicroSquirt "I/O-box" — an ESP32 + SN65HVD230 that listens to the MS2/Extra MicroSquirt CAN realtime broadcast (base ID 0x5F0, 500 kbps) and drives fan, idle control (IAC) and 6 generic low-side outputs, with the same fail-safe the real I/O-box uses (outputs off when CAN goes silent).

Because MS2/Extra has no I/O-box slave protocol (that's an MS3-only feature), this box is an autonomous "smart slave": it computes its own output logic from the broadcast data. It also implements the full Megasquirt 29-bit expansion protocol as a responder (so an MS2/Extra master can drive its outputs/ADC directly), and broadcasts a small 0x710 frame for the in-dash HMI.

Works with any MS2/Extra 3.4.x MicroSquirt V3 — no fuel/spark tune changes needed, only CAN broadcast settings.

Features

Fan — CLT hysteresis (on ≥ 200 °F / off ≤ 190 °F default, adjustable) or manual override, driven through a ULN2003A channel (default O6/GPIO23).

IAC — 30 Hz PWM on GPIO32 → IRLZ44N → 3-wire rotary ISCV. Three modes: Auto (CLT warm-up table + RPM trim), Follow (mirror the ECU's own iacstep → fully TunerStudio-tunable closed-loop idle), or Manual.

O1–O6 — generic low-side outputs (ULN2003A): manual, CLT-temp or RPM trigger. O1 defaults to a 7000 rpm shift light.

Inputs drive outputs — D1–D3 ground switches and A1–A4 analog (0-5 V, 0.15 V hysteresis) can force any output or the fan (I/O-box parity).

29-bit CAN responder — MS2/Extra remote-port protocol: MSG_REQ/MSG_CMD on table 7; remote idle PWM, remote on/off outputs, remote boost, ADC readback.

0x710 dash broadcast — A1–A4 threshold latches + D1–D3 switch states for the in-dash HMI (indicator/high-beam/brake icons). 10 Hz, always on.

GC9A01A round gauge — 1.28" 240×240 idle-control display: big IAC duty %, RPM / target RPM / CLT / idle mode, fan + CAN status line.

Fail-safe — all outputs off after 500 ms without CAN (matches the real I/O-box); IAC falls back to the ~1000-1200 rpm valve default.

Persistent config — all settings stored in NVS; loadable/settable over serial or via the included Windows diagnostic app.

Repo layout

esp32_microsquirt_iobox/

├── firmware/ PlatformIO ESP32 firmware (src/main.cpp, platformio.ini)

├── pcb/ KiCad 8 PCB design (iobox2: schematic, board, project)

├── diag/ iobox_diag.py — Windows test/configure app (Python + Tkinter)

└── docs/

├── OPERATION.md How the box works + how to use it (modes, commands, display)

├── PROTOCOL.md CAN protocol reference (0x5F0 broadcast, 0x710, 29-bit responder)

├── BUILD.md Full point-to-point build/wiring guide

└── PARTS.md Parts list with rough prices

Quick start

Build hardware — see docs/BUILD.md (wiring) and docs/PARTS.md (parts). The KiCad design in pcb/ is the current board (iobox2); the point-to-point build guide is an alternative for module wiring without a PCB.

Flash firmware:

cd firmware

pio run # build

pio run --target upload # flash over USB

pio device monitor -b 115200

Requires PlatformIO (ESP32 Arduino framework). At the serial prompt type ? for a live status dump.

Configure the MicroSquirt (one time) in TunerStudio → CAN Realtime Data Broadcasting: On, base ID 1520, rate 20 Hz, enable groups 00 (rpm), 02 (baro/map/mat/clt), 03 (tps/batt/afr), and optionally 06 (iacstep) for Follow mode. Details in docs/OPERATION.md.

Use the Windows app (diag/iobox_diag.py) to set fan thresholds, IAC mode, output triggers, input mappings and the 29-bit responder from a GUI.

Hardware snapshot

GPIOFunctionDrives5 / 4CAN TX / RXSN65HVD230 (MicroSquirt pins 2/3, CANH/CANL)32IAC PWM (30 Hz)ISCV via IRLZ44N25,26,27,14,13,23O1–O6ULN2003A (O6 = fan by default, Y<k> to change)2Status LEDonboard (CAN heartbeat / fail-safe blink)36,39,34,35A1–A4 analog 0-5 V10k/20k divider (or PCB 12 V→3.3 V dividers)16,17,18D1–D3 switchesINPUT_PULLUP, active-low to GND15,21,22,19GC9A01A round displaySCLK / MOSI / CS / DC

All outputs are low-side (ground-switching), like the real MS I/O-box. Never feed 12 V into the ESP32 or SN65HVD230 — a 12 V→5 V buck is mandatory.

Serial command cheat sheet

CommandEffect?status dumpF205 / F1 / F0fan auto @205 °F / manual on / offE190fan off hysteresis 190 °FI35 / I / I FIAC manual 35% / auto / follow-ECUT900idle target 900 rpm (auto mode)S7000shift light @7000 rpmO3 R3500 / O4 1O3 above 3500 rpm / O4 onD1 O2 / D2 Fswitch D1→O2 / D2→fanA1 O2 3.5 / A2 F 2.0analog threshold → output/fanY6fan on ULN channel 6R1 / R0 / RB529-bit responder on/off / box IDSfull command list

CAN at a glance

ECU → box: 11-bit IDs 0x5F0–0x5F8 (group N at ID 1520+N), big-endian, 8 bytes/group, 20 Hz. rpm@6, baro/map/mat/clt@16-22 (×0.1), tps/batt/afr@24-28 (×0.1), iacstep@54 (×0.392 = duty %).

Box → dash: 0x710, byte0 = A1–A4 latches, byte1 = D1–D3, byte2 = counter.

Master → box: 29-bit extended MSG_REQ/MSG_CMD (MS2/Extra remote ports).

Full byte maps and the 29-bit responder spec: docs/PROTOCOL.md.