DIY — from modules

The lazy-but-still-DIY path. Stack ready-made dev boards and breakouts, wire them together, flash the same firmware that ships on the production unit. No PCB fab, no SMD reflow, no oscilloscope required.

Tradeoffs vs the custom PCB build: bigger (a stack of breakouts won't fit in an OBD-II-sized enclosure), uglier, more wire-routing to think about. Same firmware, same web apps, same ECU communication — so if you don't mind it living in a 3D-printed hobby box on the passenger floor, this is the path.

Draft

The exact parts list is still being finalised. Treat the table below as the shape rather than a verified BOM — confirm pin mappings against the latest firmware/components/board/include/boards/waveshare.h before you wire anything up.

What you'll need

The brain

Waveshare ESP32-P4 Module DEV-KIT — the canonical development target the firmware is written against. The Waveshare ESP32-P4 Module on a breakout board with USB-C, microSD, RJ45, headers broken out.

• Waveshare product page
• Includes a mikroBUS-style header for click boards.

K-line transceiver

MikroE ISO 9141 Click — small breakout carrying an L9637D. Drops straight into the dev kit's mikroBUS header. Set its jumper to 3.3 V (the L9637D is happy at 3.3 V, no level shifter needed).

• MikroE product page

For older BMW chassis you'll also want a 20-pin-to-OBD-II adapter cable so you can reach the under-bonnet diagnostic socket.

CAN transceivers (×2)

Anything with a TJA1051T/3 or compatible CAN transceiver on a breakout. Two boards — one per CAN bus the dongle exposes.

Options (any of these work):

• MikroE CAN FD Click (uses MCP2542FD — also fine for classical CAN at the rates we use)
• MikroE CAN Isolator Click (galvanically isolated — overkill but nice for bench work)
• Any generic TJA1051T breakout from AliExpress / Adafruit with a 3.3 V logic side

You'll wire TX / RX / STBY from the dev board's GPIO header to the breakout's logic side. Confirm the breakout's logic voltage matches 3.3 V before connecting.

Storage

• microSD card — 16 GB SDHC, FAT32. The dev kit has the slot.

OBD-II cable

• OBD-II to bare wires (or to your screw-terminal block of choice). Cheap on AliExpress. You'll wire pin 6 / 14 to one CAN click, pin 7 to the K-line click, pin 16 (battery +12 V) to a buck converter (or USB-C PD trigger) feeding the dev kit.

Power

The OBD-II port provides permanent 12 V on pin 16. Two ways to get it to the dev kit:

• Buck converter — any 12 V → 5 V module rated ≥1 A. Feed the dev kit's USB-C with the regulated 5 V via a USB-C breakout or a bare cable.
• USB-C PD trigger board that takes 12 V in directly (not all do — check the datasheet) and outputs 5 V on the USB-C side.

Bench testing — skip the OBD-II side, plug the dev kit straight into your laptop's USB-C and use the cable's 5 V.

Optional

• Status LEDs + dropping resistors if you want the four-LED panel the production hardware will have. Not required for functionality.
• Small enclosure / 3D-printed box to keep the stack tidy.

Wiring

The full pin map for the dev kit lives in docs/dev-board-pinout.md. The bits you'll wire on the modules path:

Breakout	Breakout pin	Dev kit GPIO	Notes
ISO 9141 Click (K-line)	TX	GPIO 5	UART1 TX
ISO 9141 Click	RX	GPIO 4	UART1 RX
ISO 9141 Click	K (bus)	OBD-II pin 7
ISO 9141 Click	VCC	3V3	3.3 V jumper on the click
CAN breakout #0	TX	(TBD — currently (-1) on waveshare.h)	mikroBUS / GPIO header pin
CAN breakout #0	RX	(TBD)
CAN breakout #0	STBY	(TBD)	Drive low for normal mode
CAN breakout #0	CAN-H / L	OBD-II 6 / 14
CAN breakout #1	(same)	(TBD)	Second bus — pin allocation TBC

The CAN GPIO assignments on the dev board are currently (-1) in waveshare.h because there's no on-board transceiver. If you wire up CAN breakouts you'll edit waveshare.h to point to whichever free GPIOs you've cabled, then re-flash. See Free GPIOs on this board for the safe pin list.

Flash + boot

Same as the custom PCB build:

git clone https://github.com/emdzej/bimmerz-box
cd bimmerz-box/firmware
. $IDF_PATH/export.sh
idf.py set-target esp32p4
idf.py -DBOARD_VARIANT=waveshare build
idf.py -p /dev/cu.usbmodemXXXX flash monitor

Note the BOARD_VARIANT=waveshare — that selects the dev-board pin map. If you've moved CAN pins to non-default GPIOs, hand-edit waveshare.h first.

Once flashed, follow the quick start — the box hosts the same Wi-Fi AP and the same web apps regardless of how its hardware is laid out.

Cost

TBC. A finalised module list with verified prices will land once the bench-tested combinations are pinned down. As a rough sanity check the whole stack should come in under what the custom PCB build costs — you skip the PCB fab cycle, the SMD parts, and the soldering-station investment, paying instead for the markup on pre-assembled modules.

When to pick this path

• You want to start hacking the firmware without waiting for a PCB fab cycle.
• You're prototyping a new transceiver or sensor before committing to a board respin.
• You don't have an SMD soldering setup and don't want one.
• You're building one or two units, not running a small batch.

If you're building three or more, or want anything resembling a finished product, the custom PCB path is cheaper per unit and looks like a real device.