DIY — Waveshare ESP32-P4-WiFi6 devkit

An alternative to the Module DEV-KIT modules path for people who don't want the Ethernet-carrier stack and prefer a single smaller board.

The Waveshare ESP32-P4-WiFi6 Devkit puts the ESP32-P4 and an ESP32-C6 Wi-Fi 6 / BT 5.4 co-processor on one board — no SoM + carrier split, no on-board Ethernet PHY, no mikroBUS header. Wi-Fi, SD card, and USB-C flashing are all built in. You wire external K-line and CAN transceivers to the pin headers, feed the board 5 V from an automotive step-down, and you're done.

Bench-verified. The wiring in this guide matches what's running against a real BMW K-line ECU on the bench today; K-line loop-through is confirmed via the built-in klineWireTest RPC.

What you'll need

The brain

Waveshare ESP32-P4-WiFi6 Devkit — single-board ESP32-P4 + C6 combo, 16 MB flash, 32 MB PSRAM, microSD slot, USB-C.

• Waveshare product page · official docs
• The firmware ships a matching board overlay: sdkconfig.defaults.waveshare_p4_wifi6. Prebuilt binaries for this board variant are attached to every GitHub release.

K-line transceiver

MikroE ISO 9141 Click — the L9637D013TR breakout board (ST L9637D in SO-8 automotive-grade, mounted on a mikroBUS carrier). This is what the bench rig uses. The WiFi6 devkit has no mikroBUS header, so you'll wire the Click to the devkit's header with jumpers rather than plugging it in. Any generic L9637D013TR breakout works the same way.

• MikroE product page — ISO 9141 Click (L9637D013TR) — set the on-board jumper to 3.3 V logic.

CAN transceiver

Any TJA1051T/3 breakout that breaks out both Vcc and VIO as separate pins. The /3 variant is a split-supply part: Vcc is 5 V (bus-side), VIO is 3.3 V (logic-side, tied to the MCU's I/O rail). One transceiver covers the D-CAN pair (OBD pins 6 / 14) that classic BMW chassis use for OBD-II.

• Cheap generic TJA1051T/3 modules from AliExpress / Adafruit / MikroE all work — verify Vcc and VIO are separately accessible before ordering. Modules that hard-tie VIO to Vcc (i.e. run the logic side at 5 V) will drive RXD at 5 V, out of spec for the P4.
• The S (silent-mode select) pin needs to be driven — the firmware handles this from /rpc/can/0 open. Don't leave it floating.

Storage

microSD card, 16 GB SDHC, FAT32. Populate it with the SGBD / DATEN payloads before first boot — see the web-apps guide.

OBD-II connector / cable

You need something that plugs into the car's OBD-II socket (a 16-pin J1962 male connector) with wires you can access on the other side. Two ways to do it:

• Pre-made OBD-II pigtail — J1962 male plug on one end, bare wires (or a screw-terminal block) on the other. Cheapest and most common; ubiquitous on AliExpress / Amazon / eBay. Look for "OBD-II to bare wires" or "OBD2 pigtail cable".
• Bare J1962 male connector (e.g. Molex 34825-0160, TE 1-1747844-1, or generic clones) — for builders who want to solder the wires directly into their enclosure. Requires crimping / soldering the 16 pins yourself; overkill unless you're making a custom housing.

Either way, you only need to populate the pins you actually use: pin 4 or 5 (GND), pin 6 / 14 (CAN-H / CAN-L), pin 7 (K-line), and pin 16 (+12 V). The other pins can be left disconnected. For chassis-specific pin 8 routing, see the Chassis-specific K-line routing section below.

Power

The board runs off 5 V. From the OBD-II port's always-live 12 V on pin 16 you have two options:

• Automotive 12 V → 5 V buck converter — LM2596, MP1584, or any cheap generic module rated ≥1 A. Feed 5 V into the board's VSYS header pin (top-right of the header field, next to VBUS / GND / EN / 3V3). Do not feed the board raw 12 V, and do not feed the buck's output into VBUS — that pin is the USB-side 5 V rail sourced from the USB-C host. VSYS is the board's own 5 V input to its on-board 3.3 V regulator.
• 12 V-compatible USB-C car charger — trim the USB cable, solder to VSYS + GND (same reasoning). Simpler mechanically at the cost of one dead cable.

Fuse the OBD +12 V wire with an inline 1 A fast-blow. The rig draws ~280 mA peak at 12 V input — a short in the wiring would otherwise burn vehicle wiring, not the fuse.

Bench testing — skip the OBD-II side and plug the board's USB-C into a laptop. USB-C supplies 5 V on VBUS, the board powers up on laptop 5 V, and you can flash + monitor at the same time. When you switch to the in-car buck, disconnect USB and feed VSYS instead.

Optional

• SPDT toggle switch in the OBD harness between pin 7 and pin 8, routed to the L9637D K-line input — see Chassis-specific K-line routing below.
• Small enclosure — the WiFi6 devkit is small enough that a matchbox-sized 3D print holds it plus the two transceiver breakouts.

Wiring

Full pinout with the setup diagram lives in the repo: docs/wifi6-prototype.md. The relevant tables:

GPIO ↔ transceiver

Board pin	Function	Wire to
GPIO 20	K-line UART1 TX	L9637D TxD-in
GPIO 21	K-line UART1 RX	L9637D RxD-out
GPIO 33	CAN0 TWAI TX	TJA1051T/3 TXD
GPIO 32	CAN0 TWAI RX	TJA1051T/3 RXD
GPIO 27	CAN0 STBY (S)	TJA1051T/3 S (silent, active-high)
VSYS	5 V system input	Buck converter 5 V output → TJA1051T/3 Vcc. Not VBUS — that's USB-side.
3V3	3.3 V logic rail	TJA1051T/3 VIO and L9637D Vcc (logic-side supply on both).
GND	0 V	Buck GND, both transceivers' GND, OBD pins 4/5

Naming gotcha. On this board the K-line pin labels follow the L9637D datasheet (TxD = the transceiver's input, comes from the MCU's TX pin). CAN follows the MCU perspective (RX = the P4's TWAI RX line). Wire from the tables above and don't cross- reference them by feel — the two peripherals use opposite conventions.

OBD-II ↔ transceiver

OBD pin	Signal	Wire to
4	Chassis GND	Common GND rail
5	Signal GND	Common GND rail
6	CAN-H	TJA1051 CANH
7	K-line	L9637D K-line pin (bus side)
14	CAN-L	TJA1051 CANL
16	+12 V (KL30)	Buck converter input (fused)

The L9637D needs two supplies:

• Vs (bus-side, 12 V) — tie to the same fused +12 V feed as the buck. Without vehicle 12 V here the transceiver can't drive K-line low; the bus stays idle-high and the ECU never hears the box.
• Vcc (logic-side, 3.3 V) — tie to the WiFi6 board's 3V3 pin. Without it the RxD output has no supply and the P4 can't read the bus. On the MikroE ISO 9141 Click, the on-board jumper selects between 3.3 V and 5 V for this pin — set it to 3.3 V.

The TJA1051T/3 needs two supplies as well:

• Vcc (5 V) — tie to VSYS on the WiFi6 board (fed by the buck).
• VIO (3.3 V) — tie to the WiFi6 board's 3V3 pin. This is the I/O reference for TXD / RXD / S — leave it floating (or tied to Vcc) and RXD swings to 5 V, which is out of spec for the P4's 3.3 V-only GPIOs. On split-supply TJA1051T/3 breakouts this is a distinct pin from Vcc; verify against your breakout's silkscreen.

Chassis-specific K-line routing

Some BMW chassis carry the diagnostic K-line on OBD pin 8 instead of pin 7 (or on both). Two ways to handle it on the prototype rig:

• Solder a fixed jumper between OBD pin 7 and pin 8 on the socket side of your harness. Cheapest and most reliable when the box will only ever plug into one chassis type.
• Wire a physical SPDT toggle switch into the harness so K-line goes to pin 7 or pin 8 (never both simultaneously). Use when the box moves between chassis families.

Never short pin 7 to pin 8 directly. Some chassis put a switched +12 V feed on pin 8; a hard short would back-feed 12 V into the L9637D's bus pin and destroy the transceiver instantly. The final PCB handles this with a TMUX1208 analog switch driven by firmware (KLINE7_EN / KLINE8_EN) — the DIY rig has no equivalent, so the jumper / toggle stands in for it.

Flash + boot

Two paths:

From a GitHub release (fastest)

No ESP-IDF required. Grab the four .bin artefacts for the waveshare_p4_wifi6 variant from a GitHub release and push them with esptool:

pip install esptool
V=0.1.0
BOARD=waveshare_p4_wifi6
gh release download "$V" --repo emdzej/bimmerz-box \
  --pattern "bootloader-$BOARD-$V.bin" \
  --pattern "partition-table-$BOARD-$V.bin" \
  --pattern "ota_data_initial-$BOARD-$V.bin" \
  --pattern "bimmerz_box-$BOARD-$V.bin"

python -m esptool --chip esp32p4 -p /dev/cu.usbmodem<...> -b 460800 \
  --before default_reset --after hard_reset write_flash \
  --flash_mode dio --flash_size 16MB --flash_freq 80m \
  0x2000  "bootloader-$BOARD-$V.bin" \
  0x8000  "partition-table-$BOARD-$V.bin" \
  0x10000 "ota_data_initial-$BOARD-$V.bin" \
  0x20000 "bimmerz_box-$BOARD-$V.bin"

The board's USB-C connector is the ESP32-P4's native USB-Serial-JTAG — flash and console share that port. Windows / macOS / Linux all see it as a plain CDC device (no drivers).

Full instructions with alternatives are in the repo README.

From source

If you'd rather build:

git clone https://github.com/emdzej/bimmerz-box
cd bimmerz-box/firmware
. $IDF_PATH/export.sh
idf.py -DSDKCONFIG_DEFAULTS="sdkconfig.defaults;sdkconfig.defaults.waveshare_p4_wifi6" \
       set-target esp32p4
idf.py build
idf.py -p /dev/cu.usbmodem<...> flash monitor

The build pulls ediabasx-embedded as a sibling repo via a path dependency — clone it next to bimmerz-box.

First boot check

Once flashed, the box brings up the BimmerzBox open Wi-Fi AP at 172.16.7.1. Join it, open http://172.16.7.1/settings/, and confirm:

• The Firmware card shows the running version + git hash.
• Files lists the SD-card contents (SGBDs / DATEN payloads).

To confirm the K-line hardware loop end-to-end, open the browser DevTools console on any page under http://172.16.7.1/ and run:

const ws = new WebSocket('ws://172.16.7.1/rpc/ediabasx');
ws.onopen  = () => ws.send(JSON.stringify({jsonrpc:"2.0", id:1, method:"klineWireTest"}));
ws.onmessage = e => { console.log(e.data); ws.close(); };

Expected: {"loopOk":true, "rxWhenTxHigh":1, "rxWhenTxLow":0, ...}. If loopOk is false, walk the K-line wiring — see the repo's prototype doc for the debug steps.

When to pick this path (vs the other DIY options)

• This board: you like the single-board form factor, don't need Ethernet, and want the smallest bench rig that still uses off-the- shelf transceivers.
• Module DEV-KIT modules path: you want the mikroBUS-style header (click boards plug straight in), on-board Ethernet PHY for DoIP / ENET experiments, and a physically larger board to solder to.
• Custom PCB: you're going past prototype — one small board, on-board transceivers, OBD-II-dongle form factor.

Cost

TBC. The board is cheaper than the Module DEV-KIT + carrier combo; add the two transceiver breakouts and a buck module and you're under what the modules path costs, though at the cost of losing the Ethernet PHY and mikroBUS convenience.