← WTTC

The WTTC board

A board that the ESP32-S3-DevKitC-1 plugs into, carrying everything else: vehicle input with protection, 5 V, the W-Bus transceiver and connectors for the optional parts. It replaces the module build (TJA1020 board, LM2596 regulator and dupont wires): it can be ordered complete, ready for the ESP32, or with the small parts only, soldering the terminal block, sockets and headers yourself.

Untested design. Nobody has ordered or built one yet. KiCad’s checks (electrical and design rules) are clean, but that does not guarantee it works. If you order it, tell us: the first one built will show whether anything needs fixing.

JLCPCB preview with their parts, from the first order (19 Oct 2026): the «todo» set, as they assemble it

Files

Order «todo» (complete, .zip) Order «smd» (.zip) Gerbers only (.zip) BOM «todo» (all) CPL «todo» (all) BOM «smd» CPL «smd» Full bill of materials Schematic (PDF) KiCad project and generator (GitHub)

Do not upload the packages to JLCPCB as they are (it reports «smaller than 10 × 10 mm»): unzip them and upload the wttc-placa-gerber.zip inside (still zipped) as the board, and the BOM and CPL in the assembly step.

What it carries

Block	Parts	Notes
Vehicle input	3-way screw terminal: 12V · GND · WBUS	The three wires of the timer connector. Check them with a multimeter: colours vary between vehicles.
Protection	0.5 A resettable fuse, reverse-polarity diode (SS34) and transient suppressor (SMBJ24A)	The suppressor clamps below the 40 V the transceiver and regulator can take.
5 V	LMR16006X switching regulator (4–60 V, 0.6 A, 28 µA quiescent)	TI’s 5 V datasheet example. Replaces the LM2596.
W-Bus	TJA1021T/20 transceiver with the master-node resistor (1 kΩ and diode)	Same pinout as the modules’ TJA1020. The «MAESTRO» jumper comes closed; cutting it removes the resistor.
ESP32-S3	Two 22-pin female sockets, rows 25.4 mm apart	The antenna sits off the board, with no copper under it.
Display	4-pin header: GND · 3V3 · SCL · SDA	The order of 0.96" and 1.3" OLEDs. If yours differs, use dupont wires.
Thermometer	4-pin header (3V3 · GND · SCL · SDA) and Qwiic connector	SHT31 or AHT20; Qwiic for modules with a JST-SH connector.
CO sensor	4-pin header: 5V · GND · TXD · RXD	ZE07-CO: its TXD goes to IO15 and its RXD to IO6.
«Heat» button	Push button on the board and a 2-pin header for an external one	IO7 to ground, as in the module build.

The pins are the firmware’s: nothing changes in WTTC. 95 × 62 mm, two layers, ground planes on both and four M3 holes.

Ordering from JLCPCB

At jlcpcb.com → «Order now», upload the Gerber .zip. It is detected automatically: 2 layers, 95 × 62 mm. Leave the rest as is (1.6 mm thick).
Enable «PCB Assembly» on the Top side and upload the BOM and CPL of one of the two sets:
- «todo» (all, «Standard» assembly): it arrives complete, you only plug in the ESP32-S3.
- «smd» («Economic» assembly, cheaper): it arrives with the small parts; you solder the terminal block, sockets and headers.
Every part has its LCSC code. «Extended» parts cost about $3 each per order. The ESP32-S3 (bought separately and plugged in) and the optional modules are never included.
Check the part rotations in their preview: KiCad and JLCPCB do not always agree on the zero angle. It is normal to rotate the regulator, the transceiver or a diode by hand until pin 1 and the cathode band match the silkscreen.
With the «smd» set, the through-hole parts are yours to solder: the terminal block, the two 22-pin sockets and the pin headers.

Real quote (19 Oct 2026, «todo» set): €87.65 without shipping for 5 boards, 2 of them assembled. Most of it is fixed assembly fees (setup €22.90, «extended» part loading €27.57, stencil €7.36): the parts are about €8.50 per board, so assembling more boards in the same order is much cheaper per unit.

Assembly and first test

With the «smd» set, solder the terminal block, sockets and headers. Ground pins are tied solidly to the plane: they need a reasonably powerful iron.
Without the ESP32, connect 12 V to the terminal block and measure about 5.0 V between 5V and GND of the CO sensor header. If not, disconnect and check.
Measure the row spacing of your ESP32-S3: it must be 25.4 mm (Espressif’s and the usual clones). Plug it in with the antenna towards the right edge.
From there, as usual: install WTTC and check in the console that the W-Bus answers.

Careful with USB: as with the module build, do not connect the computer’s USB while the board is powered by the van until you have checked that your ESP32-S3 keeps the two supplies apart.

Known limitations (v0.1)

The transceiver’s SLP input is tied to 3V3, as in the module build. If the ESP32 is powered over USB before the 12 V is connected, the transceiver might not wake up until the next boot.
No I2C pull-ups on the board: the display and thermometer modules have them.
With the ESP32 in sockets everything is about 20 mm tall: you need a box at least 25 mm deep inside.

How it is made

Generated with Claude from code: one file describes the parts (with their LCSC codes) and their connections, and a script produces the schematic, places the parts, routes the tracks with Freerouting, runs KiCad 9’s checks and prepares the files. It opens and can be edited in a normal KiCad 9.