MHC-WLED ESP32-P4 shield — hardware reference

Terminal pinout and onboard features for the MHC-WLED ESP32-P4 shield (myhome-control), the P4-NANO carrier used on the bench (catalog deviceModel: "MHC-WLED ESP32-P4 shield", esp32p4rev1-eth firmware). Read from the board silkscreen + the builder's schematics so projectMM work reads this instead of the marketing render. The shield sits on a Waveshare ESP32-P4-NANO; GPIO numbers are the P4's.

Board revision: the terminal map and RS-485 wiring below are transcribed from a V1 board (the builder's labelled V1 photos + schematics). The overview render is a V2 render. Whether V2 keeps the identical GPIO↔terminal wiring is not confirmed here — treat the map as V1-specific and verify against your own board's silkscreen if you have a different revision.

Sources - Overview render (board V2): docs/assets/deviceModels/mhc-wled-esp32-p4-shield.jpg - Silkscreen (photographed) + the builder's V1 schematics and terminal maps (myhome-control / Wladi, 2026-07-16); the transcriptions below come from those. The schematics supersede the marketing render where they differ.

Pinout

GPIO ↔ screw-terminal map (V1 board)

The output/RS-485 terminals, left to right, with the P4 GPIO each carries:

O21 O20 O25 O5 O7 O23 O8 O27 O3 O22 O24 O4 — the level-shifted single-ended LED outputs, then the four RS-485 differential pairs.

Nothing on this shield is a bare GPIO. Every terminal routes through protection or level-shifting — the reason a direct drive-and-read WS2812 loopback jumper fails on it (see below). Four terminal groups:

12x outputs — level-shifted, single-ended (LED data)

The LED-data outputs. Each terminal is O<gpio> on the silkscreen; a level shifter drives the 5 V strand from the P4's 3.3 V. The catalog wires the Parallel LED driver (peripheral Parlio) to the first eight (21,20,25,5,22,23,24,27).

Terminal	GPIO	Note
O21 O20 O25 O5 O22 O23 O24 O27	21 20 25 5 22 23 24 27	LED lanes (Parallel LED, peripheral Parlio, default)
O7 / O8	7 / 8	also the I²C bus (SDA 7 / SCL 8, catalog I2cScan)
O3	3	also on RS-485 (A-3-B) — see note below
O4	4	also on RS-485 (A-4-B) — see note below
GND	—	ground for the output block

GPIO 3, 4, 22, 24 each appear TWICE — once here (level-shifted single-ended output, O<n>) and once in the RS-485 block (A-<n>-B). It's the same P4 GPIO fanned out to two output forms: driving the pin lights up both its O<n> terminal and its A-<n>-B transceiver at once. Wire to whichever form you need. GPIO 21/20/25/5/23/27 have only the level-shifted path (no RS-485), which is why the LED-driver default uses those + 22/24 for strips and leaves 3/4 free.

4x RS-485 — differential A/B pairs (range extender + DMX)

Each channel is A-<gpio>-B on the silkscreen: an RS-485 transceiver (an SP3485EN-L/TR, not a bare GPIO) driven by that GPIO, with 120 Ω termination, resettable fuses (nSMD010), and TVS protection (CDSOT23-SM712-ES) on the line. Each channel occupies TWO screw terminals — an A and a B (the differential pair), so the 4 channels are 8 terminals total. Channels on GPIO 4, 22, 24, 3.

RS-485 is here for two purposes:

• Range extender — RS-485's differential pair carries LED data far past what a single-ended 5 V line manages. At the LED end you need an RS-485 receiver with a 5 V data output to convert the differential signal back to the WS2812 single-ended waveform.
• DMX-512 output — DMX's physical layer is RS-485, so these channels double as DMX outputs. Wire an XLR connector to GND, <n>A, <n>B; in DMX nomenclature A is Data− (Signal−), B is Data+ (Signal+).

Three channels are transmit-only; one (GPIO 3) is switchable. On the transmit-only channels (GPIO 4, 22, 24) the transceiver's RE#/DE direction pins are hard-wired to transmit (DI in, RO disconnected):

The GPIO 3 channel adds a mechanical slide switch (SW5, MSK12C02) that ties the transceiver's RE#/DE to 3V3 or GND — i.e. it selects transmit mode (DI, GPIO 3 drives the line) or receive mode (RO, GPIO 3 reads the line):

Channel	GPIO	Terminals	Direction
A-4-B	4	A4, B4	transmit only
A-22-B	22	A22, B22	transmit only
A-24-B	24	A24, B24	transmit only
A-3-B	3	A3, B3	transmit or receive (board switch)

4x in/out header

The O46 O47 O2 O48 header plus power (GND, In5V, Out3V3):

Inputs are diode-protected with a ~16 kHz low-pass filter — designed for robust button-style inputs, not high-speed signals. GPIO 2 and 46 are P4 boot straps. This header is not usable for a WS2812 loopback (the filter and protection destroy the ~800 kHz waveform).

Line-In audio (PCM1808 → I²S)

An onboard PCM1808 ADC captures a line-in signal and outputs I²S to the P4. Catalog AudioService: SCK 32 · WS 26 · SD 33 · MCLK 36 (the P4 is I²S master, so it drives MCLK).

Ethernet (RMII)

The P4-NANO's RMII PHY: MDC 31 · MDIO 52 · RST 51 · CLK 50 (external-in) · PHY addr 1, ethType IP101, external clock. (Catalog NetworkModule.)

Loopback self-test on this shield

The loopback self-test drives a WS2812 frame out one pin and reads it back on a jumpered pin — so it needs a signal path from a Tx pin to an Rx pin. The bare-GPIO terminals can't provide it (every one is buffered), but the GPIO 3 switchable RS-485 channel can, because its board switch turns GPIO 3 into a data input:

• Set the GPIO 3 board switch to the receive (input) position, then jumper the RS-485 differential pairs A4→A3 and B4→B3 (the wiring the builder shows):

• The signal path is: GPIO 4 emits the WS2812 frame → the first RS-485 transceiver drives it as a differential signal on A4/B4 → the second transceiver reads it back → GPIO 3 receives it as a 3.3 V data input. So the loopback runs Tx = GPIO 4, Rx = GPIO 3 with the switch in the input position.
• The bare P4-NANO already proves the frame-size fix directly (GPIO 32↔33, PASS at every grid size), so the shield doesn't need to re-prove it — but this RS-485 path is the builder's intended on-shield loopback, distinct from the bare-GPIO jumper the self-test defaults to.
• To verify LED output on the shield, the other honest test is to wire a real WS2812 strip to an O<n> output and watch it light — that exercises the true path (GPIO → level shifter → strip), which is what the shield is built for.

Cross-reference

Chip-level GPIO constraints (straps, flash/PSRAM) for the P4 are in gpio-usage.md § ESP32-P4; this page is the board wiring. The catalog entry is mooninstaller/deviceModels.json (MHC-WLED ESP32-P4 shield). RS-485 / DMX-512 as a first-class projectMM output is tracked in the RS-485 / DMX-512 wired-output backlog item.