nRF24L01+ Carrier PCB (RP2350-Zero / Pico 2 W)

Two carrier PCBs that hold an nRF24L01+ mini SMD module and receive a host MCU board on header sockets, for the 24g2usb app (SF30 2.4G wireless receiver). Pick the one that matches the board you have:

• 24g2usb_rp2350zero -- Waveshare RP2350-Zero, 18.5x26mm (the Zero's own footprint, plus a comfortable margin)
• 24g2usb_pico2w -- Raspberry Pi Pico 2 W (or Pico / Pico W / Pico 2), 21x33mm, as small as the used pins allow

Neither board has been fabricated or tested yet. Both are DRC-clean and their netlists are asserted against the firmware's wiring table, but no physical board has been built from these files. The Pico 2 W variant is the less settled of the two: its module antenna overhangs the same edge the Pico's USB-C connector occupies, and that clearance has only been checked against the 3D render, not a real cable. Treat the RP2350-Zero board as the better-understood option and both as a first spin.

Both are bare 2-layer PCBs you order from a fab (JLCPCB or similar) and hand-solder: the module, the socket(s), and two decoupling caps (both boards). Full parts lists, fab order settings, and per-board assembly notes are in each board's own README -- this page covers the parts that are the same for both, and the firmware/pairing steps once either is built.

Neither board needs a KiCad GUI step before ordering -- make gerbers zip in each board's directory produces an upload-ready gerber/drill zip directly.

Wiring (both boards, fixed by the firmware -- see 24g2usb wiring)

nRF24L01+	Signal	Notes
VCC	3V3	Not 5V -- the module is not 5V tolerant on its supply
GND	GND
CE	GPIO 4
CSN	GPIO 5
SCK	GPIO 6	spi0 SCK
MOSI	GPIO 7	spi0 TX
MISO	GPIO 0	spi0 RX
IRQ	GPIO 8	Required -- the receiver is interrupt-driven

Both carriers wire the module to these exact pins; the sockets just get you there without flying leads.

What it looks like assembled

Drawn to scale from the board files. The module's body runs away from the caps, so it never covers C1/C2 -- there is 5.1mm of clear board between the module edge and C1 on the RP2350-Zero board, 3.7mm on the Pico 2 W board. The antenna end overhangs the outline (7.8mm and 6.8mm respectively) so it radiates into free air rather than over copper or FR4.

Circuit

Eight nets, no active parts. Both figures are generated from the boards by hardware/doc_images.py, reading the net attached to each pad, so they cannot drift from the copper.

Mounting: below or above the host board

Both carriers can go on either side of the host MCU board, your choice:

• Carrier below the host board: solder female sockets to the carrier's top face; the host board (with its normal male header pins) plugs in from above.
• Carrier above the host board: solder male header pins pointing down out of the carrier's bottom face instead, and plug the carrier into a host board that has female sockets fitted. This orientation gives the module's antenna clear air above it, with nothing overhead.

Either way the carrier's top face still points up and the hole-to-net mapping is unchanged -- never flip the carrier over to mate it. That mirrors the two header rows and would drive 3V3 into the SPI pins. Both boards silkscreen a "USB(-C) END" marker and a pin-1 marker on both faces (mirrored on the back) specifically so this can't be gotten wrong by feel while soldering from underneath.

Ordering

1. Read the board's own README (fab settings, BOM, known limitations). make -C hardware/<board> all regenerates the board from generate.py, runs DRC, and exports gerbers/drill/BOM/ positions/renders -- no KiCad GUI step required.
2. Print the board's fab/*-top-1to1.pdf at 100% scale and check it against your actual host board and nRF24 module with calipers before ordering -- the one thing the software can't verify for you, and module pad geometry varies between sellers. The print includes the module's true 12x18mm body (on the F.Fab reference layer, so the antenna overhang -- which is real on both boards -- is visible and checkable, not just the pads).
3. Check your module's pad order. The boards expect, along the row with the antenna pointing away from you: +3.3V, GND, CE, CSN, SCK, MOSI, MISO, IRQ. This matches the vendor drawing for the common 12x18mm module (Sunrom model 3962 -- 12x18mm, 1.27mm pitch, first pad 1.6mm from the edge), which is what the footprint was built against. But these modules are not standardised between sellers and carry no silkscreen on the pad row, so if yours came from a different source, verify before ordering: set a meter to continuity, put one probe on any bare ground on the module (the crystal can, or the ground fill around the antenna), and probe each pad. Exactly one should beep, and it must be the second pad from the +3.3V end. If GND lands anywhere else -- most commonly at the far end of the row -- that module needs a different footprint. A swapped VCC/GND destroys the module the first time it is powered.
4. Upload fab/*-gerbers.zip to your fab of choice as a bare (non-assembled) 2-layer board.

Assembly

Same order for both boards: module first (tack one corner, check alignment, finish soldering), then C1/C2 decoupling caps (both boards have them, right next to the module's VCC/GND pads), then the socket(s)/header(s) last (tallest parts, easiest to knock loose while soldering everything else).

Build and Flash

# RP2350-Zero carrier
make 24g2usb_rp2350zero
make flash-24g2usb_rp2350zero

# Pico 2 W carrier
make 24g2usb_pico2_w
make flash-24g2usb_pico2_w

Output: releases/joypad_<commit>_24g2usb_<board>.uf2. Flash by holding BOOTSEL while plugging in USB, or drag-and-drop the .uf2 onto the RPI-RP2 drive.

Pairing

Hold BOOTSEL for about 1.5 seconds to start pairing. The board LED blinks fast while looking for a controller, then goes solid once an SF30 2.4G controller links. See 24G Input -- Pairing for the full rendezvous, and the 24g2usb app docs for LED states, USB output modes, and BOOTSEL controls.

Testing

1. Plug the flashed board into a PC.
2. Pair an 8BitDo SF30 2.4G controller (hold BOOTSEL ~1.5s, then power on the controller).
3. Open a gamepad tester and confirm all buttons/sticks register.
4. If nothing pairs: re-check the fit-check step actually matched your module's pinout (VCC, GND, CE, CSN, SCK, MOSI, MISO, IRQ in that order along the row) -- a swapped VCC/GND is the most common hand-soldering mistake on these modules and won't always kill the board outright.

Troubleshooting

Symptom	Likely cause
Board doesn't enumerate at all	Bad USB cable/port; re-check 3V3 isn't shorted to GND at the module
Enumerates but never pairs	Module VCC/GND swapped, or a cold solder joint on CE/CSN/IRQ (interrupt-driven -- IRQ open or floating means the receiver never wakes)
Pairs, then drops	Missing/bad decoupling -- check C1/C2 (both boards have them, right at the module's VCC/GND pads)
LED never leaves slow-blink	No controller found -- confirm the SF30 2.4G controller is actually in pairing mode, not just powered on