Pico stretch2

Pico Stretch 2

An RP2350B dev board that breaks out all 48 GPIO pins while following the original Raspberry Pi Pico footprint for the first 20 pins on each side. It adds another 12 pins on each side — keeping the same 0.1" pitch and castellated edges so it remains breadboard-friendly.

The board supports PSRam (chip select on GP0 or GP47) and the Radio Module 2 for WiFi/BT

Features:

• USB-C connector
• Boot/Reset buttons
• SWDIO debugging header
• Radio Module 2 footprint / jumpers
• PSRam footprint / jumper
• Breaks out all 48 GPIOs
• Supports existing Pi Pico pinout projects (if there's room for a little overhang, or if you want to get adventuresome and saw the board in half)

Board views

Top

Bottom

PCB layout

F.Cu / F.Silkscreen

B.Cu / B.Silkscreen (mirrored)

Pinout

1   GPIO0           64  VBUS
2   GPIO1           63  VSYS
3   GND             62  GND
4   GPIO2           61  3v3_EN
5   GPIO3           60  3v3
6   GPIO4           59  ADC_VREF
7   GPIO5           58  GPIO28
8   GND             57  GND
9   GPIO6           56  GPIO27
10  GPIO7           55  GPIO26
11  GPIO8           54  RUN
12  GPIO9           53  GPIO22
13  GND             52  GND
14  GPIO10          51  GPIO21
15  GPIO11          50  GPIO20
16  GPIO12          49  GPIO19
17  GPIO13          48  GPIO18
18  GND             47  GND
19  GPIO14          46  GPIO17
20  GPIO15          45  GPIO16
21  GPIO23          44  GPIO47/ADC7
22  GPIO24          43  GPIO46/ADC6
23  GPIO25          42  GPIO45/ADC5
24  GPIO29          41  GPIO44/ADC4

Optional parts and pin notes

• PSRAM (U6) is not fitted by default. Solder an APS6404L-3SQR (3.3 V, SOP-8) and close one of the chip-select jumpers on the back: JP1 puts it on GPIO0, JP4 on GPIO47 (the RP2350 can use either as its second QSPI chip select, QMI CS1n). Never close both. GPIO47 keeps GPIO0 free for UART0 TX and matches other RP2350B PSRAM boards; the jumper you close takes that pin away from the castellated pad.
• Radio (U5, Raspberry Pi RM2) is not fitted by default. GPIO24 (data/IRQ) and GPIO29 (clock) are wired straight to its pads; GPIO25 (CS) and GPIO23 (WL_ON) go through JP2 and JP3. With the radio fitted and the jumpers closed, all four belong to the radio.
• The RM2 antenna hangs past the end of the board. If you solder this board onto a carrier that extends under that end, keep copper off the carrier under and around the antenna.
• Wi-Fi transmit is bursty. The 3.3 V supply is a linear regulator, so avoid sustained full-rate transmit and keep extra load on the 3V3 pin modest. Keep VSYS above about 3.5 V.
• The flash and PSRAM share a QSPI bus with three loads and no series resistors. The Pico 2 runs its flash at PICO_FLASH_SPI_CLKDIV 2. If you see flash or PSRAM errors at higher system clocks, use a larger divider (4) and test before going back down.

Back side

• Every castellated pad is labelled on the back too, with the same text as the front.
• Jumpers: JP1 = PSRAM CS on GPIO0, JP4 = PSRAM CS on GPIO47, JP2 + JP3 = radio (see above).
• Test pads: TP1 = 1V1, TP2 = 3V3, TP3 = USB D-, TP4 = USB D+ (on the connector side of the 33 Ω resistors, labelled D- and D+), TP5 = GND (labelled G).
• TP3, TP4 and TP5 sit exactly where the Pico / Pico 2 has its USB test points (its TP2 = D-, TP3 = D+, TP1 = GND), with the same 1.5 x 1.5 mm pads, so a carrier made for the Pico SMT footprint reaches USB through them.

Soldering onto a Pico footprint

The first 20 castellated pads on each side, and the USB test pads above, line up with the Raspberry Pi Pico / Pico 2 SMT footprint (Pico 2 datasheet section 3.2), so the board can be hot-plate or reflow soldered onto a carrier designed for a Pico. The other 24 pads and the radio end overhang the Pico outline.

• Nothing else on the back lands on that footprint's pads: its TP4-TP7 positions are bare board here, and its four USB shell pads (A-D) meet only this board's USB-C shell legs (GND, as on the Pico) and its plastic locating pegs, which stay inside the board.
• Leave the SWD header (J2) unfitted, or cut it flush: its pins would stop the board sitting flat.

Production files for JLCPCB

Production files live in the production/ directory, written by JLCImport's jlcimport-cli production from the board as it is:

• pico-stretch2-gerbers.zip — Gerber and drill files (the same files, unzipped, are in gerbers/)
• pico-stretch2-bom.csv — bill of materials
• pico-stretch2-cpl.csv — component placement file, with rotations solved against JLC's own footprints
• pico-stretch2-report.txt — the production check: stock, part types, fees, and the placements to look at in JLC's preview

To regenerate after a board change: jlcimport-cli production pico-stretch2.kicad_pcb (add --force to write the files even when the check reports an error, such as a part out of stock).

When ordering:

• Choose epoxy-filled and capped vias: the board has vias in pads.
• Select the castellated holes option.
• Use the JLC04161H-7628 stackup (set in the board file).
• U5 (RM2) and U6 (PSRAM) are marked DNP and left out of the BOM and placement files; clear DNP if you want JLC to fit U6.
• L1 (AOTA-B201610S3R3-101-T, C42411119) is often out of stock at JLC: pre-order it into your JLC parts library or consign it. Do not substitute another inductor; the RP2350 regulator needs this polarity-marked part.
• Check pin 1 of U1, U3, U4 and the diodes, and the LED, in JLC's placement preview.

Regenerating images

Run scripts/render-images.sh after PCB changes to regenerate everything in images/. Requires kicad-cli (KiCad ≥ 9) and ImageMagick (magick).