Lemon Wired

The Lemon Wired is a RP2040-based microcontroller for split keyboards with two USB-C ports, a VIK connector, and two FPC connectors for connecting column-flex PCBs. If you use column-flex PCBs and VIK-compatible peripherals, it’s possible to build a split keyboard without soldering any wires!

If you haven’t already, I suggest you check out the Lemon Landing page to learn more.

What are Column Flex PCBs?

Column Flex PCBs affix hotswap sockets, diodes, RGB Leds, and copper traces to a flexible polyimide backing. All the wiring is already done for you, and the polyimide is flexible enough that you can shift every socket up to 20mm in any direction.

Image of Pumpkin PCBs

There are two kinds of column flex PCBs. The fullly interconnected one I’ve pictured above is the Pumpkin PCB, which I plan to sell soon. All sockets come connected to each other. You need to be very careful with it, because if you break a connection you will either need to bridge the gap with wire or buy a whole new PCB. TheBigSkree also sells connected-column ones, where every row in a column is connected, but you will need a second flexible PCB to wire the columns together.

What’s VIK?

VIK is a standard for how keyboard modules connect to one another. It combines SPI, I2C, power, and GPIO into a single connector. The idea is that the Cosmos benefits from VIK modules for other keyboards, and any VIK modules created specifically for Cosmos will benefit the wider keyboard community,

Pinout

Go to the landing page :)

QMK Example

The best example of using QMK on the Lemon microcontroller will for now probably be the QMK implementation of my peaMK software. Currently, all this program does is print the matrix position of a key you press, but you can disable this feature by editing keymap.c. There are a few noteworthy aspects to this program:

It uses as much of the modern, data-driven QMK approach as possible.
It relies on Sadek Baroudi’s VIK library for QMK to enable quick setup of VIK modules.
Communication is done through full-duplex UART.

When using QMK, you will need to wire the Link-only connector on this microcontroller to the Link-only connector on the other microcontroller.

KMK Example

Work in progress :) I’m working on merging my changes into CircuitPython and KMK.

Arduino Core

I haven’t contributed this board upstream yet since I don’t know how popular this option is going to be. Therefore, if you do program the Lemon with Arduino then please tell me so I can prioritize this!

Expand Arduino Instructions (Caution: Not Easy)

Install Earle Philhower’s Pi Pico Core through git. If you’ve already installed it through the Arduino Board Manager, uninstall then install through git. Then, open the folder you’ve cloned and edit boards.txt. You’ll want to add the following lines:

# -----------------------------------
# Cosmos Lemon Wired
# -----------------------------------
cosmos_lemon.name=Cosmos Lemon Wired
cosmos_lemon.vid.0=0x0001
cosmos_lemon.pid.0=0x8001
cosmos_lemon.vid.1=0x0001
cosmos_lemon.pid.1=0x8101
cosmos_lemon.upload_port.0.vid=0x0001
cosmos_lemon.upload_port.0.pid=0x8001
cosmos_lemon.upload_port.1.vid=0x0001
cosmos_lemon.upload_port.1.pid=0x8101
cosmos_lemon.build.usbvid=-DUSBD_VID=0x001
cosmos_lemon.build.usbpid=-DUSBD_PID=0x8001
cosmos_lemon.build.usbpwr=-DUSBD_MAX_POWER_MA=250
cosmos_lemon.build.board=COSMOS_LEMON_RP2040
cosmos_lemon.build.mcu=cortex-m0plus
cosmos_lemon.build.chip=rp2040
cosmos_lemon.build.toolchain=arm-none-eabi
cosmos_lemon.build.toolchainpkg=pqt-gcc
cosmos_lemon.build.toolchainopts=-march=armv6-m -mcpu=cortex-m0plus -mthumb
cosmos_lemon.build.uf2family=--family rp2040
cosmos_lemon.build.variant=cosmos_lemon
cosmos_lemon.upload.maximum_size=8388608
cosmos_lemon.upload.wait_for_upload_port=true
cosmos_lemon.upload.erase_cmd=
cosmos_lemon.serial.disableDTR=false
cosmos_lemon.serial.disableRTS=false
cosmos_lemon.build.f_cpu=125000000
cosmos_lemon.build.led=
cosmos_lemon.build.core=rp2040
cosmos_lemon.build.ldscript=memmap_default.ld
cosmos_lemon.build.boot2=boot2_w25x10cl_4_padded_checksum
cosmos_lemon.build.usb_manufacturer="Cosmos"
cosmos_lemon.build.usb_product="Lemon Wired"
cosmos_lemon.menu.flash.8388608_0=8MB (no FS)
cosmos_lemon.menu.flash.8388608_0.upload.maximum_size=8384512
cosmos_lemon.menu.flash.8388608_0.build.flash_total=8388608
cosmos_lemon.menu.flash.8388608_0.build.flash_length=8384512
cosmos_lemon.menu.flash.8388608_0.build.eeprom_start=276819968
cosmos_lemon.menu.flash.8388608_0.build.fs_start=276819968
cosmos_lemon.menu.flash.8388608_0.build.fs_end=276819968
cosmos_lemon.menu.flash.8388608_65536=8MB (Sketch: 8128KB, FS: 64KB)
cosmos_lemon.menu.flash.8388608_65536.upload.maximum_size=8318976
cosmos_lemon.menu.flash.8388608_65536.build.flash_total=8388608
cosmos_lemon.menu.flash.8388608_65536.build.flash_length=8318976
cosmos_lemon.menu.flash.8388608_65536.build.eeprom_start=276819968
cosmos_lemon.menu.flash.8388608_65536.build.fs_start=276754432
cosmos_lemon.menu.flash.8388608_65536.build.fs_end=276819968
cosmos_lemon.menu.flash.8388608_131072=8MB (Sketch: 8064KB, FS: 128KB)
cosmos_lemon.menu.flash.8388608_131072.upload.maximum_size=8253440
cosmos_lemon.menu.flash.8388608_131072.build.flash_total=8388608
cosmos_lemon.menu.flash.8388608_131072.build.flash_length=8253440
cosmos_lemon.menu.flash.8388608_131072.build.eeprom_start=276819968
cosmos_lemon.menu.flash.8388608_131072.build.fs_start=276688896
cosmos_lemon.menu.flash.8388608_131072.build.fs_end=276819968
cosmos_lemon.menu.flash.8388608_262144=8MB (Sketch: 7936KB, FS: 256KB)
cosmos_lemon.menu.flash.8388608_262144.upload.maximum_size=8122368
cosmos_lemon.menu.flash.8388608_262144.build.flash_total=8388608
cosmos_lemon.menu.flash.8388608_262144.build.flash_length=8122368
cosmos_lemon.menu.flash.8388608_262144.build.eeprom_start=276819968
cosmos_lemon.menu.flash.8388608_262144.build.fs_start=276557824
cosmos_lemon.menu.flash.8388608_262144.build.fs_end=276819968
cosmos_lemon.menu.flash.8388608_524288=8MB (Sketch: 7680KB, FS: 512KB)
cosmos_lemon.menu.flash.8388608_524288.upload.maximum_size=7860224
cosmos_lemon.menu.flash.8388608_524288.build.flash_total=8388608
cosmos_lemon.menu.flash.8388608_524288.build.flash_length=7860224
cosmos_lemon.menu.flash.8388608_524288.build.eeprom_start=276819968
cosmos_lemon.menu.flash.8388608_524288.build.fs_start=276295680
cosmos_lemon.menu.flash.8388608_524288.build.fs_end=276819968
cosmos_lemon.menu.flash.8388608_1048576=8MB (Sketch: 7MB, FS: 1MB)
cosmos_lemon.menu.flash.8388608_1048576.upload.maximum_size=7335936
cosmos_lemon.menu.flash.8388608_1048576.build.flash_total=8388608
cosmos_lemon.menu.flash.8388608_1048576.build.flash_length=7335936
cosmos_lemon.menu.flash.8388608_1048576.build.eeprom_start=276819968
cosmos_lemon.menu.flash.8388608_1048576.build.fs_start=275771392
cosmos_lemon.menu.flash.8388608_1048576.build.fs_end=276819968
cosmos_lemon.menu.flash.8388608_2097152=8MB (Sketch: 6MB, FS: 2MB)
cosmos_lemon.menu.flash.8388608_2097152.upload.maximum_size=6287360
cosmos_lemon.menu.flash.8388608_2097152.build.flash_total=8388608
cosmos_lemon.menu.flash.8388608_2097152.build.flash_length=6287360
cosmos_lemon.menu.flash.8388608_2097152.build.eeprom_start=276819968
cosmos_lemon.menu.flash.8388608_2097152.build.fs_start=274722816
cosmos_lemon.menu.flash.8388608_2097152.build.fs_end=276819968
cosmos_lemon.menu.flash.8388608_3145728=8MB (Sketch: 5MB, FS: 3MB)
cosmos_lemon.menu.flash.8388608_3145728.upload.maximum_size=5238784
cosmos_lemon.menu.flash.8388608_3145728.build.flash_total=8388608
cosmos_lemon.menu.flash.8388608_3145728.build.flash_length=5238784
cosmos_lemon.menu.flash.8388608_3145728.build.eeprom_start=276819968
cosmos_lemon.menu.flash.8388608_3145728.build.fs_start=273674240
cosmos_lemon.menu.flash.8388608_3145728.build.fs_end=276819968
cosmos_lemon.menu.flash.8388608_4194304=8MB (Sketch: 4MB, FS: 4MB)
cosmos_lemon.menu.flash.8388608_4194304.upload.maximum_size=4190208
cosmos_lemon.menu.flash.8388608_4194304.build.flash_total=8388608
cosmos_lemon.menu.flash.8388608_4194304.build.flash_length=4190208
cosmos_lemon.menu.flash.8388608_4194304.build.eeprom_start=276819968
cosmos_lemon.menu.flash.8388608_4194304.build.fs_start=272625664
cosmos_lemon.menu.flash.8388608_4194304.build.fs_end=276819968
cosmos_lemon.menu.flash.8388608_5242880=8MB (Sketch: 3MB, FS: 5MB)
cosmos_lemon.menu.flash.8388608_5242880.upload.maximum_size=3141632
cosmos_lemon.menu.flash.8388608_5242880.build.flash_total=8388608
cosmos_lemon.menu.flash.8388608_5242880.build.flash_length=3141632
cosmos_lemon.menu.flash.8388608_5242880.build.eeprom_start=276819968
cosmos_lemon.menu.flash.8388608_5242880.build.fs_start=271577088
cosmos_lemon.menu.flash.8388608_5242880.build.fs_end=276819968
cosmos_lemon.menu.flash.8388608_6291456=8MB (Sketch: 2MB, FS: 6MB)
cosmos_lemon.menu.flash.8388608_6291456.upload.maximum_size=2093056
cosmos_lemon.menu.flash.8388608_6291456.build.flash_total=8388608
cosmos_lemon.menu.flash.8388608_6291456.build.flash_length=2093056
cosmos_lemon.menu.flash.8388608_6291456.build.eeprom_start=276819968
cosmos_lemon.menu.flash.8388608_6291456.build.fs_start=270528512
cosmos_lemon.menu.flash.8388608_6291456.build.fs_end=276819968
cosmos_lemon.menu.flash.8388608_7340032=8MB (Sketch: 1MB, FS: 7MB)
cosmos_lemon.menu.flash.8388608_7340032.upload.maximum_size=1044480
cosmos_lemon.menu.flash.8388608_7340032.build.flash_total=8388608
cosmos_lemon.menu.flash.8388608_7340032.build.flash_length=1044480
cosmos_lemon.menu.flash.8388608_7340032.build.eeprom_start=276819968
cosmos_lemon.menu.flash.8388608_7340032.build.fs_start=269479936
cosmos_lemon.menu.flash.8388608_7340032.build.fs_end=276819968
cosmos_lemon.menu.freq.200=200 MHz
cosmos_lemon.menu.freq.200.build.f_cpu=200000000L
cosmos_lemon.menu.freq.50=50 MHz
cosmos_lemon.menu.freq.50.build.f_cpu=50000000L
cosmos_lemon.menu.freq.100=100 MHz
cosmos_lemon.menu.freq.100.build.f_cpu=100000000L
cosmos_lemon.menu.freq.120=120 MHz
cosmos_lemon.menu.freq.120.build.f_cpu=120000000L
cosmos_lemon.menu.freq.125=125 MHz
cosmos_lemon.menu.freq.125.build.f_cpu=125000000L
cosmos_lemon.menu.freq.128=128 MHz
cosmos_lemon.menu.freq.128.build.f_cpu=128000000L
cosmos_lemon.menu.freq.133=133 MHz
cosmos_lemon.menu.freq.133.build.f_cpu=133000000L
cosmos_lemon.menu.freq.150=150 MHz
cosmos_lemon.menu.freq.150.build.f_cpu=150000000L
cosmos_lemon.menu.freq.176=176 MHz
cosmos_lemon.menu.freq.176.build.f_cpu=176000000L
cosmos_lemon.menu.freq.225=225 MHz (Overclock)
cosmos_lemon.menu.freq.225.build.f_cpu=225000000L
cosmos_lemon.menu.freq.240=240 MHz (Overclock)
cosmos_lemon.menu.freq.240.build.f_cpu=240000000L
cosmos_lemon.menu.freq.250=250 MHz (Overclock)
cosmos_lemon.menu.freq.250.build.f_cpu=250000000L
cosmos_lemon.menu.freq.276=276 MHz (Overclock)
cosmos_lemon.menu.freq.276.build.f_cpu=276000000L
cosmos_lemon.menu.freq.300=300 MHz (Overclock)
cosmos_lemon.menu.freq.300.build.f_cpu=300000000L
cosmos_lemon.menu.opt.Small=Small (-Os) (standard)
cosmos_lemon.menu.opt.Small.build.flags.optimize=-Os
cosmos_lemon.menu.opt.Optimize=Optimize (-O)
cosmos_lemon.menu.opt.Optimize.build.flags.optimize=-O
cosmos_lemon.menu.opt.Optimize2=Optimize More (-O2)
cosmos_lemon.menu.opt.Optimize2.build.flags.optimize=-O2
cosmos_lemon.menu.opt.Optimize3=Optimize Even More (-O3)
cosmos_lemon.menu.opt.Optimize3.build.flags.optimize=-O3
cosmos_lemon.menu.opt.Fast=Fast (-Ofast) (maybe slower)
cosmos_lemon.menu.opt.Fast.build.flags.optimize=-Ofast
cosmos_lemon.menu.opt.Debug=Debug (-Og)
cosmos_lemon.menu.opt.Debug.build.flags.optimize=-Og
cosmos_lemon.menu.opt.Disabled=Disabled (-O0)
cosmos_lemon.menu.opt.Disabled.build.flags.optimize=-O0
cosmos_lemon.menu.profile.Disabled=Disabled
cosmos_lemon.menu.profile.Disabled.build.flags.profile=
cosmos_lemon.menu.profile.Enabled=Enabled
cosmos_lemon.menu.profile.Enabled.build.flags.profile=-pg -D__PROFILE
cosmos_lemon.menu.rtti.Disabled=Disabled
cosmos_lemon.menu.rtti.Disabled.build.flags.rtti=-fno-rtti
cosmos_lemon.menu.rtti.Enabled=Enabled
cosmos_lemon.menu.rtti.Enabled.build.flags.rtti=
cosmos_lemon.menu.stackprotect.Disabled=Disabled
cosmos_lemon.menu.stackprotect.Disabled.build.flags.stackprotect=
cosmos_lemon.menu.stackprotect.Enabled=Enabled
cosmos_lemon.menu.stackprotect.Enabled.build.flags.stackprotect=-fstack-protector
cosmos_lemon.menu.exceptions.Disabled=Disabled
cosmos_lemon.menu.exceptions.Disabled.build.flags.exceptions=-fno-exceptions
cosmos_lemon.menu.exceptions.Disabled.build.flags.libstdcpp=-lstdc++
cosmos_lemon.menu.exceptions.Enabled=Enabled
cosmos_lemon.menu.exceptions.Enabled.build.flags.exceptions=-fexceptions
cosmos_lemon.menu.exceptions.Enabled.build.flags.libstdcpp=-lstdc++-exc
cosmos_lemon.menu.dbgport.Disabled=Disabled
cosmos_lemon.menu.dbgport.Disabled.build.debug_port=
cosmos_lemon.menu.dbgport.Serial=Serial
cosmos_lemon.menu.dbgport.Serial.build.debug_port=-DDEBUG_RP2040_PORT=Serial
cosmos_lemon.menu.dbgport.Serial1=Serial1
cosmos_lemon.menu.dbgport.Serial1.build.debug_port=-DDEBUG_RP2040_PORT=Serial1
cosmos_lemon.menu.dbgport.Serial2=Serial2
cosmos_lemon.menu.dbgport.Serial2.build.debug_port=-DDEBUG_RP2040_PORT=Serial2
cosmos_lemon.menu.dbgport.SerialSemi=SerialSemi
cosmos_lemon.menu.dbgport.SerialSemi.build.debug_port=-DDEBUG_RP2040_PORT=SerialSemi
cosmos_lemon.menu.dbglvl.None=None
cosmos_lemon.menu.dbglvl.None.build.debug_level=
cosmos_lemon.menu.dbglvl.Core=Core
cosmos_lemon.menu.dbglvl.Core.build.debug_level=-DDEBUG_RP2040_CORE
cosmos_lemon.menu.dbglvl.SPI=SPI
cosmos_lemon.menu.dbglvl.SPI.build.debug_level=-DDEBUG_RP2040_SPI
cosmos_lemon.menu.dbglvl.Wire=Wire
cosmos_lemon.menu.dbglvl.Wire.build.debug_level=-DDEBUG_RP2040_WIRE
cosmos_lemon.menu.dbglvl.Bluetooth=Bluetooth
cosmos_lemon.menu.dbglvl.Bluetooth.build.debug_level=-DDEBUG_RP2040_BLUETOOTH
cosmos_lemon.menu.dbglvl.All=All
cosmos_lemon.menu.dbglvl.All.build.debug_level=-DDEBUG_RP2040_WIRE -DDEBUG_RP2040_SPI -DDEBUG_RP2040_CORE -DDEBUG_RP2040_BLUETOOTH
cosmos_lemon.menu.dbglvl.NDEBUG=NDEBUG
cosmos_lemon.menu.dbglvl.NDEBUG.build.debug_level=-DNDEBUG
cosmos_lemon.menu.usbstack.picosdk=Pico SDK
cosmos_lemon.menu.usbstack.picosdk.build.usbstack_flags=
cosmos_lemon.menu.usbstack.tinyusb=Adafruit TinyUSB
cosmos_lemon.menu.usbstack.tinyusb.build.usbstack_flags=-DUSE_TINYUSB "-I{runtime.platform.path}/libraries/Adafruit_TinyUSB_Arduino/src/arduino"
cosmos_lemon.menu.usbstack.tinyusb_host=Adafruit TinyUSB Host (native)
cosmos_lemon.menu.usbstack.tinyusb_host.build.usbstack_flags=-DUSE_TINYUSB -DUSE_TINYUSB_HOST "-I{runtime.platform.path}/libraries/Adafruit_TinyUSB_Arduino/src/arduino"
cosmos_lemon.menu.usbstack.nousb=No USB
cosmos_lemon.menu.usbstack.nousb.build.usbstack_flags="-DNO_USB -DDISABLE_USB_SERIAL -I{runtime.platform.path}/tools/libpico"
cosmos_lemon.menu.ipbtstack.ipv4only=IPv4 Only
cosmos_lemon.menu.ipbtstack.ipv4only.build.libpicow=libipv4.a
cosmos_lemon.menu.ipbtstack.ipv4only.build.libpicowdefs=-DLWIP_IPV6=0 -DLWIP_IPV4=1
cosmos_lemon.menu.ipbtstack.ipv4ipv6=IPv4 + IPv6
cosmos_lemon.menu.ipbtstack.ipv4ipv6.build.libpicow=libipv4-ipv6.a
cosmos_lemon.menu.ipbtstack.ipv4ipv6.build.libpicowdefs=-DLWIP_IPV6=1 -DLWIP_IPV4=1
cosmos_lemon.menu.ipbtstack.ipv4btcble=IPv4 + Bluetooth
cosmos_lemon.menu.ipbtstack.ipv4btcble.build.libpicow=libipv4-bt.a
cosmos_lemon.menu.ipbtstack.ipv4btcble.build.libpicowdefs=-DLWIP_IPV6=0 -DLWIP_IPV4=1 -DENABLE_CLASSIC=1 -DENABLE_BLE=1
cosmos_lemon.menu.ipbtstack.ipv4ipv6btcble=IPv4 + IPv6 + Bluetooth
cosmos_lemon.menu.ipbtstack.ipv4ipv6btcble.build.libpicow=libipv4-ipv6-bt.a
cosmos_lemon.menu.ipbtstack.ipv4ipv6btcble.build.libpicowdefs=-DLWIP_IPV6=1 -DLWIP_IPV4=1 -DENABLE_CLASSIC=1 -DENABLE_BLE=1
cosmos_lemon.menu.ipbtstack.ipv4onlybig=IPv4 Only - 32K
cosmos_lemon.menu.ipbtstack.ipv4onlybig.build.libpicow=libipv4-big.a
cosmos_lemon.menu.ipbtstack.ipv4onlybig.build.libpicowdefs=-DLWIP_IPV6=0 -DLWIP_IPV4=1 -D__LWIP_MEMMULT=2
cosmos_lemon.menu.ipbtstack.ipv4ipv6big=IPv4 + IPv6 - 32K
cosmos_lemon.menu.ipbtstack.ipv4ipv6big.build.libpicow=libipv4-ipv6-big.a
cosmos_lemon.menu.ipbtstack.ipv4ipv6big.build.libpicowdefs=-DLWIP_IPV6=1 -DLWIP_IPV4=1 -D__LWIP_MEMMULT=2
cosmos_lemon.menu.ipbtstack.ipv4btcblebig=IPv4 + Bluetooth - 32K
cosmos_lemon.menu.ipbtstack.ipv4btcblebig.build.libpicow=libipv4-bt-big.a
cosmos_lemon.menu.ipbtstack.ipv4btcblebig.build.libpicowdefs=-DLWIP_IPV6=0 -DLWIP_IPV4=1 -DENABLE_CLASSIC=1 -DENABLE_BLE=1 -D__LWIP_MEMMULT=2
cosmos_lemon.menu.ipbtstack.ipv4ipv6btcblebig=IPv4 + IPv6 + Bluetooth - 32K
cosmos_lemon.menu.ipbtstack.ipv4ipv6btcblebig.build.libpicow=libipv4-ipv6-bt-big.a
cosmos_lemon.menu.ipbtstack.ipv4ipv6btcblebig.build.libpicowdefs=-DLWIP_IPV6=1 -DLWIP_IPV4=1 -DENABLE_CLASSIC=1 -DENABLE_BLE=1 -D__LWIP_MEMMULT=2
cosmos_lemon.menu.uploadmethod.default=Default (UF2)
cosmos_lemon.menu.uploadmethod.default.build.ram_length=256k
cosmos_lemon.menu.uploadmethod.default.build.debugscript=picoprobe_cmsis_dap.tcl
cosmos_lemon.menu.uploadmethod.default.upload.maximum_data_size=262144
cosmos_lemon.menu.uploadmethod.default.upload.tool=uf2conv
cosmos_lemon.menu.uploadmethod.default.upload.tool.default=uf2conv
cosmos_lemon.menu.uploadmethod.default.upload.tool.network=uf2conv-network
cosmos_lemon.menu.uploadmethod.picotool=Picotool
cosmos_lemon.menu.uploadmethod.picotool.build.ram_length=256k
cosmos_lemon.menu.uploadmethod.picotool.build.debugscript=picoprobe.tcl
cosmos_lemon.menu.uploadmethod.picotool.build.picodebugflags=-DENABLE_PICOTOOL_USB
cosmos_lemon.menu.uploadmethod.picotool.upload.maximum_data_size=262144
cosmos_lemon.menu.uploadmethod.picotool.upload.tool=picotool
cosmos_lemon.menu.uploadmethod.picotool.upload.tool.default=picotool
cosmos_lemon.menu.uploadmethod.picoprobe_cmsis_dap=Picoprobe/Debugprobe (CMSIS-DAP)
cosmos_lemon.menu.uploadmethod.picoprobe_cmsis_dap.build.ram_length=256k
cosmos_lemon.menu.uploadmethod.picoprobe_cmsis_dap.build.debugscript=picoprobe_cmsis_dap.tcl
cosmos_lemon.menu.uploadmethod.picoprobe_cmsis_dap.upload.maximum_data_size=262144
cosmos_lemon.menu.uploadmethod.picoprobe_cmsis_dap.upload.tool=picoprobe_cmsis_dap
cosmos_lemon.menu.uploadmethod.picoprobe_cmsis_dap.upload.tool.default=picoprobe_cmsis_dap

Then inside the variants directory create a folder named cosmos_lemon. Then add a file called pins_arduino.h inside:

variants/cosmos_lemon/pins_arduino.h

#pragma once

// LEDs
#define PIN_LED        (13u)

// NeoPixel
#define PIN_NEOPIXEL   (16u)

// Serial
#define PIN_SERIAL1_TX (0u)
#define PIN_SERIAL1_RX (1u)

// Not pinned out
#define PIN_SERIAL2_TX (31u)
#define PIN_SERIAL2_RX (31u)

// SPI
#define PIN_SPI0_MISO  (20u)
#define PIN_SPI0_MOSI  (19u)
#define PIN_SPI0_SCK   (18u)
#define PIN_SPI0_SS    (17u)

// Not pinned out
#define PIN_SPI1_MISO  (31u)
#define PIN_SPI1_MOSI  (31u)
#define PIN_SPI1_SCK   (31u)
#define PIN_SPI1_SS    (31u)

// Wire
#define __WIRE0_DEVICE i2c1
#define PIN_WIRE0_SDA  (2u)
#define PIN_WIRE0_SCL  (3u)
#define __WIRE1_DEVICE i2c0
#define PIN_WIRE1_SDA  (24u)
#define PIN_WIRE1_SCL  (25u)

#define SERIAL_HOWMANY (2u)
#define SPI_HOWMANY    (1u)
#define WIRE_HOWMANY   (1u)

// D pins
#define __PIN_D4             (6u)
#define __PIN_D5             (7u)
#define __PIN_D6             (8u)

#include "../generic/common.h"

After modifying these files, restart Arduino IDE. You should now see Cosmos Lemon Wired listed as the last option when choosing a board through Tools -> Board -> Raspberry Pi Pico -> Cosmos Lemon Wireled.

Further Documentation

Documentation for older boards, schematics and layout, and more can be found on the Wired Lemon’s GitHub page.