Pico USB Keyboard

🇩🇪 Deutsche Anleitung: README.de.md

Your phone as a USB keyboard – with nothing but a Raspberry Pi Pico 2 W and a USB cable. The Pico talks to the Blue-64 Keyboard app (iPhone and Android) via Bluetooth LE and shows up as a normal USB keyboard on the computer it is plugged into. No soldering, no wiring, no driver.

Get the app: iPhone – TestFlight beta · Android – APK in the latest release

Handy wherever a full keyboard is too much: a MiSTer, a Raspberry Pi, a media PC, an emulator like VICE, quick input on the go.

Two modes

The app shows a C64 / PC switch when it is connected to a Pico USB Keyboard.

PC mode – a normal PC or Mac keyboard in the app:

• Layouts: US, German (PC), German (Mac), US (Mac) – set the same layout on the computer
• Ctrl, Alt, Win / Cmd, AltGr / Option, Esc, F1–F12, Del, cursor keys, Caps Lock, up to 6 keys at once
• Modifier keys: tap = for the next key, double tap = locked, tap again = off
• While Shift / Option / AltGr is active the keys show the character that will be typed
• Text and snippets are typed with the chosen layout (umlauts, @ € { } [ ] \ | ~ included); the app keeps separate snippets for C64 and PC

C64 mode – the C64 keyboard of the app, made for the MiSTer C64 core. The C64 keys are sent as the PC keys the core expects, so every C64 key works – also with SHIFT and C=:

C64	PC key	C64	PC key
RUN/STOP	Esc	RESTORE	F11
C=	Tab	CTRL	left Ctrl
£	\	←	`
↑	F9	=	End
@	[	*	]
:	;	;	'

Digits 1–5 go via the keypad, 6–0 via the main row (the core ignores keypad 6–0 and remaps SHIFT + digit for a US layout – the firmware takes this into account).

Getting started

1. Flash the firmware – hold BOOTSEL on the Pico 2 W, plug it into a computer, drag pico-usb-keyboard-vX.Y.Z.uf2 from the latest release onto the RP2350 drive.
2. Plug the Pico into the computer / MiSTer you want to type on.
3. Open the app – it finds Pico USB Keyboard by itself. LED blinking = waiting, LED on = connected. Two devices (e.g. iPhone and iPad) can be connected at the same time; their keys are combined like two keyboards on one computer.
4. Choose C64 or PC at the top, and in PC mode the keyboard layout.

Mac: macOS may open the "Keyboard Setup Assistant" the first time – close it. The firmware already takes care of the two keys macOS swaps on unknown keyboards.

Debug output (optional): UART0 on GP0 (TX) / GP1 (RX), 115200 baud.

Case (3D print)

A small retro-style case with the 1MHz.de logo – files in case/:

File
top-numpad-statusbar.stl	top with number pad and frame around LED / BOOTSEL (as in the photo)
top-numpad.stl / top-statusbar.stl	the two other variants
bottom.stl	bottom plate (same for all variants)
pico-usb-keyboard-case.scad	OpenSCAD source (variant = "numpad" / "status" / "both")

• Parts: Raspberry Pi Pico 2 W without pin headers, 4 × self-tapping screws M1.7 × 10 (× 8 works too), 4 self-adhesive rubber feet Ø 8 mm (optional)
• Printing: PLA or PETG. Bottom plate flat. Top open side down with supports "on build plate only" (for the sloped roof). 0.2 mm layers work; 0.08 mm gives a much nicer logo and keys.
• Assembly: put the Pico upside down into the top – the ribs centre it –, put the bottom plate on and screw both together through the Pico's four mounting holes.
• The LED shines through the small hole; BOOTSEL can be pressed through the larger one with a paper clip (firmware update without opening the case).

Inside	Bottom

Changing the case: OpenSCAD (the 1MHz.de lettering uses the font Liberation Mono Bold).

Bluetooth protocol

Same service as Pico64 Keyboard and the BT-64 BLE keyboard extension (C64B0001-B1E6-4A64-9C64-6B7E3F1A2D00), so the app works with all three. Additions for the PC mode:

Characteristic	Content
C64B0006	USB key state [modifiers, key1 … key6] (USB HID usage IDs), write / write without response
C64B0007	PC text [flags, layout, UTF-8 …], flags bit0 first / bit1 last chunk, layout 0 US, 1 DE (PC), 2 DE (Mac), 3 US (Mac)
C64B0004	info byte 2 (capabilities): bit0 full matrix, bit1 USB key states, bit2 PC text

The C64 characteristics (C64B0002 key, C64B0003 text, C64B0005 full matrix) are described in the Pico64 protocol.

Building

Pico SDK 2.2.0 with the tinyusb submodule (git submodule update --init lib/tinyusb), ARM GCC, CMake:

cd firmware
cmake -S . -B build && cmake --build build      # -> build/pico-usb-keyboard.uf2

hid_out.c turns the C64 key states into USB HID reports, pc_keys.c handles the PC mode. The key scheduler (keys.c) and the text feed (textfeed.c) come from Pico64 Keyboard.

USB ID

The Pico USB Keyboard has its own USB ID 1209:C64B, assigned by pid.codes (from v0.4.2; earlier versions used the test ID 1209:0001).

License

Firmware and documentation: MIT – see LICENSE and NOTICE. Case (folder case/ and the photos): CC BY-NC-SA 4.0 – see LICENSE-CASE.md. Made by Martin Oswald (do2mad) – 1mhz.de.