feldd

feldd turns the Teenage Engineering SP-1 into a configurable MIDI and keyboard controller. Its 4 faders and 9 buttons become fully remappable over USB and 3.5 mm TRS MIDI, set up entirely from your browser.

The SP-1 is an unreleased TE device. This is unofficial community firmware, not affiliated with or endorsed by Teenage Engineering.

Latest firmware: v0.27.3 (stable) (get it at feldd.com). Beta in soak: v0.28.0-beta — MIDI thru (forward USB-in MIDI out the 3.5mm TRS jack, a USB-to-TRS bridge), on the ?beta=1 link.

New in 0.27: Bluetooth. feldd reprograms the SP-1's built-in radio, in place from the browser, into a wireless BLE-MIDI controller and a Bluetooth keyboard, turn it on with •• + PLAY and pair with a phone, laptop, or iPad, no cable. (0.24 added MIDI clock; PLAY is a normal mappable button.)

What it does

• 🎛️ 4 faders + 9 buttons → MIDI, map any control to any CC or note, each on its own channel; a button can also send a value you pick (set-on-press, momentary, or toggle)
• ⌨️ Keyboard mode, buttons can type keys and shortcuts (Cmd+C, Cmd+Z) so it drives any app, not just music software
• 🎵 Chords + note-sets on any button, build a chord per button as a hand-picked set, a root and quality, or a range for an M8 cluster, one press fires the whole set
• 🪜 8 layers per profile, hold PLAY to shift to a layer you pick (the side light follows), or flip PLAY to a normal mappable button
• 💾 8 profiles per mode on the device, step them live with •• + Vol, no computer needed
• 🎚️ •• is the function button, hold it and tap a control to step layers or profiles, flip MIDI/Keyboard mode, or reach the utility row (battery, LED brightness, MIDI panic); hold •• to peek your profile
• 🏷️ Name your controls, per-control labels save with your .feldd file so a shared profile explains itself
• 🎹 USB-MIDI 1.0 + TRS (3.5 mm) MIDI out, drives your DAW or your hardware
• 📶 Wireless Bluetooth (BLE-MIDI + keyboard), feldd reprograms the SP-1's onboard radio from the browser so it pairs with a phone, laptop, or iPad with no cable (0.27+)
• 🔌 Configure live in the browser, read, edit, write, and watch your controls move in real time over USB

Use it, all in the browser, no app to install

→ feldd.com

• Configure your SP-1, map the faders + buttons, manage your 8 profiles, and watch them fire live. (Chromium browser, uses WebSerial.)
• Flash the firmware, a guided walkthrough using the community Solderless tool.

Flash once, then configure and reconfigure from the browser whenever you like.

What's not in this repo

feldd's Bluetooth radio firmware is deliberately not open-sourced here. Getting the SP-1's onboard radio (a Cypress/Infineon CYW20706) to speak Bluetooth means loading a compiled radio image onto it, and that image plus the vendor's download minidriver are not ours to redistribute as source. So the following are intentionally omitted from this tree:

• firmware/app/src/cybt_blobs.h — the CYW20706 payloads (the vendor download minidriver + our compiled BLE-MIDI app image for the radio). Vendor-derived binaries, not our source to publish.
• firmware/app/src/bt_provision.*, bt_download.*, bt_probe.* and the rest of the radio-flashing subsystem, which embeds and depends on that image.
• The Bluetooth build overlays and their host tests.

The controller firmware in this repo builds and runs completely without any of that. The Bluetooth feature itself is fully written up in bluetooth/ (architecture, how the reflash works, findings), and the flashable Bluetooth build — the one that includes the radio image — is the public download at feldd.com. A few build files (CMakeLists.txt, Kconfig, config_cdc.c) still carry the conditional hooks that reference the omitted sources; they compile out by default.

🤖 Claude Code console (feldd-cc)

Turn the SP-1 into a physical console for Claude Code: the track lights show when an agent is working / needs you / done, and the buttons drive the session (Play = approve, rocker = scroll). It's a small local daemon plus Claude Code hooks, talking to feldd's led verb (shipped in 0.16.0-beta) and its button monitor stream over USB. Setup is itself a Claude Code task — point your agent at feldd-cc/ and have it follow feldd-cc/SETUP.md. The led verb + monitor stream are hardware-validated.

⚠️ Flashing safety

You're modifying an irreplaceable device. feldd links above the TE bootloader (0x20000) and keeps the Track 1 + 4 DFU escape hatch plus a charge-standby gate, so a bad flash is recoverable by re-flashing the known-good sp1_looper.bin. Read the warnings on the flash page before you start.

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Building from source

Most people never need this, just use feldd.com. This section is for developers who want to build or fork the firmware.

feldd is a Zephyr / nRF Connect SDK app for the nRF52840 inside the SP-1.

• Set up the toolchain + west workspace: scripts/setup-zephyr-ws.sh
• Get the sp1 board definition from the marisko project and point BOARD_ROOT (in scripts/fw.sh) at it
• Build: scripts/fw.sh build · flashable image: scripts/fw.sh bin · vector-table/size check: scripts/fw.sh info
• scripts/sp1ctl.py, host CLI for the JSON-lines config protocol; firmware/test/, pure-logic tests (cd firmware/test && make)
• Protocol + packed profile format: scripts/sp1-profile-format.md

Credits

• Solderless, the flash + stem-loader tools that make SP-1 hacking possible
• Tim Knapen / SP-1-dev, SP-1 developer docs + wiki
• marisko, the sp1 Zephyr board definition
• Eric Lewis / sp1-midi, gold-standard nRF52 BSP + boot-safety reference

License

MIT, see LICENSE. Dependencies (Zephyr, the board definition, etc.) under their own licenses.