PHysical Optical Tracking of Notes system

PHOTON is a modular, open-source optical sensing platform for high-resolution key and motion tracking. Each module combines a KiCad-designed linear array of VCNT2025X01 reflective sensors, TLA2518 high-speed SPI ADCs, and an RP2350 MCU. Modules can run standalone over USB-C or daisy-chain over RS-485 for large sensing surfaces.

• Sensors: VCNT2025X01 reflective array with per-sensor enable lines
• Digitization: TLA2518 SPI ADCs for high-speed readout
• MCU: RP2350 (dual-core Cortex-M33)
• Comms: THVD1424 RS-485 transceivers; main board includes RS-485 bias resistors and controllable termination
• I/O: USB-C (power + USB-MIDI/CDC), QWIIC/I2C expansion
• Open: KiCad 9 hardware, CircuitPython or C SDK firmware

• Single-sensor distance measurement in excess of 1 kHz
• Full 30-sensor scan (per board) around ~250 Hz

• Sensor boards: VCNT2025X01 array -> TLA2518 SPI ADCs -> RP2350
• Main board: RP2350 + THVD1424 RS-485 + bias resistors + termination control
• Bus: RS-485 differential, terminated at endpoints

See hardware/README.md for board-specific notes and layout sources.

Hardware

• PHOTON module(s)
• USB-C cable
• JST-SH 4-pin cables (1.0 mm pitch, reverse/opposite direction; QWIIC-compatible)

Software

• CircuitPython UF2 for RP2350 (custom build recommended)
• KiCad 9 (download: https://www.kicad.org/download/)
• DAW or MIDI viewer (Pianoteq, Ableton Live, Reaper, Max/MSP, etc.)
• Embedded software notes: see software/embedded_software/README.md

1. Hold USB-BOOT (or short USB-BOOT jumper) and connect via USB-C.
2. Copy the RP2350 CircuitPython .uf2 to the mounted drive.
3. Copy code.py and libraries to the CIRCUITPY drive.

• Firmware is primarily in CircuitPython; the RS-485 data path uses a C native module for low latency.
• Related repo: https://github.com/w4iei/klavecimbelcircuitpython

@article{photon2026,
  title       = {PHOTON: Non-Invasive Optical Tracking of Key-Lever Motion in Historical Keyboard Instruments},
  author      = {Noah Jaffe and John Ashley Burgoyne},
  journal     = {TBD},
  year        = {2026},
  doi         = {TBD},
}