Io patchbox

I/O Patchbox

A 3-channel sensor-to-actor controller designed for Manou Wistoff's approach to phygitale Kunsttherapie, part of her master thesis at Alanus Kunsthochschule.

Building on the concept of phygitale Kunsttherapie, the I/O Patchbox makes the digital tangible by bringing interactive electronics into the physical space. Interactive electronic components become material in the art therapy process, just like clay, paint, or fabric. Through process-oriented creating (Tinkering), clients combine classical crafting materials with sensors and actors connected through the I/O Patchbox, resulting in interactive artworks.

The I/O Patchbox is built on an ESP32-S3 Mini with a custom carrier PCB. Each channel auto-detects its sensor type at boot (ultrasonic HC-SR04 or capacitive touch) and drives an output (LED, motor) proportionally via PWM through a low-side NPN transistor stage.

How it works

• 3 sensor inputs (TRRS jacks) carrying power, trigger, echo, and ground
• 3 actor outputs (TRRS jacks) with 5V PWM low-side switch (2N2222 + flyback diode), load adapted in cable
• Mode switch to enable/disable all outputs and trigger recalibration
• Auto-detect probes each channel for ultrasonic echoes and falls back to touch if none are found
• Ultrasonic: brightness inversely proportional to distance (0-60 cm)
• Touch: brightness proportional to capacitive contact, with adaptive baseline and asymmetric smoothing

Project structure

i-o-patchbox/
├── firmware/
│   ├── esp32s3-mini/            # current target (LOLIN ESP32-S3 Mini)
│   │   ├── src/main.cpp
│   │   ├── platformio.ini
│   │   └── PINOUT.md
│   └── esp32-wroom-dev-board/   # earlier prototype (ESP32 WROOM DevKit)
│       ├── src/main.cpp
│       ├── platformio.ini
│       └── PINOUT.md
├── hardware/                    # KiCad 10 PCB project
│   ├── pcb.kicad_sch             # schematic
│   ├── pcb.kicad_pcb             # board layout (single-sided, home-etched)
│   ├── pcb.kicad_pro             # project file
│   ├── libs/PJ-320A/             # TRRS jack symbol + footprint library
│   ├── gerber/                   # fabrication outputs
│   ├── exports/                  # SVG renders, drill maps
│   ├── backups/                  # KiCad auto-backups
│   └── schaltplan.pdf            # schematic export
└── enclosure/                   # 3D-printable cases (OBJ)
    ├── cable-plug.obj            # cable strain relief (used by all sensors and actors)
    ├── patchbox/                 # main device enclosure
    │   ├── top.obj
    │   ├── bottom.obj

Pin assignment (ESP32-S3 Mini)

Sensors

All sensors connect via 4-pole TRRS jacks (PJ-320D). Wiring: Tip = +5V, Ring1 = TRIG, Ring2 = ECHO, Sleeve = GND.

Each channel auto-detects its sensor type at startup by probing for ultrasonic echoes. If none are found, it falls back to capacitive touch.

Actors

All actors connect via TRRS jacks. Wiring: Tip = +5V (always on), Sleeve = transistor collector (PWM-switched ground). Ring1/Ring2 unused.

The board provides a generic 5V PWM low-side driver per channel (2N2222 + 330R base resistor + 1N4007 flyback diode). The load type is adapted in the device cable with a series resistor, so no board changes are needed to swap between LEDs and motors.

PWM runs at 25 kHz (inaudible for motors), 8-bit resolution (0-255).

Building firmware

Requires PlatformIO.

cd firmware/esp32s3-mini
pio run -t upload
pio device monitor

Hardware

Single-sided carrier PCB designed in KiCad 10 for home etching (toner transfer). All copper on F.Cu, SMD TRRS jacks, THT passives soldered from the top side.

Key components: 3x PJ-320D TRRS jacks (sensor), 3x PJ-320D (actor), 3x 2N2222 NPN transistors, 3x 330R base resistors, 3x 1N4007 flyback diodes.