Fancypants

A two-part system that uses an nRF52840 + VL53L0X time-of-flight sensor to control sex toys through Intiface Engine. "Wave your hand" closer to the sensor for more intensity, pull away to reduce it.

┌─────────────────────┐     BLE      ┌──────────────────┐    WebSocket   ┌─────────────┐
│  fancypants-nrf52   │ ──────────── │  fancypants      │ ────────────── │  Intiface   │
│  Feather nRF52840   │  range_mm    │  Rust middleware │  intensity     │  Engine     │
│  + VL53L0X sensor   │  + battery   │  mapping + EMA   │  ScalarCmd     │  → toy      │
└─────────────────────┘              └──────────────────┘                └─────────────┘

Hardware

• Adafruit Feather nRF52840 Express
• Adafruit VL53L0X Time-of-Flight sensor breakout (I2C, 30-1200mm range)
• LiPo battery (optional, JST-PH connector on Feather)
• Any Buttplug-compatible toy + Intiface Central

Wiring

If your VL53L0X has a STEMMA QT / Qwiic connector, just use the cable. Otherwise:

Feather	VL53L0X
3V	VIN
GND	GND
SDA	SDA
SCL	SCL

The Adafruit VL53L0X breakout includes I2C pullups and a voltage regulator, so no additional components are needed.

Building

Everything builds in containers — no local toolchains needed. Just docker (or podman) and make.

# Build everything
make

# Build just firmware
make firmware

# Build just middleware
make middleware

# Clean all build artifacts
make clean

# See all options
make help

Build outputs land in build/:

build/
├── firmware/
│   └── zephyr.uf2          ← flash this to the Feather
├── middleware/
│   └── fancypants           ← run this on your PC
└── cargo-cache/             ← persistent Rust dependency cache

You can override the NCS version, board target, or container runtime:

make firmware NCS_TAG=v2.7-branch
make firmware BOARD=adafruit_feather_nrf52840/nrf52840/uf2
make CONTAINER=podman

For interactive debugging, drop into a build container shell:

make shell-fw    # firmware (NCS/Zephyr environment)
make shell-mw    # middleware (Rust environment)

Manual builds (without containers)

If you'd rather install toolchains locally:

Firmware — requires nRF Connect SDK (west):

cd firmware
west build -b adafruit_feather_nrf52840

Middleware — requires Rust toolchain + BlueZ dev libs:

cd middleware
cargo build --release

Part 1: fancypants-nrf52 Firmware

Flash

UF2 method (no programmer needed):

1. Connect Feather to USB
2. Double-tap the reset button — FTHR840BOOT drive appears
3. Copy the UF2 file:

cp build/firmware/zephyr.uf2 /run/media/$USER/FTHR840BOOT/
# (or wherever the drive mounts on your system)

SWD method:

west flash

Verify

Connect to the USB serial console:

# Find the USB CDC ACM device
ls /dev/ttyACM*

# Connect (115200 baud, though CDC ACM ignores baud rate)
picocom /dev/ttyACM0
# or
screen /dev/ttyACM0 115200

You should see:

[00:00:00.000,000] <inf> main: Fancypants nRF52 starting...
[00:00:00.050,000] <inf> main: VL53L0X sensor ready
[00:00:00.060,000] <inf> battery: Battery ADC initialized on AIN5
[00:00:00.070,000] <inf> range_svc: Range Service initialized
[00:00:00.200,000] <inf> main: Bluetooth initialized
[00:00:00.210,000] <inf> main: Advertising as "Fancypants"

BLE Protocol

Custom Range Service UUID: 00000001-7272-6e67-6669-6e6465720000

Characteristic	UUID	Properties	Data
Range	...0002...	Read, Notify	uint16_t LE, distance in mm
Config	...0003...	Read, Write	8-byte struct (see below)

Config struct (8 bytes, little-endian):

Offset	Type	Field
0	uint16_t	sample_interval_ms
2	uint16_t	notify_interval_ms
4	uint16_t	max_range_mm
6	uint16_t	min_range_mm

Also exposes the standard Battery Service (0x180F).

Part 2: fancypants Middleware

Prerequisites (runtime only)

• Intiface Central running (https://intiface.com/central/)
• BlueZ (Linux) or equivalent BLE stack

On Arch:

sudo pacman -S bluez bluez-utils
sudo systemctl enable --now bluetooth

Configure

Edit config.toml (or run --generate-config to create a fresh one):

# Generate default config
./build/middleware/fancypants --generate-config

# Edit as needed
$EDITOR config.toml

Key settings:

• mapping.invert = true — closer = more intense (default)
• mapping.min_range_mm / max_range_mm — active zone
• mapping.deadzone_mm — pull away past this to turn off
• mapping.smoothing — 0.3 is a good default, increase for smoother response

Run

1. Start Intiface Central and ensure your toy is connected
2. Power on the Feather (USB or battery)
3. Run the middleware:

./build/middleware/fancypants -c config.toml

# With debug logging:
./build/middleware/fancypants -c config.toml -l debug

What happens

1. Middleware scans BLE for "Fancypants" device
2. Connects and subscribes to range notifications
3. Connects to Intiface Engine via websocket
4. Finds your toy
5. Maps distance → intensity and sends commands at ~20Hz

[INFO] Found device: Fancypants
[INFO] Connected to Intiface Engine at ws://127.0.0.1:12345
[INFO] Using device: We-Vibe Melt 2 (index 0)
[INFO] Running — move your hand near the sensor!

Troubleshooting

"No Bluetooth adapters found"

• sudo systemctl start bluetooth
• Check rfkill list for blocked adapters

"Scan timeout: 'Fancypants' not found"

• Is the Feather powered and running? Check USB serial console
• Is another device already connected to it? (nRF52840 supports 1 connection)
• Try bluetoothctl → scan on to verify the device is advertising

"No Buttplug devices found"

• Open Intiface Central, make sure it's running and your toy is visible
• Check that the websocket port matches config.toml

Sensor reads 0mm or 8190mm constantly

• Check I2C wiring (SDA/SCL not swapped?)
• VL53L0X breakout getting 3.3V power?
• 8190mm typically means "out of range" or no target

Jerky/stuttery toy response

• Increase mapping.smoothing (try 0.5-0.7)
• Increase notify_interval_ms in firmware config characteristic

License

MIT