Smooth Scroll Wheel

High-resolution rotary scroll wheel using an AS5600 magnetic encoder on a Raspberry Pi Pico RP2040. Emulates a multi-touch trackpad via USB HID for smooth, inertial scrolling on any OS.

Demo

output.mp4

Hardware

• Raspberry Pi Pico RP2040 (earlephilhower core)
• AS5600 Magnetic Encoder with diametric magnet
• I2C Connection: GPIO 4 (SDA), GPIO 5 (SCL)

Wiring

RP2040 Pico    AS5600
----------     ------
GPIO 4     --> SDA
GPIO 5     --> SCL
3.3V       --> VCC
GND        --> GND

Software Setup

1. Install PlatformIO
2. Open this project in VS Code with PlatformIO extension
3. Build and upload to your Pico
4. Connect USB — device enumerates as a trackpad

How It Works

The AS5600 magnetic sensor tracks rotation at 12-bit (4096 position) precision. Instead of sending mouse wheel events, the firmware reports a virtual two-finger swipe on a touchpad HID device. Rotating the encoder moves a simulated finger up/down, which the OS interprets as smooth scrolling.

• Hysteresis noise window — deadband absorbs jitter (no drift when idle)
• Quadratic acceleration — fast spins produce proportionally faster scroll
• Momentum / inertia — velocity decays gradually (configurable friction) for a trackpad-like coasting feel
• Boundary reset — when the virtual finger reaches the trackpad edge, it lifts and re-centers, allowing continuous scrolling

Configuration

Key constants in include/AS5600ScrollWheel.h:

Constant	Default	Description
RESOLUTION	4096	AS5600 ticks per revolution (12-bit)
THRESHOLD	2048	Wrap-around detection midpoint
SCALE	4	Base sensitivity divisor (lower = faster)
NOISE_WINDOW	8	Hysteresis deadband (raw ticks absorbed)
ACCEL_THRESHOLD	4	Movement threshold before acceleration kicks in
ACCEL_DIVISOR	512	Acceleration curve steepness (lower = sharper)
MAX_MOVE	4096	Per-frame displacement safety clamp
MOMENTUM_GAIN	10	Velocity multiplier from raw movement
FRICTION_NUM/DEN	99/100	Velocity retention per frame (99%)
VELOCITY_THRESHOLD	4	Velocity floor — below this, snap to 0
BOUNDARY_LOW	5000	Virtual trackpad Y lower bound (reset point)
BOUNDARY_HIGH	27000	Virtual trackpad Y upper bound (reset point)
TOUCH_CENTER	16384	Y-center of virtual finger

Troubleshooting

• If AS5600 is not detected, check I2C address (default 0x36)
• Ensure the magnet is properly positioned over the sensor
• Verify wiring connections