PenSync: Turn Your Android Tablet into a Pro Windows Drawing Tablet

PenSync is an open-source tool that transforms any Android tablet with an active stylus (like the Moto Pad 60 Pro, Samsung Galaxy Tab S-series, etc.) into a professional digital art graphics tablet for Windows PC. It acts as an input-only drawing surface, similar to a Wacom or Huion pen tablet (without screen mirroring), offering ultra-low latency, tilt support, 8192 levels of pressure sensitivity, and customizable express keys for creative software like Photoshop, Krita, and Blender.

Part	Path	What it is
Windows app	windows/src/PenSync.App	Elevated WPF control panel and host: pairing, USB/Wi-Fi, pen settings, mapping, express keys, driver status, tray icon
Core library	windows/src/PenSync.Core	Protocol v2, crypto, host runtime, pen pipeline, HID report encoder (UI-free, fully unit-tested)
Pen driver	windows/driver/penvhf	KMDF + VHF virtual HID pen (pressure 8192 levels, X/Y tilt, eraser, barrel)
Android app	android/tablet	Pairing, USB/Wi-Fi connection, low-latency stylus capture, express-key panel
Diagnostics	windows/src/PenSync.HostCli, android/diagnostic	Headless test host; Phase-0 capability probe

Quick start

1. PC (administrator PowerShell, from the repo root):

   dotnet publish windows\src\PenSync.App -c Release -o windows\dist\PenSync
   powershell -ExecutionPolicy Bypass -File windows\setup.ps1 -Launch

   This installs the app and the driver. The first run enables test mode: reboot and run it again. See docs/driver-install.md.
2. Tablet: install android/tablet/app/build/outputs/apk/debug/app-debug.apk and enable USB debugging.
3. Pair: connect the USB cable, click Pair new tablet in PenSync on the PC, then tap Pair with this PC on the tablet. Accept only if both screens show the same 6-digit code.
4. Draw. PenSync reconnects automatically next time; tap Connect.

USB vs Wi-Fi

• USB (via adb reverse) gives the lowest and most stable latency.
  • USB 2 versus USB 3 makes no difference: a pen produces about 30 KB/s.
  • Use any good data cable.
• Wi-Fi: enable it on the PC's Connection page. It is restricted to Private networks and the local subnet.
  • Pen data uses encrypted UDP with redundancy, so a lost packet does not stall a stroke.
  • Expect a few extra milliseconds and occasional jitter.

Security

• Every connection, USB included, is mutually authenticated (ECDSA P-256) and encrypted (AES-256-GCM).
• Only paired tablets connect.
• Pairing requires the PC user to open a 2-minute window and both users to confirm a matching code.
• Express keys send only a key number; the PC decides what each key does.

Details: ADR-003 and ADR-004.

Documentation

• docs/HANDOFF.md: build, test, architecture, status and known limits (start here)
• docs/protocol-v2.md: normative wire protocol
• docs/driver-install.md: driver signing and installation
• docs/architecture/: ADR-001 to ADR-005
• docs/research/: Phase-0 hardware findings