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KVM Tutorial 01 — Getting Started

Audience: Beginners — first-time users of Openterface KVM devices

1. What Is a KVM-over-USB?

A KVM (Keyboard, Video, Mouse) device sits between your host computer (your workstation) and a target computer (server, mini PC, embedded device). It:

  • Captures the target's HDMI video output (and audio, if available)
  • Relays your keyboard and mouse input through HID emulation
  • All over a single USB cable — no network required

This is what sets KVM devices apart from remote desktop software: you can control the target even in BIOS/UEFI, during boot, or when the OS has crashed.

Openterface KVM Devices

Device Form Factor Key Feature
Mini-KVM Compact USB dongle Desktop KVM-over-USB
KVM-Go Toolkit-style portable On-the-go KVM with built-in cables
uConsole KVM Extension Internal module Built-in KVM for ClockworkPi uConsole

Looking for KeyMod (keyboard & mouse emulator only, no video)? See the KeyMod Tutorial.

2. What You Need

Hardware

  • Openterface KVM device — Mini-KVM, KVM-Go, or uConsole KVM Extension
  • Host computer — Running macOS, Windows, Linux, or Android
  • Target computer — Any computer with HDMI output
  • HDMI cable — From target's HDMI output to the KVM's HDMI input
  • USB cable — From KVM to your host computer (provides both power and data)

Optional

  • USB switch cable — From KVM to the target device's USB port (for keyboard/mouse emulation)
  • Keyboard and mouse — Plug into the KVM's USB switchable port to control either host or target

3. Installation

Host Application

Platform Application Download
macOS Openterface for macOS App Store or DMG
Windows Openterface QT GitHub Releases
Linux Openterface QT Flatpak, .deb, .rpm, AppImage
Android Openterface for Android Google Play or GitHub Releases

Android Requirements

The Android app requires:

  • Android 8.0 (API 26) or later
  • USB OTG support — most modern phones support it (Samsung, Google Pixel, OnePlus). Verify by connecting a USB flash drive with an OTG adapter
  • USB OTG cable or adapter to connect the KVM device to your phone

macOS Permissions

On first launch, macOS will request:

Permission Why
Camera Captures video from the HDMI capture chip
Microphone Captures audio from the target (if enabled)
Accessibility Required for HID mouse control in Relative mode

Linux Permissions

  • Add your user to the dialout and video groups: sudo usermod -a -G dialout,video $USER
  • Install udev rules for device access
  • BrlTTY conflict: Remove brltty or blacklist the serial chip — see Troubleshooting

Windows

  • The installer bundles the CH340 serial driver. For portable builds, install it separately.

4. Connecting the Hardware

Text Only
┌─────────────┐                        ┌──────────────────┐
│   TARGET    │─── HDMI cable ────────▶│  Openterface     │
│  COMPUTER   │                        │  KVM Device      │
└─────────────┘                        │                  │
                                       │  ◄── USB cable ──│── USB switch cable ──▶ Target USB port
                                       └──────────────────┘
                                                │
                                                ▼
                                       ┌──────────────────┐
                                       │   HOST COMPUTER  │
                                       │  (this app)      │
                                       └──────────────────┘
  1. Connect the target's HDMI output to the KVM's HDMI input
  2. Connect the KVM's USB to a USB port on your host computer
  3. (Optional) Connect the USB switch cable from the KVM to the target's USB port
  4. (Optional) Plug your keyboard/mouse into the KVM's USB switchable port
  5. Power on the target device

Device Detection

The KVM enumerates as multiple USB devices: - Video capture (MS2109/MS2109S/MS2130S) — appears as a webcam - Serial (CH9329 or CH32V208) — /dev/ttyUSB* (Linux), COM* (Windows), cu.usbserial-* (macOS) - HID — used for firmware operations

Connecting via Android Phone

When using the Android app, the connection chain uses USB OTG:

Text Only
┌──────────────┐     HDMI      ┌──────────────────┐
│              │ ────────────▶ │   Openterface     │
│  Target PC   │               │   KVM Device      │
│  (screen)    │ ◀─────────── │                   │
│              │     USB       │                   │
└──────────────┘               └────────┬─────────┘
                                        │
                                   USB OTG
                                        │
                               ┌────────▼─────────┐
                               │  Android Phone    │
                               │  (Openterface)    │
                               └──────────────────┘

Connection order for Android:

  1. HDMI: Connect target's HDMI output to the KVM's HDMI input
  2. USB (target): Connect target's USB port to the KVM's USB port — carries mouse/keyboard signals
  3. USB OTG (phone): Connect the KVM to your Android phone via USB OTG cable/adapter
  4. Power: Power on the KVM device (if separate power input) and the target computer

When connected successfully, the video preview switches from a placeholder to the target's live screen, and tapping the phone screen moves the cursor on the target.

5. First Launch

The Main Window

Text Only
┌─────────────────────────────────────────────────────────┐
│  Menu Bar / Toolbar                                     │
├─────────────────────────────────────────────────────────┤
│                                                         │
│              VIDEO DISPLAY AREA                          │
│         (shows target device screen)                     │
│                                                         │
├─────────────────────────────────────────────────────────┤
│  Status Bar │ Port │ Keys │ Mouse │ Resolution │        │
└─────────────────────────────────────────────────────────┘

Android Permissions

On first launch, the Android app requests:

Permission Why What Happens If Denied
USB Host Communicate with the Openterface hardware App can't detect your KVM device
Camera Receive video from the HDMI capture chip No video preview
Storage Save screenshots and recordings Can't save captures

Grant all permissions for full functionality. A system USB permission dialog also appears when the KVM device is detected — tap Allow.

Verifying Connection

  • HDMI indicator: green = signal detected, orange = no signal, gray = unknown
  • Keyboard indicator: green = connected, orange = not found, gray = unknown
  • Mouse indicator: green = connected, orange = not found, gray = unknown
  • Serial port: should show a port name and baud rate (9600 or 115200)

If indicators show orange or gray, see Troubleshooting.

6. Basic KVM Control

Mouse Modes

Mode Description Best For
Absolute (default) Host cursor maps directly to target screen General use, GUI navigation
Relative (HID) Mouse movements sent as deltas via HID Gaming, fast-paced interaction

Switch via the toolbar toggle or Control > Mouse Mode.

Keyboard Input

All keystrokes are forwarded to the target whenever the app window is focused: - Standard keys, function keys, modifiers - Special keys: Ctrl+Alt+Del, Print Screen - Paste to Target: Sends clipboard text as emulated keystrokes

USB Switching

Toggle the USB switchable port between: - Host — your keyboard/mouse controls the host computer - Target — your keyboard/mouse controls the target computer

7. Next Steps