Show HN: Multi-monitor KVM using just a USB switch

Original Article ↗ Hacker News Discussion ↗

A new open source tool, SimpleKVM, lets users pair a cheap USB switch with DDC monitor commands to flip keyboard, mouse and display between machines without buying a full hardware KVM. Commenters compare it to software solutions like Synergy/Barrier and to dedicated KVMs or monitors with built‑in KVMs, weighing cost, reliability, OS support (especially with locked‑down work laptops and VPNs), and high‑refresh or multi‑monitor requirements. The broader conversation highlights how surprisingly hard it still is to get seamless, high‑quality multi‑computer setups, with many people resorting to bespoke combinations of USB switches, DDC scripts, Thunderbolt docks and specialty KVM gear.

What SimpleKVM Does

  • Uses a cheap USB switch plus DDC monitor commands to simulate a KVM.
  • Each machine has its own direct video cable to the monitor; the USB switch only moves keyboard/mouse.
  • On Windows, the software detects USB device plug/unplug and switches monitor input accordingly.
  • For two PCs, it can run on only one machine: “USB added → switch to this machine; USB removed → switch to the other.”
  • Currently Windows-focused; people ask for Linux/macOS support and note some setups don’t work reliably.

Comparison to Software KVMs (Synergy, Barrier, etc.)

  • Software KVMs let each machine keep its own monitor(s) and share keyboard/mouse over the network.
  • Some prefer Barrier/input-leap/Synergy for copy-paste and multi-monitor freedom.
  • Others cannot install such tools on locked-down work laptops or over VPN, so SimpleKVM’s “run only at home” model is appealing.

Monitor Control & DDC Issues

  • Many users already script DDC/CI (e.g., via ddcutil, display-switch, vendor tools) to change inputs and brightness.
  • HDMI often accepts DDC commands even when not the active input; DisplayPort often does not.
  • DDC support is inconsistent across monitors and through some KVMs/docks; some setups fail or are flaky.

Hardware KVMs, USB Switches, and Built‑in KVMs

  • High-quality 4K/120Hz+/multi-monitor KVMs are expensive; cheap ones are often unreliable or limit resolution/refresh/EDID.
  • Many users instead:
    • Use a “dumb” USB switch plus manual input selection on the monitor.
    • Rely on monitors with built-in KVM and/or PBP (picture-by-picture).
    • DIY mechanical USB switches or custom PCBs to avoid HID quirks and latency.

Compatibility, OS, and Edge Cases

  • Mac support with KVMs and DDC is frequently problematic; sleep, window rearrangement, and brightness control are recurring complaints.
  • Some praise Level1Techs and a few other brands for EDID emulation and stability, but costs are high and DP 1.4 + EDID is rare.
  • Thunderbolt/USB‑C switching is possible but often slow, fragile, or tied to pricey hardware.
  • A niche but discussed use: KVM-over-IP (e.g., PiKVM) to appear “local” for employers or to keep monitored work laptops untouched.