Switch your monitor's input source with a keypress — from a Raspberry Pi that is always on.
A small always-on control device sits on your monitor's HDMI input, speaks DDC/CI, and exposes every control the monitor offers over HTTP, a web UI, and Home Assistant.
Deutsche Fassung · Hardware findings · Writing a monitor profile
Status: usable, not yet released. Everything works and is verified on real hardware — a Samsung Odyssey G9 driven by a Raspberry Pi Zero 2 W, including the Home Assistant integration. What has not been tried is any other monitor.
docs/status.mdis explicit about what is proven and what is not.
Two machines share one monitor. Switching between them means diving into the OSD menu with a tiny joystick behind the panel. Every single time.
The obvious fix is DDC/CI — a standard that lets software tell a monitor to change its input. Except:
- On many monitors DDC/CI simply does not work over DisplayPort. On the Samsung Odyssey G9 this project was built around, the DDC slave does not answer on DP at all. Only HDMI works.
- You cannot switch away from a machine that is switched off. If machine A is showing and machine B is asleep, neither of them can help you.
- Monitors lie about their own capabilities. The G9 reports input source values that are flatly wrong, and its read values differ from its write values.
Put a Raspberry Pi Zero 2 W on the monitor's HDMI input. It runs on 0.4–0.7 W, costs almost nothing, and is completely independent of the machines it switches between.
Because the Pi outputs a real video signal, the HDMI port stops being a sacrifice and becomes a genuine third source — and the most dangerous DDC failure mode (a monitor displaying an input with no signal wedges its DDC engine) disappears structurally.
┌──────────┐ DP1
│ Machine A├──────────┐
└──────────┘ │ ┌─────────┐
├──────┤ Monitor │
┌──────────┐ DP2 │ └────┬────┘
│ Machine B├──────────┘ │ HDMI ← DDC/CI control channel
└──────────┘ │ (and a real third source)
┌──────┴──────┐
│ Pi Zero 2W │ monitor-switch
└─────────────┘
│
┌──────────────────────┼──────────────────────┐
│ │ │
Web UI HTTP API Home Assistant
(any browser) (hotkeys, scripts) (MQTT)
- Switch inputs from a hotkey, a browser, your phone, or a Home Assistant dashboard — regardless of which machine is currently on
- Control everything else the monitor exposes: brightness, contrast, volume, mute, picture mode, colour temperature, RGB gain and black level
- Read what the monitor knows about itself: usage hours, firmware level, refresh rates, power state
- Works with any DDC/CI monitor, not just the one it was built for — every value read and written is defined in a profile you can edit
- Survives monitors that lie — profiles override auto-detection where the capabilities string is wrong
- Never strands you on a blank screen — a guard refuses to switch to the Pi's own input unless the Pi is verifiably outputting video
You need a Raspberry Pi (any model with HDMI) running Raspberry Pi OS, connected to your monitor's HDMI input, reachable over SSH.
git clone https://github.com/DimpiM/monitor-switch.git
cd monitor-switch/ansible
cp inventory.example.ini inventory.ini
cp group_vars/all.example.yml group_vars/all.yml
# edit both: your Pi's address, and which inputs you want exposed
ansible-playbook -i inventory.ini site.ymlThen open http://<your-pi>:8765/ in a browser.
The playbook installs the packages, configures I²C, forces a stable video mode, deploys the service, and refuses to finish if the health check does not answer.
Run this on the Pi once it is connected:
sudo apt install -y ddcutil i2c-tools
BUS=$(basename "$(readlink -f /sys/class/drm/card*-HDMI-A-1/ddc)" | sed 's/i2c-//')
sudo i2cdetect -y "$BUS" | grep '^30:'If 37 appears in that row, your monitor speaks DDC/CI and you are in business. If
only 30 and 50 show up, the monitor exposes an EDID but no DDC/CI on that
connector — try the other inputs, or a different cable.
Details and failure modes: docs/troubleshooting.md.
Auto-detection reads the monitor's capabilities string and builds the feature list from it. That is enough for well-behaved monitors.
It is not enough for the Samsung Odyssey G9, which declares input source values that do not exist and hides the ones that work. So profiles can override anything:
match: { mfg: SAM, model: LC49G95T }
name: Samsung Odyssey G9
features:
input_source:
vcp: 0x60
type: select
options:
# this monitor returns different values than it accepts
- { id: dp1, label: DisplayPort 1, write: 0x0f, read: 0x03 }
- { id: dp2, label: DisplayPort 2, write: 0x10, read: 0x04 }
- { id: hdmi, label: HDMI, write: 0x11, read: 0x01,
guard: local_video }A profile is picked automatically by manufacturer and model from the EDID. If yours
needs one, the probe command walks you through finding the values safely — it
reverts automatically if you do not confirm, so a wrong guess cannot strand you.
Contributing a profile for your monitor is the single most useful thing you can do for this project.
Full guide: docs/profiles.md.
The service announces itself over MQTT discovery. Every control becomes an entity — a dropdown for the input source, sliders for brightness and volume, sensors for the read-only values — and the state stays in sync because the service polls the monitor, not just its own last command.
Setup: docs/home-assistant.md.
| Part | Note |
|---|---|
| Raspberry Pi Zero 2 W | Any Pi works; the Zero 2 W is chosen for 0.4–0.7 W idle draw |
| Mini-HDMI (type C) → HDMI (type A) cable | The classic mistake. The Zero family has mini-HDMI. Micro-HDMI (type D) is the Pi 4 and Pi 5. They look alike and do not fit each other. |
| Power supply | On the PWR port, not the USB data port |
| microSD | Class 10 is plenty |
There is no authentication. The service is meant for a trusted LAN and binds to a
configurable address — not 0.0.0.0 by default. Do not expose it to the internet.
| Hardware findings | Every measurement, every pitfall, and why the design looks like this |
| Monitor profiles | Writing and contributing a profile |
| Home Assistant | MQTT discovery setup |
| Troubleshooting | When DDC misbehaves |
| Project status | What is verified on hardware, and what is not |
Built on ddcutil by Sanford Rockowitz, which does all
the actual DDC/CI work.
MIT — see LICENSE.