Sharing a monitor

Like many techies, I have a personal desktop machine that packs a bit of grunt and runs multiple monitors. I also have a company laptop—for me, it’s a Mac (which, to be honest, I’m not a fan of, despite loving my iPhone and iPad).

Like many, my challenge is that when you’re used to two large screens, a laptop monitor just doesn’t cut it. So, I want to share one of the screens between two machines. The question I’ve wrestled with is how to do that with a simple button or key press. No messing with cables, or monitor settings etc.

I initially tried to solve this with a KVM—easy, right? Wrong. It turns out Macs don’t play nice with KVM switches. I went through buying several switches and sending them back before discovering it was a MacBook Pro quirk.

For a while, I used a travel monitor, which I had acquired, to solve the same issue when I traveled extensively for my previous employer. It’s an improvement, but the travel screen is still pretty small, not to mention it takes up more desk space (my main monitors and laptop are all on arms, so I can push them back if I want more desk space).

As most decent monitors allow multiple inputs, we’ve resorted to having two inputs, the only problem is that the controls to switch between inputs aren’t easy to use – but most people don’t need to toggle back and forth several times a day (VPN related tasks are done on the Mac, everything else is the desktop).

But this week, we had a breakthrough, the core of it is finding out about ControlMyMonitor and the VCP features newer monitors have. ControlMyMonitor provides a simple UI tool that allows us to identify an ID for each monitor and a command line capability that generates and sends connected monitor instructions, which allows us to do things like switching input, changing contrast, etc. With the tool we can issues commands such as: ControlMyMonitor.exe /SetValue "\.\DISPLAY2\Monitor0" 60 15. This tells the app for display monitor 2 (as known to my desktop) to send the VCP (Virtual Control Panel) code 60 (change input source) to the input number 15. I can switch the monitor back to the desktop by supplying the input number for the connection to the desktop.

So now I can toggle between screens without feeling around the back of the monitor to navigate the menu for switching inputs. Using a command is pretty cool, but still not good enough. I could put on my desktop links to two scripts to run the relevant command. But I’d also come across AutoHotKey (aka AHK). This allows us to create scripts using AHK’s syntax, which can be configured to work with specific key combinations. So, creating a config file with a key combo to run the command shown made it really convenient. Windows+Shift+Left arrow and the monitor switches to the desktop, Windows+Shift_Right arrow, and it displays the laptop. The script will look something like this:

Requires AutoHotkey v2.0

#+Right::Run "monitor-left.bat"

#+Left::Run "monitor-right.bat"

We could embed the command directly into the AHK script, but the syntax is unusual and would require escaping quotes. By referencing a shell script, we can easily extend the process without needing to master the AHK syntax.

The only remaining problem now is for the AHK app to start when the machine boots up and load the configuration/script when the desktop boots up. We can do this by adding a shortcut the the script file. This can be done by creating a shortcut to our script that the AHK runtime will recognize to run and put that shortcut in the startup folder. The startup folder is likely to be somewhere such as C:\Users\<username>\AppData\Roaming\Microsoft\Windows\Start Menu\Programs\Startup. But we can get a file explorer to open in the right place with the command Windows+R (open the command line option from the Start Menu. Then enter the command “shell:startup“.