Help With Auto-Switch KVM: DIY USB Switching When Monitors Outpace KVMs

Is your monitor outpacing your budget for a KVM switch? With 4K and high refresh rates becoming normal, even basic multi-device setups can lead to some sticker shock. If you want to plug both your PC and laptop directly into your monitor—and have your USB devices follow along automatically—there’s a clever workaround that doesn’t cost $570.

Why Standard KVM Switches Don’t Always Cut It

Most affordable KVM switches just can’t handle modern monitors that need tons of bandwidth. If you’ve checked prices for a high-spec HDMI or DisplayPort KVM lately, you know they’re far from cheap. But if you’re happy to use your monitor’s built-in input switch and only need your keyboard and mouse to follow along, you’re halfway there.

That’s where a USB-only KVM comes in. These little boxes let you swap your USB devices between computers with a button press—but you still have to hit two buttons every time you want to switch setups. Wouldn’t it be better if the USB switch happened automatically when you changed your monitor input?

Building an Auto-Switch KVM with a Raspberry Pi Pico

The core idea is simple: when you flip your monitor’s input from PC to laptop (or vice versa), a tiny computer like a Raspberry Pi Pico notices—and then “presses” the button on your USB KVM for you.

Here’s the basic approach:

• Use an HDMI breakout board to tap into the SCL and SDA lines between the laptop and monitor.
• Connect these lines to a Raspberry Pi Pico’s GPIO pins, adding 1k ohm resistors for current protection.
• Add 100k ohm resistors from the GPIO pins to ground to prevent floating signals.
• Control a solid-state relay (SSR) with the Pico to simulate the KVM’s momentary button press.
• Wire NO (Normally Open) and COM (Common) contacts of the SSR across the physical button terminals on the USB KVM.

When you switch inputs on your monitor, the Pico detects which device is active based on activity on the SCL/SDA lines. If it sees that you’ve switched to your laptop, it sends a quick pulse through the relay—just like pressing the button by hand.

Safety Tips for Your DIY Auto-Switch KVM

Mixing electronics between expensive computers and monitors can feel risky. Here are some tips for keeping everything safe:

• Add current-limiting resistors: The 1k ohm resistors protect your Pi from accidental voltage spikes on the HDMI lines.
• Use pull-down resistors: The 100k ohm resistors make sure your GPIO pins aren’t left “floating,” which could cause weird behavior.
• Double-check relay wiring: Make sure NO and COM are in the right direction so you’re not accidentally shorting anything weird inside the KVM.
• Test with a multimeter: Before plugging in your computers, use a multimeter to confirm there are no unexpected voltages between any pins.
• Consider HDMI surge protectors: Devices like HDMI surge protectors can help protect against accidental surges—think of them as “condoms” for your expensive ports.

For extra peace of mind, unplug everything before making changes and start with cheap test hardware if you can.

Will This Auto-Switch KVM Design Actually Work?

In theory, yes! Many users have successfully built similar projects using microcontrollers and relays. The key is that most button switches (like those on basic USB KVMs) are just momentary contacts—the relay simply mimics a human finger.

A few things to keep in mind:

• Make sure your relay is rated for low voltages—usually 5V is safe for USB devices.
• If you’re unsure about polarity or voltage on the button terminals, measure carefully before connecting.
• You don’t need to connect NC (Normally Closed) if the button only uses NO and COM.
• Monitor SCL/SDA tapping is low risk, but always use proper resistors and avoid cheap cables that could introduce shorts.

If you want more technical background on using relays with Raspberry Pi Pico GPIOs, check out resources like Raspberry Pi’s official GPIO documentation.

A Quick Anecdote: Overengineering for Fun (and Maybe Learning Something New)

A lot of folks ask if it’s really worth building an auto-switch KVM just to save one button press. The truth is, sometimes “solving” little inconveniences is half about convenience and half about curiosity. If you’re already bored and tinkering with microcontrollers, this project can give you hands-on experience with GPIOs, relays, and even some light electrical safety.

And if everything goes wrong? That’s where surge protectors and careful testing come in handy. Just remember—sometimes overengineering is just another word for having fun with tech.

Could This Solution Be Even Simpler?

There are always new ways to simplify or automate home office setups. If you’ve tried something similar or have tips for protecting delicate electronics while hacking together convenience features, what would you add or change in this DIY auto-switch KVM design?