Recently I stumbled upon the piKVM project while looking for a KVM-over-IP solution. As I had an unused 1GB Pi 4 lying around, I poked around a little. For controlling the ATX Buttons (power, reset) and showing the LED status (power, disk), the creators used ORMOM G3VM-61A1 solid state relays. They are nice but very expensive, between 8-20 EUR a single piece, depending on where you buy. And you need four of them!

This is a waste of resources, I think. So I made my own little hat for the piKVM project, using four super cheap (0.10 EUR) 4N33 optocouplers. They have a transistor output but can be used easily in this case!
Attached you can find the Gerber files as a ZIP archive, ready for production. Be aware when soldering the parts, the 2×9 pin header has to sit on the bottom side. After all, this has to be plugged in like a hat 🙂

 

pikvm hat – Gerber files