Sounds very useful to anyone using a PC that predates PS/2 or USB. I use an optical PS/2 mouse with a KVM though, so not much use for me. Well done for starting this project though, amd especially for making it open source.

Thanks for the feedback!
If you use a PS/2 mouse, you might be interested in checking out my related project.
It’s a replica of an ISA adapter for a PS/2 mouse, which the system recognizes as a UART-based serial mouse:
https://github.com/Yftul/ps-2-mouse-to-isa-replica

the usb controller in this card offloads the work from the cpu? because even on a k6-2 the usb is a resource hog when in use

Yes, this controller is completely equivalent to a serial mouse and does not burden the processor with the complexities of USB implementation.

Card looks nice. Slightly off topic, but it looks a little strange when the isa contact pads are perfectly rectangular. They always used to have a semi circular top back in the day. Was there a reason for that?

Yes, it’s using the standard ISA connector footprint from KiCad.

This is great! I had an idea in my mind something like this a while ago, but I don't know anything about FPGA/CPLD... 🙁

But isn't that Altera CPLD an obsolete part? You can't buy it new anywhere - only found on eBay, AliExpress, etc. Such sources are... questionable, with good chance of being ripped off with fakes and bad parts.

It is mentioned here that ATF1504AS might be usable, but I haven’t verified it.

Yeah, the Atmel parts are usable. There even is a progarm to convert the Altera POF into Atmel format to burn on the Atmel parts.

Improved compatibility.

Yftul wrote on 2025-12-07, 08:52:

It is mentioned here that ATF1504AS might be usable, but I haven’t verified it.

Might be? Verified? I literally used it, so did other people. It works fine

Thanks for confirming! This will definitely help others who want to repeat the device.

USB PC brackets are inexpensive. Found this one with 2x USB cut outs, but the board would need a redesign.

https://au.mouser.com/ProductDetail/Keystone- … 3gsWPoKdg%3D%3D

MikeSG wrote on 2026-02-22, 14:03:

USB PC brackets are inexpensive. Found this one with 2x USB cut outs, but the board would need a redesign.

https://au.mouser.com/ProductDetail/Keystone- … 3gsWPoKdg%3D%3D

There are even cheaper ones available at Aliexpress. But does anybody know where to get brackets with just one USB A hole in it? I wasn't successful in finding those for my own converter project, so I had to just to make a hole to a solid bracket.

Did you try to reproduce my project, or were you working on another one? If it was mine, I would like to know if you had any issues during the reproduction.

Yftul wrote on 2026-02-23, 08:58:

Did you try to reproduce my project, or were you working on another one? If it was mine, I would like to know if you had any issues during the reproduction.

I'm working on my own PS/2 to serial converter project. While there are already several similar projects, they all seem to be external so I decided to do it myself. I decided to use USB A connector instead of mini DIN 6, as it's easier to find an USB mouse with PS/2 support than a PS/2 only mouse, so I ran into same issue.

Internal PS/2 to serial mouse adapter

https://github.com/Yftul/ps-2-mouse-to-isa-replica

You might be interested in this project.

Boards and BOM:
Re: Another PS/2 Mouse ISA (ISA8) card adapter

Yftul wrote on 2026-02-23, 11:34:

https://github.com/Yftul/ps-2-mouse-to-isa-replica […]
Show full quote

https://github.com/Yftul/ps-2-mouse-to-isa-replica

You might be interested in this project.

Boards and BOM:
Re: Another PS/2 Mouse ISA (ISA8) card adapter

Thanks for the link. That's an interesting project, but I have already completed my own converter and so far it seems to work well with the mice I have. 😀

I'm planning to publish my project after I have done some more testing, as some people have mentioned they have had problems with KVM switches with similar projects. It only uses an ATtiny and doesn't have SMD components, so maybe it will be useful to some people.