Ask HN: Advice for creating a USB device linking 2 computers • Hacker News Board

Re: Ask HN: Advice for creating a USB device linking 2 computers

#41

Post by Someone » Sun, Oct 26, 2025, 7:50 AM UTC

> I want to build a little device that connects two computers together via usb, and send keystrokes from one to the other.

> (I would use it to use a laptop keyboard on a headless computers).

Are you sure you need such a device? If this is to occasionally manage that headless system, wouldn’t a Remote Desktop connection work fine?

You’re mentioning a Mac Mini and a MacBook elsewhere, so https://support.apple.com/en-gb/guide/remote-desktop/apdf49e... might be sufficient for your needs.

Re: Ask HN: Advice for creating a USB device linking 2 computers

#42

Post by WorldDev » Sun, Oct 26, 2025, 9:09 AM UTC

saulrh wrote: post #39

saulrh wrote: post #14

I believe the search keyword for what you're looking for is probably "IP KVM".

You know, looking back at this eight hours later, I realize that this post sounds way worse than I intended. I was attempting to signal my own epistemic uncertainty, not imply sarcastic dismissal. Sorry. :/

No problem at all, I didn't interpret it as sarcastic.

Re: Ask HN: Advice for creating a USB device linking 2 computers

#43

Post by eimrine » Mon, Oct 27, 2025, 5:34 PM UTC

ruslan wrote: post #37

Get two FTDI FT232RL chips, connect them together on serial side (RXD->TXD, TXD->RXD, GND GND). Plug into USB ports of your computers, run terminals (or any other software that supports serial I/O), send/receive data. Can use XYZModem to send files, PPP for TCP/IP networking, etc. No programming involved. Cheap as hell.

Are there any options to connect more than 2 computers via USB using hub topology?

Re: Ask HN: Advice for creating a USB device linking 2 computers

#44

Post by WorldDev » Tue, Oct 28, 2025, 3:20 PM UTC

ruslan wrote: post #37

Get two FTDI FT232RL chips, connect them together on serial side (RXD->TXD, TXD->RXD, GND GND). Plug into USB ports of your computers, run terminals (or any other software that supports serial I/O), send/receive data. Can use XYZModem to send files, PPP for TCP/IP networking, etc. No programming involved. Cheap as hell.

Thanks for the idea. I think it's a great one, but I have a few concerns:

1) The two computers are on 2 different grounds, so I believe it could damage the computers. So I would like to isolate the ground somehow, I am not sure what the options are. I tried to look for opto-isolated options, but didn't really find something clear. Do you have any suggestion?

2) This specific chip is marked NRND (not recommended for new designs) on ftdi's website, So it feels slightly wrong to use it?

Re: Ask HN: Advice for creating a USB device linking 2 computers

#45

Post by kejaed » Tue, Oct 28, 2025, 9:31 PM UTC

rpcope1 wrote: post #7

Easy way is probably two usb-serial dongles and a null modem, if you don't need huge amounts of throughput.

You can buy an off the shelf cable for this.

https://www.digikey.ca/en/products/detail/ftdi-future-techno...

Re: Ask HN: Advice for creating a USB device linking 2 computers

#46

Post by mircerlancerous » Mon, Nov 03, 2025, 2:22 AM UTC

Neat project, regardless of some of the opinions of practicality.

What you want to do is make sure your client device is an HID device, so that it's recognized as a keyboard. I think something like this will do: https://makerspot.com/cp2110-usb-hid-to-uart-serial-adapter/

For the server side, you'll either want a USB to serial adapter with a microcontroller in between, or one of the RP2040 Raspberry pis as it can be both those at once. https://www.waveshare.com/rp2040-zero.htm

Actually you can probably do it with two RP2040s (or maybe just one) as their USB ports I believe can be configured for different roles.

Good luck, and share your results!