So, question: Can I get some suggestions for software / tips and tricks for recording and reviewing raw data coming off a serial port? I'm a very long way from trying to reverse-engineer a novel protocol myself, but that's the eventual goal, and the next step I'd like to take is compare what I'm seeing coming out of a serial mouse with documentation online to make sure I really understand what's going on and how all this works.

Uh... #retrocomputing #reverseengineering ? boosts welcome.

First draft for a less janky version of the first answer here: https://electronics.stackexchange.com/questions/63865/rs-232-serial-sniffing

All nine lines are continuous from the PC end to the Device end (device end is male with pins, all others are female sockets), with the TX and RX lines also tapped out to the TX lines of the left and right ports, and GND is shared between all four ports.

I'll be adding this to my #SimpleBreakouts project once validated, so what might make this more useful to others? All 9 lines broken out to headers maybe?

Added a 9-pin header right across the middle with pin labels. The socket mount points in these default DB-9 #Fritzing footprints aren't normally points I can attach wires to, but plonking a via in the middle of each and running a wire between those seems to produce the desired result (top right) - both in OSHPark's and JLCPCB's previews.

I know there's folks looking at this and cringing hard, but I'm not aiming for best practices here, just something that works okay for my purposes.

Okay, here's my final answer for now - time to walk away from this project for a couple of days to see if any bright ideas occur in the meantime, so they don't occur while V1 of the board is in manufacturing.

"Host" is not the right word to describe either end of a technically equal, bidirectional connection, but it's that end that defines the pinout, and in the context of "A PC, or an Arduino, plugged into a serial mouse or gaming controller from the 90s", it's fit for purpose. #PCBDesign

The extra 9-pin sockets I ordered are just around the corner, so I decided it was time to get the PCBs on the way as well - now would be an extremely funny time for someone to pipe up and suggest an obvious change or addition!

I love OSHPark, my usual go-to, but <AU$1/board on special is tough to argue with for a throwaway prototype, especially when I get to pick my own colour (I went with black to get maximum contrast and readability from the labels), so JLC it is for this project.

Nine months later, I finally have baby's first logic analyser in the post, so I thought I'd take a moment to solder one of these bad boys up.

Would anyone else in Australia like one of these? I have five and only need one.