I finally had some time to sit down and work on a few things this morning. I didn't get very far though before my allergies made it impossible to see what I was doing. I got the Raspberry Pi ready for some testing. Removed the back panel from the touchscreen terminal case, replaced it with one that can handle the GPIO extension cable, and camera cable. I had to remove the heatsink and fan, as well as comment out the overclock settings I was using in the config.txt file. I connected to my phone's hotspot and got the system fully updated. Before assembling it all, I hooked up the micro HDMI adapter and cable. That was about it for the Pi. It's ready for testing when the cart hardware arrives.
I had ordered a cheap HDMI to USB capture card so I could use my laptop as a monitopr for the Pi. That thing turned out to be garbage after a few hours of tweaking. I could not get a steady useable frame rate, or a useable image. I suspect the device was overheating, but I don't have the time or energy to deal with that. I took a chance on something cheap, and lost. Never again. I'll just save up and buy a portable monitor for the Pi 400 when I get it. So tired of cheap crap.
The prototype cart hardware should be waiting for me in the city, so I'll pick that up in a few days. I'll solder it all together and get started on programming for the SD flash chips. The goal is to just get them to auto mount and safely eject them through the test interface I made with tkinter. I bought some cheap USB flash drives for testing so I don't mess up my other drives or the flash chips. I'm having trouble mounting drives, as I don't understand how to create mount points and such in Linux. Still have a lot to learn these days. It's slowly coming together though.