I love the Sony MiniDisc. It’s the last, best physical media format. Holds as much music as a CD, but smaller than a 3.5" floppy, and it’s also incredibly durable. And with the advent of excellent third-party apps, it’s an incredibly viable media for my music collection.

I have 2 portable players, and a bookshelf system. Of the players, only one (the N505) has a DC jack. It’s a better portable, but it’s not as good a recorder as my NE410. Sadly, the NE410 chews through batteries like they’re water. So I decided to build a USB-C adapter for it. It’s not as simple as a plain USB-C to MiniUSB, as the players can’t be powered from USB.

USB-C Connector
I started with this USB-C female connector. It’s wired up so I only have to worry about 4 pins - V, D+, D-, G. I wired it up to a miniUSB connector, and made sure data transfer worked.

Next, I wired in a Mini 360 Buck Converter. This thing is tiny, and could be dialled down to 1.5v very easily.
Mini 360 Buck Converter

Casing
A little work in Fusion 360, and I had a nice compact casing. I designed it so it’s symmetrical - makes it much easier to iterate, and it fit together nice and neat.

I also printed off a fake AA Battery, which uses a couple of screws as the terminals. Remarkably fiddly to get the nuts onto the bolts to lock in the wire… so I hot glued EVERYTHING.
Battery

Assembled
Once again, I broke out the hot glue to secure all the parts into the case, to secure the wiring as well as the PCBs. Everything fit perfectly the first third time.

Finally, here it is in use! Now I can record MiniDiscs all day!
In Use