So I've gotten a prototype working with arduino, now I'm wondering about where to go next. My project only uses ground and a single I/O pin, so I'd like to make a small box with power and a connector and I don't need anything more than that. Where can I start? Do I need to print a custom PCB? Or are there small boards I should be using as a starting point? Do I need additional electronics components? Or just a chip, a pcb and a connector?
No, unless you want to make a lot of those boxes, say over 10.
I would use strip board to make your circuit on.
provide a schematic and a bit more info, and many will advise quite quickly. There may be many paths forward, but right now, every answer will likely both be absolutely correct, and utterly wrong.
Ahh, the transition from demo to production strikes again! The problems you have to solve to build one are the same as building 100 so the non-recurring engineering (NRE) cost and effort is front loaded.
Lots of fab techniques work if this is a one shot deal. But its quite another if you want to build something you can ship, stay in use for extended periods and be repairable in the field. Its called engineering and there is a LOT of it in moving from demo to product.
I started with an idea, and a year later, after learning Arduino, C++, NanoCAD, TinkerCAD, Fusion 360, 3D printing, laser engraving, cnc drilling, spending several thousand usd on parts and machinery, and making SIX prototypes to get from THIS:
Prototype, proof of concept
to THIS:
But this can be built in bulk, with all the plastic parts either 3D printed or CNC drilled, by following the plans.
Of course you need to have the BOM costed out and the labor, g&a, etc., factored in, to price it properly, spreading that nice front loaded NRE over your expected lifetime production. Easy peasy! LOL
No one has mentioned what I consider the most important part of your project! That is a BOM, bill of material, showing the component id from your schematic, the manufacturer's name and component id, the distributor name and component number. Also the component tolerance percent.
Try your best to use common values for ALL capacitors and ALL resistors. That will limit your per-component cost. It is frustrating to see three different capacitor tolerances for the same cap value on a board when the low tolerance could be used for all and end up making a cheaper board.
Where do you want to go? One personal project, a few for you and friends, or a small volume with anticipation of selling?
You do not say which Arduino Board you are using, but if UNO then that can mostly be distilled down to a single chip + 16MHz crystal + a couple of load capacitors + any small parts you may be using in your implementation. For power, you may wish to consider LiOn battery and a Boost module. And so on...
Personally, I generally like to use an Arduino mini for small projects and just work the other parts into the enclosure, like this:
I mentioned BOM's! LOL