I have a Raspberry Pi project I'm working on that will involve connecting three printed circuit boards. I'm trying to figure out a rugged and convenient way to make the connections. The drawing below is a side view of my current rough concept for how to do this. I'm hoping for feedback or suggestions on how to flesh out this plan or what would be a better plan. I'm inexperienced with DIY electronics, and what experience I had was 30 years ago.
The bottom board has a 2x20 pin header with a pitch of 0.1", as does the other large board above it. They're designed to work together, so I can just connect them with a ribbon cable, and the pinouts will match up correctly. There are also holes pre-drilled in the boards so that I can provide appropriate mechanical support, uniting these two boards into one rigid unit.
The hard part is getting the connections to the third, small board, which is a GPS receiver. It needs four connections: ground, 3.3 V power, and two UART lines. My current thought is to take a razor blade and carefully separate out the four wires from the ribbon cable, send them to some kind of connector (the circle marked "?"), and then go from that connector to soldered connections on the small pcb.
Issues I'm worried about:
The 3.3 V power line is also needed by the top large pcb, so I'd need to splice in an extra piece of wire to get that connected to both it and the small pcb.
I don't know what electrical properties are required for the UART line in order to avoid problems with things like reflected signals. The data sheet (link above) describes various speeds in various setups, but maybe 9600 baud. This seems relatively low, so maybe this kind of RF engineering stuff is not relevant?
I'm not sure what kind of connector to use. This is supposed to be a lightweight, compact unit. Molex seems like overkill. D-SUB seems kind of big and heavy.
I'm imagining a tendency for the ribbon cable to fray or split from the places where I separated the four strands from the main cable.
Not sure how to do appropriate strain relief for the soldered connections on the small pcb.
If I want to get access to other lines later, I have to do more razor-blade surgery. This suggests maybe using a crimp-on connector in the middle of the ribbon cable, but I'm not clear on how to make permanent connections onto such a thing.