Finally got around to drawing up my own Uno shield template

I ran into that same header gap a couple years back when I tried building a shield on a scrap of stripboard. Spent an hour wondering why nothing lined up before I measured it properly. The spacing between those two pins on the top row relly is wider than the rest of the board, which throws off the whole right side if you're working from a standard grid. What ended up working for me was cutting the board into two sections and wiring across the gap with jumper wire. Ugly but it held up fine and that little weather station ran on a windowsill for two winters. On the next one I just bought one of those proto shield boards with the holes allready laid out for the Uno footprint, saved myself the headache.

For paper layouts, I'd suggest doing what I eventually did: trace the actual board on paper, hold it up to a window or light box with the board on top, and mark the holes by poking a pin through. Way faster than measuring everything, and you catch wierd offsets like that gap immediatly. My first template was off by almost a full hole pitch on one side because I'd assumed everything was on a neat grid. If your projects are small, a Nano on a bit of perfboard might honestly be easier than a full shield anyway, depending on how many pins you actually need.

I stopped drawing layouts on paper years ago because of that exact pin spacing problem, plus I could never get the scale right by eye. What works for me now is using the board itself as the template. I tape an old dead Uno I keep in the drawer down onto the blank prototyping board, drop a pin or a fine marker through each header hole to mark them, then drill everthing out before lifting the board off. Takes about five minutes and the hole positions are perfect by definition, weird 7-8 gap included.

For anyone without a sacrificial board, even a working one does the job if you're careful, just don't press hard enough to bend anything in the sockets.

I'd also say don't overthink the drawing stage. My first few shields I sketched everything in fine detail and then changed half the wiring during soldering anyway. Now I only mark where the headers go and where the big components sit, and figure out the rest as I go with the board plugged in on top. The paper version always looked tidy and the real build never matched it. If you do want a printable grid, the header pitch on everything except that one spot is the usual 0.1 inch, so a standard perforated board layout mostly transfers over. Just double check that one gap against the real board before you commit to drilling.

Another trick that saved me: I print the hole pattern on a sheet of thin card instead of drawing it. I made a full size print of the header layout, taped it to a piece of MDF, poked holes with a drill bit by hand and now I use it every time I mock up a shield. Costs nothing and I can scribble component positions right on the card with a pencil before committing to solder.

Also for anyone testing a layout before soldering, a breadboard plus dupont wires to the uno headers lets you try the whole thing first. I caught two wiring mistakes that way on my last build.

Yeah that half pitch gap between pins 7 and 8 catches everyone at some point. I hit it building a sensor shield years back and the fix was just filing a small slot in the perfboard row so the header coud sit offset. Totally agree with the tracing tip too, I did the pin-poke method on my last layout and it came out dead on first try, no measuring involved.