Q: diagnal groundplane on top layer?
A: that was what the reference file came with ... Should I change it?
Hmm. The copy I downloaded has a rectangular groundplane on top. You probably accidentally deleted the bottom right corner when adding the battery; it's easy to miss doing this when the groundplane isn't filled in.
- horizontal lines: I guess I didnt' realize that was important (slap, don't be sloppy), I'll clean that up more (finer Alt setting).
It's not important on its own, but it probably contributes to some of the clearance errors.
- I was under the impression (wrong?) that the ISP header also breaks out the necessary lines for external SPI bus connections, so I didn't bother.
No, you're correct. I forgot about those, and didn't see it. I never liked connecting shields via signals on the ICSP connector, but it's probably sufficient.
- Westfw, you reminded me that it probably should have a cap next to the SCA3000 on the power line. The SCA is miniscule amperage, suitable for the 3.3 line. Should it have an electrolytic and a ceramic like the Sparkfun breakout board? I have no idea how well conditioned the 3.3v supply is.
Good question. I don't know. Sensitive analog component; I'd put as many caps near it as will easily fit on the board, and maybe an inductor or resistor connecting them to the main supply as well.
Can you fit it out for possible population with cheaper accelerometers (ie dual footprints)? Everyone with micromachining capabilities is chasing the "shake your iPod" market with cheap three-axis accelerometers (ie MMA7455L from Freescale - under $4 in ones...)
- all the little warnings were a little confusing and I couldn't find any actual problems when I checked the circuit board, but that just means I don't know what I'm doing!
Yes, you need to look at them more carefully. The design rules are already set to "typical" limits of PCB manufacturers, so anything that's closer than the 8mil clearance really ought to be cleaned up. "dimension" is less important. And I saw at least two real errors where traces carrying different signals actually collide (near (73,17) and (78,40)) I'm a big fan of making things "easy" for the PCB manufacturer...